JP2010061768A - Optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To share components and set an appropriate focus pull-in range corresponding to each optical disc format in an optical pickup for recording and reproducing with respect to plural types of optical discs using three different wavelengths. Thus, good 3 wavelength compatibility is realized.
An objective lens for condensing a light beam of each wavelength emitted from each emitting section on a signal recording surface of an optical disc, and a common light reception for receiving a light beam of returned first to third wavelengths. A light detector 41 having a section 40, a condensing optical device 36, and a light receiving section 40, each of which imparts predetermined astigmatism to the light beams of the first to third wavelengths, And a diffractive optical element 44 as an astigmatism applying device that forms a predetermined astigmatism difference.
[Selection] Figure 2

Description

  The present invention relates to an optical pickup for recording and / or reproducing information signals on three different types of optical discs and an optical disc apparatus using the same.

  In recent years, as a next-generation optical disc format, an optical disc capable of high-density recording (hereinafter referred to as a “high-density recording optical disc”) in which signals are recorded and reproduced using a light beam having a wavelength of about 405 nm by a blue-violet semiconductor laser has been proposed. ing. As this high-density recording optical disk, for example, a BD (Blu-ray Disc (registered trademark)) having a structure in which a protective layer (cover layer) for protecting the signal recording layer is thin, for example, 0.1 mm. Has been proposed.

  In providing optical pickups corresponding to these high-density recording optical disks, conventional optical disks having different formats such as a CD (Compact Disc) having a used wavelength of about 785 nm and a DVD (Digital Versatile Disc) having a used wavelength of about 655 nm. Those that are compatible with are desired. Thus, there is a need for an optical pickup and an optical disk apparatus that have compatibility between optical disks of different formats that have different disk structures and accompanying laser specifications.

  By the way, the above-described high-density recording optical discs and optical discs such as DVDs and CDs each have standards (formats) for preserving the uniformity and compatibility of popular media and devices for recording and reproducing them. These standards (format books) describe various requirements regarding product technology. In order to realize the so-called three-wavelength compatibility for realizing recording or reproduction of information signals for the three different types of optical disks as described above, particularly for a focus servo or the like which is one of the description items. It is important to satisfy the requirements for servo signals.

  In the case of performing the three-wavelength compatibility as described above, it is necessary to make it possible to realize a system for a high-density recording optical disk in addition to a conventional system for an optical disk such as a DVD or a CD. For this purpose, it is necessary to satisfy a required specification of a focus error signal suitable for a focus servo compatible with a plurality of types of formats. The required specification of the focus error signal suitable for the focus servo corresponding to the format of each optical disc varies depending on the difference in the specifications of the optical disc determined by such a plurality of types of formats.

  In particular, the waveform of the focus error signal is deeply related to the optical system and the electrical system of the optical pickup, and the S-shaped waveform pull-in range (hereinafter referred to as “return magnification”) is referred to as the optical path return magnification (hereinafter also referred to as “return magnification”). , Also referred to as “focus pull-in range”).

  For example, considering a conventional system, a focus pull-in range suitable for a BD (Blu-ray Disc (registered trademark)) which is a high-density recording optical disc is about 1.5 μm to 3.5 μm. Also, the focus pull-in range suitable for DVD and CD was about 4.0 μm to 12.0 μm.

  If the focus pull-in range does not conform to the format of each optical disc, there is a possibility that the sensitivity of the focus servo may be reduced, or the focus may be out of focus and appropriate focus servo cannot be performed. Further, this may cause a problem that recording / reproduction cannot be performed satisfactorily. In order to provide an appropriate focus pull-in range for each of the three wavelengths used, it is necessary to set an optimum return magnification. The return magnification is mainly determined by the focal length of the objective lens, the incident magnification to the objective lens, and the focal length of other optical components arranged in the return optical system. In view of the above, conventionally, for example, as shown in FIG. 22, two or more light receiving elements are used, and multiple lenses as coupling lenses having different curvatures are separately provided in optical paths other than the common optical path of the return path system. A method of placing the device on the surface has been used or studied. Here, the configuration of the optical pickup that has been conventionally studied shown in FIG. 22 will be described.

  The optical pickup 160 shown in FIG. 22 has a common objective lens corresponding to a light beam of three wavelengths, and solves the problems of the conventional optical pickup having two objective lenses. In other words, since the optical pickup 160 needs to be mounted on two actuators for driving the objective lens, it solves problems such as an increase in the weight of the actuator and a decrease in sensitivity.

  Specifically, the optical pickup 160 includes a light source unit 163 such as a laser diode having an emission unit that emits a light beam having a wavelength of about 785 nm to an optical disk such as a CD. The optical pickup 160 includes a light source unit 162 such as a laser diode having an emission unit that emits a light beam having a wavelength of about 655 nm to an optical disc such as a DVD. The optical pickup 160 has a light source unit 161 such as a laser diode having an emission unit that emits a light beam having a wavelength of about 405 nm to a high-density recording optical disk. The optical pickup 160 includes a common objective lens 164 for high-density recording optical disks, DVDs, and CDs, and a diffractive optical element 165 for correcting aberrations.

  The optical pickup 160 includes a movable collimator lens 167, a quarter wavelength plate 175, a rising mirror 176, beam splitters 168A, 168B, 169A, gratings 173A, 173B, 173C, and the like.

  Further, the optical pickup 160 has a multi-lens 172B and a photodetector 171B as a return light detection system for an optical disc such as a DVD or CD in the return optical path. Further, the optical pickup 160 includes a multi-lens 172A and a photodetector 171A as a return light detection system for a high-density recording optical disk, and a beam splitter 169B that guides a predetermined light beam to each return light detection system.

  The light beam having a wavelength of about 785 nm emitted from the light source unit 163 is reflected by the beam splitter 168B, passes through the beam splitter 169A, and enters the objective lens 164. The objective lens 164 is focused on the signal recording surface of an optical disc having a protective layer having a thickness of about 1.1 mm.

  The light beam having a wavelength of about 655 nm emitted from the light source unit 162 is reflected by the beam splitter 168A, passes through the beam splitters 168B and 169A, and enters the objective lens 164. The objective lens 164 is focused on the signal recording surface of an optical disc having a protective layer having a thickness of 0.6 mm. The return light having a wavelength of 785 nm and a wavelength of 655 nm reflected by the signal recording surface of the optical disc passes through the beam splitter 169A, is reflected by the beam splitter 169B, and is detected by the multi-lens 172B by the photodetector 171B having a photodetector or the like.

  The light beam having a wavelength of about 405 nm emitted from the light source unit 161 is transmitted through the beam splitters 168A, 168B, and 169A and enters the objective lens 164. The objective lens 164 is focused on the signal recording surface of an optical disc having a protective layer having a thickness of about 0.1 mm. The return light having a wavelength of 405 nm reflected by the signal recording surface of the optical disk passes through the beam splitter 169A, passes through the beam splitter 169B, and is detected by the multi-lens 172A by the photodetector 171A having a photodetector or the like.

  In the return optical system of the optical pickup 160, the following effects can be obtained by appropriately adjusting the focal length and arrangement of the multi-lens 172B for DVD / CD and the multi-lens 172A for high-density recording optical disk. . That is, with the above-described configuration, it is possible to set the return magnification of a light beam with a wavelength of 785 nm and a wavelength of 655 nm for an optical disc such as a DVD and a CD, and the return magnification of a light beam with a wavelength of 405 nm for a high-density recording optical disc. With this configuration, an appropriate focus pull-in range can be given for each wavelength.

  The optical pickup 160 shown in FIG. 22 as described above is provided with an objective lens 164 corresponding to a light beam of three wavelengths and a diffractive optical element 165 for correcting aberrations, thereby recording and / or recording on three different types of optical disks. Realize playback. At the same time, the optical pickup 160 sets an appropriate focus pull-in range for each optical disk, that is, realizes compatibility among a plurality of types of optical disks.

  However, the optical pickup 160 shown in FIG. 22 has a problem in terms of cost reduction and miniaturization because the number of parts is increased due to the necessity of providing two photodetectors having light receiving elements. In other words, the optical pickup 160 has a problem that, for example, two optical detectors are required, so that the cost is high. Further, the optical pickup 160 also requires an element such as a beam splitter for separating and entering the light beams corresponding to these photodetectors, and a magnification conversion lens for condensing on the light receiving elements of the respective photodetectors. A plurality of parts such as a multi lens are also required. Further, the optical pickup 160 has a complicated configuration because the wiring is further routed from two locations, which causes a problem in that the overall configuration is complicated and miniaturization of the apparatus is hindered.

  As described above, the optical pickup shown in FIG. 22 has a problem that the number of parts increases and the optical system becomes complicated. In addition, by providing a plurality of multi-lenses and light receiving elements, the number of steps for adjusting them increases, and it takes a lot of time to manufacture an optical pickup, which complicates the configuration of the apparatus and prevents miniaturization. There was a problem of becoming.

  Therefore, in order to realize further miniaturization, simplification of the configuration, simplification of the adjustment process, and the like, it is desired to configure an optical pickup having an optical system including one light receiving unit and one photodetector. However, in the case where the optical pickup is composed of only one objective lens and a photodetector having one light receiving portion, there is a problem that it is impossible to set a difference in the return path magnification for the three types of used wavelengths. Further, there is a problem that the focus servo signal waveform cannot be made appropriate, that is, as described above, a desired focus pull-in range cannot be obtained.

  Further, when reproducing a multi-layer optical disk having a plurality of signal recording surfaces as the above-described high-density recording optical disk, for example, a double-layer optical disk, stray light from a recording surface different from the recording surface on which the signal is reproduced is generated. It is necessary to consider that the light is incident on the light receiving surface. As a result, in an optical system that does not have a sufficiently large return magnification, the problem due to interference increases, and the reproduction characteristics may be adversely affected. It is desirable to have.

  Thus, from the viewpoint of making the focus pull-in range appropriate, the return magnification corresponding to each format is optimized, and the objective lens and the light receiving element for each wavelength used corresponding to each optical disc. It has been very difficult to achieve both compatibility with three wavelengths and the miniaturization of the apparatus and the simplification of the configuration by making the common use.

JP 2007-220215 A

  An object of the present invention is an optical pickup that performs recording and / or reproduction with respect to a plurality of types of optical discs using three different types of wavelengths, and simplifies the configuration and reduces the size of the apparatus by using common components. An optical pickup capable of achieving an appropriate focus pull-in range corresponding to the format of each optical disc, and achieving compatibility between three-wavelength compatibility by obtaining a compact configuration and a good servo signal. And providing an optical disk apparatus using the same.

  The optical pickup according to the present invention includes a light beam having a first wavelength that is emitted from the first emission unit and corresponding to the first optical disc, and a different type of light beam that is emitted from the second emission unit and that is different from the first optical disc. Corresponding to the second optical disc and a second light beam having a wavelength longer than the first wavelength, and a third optical disc different from the first and second optical discs emitted from the third emitting portion. In addition, the objective lens for condensing the light beam having the third wavelength longer than the second wavelength on the corresponding optical disk, and the light beams having the first to third wavelengths reflected by the optical disk are commonly received. A photodetector that receives and detects light at a portion, and an astigmatism imparting device that is provided between the objective lens and the light receiving portion and imparts astigmatism according to the wavelength of the incident light beam, Astigmatism above The applying device is formed by applying astigmatism to the light beam having the second wavelength by Δ1 as an astigmatic difference formed by applying astigmatism to the light beam having the first wavelength. When the astigmatic difference is Δ2, and the astigmatic difference formed by applying astigmatism to the third wavelength light beam is Δ3, each wavelength satisfies the relationship of Δ1 <Δ2 <Δ3. Astigmatism is given to the light beam.

  Also, the optical disc apparatus according to the present invention records information signals by selectively irradiating a plurality of light beams having different wavelengths to an optical disc that is arbitrarily selected from a plurality of types of optical discs and driven to rotate. An optical disc apparatus provided with an optical pickup that performs reproduction, and the optical pickup used in the optical disc apparatus uses the one described above.

  The present invention uses a common optical system having a common objective lens corresponding to three types of wavelengths used and a common light receiving unit to collect a light beam having a wavelength corresponding to each optical disk, and from the optical disk. In an optical pickup optical system that records and / or reproduces information signals on a plurality of types of optical discs by detecting reflected light from each other, an astigmatism imparting device provided between the objective lens and the light receiving unit is By forming an astigmatic difference having a certain relationship with giving a predetermined astigmatism to the light beam, the magnification of the return path system can be optimized according to the wavelength used. It is possible to set an appropriate focus pull-in range corresponding to the format of each optical disc, simplify the configuration and reduce the size of the device, and To achieve good recording and / or reproducing.

  Hereinafter, an optical disk apparatus using an optical pickup to which the present invention is applied will be described with reference to the drawings.

  As shown in FIG. 1, an optical disc apparatus 1 to which the present invention is applied includes an optical pickup 3 that records and reproduces information from an optical disc 2 and a spindle motor 4 that serves as a drive means for rotating the optical disc 2. The optical disk apparatus 1 also includes a feed motor 5 that moves the optical pickup 3 in the radial direction of the optical disk 2. The optical disc apparatus 1 is an optical disc apparatus that realizes compatibility between three standards capable of recording and / or reproducing information on three types of optical discs having different formats and an optical disc in which recording layers are stacked.

  The optical disk used here is, for example, an optical disk such as a CD (Compact Disc), a CD-R (Recordable), a CD-RW (ReWritable) using a semiconductor laser having an emission wavelength of about 785 nm. Such an optical disc is, for example, an optical disc such as a DVD (Digital Versatile Disc), DVD-R (Recordable), DVD-RW (ReWritable), DVD + RW (ReWritable) using a semiconductor laser having an emission wavelength of about 655 nm. Such an optical disc is a high-density recording optical disc such as a BD (Blu-ray Disc (registered trademark)) capable of high-density recording using a semiconductor laser having a shorter emission wavelength of about 405 nm (blue-violet).

  In particular, the following description will be made assuming that the following first to third optical disks 11, 12, and 13 are used as the three types of optical disks 2 for reproducing or recording information by the optical disk device 1. That is, the first optical disk 11 has a protective layer formed with a first thickness of about 0.1 mm and has the above-described BD capable of high-density recording using a light beam with a wavelength of about 405 nm as recording / reproducing light. Or the like. The second optical disk 12 is an optical disk such as a DVD having a protective layer formed with a second thickness of about 0.6 mm and using a light beam with a wavelength of about 655 nm as recording / reproducing light. The third optical disc 13 is an optical disc such as a CD having a protective layer formed with a third thickness of about 1.1 mm and using a light beam with a wavelength of about 785 nm as recording / reproducing light.

  In the optical disc apparatus 1, the spindle motor 4 and the feed motor 5 are driven and controlled in accordance with the disc type by a servo control unit 9 that is controlled based on a command from a system controller 7 that also serves as disc type discriminating means. Thereby, for example, the first optical disk 11, the second optical disk 12, and the third optical disk 13 are driven at a predetermined rotational speed.

  The optical pickup 3 is an optical pickup having a three-wavelength compatible optical system. The optical pickup 3 irradiates a recording layer of an optical disc having a different standard with a light beam having a different wavelength from the protective layer side, and reflects the light beam reflected on the recording layer. Is detected. The optical pickup 3 outputs a signal corresponding to each light beam from the detected reflected light.

  The optical disc apparatus 1 includes a preamplifier 14 that generates a focus error signal, a tracking error signal, an RF signal, and the like based on a signal output from the optical pickup 3. The optical disc apparatus 1 also includes a signal modulator / demodulator and error correction code block (hereinafter referred to as a signal modulator / demodulator & ECC block) 15 for demodulating the signal from the preamplifier 14 or modulating the signal from the external computer 17 or the like. Prepare. The optical disc apparatus 1 includes an interface 16, a D / A / A / D converter 18, an audio / visual processing unit 19, and an audio / visual signal input / output unit 20.

  The preamplifier 14 generates a focus error signal by an astigmatism method or the like based on an output from the photodetector, and generates a tracking error signal by a three beam method, a DPD method, a DPP method, or the like. Further, the preamplifier 14 further generates an RF signal, and outputs the RF signal to the signal modulator & ECC block 15. Further, the preamplifier 14 outputs a focus error signal and a tracking error signal to the servo control unit 9.

  When recording data on the first optical disc, the signal modulator & ECC block 15 performs the following processing on the digital signal input from the interface 16 or the D / A / A / D converter 18. Do. That is, the signal modulator & ECC block 15 performs error correction processing on the input digital signal by an error correction method such as LDC-ECC and BIS, and then performs modulation processing such as the 1-7PP method. The signal modulator & ECC block 15 performs error correction processing according to an error correction method such as PC (Product Code) when recording data on the second optical disc, and then performs modulation processing such as 8-16 modulation. I do. Furthermore, when recording data on the third optical disc, the signal modulator & ECC block 15 performs error correction processing by an error correction method such as CIRC, and then performs modulation processing such as 8-14 modulation processing. Then, the signal modulator & ECC block 15 outputs the modulated data to the laser control unit 21. Further, when reproducing each optical disk, the signal modulator & ECC block 15 performs demodulation processing based on the RF signal input from the preamplifier 14, further performs error correction processing, and converts the interface 16 or data to D / D. Output to the A, A / D converter 18.

  When data is compressed and recorded, a compression / decompression unit may be provided between the modulator & ECC block 15 and the interface 16 or the D / A / A / D converter 18. In this case, the data is compressed by a method such as MPEG2 or MPEG4.

  The servo controller 9 receives a focus error signal and a tracking error signal from the preamplifier 14. The servo control unit 9 generates a focus servo signal and a tracking servo signal so that the focus error signal and the tracking error signal become zero, and an objective lens such as a biaxial actuator that drives the objective lens based on these servo signals. Drive control of the drive unit. Further, a synchronization signal or the like is detected from the output from the preamplifier 14, and the spindle motor is servo-controlled by CLV (Constant Linear Velocity), CAV (Constant Angular Velocity), or a combination of these.

  The laser control unit 21 controls the laser light source of the optical pickup 3. In particular, in this specific example, the laser control unit 21 performs control to vary the output power of the laser light source between the recording mode and the reproduction mode. Also, control is performed to vary the output power of the laser light source depending on the type of the optical disc 2. The laser control unit 21 switches the laser light source of the optical pickup 3 in accordance with the type of the optical disc 2 detected by the disc type determination unit 22.

  The disc type discriminating unit 22 detects a change in the amount of reflected light from the surface reflectance, the shape and the external difference between the first to third optical discs 11, 12, and 13 to detect different formats of the optical disc 2. be able to.

  Each block constituting the optical disc apparatus 1 is configured to be able to perform signal processing based on the specification of the optical disc 2 to be mounted, according to the detection result in the disc type discriminating unit 22.

  The system controller 7 controls the entire apparatus according to the type of the optical disk determined by the disk type determination unit 22. Further, the system controller 7 sets each part based on address information and table information (TOC) recorded in premastered pits and grooves in the innermost periphery of the optical disc in response to an operation input from the user. Control. That is, the system controller 7 specifies a recording position and a reproduction position of an optical disc that performs recording and reproduction based on the above-described information, and controls each unit based on the identified position.

  The optical disc apparatus 1 configured as described above rotates the optical disc 2 by the spindle motor 4. Then, the optical disc apparatus 1 drives and controls the feed motor 5 in accordance with a control signal from the servo control unit 9, and moves the optical pickup 3 to a position corresponding to a desired recording track of the optical disc 2. On the other hand, information is recorded and reproduced.

  Specifically, when recording / reproducing is performed by the optical disc apparatus 1, the servo control unit 9 rotates the optical disc 2 by CAV, CLV, or a combination thereof. The optical pickup 3 irradiates a light beam from a light source, detects a returning light beam from the optical disc 2 by a photodetector, and generates a focus error signal and a tracking error signal. Further, the optical pickup 3 performs focus servo and tracking servo by driving the objective lens by the objective lens driving mechanism based on the focus error signal and the tracking error signal.

  When recording is performed by the optical disc apparatus 1, a signal from the external computer 17 is input to the signal modulator / demodulator & ECC block 15 through the interface 16. The signal modulator / demodulator & ECC block 15 adds a predetermined error correction code as described above to the digital data input from the interface 16 or the A / D converter 18, and further performs a predetermined modulation process and then a recording signal. Is generated. The laser control unit 21 controls the laser light source of the optical pickup 3 based on the recording signal generated by the signal modulator / demodulator & ECC block 15 and records it on a predetermined optical disk.

  When the information recorded on the optical disc 2 is reproduced by the optical disc apparatus 1, the signal modulator / demodulator & ECC block 15 demodulates the signal detected by the photodetector. If the recording signal demodulated by the signal modulator / demodulator & ECC block 15 is for data storage of a computer, it is output to the external computer 17 via the interface 16. Accordingly, the external computer 17 can operate based on the signal recorded on the optical disc 2. Further, if the recording signal demodulated by the signal modulator / demodulator & ECC block 15 is for audio visual, it is digital-analog converted by the D / A converter 18 and supplied to the audio / visual processing unit 19. Audio visual processing is performed by the audio / visual processing unit 19 and output to an external speaker or monitor (not shown) via the audio / visual signal input / output unit 20.

  Here, the recording / reproducing optical pickup 3 described above will be described in detail. As described above, the optical pickup 3 is an optical pickup for an optical disc arbitrarily selected from the three types of first to third optical discs 11, 12 and 13 having different formats such as the thickness of the protective layer. The optical pickup 3 is an optical pickup that records and / or reproduces an information signal by selectively irradiating the above optical disc with a plurality of light beams having different wavelengths.

  As shown in FIG. 2, the optical pickup 3 to which the present invention is applied includes a first light source unit 31 having a first emission unit that emits a light beam having a first wavelength. The optical pickup 3 includes a second emission unit that emits a light beam having a second wavelength longer than the first wavelength, and a third emission that emits a light beam having a third wavelength longer than the second wavelength. The 2nd light source part 32 which has a part is provided. The optical pickup 3 also includes an objective lens 34 and a diffractive optical element 35 that constitute a condensing optical device 36 that condenses the light beams emitted from the first to third emitting portions on the signal recording surface of the optical disc 2. Is provided. The optical pickup 3 also includes a collimator lens 37 that is disposed on the optical path between the first to third emission units and the condensing optical device 36 and is movable in the optical axis direction. The collimator lens 37 is a divergence angle conversion element that converts the divergence angle of the light beams having the first to third wavelengths and adjusts the divergence angle so as to obtain a substantially parallel light state or a predetermined divergence angle. Function.

  The optical pickup 3 also includes first and second beam splitters 38 and 39 that function as optical path separating means. The first and second beam splitters 38 and 39 are optical path separation means for separating the optical path of the return light beam and the optical path of each of the forward light beams emitted from the first to third emission sections. . Here, the return light beam means a return light beam having the first to third wavelengths which is focused on the signal recording surface of the optical disc 2 by the objective lens 34 and reflected by the signal recording surface. To do. Further, the optical pickup 3 has a common light receiving unit 40 for receiving the light beams of the first to third wavelengths in the return path (return) separated by the first and second beam splitters 38 and 39. A container 41 is provided. In addition, the optical pickup 3 includes a multi lens 42 provided between the first beam splitter 38 and the light receiving unit 40. The multi lens 42 functions as a magnification conversion lens (coupling lens) that condenses the light beams of the first to third wavelengths in the return path from the first beam splitter 38 on the light receiving surface of the light receiving unit 40. The optical pickup 3 is provided between the multi-lens 42 and the first beam splitter 38, and is a diffractive optical element 44 as an astigmatism imparting device that imparts astigmatism according to the wavelength of the incident light beam. With. Then, as shown in FIG. 3A, the diffractive optical element 44 diffracts so as to give a predetermined astigmatism to the light beam of the first to third wavelengths on the incident side surface. A diffractive portion 43 is provided.

  Here, the astigmatism imparting device that constitutes the optical pickup 3 is not limited to the diffractive optical element 44 as described above. For example, the diffractive portion 43 is provided integrally with a multilens having a condensing function. Such a diffractive optical element may be used. That is, instead of the above-described multi-lens 42 and diffractive optical element 44, a diffractive optical element 44B as an astigmatism applying device as shown in FIG. 3B may be provided. The diffractive optical element 44B is provided with a diffractive portion 43 similar to that described above on one surface, for example, on the incident-side surface. In addition, the diffractive optical element 44B is provided with a lens surface 42B having a magnification conversion function, for example, on the exit-side surface as the other surface, and thus is a multi-lens as a diffractive optical element.

  Further, the optical pickup 3 includes a first grating 45 provided between the first emission part of the first light source part 31 and the first beam splitter 38. The first grating 45 has a function of diffracting the light beam having the first wavelength emitted from the first emitting unit into three beams for detecting a tracking error signal or the like. In addition, the optical pickup 3 includes a second grating 46 provided between the second and third emission units of the second light source unit 32 and the second beam splitter 39. The second grating 46 has a function of diffracting the light beams of the second and third wavelengths emitted from the second and third emitting portions into three beams for detecting a tracking error signal and the like, respectively.

  Further, the optical pickup 3 is provided between the collimator lens 37 and the objective lens 34, and includes a ¼ wavelength plate 47 that gives a ¼ wavelength phase difference to the incident first to third wavelength light beams. Prepare. Further, the optical pickup 3 includes a rising mirror 48 provided between the objective lens 34 and the quarter wavelength plate 47. The raising mirror 48 reflects and raises the light beam that has passed through the above-described optical components in a plane orthogonal to the optical axes of the objective lens 34 and the diffractive optical element 35, thereby raising the objective lens 34 and the diffractive optical element 35. A light beam is emitted in the direction of the optical axis.

  The first light source unit 31 includes a first emission unit that emits a light beam having a first wavelength of about 405 nm to the first optical disc 11. The second light source unit 32 emits a light beam having a second wavelength of about 655 nm to the second optical disc 12, and a third wavelength for the third optical disc of about 785 nm. And a third emitting part for emitting the light beam. In the second light source unit 32, the second and third emission units are on the same plane orthogonal to the optical axes of the light beams having the second and third wavelengths emitted from the second and third emission units. It arrange | positions so that each light emission point may be located in the inside. Here, the first emission part is arranged in the first light source part 31 and the second and third emission parts are arranged in the second light source part 32. However, the present invention is not limited to this. Instead, the first to third emission units may be arranged in separate light source units. However, it is advantageous to simplify the configuration and reduce the size of the apparatus if the second and third emission units are arranged in a common light source unit as described above.

  The first grating 45 is provided between the first light source unit 31 and the first beam splitter 38. The first grating 45 diffracts the light beam having the first wavelength emitted from the first emission unit of the first light source unit 31 into three beams for detection of a tracking error signal or the like, and then diffracts the first beam. The light is emitted to the splitter 38 side.

  The second grating 46 is provided between the second light source unit 32 and the second beam splitter 39. The second grating 46 converts the light beams of the second and third wavelengths emitted from the second and third emission units of the second light source unit 32 into three beams for detecting a tracking error signal and the like, respectively. Diffracted and emitted to the second beam splitter 39 side. The second grating 46 is a so-called two-wavelength grating having wavelength dependence, and has a function of diffracting light beams having the second and third wavelengths into predetermined three beams.

  The first beam splitter 38 has a separation surface 38a having the following functions. The separation surface 38a reflects and emits the first wavelength light beam diffracted and incident by the first grating 45 to the second beam splitter 39 side, and also returns the first to third wavelength light in the return path. It has a function of transmitting the beam and emitting it to the multi-lens 42 side. The separation surface 38a exhibits the above-described function by being formed with wavelength dependency, polarization dependency, and the like. The first beam splitter 38 has an optical path of the light beam having the first wavelength on the return path and an optical path of the light beam having the first wavelength on the forward path emitted from the first emitting section by the separation surface 38a. It functions as an optical path separating means for separating the two.

  The second beam splitter 39 has a combined separation surface 39a having the following functions. The combining / separating surface 39a transmits the light beam having the first wavelength from the first beam splitter 38 and emits it to the collimator lens 37 side. The combined separation surface 39a reflects and guides the outgoing light beams of the second and third wavelengths from the second grating 46 to the collimator lens 37 side. At the same time, the combining / separating surface 39a has a function of transmitting the light beams having the first to third wavelengths in the return path and emitting them to the first beam splitter 38 side. The composite separation surface 39a exhibits the above-described function by being formed having wavelength dependency, polarization dependency, and the like. The second beam splitter 39 synthesizes the optical path of the light beam having the first wavelength of the forward path and the optical paths of the light beams having the second and third wavelengths on the forward path by the combining / separating surface 39a. It functions as an optical path synthesis means for guiding to the lens 37 side. In addition, the second beam splitter 39 has the combined separation surface 39a so that the optical paths of the light beams of the second and third wavelengths in the return path and the second and third paths of the forward paths emitted from the second and third emitting sections are used. It functions as an optical path separating means for separating the optical path of the light beam of the third wavelength.

  The optical pickup 3 is configured such that the first and second beam splitters 38 and 39 have a function as an optical path separating unit, and the second beam splitter 39 has a function as an optical path combining unit. However, it is not limited to this. That is, an optical path combining unit that combines the optical paths of the light beams having the first to third wavelengths in the forward path and an optical path separating unit as described below may be provided. The optical path separating means separates the optical paths of the first to third wavelength light beams in the return path from the forward optical paths of the first to third wavelength light beams and guides them to the light receiving unit 40 side. I just need it.

  The collimator lens 37 is provided between the second beam splitter 39 and the ¼ wavelength plate 47 and is movable in the optical axis direction. The collimator lens 37 functions as a divergence angle conversion element that converts the divergence angles of the first to third wavelength light beams to a predetermined divergence angle according to the moved position in the optical axis direction. Further, the optical pickup 3 is provided with collimator lens driving means 49 for driving the collimator lens 37 in the optical axis direction and moving it.

  The collimator lens 37 in the optical pickup 3 is configured so that the return light beams of the respective wavelengths guided to the common light receiving unit 40 by the multi lens 42 are appropriately condensed on the same plane, that is, on the light receiving surface of the light receiving unit 40. Moved to. For example, as shown in FIGS. 4A and 4B, the collimator lens 37 is moved to predetermined positions P1, P2, and P3 in the optical axis direction according to the type of incident light beam. . In addition, for example, the other optical components such as the first and second light source units 31 and 32 are configured to collect the light beam of each wavelength via the collimator lens 37 moved to a different position for each wavelength. It is comprised so that it may collect light appropriately. That is, the collimator lens 37 is moved to predetermined positions P1, P2, and P3 for each type of emitted light beam. The collimator lens 37 collects the light beams of the respective wavelengths on the same light receiving surface of the common light receiving unit 40 by changing the state of the light beams of the first to third wavelengths according to the moved position. Can be lighted. For example, as shown in FIG. 4A, the collimator lens 37 at the position P1 is condensed at the position of Pfλ1 via the multi lens 42. Further, as shown in FIG. 4B, the collimator lens 37 moved to the positions P2 and P3 is condensed at the positions of Pfλ2 and Pfλ3 through the multi lens 42. Here, the condensing position Pfλ1 and the condensing positions Pfλ2 and Pfλ3 are the same position, and the common light receiving surface of the light receiving unit 40 is disposed at this position. In FIG. 4B, the positions P2 and P3 are illustrated as being located at the same position for the sake of convenience. However, in actuality, they may be different positions and may be the same position.

  At this time, the collimator lens driving means 49 is controlled by the system controller 7 in accordance with the type of the optical disc 2 detected by the disc type discriminating unit 22 to drive the collimator lens 37 and the above-described first. To third positions P1, P2, and P3.

  The quarter-wave plate 47 imparts a quarter-wavelength phase to the light beams having the first to third wavelengths in the forward path whose divergence angle has been converted by the collimator lens 37, so that the circularly polarized light is converted from the linearly polarized state. The state is emitted to the rising mirror 48. The quarter-wave plate 47 gives a linearly polarized light from a circularly polarized state by giving a quarter-wave phase to the first to third wavelength light beams guided from the rising mirror 48. As a state, the light is emitted to the collimator lens 37 side.

  The rising mirror 48 reflects the light beam given the phase difference of ¼ wavelength by the ¼ wavelength plate 47, and aligns the optical axis with the optical axis of the objective lens 34, and the diffractive optical element 35. The light is emitted to the side.

  The objective lens 34 condenses the incident light beams having the first to third wavelengths on the signal recording surface of the optical disc 2. The objective lens 34 is movably held by an objective lens driving mechanism such as a biaxial actuator (not shown). The objective lens 34 is moved by a biaxial actuator or the like based on the tracking error signal and the focus error signal generated by the return light from the optical disc 2 detected by the photodetector 41. As a result, the objective lens 34 is moved in two axial directions, that is, a direction in which the objective lens 34 approaches and separates from the optical disc 2 and a radial direction of the optical disc 2. The objective lens 34 focuses the light beam from the first to third emission portions so that the light beam is always focused on the signal recording surface of the optical disc 2 and the focused light beam is focused on the optical disc 2. To follow the recording track formed on the signal recording surface. A diffractive optical element 35 (to be described later) is held in a lens holder of an objective lens driving mechanism that holds the objective lens 34 so as to be integrated with the objective lens 34. Thereby, the following effects of the diffractive portion 50 provided in the diffractive optical element 35 can be appropriately exhibited even when the field of view such as movement of the objective lens 34 in the tracking direction is performed.

  The diffractive optical element 35 is a diffractive optical element for three-wavelength compatible condensing, and as one surface thereof, for example, a diffractive portion 50 composed of a plurality of diffractive regions is provided on the incident side surface. The diffractive optical element 35 causes the diffracting unit 50 to diffract each of the first to third wavelength light beams passing through each of the plurality of diffraction regions so as to have a predetermined order and to enter the objective lens 34. That is, the diffractive optical element 35 is incident on the objective lens 34 as a light beam in a diffused state or a converged state having a predetermined divergence angle. Thereby, the diffractive optical element 35 uses this single objective lens 34 to prevent the spherical aberration from occurring on the signal recording surfaces of the three types of optical disks corresponding to the light beams of the first to third wavelengths. It is possible to collect light appropriately.

  Specifically, as shown in FIGS. 5A and 5B, the diffractive portion 50 provided on the incident side surface of the diffractive optical element 35 is provided on the innermost peripheral portion and has a substantially circular shape. 1 diffraction region (hereinafter also referred to as “inner ring zone”) 51. The diffractive portion 50 is provided outside the first diffractive region 51, and has a ring-shaped second diffractive region (hereinafter also referred to as “middle annular zone”) 52, and outside the second diffractive region 52. A third diffraction region 53 (hereinafter also referred to as an “outer ring zone”) provided.

  The first diffraction region 51 which is the inner ring zone is formed with a first diffraction structure having a ring zone shape and a predetermined depth. The first diffractive region 51 is dominated by the diffracted light of the order that is condensed to form an appropriate spot on the signal recording surface of the first optical disc via the objective lens 34 of the light beam having the first wavelength that passes therethrough. To be generated. That is, the first diffraction region 51 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light.

  In addition, the first diffraction region 51 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength passing therethrough by the first diffraction structure. It is generated so that the diffracted light of the order of light is dominant. That is, the first diffraction region 51 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light.

  In addition, the first diffraction region 51 is gathered so as to form an appropriate spot on the signal recording surface of the third optical disc through the objective lens 34 of the light beam having the third wavelength passing through the first diffraction structure. It is generated so that the diffracted light of the order of light is dominant. That is, the first diffraction region 51 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light.

  As described above, the first diffraction region 51 is formed with a diffractive structure suitable for the diffracted light of the predetermined order to be dominant with respect to the light beam of each wavelength described above. Has the following functions. That is, in the first diffraction region 51, the light beams having the respective wavelengths that have passed through the first diffraction region 51 and have become diffracted light of a predetermined order are condensed on the signal recording surface of each optical disk by the objective lens 34. It is possible to correct and reduce the spherical aberration at the time.

  The second diffractive region 52, which is the middle annular zone, is formed with a second diffractive structure that is annular and has a predetermined depth and is different from the first diffractive structure. The second diffractive region 52 is dominated by the diffracted light of the order that is condensed so as to form an appropriate spot on the signal recording surface of the first optical disc via the objective lens 34 of the light beam having the first wavelength that passes therethrough. To be generated. That is, the second diffraction region 52 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light.

  The second diffractive region 52 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength that passes through the second diffractive structure. It is generated so that the diffracted light of the order of light is dominant. That is, the second diffraction region 52 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light.

  The second diffractive region 52 is formed by the second diffractive structure so as to form an appropriate spot on the signal recording surface of the third optical disc via the objective lens 34 of the light beam having the third wavelength passing therethrough. It is generated so that diffracted light of orders other than the order of light is dominant. That is, the second diffraction region 52 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light. The second diffractive region 52 is gathered so as to form an appropriate spot on the signal recording surface of the third optical disc through the objective lens 34 of the light beam having the third wavelength passing through the second diffractive structure. The diffraction efficiency of the diffracted light of the order of light can be sufficiently reduced.

  As described above, the second diffraction region 52 is formed with a diffractive structure suitable for the diffracted light of the predetermined order to be dominant with respect to the light beam of each wavelength described above. Has the following functions. That is, in the second diffraction region 52, the first and second wavelength light beams that have been passed through the second diffraction region 52 to be diffracted light of a predetermined order are recorded on the respective optical discs by the objective lens 34. It is possible to correct and reduce spherical aberration when focused on the surface.

  The third diffractive region 53 which is an outer ring zone is formed in a third diffractive structure which is ring-shaped and has a predetermined depth and is different from the first and second diffractive structures. The third diffractive region 53 is dominated by the diffracted light of the order that is focused to form an appropriate spot on the signal recording surface of the first optical disc via the objective lens 34 of the light beam having the first wavelength that passes therethrough. To be generated. That is, the third diffraction region 53 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light.

  The third diffractive region 53 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength passing through the third diffractive structure. It is generated so that diffracted light of orders other than the order of light is dominant. That is, the third diffraction region 53 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light. The third diffractive region 53 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength passing therethrough by the third diffractive structure. The diffraction efficiency of the diffracted light of the order of light can be sufficiently reduced.

  The third diffractive region 53 is formed by the third diffractive structure so as to form an appropriate spot on the signal recording surface of the third optical disc via the objective lens 34 of the light beam having the third wavelength passing therethrough. It is generated so that diffracted light of orders other than the order of light is dominant. That is, the third diffraction region 53 is generated so as to have the maximum diffraction efficiency for other orders of diffracted light. The third diffractive region 53 is gathered so as to form an appropriate spot on the signal recording surface of the third optical disc through the objective lens 34 of the light beam having the third wavelength passing therethrough by the third diffractive structure. The diffraction efficiency of the diffracted light of the order of light can be sufficiently reduced.

  As described above, the third diffraction region 53 is formed with a diffractive structure that is suitable for the diffracted light of the predetermined order to be dominant with respect to the light beam of each wavelength described above. Has the following functions. That is, in the third diffraction region 53, the light beam having the first wavelength that has passed through the third diffraction region 53 and has been diffracted to a predetermined order is condensed on the signal recording surface of the optical disc by the objective lens. It is possible to correct and reduce the spherical aberration at the time.

  Here, in the first to third diffraction regions 51, 52, and 53 described above, for example, an annular shape centered on the optical axis and the sectional shape of the annular zone is a blazed shape or a staircase shape with a predetermined depth. It is formed to become. In each diffractive structure of each diffractive region 51, 52, 53, the groove depth and the groove width of the diffracted light of a predetermined order so that the spot condensed on the signal recording surface of the optical disc is optimum as described above. The diffraction angle and the diffraction efficiency of the diffracted light of this order are formed in a predetermined range.

  The first to third diffraction regions 51, 52, and 53 function to limit the aperture of the light beams having the respective wavelengths that pass therethrough. That is, the first diffraction region 51 is formed in a size corresponding to, for example, about NA = 0.45. The second diffraction region 52 is formed in a size corresponding to, for example, NA = 0.6, and the third diffraction region 53 is formed, for example, in a size corresponding to about NA = 0.85. Has been. The first to third diffraction regions 51, 52, and 53 can limit the aperture of the light beam having the first wavelength to pass so that the NA is, for example, about 0.85. In addition, the first to third diffraction regions 51, 52, and 53 can limit the aperture of the light beam having the second wavelength to pass so that the NA is, for example, about 0.60. In addition, the first to third diffraction regions 51, 52, and 53 can limit the aperture of the light beam having the third wavelength to pass so that the NA is, for example, about 0.45. As described above, the diffraction unit 50 including the first to third diffraction regions 51, 52, and 53 can perform aperture restriction with a numerical aperture corresponding to three types of optical disks and three types of light beams. As a result, the diffractive portion 50 does not require an aperture limiting filter or the like that has been necessary for an optical pickup in the past, or does not require adjustment when the optical pickup is disposed, thereby simplifying, downsizing, and reducing the configuration of the optical pickup. Enables cost reduction.

  Further, in the above description, as shown in FIG. 6A, the diffractive portion 50 including the three diffractive regions 51, 52, and 53 is provided on the incident side surface of the diffractive optical element 35 provided separately from the objective lens 34. However, the present invention is not limited to this. In other words, the diffractive portion having such a function may be provided on the exit side surface of the diffractive optical element 35. Further, the diffractive portion 50 having the first to third diffractive regions 51, 52, 53 may be configured to be integrally provided on the entrance side or exit side surface of the objective lens 34. For example, as shown in FIG. 6B, an objective lens 34B having a diffractive portion 50 may be provided on the incident side surface. For example, in the case where the diffractive portion 50 is provided on the incident side surface of the objective lens 34B, the surface shape of the incident side surface required as a function of the objective lens is used as a reference, and the diffractive structure as described above is used. A surface shape that matches the surface shape is formed. The objective lens 34B configured as described above has the following advantages, whereas the diffractive optical element 35 and the objective lens 34 described above function as the condensing optical device 36 by two elements. That is, the objective lens 34B functions as a condensing optical device that collects light beams of three different wavelengths appropriately with only one element so as not to generate spherical aberration on the signal recording surface of the corresponding optical disk. . By providing the diffractive portion 50 integrally with the objective lens 34B and using it as a condensing optical device constituting an optical pickup to which the present invention is applied, it is possible to further reduce the number of optical components and reduce the size of the configuration. The objective lens 34B in which the diffractive part having the same function as that of the diffractive part 50 is integrally provided on the incident side or outgoing side surface has the following advantages when used in an optical pickup. In other words, the objective lens 34B realizes the three-wavelength compatibility of the optical pickup by reducing aberrations and the like, and the number of parts can be reduced, and the configuration can be simplified and miniaturized, and high productivity and low cost can be achieved. Realize.

  As described above, the condensing optical device 36 including the objective lens 34 and the diffractive optical element 35 and the condensing optical device including the objective lens 34B have the effects described above. That is, such a condensing optical device is configured to favorably condense the light beam having the first wavelength whose divergence angle is converted by the collimator lens 37 into the substantially parallel light onto the signal recording surface of the first optical disc. ing. In addition, such a condensing optical device favorably condenses the light beam of the second wavelength converted into the diffused light having a predetermined divergence angle by the collimator lens 37 on the signal recording surface of the second optical disc. It is configured as follows. In addition, such a condensing optical device favorably condenses the light beam of the third wavelength whose divergence angle is converted by the collimator lens 37 into the diffused light having a predetermined divergence angle on the signal recording surface of the third optical disc. It is configured as follows.

  The astigmatism imparting diffractive optical element 44 constituting the astigmatism imparting device is disposed on the optical path between the first beam splitter 38 and the multi lens 42. The diffractive optical element 44 has a predetermined diffractive structure composed of a periodic structure in which unit periodic structures are continuously formed on one surface, and with respect to the incident light beams having the first to third wavelengths. Each is given a predetermined astigmatism. That is, the diffractive optical element 44 has a diffractive portion 43 having a predetermined diffractive structure on the incident side surface, and the diffractive portion 43 imparts predetermined astigmatism to the light beam of each wavelength.

  Then, the diffractive optical element 44 has first to third astigmatism differences Δ1, Δ2, Δ3 formed by applying astigmatism to the light beams of the respective wavelengths satisfy the relationship Δ1 <Δ2 <Δ3. Astigmatism is imparted to the light beam of the third wavelength. Here, Δ1 is an astigmatic difference formed when the diffractive optical element 44 imparts astigmatism to the light beam having the first wavelength, and Δ2 is light having the second wavelength by the diffractive optical element 44. It is an astigmatic difference formed by giving astigmatism to a beam. Further, Δ3 is an astigmatism formed when the diffractive optical element 44 imparts astigmatism to the light beam having the third wavelength.

  Specifically, as shown in FIG. 7A, the diffractive portion 43 of the diffractive optical element 44 includes a diffractive structure 55 composed of a hyperbolic periodic structure that generates astigmatism in the x ′ direction and the y ′ direction, and A diffractive structure 56 is formed. Then, the diffractive portion 43 has an AA cross section, which is a cross section in the y ′ direction that is the direction of astigmatism provided by the diffractive structures 55 and 56, as shown in FIG. A blazed diffractive structure formed with a thickness (depth) and a predetermined width is provided. The diffractive portion 43 has a BB cross section as a cross section in the x ′ direction, which is the direction of astigmatism provided by the diffractive structures 55 and 56, as shown in FIG. A blazed diffractive structure formed with a thickness (depth) and a predetermined width is provided.

  Specifically, among the four regions 43A1, 43A2, 43A3, and 43A4 that are divided in the x direction and the y direction that intersect at right angles and intersect on the optical axis as described later, one diagonal direction across the optical axis. A diffractive structure 55 is provided in the regions 43A2 and 43A4 that face each other. Of the four regions, the diffractive structure 56 is provided in the regions 43A1 and 43A3 facing the other diagonal direction across the optical axis. In other words, the diffractive structure 55 is a diffractive structure having a hyperbolic periodic structure provided in a pair of regions facing in the y ′ direction, and diffracts the light beam incident on the region in the y ′ direction. The diffractive structure 56 is a diffractive structure having a hyperbolic periodic structure provided in a pair of regions facing each other in the x ′ direction, and diffracts a light beam incident on the region in the x ′ direction. As described above, the diffractive portion 43 includes the first diffraction region composed of regions 43A2 and 43A4 that impart refractive power in the y ′ direction and the second diffraction composed of regions 43A1 and 43A3 that impart refractive power in the x ′ direction. And have a region.

Further, as described above, the diffractive structures 55 and 56 formed in the diffractive portion 43 have a reversed shape between the shape of the AA cross section in the y ′ direction and the shape of the BB cross section in the x ′ direction. ing. In other words, the cross-sectional shape of any one of the AA cross-section and the BB cross-section is formed toward the opposite side with respect to the reference height with respect to the other cross-sectional shape. That is, for example, the AA cross section in the y ′ direction is formed so as to fall to the element side with respect to the reference height B _H indicating the reference plane, and the BB cross section in the x ′ direction is the reference height. It is formed so as to be raised from the element side toward the air side with respect to _BH . The diffractive structure 55 configured like the shape of the AA cross section diffracts the light beam incident on the region where the diffractive structure 55 is formed in the y ′ direction and in the direction close to the optical axis. Further, the diffraction structure 56 configured like the shape of the BB cross section diffracts the light beam incident on the region where the diffraction structure 56 is formed in the x ′ direction and in the direction away from the optical axis. Such diffractive structures 55 and 56 have a function of condensing the near side in the y ′ direction and the far side in the x ′ direction with respect to the condensing position when the diffractive structures 55 and 56 are not provided. Have The diffractive portion 43 can generate astigmatism in the x ′ direction and the y ′ direction in this way, and can form a predetermined front focal line and a rear focal line to form an astigmatic difference corresponding to the diffraction angle. .

  The diffractive portion 43 having the diffractive structures 55 and 56 is such that the diffracted light of the diffraction order having a desired diffraction angle is dominant with respect to the first to third wavelengths, that is, diffracted light of the diffraction order. Are generated so that the diffraction efficiency becomes the maximum as compared with the diffraction efficiency of other orders of diffracted light. Then, the diffracting unit 43 uses the diffraction beams of the dominant diffracted light so that the above astigmatic differences satisfy the relationship of Δ1 <Δ2 <Δ3. Is provided with astigmatism.

  In the above description, as shown in FIG. 7, the diffractive portion includes a diffractive structure 55 provided in a pair of regions facing in the y ′ direction and a diffractive structure 56 provided in a pair of regions facing in the x ′ direction. However, the present invention is not limited to this. That is, as shown in FIG. 8, it may be configured to have only one diffractive structure, for example. The diffractive portion 43B shown in FIG. 8 includes a diffractive structure 55 in a region facing the y ′ direction across the optical axis among the four regions divided in the x direction and the y direction. The diffraction structure 55 has a cross-sectional shape as shown in FIG. 7B as described above. The diffractive portion 43B having the diffractive structure 55 forms a predetermined astigmatic difference by the action of condensing the light converging position in the y ′ direction on the near side with respect to the condensing position when the diffractive structures 55 and 56 are not provided. Is possible. In the above description, the diffractive structure 55 and the diffractive structure 56 are configured to have inverted shapes. However, the present invention is not limited to this, and the diffractive structures 55 and 56 may be formed in different shapes having different depths and groove widths. . However, even in the case of different shapes, it is advantageous to form a predetermined astigmatic difference by diffracting one in the direction close to the optical axis and diffracting the other in the direction away from the optical axis. .

  Compared to the case described with reference to FIG. 8 and the case where both diffraction structures are formed in different shapes, the diffractive portion 43 having the diffractive structures 55 and 56 having the inverted shapes described with reference to FIG. When a point difference is given, the diffraction grating period can be increased, which is advantageous from the viewpoint of manufacturing. Further, the diffractive portion 43 having the diffractive structures 55 and 56 described with reference to FIG. 7 can reduce manufacturing errors and the like by reducing the groove depth and the like, can prevent a decrease in diffraction efficiency, and the like. Use efficiency can be increased.

  Here, the diffractive portion 43 is configured as a blazed shape. However, the diffractive portion constituting the astigmatism applying device is not limited to the blazed shape, and is a staircase-shaped diffraction having a plurality of stepped portions. You may comprise so that a structure may be provided. Here, the groove depth d and the step number S (S = ∞ in the case of a blazed shape) are determined in consideration of the dominant diffraction order and diffraction efficiency.

  For example, instead of the blazed diffraction structure 55 described above, a step-shaped diffraction structure 57 as shown in FIG. 9 may be provided. Here, the staircase-shaped diffractive structure replacing the blazed diffractive structure 56 is configured to be symmetrical with respect to the reference plane with respect to the staircase shape described below with reference to FIG. Details are omitted here.

  The diffractive structure 57 shown in FIG. 9 is a diffractive structure in which the number of steps is 4 (S = 4), and the first to fourth steps in which the remarkable depth is substantially the same depth (d / 4). Stepped portions having portions 57s1, 57s2, 57s3 and 57s4 are continuously formed in the radial direction. The diffractive structure 57 includes first to fifth diffractive surfaces 57f1, 57f2, 57f3, 57f4, and 57f5 that are formed at the same interval of (d / 4) in the optical axis direction. . The diffractive portion configured to be provided with such a staircase-shaped diffraction structure has a desired diffraction angle with respect to each of the first to third wavelengths, as in the above-described case where the blazed diffraction structure is formed. It is generated so that the diffracted light of the diffraction order it has becomes dominant. The diffractive portion gives astigmatism to the light beams having the first to third wavelengths so that each of the astigmatic differences described above satisfies a predetermined relationship.

  Here, the diffractive structure composed of the hyperbolic periodic structure formed in the diffractive portion 43 of the diffractive optical element 44 will be further described.

The hyperbolic periodic structure means that the boundary of the periodic structure and a curve connecting positions of the same height (depth) within each period are −x ′ ² / a ² + y ′ ² / b ² = 1, And x ′ ² / a ² −y ′ ² / b ² = 1. Here, a and b are arbitrary values, but when a = b = 2 ^(1/2) , the power difference in the x ′ direction and the y ′ direction is the largest, so that the diffraction grating period is large. It is superior in manufacturing. Further, as described above, the x ′ direction and the y ′ direction are directions that pass through the optical axis and are orthogonal to each other in order to provide astigmatism. Then, when the x direction and the y direction inclined by 45 ° in the x ′ direction and the y ′ direction are set, that is, the x direction and the y direction passing through the optical axis and orthogonal to each other are set as follows: Can be expressed as That is, in the coordinate system in which the x direction and the y direction are the x axis and the y axis, the hyperbolic hyperbola of the diffraction unit 43 described above is also a curve represented by an inversely proportional expression where xy = c. Here, c is a positive or negative arbitrary value, the distance from the origin of the position indicating the pitch in A-A cross-sectional and B-B cross section described above when the r, with c = r ^2/2 Can be represented. Then, when the pitch in the x ′ direction or y ′ direction, which will be described later with reference to FIG. 13, is determined, the periodic structure described here is uniquely determined by an inversely proportional expression with this pitch being “r”. The Rukoto.

  The diffractive portion 43 of the diffractive optical element 44 is disposed on an optical path through which only the return light beam passes, and the astigmatism differences Δ1, Δ2, and Δ3 formed for the light beams of the respective wavelengths are Δ1 <Δ2 <. By being configured to satisfy the relationship of Δ3, the following effects are obtained. In other words, the diffractive portion 43 gives astigmatism to the light beams having the first to third wavelengths so as to satisfy the relationship of Δ1 <Δ2 <Δ3, so that the non-focus for detecting the focus according to the wavelength used. It is possible to optimize the point difference.

  In the optical pickup 3 having the diffractive part 43 constituting the astigmatism applying device as described above, the diffractive part 43 passes between the light receiving part 40 and the first beam splitter 38, that is, only the light beam on the return path passes. It is provided on the optical path. Then, the diffraction section 43 imparts astigmatism to the light beams having the first to third wavelengths. As a result, the optical pickup 3 uses the common objective lens 34 and the common light receiving unit 40 to determine the astigmatic difference of each wavelength in the optical system of the optical pickup that performs recording / reproduction on a plurality of types of optical disks. It is possible to have a relationship of Accordingly, the optical pickup 3 can set the focus pull-in range to a desired value suitable for each format.

Here, the focus pull-in range refers to a range in which the actuator can be driven according to a control signal to perform a focus operation. Specifically, the focus pull-in range appears when the horizontal axis indicates the defocus amount of the objective lens and the vertical axis indicates the focus error signal FE calculated as described later. It is between peaks of the S-shaped waveform (hereinafter also referred to as “S-shaped pp”). That is, the focus pull-in range is the distance in the horizontal axis direction between the upper limit peak position and the lower limit peak position. In general, the focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 suitable for each format of the first to third optical disks are as follows. Sji _λ1 for the first wavelength is 1.5 μm <Sji _λ1 <3.5 μm, and Sji _λ2 and Sji _λ3 for the second and third wavelengths are 4.0 μm <Sji _λ2 and Sji _λ3 <12.0 μm. It is.

  Next, it will be described that the focus pull-in range can be adapted by setting the astigmatic difference to a predetermined relationship. Prior to this, the principle of deriving the focus signal by the astigmatism method will be described.

  In general, in many optical pickups, an astigmatism method is used for detecting a focus error signal. As its principle, for example, astigmatism is generated in the x ′ direction and / or y ′ direction by using a cylindrical means CS such as a cylindrical lens in the optical system, and the focal position in the x ′ direction and the y ′ direction as shown in FIG. A difference is formed in the direction focal position. Here, the distance between the x′-direction focal position and the y′-direction focal position is the “astigmatic difference”. In the optical pickup 3 to which the present invention is applied, the above-described diffractive portion 43 functions as the cylindrical means CS.

In FIG. 11, the light receiving element that is the light receiving unit 40 is disposed between the so-called front focal line in the y ′ direction focal position and the rear focal line in the x ′ direction focal position. As shown in FIG. 12, the light receiving unit 40 has four divided areas 40a, 40b, 40c, and 40d. Here, in the following calculation, the output signal from the region 40a is A, the output signal from the region 40b is B, the output signal from the region 40c is C, and the output signal from the region 40d is D. As shown in FIGS. 12A to 12C, the spot shape on the light receiving unit 40 has an elliptical azimuth that is different before and after focusing. Therefore, by calculating FE = A + C−B−D Positive and negative focus signals can be obtained. 12A shows the spot shape of the spot S1 from the front focal line position f all _' to the focus position f _col , and FIG. 12B shows the spot S2 at the f _col which is the just focus position. The spot shape is shown. FIG. _12C shows the spot shape of the spot S3 from the focus position f _col to the rear focal line position f _{allx ′} . The focus signal FE is optimally focused at a position where the focus signal FE is exactly 0 as shown in FIG. Therefore, the focus position of the optical disk can be adjusted using this signal FE. The cylindrical means CS is generally configured as a cylindrical surface on one side of the multi-lens. However, in the optical pickup 3, the diffractive portion 43 of the diffractive optical element 44 serving as the astigmatism applying device described above is the cylindrical surface. It has the function of means CS. Further, as described above and below, the diffractive portion 43 can adjust the amount of astigmatism to be given for each wavelength, thereby making it possible to adapt the focus pull-in range to each optical disc 11, 12, 13. it can. In the optical pickup 3 to which the present invention is applied, the diffractive optical element 44 can change the x ′ direction and the y ′ direction to arbitrary directions by rotating in any direction. As a result, an astigmatic difference along the division pattern of the light receiving unit 40 can be generated.

Next, conditions for adjusting the focus pull-in range will be described. In general, it is known that the focus pull-in range Sji has a relationship represented by the following expression (1) when the astigmatic difference is Δn and the return magnification M of the optical system. Here, Δn is the above-described astigmatism, where n = 1 at the first wavelength, n = 2 at the second wavelength, and n = 3 at the third wavelength. The return path magnification M is a value calculated based on the focal length of an optical component arranged in the return path optical system. Here, in order to set Sji to a desired value for each wavelength, it is necessary to give wavelength selectivity to one or both of Δn and M. In general, both the astigmatism difference Δn and the return path magnification M in the case where the light receiving unit and the return path optical system are made common have almost no wavelength selectivity, and it is difficult to give them wavelength selectivity. It was. In view of this, in the optical pickup 3 to which the present invention is applied, the astigmatic difference Δn is provided with wavelength selectivity by providing the diffractive optical element 44. As described above, in order to set the focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 to desired values, it is necessary to set each astigmatic difference Δn to Δ1 <Δ2 <Δ3.

That is, as described above, by setting the astigmatic differences Δ1, Δ2, Δ3 formed in the light beams of the respective wavelengths to have a predetermined relationship, it is possible to deal with each optical disc. With the above relationship, it is possible to obtain desired focus pull-in ranges Sji _λ1 , Sji _λ2 , Sji _λ3 for each light beam of each wavelength corresponding to each optical disc.

  Here, the relationship between the diffractive structure formed in the diffractive portion 43 described above and the astigmatic differences Δ1, Δ2, and Δ3 formed in the light beams of the respective wavelengths will be described in more detail.

  The optical pickup 3 described above is a three-wavelength compatible optical pickup having a common objective lens 34 for a light beam of each wavelength and a common light receiving unit 40, which is a so-called paired object / one light receiving element. In such a three-wavelength compatible optical pickup, the diffractive optical element 44 is used instead of a cylindrical surface in a general optical pickup so as to provide a desired pull-in range. The diffractive optical element 44 includes a diffractive portion 43 provided with a diffractive structure so as to cause the astigmatic difference as described above. Here, as described above, the diffractive portion 43 of an example in which a blazed shape is formed as a diffractive structure will be described.

The phase difference function φ in the diffractive structure that causes astigmatism as shown in FIG. 7 is given by the following equation (2). In Expression (2) and Expression (3) described later, C represents a phase difference function coefficient and is the same value for each wavelength. Λ represents a wavelength, and represents one of the first wavelength λ ₁ , the second wavelength λ ₂ , and the third wavelength λ ₃ , and λ ₀ is a manufacturing wavelength, and here, the first wavelength The wavelength λ ₁ is set as follows. Moreover, x and y show the distance (mm) of the x direction and y direction shown in FIG. N represents the diffraction order. The phase difference function φ represented by the equation (2) indicates the amount of phase difference given at the position defined by x and y of the Nth order diffracted light of wavelength λ.

Here, in the x′y ′ coordinate system including the above-described x ′ direction indicating the intermediate direction between the + x direction and the + y direction and the above-described y ′ direction indicating the intermediate direction between the −x direction and the + y direction, Have the relationship. That is, the above-described phase difference function coefficient C has the relationship of the following equation (3), where the focal length in the x ′ direction by the diffraction structure is f _{dx ′} . Here, the focal length by the diffractive structure means the focal length of the thin lens having the same refractive angle as the diffraction angle given to the dominant order diffracted light diffracted by the diffractive structure. . In the case shown in FIG. 7 described above, the focal length by the diffractive structure 56 is f _{dx ′} , and the focal length by the diffractive structure 55 is f _{dy ′} described later. Here, the focal length by the diffractive structure that diffracts the incident light beam in the optical axis direction, that is, diffracts in the direction converging with respect to the incident direction, is defined as a positive focal length. Further, the focal length by the diffraction structure that diffracts the incident light beam in the direction away from the optical axis, that is, diffracts in the direction of divergence with respect to the incident direction is referred to as negative focal length.

As apparent from the equations (2) and (3), the focal lengths in the x ′ direction and the y ′ can be varied by making the phase difference function coefficient C appropriate. At this time, since the diffractive structures 55 and 56 have an inverted shape as described above, the relationship f _{dx ′} = −f _{dy ′} is established. At this time, the focal position in the x direction and the y direction, that is, the just focus position, which is an intermediate position between the focal positions in the x ′ direction and the y ′ direction, is not affected by the diffraction structures 55 and 56.

As shown in Equation (3), the focal length f _{dx ′} by the diffractive structure 55 is inversely proportional to the size of the selected diffraction order N and wavelength λ. From this, when the dispersion of the material is ignored, f _{dx ′ of} each wavelength satisfies the relationship represented by the following expression (4). In the formula (4), the focal length of the collimator lens 37 is f _col . Further, in order to simplify the relational expression, it is assumed that the collimator lens 37 is a thin lens and the multi lens 42 is not provided. Even if the multi-lens 42 is taken into consideration, the combined focal length of the collimator lens 37 and the multi-lens 42 may be used instead of f _col described later.
f _{dx1 ′} : f _{dx2 ′} : f _{dx3 ′} = 1 / N ₁ λ ₁ : 1 / N ₂ λ ₂ : 1 / N ₃ λ ₃ (4)

Here, the composite _{fallx ′} obtained by additionally providing the diffractive portion 43 having this diffractive structure is calculated by the following equation (5). In Expression (5), t is a distance between the collimator lens 37 and the diffractive portion 43 having a function as the cylindrical means CS.

When the light beam incident on the collimator lens 37 is parallel light, the object point distance S and the focal length f are the same. Similarly, for the sake of simplicity, it is assumed that the light beam incident on the collimator lens 37 is parallel light. The astigmatic difference delta, is the difference in FIG. _{11, f} allx _{'and f ally'.} That is, the astigmatic difference Δ can be calculated by the following equation (6). Further, as described above, since f _{dx ′} = −f _{dy ′} , the relationship of the following equation (7) is established. When Expression (6) is transformed using Expression (7), the following Expression (8) is obtained.
Δ = f _{allx ′} −f all _′ (6)
f _{allx ′} −f _col = − (f _{ally ′} −f _col ) (7)
Δ = 2 (f _{allx ′} −f _col ) (8)

From the relationship of the equation (8), f _{allx ′} that realizes a desired Δ is uniquely determined. Then, the following equation (9) is obtained from the equations (5) and (8). Here, assuming that f _col >>> Δ is self-evident, Equation (9) was calculated using this relationship.

From the equation (9), the ratio of the astigmatism difference Δ at each wavelength is obtained by the following equation (10) using the above equation (4).
Δ1: Δ2: Δ3 = N ₁ λ ₁ : N ₂ λ ₂ : N ₃ λ ₃ (10)

That is, as shown in Expression (10), when configuring the diffraction unit 43, the magnitude of the astigmatism Δ can be adjusted by selecting an appropriate diffraction order. The most desirable focus pull-in range is about 2 μm (= Sji _λ1 ) for the first optical disk such as BD, and about 5 μm (= Sji _λ2 ) for the second optical disk such as DVD. Is about 6 μm (= Sji _λ3 ). For example, when λ ₁ = 405 nm, λ ₂ = 655 nm, and λ ₃ = 785 nm, desired values can be obtained by selecting the orders of N ₁ = + 1, N ₂ = + 1, and N ₃ = + 1. That is, by selecting the above-mentioned orders, according to the equation (10), approximately Sji _λ1 = 3.2 μm for BD, Sji _λ2 = 4.9 μm for DVD, etc., Sji _λ3 = 5.8 μm for CD, etc. It can be a value of the degree. This is a good value within a range that can sufficiently withstand the use although the value of Sji _λ1 for BD is somewhat large. Similarly, by selecting the respective orders of N ₁ = −1, N ₂ = −1, and N ₃ = −1, according to Expression (10), good Sji _λ1 , Sji _λ2 , Sji _λ3 are obtained. It is done. Further, in the above description, the diffraction structure 55 and the focal length fdx ′ thereby focused on and the diffraction orders N ₁ , N ₂ , and N ₃ have been described. However, the diffraction orders in the diffraction structure 56 have the following relationship. . That is, since the diffraction structure 56 has the inverted shape of the diffraction structure 55 as described above, the diffraction order in the diffraction structure 55 is opposite to the positive and negative. That is, for example, if the diffraction orders (N ₁ , N ₂ , N ₃ ) = (+ 1, + 1, + 1) in the diffraction structure 55, the diffraction orders (N ₁ , N ₂ , N ₃ ) = ( −1, −1, −1).

Further, under the above-described pull-in condition, the following expression (11) is established. Considering this point further, in order to obtain an appropriate pull-in amount, the relationship between Δ1, Δ2, and Δ3 as follows from the relationship between the equations (12), (13), and (14) described in the related art. Will be led.
Δ1 <Δ2 <Δ3 (11)
1.5 μm <Sji _λ1 <3.5 μm (12)
4.0 μm <Sji _λ2 <12.0 μm (13)
4.0 μm <Sji _λ3 <12.0 μm (14)

Specifically, the expressions (12), (13), and (14) can be replaced as the following expressions (15), (16), and (17).
Sji _λ1min <Sji _λ1 <Sji _λ1max (15)
Sji _λ2min <Sji _λ2 <Sji _λ2max (16)
Sji _λ3min <Sji _λ3 <Sji _λ3max (17)

From this equation (15), equation (16), and equation (17), the relationship of Sji _λ2 / Sji _{λ1 and} the relationship of Sji _λ3 / Sji _λ1 are respectively expressed based on the maximum value and the minimum value of each pull-in range. (18), which can be obtained as equation (19).

  The following expressions (20) and (21) are obtained by transforming these expressions (18) and (19) based on the above expressions (12), (13), and (14). Can do. The equations (20) and (21) can be modified as shown in equations (22) and (23).

  Based on the equations (22) and (23), the above equation (1), and the fact that M is substantially the same for the three wavelengths, the following equations (24) and (25) are obtained. It is done.

The following formulas (26) and (27) are obtained by modifying the formulas (24) and (25).
1.14Δ1 <Δ2 <8.0Δ1 (26)
1.14Δ1 <Δ3 <8.0Δ1 (27)

In order to establish the relationship between the equations (26) and (27), the relationship between the following equations (28) and (29) is necessary. And it needs to be in the range of the following formula (30) and the following formula (31) from the formula (28) and the formula (29).
1.14λ ₁ N ₁ <N ₂ λ ₂ <8.0λ ₁ N ₁ (28)
1.14λ ₁ N ₁ <N ₃ λ ₃ <8.0λ ₁ N ₁ (29)

Here, if the diffractive part is configured from a blazed shape like the diffractive part 43 described above, the relationship of N ₁ ≧ N ₂ ≧ N ₃ and N ₁ , N ₂ , and N ₃ have the same sign due to the blazed condition. The relationship is always established. For this reason, the combination (N ₁ , N ₂ , N ₃ ) of the order of maximum diffraction efficiency of each wavelength selected by the diffractive optical element 44 is (+1, +1, +1) or (−1, −1, − In the case of 1), it can be said to be an excellent range.

That is, the diffractive optical element 44 and the diffractive portion 43 provided on the diffractive optical element 44 are configured to diffract the light beams of the respective wavelengths so as to satisfy the above-described equations (28) and (29). The point difference Δ1, Δ2, Δ3 can be set to have a predetermined relationship. Accordingly, the diffractive optical element 44 and the diffracting unit 43 can obtain desired focus pull-in ranges Sji _λ1 , Sji _λ2 , Sji _λ3 for each light beam of each wavelength corresponding to each optical disc.

The diffractive optical element 44 and the diffractive portion 43 provided on the diffractive optical element 44 are formed with a blazed diffraction structure and a combination of orders (N ₁ , N ₂ , N ₃ ) that provides the maximum diffraction efficiency for each wavelength. Is configured as described above. In other words, the diffractive optical element 44 and the diffracting unit 43 have the light beams of the respective wavelengths so that (N ₁ , N ₂ , N ₃ ) = (+ 1, +1, +1) or (−1, −1, −1). Astigmatism differences Δ1, Δ2 and Δ3 can be in an appropriate relationship. Accordingly, the diffractive optical element 44 and the diffracting unit 43 can obtain desired focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 for each optical beam corresponding to each optical disc. . Furthermore, the diffractive portion 43 having the blazed diffraction structure with the selected order can reduce the groove depth of the diffractive surface and can also reduce the influence of temperature change and the like.

  As described above, the optical pickup 3 includes the diffractive optical element 44 described above as an astigmatism applying device, whereby the astigmatic difference of each wavelength can be set to Δ1 <Δ2 <Δ3, and the focus pull-in range can be set to each format. To achieve a desired value suitable for

  Next, “pitch design” in the diffractive structures 55 and 56 formed in the diffractive portion 43 will be described. In the pitch design of the diffractive structure, in the case of a diffractive portion (diffraction surface) having a diffractive structure that imparts astigmatism as described above, the phase difference function φ is calculated by the above formula (2). Here, as shown in the above formula (1), the magnitude of Δ is determined from the desired focus pull-in range Sji and the magnification M depending on the configuration of the optical system. From this Δ and the above equation (9), the desired magnitude of fdx ′ is uniquely determined, and the phase difference function coefficient C is determined. The phase difference function φ is calculated from the phase difference function coefficient C by the equation (2).

Since the value of φ calculated by this equation (2) represents the phase at the design wavelength λ ₀ , φ ′ obtained by the relational expression of φ ′ = φ−nλ ₀ and the phase given by φ are Its effect is exactly the same. In other words, as shown in FIG. 13B, φ ′ obtained by the above relational expression is the remainder when φ is modulo by λ ₀ as shown in FIG. 13A, for example, so-called residue calculation. Is a value obtained by This φ ′ can also be said to be a phase amount to be added for determining the pitch of the actual diffractive structure. The actual diffraction structure pitch is determined from this φ ′. Specifically, as shown in FIG. 13C, it is determined so as to follow the shape of φ ′. The horizontal axis in FIGS. 13A to 13C indicates the radial position in the x ′ direction. Further, the vertical axis in FIG. 13A indicates the required phase amount φ for each position, and the vertical axis in FIG. 13B indicates the applied phase amount obtained by the remainder calculation for each position. φ ′ is shown. Moreover, the vertical axis | shaft in FIG.13 (c) shows the groove depth d. Here, in FIG. 13C, the blazed shape is shown after the pitch is determined. However, when the staircase shape is adopted as in the diffraction structure 57 described with reference to FIG. As shown in FIG. That is, in such a case, as shown in FIG. 13C, a stepped shape having a predetermined number of steps S is formed on the slope of the blaze. As described above, fdx ′ is calculated from the desired focus pull-in range and the like, and the diffraction pitch in the x ′ direction can be determined by the above-described method, and the above-mentioned hyperbola, that is, c in the inversely proportional expression obtained by modifying the hyperbola is obtained. . Similarly, the diffraction pitch in the y ′ direction may be determined by calculating fdy ′ and the like, but here, since it has an inverted shape, the pitch is the same.

  The diffractive portion 43 is formed with a diffractive structure having the above-determined pitch and the above-described hyperbolic periodic structure, thereby allowing the first to the first astigmatism to pass through the desired astigmatism. It is applied to a light beam having a wavelength of 3. Then, the diffraction unit 43 sets the focus pull-in range to a desired value suitable for each format by setting the astigmatic difference formed at each wavelength to a desired range with a relationship of Δ1 <Δ2 <Δ3. Realize.

  In the above description, the diffractive portion 43 that is provided on one surface of the diffractive optical element 44 and forms a predetermined astigmatism difference with respect to the light beam of each wavelength is used as the astigmatism imparting device constituting the optical pickup 3. Although described as being provided, the present invention is not limited to this. That is, the astigmatism imparting device is configured to include first and second diffractive portions respectively provided on any two surfaces selected from the incident side or the emission side of one or two diffractive optical elements. You may make it do.

  Here, an astigmatism providing device having diffraction portions provided on two surfaces will be described with reference to FIGS. 14 (a) and 14 (b).

  The astigmatism imparting device shown in FIG. 14A has, for example, a diffractive optical element 44C1 having a first diffractive portion 43C1 on its incident side surface, and a second diffractive portion 43C2 on its incident side surface, for example. And a diffractive optical element 44C2. Such an astigmatism imparting device imparts astigmatism to the light beams having the first to third wavelengths passing through the first and second diffracting portions 43C1 and 43C2. The diffractive optical elements 44C1 and 44C2 have first to third astigmatism differences Δ1, Δ2, and Δ3 formed by applying astigmatism to the light beams of the respective wavelengths satisfy the relationship Δ1 <Δ2 <Δ3. Astigmatism is imparted to the light beam of the third wavelength. Here, Δ1 is an astigmatism formed when the diffractive optical elements 44C1 and 44C2 add astigmatism to the light beam having the first wavelength, and Δ2 is a second difference between the diffractive optical elements 44C1 and 44C2. This is an astigmatic difference formed by giving astigmatism to a light beam having a wavelength of. Δ3 is an astigmatism formed when the diffractive optical elements 44C1 and 44C2 impart astigmatism to the light beam having the third wavelength.

The first diffractive portion 43C1 has a predetermined first diffractive structure composed of a periodic structure in which unit periodic structures are continuously formed. The second diffractive portion 43C2 has a predetermined second diffractive structure composed of a periodic structure in which unit periodic structures are continuously formed. In the following description, the first diffractive portion 43C1 uses the first diffractive structure to transmit diffracted lights of orders N ₁₁ , N ₂₁ , and N ₃₁ to the light beams having the first to third wavelengths, respectively. It is assumed that the maximum diffraction efficiency is generated with respect to the diffracted light of the order. In addition, the second diffractive portion 43C2 uses the second diffractive structure so that the diffracted lights of the orders N ₁₂ , N ₂₂ , and N ₃₂ are diffracted lights of other orders with respect to the light beams of the first to third wavelengths, respectively. The maximum diffraction efficiency is assumed to be generated.

And the 1st and 2nd diffraction parts 43C1 and 43C2 are formed so that the following formula | equation (32) may be satisfied. In Expression (32), the phase difference function coefficient by the first diffractive structure is C1, and the phase difference function coefficient by the second diffractive structure is C2. That is, the diffraction orders N ₁₁ , N ₂₁ , N ₃₁ , N ₁₂ , N ₂₂ , and N _{32 that} are dominant on each surface are formed so as to satisfy the relationship of Expression (32). Then, diffracted light is generated so as to give astigmatism to the light beam of each wavelength so as to satisfy the relationship of Δ1 <Δ2 <Δ3. In the first and second diffracting portions 43C1 and 43C2, the ratio of the astigmatism difference Δ at each wavelength is calculated by a method similar to the above-described equation (10).
Δ1: Δ2: Δ3 = (N ₁₁ C ₁ + N ₁₂ C ₂ ) λ ₁ : (N ₂₁ C ₁ + N ₂₂ C ₂ ) λ ₂ : (N ₃₁ C ₁ + N ₃₂ C ₂ ) λ ₃ (32)

And the 1st and 2nd diffraction parts 43C1 and 43C2 are, for example, N ₁₁ = + 2, N ₂₁ = + 1, N ₃₁ = + 1, N ₁₂ = + 1, N ₂₂ = −1, N ₃₂ = −2, C _By setting ₁ = −1.3C ₂ , a relationship of Δ ₁ : Δ ₂ : Δ ₃ ≈1: 2.3: 4.0 is obtained. As will be described later, this is a ratio of astigmatic difference adapted to the drawing range of each format of BD, DVD, and CD.

  The diffractive optical elements 44C1 and 44C2 as the astigmatism applying devices as described above can optimize the astigmatic difference for focus detection according to the wavelength used.

  Next, the astigmatism applying device shown in FIG. The astigmatism imparting device shown in FIG. 14B includes, for example, a diffractive optical element 44D having a first diffractive portion 43D1 on its incident side surface and a second diffractive portion 43D2 on its outgoing side surface. . Such an astigmatism imparting device imparts astigmatism to the light beams having the first to third wavelengths passing through the first and second diffracting portions 43D1 and 43D2.

  The diffractive optical element 44D includes first to third so that astigmatism differences Δ1, Δ2, and Δ3 formed by applying astigmatism to the light beams of the respective wavelengths satisfy a relationship of Δ1 <Δ2 <Δ3. Astigmatism is given to a light beam having a wavelength of. Here, the first diffractive part 43D1 has the same configuration as the first diffractive part 43C1 shown in FIG. 14A described above, and the second diffractive part 43D2 is the second diffractive part 43C1 described above. Since it is the same structure as, detailed description is abbreviate | omitted. That is, the first and second diffractive portions 43D1 and 43D2 are configured to satisfy the relationship of the expression (32). The diffractive optical element 44D as the astigmatism applying device as described above can optimize the astigmatic difference for focus detection according to the wavelength used.

  In FIG. 14A and FIG. 14B, the astigmatism imparting device constituting the optical pickup 3 is constituted by a diffractive portion constituted by two surfaces. However, the present invention is not limited to this. Absent. That is, the astigmatism imparting device may be configured to include a diffractive portion composed of one composite surface.

  Here, an astigmatism providing device having a diffractive portion in which the diffractive structure is combined will be described with reference to FIG.

  In the astigmatism imparting device shown in FIG. 14C, for example, a diffractive portion in which a diffractive structure formed so as to overlap the first basic structure and the second basic structure is formed on the incident-side surface. It comprises a diffractive optical element 44E having 43E. Such an astigmatism imparting device imparts astigmatism to the light beams having the first to third wavelengths that pass through the diffraction portion 43E.

  The diffractive optical element 44E includes first to third so that astigmatism differences Δ1, Δ2, and Δ3 formed by applying astigmatism to the light beams of the respective wavelengths satisfy a relationship of Δ1 <Δ2 <Δ3. Astigmatism is given to a light beam having a wavelength of. Here, Δ1 is an astigmatic difference formed when the diffractive optical element 44E imparts astigmatism to the light beam having the first wavelength, and Δ2 is light having the second wavelength by the diffractive optical element 44E. It is an astigmatic difference formed by giving astigmatism to a beam. Further, Δ3 is an astigmatism formed when the diffractive optical element 44E imparts astigmatism to the light beam having the third wavelength.

The first basic structure is a periodic structure in which unit periodic structures are continuously formed. For example, the first basic structure is the same as the first diffractive structure formed in the first diffractive portion 43C1 in FIG. It is structured. The second basic structure is a periodic structure in which unit periodic structures are continuously formed. For example, the second basic structure is the same as the second diffractive structure formed in the second diffractive portion 43C2 in FIG. It is structured. In the same manner as described above, the first and second basic structures have diffraction orders N ₁₁ , N ₂₁ , N ₃₁ , N ₁₂ , N ₂₂ , and N _{32 that} are dominant for each basic structure as shown in the equation (32). It is formed to satisfy the relationship. Here, C1 and C2 indicate phase difference function coefficients in the first and second basic structures, respectively. Such a first basic structure that predominates a predetermined diffraction order for each wavelength and a second basic structure that predominates a predetermined diffraction order for each wavelength are superimposed. The diffractive portion 43E having the composite diffractive structure functions as follows. In other words, the diffractive portion 43E having the composite diffractive structure has a diffractive structure as the first basic structure and a second basic structure by giving a predetermined optical path difference to the light beam of each wavelength. The same function as passing through the diffractive structure can be achieved. In other words, the diffracting unit 43E has the same effect as passing through the diffracting units 43C1 and 43C2 shown in FIG. 14A or 14B or passing through the diffracting units 43D1 and 43D2. Can be applied to the beam. The diffractive optical element 44E as the astigmatism applying device as described above makes it possible to optimize the astigmatic difference for focus detection according to the wavelength used.

  Further, in FIGS. 14A and 14B described above, the astigmatism imparting device constituting the optical pickup 3 is configured to include a diffractive portion constituted by two surfaces, but is not limited thereto. It is not a thing. That is, the astigmatism imparting device may be configured to include first to third diffractive portions provided on any three surfaces selected from the incident side or the exit side of each of the plurality of diffractive optical elements. Good.

  Here, an astigmatism imparting device having a diffractive portion provided on three surfaces will be described with reference to FIG.

  The astigmatism applying device shown in FIG. 14D is composed of, for example, a diffractive optical element 44F1 and a diffractive optical element 44F2. The diffractive optical element 44F1 has, for example, a first diffractive portion 43F1 on its incident side surface and a second diffractive portion 43F2 on its outgoing side surface. The diffractive optical element 44F2 includes, for example, a third diffractive portion 43F2 on the incident side surface thereof. Such an astigmatism imparting device imparts astigmatism to the light beams having the first to third wavelengths that pass through the first to third diffraction units 43F1, 43F2, and 43F3.

  The diffractive optical elements 44F1 and 44F2 have first to third astigmatism differences Δ1, Δ2, and Δ3 formed by giving astigmatism to the light beams of the respective wavelengths satisfy the relationship Δ1 <Δ2 <Δ3. Astigmatism is imparted to the light beam of the third wavelength. Here, Δ1 is an astigmatism formed when the diffractive optical elements 44F1 and 44F2 give astigmatism to the light beam having the first wavelength, and Δ2 is a second difference between the diffractive optical elements 44F1 and 44F2. This is an astigmatic difference formed by giving astigmatism to a light beam having a wavelength of. Δ3 is an astigmatism formed when the diffractive optical elements 44F1 and 44F2 impart astigmatism to the light beam having the third wavelength.

Each of the first to third diffractive parts 43F1, 43F2, and 43F3 has predetermined first to third diffractive structures each having a periodic structure in which unit periodic structures are continuously formed. In the following description, the first diffractive portion 43F1 uses the first diffractive structure to transmit diffracted lights of orders N ₁₁ , N ₂₁ , and N ₃₁ to the light beams having the first to third wavelengths, respectively. It is assumed that the maximum diffraction efficiency is generated with respect to the diffracted light of the order. In addition, the second diffractive portion 43F2 uses the second diffractive structure so that the diffracted lights of the orders N ₁₂ , N ₂₂ , and N ₃₂ are diffracted lights of other orders with respect to the light beams of the first to third wavelengths, respectively. The maximum diffraction efficiency is assumed to be generated. Further, the third diffractive portion 43F3 has a third diffractive structure, and the diffracted lights of the orders N ₁₃ , N ₂₃ , and N ₃₃ are diffracted lights of other orders with respect to the light beams of the first to third wavelengths, respectively. The maximum diffraction efficiency is assumed to be generated.

And the 1st thru | or 3rd diffraction parts 43F1, 43F2, and 43F3 are formed so that the following formula | equation (33) may be satisfied. In Expression (33), the phase difference function coefficient by the first diffractive structure is C1, the phase difference function coefficient by the second diffractive structure is C2, and the phase difference function coefficient by the third diffractive structure is C3. That is, the diffraction orders N ₁₁ , N ₂₁ , N ₃₁ , N ₁₂ , N ₂₂ , N ₃₂ , N ₁₃ , N ₂₃ , and N _{33 that} are dominant on each surface are formed so as to satisfy the relationship of the expression (33). Is done. Then, diffracted light is generated so as to give astigmatism to the light beam of each wavelength so as to satisfy the relationship of Δ1 <Δ2 <Δ3. In the first to third diffracting portions 43F1, 43F2, and 43F3, the ratio of the astigmatism difference Δ at each wavelength is calculated by the same method as the above-described equation (10).
Δ1: Δ2: Δ3 = (N ₁₁ C ₁ + N ₁₂ C ₂ + N ₁₃ C ₃ ) λ ₁ : (N ₂₁ C ₁ + N ₂₂ C ₂ + N ₂₃ C ₃ ) λ ₂ : (N ₃₁ C ₁ + N ₃₂ C ₂ + N ₃₃ C ₃ ) λ ₃ (33)

  The diffractive optical elements 44F1 and 44F2 as the astigmatism applying devices as described above can optimize the astigmatism for focus detection according to the wavelength used. As in the case described with reference to FIG. 14C, the diffractive portion having a composite diffractive structure in which two or three of the three surfaces shown in FIG. You may comprise so that it may have.

  In the optical pickup 3 having the astigmatism applying device shown in FIGS. 14A to 14D as described above, the diffractive optical element constituting the astigmatism providing device is used for focus detection according to the wavelength used. By setting the astigmatic difference of Δ1 <Δ2 <Δ3, there are the following advantages. That is, the optical pickup 3 can set the focus pull-in range to a desired value suitable for each format. Furthermore, the astigmatism applying device shown in FIGS. 14A to 14C adjusts the respective orders on the two surfaces and the phase difference function coefficient, as described using the equation (32). This makes it possible to obtain a more optimal astigmatic difference relationship Δ1, Δ2, Δ3. In addition, the astigmatism applying device shown in FIG. 14D is further optimized astigmatism by adjusting each order on the three surfaces and the phase difference function coefficient, as described using the equation (33). It is possible to obtain the relations Δ1, Δ2, Δ3 of the difference. Therefore, the optical pickup 3 having the astigmatism applying devices shown in FIGS. 14A to 14D realizes the focus pull-in range to a value that is more suitable for each format.

  By the way, the multi-lens 42 is disposed on the optical path between the first beam splitter 38 and the light receiving unit 40, and has, for example, a refracting surface, thereby having the following action. That is, the multi-lens 42 applies a predetermined magnification and refractive power to the light beam emitted from the diffractive optical element 44 and enters the light receiving surface of the light receiving unit 40 such as a photodetector of the photodetector 41. Condensed to The multi-lens 42 exhibits a divergence angle conversion function by functioning as an element that converts a divergence angle in order to condense incident light beams of respective wavelengths on the return path onto the common light receiving unit 40. The diffractive portion 43 of the diffractive optical element 44 described above may be configured to be integrally formed on one surface of the multi-lens 42. As described above, the diffractive portion 43 is formed so as to be integrated with the multi-lens 42, thereby further simplifying and downsizing the configuration as an optical pickup and increasing practical convenience.

  The photodetector 41 includes a light receiving unit 40 including a light receiving element such as a photodetector, and the common first light receiving unit 40 receives the light beams having the first to third wavelengths collected by the multi-lens 42. . Thereby, the photodetector 41 detects various detection signals such as a focus error signal and a tracking error signal together with the information signal.

  The optical pickup 3 configured as described above drives and displaces the objective lens 34 based on the focus error signal and the tracking error signal obtained by the photodetector 41. As a result, the optical pickup 3 moves the objective lens 34 to the in-focus position with respect to the signal recording surface of the optical disc 2, and the light beam is focused on the signal recording surface of the optical disc 2. Is recorded or reproduced.

  The optical pickup 3 includes first to third emission units that emit light beams having first to third wavelengths, and an objective lens 34 that constitutes a condensing optical device 36 that collects the light beams having each wavelength. And a diffractive portion 50 provided on one surface of the diffractive optical element 35. The diffractive portion 50 includes first to third diffraction regions 51, 52, and 53. The first to third diffraction regions 51, 52, and 53 are the predetermined first to third diffractions described above. It is comprised so that it may have a structure. The optical pickup 3 can appropriately collect the corresponding light beams on the signal recording surface using the common objective lens 34 for the three types of optical disks. Therefore, the optical pickup 3 realizes three-wavelength compatibility with the objective lens 34 in common without complicating the configuration, and realizes good information signal recording and / or reproduction with respect to each optical disc.

  Here, a condensing optical device 36 constituting the optical pickup 3 is constituted by the objective lens 34 and the diffractive optical element 35 having the diffractive portion 50 so as to realize the three-wavelength compatibility with the common objective lens. However, it is not limited to this. That is, the condensing optical device 36 constituting the optical pickup 3 may be configured by an objective lens 34B having a diffractive structure. In this case, the configuration can be further simplified and reduced in size. Here, the aberration reduction is realized by the diffractive portion 50 including the three annular zones on the so-called one surface composed of the first to third diffractive regions 51, 52, 53. However, the present invention is not limited to this. It may be realized by a diffractive structure provided on both sides. However, the configuration in which the diffractive portion 50 described above is provided is advantageous for downsizing the device, simplifying the configuration, further improving the light utilization efficiency, and omitting the adjustment process.

  As described above, the optical pickup 3 can give the optimum diffraction efficiency and diffraction angle for each region with respect to the light beam of each wavelength by the diffraction unit 50 constituting the condensing optical device 36. The optical pickup 3 can sufficiently reduce the spherical aberration on the signal recording surfaces of the three types of first to third optical disks 11, 12, and 13 having different formats such as the thickness of the protective layer. Optical components can be shared. As a result, the optical pickup 3 enables downsizing and simplification of the apparatus, and reading and writing of signals with respect to a plurality of types of optical disks 11, 12, and 13 using light beams having different three wavelengths. Is possible.

  The optical pickup 3 is provided on an optical path through which only the return light beam passes, and gives astigmatism to the light beams of the first to third wavelengths according to the wavelength of the incident light beam. It has a feature in that it includes an astigmatism imparting device composed of the diffractive portion 43 and the like. Since the optical pickup 3 has an astigmatism imparting device, an appropriate astigmatism difference can be formed for each wavelength used, and thereby the focus pull-in range can be adapted to each format.

  Here, as described above, specific numerical values are given as Example 1 regarding the fact that the desired astigmatic difference Δ and the pull-in range Sji can be obtained by providing the diffractive optical element 44 having the diffractive portion 43. explain.

<Example 1>
The first embodiment is an embodiment of the optical pickup 3 that is configured by actually inserting the diffractive optical element 44 having the diffractive portion 43 into the optical path. Various values in the optical pickup of Example 1 are shown in Table 1. As numerical values in Table 1 and Table 4 described later, the “diffraction order”, the phase difference function coefficient “c”, which is dominant for the light beam having the wavelength corresponding to each optical disc, and the “focal length f of the objective lens” for each wavelength (Mm). Further, “focal length f _col of collimator lens 37” (mm), “magnification M” at each wavelength, focus pull-in range “Sji” (μm), astigmatism difference “Δ” (mm), on light receiving unit 40 The light beam radius “Rpd” (μm) is shown. In calculation of Example 1 shown in Table 1 and Example 2 described later, the dispersion of the lens is taken into consideration, and the center of the astigmatism is positioned on the PDIC as the light receiving unit 40 by the movement of the collimator lens 37. It is adjusted so that. Therefore, the value is slightly different from the theoretical value, but there is no problem in actual use.

  Table 2 shows lens design values of the optical pickup of Example 1. In Table 2 and Tables 5 and 8 to be described later, the 0th surface represents a light source, and here, it is parallel light from infinity (∞). The 1st surface and the 2nd surface have shown the surface of the entrance side and the exit side of a collimator lens. The light beam from the light source is converted into convergent light by a collimator lens composed of a first surface and a second surface, and then passes through an air layer between the second surface and the third surface. As described above, the surface interval t at this time is such a value that the return light is collected on the light receiving surface of the light receiving unit 40 when the collimator lens 37 is driven by the collimator lens driving means 49. Next, it is changed for each wavelength λ. The third surface and the fourth surface are surfaces on the incident side and the emission side of the multilens 44B as the diffractive optical element described in FIG. That is, the diffraction surface 43 is provided on the third surface, and the lens surface 42B having a magnification conversion function is provided on the fourth surface.

  Strictly speaking, the values shown in Table 2 are slightly different from the values derived from the equations (9) and (10). And the curvature of the lens surface 42B on the exit side of the multi-lens. That is, the relationship between the expressions (9) and (10) is approximately satisfied.

  Further, specific numerical values of the blaze depth / efficiency design of the diffractive portion 43 constituting the optical pickup of Example 1 are shown in FIG. 15 and Table 3.

Here, FIG. 15 and Table 3 show the depth / efficiency design of the blaze when (N ₁ , N ₂ , N ₃ ) is (+1, +1, +1). FIG. 15 shows the change in diffraction efficiency with respect to the groove depth d when the diffraction structure is a blaze shape with S = ∞ and (N ₁ , N ₂ , N ₃ ) = (+ 1, + 1, + 1). It is. FIG. 15A is a diagram showing a change in the diffraction efficiency of the + 1st order diffracted light of the light beam of the first wavelength, and FIG. 15B is a diagram of the + 1st order diffracted light of the light beam of the second wavelength. It is a figure which shows the change of diffraction efficiency. FIG. 15C is a diagram showing a change in the diffraction efficiency of the + 1st order diffracted light of the light beam having the third wavelength. 15A to 15C, the horizontal axis represents the groove depth (nm), and the vertical axis represents the diffraction efficiency (light intensity).

As shown in FIG. 15 and Table 3, the diffraction efficiency eff1 = 0.84 of the diffraction order N ₁ = + 1 of the light beam of the first wavelength when the groove depth d = 950 nm, and the second wavelength The diffraction efficiency eff2 = 0.79 of the diffraction order N ₂ = + 1 of the light beam. The diffraction efficiency eff3 = 0.59 for the diffraction order N ₃ = + 1 of the light beam of the third wavelength. That is, each efficiency can be BD84%, DVD79%, CD59%, and it is shown that it has sufficient efficiency.

  As shown in Tables 1 to 3, the optical pickup of Example 1 and the diffractive portion as the astigmatism applying device can obtain a desired astigmatism difference Δ with sufficient efficiency, As a result, it is possible to obtain a desired pull-in Sji suitable for the format.

  In the first embodiment described above, the case where the diffractive portion is formed on one surface has been described. However, an example in which the diffractive portion has a two-surface configuration and gives different diffractive power will be described as a second embodiment.

<Example 2>
In the second embodiment, the optical pickup 3 actually configured by inserting the diffractive optical element having the diffractive portions 43C1 and 43C2 or the diffractive portions 43D1 and 43D2 described with reference to FIGS. 14A and 14B described above. This is an example. Various values in the optical pickup of Example 2 are shown in Table 4. The numerical values in Table 4 are as described above, but are shown as “diffraction order (first surface)” and “diffraction order (second surface)” which are dominant by each diffraction section of the plurality of diffraction sections. . In addition, the phase difference function coefficient in each diffraction section is “c (first surface)” and “c (second surface)”, and the ratio of each phase difference function coefficient is “c coefficient ratio” (= c (first surface). ) / C (second surface)).

  Table 5 shows the lens design values of the optical pickup of Example 2. In Table 5, description will be made assuming that the third surface is provided with the diffractive surface 1 corresponding to the first surface and the diffractive surface 2 corresponding to the second surface. Since the other configurations shown in Table 5 are the same as those in Table 2 described above, details are omitted.

  16 and 17 and Table 6 show specific numerical values of the blaze depth / efficiency design of the first and second diffractive parts constituting the optical pickup of Example 2. FIG.

Here, FIG. 16, FIG. 17 and Table 6 show that N ₁₁ = + 2, N ₂₁ = + 1, N ₃₁ = + 1, N ₁₂ = + 1, N ₂₂ = −1, N ₃₂ = −2, C ₁ = −1. It shows a blaze depth and efficiency design when designed as .3C _2. In addition, according to the relationship of Formula (32), the combination of such diffraction orders is Δ ₁ : Δ ₂ : Δ ₃ ≈1: 2.3: 4.0 (= 2: 4.6: 8.0). is there. This means that the ratio of Sji can be about 2: 4.6: 8, assuming that M does not have wavelength dependency as in equation (1) and Δ and Sji are approximately proportional. This is because the astigmatic difference between the first optical disk (BD, etc.) and the second optical disk (DVD, etc.) can be separated compared to the case of the first embodiment, and the focus pull-in range is also increased accordingly. Since it can be made appropriate, the configuration is more suitable for practical use.

In the case of such a configuration, the shape of the second surface is a step structure in order to give a relationship of N ₁₂ = + 1, N ₂₂ = −1, and N ₃₂ = −2. In the case of a step structure, the efficiency of each order can be changed by varying both the number of steps and the depth.

FIG. 16 shows the change in diffraction efficiency with respect to the groove depth d when the diffraction structure is a blaze shape with S = ∞ and (N ₁₁ , N ₂₁ , N ₃₁ ) = (+ 2, +1, +1). It is shown. FIG. 16A is a diagram showing a change in the diffraction efficiency of the + 2nd order diffracted light of the light beam of the first wavelength, and FIG. 16B is a diagram of the + 1st order diffracted light of the light beam of the second wavelength. It is a figure which shows the change of diffraction efficiency. FIG. 16C is a diagram showing a change in the diffraction efficiency of the + 1st order diffracted light of the light beam having the third wavelength.

Further, FIG. 17 shows the diffraction with respect to the groove depth d when the diffraction structure is a stepped shape having the number of steps S = 4 and (N ₁₂ , N ₂₂ , N ₃₂ ) = (+ 1, −1, −2). It shows the change in efficiency. FIG. 17A is a diagram showing a change in the diffraction efficiency of the + 1st order diffracted light of the light beam having the first wavelength, and FIG. 17B is a -1st order diffracted light of the light beam having the second wavelength. It is a figure which shows the change of diffraction efficiency. FIG. 17C is a diagram showing a change in the diffraction efficiency of the −2nd order diffracted light of the light beam having the third wavelength. 16 (a) to 16 (c) and 17 (a) to 17 (c), the horizontal axis represents the groove depth (nm), and the vertical axis represents the diffraction efficiency (light intensity). FIG.

As shown in FIG. 16, FIG. 17 and Table 6, the first surface (first diffractive portion) configured as a blaze has a first depth when the groove depth d = 1600 nm as shown in FIG. The diffraction efficiency eff1 = 0.98 of the diffraction order N ₁₁ = + 2 of the light beam of 1 wavelength. Further, the diffraction efficiency eff2 = 0.83 of the diffraction order N ₂₁ = + 1 of the light beam of the second wavelength, and the diffraction efficiency eff3 = 1.00 of the diffraction order N ₃₁ = + 1 of the light beam of the third wavelength. is there. That is, since each efficiency can ensure BD98%, DVD83%, and CD100%, the light quantity loss by this structure is suppressed and it has shown that it has sufficient efficiency.

In the second surface (second diffractive portion) configured as a staircase shape, as shown in FIG. 17, the first wavelength when the number of steps is s = 4 and the groove depth is d = 3800 nm. The diffraction efficiency eff1 = 0.81 for the diffraction order N ₁₂ = + 1 of the light beam. Also, the diffraction efficiency eff2 = 0.62 of the diffraction order N ₂₂ = −1 of the light beam of the second wavelength, and the diffraction efficiency eff3 = 0.02 of the diffraction order N ₃₂ = −2 of the light beam of the third wavelength. 57. That is, each efficiency can be BD81%, DVD62%, CD57%, and it is shown that it has sufficient efficiency.

  As shown in Tables 4 to 6, the first and second diffractive portions as the optical pickup and the astigmatism applying device of Example 2 have a desired astigmatism Δ in a state having sufficient efficiency. Can be obtained. Thereby, the optical pickup and the astigmatism imparting device can realize obtaining a desired pull-in Sji suitable for the format.

  As a modification of the second embodiment, the results shown in Tables 4 to 6 can be obtained even when the composite diffraction section is configured by superposition as shown in FIG. Then, specifically, for example, the superposition of two types of diffraction structures is shown in FIG. That is, in FIG. 18, Ls1 indicates the shape of the first surface shown in Example 2, that is, the periodic structure of the first basic structure. Moreover, Ls2 shows the shape of the 2nd surface shown in Example 2, ie, the periodic structure of a 2nd foundation structure. Lg12 indicates a diffractive structure in which the first and second basic structures are superimposed. In FIG. 18, the horizontal axis indicates the position in the radial direction and the x ′ direction, and the vertical axis indicates the groove depth. The composite surface indicated by Lg12 in FIG. 18 shows a cross-sectional shape in the x ′ direction.

  As shown in the first and second embodiments described above, an astigmatism providing device is provided in the optical pickup 3 that uses the light beams of three different wavelengths and uses the objective lens 34 and the light receiving unit 40 in common. Thus, the following effects can be obtained. That is, by providing a diffractive portion as an astigmatism applying device with a predetermined order selected, a predetermined astigmatism is given to the light beam of each wavelength to form an appropriate astigmatism difference. Can do. In addition, the astigmatism applying device gives a predetermined astigmatism to the light beam of each wavelength, and generates an astigmatism satisfying the relationship of Δ1 <Δ2 <Δ3 with respect to the light beam of each wavelength. By doing so, the focus pull-in can be adapted to each format.

  That is, the optical pickup 3 including the diffractive portion 43 or the like as the astigmatism imparting device as described above has a configuration in which only one light receiving portion 40 is disposed with respect to the objective lens 34 that realizes three-wavelength compatibility. The focus pull-in range can be realized. The optical pickup 3 uses the objective lens 34 and the light receiving unit 40 in common, thereby realizing cost reduction and device miniaturization. The optical pickup 3 can suppress the lens stroke amount of the collimator lens 37 to be sufficiently small as shown in the first and second embodiments, and can reduce the size of the optical pickup 3. .

  Further, in the optical pickup 3, a collimator lens 37 as a divergence angle conversion element is moved to a predetermined position in the optical axis direction for each type of light beam emitted from the first to third wavelength light beams. It is comprised so that. The optical pickup 3 changes the state of the light beams of the first to third wavelengths according to the position of the optical axis direction in which the collimator lens 37 is moved, so that the light beam of each wavelength is the same as that of the light receiving unit 40. It can be condensed on the light receiving surface. That is, the optical pickup 3 has an effect of realizing compatibility with the common objective lens 34 and the common light receiving unit 40 corresponding to the three wavelengths.

  As described above, the optical pickup 3 realizes appropriate three-wavelength compatibility including the focus pull-in range and the like by the common objective lens 34 and the common light receiving unit 40, and the optical components of the objective lens 34 and the photodetector 41. Can be used in common to reduce the number of parts. Further, the optical pickup 3 can realize a reduction in size and cost by realizing common use of various optical components arranged on the optical path between the objective lens 34 and the photodetector 41. Further, the optical pickup 3 can improve the characteristics as an optical pickup by preventing the influence when there is a characteristic variation for each component provided for each wavelength due to the sharing of the components.

  Further, this optical pickup 3 realizes the three-wavelength compatibility by using one objective lens 34, thereby eliminating the problems caused when a plurality of objective lenses are used. In other words, the optical pickup 3 eliminates problems such as a decrease in actuator sensitivity and problems such as deterioration in characteristics when there is an error in the mounting angle of each objective lens to the actuator. Realize the characteristics. In addition, this optical pickup 3 realizes the three-wavelength compatibility by the single light receiving unit 40, which is a problem when a plurality of light receiving units (light receiving elements) are provided, and the configuration for routing a plurality of wirings is complicated. The problem of obstructing or miniaturization is solved. Further, the optical pickup 3 as a whole reduces the number of components as described above, thereby reducing the number of adjustment steps required in manufacturing and realizing easy manufacturing and cost reduction.

  Next, the optical path of the light beam emitted from each emission part of the first and second light source parts 31 and 32 in the optical pickup 3 configured as described above will be described with reference to FIG. First, an optical path when information is read or written by emitting a light beam having a first wavelength to the first optical disc 11 will be described.

  Next, the optical path of the light beam emitted from each emission part of the first and second light source parts 31 and 32 in the optical pickup 3 configured as described above will be described with reference to FIG. First, an optical path when information is read or written by emitting a light beam having a first wavelength to the first optical disc 11 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the first optical disc 11 emits a light beam having the first wavelength from the first emitting unit of the first light source unit 31.

  The light beam of the first wavelength emitted from the first emission unit is divided into three beams for detection of a tracking error signal or the like by the first grating 45 and is incident on the first beam splitter 38. The light beam having the first wavelength incident on the first beam splitter 38 is reflected by the separation surface 38a and emitted to the second beam splitter 39 side.

  The light beam having the first wavelength incident on the second beam splitter 39 is transmitted through the combined separation surface 39a, is emitted to the collimator lens 37 side, the divergence angle is converted by the collimator lens 37, and ¼. A predetermined phase difference is given to the wave plate 47. Then, this light beam is reflected by the rising mirror 48 and emitted to the diffractive optical element 35 side of the condensing optical device 36. At this time, the collimator lens 37 is moved to the first position by the collimator lens driving means 49 and controlled so as to emit the light beam having the first wavelength in a predetermined state.

  The light beam having the first wavelength incident on the diffractive optical element 35 is transmitted through each region by the first to third diffraction regions 51, 52, and 53 of the diffractive portion 50 provided on the incident side surface. Each of the beams is emitted such that a predetermined diffraction order is dominant as described above. Such a light beam is incident on the objective lens 34 of the condensing optical device 36. The light beam of the first wavelength emitted from the diffractive optical element 35 is not only in a predetermined divergence angle state but also in a predetermined aperture restriction state.

  Since the light beam having the first wavelength incident on the objective lens 34 is incident at a divergence angle such that the light beam that has passed through each of the regions 51, 52, and 53 can reduce spherical aberration, the objective lens 34 The light is appropriately condensed on the signal recording surface of the first optical disc 11.

  The light beam collected by the first optical disk 11 is reflected by the signal recording surface and passes through the objective lens 34, the diffractive optical element 35, the rising mirror 48, the quarter wavelength plate 47, and the collimator lens 37. The light beam is transmitted through the combining / separating surface 39a of the second beam splitter 39, transmitted through the separating surface 38a of the first beam splitter 38, and emitted to the diffractive optical element 44 side.

  The diffractive optical element 44 gives a predetermined astigmatism to the light beam of the first wavelength branched from the optical path of the forward light beam by the first and second beam splitters 38 and 39. The light beam having the first wavelength is given a predetermined refractive power by the multi-lens 42 and is focused on the light receiving surface of the light receiving unit 40 of the photodetector 41 and detected. At this time, the astigmatism difference Δ1 formed by applying astigmatism by the diffractive portion 43 of the diffractive optical element 44 is as described above in relation to Δ2 and Δ3 described later.

  Next, an optical path when information is read or written by emitting a light beam of the second wavelength to the second optical disc 12 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the second optical disc 12 emits a light beam having the second wavelength from the second emitting unit of the second light source unit 32.

  The light beam of the second wavelength emitted from the second emission part is divided into three beams for detection of a tracking error signal or the like by the second grating 46 and is incident on the second beam splitter 39. The light beam of the second wavelength incident on the second beam splitter 39 is reflected by the combined separation surface 39a, emitted to the collimator lens 37 side, the divergence angle is converted by the collimator lens 37, and the quarter wavelength. A predetermined phase difference is given to the plate 47. Then, the light beam is reflected by the rising mirror 48 and emitted to the diffractive optical element 35 side of the condensing optical device 36. At this time, the collimator lens 37 is controlled to be moved to the second position by the collimator lens driving means 49 and to emit the light beam having the second wavelength in a predetermined state.

  The light beam having the second wavelength incident on the diffractive optical element 35 is transmitted through each region by the first to third diffraction regions 51, 52, and 53 of the diffractive portion 50 provided on the incident-side surface. Each of the beams is emitted such that the predetermined diffraction order is dominant as described above. Such a light beam is incident on the objective lens 34 of the condensing optical device 36. The light beam of the second wavelength emitted from the diffractive optical element 35 is not only in a predetermined divergence angle state but also in a state where an aperture limiting effect is obtained by being incident on the objective lens 34. Has been.

  Since the light beam having the second wavelength incident on the objective lens 34 is incident at a divergence angle so that the light beam that has passed through the first and second diffraction regions 51 and 52 can reduce spherical aberration, The objective lens 34 is appropriately focused on the signal recording surface of the second optical disk 12.

  The return path of the light beam reflected by the signal recording surface of the second optical disk 12 is the same as that of the light beam having the first wavelength described above, and is therefore omitted. However, at this time, the astigmatism difference Δ2 formed by applying astigmatism by the diffractive portion 43 of the diffractive optical element 44 in the return optical system from the second optical disc is Δ1 and Δ3 described later. Thus, the above-described relationship is established. In addition, since the collimator lens 37 is moved to the second position, the common light receiving unit 40 can reliably receive and detect the returning light beam.

  Next, an optical path when information is read or written by emitting a light beam of the third wavelength to the third optical disc 13 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the third optical disc 13 emits a light beam having the third wavelength from the third emitting unit of the second light source unit 32.

  The light beam of the third wavelength emitted from the third emission unit is divided into three beams for detection of a tracking error signal or the like by the second grating 46 and is incident on the second beam splitter 39. The light beam of the third wavelength incident on the second beam splitter 39 is reflected by the combined separation surface 39a, emitted to the collimator lens 37 side, and the divergence angle is converted by the collimator lens 37. The light beam is given a predetermined phase difference to the quarter-wave plate 47, reflected by the rising mirror 48, and emitted to the diffractive optical element 35 side of the condensing optical device 36. At this time, the collimator lens 37 is controlled to be moved to the third position by the collimator lens driving means 49 and to emit the light beam having the third wavelength in a predetermined state.

  The light beam having the third wavelength incident on the diffractive optical element 35 is transmitted through each region by the first to third diffraction regions 51, 52, and 53 of the diffractive portion 50 provided on the incident side surface. Each of the beams is emitted such that the predetermined diffraction order is dominant as described above. Such a light beam is incident on the objective lens 34 of the condensing optical device 36. The light beam of the third wavelength emitted from the diffractive optical element 35 is not only in a predetermined divergence angle state but also in a state in which an aperture limiting effect is obtained by entering the objective lens 34. Has been.

  Since the light beam having the third wavelength incident on the objective lens 34 is incident in a state of a divergence angle so that the light beam that has passed through the first diffraction region 51 can reduce spherical aberration, the objective lens 34 The light is appropriately condensed on the signal recording surface of the third optical disc 13.

  The optical path of the return path of the light beam reflected by the signal recording surface of the third optical disc 13 is the same as that of the light beam having the first wavelength described above, and is therefore omitted. However, at this time, in the optical system returning from the third optical disk, the astigmatism difference Δ3 formed by applying astigmatism by the diffractive portion 43 of the diffractive optical element 44 is related to Δ1 and Δ2. Thus, the relationship is as described above. Further, since the collimator lens 37 has been moved to the third position, the common light receiving unit 40 can reliably receive and detect the returning light beam.

  The optical pickup 3 to which the present invention is applied includes a common condensing optical device 36, a photodetector 41 having a common light receiving unit 40, and an astigmatism applying device such as the diffractive optical element 44 described above. Has characteristics. The optical pickup 3 uses a common optical system having a common condensing optical device 36 and a common light receiving unit 40 corresponding to these three types of used wavelengths, and a light beam having a wavelength corresponding to each optical disc. And the reflected light from the optical disc is detected. The optical pickup 3 makes it possible to record and / or reproduce information signals on a plurality of types of optical disks while achieving downsizing of the apparatus and simplification of the configuration. Moreover, the optical pickup 3 can optimize the astigmatism difference formed according to each use wavelength in such a common optical system by an astigmatism applying device. Here, the astigmatism providing device can make the relationship of astigmatism formed at each wavelength an appropriate relationship of Δ1 <Δ2 <Δ3. Therefore, the optical pickup 3 can thereby set a focus pull-in range corresponding to the format of each optical disc, and can exhibit more compatibility with each optical disc. Thus, the optical pickup 3 realizes a simple structure and a small apparatus, and exhibits good compatibility with each optical disc to realize good recording and / or reproduction.

Further, the optical pickup 3 can reliably obtain the above-described effects with a simple configuration by forming the astigmatism applying device by the diffractive optical element 44 having the diffractive portion 43. In the optical pickup 3, the diffraction unit 43 includes a relationship of 1.14λ ₁ N ₁ <N ₂ λ ₂ <8.0λ ₁ N ₁ and 1.14λ ₁ N ₁ <N ₃ λ ₃ <8.0λ _1. It is configured to satisfy the relation of N _1. Thereby, the diffraction part 43 and the optical pickup 3 can obtain a desired astigmatic difference relationship with respect to each wavelength, thereby realizing an optimum focus pull-in range corresponding to each format. In the optical pickup 3, the diffraction unit 43 has a combination of diffraction orders (N ₁ , N ₂ , N ₃ ) generated so as to be dominant (+1, +1, +1) or (−1, −1, -1). Thereby, the diffraction part 43 and the optical pickup 3 can obtain a desired astigmatic difference relationship with respect to each wavelength, thereby realizing an optimum focus pull-in range corresponding to each format. Here, the optical pickup 3 has a blazed diffractive portion 43 that is a combination of such diffraction orders, so that the groove depth of the diffractive surface can be reduced and the influence of temperature change and the like can be reduced. Moreover, the optical pickup 3 can obtain a desired astigmatic relationship with respect to each wavelength by configuring the diffractive portion 43 to have the relationship of the above-described formula (10). Achieves the optimum focus pull-in range corresponding to each format.

  In addition, the optical pickup 3 is replaced with the diffractive part 43, as shown in FIGS. 14A to 14D, diffractive parts 43C1, 43C2, diffractive parts 43D1, 43D2, diffractive part 43E, or diffractive part 43F1, as shown in FIG. It is characterized by an astigmatism providing device comprising 43F2 and 43F3. The optical pickup 3 has such a two-sided or three-sided configuration or a configuration in which these are superimposed. Accordingly, the astigmatism applying device and the optical pickup 3 are configured to satisfy the relationship of the expression (32) or the expression (33), thereby further improving the astigmatism to be applied to each wavelength. Allows adjustment to range. Therefore, the optical pickup 3 realizes obtaining an optimum focus pull-in range corresponding to each format.

  Further, the optical pickup 3 converts the divergence angle of the incident light beams having the first to third wavelengths between the first beam splitter 38 and the light receiving unit 40 to condense on the light receiving unit 40. A multi lens 44B having an angle conversion function is provided. Further, by adopting a configuration in which the diffractive portion 43 is integrally formed on one surface of the multi-lens 44B, in addition to the above-described effects, further simplification and downsizing of the configuration as an optical pickup are realized.

  The optical pickup 3 is characterized in that it includes a collimator lens 37 as a divergence angle conversion element that is movable in the optical axis direction. The collimator lens 37 is moved to a predetermined position in accordance with the type of the light beam, and changes the state of the light beam having the first to third wavelengths, so that the light beam of each wavelength is the same as that of the light receiving unit 40. The light is condensed on the light receiving surface. The optical pickup 3 realizes adapting to each format of a plurality of types of optical discs with a common optical component by using the collimator lens 37 and the astigmatism applying device. The optical pickup 3 realizes simple recording and / or reproduction by realizing the simplification of the configuration and the miniaturization of the apparatus and exhibiting compatibility with each optical disc. Further, in the optical pickup 3, the stroke amount of the collimator lens 37 can be kept small, so that the optical pickup can be downsized.

  In addition, since the objective lens 34 can be made common to the three wavelengths, the optical pickup 3 can prevent the occurrence of problems such as a decrease in sensitivity due to an increase in the weight of the movable part in the actuator. In addition, the optical pickup 3 to which the present invention is applied can sufficiently reduce spherical aberration, which is a problem when using the common objective lens 34 for three-wavelength compatibility, by the diffraction unit 50 provided on one surface of the optical element. As a result, the optical pickup 3 has problems such as alignment between the diffractive parts when a diffractive part for reducing spherical aberration as described above is provided on a plurality of surfaces, and a decrease in diffraction efficiency due to the provision of a plurality of diffractive parts. Can be prevented. That is, the optical pickup 3 realizes simplification of the assembly process and improvement of light use efficiency. Further, the optical pickup 3 to which the present invention is applied has a diffractive portion 50 in place of the objective lens 34 and the diffractive optical element 35 by enabling the configuration in which the diffractive portion 50 is provided on one surface of the optical element as described above. It is possible to configure to have the objective lens 34B. Such an optical pickup 3 has a structure in which the diffractive part 50 is integrated with the objective lens, thereby further simplifying the structure, reducing the weight of the movable part of the actuator, simplifying the assembly process, and improving the light utilization efficiency. Realize.

  Further, the optical pickup 3 not only realizes three-wavelength compatibility by the diffractive portion 50 provided on one surface of the diffractive optical element 35 described above, but also apertures corresponding to three types of optical disks and three types of light beams. The aperture can be limited by a number. As a result, the optical pickup 3 does not require an aperture limiting filter or the like that has been necessary in the past, and does not require adjustment when the filter is disposed, and further simplifies the configuration, reduces the size, and reduces the cost. .

  In the optical pickup 3 described above, an example having an astigmatism imparting device including the diffractive optical element 44 and the like has been described. However, the astigmatism imparting device constituting the optical pickup to which the present invention is applied is limited to this. It is not a thing. For example, the astigmatism applying device may be configured to use a liquid lens that changes the refractive power of light by an applied voltage.

  Next, an example using a liquid lens as an astigmatism applying device will be described with reference to FIG. The optical pickup 60 shown in FIG. 19 is the same as the above except that the liquid lens 64 is used instead of the diffractive optical element 44 with respect to the optical pickup 3 described above. Omitted.

  As shown in FIG. 19, the optical pickup 60 includes a first light source unit 31, a second light source unit 32, an objective lens 34 and a diffractive optical element 35 that constitute a condensing optical device 36, a collimator lens 37, and the like. Is provided. The optical pickup 60 includes first and second beam splitters 38 and 39, a photodetector 41 having a light receiving unit 40, and a multilens 42. Further, as shown in FIGS. 19 and 21A, the optical pickup 60 is provided between the multi-lens 42 and the first beam splitter 38, and has astigmatism corresponding to the wavelength of the incident light beam. A liquid lens 64 is provided as an astigmatism applying device. The optical pickup 60 includes first and second gratings 45 and 46, a quarter wavelength plate 47, and a rising mirror 48.

  As shown in FIGS. 20A to 20C, the liquid lens 64 serving as an astigmatism applying device includes a first medium 64a and a second medium 64b, which are two media having different refractive indexes. It is sealed with a glass layer 64c serving as a sealing layer. Here, for example, insulating oil is used as the first medium 64a. For example, a conductive aqueous solution is used as the second medium 64b. The liquid lens 64 is provided with electrodes 67 and 68 via insulating layers 65 and 66. The interface shape between the first and second magnifications 64 a and 64 b is configured to change according to the voltage applied to the electrodes 67 and 68. Then, the liquid lens 64 changes the interface shape so as to change the water repellency of the aqueous solution in accordance with the voltage so as to exhibit a desired refractive power. The liquid lens 64 is configured such that the interface shape that functions as the lens surface is a cylindrical shape. Specifically, as shown in FIGS. 20A and 20B, the liquid lens 64 is configured such that the electrodes 67 and 68 are arranged in only one direction. In the liquid lens 64, when a voltage is applied between the electrodes 67 and 68, the curvature in the x 'direction is increased by this voltage, but hardly changes in the y' direction. For this reason, the liquid lens 64 acts as a cylindrical surface of the above-described cylindrical means. Thus, the liquid lens 64 is configured to have a refractive power only in the above-described x ′ direction, for example.

  As described above, the liquid lens 64 changes the refractive power of the light by changing the curvature of the interface shape in, for example, the x ′ direction among the x ′ direction and the y ′ direction orthogonal to each other in accordance with the applied voltage. As a result, they have different curvatures with respect to the orthogonal x ′ direction and y ′ direction. In other words, the liquid lens 64 is configured to apply an electric field in one direction as described above so as to have different curvatures with respect to the orthogonal x ′ direction and y ′ direction. Note that the configuration of the liquid lens used in the optical pickup 60 is not limited to this, and any liquid lens may be used as long as it has a cylindrical function capable of providing astigmatism, and the medium used is not limited to the above. Absent.

  Further, the astigmatism imparting device constituting the optical pickup 60 is not limited to the liquid lens 64 shown in FIG. 21A as described above. For example, a liquid lens integrated with a multilens having a condensing function is used. May be a composite optical element in which is provided. That is, instead of the multi lens 42 and the liquid lens 64 described above, a composite optical element 74 as an astigmatism applying device as shown in FIG. 21B may be provided. The composite optical element 74 is provided with a liquid lens 64 similar to the above on one side, for example, on the incident side. In addition, the composite optical element 74 is provided with a lens surface 42B having a magnification conversion function on the exit side surface. The composite optical element 74 has both the functions of the multi lens 42 and the liquid lens 64 described above.

  The liquid lens 64 shown in FIG. 20 can change the refractive power in the x ′ direction by changing the applied voltage. Here, the liquid lens 64 imparts a refractive power of Rx′1 in the x ′ direction to the light beam having the first wavelength. Further, it is assumed that a refractive power of Rx′2 is given to the light beam of the second wavelength in the x ′ direction. Furthermore, it is assumed that a refractive power of Rx′3 is given to the light beam of the third wavelength in the x ′ direction. Here, the liquid lens 64 is arranged so as to impart refractive power in the x ′ direction. However, the liquid lens is provided so as to impart predetermined refractive power in the y ′ direction and for each wavelength. It may be configured. Furthermore, a liquid lens may be used in which electrodes are arranged in both the x ′ direction and the y ′ direction and a voltage is applied in each direction so as to have different curvature radii. In this case, the ratio of the power differences Rxy′1, Rxy′2, and Rxy′3 in the x ′ direction and the y ′ direction may be in the relationship of Rxy′1> Rxy′2> Rxy′3 as described later. .

  The liquid lens 64 imparts predetermined astigmatism to the light beams having the first to third wavelengths. The liquid lens 64 includes first to second astigmatism differences Δ1, Δ2, Δ3 formed by applying astigmatism to the light beams of the respective wavelengths satisfy the relationship Δ1 <Δ2 <Δ3. Astigmatism is imparted to the light beam having the third wavelength. That is, the liquid lens 64 is configured to give a refractive power that satisfies the relationship of Rx′1> Rx′2> Rx′3 to the light beams having the first to third wavelengths.

  As described above, the liquid lens 64 as the astigmatism applying device applies the refractive powers Rx′1, Rx′2, and Rx′3 having the above-described relationship, thereby reducing the astigmatic difference of each wavelength by Δ1. <Δ2 <Δ3. As a result, the liquid lens 64 realizes the focus pull-in range to a desired value suitable for each format.

  Here, a specific numerical value will be described as Example 3 to provide a desired astigmatic difference Δ and a pull-in range Sji by providing the liquid lens 64 as described above.

<Example 3>
The third embodiment is an embodiment of the optical pickup 3 configured by actually inserting this liquid lens into the optical path. As described above, the liquid lens can have a variable curvature in one direction by using the cylindrical means CS as a liquid lens. In order to realize the most suitable astigmatic difference amount, the relationship of the following equation (34) is necessary. Here, the most suitable astigmatism amount is 2 μm (= Sji _λ1 ) for the first optical disc (BD etc.), 5 μm (= Sji _λ2 ) for the second optical disc (DVD etc.), It is about 6 μm (= Sji _λ3 ) for 3 optical discs (CD and the like).

  The relationship of the equation (34) is necessary because, in a normal lens, the reciprocal of the lens radius defines the power in the lens. It is generally known that the amount of astigmatism becomes a size corresponding to the above relation when the above relation is satisfied.

  Table 7 shows various numerical values such as the magnitude of Sji in the optical pickup of the third embodiment as described above. In this case, Rx ′ approximately satisfies the equation (34), and it is shown that a value close to the desired Sji pull-in is obtained. Further, when a liquid lens is used, there is almost no decrease in transmittance, and since the amount of Sji to be given can be controlled flexibly, the degree of freedom in design is great.

  Table 8 shows the lens design values of the optical pickup of Example 3. In Table 8, a description will be given assuming that the liquid lens described above is provided on the third surface. In the example of Table 8, it is assumed that the interface is not an interface composed of two liquids but merely an interface between air and a glass material. In practice, the interface curvature of the two liquids is set so as to have the same power. What is necessary is just to control, and it is also possible to give an equivalent effect. The other configurations shown in Table 8 are the same as those in Table 2 described above, and the details are omitted.

  The optical pickup 60 to which the present invention is applied is characterized in that it includes a condensing optical device 36, a photodetector 41 having a common light receiving unit 40, and a liquid lens 64 as an astigmatism applying device. The optical pickup 60 having the liquid lens 64 is compatible with each optical disk by using a common optical system having a common condensing optical device 36 and a common light receiving unit 40 corresponding to the three types of wavelengths used. A light beam having a wavelength to be focused is condensed. At the same time, the optical pickup 60 detects reflected light from the optical disk. The optical pickup 60 can record and / or reproduce information signals on a plurality of types of optical disks while achieving downsizing of the apparatus and simplification of the configuration. Further, the optical pickup 60 can optimize the astigmatism difference formed according to each use wavelength in such a common optical system by the astigmatism applying device. Here, the astigmatism providing device can make the relationship of astigmatism formed at each wavelength an appropriate relationship of Δ1 <Δ2 <Δ3. Therefore, the optical pickup 60 can thereby set a focus pull-in range corresponding to the format of each optical disc, and can exhibit more compatibility with each optical disc. Thus, the optical pickup 60 realizes a simple configuration and a reduction in size of the apparatus, and exhibits compatibility with each optical disc to realize good recording and / or reproduction. Further, such an optical pickup 60 uses a liquid lens as an astigmatism imparting device, thereby having a high degree of freedom, being hardly affected by stray light and the like, and can maintain a high SN ratio even when a liquid lens is inserted. .

  The optical disc apparatus 1 to which the present invention is applied records by selectively irradiating a plurality of light beams having different wavelengths to a plurality of types of optical discs that are driven to rotate while holding the optical disc. And / or an optical pickup that performs reproduction. The optical disk apparatus 1 uses the above-described optical pickups 3 and 60 as the optical pickup, so that the diffraction unit 50 uses the common objective lens 34 to respectively correspond to the three types of optical disks. Can be appropriately condensed on the signal recording surface. In addition, the optical disk device 1 can simplify the configuration and reduce the size of the device by sharing the components such as the objective lens 34 and the light receiving unit 40. At the same time, the optical disc apparatus 1 can set an appropriate focus pull-in range corresponding to the format of each optical disc by an astigmatism applying device such as the diffractive optical element 44. As a result, the optical disk apparatus 1 realizes both the downsizing of the configuration and the three-wavelength compatibility by obtaining a good servo signal and obtaining good recording / reproducing characteristics.

1 is a block circuit diagram showing an optical disc apparatus to which the present invention is applied. It is an optical path diagram showing an optical system of an optical pickup to which the present invention is applied. It is a figure for demonstrating the astigmatism provision device which comprises the optical pick-up to which this invention is applied, (a) is the example which provided the diffractive optical element as an astigmatism provision device separately from the multi lens FIG. (B) is a figure of the example which provided the diffractive optical element as an astigmatism provision device integrally with the multi lens. It is a figure for demonstrating that the light beam of 3 wavelengths is condensed on the light-receiving surface of a common light-receiving part by moving a collimator lens in the optical pick-up to which this invention is applied. (A) is a figure which shows that the light beam of the 1st wavelength is condensed on the predetermined condensing point by the collimator lens arrange | positioned in the position used as a reference | standard. (B) The light beams of the second and third wavelengths are condensed at the same condensing point as the light beam of the first wavelength by the collimator lens moved in the optical axis direction from the reference position. FIG. It is a figure for demonstrating the diffractive optical element of the condensing optical device which comprises the optical pickup to which this invention is applied, (a) is a top view of a diffractive optical element, (b) is a diffractive optical element of FIG. It is sectional drawing. It is a figure for demonstrating the example of the condensing optical device which comprises the optical pick-up to which this invention is applied. (A) is sectional drawing which shows the condensing optical device of the example comprised by the diffraction optical element for 3 wavelength condensing compatibility which has a diffraction part in the surface of an incident side, and an objective lens. (B) is sectional drawing which shows the condensing optical device of the example comprised by the objective lens by which the diffraction part was integrally formed in the surface of the incident side. It is a figure for demonstrating the diffractive optical element as an astigmatism provision device which comprises the optical pick-up to which this invention is applied, (a) is a top view of the diffractive optical element provided with the diffraction part. (B) is a cross-sectional view in the y ′ direction of the diffractive optical element showing the AA cross section, and (c) is a cross-sectional view in the x ′ direction of the diffractive optical element showing the BB cross section. It is a figure which shows the other example of the astigmatism provision device which comprises the optical pick-up to which this invention is applied, It is a top view of the example of the explanation optical element of the example provided with the diffraction part which has a diffraction effect only in y 'direction . It is a figure which shows the other example of the diffractive optical element which comprises the optical pick-up to which this invention is applied, and is a top view of the diffractive optical element provided with the step-shaped diffraction part. It is a figure which shows the relationship between the defocus amount of an objective lens, and a focus error signal, and a focus drawing-in range. It is a figure explaining the astigmatism difference which arises by the astigmatism provided by a return optical system, and the condensing position of the x direction by passing through the multi lens which provides astigmatism, and the condensing position of ay direction It is a figure which shows typically the astigmatic difference which is the space | interval of these positions. It is a figure for demonstrating the detection of the focus error signal by an astigmatism method, (a) is a top view which shows the spot shape on a light-receiving part in the position close | similar to a focus position. (B) is a top view which shows the spot shape on the light-receiving part in a focus position. (C) is a top view which shows the spot shape on a light-receiving part in case it exists in a position far from a focus position. It is a figure for demonstrating the method of determining the pitch of the diffractive structure which provides astigmatism, (a) is a figure which shows design phase amount (phi) intended to provide to design wavelength (lambda) ₀ for every position of a radial direction. It is. (B) is a figure which shows phase amount (phi) 'actually given for every position of a radial direction based on (phi) shown by (a), (c) is phase amount (phi)' shown by (b). It is a figure which shows notionally the shape of the diffraction structure which provides. It is a figure for demonstrating the further another example of the diffractive optical element as an astigmatism provision device. (A) is a figure of the example in which the 1st and 2nd diffractive part was provided in several diffractive optical elements, (b) is the 1st and 2nd diffractive part provided in one diffractive optical element. FIG. (C) is a diagram of an example in which a composite diffractive part in which a plurality of basic structures are superimposed is provided, and (d) is an example in which first to third diffractive parts are provided in a plurality of diffractive optical elements. FIG. It is a graph for calculating the diffraction efficiency of the diffraction part of the diffractive optical element of Example 1, and it is a blaze shape (S = ∞) and (N ₁ , N ₂ , N ₃ ) = (+ 1, +1, +1) It is a figure which shows the change of the diffraction efficiency of the light beam of each wavelength with respect to the change of the groove depth d at the time of doing. 6 is a graph for calculating the diffraction efficiency of a first diffractive portion (first surface) of the diffractive optical element of Example 2. FIG. A change in the diffraction efficiency of the light beam of each wavelength with respect to a change in the groove depth d in a blazed shape (S = ∞) when (N ₁₁ , N ₂₁ , N ₃₁ ) = (+ 2, +1, +1) is shown. FIG. Is a graph for calculating the diffraction efficiency of the second diffraction portion of the diffractive optical element of Example 2 (second _{surface), S = 4, (N} 12, N 22, N 32) = (+ 1, -1 , -2) is a diagram showing a change in diffraction efficiency of a light beam of each wavelength with respect to a change in groove depth d. As a modified example of the second embodiment, the composite in the case where the composite diffractive portion is configured by superposition when the first surface of FIG. 16 is the first basic structure and the second surface of FIG. 17 is the second basic structure. It is a figure for demonstrating the diffraction structure of a diffraction structure. It is a figure which shows the groove depth with respect to the position of the radial direction (x 'direction) of a composite diffraction structure. It is an optical path diagram which shows the optical system of the example which used the liquid lens as an astigmatism provision device of the optical pick-up to which this invention is applied. It is a figure for demonstrating the liquid lens as an astigmatism provision device which comprises the optical pick-up to which this invention is applied, (a) is a top view of a liquid lens. (B) is a cross-sectional view in a direction including the x ′ direction and the y ′ direction, and (c) is a cross-sectional view in a direction different from the cross section shown in (b). It is a figure for demonstrating the astigmatism provision device which comprises the optical pick-up shown in FIG. 19, (a) is a figure of the example which provided the liquid lens as an astigmatism provision device separately from the multi lens It is. (B) is the figure of the example which provided the liquid lens as an astigmatism provision device integrally with the multi lens. It is a figure which shows the example of the optical system of the conventional optical pick-up, and is an optical path figure which shows the optical pick-up which has two or more light receiving elements.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical disk apparatus, 2 Optical disk, 3 Optical pick-up, 4 Spindle motor, 5 Feed motor, 9 Servo control part, 22 Disk type discrimination | determination part, 31 1st light source part, 32 2nd light source part, 34 Objective lens, 35 Diffraction Optical element, 36 Condensing optical device, 37 Collimator lens, 38 First beam splitter, 39 Second beam splitter, 40 Light receiving unit, 41 Photo detector, 42 Multi lens, 43 Diffraction unit, 44 Diffraction optical element, 45 First grating, 46 Second grating, 47 1/4 wavelength plate, 48 Rising mirror, 49 Collimator lens driving means, 50 Diffraction unit, 51 First diffraction region, 52 Second diffraction region, 53 Third Diffraction region

Claims (10)

It corresponds to the first wavelength light beam emitted from the first emission part and corresponding to the first optical disk, and corresponds to the second optical disk different from the first optical disk emitted from the second emission part and the above. Corresponds to a light beam having a second wavelength longer than the first wavelength, and a third optical disk different from the first and second optical disks emitted from the third light emitting section, and longer than the second wavelength. An objective lens that focuses the light beam of the third wavelength on the corresponding optical disk;
A photodetector that receives and detects the light beams of the first to third wavelengths reflected by the optical disc by a common light receiving unit;
An astigmatism imparting device that is provided between the objective lens and the light receiving unit and imparts astigmatism according to the wavelength of the incident light beam;
The astigmatism imparting device imparts astigmatism to the light beam of the second wavelength by setting an astigmatism difference formed by imparting astigmatism to the light beam of the first wavelength as Δ1. When the astigmatic difference formed by this is Δ2, and the astigmatic difference formed by applying astigmatism to the light beam of the third wavelength is Δ3, the relationship of Δ1 <Δ2 <Δ3 is satisfied. An optical pickup that gives astigmatism to a light beam of each wavelength.   2. The optical pickup according to claim 1, wherein the astigmatism imparting device is a diffractive optical element having a diffracting section that diffracts the first to third light beams so as to impart the astigmatism. The diffractive optical element includes an order N ₁ that is the maximum diffraction efficiency of the light beam having the first wavelength that passes through, an order N ₂ that is the maximum diffraction efficiency of the light beam having the second wavelength that passes through, The order N _3, which is the maximum diffraction efficiency of the light beam of the third wavelength that passes, is the first wavelength λ ₁ , the second wavelength λ _2, and the third wavelength λ _3. The optical pickup according to claim 2, wherein when ₃ , the light beam of each wavelength is diffracted so as to satisfy the expressions (1) and (2).
1.14λ ₁ N ₁ <N ₂ λ ₂ <8.0λ ₁ N ₁ (1)
1.14λ ₁ N ₁ <N ₃ λ ₃ <8.0λ ₁ N ₁ (2) In the diffractive optical element, the combination of orders (N ₁ , N ₂ , N ₃ ) that provides the maximum diffraction efficiency for each wavelength is (+1, +1, +1) or (−1, −1, −1). 4. The optical pickup according to claim 3, wherein a blazed diffraction structure is provided so as to diffract the light beam of each wavelength. The diffractive optical element includes the diffractive portion in which a diffractive structure including a periodic structure in which unit periodic structures are continuously formed is formed on an incident side or an exit side surface,
The diffracting unit is configured so that the diffracted light of the orders N ₁₁ , N ₂₁ , and N _{31 has} the maximum diffraction efficiency with respect to the diffracted lights of the other orders with respect to the light beams having the first to third wavelengths. Generate
The diffraction portion, the phase difference function coefficients by the diffractive structure and C _1, and ₁ the first wavelength lambda, the above second wavelength and lambda _2, when the third wavelength and lambda _3, Δ1: Δ2: Δ3 = (N ₁₁ C ₁ ) λ ₁ : (N ₂₁ C ₁ ) λ ₂ : (N ₃₁ C ₁ ) λ ₃ is formed so as to satisfy the relationship, and the first to third wavelengths are formed. 3. The optical pickup according to claim 2, wherein a diffracted light beam having a dominant order is generated so as to give the astigmatism to the light beam. The astigmatism imparting device has first and second diffractive sections provided on arbitrary surfaces selected from the respective incident side or exit side surfaces of the one or two diffractive optical elements, Providing the astigmatism to the first to third light beams passing through the first and second diffraction sections,
The first diffractive portion has a first diffractive structure having a periodic structure in which unit periodic structures are continuously formed, and the orders N ₁₁ , N ₁₁ , N ₂₁ and N ₃₁ diffracted light is generated so as to have the maximum diffraction efficiency with respect to other orders of diffracted light,
The second diffractive portion has a second diffractive structure composed of a periodic structure in which unit periodic structures are continuously formed, and the orders N ₁₂ , respectively, with respect to the light beams having the first to third wavelengths, N ₂₂ and N ₃₂ diffracted light is generated so as to have the maximum diffraction efficiency with respect to other orders of diffracted light,
The first and second diffracting sections have a phase difference function coefficient of C ₁ as a result of the first diffractive structure, C ₂ as a phase difference function coefficient of the second diffractive structure, and λ as the first wavelength. ₁ , when the second wavelength is λ ₂ and the third wavelength is λ ₃ , Δ1: Δ2: Δ3 = (N ₁₁ C ₁ + N ₁₂ C ₂ ) λ ₁ : (N ₂₁ C ₁ + N ₂₂ C ₂ ) λ ₂ : (N ₃₁ C ₁ + N ₃₂ C ₂ ) λ ₃ is formed, and the astigmatism is given to the light beams having the first to third wavelengths. 2. The optical pickup according to claim 1, wherein the diffracted light having the dominant order is generated. The diffractive optical element includes the diffractive portion in which a diffractive structure formed so as to overlap at least the first basic structure and the second basic structure is formed on the incident side or the outgoing side surface,
The first basic structure is a periodic structure in which unit periodic structures are continuously formed, and diffracted lights of orders N ₁₁ , N ₂₁ , and N ₃₁ with respect to the light beams having the first to third wavelengths, respectively. Is generated to have the maximum diffraction efficiency for other orders of diffracted light,
The second basic structure is a periodic structure in which unit periodic structures are continuously formed, and diffracted lights of orders N ₁₂ , N ₂₂ , and N ₃₂ with respect to the light beams having the first to third wavelengths, respectively. Is generated to have the maximum diffraction efficiency for other orders of diffracted light,
The diffractive portion has a phase difference function coefficient of C ₁ as the _first basic structure, C ₂ as a phase difference function coefficient of the second basic structure, λ ₁ as the first wavelength, Is λ ₂ and the third wavelength is λ ₃ , Δ1: Δ2: Δ3 = (N ₁₁ C ₁ + N ₁₂ C ₂ ) λ ₁ : (N ₂₁ C ₁ + N ₂₂ C ₂ ) λ ₂ : (N ₃₁ C ₁ + N ₃₂ C ₂ ) λ ₃ is formed so as to satisfy the relationship, and it becomes dominant to give the astigmatism to the light beams having the first to third wavelengths. The optical pickup according to claim 2, which generates diffracted light of the order. It is provided between the objective lens and the light receiving unit, and is movable in the optical axis direction. A divergence angle of the light beam having the first to third wavelengths is set to a predetermined value according to the moved position in the optical axis direction. Provided with a divergence angle conversion element that converts to a divergence angle,
The divergence angle conversion element is moved to a predetermined position in the optical axis direction for each type of light beam emitted from the light beams having the first to third wavelengths, and is moved to the moved optical axis direction position. 2. The optical pickup according to claim 1, wherein the light beam having each wavelength is condensed on the same light receiving surface of the light receiving unit by changing the state of the light beam having the first to third wavelengths accordingly.   The astigmatism imparting device is a liquid lens having a different curvature with respect to the orthogonal direction by changing the curvature of one or both of the orthogonal directions corresponding to the applied voltage. 2. The optical pickup according to claim 1, wherein a predetermined refractive power is imparted to the light beams having the first to third wavelengths so as to impart the astigmatism. An optical pickup that is arbitrarily selected from a plurality of types of optical discs, and that records and / or reproduces information signals by selectively irradiating a plurality of light beams having different wavelengths to a rotationally driven optical disc,
The above optical pickup
It corresponds to the first wavelength light beam emitted from the first emission part and corresponding to the first optical disk, and corresponds to the second optical disk different from the first optical disk emitted from the second emission part and the above. Corresponds to a light beam having a second wavelength longer than the first wavelength, and a third optical disk different from the first and second optical disks emitted from the third light emitting section, and longer than the second wavelength. An objective lens that focuses the light beam of the third wavelength on the corresponding optical disk;
A photodetector that receives and detects the light beams of the first to third wavelengths reflected by the optical disc by a common light receiving unit;
An astigmatism imparting device that is provided between the objective lens and the light receiving unit and imparts astigmatism according to the wavelength of the incident light beam;
The astigmatism imparting device imparts astigmatism to the light beam of the second wavelength by setting an astigmatism difference formed by imparting astigmatism to the light beam of the first wavelength as Δ1. When the astigmatic difference formed by this is Δ2, and the astigmatic difference formed by applying astigmatism to the light beam of the third wavelength is Δ3, the relationship of Δ1 <Δ2 <Δ3 is satisfied. In this way, an optical disc apparatus that applies astigmatism to a light beam of each wavelength.

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