JP2009020988A - Optical pickup apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus in which the adverse effects due to flare light are increased, when numerical aperture of an objective lens is made small, is improved. <P>SOLUTION: The optical pickup apparatus is provided with an objective lens 12 in which an annular diffraction grating is formed in accordance with numerical aperture; and a photodetector 14 includes a square-shaped light-receiving part P which is irradiated with, as a spot, the return light reflected from a signal recording layer, while generating at least a focus error signal, wherein the light receiving part P is constituted of square-shaped quadripartite sensor, while influence by the flare light increased when numerical aperture of the objective lens 12 set, corresponding to a laser beam having a long wavelength is made small, is excluded by making the major axis of an elliptical spot in which the level of the focus error signal obtained from the light-receiving part P correspond to the maximum with length of a diagonal line of the light-receiving part P. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup apparatus that performs an operation of reading a signal recorded on an optical disc and an operation of recording a signal on the optical disc.

  2. Description of the Related Art Optical disk apparatuses that can perform signal reading operation and signal recording operation by irradiating a signal recording layer of an optical disk with laser light emitted from an optical pickup device have become widespread.

  As an optical disk apparatus, an apparatus using an optical disk called CD or DVD is widely used, but recently, an optical disk with improved recording density, that is, a Blu-ray standard or an HD DVD (High Density Digital Versatile Disk) standard. Those using optical discs (new generation optical discs) have been developed.

  As a laser beam for performing an operation for reading a signal recorded on a CD standard optical disk, an infrared light having a wavelength of 780 nm is used, and a laser beam for performing an operation for reading a signal recorded on a DVD standard optical disk. In this case, red light having a wavelength of 650 nm is used.

  The protective layer provided on the upper surface of the signal recording layer in the CD-standard optical disc has a thickness of 1.2 mm, and an aperture of an objective lens used for performing a signal reading operation from the signal recording layer. The number is defined as 0.45. Further, the thickness of the protective layer provided on the upper surface of the signal recording layer in the DVD standard optical disc is 0.6 mm, and the numerical aperture of the objective lens used for performing the signal reading operation from the signal recording layer Is defined as 0.6.

  As a laser beam for performing a read operation of a signal recorded on an optical disc of the Blu-ray standard or the HD DVD standard with respect to the optical disc of the CD standard and the DVD standard, a laser beam having a short wavelength, for example, a wavelength of 405 nm is used. Blue-violet light is used.

  The thickness of the protective layer provided on the upper surface of the signal recording layer in the Blu-ray standard optical disc is 0.1 mm, and the aperture of the objective lens used to read out signals from the signal recording layer The number is defined as 0.85.

  On the other hand, the thickness of the protective layer provided on the upper surface of the signal recording layer in the HD DVD standard optical disc is 0.6 mm, and the objective lens used for performing the signal reading operation from the signal recording layer is used. The numerical aperture is defined as 0.65.

  As described above, blue laser light having a wavelength of 405 nm can be used as a laser beam for performing a read operation of a signal recorded on an optical disc of Blu-ray standard or HD DVD standard. By using both, it is possible to make an optical pickup device capable of reading signals from optical disks of both standards.

However, in order to read signals from both optical disks, the position of the signal recording layer is greatly different and the numerical aperture required by the objective lens is greatly different. Therefore, it is necessary to switch the numerical aperture corresponding to each optical disk. Optical pickup devices that can perform such operations have been developed. (See Patent Document 1.)
Recently, an optical disc apparatus that can use not only the optical discs of the CD standard and the DVD standard but also the Blu-ray standard and the HD DVD standard, which are new generation optical discs, has been commercialized. An optical pickup device used in such an optical disc apparatus can perform a signal reading operation from a signal recording layer provided in an applicable standard optical disc and a signal recording operation to the signal recording layer. Will be configured.

In such an optical pickup device, it is difficult to irradiate the signal recording layer of the optical disc with the laser light having the above-mentioned wavelength with a single objective lens. Two objective lenses are used: an objective lens and an objective lens that irradiates laser light onto, for example, a Blu-ray standard optical disc. (See Patent Document 2.)
The optical disc apparatus that can use the new generation optical disc can use the conventional optical discs of the CD standard and the DVD standard. The optical pickup device incorporated in such an optical disc apparatus includes the two optical pickup devices described above. A thing provided with an objective lens is common.

Such an optical pickup device is configured to condense laser beams of different wavelengths onto the signal recording layer of an optical disc of CD standard and DVD standard by one objective lens. In order to focus laser beams of different wavelengths on optical discs of different standards, a technique has been developed that uses an objective lens in which a ring-shaped diffraction grating is formed on the incident surface. (See Patent Document 3)
In addition, in an optical pickup device, a focus control operation for accurately condensing a spot generated by focusing on an objective lens on a signal recording layer on an optical disc and a tracking control operation for following a signal track are well known. Three beams separated and generated by the diffraction grating, that is, a main beam that is zero-order diffracted light and a sub beam that is ± first-order diffracted light are used.
JP 2006-172605 A Japanese Patent Laid-Open No. 11-23960 JP 2000-81666 A

  When diffracting the laser light of each wavelength using the objective lens with a diffraction grating and condensing it on the signal recording layer in order to correspond to each standard optical disc, the diffraction efficiency of the diffracted light used for each laser light of each wavelength is increased. To improve the design, the diffraction groove of the diffraction grating is designed. When designing such a diffraction grating, it is difficult to ensure the best diffraction efficiency for laser light of all wavelengths, at the expense of the diffraction efficiency of low-priority laser light to the diffraction grating. Designed.

  For example, it is necessary to increase the priority of diffraction efficiency for an optical disc having a high recording density due to the fact that the maximum light output is lower for shorter wavelength lasers, so the generation is the oldest and the recording density is the lowest. It sacrifices the diffraction efficiency for CD laser light. In this case, the diffraction efficiency set for the laser light for other optical discs is balanced, but depending on the design, the diffraction efficiency of the laser light for CD is about 40%, and unnecessary diffracted light called flare light is used. It may be lower than (60%).

With such a diffraction efficiency, the amount of light received by the sub-beam light receiving region provided in the photodetector for the flare light generated from the main beam having the highest light intensity among the three beams described above cannot be ignored. There is a problem that the tracking servo operation and the focus servo operation become unstable.

  The diffraction grating formed on the objective lens is designed to have a numerical aperture suitable for each optical disc in accordance with the wavelength of the laser beam for CD and the wavelength of the laser beam for DVD. The optical pickup device has a characteristic that, when the numerical aperture of the objective lens is reduced, the characteristic deterioration based on the inclination of the objective lens with respect to the signal surface of the optical disk is reduced.

  Condensing operation of laser light onto a signal recording layer provided on a CD standard optical disk and laser light onto a signal recording layer provided on a DVD standard optical disk by an objective lens in which an annular diffraction grating is formed In the optical pickup device configured to perform the above-described condensing operation, since the tilt of the objective lens is set with priority given to the characteristics for the DVD standard optical disk, the characteristics for the CD standard optical disk are deteriorated.

  As a method for improving this point, a method of reducing the numerical aperture of the objective lens set corresponding to the CD standard optical disk in consideration of the above-described characteristics can be considered. The amount of flare light received by the provided light receiving area increases so as not to be ignored. As a result, since an accurate focus error signal cannot be obtained, there is a problem that a focus servo operation performed using the focus error signal becomes unstable.

  The present invention is intended to provide an optical pickup device that can solve such a problem.

  The present invention includes an objective lens in which a ring-shaped diffraction grating is formed in accordance with a numerical aperture so as to focus laser beams having different wavelengths on optical disks having different thicknesses of a cover layer covering a signal recording layer, and the signal recording layer. And a photodetector that is provided with a square-shaped light receiving unit that emits reflected light as a spot and generates at least a focus error signal. The light receiving unit is configured by a quadrangular quadrant sensor. In addition, the aperture of the objective lens set corresponding to the laser beam having a long wavelength by matching the major axis of the elliptical spot where the level of the focus error signal obtained from the light receiving unit is maximum and the diagonal length of the light receiving unit are matched. It is configured to eliminate the influence of flare light that increases when the number is reduced.

  The present invention also provides an objective lens in which an annular diffraction grating is formed in accordance with the numerical aperture so that laser beams having different wavelengths are focused on optical disks having different thicknesses of cover layers covering the signal recording layer. A mask means for masking a part of the light receiving portion, comprising: a light receiving portion provided with a square light receiving portion that generates at least a focus error signal while irradiating return light reflected from the layer as a spot; The flare light is irradiated on the light receiving portion by the mask means so that the major axis of the elliptical spot where the level of the focus error signal obtained from the light receiving portion is maximum matches the diagonal length of the light receiving portion. By blocking, the influence of flare light that increases when the numerical aperture of the objective lens set corresponding to laser light with a long wavelength is reduced is eliminated. It is configured to.

  The present invention is characterized in that a liquid crystal control element is used as a mask means for masking a part of the light receiving portion.

  Further, the present invention is characterized in that a focus error signal is generated by using a spot at a portion where the intensity of the laser beam is a predetermined value or more.

The present invention is characterized in that a focus error signal is generated by using a spot at a portion of 1 / e ² or more with respect to the maximum intensity.

  An optical pickup device according to the present invention includes an objective lens in which a ring-shaped diffraction grating is formed in accordance with a numerical aperture so as to focus laser beams having different wavelengths on optical disks having different thicknesses of a cover layer covering a signal recording layer. And a photodetector that is provided with a square-shaped light receiving section that emits at least a return light reflected from the signal recording layer as a spot and generates a focus error signal. And the length of the elliptical spot where the level of the focus error signal obtained from the light receiving unit is maximized and the length of the diagonal line of the light receiving unit are set to correspond to the laser light having a long wavelength. Since the adverse effect of flare light that increases when the numerical aperture of the objective lens is reduced is eliminated, the numerical aperture of the objective lens is reduced. The focus servo operation hindrance that can be performed without also.

  FIG. 1 is an optical layout diagram showing one embodiment of an optical pickup device according to the present invention, FIG. 2 is a schematic diagram showing one embodiment of a photodetector according to the present invention, and FIG. 3 is a schematic diagram showing a conventional photodetector. FIG. 4 is a diagram for explaining the operation of generating a focus error signal, FIG. 5 is a characteristic diagram showing a level change of the focus error signal, and FIG. 6 is a characteristic for explaining the intensity distribution of the laser beam according to the present invention. FIG. In this embodiment, a description will be given of a case where the present invention is applied to an optical pickup device adapted to a CD standard optical disc and a DVD standard optical disc.

  In FIG. 1, reference numeral 1 denotes a CD standard optical disk, that is, a first laser diode that emits a laser beam condensed on a first optical disk D1 in which a signal recording layer L1 is provided at a position indicated by a solid line in FIG. A first wavelength in the infrared wavelength band of 765 nm to 805 nm, for example, a first laser beam having a wavelength of 780 nm, for example, is generated. Reference numeral 2 denotes a DVD standard optical disk, that is, a second laser diode that emits a laser beam focused on a second optical disk D2 provided with a signal recording layer L2 at a position indicated by a broken line in FIG. A second laser beam having a band of 645 nm to 675 nm, for example, 650 nm, is generated.

  Reference numeral 3 denotes a first laser light diffraction grating provided at a position where the first laser light emitted from the first laser diode 1 is incident, which is a main beam which is zero-order diffracted light and ± first-order diffracted light. The sub-beam is separated and generated. Reference numeral 4 denotes a first laser light half-wave plate on which the first laser light transmitted through the first laser light diffraction grating 3 is incident, and functions to adjust the polarization direction.

  Reference numeral 5 denotes a diffraction grating for second laser light provided at a position where the second laser light emitted from the second laser diode 2 is incident, which is a main beam which is zero-order diffracted light and ± first-order diffracted light. The sub-beam is separated and generated. Reference numeral 6 denotes a second laser light half-wave plate on which the second laser light transmitted through the second laser light diffraction grating 5 is incident, and serves to adjust the polarization direction.

  Reference numeral 7 denotes a dichroic prism on which the first laser light transmitted through the first laser light half-wave plate 4 and the second laser light transmitted through the second laser light half-wave plate 6 are incident from different directions. And a filter surface 7a for transmitting the first laser light and reflecting the second laser light is provided.

The dichroic prism 7 plays a role of arranging the first laser diode 1 and the second laser diode 2 in separate optical paths, and the filter surface 7a of the dichroic prism 7 transmits a 780 nm laser beam having a first wavelength. A reflection / transmission coat having a wavelength selectivity that secures a reflectance of 95% or more and a transmittance of the second wavelength of 650 nm laser light of less than 5%, that is, a reflectance of 95% or more is applied. .

  Reference numeral 8 denotes a polarization beam splitter into which the first laser light transmitted through the filter surface 7a of the dichroic prism 7 and the second laser light reflected by the filter surface 7a are incident. The polarization beam splitter 8 transmits S-polarized light and transmits S-polarized light. A polarizing filter surface 8a for reflecting light is provided. The first laser light emitted from the first laser diode 1 is converted into P-polarized light by the first laser light half-wave plate 4, and the second laser light emitted from the second laser diode 2. Is configured to be converted into P-polarized light by the second laser light half-wave plate 6. Accordingly, the first laser light and the second laser light incident on the polarizing beam splitter 8 are transmitted through the polarizing filter surface 8a.

  Reference numeral 9 denotes a collimator lens provided at a position where the first laser light and the second laser light transmitted through the polarizing beam splitter 8 are incident. The collimator lens 9 functions to convert the incident laser light into parallel light. is there. Reference numeral 10 denotes a reflection mirror on which the first laser light and the second laser light converted into parallel light by the collimator lens 9 are incident, and has an action of changing the optical axis in a perpendicular direction.

  Reference numeral 11 denotes a quarter-wave plate provided at a position where the first laser beam and the second laser beam reflected by the reflection mirror 10 are incident. The laser beam is changed from linearly polarized light to circularly polarized light, On the contrary, it has an action of polarizing from circularly polarized light to linearly polarized light. Reference numeral 12 denotes an objective lens provided at a position where the first laser light and the second laser light transmitted through the quarter-wave plate 11 are irradiated, and the first laser light is transmitted to the signal recording layer L1 of the first optical disc D1. And the second laser beam is focused on the signal recording layer L2 of the second optical disc D2.

  The objective lens 12 is recorded on the first laser beam having the first wavelength used for the reading operation of the signal recorded on the signal recording layer L1 of the first optical disc D1 and the signal recording layer L2 of the second optical disc D2. A diffraction grating 12a that diffracts the second laser light of the second wavelength used for the readout operation of a signal in accordance with each optical characteristic is formed in an annular shape around the optical axis on the incident surface side. The first laser beam and the second laser beam that are incident on the objective lens 12 through the quarter-wave plate 11 are diffracted by the diffraction grating 12a and are transmitted to the signal recording layer L1 of the first optical disc D1 and the signal of the second optical disc D2. Although the light is focused on the recording layer L2, the spherical aberration is designed to be corrected at this time.

  The annular diffraction grating 12a formed on the objective lens 12 focuses the first laser light incident on the signal recording layer L1 of the first disk D1 by the diffraction action. In this case, the numerical aperture is It is set to a value suitable for the first optical disc D1. The diffraction grating 12a focuses the second laser beam incident on the signal recording layer L2 of the second optical disc D2 by the diffraction action. In this case, the numerical aperture is set to a value suitable for the second optical disc D2. It is set to be.

  The first laser light and the second laser light focused on the signal recording layer L1 provided on the first optical disc D1 and the signal recording layer L2 provided on the second optical disc D2 are respectively transmitted to the signal recording layers L1, The light is reflected by L2 and enters the objective lens 12 as return light from the optical discs D1 and D2 side. The return light incident on the objective lens 12 passes through the objective lens 12 and then enters the quarter-wave plate 11.

The return light incident on the quarter-wave plate 11 is converted from circularly polarized light to linearly-polarized light by the quarter-wave plate 11, but the laser light applied to the optical discs D1 and D2 is P-polarized light. In contrast to light, the return light is S-polarized light. The return light converted into S-polarized light by the quarter-wave plate 11 is reflected by the reflection mirror 10 and then enters the collimator lens 9.

  The return light incident on the collimator lens 9 is transmitted through the collimator lens 9 and incident on the polarization beam splitter 8. Since the return light incident on the polarizing beam splitter 8 is converted into S-polarized light by the quarter-wave plate 11 as described above, it passes through the polarizing filter surface 8a provided on the polarizing beam splitter 8. It is reflected without doing.

  A servo lens 13 is provided at a position where the return light reflected by the polarizing filter surface 8a provided in the polarizing beam splitter 8 is incident, and is a signal recording layer provided in the optical disks D1 and D2. This produces the focus error component of the laser light irradiated to L1 and L2, and also irradiates the photodetector 14 with the return light.

  Here, the structure of the photodetector 14 generally used in the past will be described with reference to FIG. FIG. 3 shows a photodetector generally configured as a four-divided sensor, which is composed of a light receiving portion P including four sensor portions A, B, C, and D, and is configured to have a rectangular shape. Yes. In such a configuration, when the first laser beam or the second laser beam is correctly focused on the signal recording layer L1 or L2, that is, when it is in focus, the sensor unit of the photodetector 14 is focused. The main beam used for the focus control operation is irradiated in a circular laser spot shape as indicated by the solid line S1, but the first laser beam or the second laser beam is correctly applied to the signal recording layer L1 or L2. When the light is not condensed, that is, when it is out of focus, the sensor portion of the photodetector 14 is irradiated with an elliptical laser spot shape as indicated by a broken line S2 or S3.

  As is well known, the focus control operation in the optical pickup device is moved to an operating position where the objective lens 12 can be displaced in the direction perpendicular to the signal surface of the first optical disc D1 or the second optical disc D2 to perform the focus control operation. To start with. The operation of displacing the objective lens 12 to the operating position is performed by changing the DC voltage value of the drive signal supplied to the focus coil.

  That is, when the DC voltage value of the drive signal supplied to the focus coil is continuously changed, the objective lens 12 approaches or approaches from the position away from the signal surface of the first optical disc D1 or the second optical disc D2. It is displaced in the direction away from the position. When the objective lens 12 is displaced with respect to the optical discs D1 and D2 as described above, a spot formed by irradiating the sensor unit constituting the light receiving unit P provided in the photodetector 14 with the displacement operation. Changes as S2, S1, S3 or S3, S1, S2.

  Next, a focus error signal generation operation will be described with reference to FIG. In FIG. 4, reference numeral 15 denotes a first addition circuit for adding signals obtained from the sensor part A and the sensor part C of the light receiving part P constituting the light detector 14, and 16 denotes a light receiving part P constituting the light detector 14. The second addition circuit 17 adds the signals obtained from the sensor unit B and the sensor unit D, and 17 is a subtraction circuit that subtracts the output of the second addition circuit 16 from the output of the first addition circuit 15. The output signal is a focus error signal.

  That is, since the focus error signal FE can be obtained as FE = (A + C) − (B + D), the focus error signal can be generated by the circuit shown in FIG.

  FIG. 5 shows the level change of the focus error signal FE obtained when the objective lens 12 is displaced in the direction perpendicular to the signal surfaces of the optical discs D1 and D2. In the figure, the horizontal axis indicates the distance between the optical discs D1 and D2 and the objective lens 12, and the vertical axis indicates the level of the focus error signal FE.

  As is clear from the characteristics of FIG. 5, when the distance between the optical disks D1 and D2 and the objective lens 12 is T1, the level of the focus error signal FE becomes maximum, and when the distance between the optical disks D1 and D2 and the objective lens 12 is T2. The level of the focus error signal FE is minimized. The objective lens 12 is displaced from the position corresponding to the distance T1 to the position corresponding to the distance T2, that is, in the range of the distance T, and there is a position in which the focus error signal FE becomes zero.

  When the objective lens 12 is positioned at a position where the focus error signal FE becomes zero, the first laser beam or the second laser beam is focused on the signal recording layer L1 or L2 provided on the optical disc D1 or D2. That is, it will be in the focused state. Accordingly, the focus control operation is performed by controlling the position of the objective lens 12 so that the level of the focus error signal FE becomes zero.

  Such a focus control operation uses a focus error signal FE generated based on a signal obtained from the photodetector 14, and drives the objective lens in a direction in which the level of the focus error signal FE becomes zero. The operation is performed by supplying a signal to the focus coil. Since such an operation is well known, a description thereof will be omitted.

  As described above, the generation operation of the focus error signal FE is performed. Next, the focus error signal FE and the spot generated by irradiating the return light to the light receiving unit P provided in the photodetector 14 are generated. The relationship will be described.

  As described above, when the objective lens 12 is displaced in the direction perpendicular to the signal surfaces of the optical discs D1 and D2, the spots formed by irradiating the sensor unit constituting the light receiving unit P are S2, S1, S3 or S3, S1. , S2 changes.

  As shown in FIG. 5, when the distance between the signal recording layers L1 and L2 of the optical discs D1 and D2 and the objective lens 12 is T1, the level of the focus error signal FE becomes maximum, but the spot shape at this time is as shown in S2. In the sensor part A and sensor part C direction, an elliptical spot having a long diameter is formed. Further, when the distance between the optical discs D1 and D2 and the objective lens 12 is T2, the level of the focus error signal FE is minimized, but the spot shape at this time has a long diameter in the sensor part B and sensor part D directions as in S3. It becomes an elliptical spot. When the focus error signal FE becomes zero, that is, in a focused state, the spot shape becomes a circular spot as in S1.

  As described above, when the distance between the signal recording layers L1 and L2 of the optical discs D1 and D2 and the objective lens 12 changes from T1 to T2, the shape of the spot formed on the sensor part constituting the light receiving part P changes from S2 to S1. The focus error signal FE changes from the maximum to the minimum during the period from S1 to S3.

  In such a configuration, the numerical aperture of the objective lens is advantageous to the optical axis deviation in order to focus the first laser beam having the first wavelength, which is a long wavelength, on the signal recording layer L1 of the first optical disc D1. If is reduced, flare light increases as described above. When such flare light increases, the flare light is irradiated not on the center of each sensor part A, B, C, D constituting the light receiving part P but on a wide light receiving area.

  In this way, the flare light applied to each of the sensor portions A, B, C, and D is not only applied to the portions where the spots S1, S2, and S3 are irradiated, but also to other portions, that is, the remaining portions. Will be irradiated.

  Thus, when flare light increases, flare light is irradiated to the wide area | region of each sensor part A, B, C, D which comprises the light-receiving part P of the said photodetector 14, but each sensor part A , B, C, and D are not uniform in flare light, and the signal output obtained according to the amount of flare light received differs greatly between the sensor units.

  If a large difference occurs in the signal output obtained from each sensor unit, the focus error signal can be obtained from FE = (A + C) − (B + D) as described above, so that an accurate focus error signal cannot be obtained. As a result, the focus servo operation cannot be performed accurately, and the first laser beam and the second laser beam cannot be accurately focused on the signal recording layers L1 and L2 provided on the optical discs D1 and D2. The problem occurs.

  In the present invention, in order to improve such a point, the sizes of the four sensor portions A, B, C, and D constituting the light receiving portion P are devised as shown in FIG. That is, the length of the diagonal line of the light receiving part P which is a quadrangle formed by the four sensor parts A, B, C and D is made to coincide with the length of the major axis of the elliptical spot where the level of the focus error signal FE is maximum. It is characterized by that.

  When the size of the light receiving portion P incorporated in the photodetector 14 is set as described above, the main beam used for the focus control operation in the sensor portions A, B, C, and D is irradiated and generated. Since the ratio occupied by the irradiation areas of the laser spots S1, S2, and S3 increases, the influence of flare light can be reduced. Therefore, an accurate focus error signal can be obtained even if flare light increases due to a reduction in the numerical aperture for the first laser beam set in correspondence with the first optical disk D1 of the objective lens 12. Therefore, stable focus servo operation can be performed.

  As described above, in the present invention, since the shape of the light receiving portion P provided in the photodetector 14 is rectangular in the same manner as the conventional shape, it is compared with the case where a photodetector having a special shape is manufactured. Thus, it can be manufactured easily and inexpensively.

  In the present embodiment, the length of the rectangular light receiving portion P in the diagonal direction is made equal to the major axis of the elliptical spot so as to eliminate the influence of flare light. A mask means such as a liquid crystal control element is provided between the lens 13 and the photodetector 14, and the irradiation range of the return light irradiated to the light receiving unit can be regulated by controlling the liquid crystal control element. I can do it.

  Such a liquid crystal control element includes a liquid crystal panel on which a pattern for setting a light transmission range is formed, and changes a liquid crystal state by applying a drive control voltage to a control electrode provided in the liquid crystal panel. It is configured as follows. Since such a liquid crystal control element is well known, its description is omitted.

  As described above, the photodetector 14 according to the present invention is configured. Next, the spots generated by irradiating the light receiving unit P provided in the photodetector 14 with the return light are shown in FIG. This will be described with reference to the characteristic diagram shown in FIG.

The laser light emitted from the laser diode has a characteristic called Gaussian, and FIG. 6 shows the intensity distribution characteristic of the laser light having such a Gaussian characteristic. Further, in the optical pickup device, the numerical aperture of lenses used in the optical system such as the objective lens 12 and the servo lens 13, the laser intensity necessary for performing the reproduction operation of the signal recorded on the optical disc, and the signal on the optical disc. In order to obtain a laser beam necessary for recording, a diameter used as a spot is set.

The diameter of the spot to be used is set within a range in which a necessary laser intensity can be obtained in the characteristic diagram shown in FIG. For example, in FIG. 6, when the maximum intensity of the laser beam is 1.0, the intensity is higher than 0.5, that is, a 50% intensity position where the intensity is half of the maximum intensity, a position called a so-called half width. The spot diameter is set so that the laser beam portion is used as a spot, or 0.135, that is, the position of 13.5% intensity where the intensity is 1 / e ² (e is the base of natural logarithm) with respect to the maximum intensity. The spot diameter is set so that a portion of the laser beam having a higher intensity is used as a spot.

  As described above, the spot diameter is set based on the laser intensity distribution. However, the laser light intensity range used as a spot has priority over the spot size, spot peak light intensity, and spot total power. It is decided by what to do.

In the current optical pickup apparatus, the spot diameter set based on the intensity distribution of the laser beam is set in consideration of the power loss of the laser beam. Generally, the intensity is 1 / e ^{2 with} respect to the maximum intensity. The portion of the laser beam having a higher intensity than the 13.5% intensity position is set to be used as a spot. By setting the spot diameter in this way, it is possible to obtain a spot diameter that satisfies the reproduction characteristics and recording characteristics of many optical pickup devices.

  Since the spot diameter is set as described above, if the length of the light receiving part constituting the photodetector is set in accordance with the intensity range of the laser beam that determines the spot diameter, it is used for generating a focus error signal. It is possible to set the size of the light receiving portion to be minimized, and as a result, it is possible to minimize the adverse effects of flare.

It is an optical arrangement | positioning figure which shows one Example of the optical pick-up apparatus which concerns on this invention. It is the schematic which shows one Example of the photodetector which concerns on this invention. It is the schematic which shows the conventional photodetector. It is a figure for demonstrating the production | generation operation | movement of a focus error signal. It is a characteristic view which shows the level change of a focus error signal. It is a characteristic view for demonstrating the intensity distribution of the laser beam based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st laser diode 2 2nd laser diode 7 Dichroic prism 8 Polarizing beam splitter 9 Collimator lens 12 Objective lens 13 Servo lens 14 Photodetector P Light-receiving part

Claims (5)

An annular diffraction grating is formed according to the numerical aperture so as to focus laser beams of different wavelengths onto optical discs with different thicknesses of the cover layer covering the signal recording layer and the return reflected from the signal recording layer And an optical pickup device provided with a photodetector having a rectangular light-receiving unit that emits light as a spot and generates at least a focus error signal. The light-receiving unit is formed by a quadrangular quadrant sensor. An objective lens configured to correspond to laser light having a long wavelength by making the major axis of the elliptical spot having the maximum level of the focus error signal obtained from the light receiving unit and the diagonal length of the light receiving unit coincide with each other An optical pickup device characterized in that the influence of flare light that increases when the numerical aperture of the optical disk is reduced is eliminated. An annular diffraction grating is formed according to the numerical aperture so as to focus laser beams of different wavelengths onto optical discs with different thicknesses of the cover layer covering the signal recording layer and the return reflected from the signal recording layer And an optical pickup device provided with a photodetector provided with at least a square light-receiving unit that generates a focus error signal while irradiating light as a spot, and mask means for masking a part of the light-receiving unit The flare light is irradiated on the light receiving portion by the mask means so that the major axis of the elliptical spot where the level of the focus error signal obtained from the light receiving portion is maximum matches the diagonal length of the light receiving portion. The shadow caused by flare light increases when the numerical aperture of the objective lens set to correspond to the laser light having a long wavelength is reduced by blocking. The optical pickup apparatus is characterized in that so as to eliminate. 3. The optical pickup device according to claim 2, wherein a liquid crystal control element is used as the mask means. 3. The optical pickup device according to claim 1, wherein a focus error signal is generated using a spot at a portion where the intensity of the laser beam is a predetermined value or more. 5. The optical pickup device according to claim 4, wherein the predetermined value is 1 / e ² (e is a base of natural logarithm) with respect to the maximum intensity.

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