JP2010211859A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and compact single-beam detection optical system having a small number of light receiving elements and causing less noise, in an optical pickup device. <P>SOLUTION: In the single-beam detection optical system of the optical pickup device, a return luminous flux is divided in a main push pull (MPP) signal region and to a sub push pull (SPP) signal region of a tracking error with a diffraction optical element 8, and astigmatism is given to either of them and light is received with a quadrant light receiving element 9. A tracking error signal corresponding to differential push pull (DPP) is generated by using a differential in a radial direction and that in a tangential direction, and all necessary signals such as a focus error signal based on an astigmatism method are obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a servo signal detection method in an optical pickup device.

  Conventionally, optical discs such as “CD” (Comapct Disk) and “DVD” (Digital Versatile Disk) have been proposed as information recording media. In recent years, “BD” (Blu-ray Disk) capable of recording a larger capacity has been proposed. “BD” includes a single-layer disc having only one recording layer and a dual-layer disc having two recording layers. In “BD”, both discs are similarly popular.

  At the time of recording or reproducing an optical disk, it is necessary that the light beam that has passed through the objective lens of the optical pickup device is condensed at a correct position in both the track and the focus direction of the optical disk. Therefore, control by tracking servo and focus servo is performed. As a tracking servo method, the DPP (Differential Push-Pull) method is generally used. The DPP method uses a grating to split a light beam from a laser light source into a central main beam and two sub beams. This is a method of canceling the DC offset caused by the lens shift generated in the push-pull signal (hereinafter referred to as MPP) with a sub-beam push-pull signal (hereinafter referred to as SPP). Since “BD” has a problem of laser power shortage in particular, the intensity of the sub beam is often set as weak as about 10% with respect to the intensity of the main beam in order to cope with the optical double speed.

  By the way, when reproducing a two-layer disc, there is a problem in that reflected light from a layer that is not reproduced (out of focus) is mixed in the signal as crosstalk light and disturbs the tracking error signal. In the tracking servo based on the DPP method described above, the influence of the MPP crosstalk light on the low-power SPP is particularly remarkable. Therefore, instead of the DPP method in which the beam is branched into three, one beam is branched by a hologram, a beam splitter, or the like as necessary, and the region is divided so that each servo signal is received by an individual light receiving element. Beam detection has been proposed. One beam detection is effective when integrating a laser light source and a light receiving element. Therefore, one-beam detection is used for in-vehicle use and the like, and application development to an integrated unit that can obtain a large tolerance (tolerance) of an optical system is also required.

  In Non-Patent Document 1, a diffractive optical element that divides a light beam into two for detecting a focus error signal and detecting a tracking error signal is used. By this diffractive optical element, astigmatism is given to the light beam for focus error, and focus error detection is performed by a general astigmatism method using a four-divided cell. On the other hand, the light beam for tracking error is composed of two regions corresponding to MPP and two regions corresponding to SPP, and is condensed on a four-divided cell different from that for focus error detection signal, and detects a tracking error signal corresponding to the DPP method.

  In Patent Document 1, the influence of the objective lens shift is reduced by using a diffractive optical element having an asymmetric region in the radial direction and the tangential direction. According to this method, focus error signal detection by the SSD (Spot Size Detection) method and tracking error signal detection by the DPP method can be performed.

  In Patent Document 2, a light beam divided into six by a diffractive optical element having three dividing lines is received by eight light receiving elements arranged in an appropriate positional relationship, whereby a focus error by the astigmatism method is obtained. Both signal detection and tracking error signal detection corresponding to the DPP method can be performed.

JP 2007-265595 A JP 2008-171470 A

Kousei SANO, et.al., “Novel One-Beam Tracking Detection Method for Dual-Layer Blu-ray Discs”, Japanese Journal of Applied Physics Vol. 45, No. 2B, 2006, pp. 1174-1177

  By the way, in Non-Patent Document 1, it is said that a lot of light receiving elements are required in addition to splitting the light beam into two for detecting the tracking error signal and the focus error signal, so that there is a lot of noise and it is difficult to obtain the S / N of the main signal. There's a problem. Furthermore, both a cylindrical lens and a diffractive optical element are required, which increases the number of parts and increases the detection system. In addition, when a position signal is obtained as a signal indicating the positional accuracy of the light receiving element and the diffractive optical element, it is necessary to detect another signal that is not used as a servo signal, so that the number of output terminals increases.

  In Patent Document 1, when the focus error signal and the SPP are detected with the same light beam, it is necessary to divide the light beam into two for the detection of MPP and SPP. When the SPP and MPP are detected with the same light beam, It is necessary to split the light beam into two for detection of the error signal and tracking error signal. Therefore, in any of the above-described configurations, the number of elements and light receiving elements that branch the light flux increases, noise increases, and the apparatus is increased in size and configuration is complicated. Further, when a position signal is obtained as a signal indicating the positional accuracy of the light receiving element, it is necessary to detect another signal that is not used as a servo signal, so that the number of output terminals increases.

  Further, in Patent Document 2, since eight light receiving elements having a complicated shape are required, there are still a lot of noise and the configuration is complicated. In addition, the shape of the light receiving element is complicated, and each of the light receiving elements is large. There is a problem that it is difficult to adjust the position because of the distance.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and does not branch the reflected light beam from the optical disk, and with a small number of light receiving elements and output terminals, the focus error signal, tracking error signal, and An object of the present invention is to provide a simple and small optical pickup device capable of obtaining a position signal for position adjustment.

  In order to solve the above-described problems of the conventional technology, an optical pickup device according to the present invention has any of the following configurations.

[Configuration 1]
A laser light source for irradiating the optical disk with a light beam, a first diffraction region where a light beam overlapping a component diffracted by a recording track of the optical disk and a component not diffracted is incident, and a light beam of a component not diffracted by the recording track of the optical disk A light beam reflected from the optical disc is diffracted at a predetermined order in the first diffraction region and the second diffraction region, and one of the first diffraction region and the second diffraction region is provided. Are divided into four light-receiving regions by a diffractive optical element that gives astigmatism at 1 and a dividing line in a direction corresponding to the recording track direction of the optical disc and a dividing line in a direction perpendicular to the recording track direction. And a light receiving element that receives light diffracted by the second diffraction region and the second diffraction region.

[Configuration 2]
In the optical pickup device having the configuration 1, the first diffraction region of the diffractive optical element is incident with a light beam in which a component that is diffracted in the + 1st order by a recording track of the optical disc and a component that is not diffracted overlap, and the recording track direction of the optical disc And a light beam in which a component that is diffracted in the −1st order and a component that is not diffracted by the recording track of the optical disc overlap, and is perpendicular to the recording track direction of the optical disc. Each region has four divided regions that diffract an incident light beam in different directions, and the second diffraction region of the diffractive optical element is an optical disc recording medium. A light beam of a component that is not diffracted by the track is incident and is divided by a dividing line corresponding to a direction perpendicular to the recording track direction. The light having two divided regions diffracting in the direction and diffracted by the four divided regions of the first diffractive region is received by different light receiving regions of the light receiving element. The light diffracted by each of the two divided regions is divided into two regions included on the same side when divided by the dividing line corresponding to the direction perpendicular to the recording track direction among the four regions of the light receiving element. In this case, the light is received respectively.

[Configuration 3]
In the optical pickup device having the configuration 1, the first diffractive region of the diffractive optical element includes a region where a light beam in which a component diffracted in the + 1st order and a component not diffracted by the recording track of the optical disc are incident, and a recording track of the optical disc -1 is composed of regions where a light beam in which a component diffracted in the first order and a component that is not diffracted overlap is incident. Each region has two divided regions that diffract the incident light beam in different directions. The second diffraction region of the element is divided by a direction corresponding to the recording track direction and a dividing line corresponding to a direction perpendicular to the recording track direction, with a light beam having a component that is not diffracted by the recording track of the optical disc. Each of the four divided regions diffracting in different directions, and the light diffracted by the two divided regions of the first diffraction region, When divided by a dividing line corresponding to a direction perpendicular to the recording track direction, the light is received by each of the two areas included on the same side and is divided by the four divided areas of the second diffraction area. The diffracted light is received by different light receiving regions of the light receiving element.

[Configuration 4]
In the optical pickup device having any one of Configurations 1 to 3, light reception included in the same side when divided by a dividing line in a direction corresponding to the recording track direction of the optical disc among the four light receiving regions of the light receiving element. The first and second addition signals are obtained by adding the photodetection signals of the regions, respectively, and the first difference signal is calculated by subtracting the second addition signal from the first addition signal. When the light receiving areas are divided by the dividing line in the direction corresponding to the direction perpendicular to the recording track direction of the optical disc, the light detection signals of the light receiving areas included on the same side are added to each of the third and fourth light receiving areas. The first signal is obtained by obtaining the addition signal, subtracting the fourth addition signal from the third addition signal to calculate the second difference signal, and calculating the tracking error signal using the first and second difference signals. It has a control unit Is intended to.

[Configuration 5]
In the optical pickup device having any one of Configurations 1 to 4, among the four light receiving regions of the light receiving element, the light detection signals of the light receiving regions arranged on the diagonal lines are added to respectively add the fifth and sixth A second control unit that obtains an addition signal and subtracts the sixth addition signal from the fifth addition signal to calculate a focus error signal is provided.

  In the optical pickup device according to the present invention, since all the servo signals can be detected only by the light receiving element having the first to fourth light receiving areas, it is not necessary to split the light beam into two. Therefore, unlike the prior art described in Patent Document 1 and Non-Patent Document 1, it is not necessary to branch into two light beams by the detection optical system, and the number of light receiving elements can be reduced. Simplification of the configuration can be expected.

  Furthermore, since the tracking error signals MPP and SPP are directly used as position signals, the number of terminals can be reduced.

  Furthermore, compared with the conventional technique described in Patent Document 2, in addition to reducing the number of cells of the light receiving element, only the light receiving elements having the first light receiving region to the fourth light receiving region adjacent to or close to each other are used. Since it can detect, alignment of a light receiving element can be made easy.

  That is, the present invention can easily obtain a focus error signal, a tracking error signal, and a position signal for position adjustment without branching the reflected light beam from the optical disk and with a small number of light receiving elements and output terminals. In addition, a small optical pickup device can be provided.

It is the figure which showed typically the whole structure of the optical pick-up apparatus of the 1st Embodiment of this invention. It is sectional drawing which shows the example of the structure of a diffractive optical element. It is a figure explaining the positional relationship of the diffractive optical element and light receiving element of the 1st Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 1st Embodiment of this invention. It is the figure which showed typically the whole structure of the optical pick-up apparatus of the 2nd Embodiment of this invention. It is a block diagram which shows another example of the structure of a diffractive optical element. It is a figure explaining the positional relationship of the diffractive optical element and light receiving element of the 2nd Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 2nd Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 3rd Embodiment of this invention. It is the figure which showed typically the whole structure of the optical pick-up apparatus of the 4th Embodiment of this invention. It is a block diagram which shows another example of the structure of a diffractive optical element. It is a figure explaining the positional relationship of the diffractive optical element and light receiving element of the 4th Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 4th Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 5th Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 6th Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 7th Embodiment of this invention. It is a figure explaining the pattern of the diffractive optical element and light receiving element of the 8th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
A first embodiment will be described with reference to FIGS. 1 to 4. FIG. 1 is a diagram schematically showing the overall configuration of the optical pickup device of the first embodiment.

  In the optical pickup device according to the present invention, as shown in FIG. 1, the divergent light emitted from the laser light source 1 passes through the polarization beam splitter (PBS) 2 and passes through the quarter-wave plate 3. Circularly polarized light. The divergent light transmitted through the quarter-wave plate 3 is converted into substantially parallel light by the collimator lens 4, and the direction of the light beam is deflected by the rising mirror 5. The light deflected in the direction of the light beam by the rising mirror 5 is collected by the objective lens 6 and collected on the signal recording surface of the optical disc 7. The light reflected by the signal recording surface of the optical disc 7 is transmitted through the objective lens 6 in the reverse order of the forward path, deflected by the rising mirror 5, and transmitted through the collimator lens 4. The light transmitted through the collimator lens 4 is transmitted through the quarter-wave plate 3 again, and becomes linearly polarized light whose polarization direction is rotated by 90 degrees with respect to the light emitted from the laser 1. The linearly polarized light transmitted through the quarter-wave plate 3 is reflected by the PBS 2, divided by the diffractive optical element 8, diffracted and condensed on the light receiving element 9. The light received by the light receiving element 9 is spotted and then subjected to predetermined calculation processing by a control unit (not shown) to detect a focus error signal and a tracking error signal.

  Although there may be various diffraction orders used for diffraction in the diffractive optical element 8, in the following description of the present invention, light diffracted at the order having the highest diffraction efficiency is detected by the light receiving element 9, and each signal is detected. We will use it. Further, the diffractive optical element 8 only needs to be closer to the light source than the quarter-wave plate 3 when viewed from the objective lens 6, and is not limited to the configuration of FIG. A configuration in which the objective lens 6, the quarter-wave plate 3 and the diffractive optical element 8 are all incorporated in the actuator is also conceivable. However, in this case, the diffractive optical element 8 needs to have polarization selectivity.

  FIG. 2 is a cross-sectional view showing an example of the structure of the diffractive optical element 8.

  As shown in FIG. 2, the structure of the diffractive optical element 8 is a saw-like shape, and the depth of the groove is set to a depth at which + 1st order diffracted light becomes 100%. However, the structure is not limited to this as long as a necessary amount of light is obtained and the influence of stray light is reduced.

  FIG. 3 is a diagram illustrating the positional relationship between the diffractive optical element 8 and the light receiving element 9 according to the first embodiment.

  As shown in FIG. 3, when the reflected light from the optical disk 7 is perpendicularly incident on the diffractive optical element 8, the center 8P of the diffractive optical element 8 and the center 9P of the light receiving element coincide with the optical axis direction. That is, when there is zero-order light that is not diffracted by the diffractive optical element 8, the zero-order light is incident on the center 9 </ b> P of the light receiving element 9.

  FIG. 4 is a diagram illustrating patterns of the diffractive optical element 8 and the light receiving element 9 according to the first embodiment. FIG. 4A shows a diffraction pattern of each region of the diffractive optical element 8.

  As shown in FIG. 4A, the diffractive optical element 8 is divided into three regions of first to third regions 8a1, 8a2, and 8b, and each region has a different diffraction pattern.

  FIG. 4B shows spots on the diffractive optical element 8 by omitting the diffraction pattern of FIG. A region surrounded by a broken line in FIG. 4B shows a light beam on the diffractive optical element 8 when there is no lens shift of the objective lens 6 (hereinafter simply referred to as a lens shift). Of the region indicated by the broken line, the light beams 8s1 and 8s2 indicated by hatching are the diffraction components of the recording track of the optical disc 7, that is, the light beams resulting from the overlap of the 0th-order light and the primary light diffracted by the recording track. Further, the unhatched light beam 8s3 does not include a diffraction component by the recording track, that is, only the 0th-order light beam diffracted by the recording track.

  The diffraction component of the signal recording surface of the optical disc 7, that is, the first and second regions 8 a 1 and 8 a 2 mainly including the light beams 8 s 1 and 8 s 2, and the third region 8 b other than the diffractive optical element 8. When the region is divided, only one of the region including both the first and second regions 8a1 and 8a2 or the third region 8b gives astigmatism, and the other region. Is a region where no astigmatism is given. In the first embodiment, astigmatism is given in the third region 8b.

  Next, the spot shape of the light beam incident on the light receiving element 9 will be described with reference to FIG. FIG. 4C shows a division pattern and a spot shape of the light receiving element 9.

  The light receiving element 9 is divided into two parts in the radial direction and two parts in the tangential direction, and is composed of cells divided into four parts into first to fourth regions 9A, 9B, 9C, 9D.

  Moreover, the area | region enclosed with the dashed-dotted line of FIG. 4 shows spot shape. The first spot 9a1 is a spot formed by the + 1st order diffracted light diffracted by the first region 8a1, and the second spot 9a2 is formed by the + 1st order diffracted light diffracted by the second region 8a2. The third spot 9b is a spot formed by + 1st order diffracted light diffracted by the third region 8b.

  The area indicated by hatching in FIG. 4C corresponds to the light beam indicated by hatching in FIG. That is, the light beams 9s1 and 9s2 indicated by hatching in FIG. 4B are caused by the lights that formed the light beams 8s1 and 8s2 on the diffractive optical element 8, respectively. Of the light that forms the light beam 8s3 on the diffractive optical element 8, the light beam that overlaps the first region 8a1 is included in the first spot 9a1, and the light beam that overlaps the second region 8a2 is the second spot. The light beam included in 9a2 and overlapping the third region 8b is included in the third spot 9b.

  The relationship between the first to third regions of the diffractive optical element 8 and the spot on the light receiving element 9 will be described in more detail.

  The + 1st order diffracted light diffracted in the third region 8b giving astigmatism has a shape indicated by the third spot 9b in FIG. 4C because the relationship between the radial direction and the tangential direction on the light receiving element 9 is reversed. Is incident on the light receiving element 9. On the other hand, the + 1st order diffracted light diffracted in the first and second regions 8a1 and 8a2 not provided with astigmatism does not change in the relationship between the radial direction and the tangential direction, does not overlap the spot 9b, and The first and second regions 8a1 and 8a2 become the first and second spots 9a1 and 9a2 on the light receiving element 9 so that the size and the positional relationship are slightly different.

Here, the light amounts detected by the first to fourth regions 9A, 9B, 9C, and 9D in the light receiving element 9 are A, B, C, and D, respectively. A control unit (not shown) can calculate the MPP from the first and second spots 9a1 and 9a2 mainly including diffraction components due to the recording track. MPP is represented by the following formula (1).
MPP = (A + D) − (B + C) (1)

On the other hand, the third direction 8b of the diffractive optical element 8 and the corresponding third spot 9b on the light receiving element 9 are switched between the radial direction and the tangential direction. The control unit (not shown) can calculate an SPP that cancels the offset component from the third spot 9b that mainly includes the offset component due to the lens shift. SPP is represented by the following formula (2).
SPP = (A + B) − (C + D) (2)

Further, if the parameter for canceling the offset component due to lens shift is k, the control unit (not shown) provides a tracking error signal APP (Advanced Push Pull) improved from the DPP method by the following equation (3).
APP = MPP + k * SPP (3)

Further, astigmatism is given to the third spot 9b in FIG. 4B as described above, focus detection by the astigmatism method is possible. A control unit (not shown) can calculate the focus error signal FES. FES is given by the following equation (4).
FES = (A + C) − (B + D) (4)

Further, the position signal PosX indicating the radial position of the first to third spots 9a1, 9a2 and 9b on the light receiving element 9 and the position signal PosY indicating the position in the tangential direction are the same as MPP and SPP, respectively. A control unit (not shown) calculates position signals PosX and PosY by the following equations (5) and (6), respectively.
PosX = MPP (5)
PosY = SPP (6)

Furthermore, tracking detection by the DPD (Differential Phase Detection) method is necessary for a read-only disk (ROM). However, since the DPD method is represented by the phase difference of the diagonal components of the four light receiving elements, the phase of x is expressed as φ. If expressed as (x), the tracking error signal DPD is expressed by the following equation (7).
DPD = φ (A + C) −φ (B + D) (7)

  The patterns of the diffractive optical element 8 and the light receiving element 9 are not limited to those shown in FIG. Further, astigmatism is given to both the first and second regions 8a1 and 8a2 mainly including the diffraction components by the recording track, that is, the light beams 8s1 and 8s2, and the other third region 8b is astigmatized. The case where no aberration is given can be dealt with by calculating the tracking error signal APP by exchanging MPP and SPP.

  As described above, all the servo signal detection including the signal for detecting the position of the light receiving element 9 is performed by only one diffractive optical element 8 and the light receiving element 9 having four cells without branching the light beam. Therefore, it is possible to provide an optical pickup device that has a small signal and a small and simple optical configuration.

<Second Embodiment>
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a diagram schematically showing the overall configuration of the optical pickup device of the second embodiment.

  The optical configuration of the second embodiment shown in FIG. 5 will be described focusing on the differences from the first embodiment shown in FIG.

  The optical configuration in the second embodiment is such that the branching prism 10 instead of the PBS 2, the diffractive optical element 18 instead of the diffractive optical element 8, and the light receiving element 19 instead of the light receiving element 9 are arranged in a space-saving manner. Other optical configurations are the same as those in the first embodiment.

  FIG. 6 is a cross-sectional view showing an example of the structure of the diffractive optical element 18 of the second embodiment.

  As shown in FIG. 6, the structure of the diffractive optical element 18 is stepped, and the depth of the groove is a four-stage structure in which light corresponding to one wavelength of light emitted from the laser light source 1 is divided into four parts. The step-like diffractive optical element 18 is easy to manufacture a mold, but the + 1st-order diffraction efficiency is 96% at the maximum, and is further lowered due to the depth of the groove and the step-like shape error. Theoretically, a slight amount of -3rd order diffracted light is generated, and if there is a shape error, 0th order light that is not subjected to diffracting action is also generated. These −3rd order diffracted light and 0th order light become stray light and cause each signal to deteriorate.

  FIG. 7 is a diagram illustrating the positional relationship between the diffractive optical element 18 and the light receiving element 19 according to the second embodiment.

  As shown in FIG. 7, the diffractive optical element 18 and the light receiving element 19 of the second embodiment have a positional relationship that reduces the influence of stray light. That is, when the reflected light from the optical disk 7 enters the diffractive optical element 18 vertically, the center of the light receiving element 19 is located at a predetermined distance d from the extension line in the optical axis direction passing through the center 18P of the diffractive optical element 18. There are 19P. That is, when there is zero-order light that is not diffracted by the diffractive optical element 18, zero-order light is not incident on the light receiving element 19, and the -3rd-order diffracted light has an optical axis different from that of the + 1st-order diffracted light used for signal detection. Since the light is diffracted in the opposite direction by 180 °, the light does not enter the light receiving element 19. Therefore, according to the positional relationship between the diffractive optical element 18 and the light receiving element 19 of the second embodiment shown in FIG. 7, the influence of the stray light described above can be suppressed. However, when it can be considered that the influence of stray light is small, the positional relationship between the diffractive optical element 8 and the light receiving element 9 shown in FIG. 3 may be applied to the positional relationship between the diffractive optical element 18 and the light receiving element 19.

  FIG. 8 is a diagram illustrating patterns of the diffractive optical element 18 and the light receiving element 19 according to the second embodiment. FIG. 8A shows spots on the diffractive optical element 18 with the diffraction pattern omitted.

  As shown in FIG. 8A, the diffractive optical element 18 is divided into six regions of first to sixth regions 18a11, 18a12, 18a21, 18a22, 18b1, and 18b2, and each region has a different diffraction pattern.

  A region surrounded by a broken line in FIG. 8A shows a light beam on the diffractive optical element 18 when there is no lens shift. In the area indicated by the broken line, the light beams 18s1 and 18s2 indicated by hatching in FIG. 8A are diffracted by the recording track of the optical disc 7, that is, the overlap of the 0th order light and the 1st order light diffracted by the recording track. Luminous flux. Further, the unhatched light beam 18s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the second embodiment, astigmatism is given in the fifth and sixth regions 18b1 and 18b2.

  Next, the spot shape of the light beam incident on the light receiving element 19 will be described with reference to FIG. FIG. 8B shows a division pattern and a spot shape of the light receiving element 19.

  The light receiving element 19 is divided into two parts in the radial direction and two parts in the tangential direction, and is composed of cells divided into four parts into first to fourth regions 19A, 19B, 19C, and 19D. Moreover, the area | region enclosed with the dashed-dotted line of FIG.8 (b) shows spot shape. The first spot 19a11 is a spot formed by + 1st order diffracted light diffracted by the first region 18a11, and the second spot 19a12 is formed by + 1st order diffracted light diffracted by the second region 18a12. The third spot 19a21 is a spot formed by + 1st order diffracted light diffracted by the third region 18a21, and the fourth spot 19a22 is + 1st order diffracted light diffracted by the fourth region 18a22. The fifth spot 19b1 is a spot formed by + 1st order diffracted light diffracted by the fifth region 18b1, and the sixth spot 19b2 is diffracted by the sixth region 18b2. This is a spot formed by + 1st order diffracted light.

  Among the light beams 18s1 indicated by hatching on the diffractive optical element 18 in FIG. 8A, the light beam that overlaps the first region 18a11 is the light beam that overlaps the first spot 19a11 and the second region 18a12 is the second light beam. It is included in the spot 19a12. In addition, among the light beams 18s2 indicated by hatching on the diffractive optical element 18 in FIG. 8A, the light beam that overlaps the third region 18a21 is the light beam that overlaps the third spot 19a21 and the light beam that overlaps the fourth region 18a22. 4 spots 19a22.

  The relationship between each region of the diffractive optical element 18 and each spot on the light receiving element 19 will be described in more detail.

  The + 1st order diffracted light diffracted in the fifth and sixth regions 18b1 and 18b2 giving astigmatism is reversed on the light receiving element 19 in the relationship between the radial direction and the tangential direction, and the fifth and sixth spots 19b1 respectively. , 19b2 is incident on the light receiving element 19. On the other hand, the + 1st order diffracted light diffracted in the first to fourth regions 18a11, 18a12, 18a21, 18a22 to which no astigmatism is given has no change in the relationship between the radial direction and the tangential direction, and the fifth and sixth regions. The first to fourth spots 19a11, 19a12, 19a21, and 19a22 are formed so as not to overlap with the spots 19b1 and 19b2 and to substantially focus on the light receiving element 19, respectively.

  Here, assuming that the light amounts detected by the first to fourth regions 19A, 19B, 19C, and 19D in the light receiving element 19 are A, B, C, and D, respectively, by the same calculation as in the first embodiment, Each servo signal and position detection signal are obtained.

  As described above, it is possible to detect all the servo signals including the signal for detecting the position of the light receiving element with only one diffractive optical element and the light receiving element having four cells without branching the light beam. Therefore, it is possible to provide a small and simple optical pickup device with a signal with less noise.

<Third Embodiment>
Next, a third embodiment of the present invention will be described with reference to FIG. The optical configuration of the third embodiment is the same as the optical configuration of the second embodiment shown in FIG. 5, but the diffractive optical element 28 instead of the diffractive optical element 18 and the light receiving element 29 instead of the light receiving element 19. Is used.

  FIG. 9 is a diagram illustrating patterns of the diffractive optical element and the light receiving element according to the third embodiment of the invention. FIG. 9A shows spots on the diffractive optical element 28 with the diffraction pattern omitted.

  As shown in FIG. 9A, the diffractive optical element 28 is radially divided into six regions of first to sixth regions 28a11, 28a12, 28a21, 28a22, 28b1, and 28b2, and has different diffraction patterns for each region. Have.

  A region surrounded by a broken line in FIG. 9A indicates a light beam on the diffractive optical element 28 when there is no lens shift. In the region indicated by the broken line, the light beams 28s1 and 28s2 indicated by hatching in FIG. 9A are diffracted by the recording track of the optical disc 7, that is, due to the overlap of the 0th order light and the 1st order light diffracted by the recording track. Luminous flux. Further, the unhatched light beam 18s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the third embodiment, astigmatism is given in the fifth and sixth regions 28b1 and 28b2.

  Next, the spot shape of the light beam incident on the light receiving element 29 will be described with reference to FIG. FIG. 9B shows a division pattern and a spot shape of the light receiving element 29.

  The light receiving element 29 is divided into two parts in the radial direction and two parts in the tangential direction, and is composed of cells divided into four parts into first to fourth regions 29A, 29B, 29C, and 29D. Moreover, the area | region enclosed with the dashed-dotted line of FIG.9 (b) shows spot shape. The first spot 29a11 is a spot formed by + 1st order diffracted light diffracted by the first region 28a11, and the second spot 29a12 is formed by + 1st order diffracted light diffracted by the second region 28a12. The third spot 29a21 is a spot formed by + 1st order diffracted light diffracted by the third region 28a21, and the fourth spot 29a22 is + 1st order diffracted light diffracted by the fourth region 28a22. The fifth spot 29b1 is a spot formed by + 1st order diffracted light diffracted by the fifth region 28b1, and the sixth spot 29b2 is diffracted by the sixth region 28b2. This is a spot formed by + 1st order diffracted light.

  Among the light beams 28s1 indicated by hatching on the diffractive optical element 28 in FIG. 9A, the light beam that overlaps the first region 28a11 is the light beam that overlaps the first spot 29a11 and the light beam that overlaps the second region 28a12 is the second light beam 28s1. It is included in the spot 29a12. In addition, among the light beams 28s2 indicated by hatching on the diffractive optical element 28 in FIG. 9A, the light beam that overlaps the third region 28a21 is the light beam that overlaps the third spot 29a21 and the light beam that overlaps the fourth region 28a22. 4 spots 29a22.

  The relationship between each region of the diffractive optical element 28 and each spot on the light receiving element 29 will be described in more detail.

  The + 1st order diffracted light diffracted by the fifth and sixth regions 28b1 and 28b2 giving astigmatism is reversed on the light receiving element 29 in the relationship between the radial direction and the tangential direction, so that the fifth and sixth spots 29b1 are respectively obtained. , 29b2 and incident on the light receiving element 29. On the other hand, the + 1st order diffracted light diffracted in the first to fourth regions 28a11, 28a12, 28a21, 28a22 to which astigmatism is not given has no change in the relationship between the radial direction and the tangential direction, and the fifth and sixth regions. The first to fourth spots 29a11, 29a12, 29a21, and 29a22 are formed so as not to overlap with the spots 29b1 and 29b2 and substantially focus on the light receiving element 29, respectively.

  Here, assuming that the light amounts detected by the first to fourth regions 29A, 29B, 29C, and 29D in the light receiving element 29 are A, B, C, and D, respectively, by the same calculation as in the first embodiment, Each servo signal and position detection signal are obtained.

<Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 10 is a diagram schematically showing the overall configuration of the optical pickup device according to the fourth embodiment of the present invention.

  The optical configuration of the fourth embodiment shown in FIG. 10 will be described focusing on the differences from the first embodiment shown in FIG.

  In the optical configuration in the fourth embodiment, the laser light source 1 and the light receiving elements 39 and 40 are integrated in a small area to constitute an optical integrated unit. In the fourth embodiment, the size can be further reduced as compared with the optical system of the second embodiment.

  This optical system has a diffractive optical element 38 instead of the diffractive optical element 8, and the diffractive optical element 38 also has a function of replacing PBS2. That is, PBS2 is not used in this optical system. Further, in place of the light receiving element 9, the light receiving elements 39 and 40 are arranged in a space-saving manner. Other optical configurations are the same as those in the first embodiment.

  FIG. 11 is a cross-sectional view showing an example of the structure of the diffractive optical element 38 of the fourth embodiment.

  As shown in FIG. 11, the structure of the diffractive optical element 38 is a binary structure in which the mold can be easily manufactured, and the depth of the groove is divided into two parts corresponding to one wavelength of the light emitted from the laser light source 1. It has a two-stage structure. The diffractive optical element 38 having a binary structure can be easily manufactured in a mold, but the + 1st order diffraction efficiency is 40% at the maximum, and is further lowered due to the depth of the groove and the shape error of the binary structure. Theoretically, -1st order diffracted light is generated with the same diffraction efficiency. In addition, when there is a shape error, zero-order light that is not subjected to diffraction action is also generated. This 0th-order light becomes stray light and causes each signal to deteriorate.

  FIG. 12 is a diagram illustrating the positional relationship between the diffractive optical element 38 and the light receiving elements 39 and 40 according to the fourth embodiment.

  When the reflected light from the optical disk 7 is perpendicularly incident on the diffractive optical element 38, it is symmetrical with respect to the optical axis at a predetermined distance d from the extension line in the optical axis direction passing through the center 38P of the diffractive optical element 38. There are centers 39P and 40P of the light receiving elements 39 and 40, respectively. That is, when there is zero-order light that is not diffracted by the diffractive optical element 38, zero-order light is not incident on the light receiving elements 39 and 40, and ± 1st-order diffracted light used for signal detection is 180 across the optical axis. ° Diffracts in the opposite direction. Therefore, stray light due to zero-order light that is not diffracted by the diffractive optical element 38 does not enter the light receiving elements 39 and 40. Further, both of the ± first-order diffracted lights can be received by the light receiving elements 39 and 40 having the same configuration arranged on the opposite side when viewed from the center of the optical axis.

  In the fourth embodiment, the number of cells of the light receiving elements 39 and 40 is doubled, but a constant light amount can be obtained using the binary-shaped diffractive optical element 38 that is easy to manufacture as shown in FIG. . Further, according to the positional relationship between the diffractive optical element 38 and the light receiving elements 39 and 40 of the fourth embodiment shown in FIG. 12, the influence of the above stray light can be suppressed.

  FIG. 13 is a diagram illustrating patterns of the diffractive optical element 38 and the light receiving elements 39 and 40 according to the fourth embodiment. FIG. 13A shows spots on the diffractive optical element 38 with the diffraction pattern omitted.

  As shown in FIG. 13A, the diffractive optical element 38 is divided into six regions of first to sixth regions 38a11, 38a12, 38a21, 38a22, 38b1, and 38b2, and each region has a different diffraction pattern.

  A region surrounded by a broken line in FIG. 13A indicates a light beam on the diffractive optical element 38 when there is no lens shift. In the region indicated by the broken line, the light beams 38s1 and 38s2 indicated by hatching in FIG. 13A are diffracted by the recording track of the optical disc 7, that is, due to the overlap of the 0th order light and the 1st order light diffracted by the recording track. Luminous flux. Further, the unhatched light beam 38s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the fourth embodiment, astigmatism is given in the fifth and sixth regions 38b1 and 38b2.

  Next, the spot shape of the light beam incident on the light receiving elements 39 and 40 will be described with reference to FIG. FIG. 13B shows a division pattern and a spot shape of the light receiving elements 39 and 40.

  Each of the light receiving elements 39 and 40 is divided into two in the radial direction and also divided into two in the tangential direction, and each of the first to fourth regions 39A, 39B, 39C, 39D, 40A, 40B, 40C, The cell is divided into 40D cells. Moreover, the area | region enclosed with the dashed-dotted line of FIG.13 (b) shows spot shape. The + 1st order diffracted light diffracted by the diffractive optical element 38 enters one light receiving element 39, and the −1st order diffracted light diffracted by the diffractive optical element 38 enters the other light receiving element 40. A spot is incident on these light receiving elements 39 and 40 at a point-symmetrical position with respect to the optical axis center. Therefore, if the cell names of the light receiving elements 39 and 40 are the first to fourth regions 39A to 39D in one light receiving element 39 and the first to fourth regions 40A to 40D in the other light receiving element 40, 39A and 40C, 39B and 40D, 39C and 40A, and 39D and 40B are respectively arranged at corresponding positions with the optical axis center in between.

  In one light receiving element 39, the first spot 39a11 is a spot formed by + 1st order diffracted light diffracted in the first region 38a11, and the second spot 39a12 is diffracted in the second region 38a12. The third spot 39a21 is a spot formed by the + 1st order diffracted light diffracted by the third region 38a21, and the fourth spot 39a22 is the fourth region 38b22. The fifth spot 39b1 is a spot formed by the + 1st order diffracted light diffracted by the fifth region 38b1, and the sixth spot 39b2 is the spot formed by the + 1st order diffracted light diffracted at 6 is a spot formed by + 1st order diffracted light diffracted by the region 38b2.

  Among the light beams 38s1 indicated by hatching on the diffractive optical element 38 in FIG. 13A, the light beam that overlaps the first region 38a11 is the light beam that overlaps the first spot 39a11 and the light beam that overlaps the second region 38a12 is the second light beam 38s11. It is included in the spot 39a12. In addition, among the light beams 38s2 indicated by hatching on the diffractive optical element 38 in FIG. 13A, the light beam that overlaps the third region 38a21 is the light beam that overlaps the third spot 39a21 and the light beam that overlaps the fourth region 38a22. 4 spots 39a22.

  In the other light receiving element 40, the first spot 40a11 is a spot formed by −1st order diffracted light diffracted by the first region 38a11, and the second spot 40a12 is diffracted by the second region 38a12. The third spot 40a21 is a spot formed by the −1st order diffracted light diffracted by the third region 38a21, and the fourth spot 40a22 is the fourth spot 40a22. The fifth spot 40b1 is a spot formed by the −1st order diffracted light diffracted by the fifth area 38b1, and is a spot formed by the −1st order diffracted light diffracted by the area 38b22. The spot 40b2 is a spot formed by −1st order diffracted light diffracted by the sixth region 38b2.

  Among the light beams 38s1 indicated by hatching on the diffractive optical element 38 in FIG. 13A, the light beam that overlaps the first region 38a11 is the light beam that overlaps the first spot 40a11 and the second region 38a12 is the second light beam. It is included in the spot 40a12. In addition, among the light beams 38s2 indicated by hatching on the diffractive optical element 38 in FIG. 13A, the light beam that overlaps the third region 38a21 is the light beam that overlaps the third spot 40a21 and the light beam that overlaps the fourth region 38a22. 4 spots 40a22.

  The relationship between each region of the diffractive optical element 38 and each spot on the light receiving elements 39 and 40 will be described in more detail.

  The ± first-order diffracted light diffracted in the fifth and sixth regions 38b1 and 38b2 giving astigmatism is reversed on the light receiving elements 39 and 40 in the relationship between the radial direction and the tangential direction, respectively. Are incident on the light receiving elements 39, 40 in the shapes shown in the spots 39b1, 39b2, 40b1, 40b2. On the other hand, the ± first-order diffracted light diffracted in the first to fourth regions 38a11, 38a12, 38a21, 38a22 to which astigmatism is not given has no change in the relationship between the radial direction and the tangential direction, and the fifth and fifth regions. The first to fourth spots 39a11, 39a12, 39a21, 39a22, 40a11, and 40a12 are not overlapped with the six spots 39b1, 39b2, 40b1, and 40b2, and are substantially focused on the light receiving elements 39 and 40, respectively. , 40a21, 40a22.

Here, the light amounts detected by the first to fourth regions 39A, 39B, 39C, 39D, 40A, 40B, 40C, 40D in the light receiving elements 39, 40 are respectively A1, B1, C1, D1, A2, and A2. B2, C2, and D2, and outputs A, B, C, and D from the light receiving element are defined by the following equation (8).
A = A1 + A2
B = B1 + B2
C = C1 + C2
D = D1 + D2 (8)

  As shown in the equation (8), by defining the light amounts detected by the light receiving elements 39 and 40 as A, B, C, and D, respectively, the servo signals and the servo signals are calculated by the same calculation as in the first embodiment. A position detection signal is obtained.

  As explained above, all the servo signal detection including the signal for detecting the position of the light receiving element is performed by only one diffractive optical element and two light receiving elements each having four cells without branching the light beam. Therefore, it is possible to provide a small and simple optical pickup device with a low noise signal.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described with reference to FIG. The optical configuration of the fifth embodiment is the same as the optical configuration of the second embodiment shown in FIG. 5, but the diffractive optical element 48 instead of the diffractive optical element 18 and the light receiving element 49 instead of the light receiving element 19. Is used.

  FIG. 14 is a diagram illustrating patterns of a diffractive optical element and a light receiving element according to the fifth embodiment of the invention. FIG. 14A shows spots on the diffractive optical element 48 with the diffraction pattern omitted.

  As shown in FIG. 14A, the diffractive optical element 48 is radially divided into eight regions of first to eighth regions 48a11, 48a12, 48a21, 48a22, 48b11, 48b12, 48b21, and 48b22. Have different diffraction patterns.

  A region surrounded by a broken line in FIG. 14A shows a light beam on the diffractive optical element 48 when there is no lens shift. In the area indicated by the broken line, the light beams 48s1 and 48s2 indicated by hatching in FIG. Luminous flux. Further, the unhatched light beam 18s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the fifth embodiment, astigmatism is given in the fifth to eighth regions 48b11, 48b12, 48b21, and 48b22.

  Next, the spot shape of the light beam incident on the light receiving element 49 will be described with reference to FIG. FIG. 14B shows a division pattern and a spot shape of the light receiving element 49.

  The light receiving element 49 is divided into two parts in the radial direction and two parts in the tangential direction. The light receiving element 49 includes four cells divided into first to fourth regions 49A, 49B, 49C, and 49D. Moreover, the area | region enclosed with the dashed-dotted line of FIG.14 (b) shows spot shape. The first spot 49a11 is a spot formed by + 1st order diffracted light diffracted by the first region 48a11, and the second spot 49a12 is formed by + 1st order diffracted light diffracted by the second region 48a12. The third spot 49a21 is a spot formed by + 1st order diffracted light diffracted by the third region 48a21, and the fourth spot 49a22 is + 1st order diffracted light diffracted by the fourth region 48a22. The fifth spot 49b11 is a spot formed by + 1st order diffracted light diffracted by the fifth region 48b11, and the sixth spot 49b12 is diffracted by the sixth region 48b12. The seventh spot 49b21 is a spot formed by the + 1st order diffracted light. A spot formed by the + 1st-order diffracted light diffracted by 21, eighth spot 49b22 is a spot formed by the + 1st-order diffracted light diffracted in the eighth region 48B22.

  Among the light beams 48s1 indicated by hatching on the diffractive optical element 48 in FIG. 14A, the light beam overlapping the first region 48a11 is the first light beam 49a11 and the light beam overlapping the second region 48a12 is the second light beam 48s11. It is included in the spot 49a12. In addition, among the light beams 48s2 indicated by hatching on the diffractive optical element 48 in FIG. 14A, a light beam that overlaps the third region 48a21 has a light beam that overlaps the third spot 49a21 and a light beam that overlaps the fourth region 48a22. 4 spots 49a22.

  The relationship between each region of the diffractive optical element 48 and each spot on the light receiving element 49 will be described in more detail.

  The + 1st order diffracted light diffracted in the fifth to eighth regions 48b11, 48b12, 48b21, and 48b22 giving astigmatism is reversed on the light receiving element 49 in the relationship between the radial direction and the tangential direction. Eight spots 49b11, 49b1249b21, 49b22 are incident on the light receiving element 49 in the shape shown in FIG. On the other hand, the + 1st order diffracted light diffracted in the first to fourth regions 48a11, 48a12, 48a21, 48a22 to which no astigmatism is given does not change in the relationship between the radial direction and the tangential direction, and the fifth to eighth regions. The first to fourth spots 49a11, 49a12, 49a21, and 49a22 are not overlapped with the spots 49b11, 49b12, 49b21, and 49b22, and are substantially focused on the light receiving element 49, respectively.

  Here, assuming that the light amounts detected by the first to fourth regions 49A, 49B, 49C, and 49D in the light receiving element 49 are A, B, C, and D, respectively, by the same calculation as in the first embodiment, Each servo signal and position detection signal are obtained.

  In this embodiment, as shown in FIG. 14B, the fifth to eighth spots 49b11, 49b12, which have passed through the fifth to eighth regions 48b11, 48b12, 48b21, 48b22 of the diffractive optical element 48, Since 49b21 and 49b22 are separated from each other, it is possible to suppress unnecessary offset from being applied to the servo signal even when the spot moves on the light receiving element 49.

<Sixth Embodiment>
Next, a sixth embodiment of the present invention will be described with reference to FIG. The optical configuration of the sixth embodiment is the same as the optical configuration of the second embodiment shown in FIG. 5, but the diffractive optical element 58 instead of the diffractive optical element 18 and the light receiving element 59 instead of the light receiving element 19. Is used.

  FIG. 15 is a diagram illustrating patterns of a diffractive optical element and a light receiving element according to the sixth embodiment of the present invention. FIG. 15A shows spots on the diffractive optical element 58 with the diffraction pattern omitted.

  As shown in FIG. 15A, the diffractive optical element 58 is radially divided into eight regions of first to eighth regions 58a11, 58a12, 58a21, 58a22, 58b11, 58b12, 58b21, 58b22. Have different diffraction patterns.

  A region surrounded by a broken line in FIG. 15A shows a light beam on the diffractive optical element 58 when there is no lens shift. In the region indicated by the broken line, the light beams 58s1 and 58s2 indicated by hatching in FIG. 15A are diffracted by the recording track of the optical disc 7, that is, due to the overlap of the 0th order light and the 1st order light diffracted by the recording track. Luminous flux. Further, the unhatched light beam 18s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the sixth embodiment, astigmatism is given in the fifth to eighth regions 58b11, 58b12, 58b21, and 58b22.

  Next, the spot shape of the light beam incident on the light receiving element 59 will be described with reference to FIG. FIG. 15B shows the division pattern and spot shape of the light receiving element 59.

  The light receiving element 59 is divided into two parts in the radial direction and two parts in the tangential direction, and is composed of cells divided into four parts in the first to fourth regions 59A, 59B, 59C, 59D.

  In the sixth embodiment, the first to fourth regions 59A, 59B, 59C, 59D of the light receiving element 59 are arranged to be separated from each other, and between the regions 59A, 59B, 59C, 59D. A dead zone that does not detect the amount of light is formed.

  A region surrounded by an alternate long and short dash line in FIG. 15B indicates a spot shape. The first spot 59a11 is a spot formed by + 1st order diffracted light diffracted by the first region 58a11, and the second spot 59a12 is formed by + 1st order diffracted light diffracted by the second region 58a12. The third spot 59a21 is a spot formed by + 1st order diffracted light diffracted by the third region 58a21, and the fourth spot 59a22 is + 1st order diffracted light diffracted by the fourth region 58a22. The fifth spot 59b11 is a spot formed by + 1st order diffracted light diffracted by the fifth region 58b11, and the sixth spot 59b12 is diffracted by the sixth region 58b12. The seventh spot 59b21 is a spot formed by the + 1st order diffracted light. A spot formed by the + 1st-order diffracted light diffracted by 21, eighth spot 59b22 is a spot formed by the + 1st-order diffracted light diffracted in the eighth region 58B22.

  Among the light beams 58s1 indicated by hatching on the diffractive optical element 58 in FIG. 15A, the light beam that overlaps the first region 58a11 is the light beam that overlaps the first spot 59a11 and the light beam that overlaps the second region 58a12. It is included in the spot 59a12. In addition, among the light beams 58s2 indicated by hatching on the diffractive optical element 58 in FIG. 15A, the light beam that overlaps the third region 58a21 is the light beam that overlaps the third spot 59a21 and the light beam that overlaps the fourth region 58a22. 4 spots 59a22.

  The relationship between each region of the diffractive optical element 58 and each spot on the light receiving element 59 will be described in more detail.

  The + 1st order diffracted light diffracted in the fifth to eighth regions 58b11, 58b12, 58b21, 58b22 giving astigmatism is reversed on the light receiving element 59 in the relationship between the radial direction and the tangential direction. Eight spots 59b11, 59b1259b21, 59b22 are incident on the light receiving element 59 in the shape shown in FIG. On the other hand, the + 1st order diffracted light diffracted in the first to fourth regions 58a11, 58a12, 58a21, 58a22 to which astigmatism is not given has no change in the relationship between the radial direction and the tangential direction, and the fifth to eighth regions. The first to fourth spots 59a11, 59a12, 59a21, and 59a22 are formed so as not to overlap with the spots 59b11, 59b12, 59b21, and 59b22 and to substantially focus on the light receiving element 59, respectively.

  Here, assuming that the light amounts detected by the first to fourth regions 59A, 59B, 59C, 59D in the light receiving element 59 are A, B, C, D, respectively, by the same calculation as in the first embodiment, Each servo signal and position detection signal are obtained.

  In the sixth embodiment, as shown in FIG. 15B, the fifth to eighth spots 59b11, which have passed through the fifth to eighth regions 58b11, 58b12, 58b21, 58b22 of the diffractive optical element 58, 59b12, 59b21, 59b22 are separated from each other, and the first to fourth regions 59A, 59B, 59C, 59D of the light receiving element 59 are separated from each other, so that the spot moves on the light receiving element 59. In this case, it is possible to suppress an unnecessary offset from being applied to the servo signal.

<Seventh Embodiment>
Next, a seventh embodiment of the present invention will be described with reference to FIG. The optical configuration of the seventh embodiment is the same as the optical configuration of the second embodiment shown in FIG. 5, but the diffractive optical element 68 instead of the diffractive optical element 18 and the light receiving element 69 instead of the light receiving element 19. Is used.

  FIG. 16 is a diagram illustrating patterns of the diffractive optical element and the light receiving element according to the seventh embodiment of the present invention. FIG. 16A shows spots on the diffractive optical element 68 with the diffraction pattern omitted.

  As shown in FIG. 16A, the diffractive optical element 68 is divided into six regions of first to sixth regions 68a1, 68a2, 68b11, 68b12, 68b21, and 68b22 in accordance with regions containing diffraction components by the optical disc 7. And each region has a different diffraction pattern.

  A region surrounded by a broken line in FIG. 16A indicates a light beam on the diffractive optical element 68 when there is no lens shift. In the area indicated by the broken line, the light beams 68s1 and 68s2 indicated by hatching in FIG. 16A are diffracted by the recording track of the optical disc 7, that is, due to the overlap of the zeroth order light and the first order light diffracted by the recording track. Luminous flux. Further, the unhatched light beam 18s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the seventh embodiment, astigmatism is given in the first and second regions 68a1 and 68a2.

  Next, the spot shape of the light beam incident on the light receiving element 69 will be described with reference to FIG. FIG. 16B shows a division pattern and a spot shape of the light receiving element 69.

  The light receiving element 69 is divided into two parts in the radial direction and two parts in the tangential direction, and is composed of cells divided into four parts in the first to fourth regions 69A, 69B, 69C, and 69D. Moreover, the area | region enclosed with the dashed-dotted line of FIG.16 (b) shows spot shape. The first spot 69a1 is a spot formed by + 1st order diffracted light diffracted by the first region 68a1, and the second spot 69a2 is formed by + 1st order diffracted light diffracted by the second region 68a2. The third spot 69b11 is a spot formed by + 1st order diffracted light diffracted by the third region 68b11, and the fourth spot 69b12 is + 1st order diffracted light diffracted by the fourth region 68b12. The fifth spot 69b21 is a spot formed by + 1st order diffracted light diffracted by the fifth region 68b21, and the sixth spot 69b22 is diffracted by the sixth region 68b22. This is a spot formed by + 1st order diffracted light.

  The area indicated by hatching in FIG. 16B corresponds to the light flux indicated by hatching in FIG. That is, the light beams 69 s 1 and 69 s 2 indicated by hatching in FIG. 16B are due to the light that respectively formed the light beams 68 s 1 and 68 s 2 on the diffractive optical element 68. Of the light that forms the light beam 68s3 on the diffractive optical element 68, the light beam that overlaps the first region 68a1 is included in the first spot 69a1, and the light beam that overlaps the second region 68a2 is the second spot. 69a2.

  The relationship between each region of the diffractive optical element 68 and each spot on the light receiving element 69 will be described in more detail.

  The + 1st order diffracted light diffracted in the first and second regions 68a1 and 68a2 giving astigmatism is reversed on the light receiving element 69 in the relationship between the radial direction and the tangential direction, and the first and second spots 69a1 are respectively obtained. , 69a2 and is incident on the light receiving element 69. On the other hand, the + 1st order diffracted light diffracted in the third to sixth regions 68b11, 68b12, 68b21, 68b22 to which astigmatism is not applied has no change in the relationship between the radial direction and the tangential direction, and the first and second regions. The third to sixth spots 69b11, 69b12, 69b21, and 69b22 are formed so as not to overlap with the spots 69a1 and 69a2 and to substantially focus on the light receiving element 69, respectively.

  Here, assuming that the light amounts detected by the first to fourth regions 69A, 69B, 69C, and 69D in the light receiving element 69 are A, B, C, and D, respectively, by the same calculation as in the first embodiment, Each servo signal is obtained.

Also in the seventh embodiment, the position signals PosX (radial direction) and PosY (tangential direction) are SPP and MPP itself. However, as shown in FIG. 16, the + 1st order diffracted light diffracted by the first and second regions 68a1 and 68a2 of the diffractive optical element becomes a spot rotated by 90 ° on the light receiving element 69. Therefore, unlike the first to sixth embodiments, the following expressions (9) and (10) are used.
PosX = SPP (9)
PosY = MPP (10)

<Eighth Embodiment>
Next, an eighth embodiment of the present invention will be described with reference to FIG. The optical configuration of the eighth embodiment is the same as the optical configuration of the second embodiment shown in FIG. 5, but the diffractive optical element 78 instead of the diffractive optical element 18 and the light receiving element 79 instead of the light receiving element 19. Is used.

  FIG. 17 is a diagram illustrating patterns of a diffractive optical element and a light receiving element according to the eighth embodiment of the present invention. FIG. 17A shows spots on the diffractive optical element 78 with the diffraction pattern omitted.

  As shown in FIG. 17A, the diffractive optical element 78 is radially divided into six regions of first to sixth regions 78a1, 78a2, 78b11, 78b12, 78b21, 78b22, and has a different diffraction pattern for each region. Have.

  A region surrounded by a broken line in FIG. 17A shows a light beam on the diffractive optical element 78 when there is no lens shift. In the area indicated by the broken line, the light beams 78s1 and 78s2 indicated by hatching in FIG. 17A are due to the diffraction component of the recording track of the optical disc 7, that is, the overlap of the 0th order light and the 1st order light diffracted by the recording track. Luminous flux. Further, the unhatched light beam 18s3 does not include a diffraction component due to the recording track, that is, only the 0th-order light beam diffracted by the recording track. In the eighth embodiment, astigmatism is given in the first and second regions 78a1 and 78a2.

  Next, the spot shape of the light beam incident on the light receiving element 79 will be described with reference to FIG. FIG. 17B shows a division pattern and a spot shape of the light receiving element 79.

  The light receiving element 79 is divided into two parts in the radial direction and two parts in the tangential direction. The light receiving element 79 is composed of cells divided into first to fourth regions 79A, 79B, 79C, and 79D. Moreover, the area | region enclosed with the dashed-dotted line of FIG.17 (b) shows spot shape. The first spot 79a1 is a spot formed by + 1st order diffracted light diffracted by the first region 78a1, and the second spot 79a2 is formed by + 1st order diffracted light diffracted by the second region 78a2. The third spot 79b11 is a spot formed by + 1st order diffracted light diffracted by the third region 78b11, and the fourth spot 79b12 is + 1st order diffracted light diffracted by the fourth region 78b12. The fifth spot 79b21 is a spot formed by + 1st order diffracted light diffracted by the fifth region 78b21, and the sixth spot 79b22 is diffracted by the sixth region 78b22. This is a spot formed by + 1st order diffracted light.

  The area indicated by hatching in FIG. 17B corresponds to the light flux indicated by hatching in FIG. That is, the light beams 79 s 1 and 79 s 2 indicated by hatching in FIG. 17B are due to the light that respectively formed the light beams 78 s 1 and 78 s 2 on the diffractive optical element 78. Of the light that forms the light beam 78s3 on the diffractive optical element 78, the light beam that overlaps the first region 78a1 is included in the first spot 79a1, and the light beam that overlaps the second region 78a2 is the second spot. 79a2.

  The relationship between each region of the diffractive optical element 78 and each spot on the light receiving element 79 will be described in more detail.

  The + first order diffracted light diffracted by the first and second regions 78a1 and 78a2 giving astigmatism is reversed on the light receiving element 79 in the radial direction and the tangential direction. The light is incident on the light receiving element 79 in the shapes indicated by 79a1 and 79a2. On the other hand, the + first-order diffracted light diffracted in the third to sixth regions 78b11, 78b12, 78b21, 78b22 to which astigmatism is not given has no change in the relationship between the radial direction and the tangential direction, and the first and first regions The second spots 79a1 and 79a2 do not overlap with each other, and become third to sixth spots 79b11, 79b12, 79b21, and 79b22 so as to substantially focus on the light receiving element 79, respectively.

  Here, assuming that the light amounts detected by the first to fourth regions 79A, 79B, 79C, and 79D in the light receiving element 79 are A, B, C, and D, respectively, by the same calculation as in the first embodiment, Each servo signal is obtained.

  Also in the eighth embodiment, as shown in FIG. 17, the + 1st order diffracted light diffracted by the first and second regions 78a1 and 78a2 of the diffractive optical element becomes a spot rotated by 90 ° on the light receiving element 79. . For this reason, the same expressions (9) and (10) as those in the seventh embodiment are used.

  The first to eighth embodiments of the present invention have been described above. Each embodiment includes an optical configuration (shown in FIGS. 1, 5 and 10), a structure of a diffractive optical element (shown in FIGS. 3, 6 and 11), a positional relationship between the diffractive optical element and the light receiving element, and Depending on the combination of the configuration of the light receiving element (shown in FIGS. 4, 7, and 12), the method of dividing the diffractive optical element, and the correspondence of the light receiving elements (shown in FIGS. 2, 8, 9, and 13 to 17) Although configured, the effects of the present invention can be achieved by any combination, and are not limited to the combinations shown in the embodiments.

  The present invention is applied to an optical pickup device for reproducing and / or recording an optical disc.

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Polarizing beam splitter 3 1/4 wavelength plate 4 Collimator lens 5 Standing mirror 6 Objective lens 7 Disc 8 Diffraction optical element 9 Light receiving element 10 Branching prism 18 Diffraction optical element 19 Light receiving element 28 Diffraction optical element 29 Light receiving element 38 diffractive optical element 39 light receiving element 40 light receiving element 48 diffractive optical element 49 light receiving element 58 diffractive optical element 59 light receiving element 68 diffractive optical element 69 light receiving element 78 diffractive optical element 79 light receiving element

Claims (5)

A laser light source for irradiating the optical disc with a light beam;
A first diffractive region where a light beam overlapping a component diffracted by a recording track of the optical disc and a non-diffracted component is incident; and a second diffractive region where a light beam of a component not diffracted by the recording track of the optical disc is incident The light beam reflected from the optical disc is diffracted at a predetermined order in the first diffraction region and the second diffraction region, and is not in any one of the first diffraction region or the second diffraction region. A diffractive optical element that gives point aberration;
The optical disc is divided into four light receiving regions by a dividing line in a direction corresponding to the recording track direction of the optical disc and a dividing line in a direction perpendicular to the recording track direction, and the first diffraction region and the first diffraction region An optical pickup device comprising: a light receiving element that receives light diffracted in the two diffraction regions. The first diffractive region of the diffractive optical element is incident with a light beam in which a component diffracted in the + 1st order by a recording track of the optical disc and a component that is not diffracted overlap, and is divided in a direction corresponding to the recording track direction of the optical disc. A dividing line corresponding to a direction perpendicular to the recording track direction of the optical disc, in which a light beam in which a region divided by a line and a component diffracted in the first order by a recording track of the optical disc overlap with a non-diffracting component is incident. Each region has four divided regions that diffract the incident light flux in different directions,
The second diffractive region of the diffractive optical element is incident with a light beam having a component that is not diffracted by the recording track of the optical disc, and is divided by a dividing line corresponding to a direction perpendicular to the recording track direction in different directions. Having two divided regions to diffract;
The light diffracted by the four divided regions of the first diffraction region is received by the different light receiving regions of the light receiving element and is diffracted by the two divided regions of the second diffraction region. When light is divided by a dividing line corresponding to a direction perpendicular to the recording track direction among the four areas of the light receiving element, light is received by two areas included on the same side. 2. The optical pickup device according to claim 1, wherein The first diffractive region of the diffractive optical element is diffracted in the −1st order by the region where a light beam in which a component diffracted in the + 1st order by the recording track of the optical disc and a component not diffracted are incident, and the recording track of the optical disc And a region where a light beam that overlaps a component that is not diffracted is incident, and each region has two divided regions that diffract the incident light beam in different directions,
The second diffractive region of the diffractive optical element is divided into a direction corresponding to the direction of the recording track and a direction perpendicular to the direction of the recording track in which a light beam having a component that is not diffracted by the recording track of the optical disc is incident. 4 divided regions that are divided by lines and diffracted in different directions,
The light diffracted by the two divided regions of the first diffraction region is the same when divided by the dividing line corresponding to the direction perpendicular to the recording track direction among the four regions of the light receiving element. The light received by each of the two regions included on the side and diffracted by the four divided regions of the second diffraction region are received by the different light receiving regions of the light receiving element. 2. The optical pickup device according to claim 1, wherein   Of the four light receiving areas of the light receiving element, the first and first light detection signals of the light receiving areas included on the same side are added when divided by a dividing line in a direction corresponding to the recording track direction of the optical disc. 2 is obtained, a first difference signal is calculated by subtracting the second addition signal from the first addition signal, and the recording of the optical disc among the four light receiving areas of the light receiving element is performed. When divided by a dividing line in a direction corresponding to a direction perpendicular to the track direction, the light detection signals of the light receiving areas included on the same side are added to obtain third and fourth addition signals, respectively, A first control unit that calculates a second difference signal by subtracting the fourth addition signal from the addition signal and calculates a tracking error signal using the first and second difference signals is provided. Any of claims 1 to 3 Or the optical pickup apparatus described in (1).   Of the four light receiving regions of the light receiving element, the light detection signals of the light receiving regions arranged on the diagonal lines are added to obtain fifth and sixth addition signals, respectively, 5. The optical pickup device according to claim 1, further comprising: a second control unit that subtracts the addition signal of 6 to calculate a focus error signal.

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