JP2007149190A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently detect tracking error even when there is μm-order misalignment in the positional alignment between a diffraction element and a photo-detector. <P>SOLUTION: When obtaining a tracking error signal and a focus error signal using photoelectrically converted signals by receiving diffracted light through the photo-detector 7 having two or more light-receiving areas after condensing laser light on a track of an optical disk D and forming the diffracted light of the light reflected by this track through the diffraction element 6, the diffraction element 6 includes a 1st diffraction part 10 which forms zero-order light and ± primary diffracted light by diffracting the reflected light onto one surface 9A and 2nd to 4th diffraction parts 11 to 13 which diffract or project the zero-order light and ± primary diffracted light formed by the 1st diffraction part 10 onto the other surface 9B, and the photo-detector 7 includes 1st to 3rd light-receiving parts 21 to 23 which receive the light diffracted or projected by the 2nd to 4th diffraction parts. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pickup device that corrects a tracking error signal caused by an objective lens shift and a misalignment between a diffraction element and a light receiving element.

An optical pickup device that performs tracking servo using a tracking error signal is described in Patent Document 1. The optical pickup device described in Patent Document 1 will be described with reference to FIGS.
FIG. 9 is a schematic diagram of an optical pickup device described in Patent Document 1. FIG. 10 is a perspective view showing the positional relationship between the diffraction element and the second photodetector.
That is, as shown in FIG. 9, the optical pickup device described in Patent Document 1 includes a semiconductor laser 100 that emits laser light to an optical disc E, a collimator lens 101 that collimates the laser light, and a collimator lens 101 that is parallel. The first polarization beam splitter 102 having the polarization separation film 102A that transmits the laser light that has been transmitted and reflects the laser light reflected by the optical disc E, and the laser that has passed through the polarization separation film 102A of the first polarization beam splitter 102 The reflected light from the optical disk E reflected by the objective lens 103 for condensing the light on the optical disk E and the polarization separation film 102A of the first polarizing beam splitter 102 reflects the component light including the magneto-optical signal. And a second polarization beam splitter 104 having a polarization separation film 104A that transmits light other than the above.

Further, this optical pickup device includes a Wollaston prism 105 having a separation film 105A for separating the component light including the magneto-optical signal reflected by the polarization separation film 104A of the second polarization beam splitter 104 into two polarization components. Diffraction that diffracts light that does not include a magneto-optical signal that has passed through a spot lens 107 that condenses on a first photodetector 106 having two light receiving elements 106A and 106B and a polarization separation film 104A of a second polarization beam splitter 104. An element 108 and a second photodetector 111 that detects ± first-order diffracted light and zero-order light diffracted by the diffraction element 108 through a cylindrical lens 109 and a spot lens 110 are included.
The two light receiving elements 106 </ b> A and 106 </ b> B reproduce the information on the optical disc E by detecting the two polarization components separated by the separation film 105 </ b> A of the Wollaston prism 105.
As shown in FIG. 10, the second photodetector 111 includes a first light receiving unit 111A having four light receiving regions M to P divided in a cross shape at the center, and predetermined values on both sides of the first light receiving unit 111A. It has a pair of 2nd, 3rd light-receiving part 111B, 111C arrange | positioned spaced apart.

  In the diffraction element 108, the grating pitch is the same, and the duty ratio between the width of the peak portion and the width of the valley portion decreases or increases in one direction. The zero-order diffracted light increases and the zero-order diffracted light increases.

  The focus error signal using this optical pickup device is reflected from the optical disk, and the light diffracted by the diffraction element 108 is photoelectrically converted by the four light receiving regions of the first light receiving unit 111A in the second photodetector 111 and output. The astigmatism method can be obtained from the obtained signal.

On the other hand, the tracking error signal can be obtained as follows.
First, an offset correction signal for correcting the offset of the objective lens 103 is obtained. The offset correction signal is photoelectrically converted by the second and third light receiving units 111B and 111C from the first addition value obtained by adding the signals photoelectrically converted by the four light receiving regions M to P of the first light receiving unit 111A. It is obtained by subtracting a multiplication value obtained by multiplying the second addition value obtained by adding the obtained signals by a predetermined gain.
This offset correction signal changes positively and negatively depending on the direction and amount of shift of the objective lens 103.

  Next, among the four light receiving areas M to P of the first light receiving unit 111, a third addition value obtained by adding together the signals photoelectrically converted in one of the two light receiving areas divided in parallel with the track direction of the optical disc E. A push-pull signal is obtained by subtracting a fourth addition value obtained by adding the signals photoelectrically converted in the other two light receiving regions.

Next, a tracking error signal can be obtained by subtracting a multiplication value obtained by multiplying the offset correction signal by a predetermined constant from the push-pull signal.
JP 2003-123279 A

However, since the 0th-order light diffracted by the diffraction element 108 needs to be incident on the four light receiving regions M to P of the first light receiving unit 111A, the diffraction element 108 and the first light receiving unit 111A are about several μm. Even when a slight misalignment occurs, the tracking error signal offset cannot be eliminated.
In addition, since the astigmatism method is used to perform focus error detection, the Wollaston prism 105 and the first photodetector 106 are required, and an inexpensive optical pickup device cannot be provided.
Therefore, the present invention is proposed in view of the above-described problems, and can perform good tracking error detection even if a deviation of the order of μm occurs in the alignment between the diffraction element and the photodetector. Another object of the present invention is to provide an inexpensive optical pickup device.

A first invention in the present invention comprises an objective lens that condenses laser light on a track of an optical disc, a diffraction element that generates diffracted light from reflected light reflected by the track, and a plurality of light receiving regions, A light detector that photoelectrically converts diffracted light by receiving the diffracted light, and an optical pickup device that performs tracking error detection and focus error detection using a signal photoelectrically converted in each light receiving region. A first diffractive portion formed on one surface of the transmissive substrate and diffracting the reflected light to generate 0th order light and ± 1st order diffracted light; and a diffraction region formed on the other surface of the light transmissive substrate. And a second diffracting unit that diffracts the zero-order light generated by the first diffracting unit, and third and fourth diffractions that branch the ± first-order diffracted light generated by the first diffracting unit. And the second diffraction The diffraction region of the first portion includes first to eighth diffraction regions, a dividing line that divides the diffraction region into two equal parts parallel to the track direction of the optical disc is defined as a first dividing line, parallel to the track direction, and the first A dividing line formed at an equal distance from one dividing line is divided into second and third dividing lines, a dividing line dividing into two equal parts parallel to the radial direction of the optical disc is a fourth dividing line, parallel to the radial direction, and When the dividing lines formed equidistant from the four dividing lines are the fifth and sixth dividing lines, the first diffraction region includes the second dividing line, the fourth dividing line, the fifth dividing line, and the A region surrounded by an outer peripheral edge of the diffraction region, the second diffraction region includes the second dividing line, the fourth dividing line, the sixth dividing line, and a region surrounded by the outer peripheral edge of the diffraction region; Three diffraction regions are the third dividing line, the fourth dividing line, the fifth dividing line, and The region surrounded by the outer peripheral edge of the diffraction region and the fourth diffraction region are the third dividing line, the fourth dividing line, the sixth dividing line, and the region surrounded by the outer peripheral edge of the diffraction region, 5 diffraction regions, the first dividing line, the fifth dividing line, the first region surrounded by the outer periphery of the diffraction region, the sixth diffraction region, the first dividing line, the sixth dividing line, The third region and the seventh diffraction region surrounded by the outer peripheral edge of the diffraction region are the first dividing line, the fifth dividing line, and the second region surrounded by the outer peripheral edge of the diffraction region, the eighth. The diffraction region is a fourth region surrounded by the first dividing line, the sixth dividing line, and an outer peripheral edge of the diffraction region, and the photodetector is diffracted by the first diffraction region. A first light receiving region for detecting folding light and + 1st order diffracted light diffracted in the seventh and eighth diffraction regions, the second diffraction region, The second light receiving region for detecting the −1st order diffracted light diffracted in the seventh diffraction region and the 8th diffraction region, and the + 1st order diffracted light diffracted in the third diffraction region, the fifth and sixth diffraction regions, A third light receiving region to detect, a fourth light receiving region to detect + 1st order diffracted light diffracted in the fourth diffraction region and a −1st order diffracted light diffracted in the fifth and sixth diffraction regions, and the third, There is provided an optical pickup device comprising: second and third light receiving portions that detect branched light branched by a fourth diffraction portion.
In the second invention, each of the third and fourth diffracting portions is formed so as to surround the first circular diffraction region having the same size as the spot diameter of the reflected light, and the first circular diffraction region. The optical pickup device according to claim 1, further comprising a second circular diffraction region.
According to a third aspect of the invention, the two light receiving portions have fifth and sixth light receiving regions that are divided into two equal parts in parallel to the radial direction, and the fifth light receiving region is the first circular diffraction in the third diffraction portion. The first light emitted from the region is detected, the sixth light receiving region detects the second light emitted from the second circular diffraction region, and the third light receiving portion The seventh and eighth light receiving regions are divided into two equal parts in parallel, and the seven light receiving regions detect third emitted light emitted from the first circular diffraction region in the fourth diffractive portion, and The optical pickup device according to claim 2, wherein the eight light receiving regions detect the fourth emitted light emitted from the second circular diffraction region.
According to a fourth aspect of the invention, the first diffractive part condenses one of the ± first-order diffracted lights generated from the reflected light of the optical disc before the third diffractive part or the fourth diffractive part, 4. The optical pickup device according to claim 1, further comprising: a diffraction region that condenses light on the photodetector side of the third diffraction portion or the fourth diffraction portion. I will provide a.

  According to the present invention, the second diffractive portion has the first to eighth diffraction regions, and receives the diffracted light diffracted from the first to eighth diffraction regions by the first to fourth light receiving regions of the photodetector. Therefore, it is possible to provide a good tracking error detection even when a deviation of the order of μm occurs in the alignment between the diffraction element and the photodetector, and to provide an inexpensive optical pickup device. The first diffracting unit condenses one of the ± first-order diffracted lights in front of the third diffracting unit or the fourth diffracting unit and the other of the third diffracting unit or the fourth diffracting unit. Since it has a diffraction region to be condensed on the photodetector side, a focus error signal using the SSD method can be obtained.

Hereinafter, embodiments of an optical pickup device according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing an optical pickup device according to the present invention. FIG. 2 is a perspective view showing the relationship between the diffraction element and the photodetector. FIG. 3 shows the relationship between the position of diffracted light diffracted in each region of the second diffractive portion of the diffractive element and the position reaching each light receiving region of the photodetector. The figure which shows the several divided diffraction area, (B) is a figure which shows the relationship with the light radiate | emitted from each diffraction area of the diffraction element which reaches | attains each light reception area | region of a 1st detection part. FIG. 4 is a diagram illustrating a connection relationship between the photodetector and the push-pull circuit. FIG. 5 is a diagram showing a tracking error signal when the objective lens shift is 0 μm. FIG. 6 is a diagram showing a tracking error signal when the objective lens shift is 150 μm. FIG. 7 is a diagram showing a tracking error signal when the objective lens shift is 300 μm. FIG. 8 is a diagram showing an S-shaped curve by the focus error signal.

  As shown in FIG. 1, an optical pickup device 1 according to the present invention includes a semiconductor laser 2 that emits laser light that irradiates a track of an optical disc D, and a collimator lens 3 that collimates the laser light emitted from the semiconductor laser 2. A polarizing beam splitter 4 having a polarization separation film 4A that transmits laser light and reflects reflected light from the optical disk D, and an objective lens 5 that focuses the laser light transmitted through the polarizing beam splitter 4 onto a track of the optical disk D. It consists of and. The objective lens 5 is movable in a direction (radial direction) orthogonal to the track direction.

  Further, the optical pickup device 1 detects and photoelectrically converts the diffracted element 6 that generates diffracted light from the reflected light of the track of the optical disk D reflected by the polarization beam splitter 4 and the diffracted light generated by the diffractive element 6. The photo detector 7 includes a plurality of light receiving regions, and a push-pull circuit 8 that generates a tracking error signal and a focus error signal from a signal photoelectrically converted by the photo detector. On the optical disc D, a groove Q and a groove R are formed, and the track in this case is the groove Q.

Below, the structure and arrangement | positioning relationship of the diffraction element 6 and the photodetector 7 are demonstrated in detail using FIG.2 and FIG.3.
First, the configuration of the diffraction element 6 will be described.
As shown in FIG. 2, on one surface 9A of the rectangular parallelepiped light-transmitting substrate 9, circular 0th-order light and circular ± first-order diffracted light from circular reflected light reflected by the track of the optical disk D are received. A first diffracting unit 10 to be generated is formed, and on the other surface 9B, a second diffracting unit 11 that generates ± first-order diffracted light from circular zero-order light generated by the first diffracting unit 10, and a first A third diffractive portion 12 that emits circular + 1st order diffracted light generated by the diffracting portion 10 at a predetermined angle, and a fourth diffracted light that emits circular −1st order diffracted light generated by the first diffractive portion 10 at a predetermined angle. It is comprised from the diffraction part 13. FIG.

  Further, the first diffractive portion 10 is focused on one of the circular ± first-order diffracted lights generated from the reflected light of the optical disc D in front of the other surface 9B, and the other is located behind the other surface 9B. A diffraction region is formed so as to form a focal point. For this reason, the SSD method can be used for focus error detection.

Here, the reflected light from the optical disc D that enters the first diffraction section 10 will be described.
The light intensity of the laser light that irradiates the track of the optical disk D has a strong Gaussian distribution in the central part and a weak Gaussian distribution in the peripheral part. For this reason, the reflected light from the track of the optical disc D becomes light in a state where the Gaussian distribution is maintained and diffraction is generated at the boundary between the groove Q and the land R.

  The reflected light from the central portion of the groove Q is a laser beam having a high light intensity that is incident on the first diffractive portion 10 as it is, and the light diffracted at the boundary portion between the groove Q and the lands R on both sides adjacent to the groove Q is Then, the light is incident on the first diffractive portion 10 in a state of being superimposed on a part of the reflected light from the central portion of the groove Q. As a result, as shown in FIG. 2, the reflected light from the optical disc D incident on the first diffractive portion 10 is reflected light L1 from the central portion of the groove Q and a part of the reflected light from the central portion of the groove Q. And a pair of reflected lights L2 and L3 on which light diffracted at the boundary between the groove Q and the land R on both sides adjacent to the groove Q is superimposed. Since the reflected light L1 and the light diffracted at the boundary between the groove Q and the land R are also circular, the pair of reflected lights L2 and L3 are the boundary between the reflected light L1, the groove Q, and the land R adjacent to the groove Q. The light is cut out at the common part of the light diffracted at, and has a rugby ball shape.

As shown in FIG. 3A, the second diffractive portion 11 includes a square-shaped diffractive region 14 having a rectangular opening 14A (region that is not a diffractive region) at the center.
The diffraction region 14 has first to eighth diffraction regions S11 to S14 and S21 to S24.
The first to eighth diffraction regions S11 to S14 and S21 to S24 are divided by the following first to sixth dividing lines 15 to 20.

Each dividing line will be described below.
The first dividing line 15 is a dividing line that bisects in the track direction of the optical disc D, and the second dividing line 16 is parallel to the track direction of the optical disc D and on one side of the rectangular opening 14A. The third dividing line 17 is a dividing line parallel to the track direction of the optical disc D and in contact with the other side of the rectangular opening 14A, and the fourth dividing line 18 is a radial line of the optical disc D. The fifth dividing line 19 is a dividing line parallel to the radial direction of the optical disc D and in contact with a side orthogonal to one side of the rectangular opening 14A. The dividing line 20 is a dividing line that is parallel to the radial direction of the optical disc D and is in contact with the side orthogonal to the other side of the rectangular opening 14A.

The first diffraction region S <b> 11 is a region surrounded by the second dividing line 16, the fourth dividing line 18, the fifth dividing line 19, and the first outer peripheral edge 14 a of the diffraction region 14.
The second diffraction region S <b> 12 is a region surrounded by the second dividing line 16, the fourth dividing line 18, the sixth dividing line 20, and the first outer peripheral edge 14 a of the diffraction region 14.
The third diffraction region S <b> 21 is a region surrounded by the third dividing line 17, the fourth dividing line 18, the fifth dividing line 19, and the second outer peripheral edge 14 b of the diffraction region 14.
The fourth diffraction region S22 is a region surrounded by the third dividing line 17, the fourth dividing line 18, the sixth dividing line 20, and the second outer peripheral edge 14b of the diffraction region 14.

The fifth diffraction region S13 is a region surrounded by the first dividing line 15, the fifth dividing line 19, and the first and third outer peripheral edges 14a and 14c of the diffraction region 14.
The sixth diffraction region S14 is a region surrounded by the first dividing line 15, the sixth dividing line 20, and the first and fourth outer peripheral edges 14a and 14d of the diffraction region 14.
The seventh diffraction region S23 is a region surrounded by the first dividing line 15, the fifth dividing line 19, and the second and third outer peripheral edges 14b and 14c of the diffraction region 14.
The eighth diffraction region S24 is a region surrounded by the first dividing line 15, the sixth dividing line 20, and the second and fourth outer peripheral edges 14b and 14d of the diffraction region 14.

  Circular second-order light generated by the first diffractive unit 10, that is, reflected light L1, and a pair of circular reflected lights L2 and L3 are incident on the second diffractive unit 11 as they are. The first reflected light L1 is incident on each of the first to eighth diffraction regions S11 to S14 and S21 to S24, and the reflected light L2 is incident on the first and second diffraction regions S11 and S12. The third and fourth diffraction regions S21 and S22 are formed so that the reflected light L3 is incident thereon. Then, the sides of the first and second diffraction regions S11 and S12 and the third and fourth diffraction regions on the side facing the rectangular opening 14A are tangents to the reflected lights L2 and L3.

When the wavelength of the laser beam is λ, the side of the diffraction region 14 is 6000λ, and the distances from the first dividing line 15 to the second dividing line 16 and the third dividing line 17 are both 2000λ. The distance from the fourth dividing line 18 to the fifth dividing line 19 and the sixth dividing line 20 is 1000λ.
That is, the first to fourth diffraction regions S11 to S14 are squares of 2000λ × 2000λ, and the fifth to eighth diffraction regions S21 to S24 are rectangles of 3000λ × 1000λ.

The third diffracting unit 12 includes a first circular diffracting unit 12A having the same size as the spot diameter of the + 1st order diffracted light generated by the first diffracting unit 10 when the laser beam is just focused on the track of the optical disc D. And a second circular diffractive part 12B surrounding the first circular diffractive part 12A.
The + 1st order diffracted light diffracted by the first diffracting unit 10 is incident on the first and second circular diffracting units 12A and 12B.

The fourth diffractive portion 13 has a first circular diffracting portion 13A having the same size as the spot diameter of the −1st order diffracted light generated by the first diffracting portion 10 when the laser light is just focused on the track of the optical disc D. And a second circular diffraction portion 13B surrounding the first circular diffraction portion 13A.
The −1st order diffracted light diffracted by the first diffracting unit 10 is incident on the first and second circular diffracting units 13A and 13B.

As shown in FIG. 2, the photodetector 7 receives the first light receiving unit 21 that detects ± first-order diffracted light generated by the second diffracting unit 11 and the light emitted from the third and fourth diffracting units 12. It comprises second and third light-receiving units 22 and 23 that detect each.
The first light receiving unit 21 includes first to fourth light receiving regions A to D that are divided into four equal parts by a dividing line 24 in a direction parallel to the track direction and a dividing line 25 in a direction orthogonal to the track direction. Yes.

The first to eighth spot lights T1a to T8b are defined as follows.
The first spot light T1b is spot light in which the −1st order diffracted light diffracted in the first diffraction region S11 is incident on the first light receiving region A, and the first spot light T1a is diffracted in the first diffraction region S11. + 1st order diffracted light is spot light that is incident on a region other than the first to fourth light receiving regions A to D.
The second spot light T2b is spot light in which the −1st order diffracted light diffracted in the second diffraction region S12 enters the second light receiving region B, and the second spot light T2b is diffracted in the second diffraction region S12. The first-order diffracted light is spot light that enters a region other than the first to fourth light receiving regions A to D.

The third spot light T3a is spot light in which the + 1st order diffracted light diffracted in the third diffraction region S21 enters the third light receiving region C, and the third spot light T3b is diffracted in the third diffraction region S12 − The first-order diffracted light is spot light that enters a region other than the first to fourth light receiving regions A to D.
The fourth spot light T4a is spot light in which the + 1st order diffracted light diffracted in the fourth diffraction region S22 enters the fourth light receiving region D, and the fourth spot light T4b is diffracted in the fourth diffraction region S22 − The first-order diffracted light is spot light that enters a region other than the first to fourth light receiving regions.

The fifth spot light T5a is spot light in which the + 1st order diffracted light diffracted in the fifth diffraction region S13 is incident on the third light receiving region C, and the fifth spot light T5b is diffracted in the fifth diffraction region S13 − The first-order diffracted light is spot light incident on the fourth light receiving region D.
The sixth spot light T6a is spot light in which the + 1st order diffracted light diffracted in the sixth diffraction region S14 is incident on the third light receiving region C, and the sixth spot light T6b is diffracted in the sixth diffraction region S14− The first-order diffracted light is spot light incident on the fourth light receiving region D.

The seventh spot light T7a is spot light in which the + 1st order diffracted light diffracted in the seventh diffraction region S23 is incident on the first light receiving region A, and the seventh spot light T7b is diffracted in the seventh diffraction region S23 − The first-order diffracted light is spot light incident on the second light receiving region B.
The eighth spot light T8a is spot light in which the + 1st order diffracted light diffracted in the fourth diffraction region S24 is incident on the first light receiving region A, and the eighth spot light T8b is diffracted in the second diffraction region S24− The first-order diffracted light is spot light incident on the second light receiving region B.

Accordingly, the light receiving areas A to D are irradiated with spot light as follows.
The first light receiving region A detects the first spot light T1b, the seventh spot T7a, and the eighth spot light T8a.
The second light receiving region B detects the second spot light T2b, the seventh spot light T7b, and the eighth spot light T8b.

The third light receiving region C detects the third spot light T3a, the fifth spot light T5a, and the sixth spot light T6a.
The fourth light receiving region D detects the fourth spot light T4a, the fifth spot light T5b, and the sixth spot light T6b.

  Therefore, the first and second spot lights T1a and T2a of the + 1st order diffracted light diffracted by the first diffraction region S11 and the second diffraction region S12 are diffracted by the third diffraction region S21 and the fourth diffraction region S22 −. The third and fourth spot lights T3b and T4b of the first-order diffracted light enter the areas other than the first to fourth light receiving areas A to D, and are not detected in the first to fourth light receiving areas A to D.

The second light receiving unit 22 includes fifth and sixth light receiving regions G and H that are equally divided by a dividing line 26 parallel to the radial direction.
The fifth light receiving region G detects the first emitted spot light U1 emitted from the second circular diffracting portion 12B, and the sixth light receiving region H is the second emitted spot light U2 emitted from the first circular diffracting portion 12A. Is detected.

The third light receiving unit 23 includes seventh and eighth light receiving regions I and J that are equally divided by a dividing line 27 parallel to the radial direction.
The seventh light receiving region I detects the third emission spot light U3 emitted from the first circular diffraction unit 13A, and the eighth light reception region J includes the fourth emission spot U4 light emitted from the second circular diffraction unit 12B. Is detected.

  The rectangular opening 14A is formed at the center of the second diffractive portion 11 described above when the diffractive element 6 and the photodetector 7 are misaligned. This is to prevent the light receiving areas of the first to eighth spot lights T1b to T8b incident on each of .about.D from becoming equal and the detection signal from being corrected.

In addition, the diameter of the first circular diffracting portion 12A of the third diffracting portion 12 is set to the same size as the spot diameter of the + 1st order diffracted light generated by the first diffracting portion 10 when just focused. In the case of deviating from the just focus, the diameter of the second exit spot light U2 exiting from the first circular diffractive part 12A of the third diffractive part 12 is wide, and is detected in the fifth light receiving region G. This is because focus error detection is performed by obtaining a focus error signal.
For the same reason, the diameter of the first circular diffracting portion 13A of the fourth diffracting portion 13 is the same as the spot diameter of the −1st order diffracted light generated by the first diffracting portion 10 when the focus is just focused. It is. Therefore, when the sixth and seventh light receiving regions H and I are irradiated with the second and third exit spot lights U2 and U3 emitted from the third and fourth diffracting units 12 and 13, the just focusing is performed. .

  As shown in FIG. 4, the push-pull circuit 8 includes a first operational amplifier 28 and a second operational amplifier 29. The first operational amplifier 28 includes a positive input terminal 28A commonly connected to the first and second light receiving areas A and B of the photodetector 7, and a negative input terminal 28B commonly connected to the third and fourth light receiving areas C and D. And one output terminal 28C. The second operational amplifier 29 includes a + input terminal 29A commonly connected to the sixth and seventh light receiving regions H and I, a −input terminal 29B commonly connected to the fifth and eighth light receiving regions G and J, and one output terminal. 29C.

Next, tracking detection and focus error detection will be described in detail with reference to FIGS.
First, the tracking error signal TE will be described with reference to FIGS.
5 to 7, the first to twelfth spot lights T1b to T8b other than the first spot light T1a, the second spot light T2a, the third spot light T3b, and the fourth spot light T4b are used as the first to twelfth spot lights T1b to T8b. It will be treated as a signal obtained in the fourth light receiving areas A to D.

5 to 7, the horizontal axis indicates the laser spot deviation amount (μm) from the center of the groove Q at one track pitch, and the vertical axis indicates a value obtained by standardizing signals obtained from the light receiving areas A to D. Is shown.
Here, one track pitch is 0.74 μm.
The tracking error signals TE and TE1 and the correction signal TE2 are expressed by the following equations.

  5 to 7, ◇ is T1b + T2b, □ is T3a + T4a, + is TE1, + is T5a + T5b + T6a + T6b, ○ is T7a + T7b + T8a + T8b, * is a correction signal TE2, and Δ is a tracking error signal TE.

(When the shift amount of the objective lens 5 is 0 μm)
In FIG. 2, when the shift amount of the objective lens 5 is 0 μm (no objective lens shift), the tracking error signal is 0 on the groove Q and the land R as shown in FIG. Between the R and the land R and the adjacent groove Q, the sizes are equal and symmetrical in the positive and negative directions, and no offset occurs.

(When the shift amount of the objective lens is 150 μm)
When the shift amount of the objective lens 5 in FIG. 2 is 150 μm, as shown in FIG. 6, the tracking error signal is the groove Q and the groove Q as in (when the shift amount of the objective lens 5 is 0 μm). On land R, it is 0, and between land R and groove Q adjacent to land R, the size is equal and symmetrical, and no offset occurs.

(When the shift amount of the objective lens is 300 μm)
Similarly, when the shift amount of the objective lens 5 in FIG. 2 is 300 μm, an offset occurs in the tracking error signal as shown in FIG. 7 (when the shift amount of the objective lens is 150 μm). Not.
As described above, tracking detection can be performed even if the objective lens 5 is shifted. Further, since the first to eighth spot lights T1b to T8b do not enter the dividing lines 24 and 25 of the light receiving areas A to B of the photodetector 7, the diffraction element 6 and the first photodetector 7 Even if there is a deviation of μm order in the alignment, the tracking error detection is not affected.

Next, the focus error signal will be described with reference to FIG.
In FIG. 8, the first to fourth emission spot lights U1 to U4 are treated as signals obtained in the fifth to eighth light receiving areas G to J, and the light receiving areas G to J of the photodetector 7 are used. , U1 to U4 are obtained.
The horizontal axis in FIG. 7 indicates the distance (μm) in the direction in which the objective lens 5 approaches the optical disc D from the just focus position, the vertical axis indicates the relative value of the signal obtained from each light receiving region, and ○ is U1, ◇ are U2, Δ is U3, * is U4, and □ is a focus error signal FE.

As shown in FIG. 8, the curve of the focus error signal when the objective lens 5 approaches the optical disc side from the just focus position is a half curve of the S-shaped curve.
In FIG. 8, only the curve in the direction in which the objective lens 5 approaches the optical disc D from the just focus position is shown. However, the origin of the curve in the direction away from the origin is relative to the curve in the approach direction. It has a point-symmetric relationship with the center. For this reason, the focus error signal draws an S-shaped curve indicating the case where the objective lens 5 approaches or moves away from the optical disc D, and the first to fourth emission spot lights U1 to U4 in such fifth to eighth light receiving regions. By detecting this, focus error can be detected by the SSD method.

Next, the operation will be described.
Laser light from the semiconductor laser 2 is collimated by the collimator lens 3 and enters the polarization beam splitter 4. The parallel light incident on the polarization beam splitter 4 passes through the polarization separation film 4A and is condensed on the track of the optical disk D by the objective lens 5.
Thereafter, the laser light focused on the optical disk D is reflected by the track to generate circular reflected light. The reflected light enters the polarization beam splitter 4, is reflected by the polarization separation film 4 A, and enters the diffraction element 6.

The first diffractive element 10 of the diffractive element 6 generates circular 0th order light and ± 1st order diffracted light. The 0th order light is transmitted to the second diffracting part 11 and the + 1st order diffracted light is transmitted to the third diffracting part 12. The first-order diffracted light is incident on the fourth diffracting unit 13.
At this time, the first diffracting portion 10 is diffracted so that one of the ± first-order diffracted lights is focused before the other surface 9B and the other is focused behind the other surface 9B as described above. Since the region is formed, focus error detection by the SSD method can be performed.

The 0th-order light incident on the second diffractive portion 11 includes reflected lights L1, L2, and L3.
The first reflected light L1 is incident on the first to eighth diffraction regions S11 to S14 and S21 to S24 of the second diffractive portion 11, and the reflected light L2 is incident on the first and second diffraction regions S11 and S12. The reflected light L3 is incident on the third and fourth diffraction regions S21 and S22.

The first spot light T1b diffracted by the first diffraction region S11 of the second diffraction section 11 and the + 1st order diffracted light diffracted by the seventh diffraction region S23 and the eighth diffraction region S24 are respectively converted into seventh and eighth spot light T7a, T8a enters the first light receiving region A.
The second spot light T2b, the seventh spot light T7b, and the eighth spot light T7b diffracted by the second diffraction area S12, the seventh diffraction area S23, and the eighth diffraction area S24 are incident on the second light receiving area B.

The third spot light T3a, the fifth and sixth spot lights T5a, T6a diffracted by the third diffraction region S21, the fifth diffraction region S13, and the sixth diffraction region S14 are incident on the third light receiving region C.
The fourth spot light T4a diffracted by the fourth diffraction region S22 and the fifth and sixth spot light T5b, T6b diffracted by the fifth diffraction region S13 and the sixth diffraction region S14 enter the fourth light receiving region D. .

The first exit spot light U1 emitted from the second circular diffraction unit 12B of the third diffraction unit 12 enters the fifth light receiving region G. The second emission spot light U2 emitted from the first circular diffraction portion 12A enters the sixth light receiving region H.
The third exit spot light U3 emitted from the first circular diffraction unit 13A of the fourth diffraction unit 13 enters the seventh light receiving region I. The fourth emission spot light U4 emitted from the second circular diffraction portion 12B is incident on the eighth light receiving region J.

  A signal obtained by adding the first spot light T1b, the second spot light T2b, the seventh spot lights T7a and T7b, and the eighth spot lights T8a and T8b photoelectrically converted in the first and second light receiving regions A and B is a first operational amplifier. The third spot light T3a, the fourth spot light T4a, the fifth spot lights T5a and T5b, and the sixth spot light T6a photoelectrically converted in the third and fourth light receiving regions C and D. , T6b are added to the negative input terminal 28B, the difference is calculated and output from the output terminal 28C to obtain a tracking error signal.

  A signal obtained by adding the first and second emission spot lights U2 and U3 photoelectrically converted in the sixth and seventh light receiving regions H and I is input to the + input terminal 29A of the second operational amplifier 29, and the fifth and eighth light receiving parts are received. A signal obtained by adding the third and fourth spot lights U1 and U4 photoelectrically converted in the regions G and J is input to the −input terminal 29B, and the difference is calculated and output from the output terminal 29C to generate a focus error signal. obtain.

  As described above, according to the embodiment of the present invention, the first diffracting unit 10 focuses one of the circular ± first-order diffracted lights generated from the reflected light of the optical disc D before the other surface 9B. Since the second diffractive part 11 is formed of a square diffractive area 14 having a rectangular opening 14A at the center, the diffractive area is formed so that the other is focused behind the other surface 9B. Even if a shift of the objective lens 5 or misalignment between the diffraction element 6 and the photodetector 7 occurs, accurate tracking error detection can be performed, and focus error detection by the SSD method can be performed. In addition, when recording and reproducing HD-DVD (High Density Digital Versatile Disc) and BD (Blu-Ray Disc) with a single pickup using the three-beam method, two objective lenses are required. In this case, it is necessary to perform off-center adjustment for the two objective lenses. In this regard, when performing with one beam as in the embodiment of the present invention, it is not necessary to perform off-center adjustment.

  In the embodiment, the second diffractive portion 11 has the rectangular opening 14A, but it may be a circular opening or a polygonal opening. In addition, although the first to fourth diffraction regions S11 to S14 are square and S21 to S24 are rectangular, they may be polygonal. The second circular diffractive portions 12B and 13B are not limited to being circular, but may be polygonal or elliptical. In the embodiment, the track is the groove Q, but the same applies to the land R.

It is the schematic which shows the optical pick-up apparatus which concerns on this invention. It is a perspective view which shows the relationship between a diffraction element and a photodetector. It is a figure which shows the relationship between the position of the diffracted light diffracted in each area | region of the 2nd diffraction part of a diffraction element, and the position which reaches | attains each light reception area | region of a photodetector. It is a figure which shows the connection relation of a photodetector and a push pull circuit. It is a figure which shows a tracking error signal in case an objective lens shift is 0 micrometer. It is a figure which shows a tracking error signal in case an objective lens shift is 150 micrometers. It is a figure which shows a tracking error signal in case objective lens shift is 300 micrometers. It is a figure which shows the S-shaped curve by a focus error signal. 1 is a schematic diagram of an optical pickup device described in Patent Document 1. FIG. It is a perspective view which shows the positional relationship of a diffraction element and a 2nd photodetector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical pick-up apparatus, 2 ... Semiconductor laser, 3 ... Collimating lens, 4 ... Polarization beam splitter, 4A ... Polarization separation film, 5 ... Objective lens, 6 ... Diffraction element, 7 ... Photo detector, 8 ... Push-pull circuit, DESCRIPTION OF SYMBOLS 9 ... Light transmissive board | substrate, 9A ... One side, 9B ... The other side, 10 ... 1st diffraction part, 11 ... 2nd diffraction part, 12 ... 3rd diffraction part, 13 ... 4th diffraction part, 12A, 13A ... 1st circular diffraction part, 12A, 13B ... 2nd circular diffraction part, 14 ... diffraction area, 14A ... rectangular opening, 15 ... 1st dividing line, 16 ... 2nd dividing line, 17 ... 3rd dividing line, 18 ... 4th dividing line, 19 ... 5th dividing line, 20 ... 6th dividing line, 21 ... 1st light-receiving part, 22 ... 2nd light-receiving part, 23 ... 3rd light-receiving part, 24, 25, 26, 27 ... Dividing line 28 ... first operational amplifier 29 ... second operational amplifier S11 ... first diffraction region S12 ... 2 diffraction region, S21 ... 3rd diffraction region, S22 ... 4th diffraction region, S13 ... 5th diffraction region, S14 ... 6th diffraction region, S23 ... 7th diffraction region, S24 ... 8th diffraction region, L1, L2, L3 ... reflected light, A ... first light receiving region, B ... second light receiving region, C ... third light receiving region, D ... fourth light receiving region, G ... fifth light receiving region, H ... sixth light receiving region, I ... first 7 light receiving area, J ... 8th light receiving area

Claims (4)

An objective lens that condenses the laser light on the track of the optical disc, a diffraction element that generates diffracted light from the reflected light reflected by the track, and a plurality of light receiving regions. The diffracted light is received and photoelectrically converted. In an optical pickup device comprising a photodetector, and performing tracking error detection and focus error detection using a signal photoelectrically converted in each light receiving region,
The diffraction element is
A first diffractive portion that is formed on one surface of the light-transmitting substrate and diffracts the reflected light to generate 0th order light and ± 1st order diffracted light;
A second diffractive portion having a diffractive region formed on the other surface of the light transmissive substrate and diffracting the zero-order light generated by the first diffractive portion;
A third and a fourth diffracting section for branching the ± first-order diffracted light generated by the first diffracting section,
The diffraction region of the second diffractive portion includes first to eighth diffraction regions, and a dividing line that divides the diffraction region into two equal parts parallel to the track direction of the optical disc is defined as a first dividing line and parallel to the track direction. The dividing lines formed at the same distance from the first dividing line are the second and third dividing lines, the dividing line that bisects the optical disk in parallel with the radial direction of the optical disc is the fourth dividing line, and is parallel to the radial direction. And when the dividing lines formed equidistant from the fourth dividing line are the fifth and sixth dividing lines,
The first diffraction region is a region surrounded by the second dividing line, the fourth dividing line, the fifth dividing line, and an outer periphery of the diffraction region, and the second diffraction region is the second dividing line, The fourth dividing line, the sixth dividing line, the region surrounded by the outer periphery of the diffraction region, the third diffraction region includes the third dividing line, the fourth dividing line, the fifth dividing line, and the The region surrounded by the outer periphery of the diffraction region, the fourth diffraction region, the third dividing line, the fourth dividing line, the sixth dividing line, and the region surrounded by the outer periphery of the diffraction region, the fifth The diffraction area is the first dividing line, the fifth dividing line, the first area surrounded by the outer periphery of the diffraction area, the sixth diffraction area is the first dividing line, the sixth dividing line, the The third region surrounded by the outer periphery of the diffraction region, the seventh diffraction region, the first dividing line, the fifth dividing line, and the diffraction The second region, the eighth diffractive region surrounded by the outer peripheral edge of the band, the first dividing line, a fourth region surrounded by the outer peripheral edge of said sixth dividing line and the diffraction region,
The photodetector is
A first light receiving region for detecting −1st order diffracted light diffracted in the first diffraction region and + 1st order diffracted light diffracted in the seventh and eighth diffraction regions;
A second light receiving region for detecting −1st order diffracted light diffracted in the second diffraction region, the seventh diffraction region, and the eighth diffraction region;
A third light receiving region for detecting + 1st order diffracted light diffracted in the third diffraction region, the fifth and sixth diffraction regions,
A fourth light receiving region for detecting + 1st order diffracted light diffracted in the fourth diffraction region and -1st order diffracted light diffracted in the fifth and sixth diffraction regions;
An optical pickup device comprising: second and third light receiving parts for detecting branched light branched by the third and fourth diffraction parts.   Each of the third and fourth diffracting portions includes a first circular diffraction region having the same size as the spot diameter of the reflected light, and a second circular diffraction region formed so as to surround the first circular diffraction region. The optical pickup device according to claim 1, further comprising:   The two light receiving portions include fifth and sixth light receiving regions that are equally divided into two in parallel with the radial direction, and the fifth light receiving region is a first light emitted from the first circular diffraction region in the third diffraction portion. 1 is detected, the sixth light receiving region detects the second emitted light emitted from the second circular diffraction region, and the third light receiving unit is divided into two equal parts parallel to the radial direction. The seventh light receiving region detects the third light emitted from the first circular diffraction region in the fourth diffraction section, and the eighth light receiving region The optical pickup device according to claim 2, wherein the fourth emitted light emitted from the second circular diffraction region is detected. The first diffracting unit condenses one of ± first-order diffracted lights generated from the reflected light of the optical disc before the third diffracting unit or the fourth diffracting unit, and the other is the third diffracting unit or 4. The optical pickup device according to claim 1, further comprising a diffraction region that is focused on the photodetector side of the fourth diffraction section. 5.

Images