JP2001351255A - Optical head device and optical information recording/ reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head device and an optical information recording/reproducing device where substrate thickness irregularity is detected, even to a disk to which a RF signal has not been preliminarily recorded. SOLUTION: Emitted light from a semiconductor laser 1 is divided into three lights of zeroth-order light being a main beam and ±1st-order diffraction light which is a sub beam by a diffraction optical device 3, a light-condensing spot of the main beam is focused on the disk 7, and light-condensing spots of two sub beams are defocused slightly in the reverse direction each other on the disk 7. Three reflected lights from the disk 7 are received by a photodetector 10. When substrate thickness deviation exists in the disk 7, the amplitudes of push-pull signals detected from each of two sub beams are different. Substrate thickness deviation of the disk 7 is detected, based on the difference between amplitudes of the push-pull signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device and an optical information recording / reproducing apparatus for recording / reproducing information on / from an optical recording medium, and more particularly to detecting a thickness deviation of a substrate of the optical recording medium. The present invention relates to an optical head device and an optical information recording / reproducing device.

[0002]

2. Description of the Related Art The recording density of an optical information recording / reproducing apparatus is inversely proportional to the square of the diameter of a condensed spot formed on an optical recording medium by an optical head device. That is, the smaller the diameter of the condensed spot, the higher the recording density. The diameter of the converging spot is inversely proportional to the numerical aperture of the objective lens in the optical head device. That is, the higher the numerical aperture of the objective lens, the smaller the diameter of the condensed spot.

On the other hand, if the thickness of the substrate of the optical recording medium deviates from the design value, the shape of the condensed spot is disturbed due to spherical aberration caused by the thickness deviation of the substrate, and the recording / reproducing characteristics deteriorate. Since the spherical aberration is proportional to the fourth power of the numerical aperture of the objective lens, the higher the numerical aperture of the objective lens, the narrower the margin of the substrate thickness deviation of the optical recording medium with respect to the recording / reproducing characteristics. Therefore, in an optical head device and an optical information recording / reproducing device in which the numerical aperture of an objective lens is increased in order to increase the recording density, the substrate thickness deviation of the optical recording medium is detected and corrected in order not to deteriorate the recording / reproducing characteristics. It is necessary.

FIG. 29 shows a configuration of an optical head device described in Japanese Patent Application Laid-Open No. 2000-40237 capable of detecting a deviation in substrate thickness of an optical recording medium. The outgoing light 152 from a semiconductor laser (not shown) is
Are focused on the disk 147 by a pair of objective lenses composed of the lens 150. First lens 148
Is mounted on the first actuator 149, and the first
Is driven in the optical axis direction by the actuator 149 of FIG.
Further, the first actuator 149 is mounted on the second actuator 151 together with the second lens 150, and is driven in the optical axis direction by the second actuator.

That is, the distance between the first lens 148 and the second lens 150 is adjusted by the first actuator 149, and the second actuator 151 comprises the first lens 148 and the second lens 150. The distance between the objective lens of the sheet set and the disk 147 is adjusted. In the above optical head device, changing the distance between the first lens 148 and the second lens 150 changes the spherical aberration, and changing the distance between the two objective lenses and the disk 147 changes the focus offset.

The operation of correcting the substrate thickness deviation by the optical head device will be briefly described below. If the disc 147 has a substrate thickness deviation, the amplitude of the RF signal recorded on the disk 147 decreases due to the spherical aberration caused by the substrate thickness deviation. In addition, the disc 1
The amplitude of the RF signal recorded at 47 decreases. Therefore,
The first actuator is driven while observing the amplitude of the RF signal recorded on the disk 147 to drive the first lens 14.
The distance between the first lens 148 and the second lens 150 is adjusted by changing the distance between the first lens 148 and the second lens 150 so that the amplitude of the RF signal is maximized. Further, while observing the amplitude of the RF signal recorded on the disk 147, the second actuator is driven to drive the two objective lens and the disk 14 together.
7, the distance between the objective lens and the disk 147 is adjusted so that the amplitude of the RF signal is maximized.

That is, the detection of the substrate thickness deviation of the disk 147 is performed by observing the amplitude of the RF signal recorded on the disk 147, and the correction of the substrate thickness deviation of the disk 147 is performed by the first lens 148 and the second lens 148. This is performed by adjusting the distance between the lenses 150 to generate a spherical aberration in the optical head device that cancels out the spherical aberration caused by the substrate thickness deviation.

[0008]

In the above-mentioned conventional optical head device, when detecting the deviation of the substrate thickness of the optical recording medium,
In order to observe the amplitude of the RF signal, the RF signal needs to be recorded in advance. In other words, the above-mentioned conventional optical head device can detect the thickness deviation of the substrate because the RF signal is recorded in advance in the read-only optical recording medium. However, in the write-once and rewritable optical recording media, Is R
There is a problem that the substrate thickness deviation cannot be detected because the F signal is not recorded in advance.

Although a method of detecting the substrate thickness deviation after recording an RF signal for detecting the substrate thickness deviation by an optical head device is conceivable, in this method, the substrate thickness deviation is not corrected. Since the RF signal is written by the optical head device, the shape of the condensed spot is disturbed due to the spherical aberration caused by the substrate thickness deviation, and the RF signal cannot be correctly recorded.

An object of the present invention is to solve the above-mentioned problems in a conventional optical head device capable of detecting a substrate thickness deviation of an optical recording medium, and to provide an optical recording medium in which an RF signal is not recorded in advance. An object of the present invention is to provide an optical head device and an optical information recording / reproducing device capable of detecting a substrate thickness deviation.

[0011]

In order to achieve the above-mentioned object, the present invention employs the following constitution. 2. The optical head device according to claim 1, wherein a main beam and a plurality of sub-beams are generated from light emitted from a light source, and recording or reproduction is performed on an optical recording medium by the main beam, and optical recording is performed on the plurality of sub-beams. Providing phase distributions of opposite signs in the radial direction of the medium, and detecting a substrate thickness deviation of the optical recording medium based on a difference in amplitude of a push-pull signal detected from each of the plurality of sub-beams. .

In the case where there is no substrate thickness deviation in the optical recording medium between the main beam detected by the photodetector of the optical head device and the two sub-beams, the cross-sectional shapes of the converging spots of the two sub-beams are the same. . Therefore, the amplitude of the push-pull signal detected from each of the two sub-beams is also the same. On the other hand, when the optical recording medium has a substrate thickness deviation, the sectional shapes of the converging spots of the two sub beams are different. That is, the cross-sectional shape of the converging spot of one sub-beam has a relatively small diameter and the side lobe height is relatively high, and the cross-sectional shape of the converging spot of the other sub-beam has a relatively large diameter and the side lobe height Is relatively low. Therefore, the amplitude of the push-pull signal detected from each of the two sub-beams is also different. That is, the amplitude of the pull-up signal detected from one sub-beam is relatively small, and the amplitude of the push-pull signal detected from the other sub-beam is relatively large. The substrate thickness deviation of the optical recording medium is detected based on the difference between the amplitudes of the push-pull signals.

An optical head device according to a second aspect of the present invention has a diffractive optical element or a polarizing diffractive optical element for dividing light emitted from the light source into a plurality of light beams between the light source and the objective lens. The zero-order light from the optical element or the polarizing diffractive optical element is used as the main beam, and the ± first-order diffracted light from the diffractive optical element or the polarizing diffractive optical element is used as the sub-beam.

In the above-described optical head device, the diffractive optical element or the polarizing diffractive optical element functions as a convex lens (or concave lens) for + 1st-order diffracted light. However, it is possible to adopt a configuration that functions as a concave lens (or a convex lens) for the -1st-order diffracted light. Alternatively, as described in claim 4, the diffractive optical element or the polarizing diffractive optical element may be a cylindrical convex lens (or a cylindrical concave lens) whose generating line is parallel to the tangential direction of the optical recording medium for + 1st-order diffracted light. Work,
With respect to the -1st-order diffracted light, the generatrix can function as a cylindrical concave lens (or a cylindrical convex lens) parallel to the tangential direction of the optical recording medium. Alternatively, as described in claim 5, the diffractive optical element or the polarizing diffractive optical element imparts a third-order positive spherical aberration (or a third-order negative spherical aberration) to + 1st-order diffracted light. Work,
Third order negative spherical aberration (or 3rd order
The following positive spherical aberration may be provided.

On the other hand, the light source may have a plurality of light sources, and light emitted from the plurality of light sources may be used as a main beam and a plurality of sub beams, respectively. Can be.

In the above-mentioned optical head device, a collimator lens may be provided between the light source and the objective lens, and a position of the light source with respect to one of the sub-beams may be a focal point of the collimator lens. And the position of the light source with respect to the other of the sub-beams is shifted rearward (or forward) of the focal point of the collimator lens. Furthermore, a convex lens (or a concave lens) is inserted in an optical path for one of the sub-beams between the collimator lens and the objective lens between the collimator lens and the objective lens. A configuration in which a concave lens (or a convex lens) is inserted in the optical path for the other of the sub beams may be adopted. Alternatively, a cylindrical convex lens (or a cylindrical concave lens) whose generatrix is parallel to a tangential direction of the optical recording medium is inserted in an optical path between the collimator lens and the objective lens for one of the sub-beams. And a cylindrical concave lens (or cylindrical convex lens) whose generatrix is parallel to the tangential direction of the optical recording medium is inserted in the optical path between the collimator lens and the objective lens for the other of the sub-beams. . Alternatively, as in claim 10, a lens (or 3) that provides a third order positive spherical aberration in the optical path for one of the sub-beams between the collimator lens and the objective lens.
Lens that gives the next negative spherical aberration)
A configuration may be employed in which a lens that gives a third-order negative spherical aberration (or a lens that gives a third-order positive spherical aberration) is inserted in an optical path between the collimator lens and the objective lens with respect to the other of the sub-beams. .

In the optical head device according to the eleventh aspect, the converging spots of the plurality of sub-beams may be positioned on one of the grooves of the optical recording medium with respect to the converging spot of the main beam.
The optical recording medium may be arranged so as to be shifted in the radial direction of the optical recording medium in the opposite direction by / 4 period.

Alternatively, as in the optical head device according to the twelfth aspect, the phases of the plurality of sub-beams incident on the objective lens are shifted on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. It is also possible to adopt a configuration in which they are shifted in opposite directions by π / 2. Further, as described in claim 13, the diffractive optical element or the polarizing diffractive optical element has a configuration in which a diffraction grating is formed in a region including an effective diameter of the objective lens. A straight line parallel to the tangential direction of the optical recording medium is divided into a first region on the left and a second region on the right, and the phase of the grating in the first region and the second region is The structure may be shifted by π / 2, or the diffractive optical element or the polarizing diffractive optical element may be shifted by π / 2.
It is also possible to apply a configuration in which the diffraction optical element or the polarizing diffractive optical element is divided into six parts.

The optical head device according to claim 16, wherein the phases of the plurality of sub-beams incident on the objective lens are π / 2 on the left and right sides of a straight line passing through the optical axis and parallel to the tangential direction of the optical recording medium. They are configured to be shifted in opposite directions. In the optical head device, as described in claim 17, in a light path for the plurality of sub-beams, a phase of the plurality of sub-beams incident on the objective lens passes through an optical axis in a tangential direction of the optical recording medium. It is also possible to adopt a configuration in which a phase control element for shifting the parallel straight line to the left and right sides in opposite directions is inserted. Further, in the optical head device, as described in claim 18, the phase control element is a parallel flat plate having different thicknesses on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. A certain configuration is also possible.

In the above-mentioned optical head device, a nineteenth aspect is provided.
A land / groove position detection signal is generated based on a push-pull signal generated by the condensed spot of the sub beam, and the condensed spot of the main beam is generated by the light of the land / groove position detection signal. It is possible to detect whether the recording medium is located on a groove or a land. Alternatively, the thickness deviation of the substrate of the optical recording medium can be detected from the sum of the push-pull signals detected from each of the plurality of sub-beams.

The optical head device according to claim 21, wherein the condensed spots of the plurality of sub-beams with respect to the condensed spot of the main beam are radius of the optical recording medium by a half period of the groove of the optical recording medium. The optical head device according to claim 22, wherein a phase of the sub beam incident on the objective lens is shifted in a tangential direction of the optical recording medium through an optical axis. The left and right sides of the parallel straight line are shifted from each other by π in opposite directions. In the above optical head device,
According to a twenty-third aspect, a substrate thickness deviation of the optical recording medium can be detected from a difference between push-pull signals detected from each of the sub-beams.

An optical information recording / reproducing apparatus according to claim 24 is
Optical information recording / reproducing apparatus including a light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and an optical head device having a photodetector for receiving reflected light from the optical recording medium A main beam and a plurality of sub-beams are generated from light emitted from the light source, and recording or reproduction is performed on the optical recording medium with the main beam, and the sub-beams are radially aligned with the optical recording medium. Giving phase distributions of opposite signs to each other, detecting the substrate thickness deviation of the optical recording medium based on the difference in the amplitude of the push-pull signal detected from each of the sub-beams, and correcting the substrate thickness deviation of the optical recording medium It is characterized by doing.

In the above optical information recording / reproducing apparatus,
According to a twenty-fifth aspect, a collimator lens is provided between the light source and the objective lens, and the displacement of the substrate thickness of the optical recording medium is corrected by moving the collimator lens in the optical axis direction. be able to. Or,
27. The substrate of the optical recording medium according to claim 26, further comprising two relay lenses between the light source and the objective lens, and moving one of the two relay lenses in the optical axis direction. It is also possible to adopt a configuration for correcting the thickness deviation. 28. A structure according to claim 27, further comprising a liquid crystal optical element between the light source and the objective lens, and correcting a substrate thickness deviation of the optical recording medium by applying a voltage to the liquid crystal optical element. It can also be.

In the above optical information recording / reproducing apparatus,
29. The optical recording medium according to claim 28, wherein it is detected whether the focused spot of the main beam is located on a groove or a land of the optical recording medium. The polarity of a circuit for correcting the substrate thickness deviation can be switched. In addition, as described in claim 29, by reproducing address information formed on the optical recording medium, the focused spot of the main beam is positioned on either the groove or the land of the optical recording medium. It is also possible to adopt a configuration for detecting whether to do so. In addition, as described in claim 30, a land / groove position detection signal is generated based on a push-pull signal generated by the converged spots of the plurality of sub-beams, and a sign of the land / groove position detection signal is used to generate the main / land position. It may be configured to detect whether the focused spot of the beam is located on the groove or the land of the optical recording medium.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. First, the configuration of the first embodiment of the optical head device of the present invention will be described with reference to FIG. The optical head device of the present embodiment shown in FIG. 1 has a collimator lens 2, a diffractive optical element 3, a polarizing beam splitter 4,
In this configuration, a １ ／ wavelength plate 5 and an objective lens 6 are arranged, and a hologram optical element 8, a lens 9, and a photodetector 10 are arranged in the direction of reflection from the polarizing beam splitter 4. Reference numeral 7 indicates a disk.

The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and is divided by the diffractive optical element 3 into three lights, ie, a 0th-order light as a main beam and ± 1st-order diffracted lights as sub-beams. These lights are incident on the polarization beam splitter 4 as P-polarized light, and are transmitted by almost 100%.
The light passes through the wavelength plate 5 and is converted from linearly polarized light into circularly polarized light, and is condensed on the disk 7 by the objective lens 6. The three reflected lights from the disk 7 pass through the objective lens 6 in the opposite direction, pass through the quarter-wave plate 5, and are converted from circularly polarized light into linearly polarized light whose polarization direction is orthogonal to the outward path. Incident as S-polarized light, almost 100% reflected,
Almost 100 as the + 1st-order diffracted light by the hologram optical element 8
% Is diffracted, transmitted through the lens 9 and received by the photodetector 10.

FIG. 2 is a plan view of the diffractive optical element 3 shown in FIG. The diffractive optical element 3 has a configuration in which a diffraction grating is formed in a region including the effective diameter of the objective lens 6 indicated by a dotted line in FIG. In FIG. 2, the upward arrow indicates the disc 7
The right arrow indicates the radial direction of the disk 7. The direction of the grating in the diffraction grating is substantially parallel to the radial direction of the disk 7, and the pattern of the grating is off-axis concentric with respect to the diffractive optical element 3 and centered on the upper side in the tangential direction of the disk 7. Assuming that the phase difference between the line portion and the space portion of the grating is, for example, 0.232π, about 87.3% of the incident light is transmitted as the zero-order light, and ± 1
Approximately 5.1% is diffracted as second-order diffracted light, respectively. FIG.
In the above, if the light diffracted in the upward direction in FIG. 2 by the diffractive optical element 3 is + 1st-order diffracted light and the light diffracted in the downward direction in FIG. It functions as a convex lens on the other hand, and functions as a concave lens on -1st-order diffracted light. Thereby, quadratic function-like phase distributions of opposite signs are given to the two sub-beams. In this case, a phase distribution is given to both the radial direction and the tangential direction of the disk 7.

FIG. 3 shows the arrangement of the converging spots on the disk 7. FIG. 3A is a plan view, and FIG. 3B is a side view. Here, when viewed from the side of the light incident on the disk 7, the convex portion of the groove formed in the disk 7 is called a groove, the concave portion is called a land, and both are used as tracks. The condensed spots 12, 13, and 14 correspond to the 0th order light, the + 1st order diffracted light, and the -1st order diffracted light from the diffractive optical element 3, respectively. As shown in FIG. 3A, the condensed spot 12 is located on the track 11 (groove or land).
Numeral 3 is located on the boundary between the track 11 and a track (land or groove) adjacent to the left side thereof, and the condensing spot 14 is located on the boundary between the track 11 and the track (land or groove) adjacent to the right side thereof. Since the diffractive optical element 3 has a lens power, FIG.
As shown in FIG. 7, the focused spot 12 as the main beam is focused on the disk 7, while the focused spots 13 and 14 as the sub-beams are slightly defocused on the disk 7. The converging spot 13 is located behind the focal point when viewed from the incident side, and the converging spot 14 is located ahead of the focal point when viewed from the incident side. Therefore, the diameters of the condensed spots 13 and 14 as the sub-beams are slightly larger than those of the condensed spots 12 as the main beam.

FIG. 4 is a plan view of the hologram optical element 8 shown in FIG. 1. In FIG.
, And the right-pointing arrow indicates the radial direction of the disk 7. The hologram optical element 8 has a configuration in which a diffraction grating is formed in a region including the effective diameter of the objective lens 6 indicated by a dotted line in the figure, and a dividing line parallel to the radial direction of the disk 7 and a dividing line parallel to the tangential direction. , And is divided into four regions 15 to 18. The direction of the grating in the diffraction grating is parallel to the tangential direction of the disk 7 in any of the regions 15 to 18. Also, the pattern of the lattice is the area 15-18.
Are linear at equal intervals, and the
The interval at 17 is wider than the intervals at regions 15 and 18. Furthermore, the cross-sectional shape of the grating is saw-toothed in any of the regions 15 to 18. If the phase difference between the upper and lower portions of the saw-tooth is 2π, almost 100% of the light incident on each region is diffracted as + 1st-order diffracted light. Is done. Regions 15, 1
The direction of the sawtooth at 6 is set such that the + 1st-order diffracted light is deflected to the left in FIG. 4, and the direction of the sawtooth in the regions 17 and 18 is set so that the + 1st-order diffracted light is deflected to the right in FIG. Is set.

FIG. 5 shows the pattern of the light receiving portion of the photodetector 10 shown in FIG. 1 and the arrangement of the light spots on the photodetector 10. In FIG. 5, the upward arrow indicates the tangential direction of the disk 7, and the right arrow indicates the radial direction of the disk 7. The light spot 35 corresponds to the + 1st-order diffracted light from the region 15 of the hologram optical element 8 among the 0th-order light from the diffractive optical element 3, and is divided by 2 in the radial direction of the disk 7.
The light is condensed on the boundary between the light receiving units 19 and 20 divided into two. The light spot 36 corresponds to the + 1st-order diffracted light from the area 16 of the hologram optical element 8 out of the 0th-order light from the diffractive optical element 3, and is divided into two by a dividing line parallel to the radial direction of the disk 7. Light is condensed on the boundary line between 21 and 22. The light spot 37 corresponds to the + 1st-order diffracted light from the area 17 of the hologram optical element 8 out of the 0th-order light from the diffractive optical element 3, and is divided into two by a dividing line parallel to the radial direction of the disk 7. Light is condensed on the boundary between 23 and 24. The light spot 38 corresponds to the + 1st-order diffracted light from the area 18 of the hologram optical element 8 among the 0th-order light from the diffractive optical element 3, and is divided into two by a dividing line parallel to the radial direction of the disk 7. Light is condensed on the boundary line between 25 and 26. The light spot 39 corresponds to the + 1st-order diffracted light from the region 15 of the hologram optical element 8 among the + 1st-order diffracted light from the diffractive optical element 3, and is converged on a single light receiving section 27. The light spot 40 corresponds to the + 1st-order diffracted light from the region 16 of the hologram optical element 8 among the + 1st-order diffracted light from the diffractive optical element 3, and is converged on a single light receiving unit 28. The light spot 41 corresponds to the + 1st-order diffracted light from the region 17 of the hologram optical element 8 among the + 1st-order diffracted light from the diffractive optical element 3, and is converged on a single light receiving section 29. Light spot 42
Corresponds to the + 1st-order diffracted light from the region 18 of the hologram optical element 8 among the + 1st-order diffracted light from the diffractive optical element 3, and is converged on a single light receiving section 30. The light spot 43 corresponds to the + 1st-order diffracted light from the region 15 of the hologram optical element 8 among the -1st-order diffracted light from the diffractive optical element 3 and is collected on a single light receiving section 31. The light spot 44 corresponds to the + 1st-order diffracted light from the region 16 of the hologram optical element 8 among the -1st-order diffracted light from the diffractive optical element 3, and
2 are collected. The light spot 45 is a region 1 of the hologram optical element 8 in the -1st-order diffracted light from the diffractive optical element 3.
It corresponds to the + 1st-order diffracted light from No. 7 and is collected on a single light receiving section 33. The light spot 46 is generated from the diffractive optical element 3
Of the first-order diffracted light, it corresponds to the + 1st-order diffracted light from the region 18 of the hologram optical element 8 and is converged on a single light receiving section 34.

Assuming that the outputs from the light receiving units 19 to 34 shown in FIG.
6) It is obtained from the calculation of-(V20 + V22 + V23 + V25). The track error signal is calculated by the push-pull method.
(V19 + V20 + V23 + V24)-(V21 + V2
2 + V25 + V26). Disk 7
The substrate thickness deviation detection signal for detecting the substrate thickness deviation of (V27 + V29 + V31 + V33)-(V28 + V3
0 + V32 + V34). Further, the RF signal from the condensed spot 12 as the main beam is V1
9 + V20 + V21 + V22 + V23 + V24 + V25
+ V26.

The reason why the substrate thickness deviation of the disk 7 can be detected by the above calculation will be described with reference to FIGS. 6 and 7 show examples of calculating the cross-sectional shape of the converging spot in the radial direction of the disk 7, and FIGS. 8 to 11 show the calculation of the push-pull signal when the converging spot crosses the track of the disk 7 in the radial direction. An example is shown, and FIG. 12 is a view showing a substrate thickness deviation detection characteristic. 6 and 7, the calculations are performed at a wavelength of 660 nm of the semiconductor laser 1, a numerical aperture of the objective lens 6 of 0.65, a thickness of the substrate of the disk 7 of 0.6 mm, a refractive index of the substrate of the disk 7 of 1.58, and a data of the sub-beam. The focusing was performed under the condition of ± 0.5 μm. (A) of FIGS.
6A and 6B are cross-sectional shapes of the converging spot 13 which is the sub-beam 1 corresponding to the + 1st-order diffracted light from the diffractive optical element 3, and FIGS. (C) is a cross-sectional shape of the converging spot 14 which is the sub-beam 2 corresponding to the -1st-order diffracted light from the diffractive optical element 3.

The solid line in FIGS. 6A to 6C
And the dotted line indicates the case where the substrate thickness deviation of the disk 7 is +50 μm. When the substrate thickness deviation of the disk 7 is 0 μm, the cross-sectional shape of the converging spot of the sub-beam 1 and the cross-sectional shape of the converging spot of the sub-beam 2 are the same. The cross-sectional shape of the converging spot of the sub-beams 1 and 2 is slightly larger than the cross-sectional shape of the converging spot of the main beam because the cross-sectional shape is slightly defocused on the disk 7. On the other hand, when the substrate thickness deviation of the disk 7 is +50 μm, the sectional shape of the focused spot of the sub-beam 1 and the sectional shape of the focused spot of the sub-beam 2 are different. That is, as shown in FIG. 6B, the cross-sectional shape of the focused spot of the sub-beam 1 is slightly smaller in diameter than the case where the substrate thickness deviation of the disk 7 is 0 μm, and the height of the side lobe is slightly higher. As shown in FIG. 6C, the cross-sectional shape of the condensed spot has a slightly larger diameter and a slightly lower side lobe than when the substrate thickness deviation of the disk 7 is 0 μm.

The solid line in FIGS.
And the dotted line shows the case where the substrate thickness deviation of the disk 7 is -50 μm. When the substrate thickness deviation of the disk 7 is 0 μm, the cross-sectional shape of the converging spot of the sub-beam 1 and the cross-sectional shape of the converging spot of the sub-beam 2 are the same. The cross-sectional shape of the converging spot of the sub-beams 1 and 2 is slightly larger than the cross-sectional shape of the converging spot of the main beam because the cross-sectional shape is slightly defocused on the disk 7. On the other hand, when the substrate thickness deviation of the disk 7 is −50 μm, the sectional shape of the focused spot of the sub-beam 1 and the sectional shape of the focused spot of the sub-beam 2 are different. That is, as shown in FIG. 7B, the cross-sectional shape of the converging spot of the sub-beam 1 is slightly larger in diameter than the case where the substrate thickness deviation of the disk 7 is 0 μm, and the height of the side lobe is slightly lower. As shown in FIG. 7C, the cross-sectional shape of the condensed spot has a slightly smaller diameter and a slightly higher side lobe height than the case where the substrate thickness deviation of the disk 7 is 0 μm.

8 to 11 show examples of calculation of the push-pull signal when the focused spot crosses the track of the disk 7 in the radial direction. The calculation was performed under the conditions of the calculation example shown in FIGS. 6 and 7, the track pitch of the disk 7 being 0.5 μm, and the groove depth of the disk 7 being 80 nm. 8 and 10
(A) is a push-pull signal by the converging spot 12 as a main beam, and (b) of FIGS. 8 and 10 are push-pull by a converging spot 13 which is a sub-beam 1 corresponding to + 1st-order diffracted light from the diffractive optical element 3. FIGS. 8 and 10 (c) are push-pull signals by the converging spot 14 which is a sub-beam 2 corresponding to the -1st-order diffracted light from the diffractive optical element 3, and FIGS. The sum of the push-pull signals by the condensing spots 13 and 14,
FIGS. 9 and 11 (b) show the difference between the push-pull signals due to the converging spots 13 and 14, which are the sub-beams 1 and 2. FIG. The horizontal axis in FIGS. 8 to 11 shows the positional deviation (for one period of the groove) between the focused spot and the track when the focused spot crosses the track of the disk 7 from the left to the right in the radial direction. Corresponds to a state where the converging spot 12 as the main beam is located on the groove, and a position L in the figure corresponds to a state where the converging spot 12 as the main beam is located on the land. I have. The push-pull signal in FIGS. 8 to 11 is standardized by the sum signal of the light incident on the disk 7 for both the main beam and the sub beam.

The solid lines in FIGS.
And the dotted line indicates the case where the substrate thickness deviation of the disk 7 is +50 μm. (V19 + V20 + V23 + V24)-(V2)
The waveform of (1 + V22 + V25 + V26) is as shown in FIG. The condensed spot 13 which is the sub-beam 1 is shifted from the condensed spot 12 in the radial direction of the disk 7 to the left side of FIG. (V27 + V29)-(V28 + V
The waveform of FIG. 30) is different from the waveform of FIG.
The waveform shown in FIG. 8B is delayed by two. The condensed spot 14 which is the sub-beam 2 is shifted from the condensed spot 12 to the right in FIG. (V3)
The waveform of (1 + V33)-(V32 + V34) is shown in FIG.
The phase advances by π / 2 with respect to the waveform of FIG.
The waveform is as shown in FIG.

In FIGS. 8B and 8C, the disk 7
When the substrate thickness deviation is 0 μm, the cross-sectional shape of the focused spot of the sub-beam 1 and the cross-sectional shape of the focused spot of the sub-beam 2 are the same. The push-pull signals due to spots have the same amplitude. Since the cross-sectional shape of the converging spot of the sub-beams 1 and 2 is slightly larger than the cross-sectional shape of the converging spot of the main beam,
The push-pull signal generated by the converging spots of the sub beams 1 and 2 has a slightly smaller amplitude than the push-pull signal generated by the condensing spot of the main beam. On the other hand, disk 7
When the substrate thickness deviation is +50 μm, the cross-sectional shape of the converging spot of the sub-beam 1 and the cross-sectional shape of the converging spot of the sub-beam 2 are different. Push-pull signals have different amplitudes. That is, the amplitude of the push-pull signal due to the converging spot of the sub-beam 1 is smaller than that of the push-pull signal due to the converging spot of the sub-beam 2.

Since the waveforms of FIG. 8B and FIG. 8C are opposite in phase to each other, the push-pull signal by the condensing spot 13 as the sub-beam 1 and the push-pull signal by the condensing spot 14 as the sub-beam 2 Sum, that is, a substrate thickness deviation detection signal (V27 + V29 + V31 + V33)
The waveform of-(V28 + V30 + V32 + V34) is shown in FIG.
The waveform is as shown in FIG. The difference between the push-pull signal generated by the focused spot 13 as the sub-beam 1 and the push-pull signal generated by the focused spot 14 as the sub-beam 2 is (V27 + V29 + V32 + V34)-(V
The waveform of (28 + V30 + V31 + V33) is as shown in FIG. 9B.

10 (a) to 10 (c), the solid line indicates the case where the substrate thickness deviation of the disk 7 is 0 μm, and the dotted line indicates the case where the substrate thickness deviation of the disk 7 is −50 μm. (V19 + V20 + V23 + V24)-(V
21 + V22 + V25 + V26) is shown in FIG.
The waveform is as shown in FIG. The condensed spot 13 which is the sub-beam 1 is shifted from the condensed spot 12 in the radial direction of the disk 7 to the left side of FIG. (V27 + V29)-(V28)
The waveform of (+ V30) becomes a waveform shown in FIG. 10B with a phase delayed by π / 2 with respect to the waveform of FIG. The condensed spot 14 which is the sub-beam 2 is shifted from the condensed spot 12 to the right in FIG. The waveform of (V31 + V33)-(V32 + V34) which is the push-pull signal by
The phase shown in FIG. 10A is advanced by π / 2 with respect to the waveform shown in FIG.

In FIGS. 10B and 10C, when the substrate thickness deviation of the disk 7 is 0 μm, the sectional shape of the focused spot of the sub-beam 1 and the sectional shape of the focused spot of the sub-beam 2 are the same. The push-pull signal generated by the focused spot of the sub-beam 1 and the push-pull signal generated by the focused spot of the sub-beam 2 have the same amplitude. Since the cross-sectional shape of the converging spots of the sub-beams 1 and 2 is slightly larger than the cross-sectional shape of the converging spot of the main beam, the push-pull signal by the converging spots of the sub-beams 1 and 2 is not focused on the main beam. The amplitude is slightly smaller than the push-pull signal due to the spot. On the other hand, when the substrate thickness deviation of the disk 7 is −50 μm, the cross-sectional shape of the converging spot of the sub-beam 1 is different from the cross-sectional shape of the converging spot of the sub-beam 2. The push-pull signal due to the converging spot of the sub-beam 2 has a different amplitude. That is, the push-pull signal generated by the converging spot of the sub-beam 1 has a larger amplitude than the push-pull signal generated by the condensing spot of the sub-beam 2.

Since the waveforms in FIGS. 10B and 10C have opposite phases to each other, the converging spot 1 which is the sub-beam 1
3 is the sum of the push-pull signal due to the sub-beam 2 and the push-pull signal due to the condensed spot 14, that is, the substrate thickness deviation detection signal (V27 + V29 + V31 + V3).
3) The waveform of-(V28 + V30 + V32 + V34) is as shown in FIG. Also, it is the difference between the push-pull signal due to the focused spot 13 as the sub-beam 1 and the push-pull signal due to the focused spot 14 as the sub-beam 2 (V27 + V29 + V32 + V34) −
The waveform of (V28 + V30 + V31 + V33) is shown in FIG.
The waveform is as shown in FIG.

The following can be said from FIGS. 9A and 11A. First, consider the case where track servo is performed on a groove. Substrate thickness deviation of disk 7 is 0μ
In the case of m, +50 μm, and −50 μm, FIG.
The values of the substrate thickness deviation detection signals shown in FIG.
Negative and positive. Therefore, the substrate thickness deviation of the disk 7 can be detected using the substrate thickness deviation detection signal. Next, a case where track servo is performed on a land will be considered. Substrate thickness deviation of disk 7 is 0 μm, +50 μm
In the case of m and −50 μm, the values of the substrate thickness deviation detection signals shown in FIGS. 9A and 11A are 0, positive, and negative, respectively. Therefore, the substrate thickness deviation of the disk 7 can be detected using the substrate thickness deviation detection signal.

FIG. 12 shows a calculation example of the substrate thickness deviation detection characteristic. The horizontal axis in FIG. 12 is the substrate thickness deviation, and the vertical axis is the substrate thickness deviation detection signal. The calculations were performed under the same conditions as the calculation examples shown in FIGS. The solid line in the figure indicates the case where track servo is performed on the groove, and the dotted line indicates the case where track servo is performed on the land. When track servo is performed on the groove, when the substrate thickness deviation of the disk 7 is 0, positive, and negative, the values of the substrate thickness deviation detection signals are 0, negative, and positive, respectively, and the track servo is performed on the land. In this case, when the substrate thickness deviation of the disk 7 is 0, positive, and negative, the values of the substrate thickness deviation detection signal are 0, positive, and negative, respectively. Also, when track servo is applied to either the groove or the land, it can be seen that the greater the absolute value of the substrate thickness deviation, the greater the absolute value of the substrate thickness deviation detection signal.

On the other hand, the focused spot 1 which is the sub beam 1
The difference between the push-pull signal by No. 3 and the push-pull signal by the condensed spot 14 as the sub-beam 2 is referred to as a land / groove position detection signal. At this time, FIG.
11B, the value of the land / groove position detection signal shown in FIG. 11B is positive when the condensed spot 12, which is the main beam, is located on the groove of the disk 7, and negative when it is located on the land. Becomes Therefore, it is possible to detect whether the converging spot 12 is located on the groove or the land of the disk 7 based on the sign of the land / groove position detection signal.

FIG. 13 shows a first embodiment of the optical information recording / reproducing apparatus of the present invention. This embodiment has the same configuration as the first embodiment of the optical head device shown in FIG. 1 except that an arithmetic circuit 47 and a drive circuit 48 shown in FIG. 13 are added. In FIG. 13, the same components as those in FIG.
The same reference numerals are given and the description is omitted or briefly described. In the optical information recording / reproducing apparatus of this embodiment shown in FIG. 13, the arithmetic circuit 47 is connected to the photodetector 10, and the drive circuit 48 is connected to the arithmetic circuit 47 and the collimator lens 2. It has become. The arithmetic circuit 47 calculates a substrate thickness deviation detection signal based on an output from each light receiving section of the photodetector 10 and a driving circuit 48
Moves the collimator lens 2 surrounded by the dotted line in FIG. 13 in the optical axis direction by an actuator (not shown) so that the substrate thickness shift detection signal becomes 0. When the collimator lens 2 is moved in the optical axis direction, the magnification of the objective lens 6 changes, and the spherical aberration changes. Therefore, by adjusting the position of the collimator lens 2 in the optical axis direction, the objective lens 6 generates a spherical aberration that cancels out the spherical aberration caused by the substrate thickness deviation of the disk 7. As a result, the substrate thickness deviation of the disk 7 is corrected, and the adverse effect on the recording / reproducing characteristics is eliminated.
As shown in FIG. 12, the sign of the substrate thickness deviation detection signal is reversed between the case where track servo is performed on the groove and the case where track servo is performed on the land. The polarity of a circuit composed of an arithmetic circuit 47 and a drive circuit 48 for performing the above operation is switched.

FIG. 14 shows a second embodiment of the optical information recording / reproducing apparatus of the present invention. This embodiment is different from the first embodiment of the optical head device of the present invention shown in FIG.
The optical head device has the same configuration as that of the first embodiment except that relay lenses 49 and 50 and a drive circuit 51 are added. In FIG. 14, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted or briefly described.
In the optical information recording / reproducing apparatus of the present embodiment shown in FIG. 14, the arithmetic circuit 47 is connected to the photodetector 10, the drive circuit 51 is connected to the arithmetic circuit 47, and the relay lens 49 , 50 are arranged on the optical axis between the quarter-wave plate 5 and the objective lens 6 and connected to the drive circuit 51. The arithmetic circuit 47 calculates the substrate thickness deviation detection signal based on the output from each light receiving section of the photodetector 10, and the drive circuit 51 uses the dotted line in FIG. 14 so that the substrate thickness deviation detection signal becomes zero. One of the enclosed relay lenses 49 and 50 is moved in the optical axis direction by an actuator (not shown). Relay lens 49, 5
When any one of 0 is moved in the optical axis direction, the magnification in the objective lens 6 changes, and the spherical aberration changes. Thus, the position of one of the relay lenses 49 and 50 in the direction of the optical axis is adjusted, and the objective lens 6 generates a spherical aberration that cancels out the spherical aberration caused by the substrate thickness deviation of the disk 7. As a result, the substrate thickness deviation of the disk 7 is corrected, and the adverse effect on the recording / reproducing characteristics is eliminated. As shown in FIG. 12, when track servo is performed on the groove and when track servo is performed on the land, the sign of the substrate thickness deviation detection signal is reversed.
The polarity of a circuit composed of an arithmetic circuit 47 for correcting the substrate thickness deviation and a drive circuit 51 is switched.

FIG. 15 shows a third embodiment of the optical information recording / reproducing apparatus of the present invention. This embodiment is different from the first embodiment of the optical head device of the present invention shown in FIG.
The optical head device has the same configuration as the first embodiment of the optical head device except that a liquid crystal optical element 52 and a drive circuit 53 are added.
In FIG. 15, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description will be omitted or simply described. FIG.
5, the arithmetic circuit 47 is connected to the photodetector 10 and the drive circuit 53 is connected to the arithmetic circuit 47.
The liquid crystal optical element 52 is connected to the polarizing beam splitter 4 and 1 /
The driving circuit 53 is disposed on the optical axis between the four-wavelength plates 5.
It is a configuration connected to. The arithmetic circuit 47 includes the photodetector 1
The driving circuit 53 calculates the substrate thickness deviation detection signal on the basis of the output from each light-receiving unit of 0, and the driving circuit 53 sets the liquid crystal optical element 52 enclosed by the dotted line in FIG.
Voltage. The liquid crystal optical element 52 is divided into a plurality of concentric regions, and when the voltage applied to each region is changed, the spherical aberration with respect to the transmitted light changes. Therefore, by adjusting the voltage applied to the liquid crystal optical element 52, the liquid crystal optical element 52 generates a spherical aberration that cancels out the spherical aberration caused by the substrate thickness deviation of the disk 7. As a result, the substrate thickness deviation of the disk 7 is corrected, and the adverse effect on the recording / reproducing characteristics is eliminated. As shown in FIG. 12, the sign of the substrate thickness deviation detection signal is reversed between the case where track servo is performed on the groove and the case where track servo is performed on the land. The polarity of the circuit composed of the arithmetic circuit 47 and the drive circuit 53 for performing the above is switched.

In the second embodiment of the optical head device of the present invention, the diffractive optical element 3 in the first embodiment of the optical head device of the present invention shown in FIG. 1 is replaced with a diffractive optical element 54 shown in FIG. Otherwise, the configuration is the same as that of the first embodiment. In the following, the present embodiment will be described with reference to FIG. 1 for the above reasons. FIG. 16 is a plan view of the diffractive optical element 54. The upward arrow in FIG. 16 indicates the tangential direction of the disk 7 shown in FIG. The diffractive optical element 54 has a configuration in which a diffraction grating is formed in a region including the effective diameter of the objective lens 6 indicated by a dotted line in FIG. 16, and is a straight line passing through the optical axis of the incident light and parallel to the tangential direction of the disk 7. The area is divided into two areas 55 and 56. The direction of the grating in the diffraction grating is substantially parallel to the radial direction of the disk 7 in each of the regions 55 and 56, and the pattern of the grating is
6 is an off-axis concentric circle centered on the upper side of the disk 7 in the tangential direction.

In the diffractive optical element 54, a region 55
And the phase of the grating in the region 56 is shifted by π / 2. The phase difference between the line portion and the space portion of the grating is set to, for example, 0.
Assuming that the incident light is 232π, the incident light is about 87.3% as the zero-order light.
Are transmitted, and about 5.1% of each is diffracted as ± 1st-order diffracted light. Assuming that the light diffracted upward in FIG. 16 is the + 1st-order diffracted light and the light diffracted downward in FIG. 16 is the −1st-order diffracted light, the diffractive optical element 54 functions as a convex lens for the + 1st-order diffracted light. Acts as a concave lens with respect to the -1st-order diffracted light. Thereby, quadratic function-like phase distributions of opposite signs are given to the two sub-beams. In this case, a phase distribution is given to both the radial direction and the tangential direction of the disk 7. The + 1st-order diffracted light from the region 55 has a phase advance of π / 2 with respect to the + 1st-order diffracted light from the region 56, and the −1st-order diffracted light from the region 55 has a phase with respect to the −1st-order diffracted light from the region 56. Delay by π / 2.

FIG. 17 shows the arrangement of condensed spots on the disk 7 in the optical head device of this embodiment. The condensed spots 212, 213, and 214 correspond to the 0th order light, the + 1st order diffracted light, and the -1st order diffracted light from the diffractive optical element 54, respectively, and are arranged on the same track 211 (groove or land). Referring to FIG.
Has two peaks with high intensity on the left side in the radial direction of the disk 7 and low intensity on the right side.
The disk 7 has two peaks with weak intensity on the left side in the radial direction and strong intensity on the right side.

The diffraction optical element 54 passes through the optical axis of the incident light and passes through regions 55 and 56 as straight lines parallel to the tangential direction of the disk 7.
By shifting the phase of the grating in the region 55 and the region 56 by π / 2, the phase of the sub-beam incident on the objective lens 6 can be changed to a straight line parallel to the tangential direction of the disk 7 through the optical axis. Shifting by π / 2 between the left and right sides means that the converging spots of the two sub-beams on the disc 7 are shifted from the converging spot of the main beam in the radial direction of the disc 7 by 周期 period of the groove of the disc 7. Arranging them in opposite directions is equivalent to a push-pull signal. Regarding the reason, for example, Japanese Journal of Applied Physics
It is described in Vol. 8, Part 1 No. 3B, pp. 1761-1767. Therefore, various waveforms related to the push-pull signal in the second embodiment of the optical head device of the present invention are shown in FIG.
11 to 11 are the same as various waveforms related to the push-pull signal in the first embodiment of the optical head device of the present invention. That is, in the second embodiment of the optical head device according to the present invention, similarly to the first embodiment of the optical head device according to the present invention, it is possible to detect the substrate thickness deviation of the disk 7. Further, it is possible to detect whether the focused spot 212 as the main beam is located on the groove or the land of the disk 7.

In the third embodiment of the optical head device of the present invention, the diffractive optical element 3 in the first embodiment of the optical head device of the present invention shown in FIG. 1 is replaced with a diffractive optical element 59 shown in FIG. Otherwise, the configuration is the same as that of the first embodiment. In the following, the present embodiment will be described with reference to FIG. 1 for the above reasons. FIG. 18 is a plan view of the diffractive optical element 59. The upward arrow in FIG. 18 indicates the tangential direction of the disk 7, and the right arrow indicates the radial direction of the disk 7. The diffractive optical element 59 has a configuration in which a diffraction grating is formed in a region including the effective diameter of the objective lens 6 indicated by a dotted line in FIG. The region is divided into four regions 60 to 63 by a straight line parallel to the direction. The direction of the grating in the diffraction grating is substantially parallel to the radial direction of the disk 7 in any of the regions 60 to 63. And the regions 62 and 63 have an off-axis concentric shape centered below the tangential direction of the disk 7.

In the diffractive optical element 59, the area 6
The phase of the grating between 0 and 63 and the regions 61 and 62 is π / 2
It is only shifted. Assuming that the phase difference between the line portion and the space portion of the grating is, for example, 0.232π, about 87.3% of the incident light is transmitted as 0th-order light, and about 5.1% is diffracted as ± 1st-order diffracted light, respectively. The light diffracted upward in FIG. 18 is + 1st-order diffracted light, and the light diffracted downward in FIG.
Assuming that the diffracted light is the next-order diffracted light, the diffractive optical element 59 includes the regions 60 and 61.
Acts as a convex lens on the + 1st order diffracted light from
Acts as a concave lens with respect to the -1st-order diffracted light from the lens and the + 1st-order diffracted light from the regions 62 and 63. This allows
A quadratic function-like phase distribution of opposite signs is given to the two sub-beams. In this case, a phase distribution is given to both the radial direction and the tangential direction of the disk 7. The + 1st-order diffracted light from the regions 60 and 63 is
The phase advances by π / 2 with respect to the + 1st-order diffracted light from 2,
The phase of the -1st-order diffracted light from the regions 60 and 63 is delayed by π / 2 with respect to the phase of the -1st-order diffracted light from the regions 61 and 62.

FIG. 19 shows the arrangement of the focused spots on the disk 7. The converging spots 312, 313, and 314 respectively include the 0th-order light, the + 1st-order diffracted light from the diffractive optical element 59,
It corresponds to the -1st-order diffracted light and is arranged on the same track 311 (groove or land). Focusing spot 3
13 and 314 have four side lobes in a direction ± 45 ° with respect to the tangential direction and the radial direction of the disk 7.

The waveform of the push-pull signal by the converging spot 312 as the main beam is shown in FIGS.
The waveform is similar to that shown in FIG. Here, the + 1st-order diffracted light from the regions 60 and 61 of the diffractive optical element 59, the region 62,
The push-pull signals due to the + 1st-order diffracted light from 63 are referred to as the front push-pull signal and the rear push-pull signal by the condensed spot 313 which is the sub beam 1, and the -1st-order diffracted light from the regions 60 and 61 of the diffractive optical element 59 The push-pull signals based on the -1st-order diffracted light from the regions 62 and 63 are referred to as a front push-pull signal and a rear push-pull signal by the focused spot 314 that is the sub beam 2, respectively. At this time, the focused spot 313 which is the sub beam 1
The waveforms of V27-V28, which is the front push-pull signal, and V33-V34, which is the rear push-pull signal due to the condensing spot 314, which is the sub beam 2, are shown in FIG.
The waveform is the same as that shown in FIG. Further, V29-V30 which is a rear push-pull signal by the converging spot 313 which is the sub beam 1, and V31 which is a front push-pull signal by the condensing spot 314 which is the sub beam 2.
The waveform of -V32 is similar to the waveforms shown in FIGS. 8 (c) and 10 (c). Therefore, it is the substrate thickness deviation detection signal (V
27 + V29 + V31 + V33)-(V28 + V30 +
The waveform of (V32 + V34) is similar to the waveforms shown in FIGS. 9A and 11A. That is, in the third embodiment of the optical head device according to the present invention, similarly to the first embodiment of the optical head device according to the present invention, a deviation in the substrate thickness of the disk 7 can be detected.

On the other hand, the condensed spot 3 which is the sub beam 1
13, the sum of the front push-pull signal by the sub-beam 2 and the rear push-pull signal by the converging spot 314, and the sub-beam 1 by the converging spot 313 and the converging spot 3 by the sub-beam 2
14 is the difference between the sum of the front push-pull signals
This is called a groove position detection signal. At this time, a land / groove position detection signal (V27 + V30 + V32 + V
33)-(V28 + V29 + V31 + V34) are the same as the waveforms shown in FIGS. 9 (b) and 11 (b). That is, in the third embodiment of the optical head device of the present invention, similarly to the first embodiment of the optical head device of the present invention, the condensed spot 312 which is the main beam is formed on either the groove It is possible to detect whether or not it is located above.

In the fourth embodiment of the optical head device of the present invention, the diffractive optical element 3 in the first embodiment of the optical head device of the present invention shown in FIG. 1 is replaced with a diffractive optical element 66 shown in FIG. Other than the above, the configuration is the same as that of the first embodiment. FIG. 20 is a plan view of the diffractive optical element 66,
The upward arrow in FIG. 20 indicates the tangential direction of the disk 7, and the right arrow indicates the radial direction of the disk 7. The diffractive optical element 66 has a configuration in which a diffraction grating is formed in a region including the effective diameter of the objective lens 6 indicated by a dotted line in FIG. 20, and has a straight line and a radius that pass through the optical axis of the incident light and are parallel to the tangential direction of the disk 7. The region is divided into six regions 67 to 72 by two straight lines parallel to the direction. Inside the effective diameter of the objective lens 6, the area occupied by the regions 67 and 68 is
2 is larger than the area occupied. The direction of the grating in the diffraction grating is substantially parallel to the radial direction of the disk 7 in any of the regions 67 to 72, and the pattern of the grating is
Reference numeral 68 denotes an off-axis concentric circle having a center on the upper side of the disk 7 in the tangential direction, and regions 69 to 72 have an off-axis concentric circle having a center on the lower side of the disk 7 in the tangential direction.

In the diffractive optical element 66, the area 6
The phases of the gratings at 7, 70, 72 and the regions 68, 69, 71 are shifted by π / 2. Assuming that the phase difference between the line portion and the space portion of the grating is, for example, 0.232π, about 87.3% of the incident light is transmitted as 0th-order light, and about 5.1% is diffracted as ± 1st-order diffracted light, respectively. Assuming that the light diffracted upward in FIG. 20 is the + 1st-order diffracted light and the light diffracted downward in FIG. 20 is the −1st-order diffracted light, the diffractive optical element 66 includes the + 1st-order diffracted light from the regions 67 and 68 and the region 69. ~ 72
Acts as a convex lens with respect to the −1st order diffracted light from
Acts as a concave lens for the + 1st-order diffracted light from.
Thereby, quadratic function-like phase distributions of opposite signs are given to the two sub-beams. In this case, a phase distribution is given to both the radial direction and the tangential direction of the disk 7. Further, the + 1st-order diffracted light from the regions 67, 70, and 72 has a phase advance of π / 2 with respect to the + 1st-order diffracted light from the regions 68, 69, and 71, and − from the regions 67, 70, and 72.
The first-order diffracted light has a phase delayed by π / 2 with respect to the −1st-order diffracted light from the regions 68, 69, and 71.

FIG. 21 shows the arrangement of the converging spots on the disk 7. The condensed spots 412, 413, and 414 are respectively the 0th-order light, the + 1st-order diffracted light from the diffractive optical element 66,
It corresponds to the -1st-order diffracted light and is arranged on the same track 411 (groove or land). Focusing spot 4
13 has one peak with strong intensity at the center of the disk 7 in the tangential direction and on the left side in the radial direction, and two peaks with low intensity on the front and rear sides in the tangential direction of the disk 7 and on the right side in the radial direction. The spot 414 has one strong peak at the center in the tangential direction of the disk 7 and on the right side in the radial direction, and two peaks with weak intensity on the front and rear sides of the disk 7 in the tangential direction and on the left side in the radial direction.

The waveform of the push-pull signal due to the converging spot 412 as the main beam is shown in FIGS.
The waveform is similar to that shown in FIG. Here, the + 1st-order diffracted light from the regions 67 and 68 of the diffractive optical element 66, the region 69,
The push-pull signal by the + 1st-order diffracted light from 70 and the + 1st-order diffracted light from the regions 71 and 72 is
Are referred to as a central push-pull signal, a front push-pull signal, and a rear push-pull signal due to the converging spot 413. Folding light, area 71,
The push-pull signals based on the -1st-order diffracted light from 72 are referred to as a central push-pull signal, a front push-pull signal, and a rear push-pull signal by the condensed spot 414 which is the sub beam 2, respectively. At this time, the waveforms of the center push-pull signal by the condensed spot 413 as the sub-beam 1 and the front push-pull signal and the rear push-pull signal by the condensed spot 414 as the sub-beam 2 are shown in FIGS.
The waveform is similar to the waveform shown in FIG. In addition, sub beam 1
The waveforms of the front push-pull signal and the rear push-pull signal by the converging spot 413, and the center push-pull signal by the condensing spot 414, which is the sub beam 2, are shown in FIG.
(C) and the waveforms shown in FIG. Accordingly, the waveform of the substrate thickness deviation detection signal is shown in FIGS.
The waveform is similar to that shown in FIG. That is, in the fourth embodiment of the optical head device according to the present invention, similarly to the first embodiment of the optical head device according to the present invention, it is possible to detect the substrate thickness deviation of the disk 7. Further, it is possible to detect whether the focused spot 412 as the main beam is located on the groove or the land of the disk 7.

FIG. 22 shows a fifth embodiment of the optical head device according to the present invention. The optical head device of the present embodiment shown in FIG. 22 uses the hologram optical element 8 and the photodetector 10 of the optical head device of the first embodiment shown in FIG.
The configuration is the same as that of the first embodiment except that the fifth embodiment is replaced with a photodetector 76. In FIG. 22, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description is omitted or briefly described. The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and is divided by the diffractive optical element 3 into three lights of a 0th order light as a main beam and ± 1st order diffracted lights as sub beams. These lights enter the polarization beam splitter 4 as P-polarized light, pass through almost 100%, pass through the quarter-wave plate 5, are converted from linearly polarized light to circularly polarized light, and are collected on the disk 7 by the objective lens 6. Be lighted. The three reflected lights from the disk 7 pass through the objective lens 6 in the opposite direction, pass through the quarter-wave plate 5, and are converted from circularly polarized light into linearly polarized light whose polarization direction is orthogonal to the outward path. Almost 100% of the incident light is reflected as S-polarized light, transmitted through the cylindrical lens 75 and the lens 9, and received by the photodetector 76. The light detector 76 is a cylindrical lens 75,
The lens 9 is provided between the two focal lines.

The plan view of the diffractive optical element 3 in the fifth embodiment of the optical head device according to the present invention is shown in FIG. 2, which is a plan view of the diffractive optical element 3 in the first embodiment of the optical head device according to the present invention. Is the same as The arrangement of the converging spots on the disk 7 in the fifth embodiment of the optical head device of the present invention is the same as that of the converging spot on the disk 7 in the first embodiment of the optical head device of the present invention shown in FIG. Is the same as the arrangement.

FIG. 23 shows the pattern of the light receiving portion of the photodetector 76 and the arrangement of the light spots on the photodetector 76. The light spot 85 corresponds to the zero-order light from the diffractive optical element 3, and is divided into four light receiving portions 77 to 77 by a dividing line parallel to the tangential direction of the disk 7 passing through the optical axis and a dividing line parallel to the radial direction. Light is received at 80. The light spot 86 is formed by the +
The light corresponds to the first-order diffracted light, and is received by the light receiving units 81 and 82 divided into two by a dividing line parallel to the tangential direction of the disk 7. The light spot 87 corresponds to the -1st-order diffracted light from the diffractive optical element 3 and is divided by a dividing line parallel to the tangential direction of the disk 7 into two.
The light is received by the light receiving units 83 and 84 divided into two. The row of the condensed spots 12 to 14 on the disk 7 is tangential, but the row of the light spots 85 to 87 on the photodetector 76 is radial due to the action of the cylindrical lens 75 and the lens 9.

The outputs from the light receiving sections 77 to 84 are
Assuming that 77 to V84, the focus error signal is obtained from the calculation of (V77 + V80)-(V78 + V79) by the astigmatism method. The track error signal is obtained from the calculation of (V77 + V79)-(V78 + V80) by the push-pull method. The substrate thickness deviation detection signal for detecting the substrate thickness deviation of the disk 7 is (V81 + V83)-(V8
2 + V84). The RF signal from the condensed spot 12, which is the main beam, is V77 + V7
8 + V79 + V80. On the other hand, the land / groove position detection signal is (V81 + V84)-(V8
2 + V83). In the fifth embodiment of the optical head device of the present invention, the substrate thickness shift of the disk 7 is performed by the same method as described in the first embodiment of the optical head device of the present invention with reference to FIGS. Can be detected. Further, it is possible to detect whether the condensed spot 12, which is the main beam, is located on the groove or the land of the disk 7.

FIG. 24 shows a sixth embodiment of the optical head device according to the present invention. The sixth embodiment of the optical head device shown in FIG.
9, a photodetector 90, a collimator lens 202, a polarizing diffractive optical element 91, a polarizing hologram optical element 92, a quarter-wave plate 205, and an objective lens 206 arranged on the optical axis of the semiconductor laser 89. Is done. Note that reference numeral 2
07 indicates a disk. The emitted light from the semiconductor laser 89 is collimated by the collimator lens 202 and is incident on the polarizing diffractive optical element 91 as extraordinary light to be converted into three lights of a 0th-order light as a main beam and ± 1st-order diffracted lights as sub-beams. Divided. These lights are polarized by the hologram optical element 9.
2 as ordinary light, almost 100% is transmitted, and 1/4
The light passes through the wave plate 205 and is converted from linearly polarized light to circularly polarized light, and is condensed on the disk 207 by the objective lens 206. The three reflected lights from the disk 207 are
06 is transmitted in the opposite direction, passes through the quarter-wave plate 205, and is converted from circularly polarized light into linearly polarized light having a polarization direction orthogonal to the outward path. And almost 100% is diffracted, and enters the polarizing diffractive optical element 91 as ordinary light and almost 100%
Is transmitted, passes through the collimator lens 202, and is received by the photodetector 90.

A plan view of the polarizing diffractive optical element 91 in the sixth embodiment of the optical head device of the present invention is shown in FIG. 2 as a plane view of the diffractive optical element 3 in the first embodiment of the optical head device of the present invention. Since it is the same as the figure, it will be described below with reference to FIG. The polarizing diffractive optical element 91 has a two-layer diffraction structure including a proton exchange region and a dielectric film on a birefringent lithium niobate substrate in a region including the effective diameter of the objective lens 206 indicated by a dotted line in the drawing. This is a configuration in which a lattice is formed. By appropriately designing the depth of the proton exchange region and the thickness of the dielectric film, the phase difference between the line portion and the space portion of the lattice can be independently defined for ordinary light and extraordinary light. For the extraordinary light on the outward path, the phase difference between the line portion and the space portion of the grating is set to, for example, 0.232π.
Then, about 87.3% of the incident light is transmitted as the 0th-order light, and about 5.1% is diffracted as ± 1st-order diffracted light, respectively. On the other hand, for the ordinary light on the return path, assuming that the phase difference between the line portion and the space portion of the grating is 0, almost 100% of the incident light is transmitted as the zero-order light.

The arrangement of the condensed spots on the disk 207 in the sixth embodiment of the optical head device of the present invention is shown in FIG.
Since the arrangement of the condensed spots on the disk 207 in the first embodiment of the optical head device of the present invention shown in FIG. 1 is the same as that of FIG.

A plan view of the polarizing hologram optical element 92 in the sixth embodiment of the optical head device of the present invention is shown in FIG.
Since it is the same as the plan view of the hologram optical element 8 in the first embodiment of the optical head device of the present invention shown in FIG. The polarizing hologram optical element 92 is connected to the objective lens 20 shown by a dotted line in FIG.
In a region including the effective diameter of 6, a two-layer diffraction grating composed of a proton exchange region and a dielectric film is formed on, for example, a lithium niobate substrate having birefringence. The cross-sectional shape of the lattice is a two-layer saw-tooth shape in any of the regions 15 to 18. By appropriately designing the depth of the proton exchange region and the thickness of the dielectric film, the phase difference between the upper and lower portions of the saw-tooth is reduced. It can be defined independently for ordinary light and extraordinary light.
For ordinary light on the outward path, the phase difference between the upper and lower parts of the sawtooth is set to 0.
Then, almost 100% of the incident light to each region is transmitted as the zero-order light. On the other hand, for the extraordinary light on the return path, if the phase difference between the upper part and the lower part of the sawtooth is 2π, the incident light to each area is almost 100% as + 1st order diffracted light.
Is diffracted.

FIG. 25 shows the pattern of the light receiving portion of the photodetector 90 and the arrangement of the light spots on the photodetector 90. Photodetector 9
A semiconductor laser 89 and a mirror 93 are provided on 0, and light emitted from the semiconductor laser 89 is reflected by the mirror 93 and travels toward the disk 207. In FIG. 25, the upward arrow indicates the tangential direction of the disk 207,
The right-pointing arrow indicates the radial direction of the disk 207. The light spot 110 is composed of the + th order light from the region 15 of the polarizing hologram optical element 92 out of the zero-order light from the polarizing diffraction optical element 91.
It corresponds to the first-order diffracted light, and is condensed on the boundary between the light receiving portions 94 and 95 divided into two by a dividing line parallel to the radial direction of the disk 207. The light spot 111 is the polarization hologram optical element 9 of the zero-order light from the polarization diffraction optical element 91.
2 corresponds to the + 1st order diffracted light from the region 16 of the disk 2
Light is condensed on the boundary between the light receiving units 96 and 97 divided into two parts by a dividing line parallel to the radial direction 07. Light spot 11
Numeral 2 corresponds to the + 1st-order diffracted light from the region 17 of the polarizing hologram optical element 92 among the 0th-order light from the polarizing diffractive optical element 91, and was divided into two by a dividing line parallel to the radial direction of the disk 207. The light is focused on the boundary between the light receiving sections 98 and 99. The light spot 113 is a region 1 of the polarizing hologram optical element 92 in the zero-order light from the polarizing diffractive optical element 91.
8, the light receiving unit 100 divided into two by a dividing line parallel to the radial direction of the disk 207,
The light is condensed on the boundary line 101. The light spot 114 corresponds to the + 1st-order diffracted light from the region 15 of the polarizing hologram optical element 92 among the + 1st-order diffracted light from the polarizing diffractive optical element 91, and is converged on a single light receiving unit 102. The light spot 115 corresponds to the + 1st-order diffracted light from the region 16 of the polarizing hologram optical element 92 among the + 1st-order diffracted light from the polarizing diffractive optical element 91, and is converged on a single light receiving unit 103. The light spot 116 is the polarization hologram optical element 92 of the + 1st-order diffracted light from the polarization diffraction optical element 91.
Corresponding to the + 1st-order diffracted light from the region 17 of FIG. The light spot 117 corresponds to the + 1st-order diffracted light from the region 18 of the polarizing hologram optical element 92 among the + 1st-order diffracted light from the polarizing diffractive optical element 91, and is converged on a single light receiving unit 105. Light spot 1
Reference numeral 18 denotes +1 from the region 15 of the polarizing hologram optical element 92 in the -1st-order diffracted light from the polarizing diffractive optical element 91.
The light corresponds to the next-order diffracted light, and is collected on a single light receiving unit 106. The light spot 119 corresponds to the + 1st-order diffracted light from the region 16 of the polarizing hologram optical element 92 out of the -1st-order diffracted light from the polarizing diffractive optical element 91, and
7 are collected. The light spot 120 corresponds to the + 1st-order diffracted light from the region 17 of the polarizing hologram optical element 92 among the −1st-order diffracted light from the polarizing diffractive optical element 91, and is converged on a single light receiving unit 108. The light spot 121 corresponds to the + 1st-order diffracted light from the region 18 of the polarizing hologram optical element 92 among the -1st-order diffracted light from the polarizing diffractive optical element 91, and is converged on a single light receiving unit 109.

Assuming that the outputs from the light receiving units 94 to 109 are V94 to V109, the focus error signal is (V94 + V96 + V99 + V101) by the Foucault method.
−V95 + V97 + V98 + V100. The track error signal is calculated by the push-pull method.
(V94 + V95 + V98 + V99)-(V96 + V9
7 + V100 + V101). The substrate thickness deviation detection signal for detecting the substrate thickness deviation of the disk 7 is (V102 + V104 + V106 + V108)-(V
103 + V105 + V107 + V109). The RF signal from the condensed spot 12 as the main beam is V94 + V95 + V96 + V97 + V9
8 + V99 + V100 + V101.
On the other hand, the land / groove position detection signal is (V102 + V
104 + V107 + V109)-(V103 + V105
+ V106 + V108).

In the sixth embodiment of the optical head device of the present invention, the disk 207 is formed by the same method as that described in the first embodiment of the optical head device of the present invention with reference to FIGS. Substrate thickness deviation can be detected. Further, it is possible to detect whether the converging spot 12, which is the main beam, is located on the groove or the land of the disk 207.

FIG. 26 shows a seventh embodiment of the optical head device according to the present invention. A seventh embodiment of the optical head device shown in FIG. 26 includes a semiconductor laser 389 and a photodetector 123 installed in a module 122, a collimator lens 302 arranged on the optical axis of the semiconductor laser 389, and a polarizer. Diffractive optical element 391, polarizing hologram optical element 124,
It comprises a quarter-wave plate 305 and an objective lens 306. Reference numeral 307 indicates a disk. Semiconductor laser 3
The outgoing light from 89 is collimated by the collimator lens 302, enters the polarizing diffractive optical element 391 as extraordinary light, and is divided into three lights of a 0th-order light as a main beam and ± 1st-order diffracted lights as sub-beams. You. These lights enter the polarizing hologram optical element 124 as ordinary light, and
0% is transmitted, transmitted through the １ ／ wavelength plate 305 and converted from linearly polarized light into circularly polarized light.
07. The three reflected lights from the disc 307 pass through the objective lens 306 in the opposite direction, pass through the quarter-wave plate 305, and are converted from circularly polarized light into linearly polarized light whose polarization direction is orthogonal to the outward path. 124
Is incident as extraordinary light, most of it is diffracted as ± 1st-order diffracted light, is incident on the polarizing diffractive optical element 391 as ordinary light, transmits almost 100%, passes through the collimator lens 302, and is received by the photodetector 123. Is done. The photodetector 123 includes a polarizing hologram optical element 124 and a collimator lens 3.
02 is located between the two focal lines.

The plan view of the polarizing diffractive optical element 391 in the seventh embodiment of the optical head device of the present invention is shown in FIG. 2 for the diffractive optical element 3 in the first embodiment of the optical head device of the present invention. Since this is the same as the plan view, FIG. 2 will be referred to in the following description. Polarizing diffractive optical element 391
Is a structure in which a two-layer diffraction grating composed of a proton exchange region and a dielectric film is formed on, for example, a lithium niobate substrate having birefringence in a region including the effective diameter of the objective lens 306 shown by a dotted line in FIG. It is. By appropriately designing the depth of the proton exchange region and the thickness of the dielectric film, the phase difference between the line portion and the space portion of the lattice can be independently defined for ordinary light and extraordinary light. For extraordinary light on the outbound path,
The phase difference between the line portion and the space portion of the grating is, for example, 0.23.
Assuming 2π, about 87.3% of the incident light is transmitted as the 0th-order light, and about 5.1% is diffracted as ± 1st-order diffracted light, respectively. On the other hand, for the ordinary light on the return path, assuming that the phase difference between the line portion and the space portion of the grating is 0, almost 100% of the incident light is transmitted as the zero-order light.

The arrangement of the converging spots on the disk 307 in the seventh embodiment of the optical head device of the present invention is shown in FIG.
Since the arrangement of the converging spot on the disk 307 in the first embodiment of the optical head device of the present invention shown in FIG. FIG.
Is a plan view of the polarizing hologram optical element 124. FIG. The polarizing hologram optical element 124 has a two-layer structure including a proton exchange region and a dielectric film on a birefringent lithium niobate substrate in a region including the effective diameter of the objective lens 306 shown by a dotted line in FIG. This is a configuration in which a diffraction grating is formed. The direction of the grating in the diffraction grating is disk 3
07 is substantially parallel to the tangential direction, and the pattern of the lattice is hyperbolic with the tangential and radial directions of the disk 307 asymptote. By appropriately designing the depth of the proton exchange region and the thickness of the dielectric film, the phase difference between the line portion and the space portion of the lattice can be independently defined for ordinary light and extraordinary light. As for the ordinary light on the outward path, assuming that the phase difference between the line portion and the space portion of the grating is 0, almost 100% of the incident light is transmitted as the 0th-order light. On the other hand, with respect to the extraordinary light on the return path, if the phase difference between the line part and the space part of the grating is π, the incident light will be approximately 40.5 order diffracted light, respectively.
% Are diffracted. The polarization hologram optical element 124 is ±
The first-order diffracted light functions as a cylindrical lens, and the generatrix of the + 1st-order diffracted light and the generatrix of the -1st-order diffracted light form angles of + 45 ° and −45 ° with respect to the radial direction of the disk 307, respectively.

FIG. 28 shows the pattern of the light receiving portion of the photodetector 123 and the arrangement of the light spots on the photodetector 123. A semiconductor laser 389 and a mirror 393 are provided on the photodetector 123.
Is installed. Note that the upward arrow in FIG. 28 indicates the tangential direction of the disk 307, and the right arrow indicates the radial direction of the disk 307. Light emitted from the semiconductor laser 389 is reflected by the mirror 393 and travels to the disk 307. The light spot 141 corresponds to the + 1st-order diffracted light from the polarizing hologram optical element 124 out of the 0th-order light from the polarizing diffractive optical element 391, and is divided into the dividing line parallel to the tangential direction of the disk 307 passing through the optical axis and the radial direction. Light is received by the light receiving units 125 to 128 divided into four by parallel dividing lines.
The light spot 142 is the light spot from the polarizing diffractive optical element 391.
Of the next light, -1 from the polarizing hologram optical element 124
It corresponds to the next-order diffracted light, and is received by the light receiving units 129 to 132 divided into four by a dividing line parallel to the tangential direction and a dividing line parallel to the radial direction of the disk 307 passing through the optical axis. The light spot 143 is a part of the + 1st-order diffracted light from the polarizing diffractive optical element 391,
The light corresponds to the first-order diffracted light, and is received by the light receiving units 133 and 134 divided into two by a dividing line parallel to the tangential direction of the disk 307. The light spot 144 is the polarizing diffractive optical element 39.
Among the + 1st-order diffracted light from 1, it corresponds to the -1st-order diffracted light from the polarizing hologram optical element 124, and is divided into two by the light-receiving unit 13 divided by a dividing line parallel to the tangential direction of the disk 307.
5, and 136 are received. The light spot 145 corresponds to the + 1st-order diffracted light from the polarizing hologram optical element 124 among the -1st-order diffracted light from the polarizing diffractive optical element 391, and is divided into two by a dividing line parallel to the tangential direction of the disk 307. The light is received by the light receiving units 137 and 138. Light spot 1
Numeral 46 denotes the -1st-order diffracted light from the polarizing hologram optical element 124 out of the -1st-order diffracted light from the polarizing diffractive optical element 391, and the light-receiving light divided into two by a dividing line parallel to the tangential direction of the disk 307. The light is received by the units 139 and 140.

Referring to FIG. 3, the row of the condensed spots 12 to 14 on the disk 307 is tangential, but the polarization hologram optical element 124 and the collimator lens 30
2, the light spot 14 on the photodetector 123
1, 143, 145 and light spots 142, 144,
Rows 146 are radial. Further, since the two generatrix of the ± 1st-order diffracted light of the polarizing hologram optical element 124 are orthogonal to each other, the light spots 141, 143, and 1
45 and the light spots 142, 144, and 146 have vertical and horizontal intensity distributions that are opposite to each other.

Assuming that the outputs from the light receiving sections 125 to 140 are V125 to V140, the focus error signal is (V125 + V128 + V130 +
V131)-(V126 + V127 + V129 + V13
It is obtained from the operation of 2). The track error signal is obtained by the push-pull method (V125 + V127 + V130 + V1
32)-(V126 + V128 + V129 + V131)
From the calculation of The board thickness shift detection signal for detecting the board thickness shift of the disk 307 is (V133 + V13
6 + V137 + V140)-(V134 + V135 + V
138 + V139). The RF signal from the condensed spot 12, which is the main beam, is V12
5 + V126 + V127 + V128 + V129 + V13
It is obtained from the calculation of 0 + V131 + V132. On the other hand, the land / groove position detection signal is (V133 + V136 +
V138 + V139)-(V134 + V135 + V13
7 + V140).

In the seventh embodiment of the optical head device of the present invention, the disk 307 is formed by the same method as that described with reference to FIGS. 6 to 12 in the first embodiment of the optical head device of the present invention. Substrate thickness deviation can be detected. Further, it is possible to detect whether the condensed spot 12, which is the main beam, is located on the groove or the land of the disk 307.

As an embodiment of the optical head device of the present invention, the diffractive optical element 3 in the fifth embodiment shown in FIG. 22, the polarizing diffractive optical element 91 in the sixth embodiment shown in FIG. The embodiment in which the polarizing diffractive optical element 391 in the seventh embodiment shown in (1) is replaced by another diffractive optical element or a polarizing diffractive optical element is also conceivable. A plan view of another diffractive optical element or polarizing diffractive optical element is shown in FIG.
The plan view of the diffractive optical element 54 shown in FIG. 6, the plan view of the diffractive optical element 59 shown in FIG. 18, or the plan view of the diffractive optical element 66 shown in FIG.

In the first to seventh embodiments of the optical head device according to the present invention, the + 1st-order diffracted light acts as a convex lens or a concave lens, and the -1st-order diffracted light acts as a concave lens or a convex lens. By using the diffractive optical element or the polarizing diffractive optical element, the two sub-beams are given quadratic function-like phase distributions with opposite signs. In this case, a phase distribution is provided both in the radial direction and the tangential direction of the disk.

On the other hand, for the + 1st-order diffracted light, the generatrix acts as a cylindrical convex lens or a cylindrical concave lens in which the generatrix is parallel to the tangential direction of the disk, and for the −1st-order diffracted light, the generatrix is parallel to the tangential direction of the disc. A configuration is also conceivable in which a diffractive optical element or a polarizing diffractive optical element that functions as a cylindrical concave lens or a cylindrical convex lens gives a quadratic function-like phase distribution of opposite signs to two sub-beams. In this case, the phase distribution is given only in the radial direction of the disk, but not in the tangential direction.

Also, it functions to give a third-order positive spherical aberration or a third-order negative spherical aberration to the + 1st-order diffracted light,
With respect to the -1st-order diffracted light, a diffractive optical element or a polarizing diffractive optical element which functions to give a third-order negative spherical aberration or a third-order positive spherical aberration to form a fourth-order function for two sub-beams. A form in which phase distributions of opposite signs are provided is also conceivable. In this case, a phase distribution is provided both in the radial direction and the tangential direction of the disk.

Similarly, the shape of the phase distribution of the opposite sign given to the two sub-beams is not limited to a quadratic function or a quadratic function, but may be a higher-order function or a combination thereof. The direction may be not only the radial direction of the disk but also both the radial direction and the tangential direction of the disk.

In an embodiment of the optical head device according to the present invention, light emitted from one semiconductor laser is divided into three lights by a diffractive optical element or a polarizing diffractive optical element to form a main beam and two sub-beams. Instead of using 3
It is also possible to use a form in which light emitted from the semiconductor lasers is used as a main beam and two sub-beams, respectively. In this case, in order to give the two sub-beams phase distributions of opposite signs in the radial direction of the disk, the sub-beams 1
The position of the semiconductor laser with respect to the sub-beam 2 is shifted forward or rearward of the focal point of the collimator lens, and the position of the semiconductor laser with respect to the sub-beam 2 is shifted rearward or forward of the focal point of the collimator lens. Alternatively, a convex lens or a concave lens, or a cylindrical convex lens or a cylindrical concave lens whose generating line is parallel to the tangential direction of the disk is inserted in the optical path for the sub-beam 1 between the collimator lens and the objective lens. In the optical path for the sub-beam 2, a concave lens or a convex lens, or a cylindrical concave lens or a cylindrical convex lens whose generating line is parallel to the tangential direction of the disk is inserted. Or
A lens that gives a third order positive spherical aberration or a lens that gives a third order negative spherical aberration is inserted in the optical path for the sub-beam 1 between the collimator lens and the objective lens. Sub beam 2
A lens that gives a third order negative spherical aberration or a lens that gives a third order positive spherical aberration is inserted in the optical path corresponding to.

Further, the converging spots of the two sub-beams are shifted from the converging spots of the main beam in a direction opposite to each other in the radial direction of the disc by １ ／ period of the groove of the disc, or are disposed on the objective lens. By shifting the phases of the two incident sub-beams in opposite directions by π / 2 on the left and right sides of a straight line passing through the optical axis and parallel to the tangential direction of the disk, the first to seventh optical head devices of the present invention can be shifted. As in the embodiment, it is possible to detect whether the focused spot of the main beam is located on the groove or the land of the disk. In the latter case, in the optical path for the two sub-beams, phase control for shifting the phases of the two sub-beams incident on the objective lens in opposite directions on the left and right sides of a straight line passing through the optical axis and parallel to the tangential direction of the disk. An element such as an element is inserted. As a form of the phase control element, a parallel plate having different thicknesses on the left and right sides of a straight line passing through the optical axis and parallel to the tangential direction of the disk can be considered.

In the first to seventh embodiments of the optical head device of the present invention, the converging spot of the two sub-beams is 1 / one of the groove of the disk with respect to the converging spot of the main beam.
The two sub-beams incident on the objective lens may be shifted in the opposite directions in the radial direction of the disc by four periods, or the phases of the two sub-beams incident on the objective lens may be shifted by π / By shifting the push-pull signals detected from each of the two sub-beams in the opposite directions by shifting the push-pull signals detected by the two sub-beams in opposite directions, the substrate thickness deviation of the disc is calculated from the sum of the push-pull signals detected from the two sub-beams. Has been detected. In contrast,
The converging spots of the two sub-beams are shifted from the converging spot of the main beam in the radial direction of the disc by a half period of the groove of the disc in a direction opposite to each other;
Push-pull detected from each of the two sub-beams by shifting the phases of the two sub-beams incident on the objective lens in opposite directions by π on the left and right sides of a straight line passing through the optical axis and parallel to the tangential direction of the disc. A form is also conceivable in which the waveforms of the signals are in phase with each other, and the thickness deviation of the disk substrate is detected from the difference between the push-pull signals detected from each of the two sub-beams. Similarly, any configuration may be used as long as the substrate thickness deviation of the disk is detected based on the difference in the amplitude of the push-pull signal detected from each of the two sub-beams.

In the first to third embodiments of the optical information recording / reproducing apparatus according to the present invention shown in FIGS. 13 to 15, the first embodiment of the optical head apparatus according to the present invention shown in FIG. Although a drive circuit and the like are added, a form in which an arithmetic circuit, a drive circuit, and the like are added to the second to seventh embodiments of the optical head device of the present invention can be considered. In the first to third embodiments of the optical information recording / reproducing apparatus of the present invention shown in FIGS. 13 to 15, the groove and the land are composed of an arithmetic circuit and a drive circuit for correcting the substrate thickness deviation. Switch the polarity of the circuit. At that time, it is necessary to detect whether the focused spot of the main beam is located on the groove or the land of the disk. If the address information formed on the disk is reproduced, such land / groove position detection can be performed intermittently. However, in the first to seventh embodiments of the optical head device of the present invention, In a form in which an arithmetic circuit, a drive circuit, and the like are added, the use of the land / groove position detection signal enables continuous detection of such land / groove positions without reproducing address information formed on the disk. It is possible to do.

[0088]

As described in detail above, according to the optical head device of the present invention, a main beam and a plurality of sub-beams are generated from light emitted from a light source, and are recorded on an optical recording medium by the main beam. Alternatively, while performing reproduction, phase distributions of opposite signs are given to the plurality of sub-beams in the radial direction of the optical recording medium, and the substrate thickness of the optical recording medium is determined based on the difference in the amplitude of the push-pull signal detected from the sub-beams. Since the deviation can be detected, the substrate thickness deviation can be detected even for an optical recording medium on which an RF signal has not been written in advance.

In the optical head device, a 0th order light and a ± 1st order diffracted light are generated from the light emitted from the light source by using a diffractive optical element or a polarizing diffractive optical element. Similar effects can be obtained by using the difference in the amplitude of the push-pull signal even when the ± first-order diffracted light is used as two sub-beams.

According to the optical head device of the present invention, the difference between the amplitudes of the push-pull signals is used even when the light source is composed of a plurality of light sources and each of the emitted lights is used as a main beam and a plurality of sub-beams. Thus, a similar effect can be obtained.

Further, in the optical information recording / reproducing apparatus of the present invention, by using the optical head apparatus of the present invention capable of detecting the thickness deviation of the substrate of the optical recording medium, there is no adverse effect on the recording / reproducing characteristics. The deviation of the substrate thickness of the optical recording medium can be corrected.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical head device according to the present invention.

FIG. 2 is a plan view of a diffractive optical element in the first embodiment of the optical head device according to the present invention.

FIG. 3 is a diagram showing an arrangement of condensed spots on a disk in the first embodiment of the optical head device of the present invention.

FIG. 4 is a plan view of a hologram optical element according to the first embodiment of the optical head device of the present invention.

FIG. 5 is a diagram showing a pattern of a light receiving portion of the photodetector and an arrangement of light spots on the photodetector in the first embodiment of the optical head device of the present invention.

FIG. 6 is a diagram showing a calculation example of a sectional shape of a converging spot in the first embodiment of the optical head device of the present invention.

FIG. 7 is a diagram showing a calculation example of a sectional shape of a converging spot in the first embodiment of the optical head device of the present invention.

FIG. 8 is a diagram showing a calculation example of a push-pull signal in the first embodiment of the optical head device of the present invention.

FIG. 9 is a diagram illustrating a calculation example of a push-pull signal in the first embodiment of the optical head device of the present invention.

FIG. 10 is a diagram showing a calculation example of a push-pull signal in the first embodiment of the optical head device of the present invention.

FIG. 11 is a diagram showing a calculation example of a push-pull signal in the first embodiment of the optical head device of the present invention.

FIG. 12 is a diagram showing a calculation example of a substrate thickness deviation detection characteristic in the first embodiment of the optical head device of the present invention.

FIG. 13 is a diagram showing a configuration of a first embodiment of the optical information recording / reproducing apparatus of the present invention.

FIG. 14 is a diagram showing a configuration of an optical information recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 15 is a diagram showing a configuration of an optical information recording / reproducing apparatus according to a third embodiment of the present invention.

FIG. 16 is a plan view of a diffractive optical element according to a second embodiment of the optical head device of the present invention.

FIG. 17 is a diagram showing the arrangement of condensed spots on a disk in a second embodiment of the optical head device of the present invention.

FIG. 18 is a plan view of a diffractive optical element according to a third embodiment of the optical head device of the present invention.

FIG. 19 is a view showing the arrangement of condensed spots on a disc in a third embodiment of the optical head device of the present invention.

FIG. 20 is a plan view of a diffractive optical element in an optical head device according to a fourth embodiment of the present invention.

FIG. 21 is a diagram showing an arrangement of condensed spots on a disk in an optical head device according to a fourth embodiment of the present invention.

FIG. 22 is a diagram showing a configuration of an optical head device according to a fifth embodiment of the present invention.

FIG. 23 is a diagram showing a pattern of a light receiving section of a photodetector and an arrangement of light spots on the photodetector in a fifth embodiment of the optical head device according to the present invention.

FIG. 24 is a diagram showing a configuration of an optical head device according to a sixth embodiment of the present invention.

FIG. 25 is a diagram showing a pattern of a light receiving section of a photodetector and an arrangement of light spots on the photodetector in a sixth embodiment of the optical head device of the present invention.

FIG. 26 is a diagram showing a configuration of an optical head device according to a seventh embodiment of the present invention.

FIG. 27 is a plan view of a polarizing hologram optical element according to a seventh embodiment of the optical head device of the present invention.

FIG. 28 is a diagram showing a pattern of a light receiving section of a photodetector and an arrangement of light spots on the photodetector in a seventh embodiment of the optical head device of the present invention.

FIG. 29 is a diagram showing an example of a configuration of a conventional optical head device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2, 202, 302 Collimator lens 3 Diffractive optical element 4 Polarization beam splitter 5, 205, 305 Quarter-wave plate 6, 206, 306 Objective lens 7, 207, 307 Disk 8 Hologram optical element 9 Lens 10 Light detection Containers 11, 211, 311 and 411 Tracks 12 to 14, 212 to 214, 312 to 314 and 412
414 Focused spot 15-18 Area 19-34 Light receiving section 35-46 Light spot 47 Arithmetic circuit 48 Drive circuit 49, 50 Relay lens 51 Drive circuit 52 Liquid crystal optical element 53 Drive circuit 54 Diffractive optical element 55, 56 Area 59 Diffraction Optical element 60 to 63 Area 66 Diffractive optical element 67 to 72 Area 75 Cylindrical lens 76 Photodetector 77 to 84 Light receiving section 85 to 87 Light spot 88 Module 89, 389 Semiconductor laser 90 Photodetector 91, 391 Polarizing diffractive optical element 92 Polarizing hologram optical element 93, 393 Mirror 94-109 Light receiving section 110-121 Light spot 122 Module 123 Photodetector 124 Polarizing hologram optical element 125-140 Light receiving section 141-146 Light spot

Continued on the front page F-term (reference) 2H049 AA04 AA14 AA25 AA34 AA51 AA57 AA65 AA66 CA05 CA08 CA09 CA20 5D118 AA14 AA18 BA01 BB02 BF02 BF03 CC03 CC12 CD02 CD03 CD08 CD14 CF03 CF06 CG23 DA20 DA35 DA40 DC09 A01 DA01 A EA03 EB12 EC01 EC13 EC40 JA12 JA30 KA02 KA17 KA19 KA24

Claims (30)

[Claims] 1. An optical head device comprising: a light source; an objective lens for condensing light emitted from the light source on an optical recording medium; and a photodetector for receiving reflected light from the optical recording medium. A main beam and a plurality of sub-beams are generated from light emitted from the optical recording medium, and recording or reproduction is performed on the optical recording medium by the main beam, and the plurality of sub-beams are opposite to each other in a radial direction of the optical recording medium. An optical head device, wherein a code phase distribution is provided, and a substrate thickness deviation of the optical recording medium is detected based on a difference in amplitude of a push-pull signal detected from each of the plurality of sub-beams. 2. A diffractive optical element or a polarizing diffractive optical element for dividing light emitted from the light source into a plurality of light beams between the light source and the objective lens, wherein the diffractive optical element or the polarizing diffractive optical element is provided. 2. The optical head according to claim 1, wherein zero-order light from an optical element is used as the main beam, and ± first-order diffracted lights from the diffractive optical element or the polarizing diffractive optical element are used as the plurality of sub-beams. apparatus. 3. The diffractive optical element or the polarizing diffractive optical element functions as a convex lens for + 1st-order diffracted light, a concave lens for −1st-order diffracted light, or a concave lens for + 1st-order diffracted light, 3. The optical head device according to claim 2, wherein the optical head device functions as a convex lens for the -1st-order diffracted light. 4. The diffractive optical element or the polarizing diffractive optical element has a cylindrical convex lens whose generating line is parallel to a tangential direction of the optical recording medium for + 1st-order diffracted light, and has a generating line for -1st-order diffracted light. Acting as a cylindrical concave lens parallel to the tangential direction of the optical recording medium, or a cylindrical concave lens whose generating line is parallel to the tangential direction of the optical recording medium for + 1st-order diffracted light,
3. The optical head device according to claim 2, wherein the generatrix acts as a cylindrical convex lens parallel to the tangential direction of the optical recording medium for the -1st-order diffracted light. 5. The function of the diffractive optical element or the polarizing diffractive optical element to impart a third positive spherical aberration to the + 1st-order diffracted light and a third negative spherical aberration to the −1st-order diffracted light. 3. The light according to claim 2, wherein the light has the function of giving a third-order negative spherical aberration to the + 1st-order diffracted light and a third-order positive spherical aberration to the -1st-order diffracted light. Head device. 6. The light source according to claim 1, wherein a plurality of light sources are provided, and light emitted from the plurality of light sources is used as a main beam and a plurality of sub beams, respectively.
The optical head device as described in the above. 7. A collimator lens between the light source and the objective lens, wherein a position of the light source with respect to one of the sub-beams is shifted forward or rearward of a focal point of the collimator lens, and a light source with respect to the other of the sub-beams 7. The optical head device according to claim 6, wherein the position is shifted backward or forward of the focal point of the collimator lens. 8. A collimator lens between the light source and the objective lens, a convex lens in an optical path for one of the sub-beams between the collimator lens and the objective lens, and a collimator lens between the collimator lens and the objective lens A concave lens is inserted in the optical path for the other of the sub-beams, or a concave lens in the optical path for one of the sub-beams between the collimator lens and the objective lens, the other of the sub-beams between the collimator lens and the objective lens 7. The optical head device according to claim 6, wherein a convex lens is inserted in an optical path for the optical head. 9. A collimator lens between the light source and the objective lens, wherein a generating line is parallel to a tangential direction of the optical recording medium in an optical path for one of the sub-beams between the collimator lens and the objective lens. A cylindrical convex lens, a cylindrical concave lens whose generating line is parallel to the tangential direction of the optical recording medium is inserted in the optical path for the other of the sub-beams between the collimator lens and the objective lens, or the collimator lens and the objective lens In the optical path for one of the sub-beams, the generatrix is a cylindrical concave lens parallel to the tangential direction of the optical recording medium, and the generatrix is in the optical path for the other of the sub-beams between the collimator lens and the objective lens. 7. The optical head device according to claim 6, wherein a cylindrical convex lens parallel to a tangential direction is inserted. 10. A collimator lens between the light source and the objective lens, wherein a collimator lens is provided between the collimator lens and the objective lens in an optical path for one of the sub-beams.
A lens that gives the next positive spherical aberration, a lens that gives a third order negative spherical aberration in the optical path for the other of the sub-beams between the collimator lens and the objective lens, or the collimator lens and the A lens providing a third order negative spherical aberration in an optical path for one of the sub-beams between the objective lenses, and a third order positive spherical aberration in an optical path for the other of the sub-beams between the collimator lens and the objective lens; 7. The optical head device according to claim 6, wherein a lens to be provided is inserted. 11. The focused spots of the plurality of sub-beams are shifted from the focused spots of the main beam in the radial direction of the optical recording medium in opposite directions by a quarter period of a groove of the optical recording medium. The optical head device according to claim 1, wherein the optical head device is disposed at an angle. 12. The phase of the plurality of sub-beams incident on the objective lens is shifted in opposite directions by π / 2 on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. The optical head device according to claim 2, wherein: 13. The diffractive optical element or the polarizing diffractive optical element has a configuration in which a diffraction grating is formed in a region including an effective diameter of the objective lens, and passes through an optical axis of incident light to form the optical recording medium. A straight line parallel to the tangential direction is divided into a first region on the left and a second region on the right, and the phases of the gratings in the first region and the second region are shifted by π / 2. The optical head device according to claim 12, wherein: 14. The diffractive optical element or the polarizing diffractive optical element has a structure in which a diffraction grating is formed in a region including an effective diameter of the objective lens, and passes through an optical axis of incident light to form the optical recording medium. A straight line parallel to the tangential direction and a straight line parallel to the radial direction, four of a first region on the upper left, a second region on the upper right, a third region on the lower left, and a fourth region on the lower right 13. The optical head device according to claim 12, wherein the phases of the gratings in the first and fourth areas and the second and third areas are shifted by π / 2. 15. The diffractive optical element or the polarizing diffractive optical element has a structure in which a diffraction grating is formed in a region including an effective diameter of the objective lens, and passes through an optical axis of incident light to form the optical recording medium. With a straight line parallel to the tangential direction and two straight lines parallel to the radial direction, the first area at the left center, the second area at the right center, the third area at the upper left, the fourth area at the upper right,
It is divided into six, a lower left fifth region and a lower right sixth region, and the phase of the grating in the first, fourth, and sixth regions and the second, third, and fifth regions. 13. The optical head device according to claim 12, wherein は is shifted by π / 2. 16. The phase of the plurality of sub-beams incident on the objective lens is shifted in opposite directions by π / 2 on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. The optical head device according to claim 6, wherein: 17. In the optical path for the plurality of sub-beams, the phase of the sub-beam incident on the objective lens is opposite to each other on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. 17. The optical head device according to claim 16, wherein a phase control element for shifting is inserted. 18. The light according to claim 17, wherein the phase control element is a parallel flat plate having different thicknesses on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. Head device. 19. A land / groove position detection signal is generated based on a push-pull signal generated by the converged spot of the sub-beam, and the condensed spot of the main beam is recorded on the optical recording by the sign of the land / groove position detection signal. 19. The optical head device according to claim 11, wherein the optical head device detects whether the medium is located on a groove or a land. 20. A substrate thickness deviation of said optical recording medium is detected from a sum of push-pull signals detected from each of said plurality of sub-beams.
9. The optical head device according to 8. 21. The condensed spots of the plurality of sub-beams are shifted in the radial direction of the optical recording medium in directions opposite to each other by a half period of a groove of the optical recording medium with respect to the condensed spots of the main beam. The optical head device according to claim 1, wherein the optical head device is disposed at an angle. 22. The phase of the plurality of sub-beams incident on the objective lens is shifted in opposite directions by π on the left and right sides of a straight line passing through an optical axis and parallel to a tangential direction of the optical recording medium. The optical head device according to claim 1, wherein 23. The optical head device according to claim 21, wherein a substrate thickness deviation of said optical recording medium is detected from a difference between push-pull signals detected from each of said plurality of sub-beams. 24. An optical system comprising a light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and an optical head device having a photodetector for receiving reflected light from the optical recording medium. In a formula information recording / reproducing apparatus, a main beam and a plurality of sub-beams are generated from light emitted from the light source, and recording or reproduction is performed on the optical recording medium with the main beam, and the plurality of sub-beams are recorded on the optical recording medium. Giving phase distributions of opposite signs to each other in the radial direction of the optical recording medium, and detecting a substrate thickness deviation of the optical recording medium based on a difference in amplitude of a push-pull signal detected from each of the plurality of sub-beams, An optical information recording / reproducing apparatus for correcting a substrate thickness deviation of an optical recording medium. 25. The optical recording medium according to claim 25, further comprising a collimator lens between said light source and said objective lens, wherein said collimator lens is moved in an optical axis direction to correct a substrate thickness deviation of said optical recording medium. 25. The optical information recording / reproducing apparatus according to 24. 26. A device comprising two relay lenses between the light source and the objective lens, wherein one of the two relay lenses is moved in the optical axis direction to correct a substrate thickness deviation of the optical recording medium. 25. The method according to claim 24, wherein
The optical information recording / reproducing apparatus according to claim 1. 27. A liquid crystal optical element between the light source and the objective lens, wherein a voltage difference is applied to the liquid crystal optical element to correct a substrate thickness deviation of the optical recording medium. 25. The optical information recording / reproducing apparatus according to 24. 28. Detecting whether the converging spot of the main beam is located on a groove or a land of the optical recording medium, and detecting a difference in substrate thickness of the optical recording medium between the groove and the land of the optical recording medium. 28. The optical information recording / reproducing apparatus according to claim 24, wherein the polarity of a circuit for performing the correction is switched. 29. Reproducing address information formed on the optical recording medium to detect whether the focused spot of the main beam is located on a groove or a land of the optical recording medium. 29. The optical information recording / reproducing apparatus according to claim 28, wherein: 30. A land / groove position detection signal is generated based on a push-pull signal based on a converging spot of the sub beam, and the converging spot of the main beam is recorded on the optical recording by a sign of the land / groove position detecting signal. 29. The optical information recording / reproducing apparatus according to claim 28, wherein the optical information recording / reproducing apparatus detects whether the medium is located on a groove or a land of the medium.