JP2007042202A - Optical head and disk reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head capable of limiting a crosstalk component caused by a reflected light on the land of an optical recording medium so as to reduce errors without causing any problems that cost is increased or an optical head is made large in size, thereby preventing the degradation of reproducing characteristics. <P>SOLUTION: An optical element 24 that includes a lightseparation part 30 for separating a outgoing light from a returning light and a phase compensation part 31 for giving phase compensation to an incident light is disposed on the optical path of the returning light between an objective lens 26 and a photodetector 28 so that the phase compensation part 31 is nearer the photodetector 28 than the light separation part 30. Thus, phase compensation is given to the returning light, and the degradation of reproducing characteristics of an optical recording medium is prevented. In this configuration, it is unnecessary to use a light separation element such as a beam splitter, thereby making the optical head small in size and low in cost. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical head and a disk reproducing apparatus.

  Some disk reproducing apparatuses are capable of recording and / or reproducing a plurality of types of magneto-optical recording media having different physical formats, for example, MD (Mini Disk: registered trademark) and Hi-MD (registered trademark). An optical head provided in a disk reproducing apparatus that reproduces at least the plurality of types of magneto-optical recording media has a light source that emits laser light, and the laser light emitted from the light source is focused on the information recording surface of the magneto-optical recording medium. And an optical system that separates the laser light that is the return light reflected from the information recording surface of the magneto-optical recording medium, and a signal conversion means that converts the laser light separated by the optical system into an electrical signal.

  Magneto-optical recording media such as MD and Hi-MD are provided with guide grooves called grooves on the information recording surface. When reproducing a magneto-optical recording medium, the disk reproducing device irradiates the groove with laser light emitted from a light source, and reads information recorded in the groove by reflected light of the irradiated light. In recent years, the track pitch has been narrowed so that as many information signals as possible can be recorded on the magneto-optical recording medium, and the density of the magneto-optical recording medium has been increased.

The track pitch of MD used conventionally is 1.6 μm, and the track pitch of Hi-MD that can realize high-density recording developed in recent years is 1.25 μm. Further, EFM (Eight to Fourteen Modulation) modulated data is recorded in the MD groove, and RLL (1-7), which is a physical format for high-density recording, is used in the Hi-MD groove. PP (RLL: Run Length Limited, PP: Party preserve / Prohibit rmtr (
Repeated Minimum Transition Runlength)) Modulated data is recorded. Thus, as an optical head having compatibility between MD and Hi-MD having different physical formats, the wavelength of the laser light emitted from the light source is 780 nm, and the numerical aperture NA of the objective lens is 0.45. Things are used.

  When such an optical head is used, the spot diameter of the laser light emitted from the light source may be larger than the track pitch, and the spot diameter may protrude from the groove. The light that protrudes from the groove is reflected on the surface of the land adjacent to the groove, mixed into the light reflected by the groove, and converted into an electrical signal. Such a phenomenon is called crosstalk, which causes many errors in an electrical signal converted by mixing other light into the light reflected by the groove, for example, an information reproduction signal (RF signal), and degrades reproduction characteristics. Cause.

  Therefore, an optical head has been proposed in which a phase compensation element is inserted in the optical path of the reflected light from the magneto-optical recording medium to limit the crosstalk component from the land, thereby reducing errors and preventing deterioration in reproduction characteristics. (For example, refer to Patent Document 1).

  FIG. 11 is a side view schematically showing the configuration of the optical head 1 disclosed in Patent Document 1. As shown in FIG. An optical head 1 that is a discrete optical system includes a semiconductor laser element 2 that emits laser light, a grating 3 that separates light emitted from the semiconductor laser element 2, a beam splitter 4 that transmits or reflects incident light, and an incident light A collimating lens 5 that collimates the light, an objective lens 6 that focuses the laser light on the magneto-optical recording medium 11, a phase compensation element 7 that adjusts the phase of the incident light, and a Wollaston prism 8 that separates the incident light. And a cylindrical lens 9 that generates astigmatism in the incident light, and a photodetector 10 that is a light receiving element that converts the incident light into an electrical signal.

  For example, when the magneto-optical recording medium 11 is MD or Hi-MD, the semiconductor laser element 2 that is a light source that emits light emits laser light having a wavelength of 780 nm. The semiconductor laser element 2 is connected to an external circuit that supplies a drive current (not shown), and the intensity of the laser beam can be changed according to the amount of current from the external circuit.

  The grating 3 is a diffraction grating that separates light emitted from the semiconductor laser element 2 into 0th-order diffracted light, −1st-order diffracted light, and + 1st-order diffracted light. The beam splitter 4 transmits the forward light emitted from the semiconductor laser element 2 and directed to the magneto-optical recording medium 11, and reflects the return light reflected by the magneto-optical recording medium 11. The collimating lens 5 emits the diffused light emitted from the semiconductor laser element 2 and made incident as parallel light.

  The objective lens 6 has, for example, a numerical aperture NA of 0.45, and has an objective lens in a focus direction that is parallel to the optical axis of incident light and a tracking direction that is parallel to the radial direction of the magneto-optical recording medium 11. It is mounted on an actuator (not shown) that holds 6 in a movable manner. The objective lens 6 focuses the forward light emitted from the semiconductor laser element 2 on the information recording surface of the magneto-optical recording medium 11 to form a light spot.

  The phase compensation element 7 applies phase compensation to the return light from the magneto-optical recording medium 11 that is incident light, restricts the crosstalk component from the land, reduces errors, and obtains good reproduction characteristics. To do. Note that the phase compensation element 7 has a phase compensation amount that can provide good reproduction characteristics in both cases where the magneto-optical recording medium 11 is MD and Hi-MD, and MD, Hi-MD, To give the same phase compensation amount to the incident light.

  The Wollaston prism 8 separates the return light that is reflected by the magneto-optical recording medium 11 and reflected by the beam splitter 4, passes through the phase compensation element 7, and passes through the cylindrical lens 9. Then, the light is incident on a predetermined light receiving area of the photodetector 10 described later. The cylindrical lens 9 gives astigmatism to incident light so that the photodetector 10 can output a focus error signal (FE signal). The photodetector 10 is a signal conversion means in which a predetermined light receiving region is formed. The photodetector 10 converts the incident laser light into an electric signal and performs an operation, thereby performing the above-described FE signal, RF signal, and tracking error signal (TE signal). Is output.

  Laser light emitted from the semiconductor laser element 2 passes through the grating 3, the beam splitter 4 and the collimator lens 5, enters the objective lens 6, and is condensed on the information recording surface of the magneto-optical recording medium 11. The laser beam condensed on the information recording surface of the magneto-optical recording medium 11 is reflected on the reflecting surface of the magneto-optical recording medium 11, passes through the objective lens 6 and the collimating lens 5, and is reflected by the beam splitter 4. The light is transmitted through the compensation element 7, separated by the Wollaston prism 8, and further transmitted through the cylindrical lens 9 and received by the photodetector 10. In the photodetector 10, the received laser beam is converted into an electrical signal, and each signal is output.

  In the optical head 1 disclosed in Patent Document 1, the phase of the light reflected by the magneto-optical recording medium 11 is suitably adjusted by the phase compensation element 7 and the phase of the light reflected by the land is adjusted. Is reduced, and the deterioration of the reproduction characteristics of MD and Hi-MD can be prevented for any of the magneto-optical recording media 11.

  However, in the optical head 1 disclosed in Patent Document 1, since the phase compensation element 7 is inserted, there is a problem that the cost is increased and the size is increased as compared with the optical head in which the phase compensation element is not used. Therefore, without causing the problem of increase in cost and enlargement of the optical head, the error can be reduced by limiting the crosstalk component due to the reflected light at the land of the magneto-optical recording medium, and the reproduction characteristics can be prevented from deteriorating. There is a need for optical heads that can be used.

JP 2003-296960 A (pages 14-15, FIG. 16)

  In view of such a requirement, the applicant of the present application previously described in Japanese Patent Application No. 2005-205733 by providing a phase compensation element using a liquid crystal element so as to be inclined with respect to the optical axis of the return path light. As an arrangement that provides astigmatism and does not require the use of a cylindrical lens, an optical head that realizes miniaturization and cost reduction while providing phase compensation to the return light is proposed.

  FIG. 12 is a side view schematically showing the configuration of the optical head 12 in which the liquid crystal element 13 is disposed at an inclination. The optical head 12 is similar to the optical head 1 of FIG. 11 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. The optical head 12 includes a liquid crystal element 13 provided on the optical path of the return light between the beam splitter 4 and the photodetector 10, a voltage applying unit 14 for applying a voltage to the liquid crystal element 13, and operations of the voltage applying unit 14. And control means 15 for controlling.

  The liquid crystal element 13 is configured to have divided regions, and a voltage is applied from the voltage applying unit 14 controlled by the control unit 15 to individually change the refractive index of the liquid crystal in each divided region constituting the liquid crystal element 13. Thus, appropriate phase compensation is given to the incident light. In the optical head 12, the liquid crystal element 13 is provided to be inclined with respect to the optical axis of the return path light between the beam splitter 4 and the photodetector 10, so that astigmatism is generated with respect to the incident light to the liquid crystal element 13. It is not necessary to provide an optical component for generating astigmatism such as a cylindrical lens. For this reason, it can be said that cost reduction and reduction in size of the optical head can be realized by reducing the number of parts.

  However, in recent years, the optical head is mounted on, for example, a notebook personal computer, a mobile optical information recording / reproducing apparatus, etc., and is widely used. The optical head 12 shown in FIG. 12 also has room for improvement, and further cost reduction and downsizing are required.

  The object of the present invention is to reduce errors by preventing crosstalk components caused by reflected light from the land of an optical recording medium without increasing the cost and increasing the size of the optical head, thereby preventing deterioration of reproduction characteristics. It is an object to provide an optical head and a disk reproducing apparatus that can be used.

The present invention relates to an optical head for recording and / or reproducing information by irradiating light onto an optical recording medium.
A light source that emits light;
An objective lens for condensing the outward light emitted from the light source onto the optical recording medium;
A light receiving element that receives the return light emitted from the light source and reflected by the optical recording medium;
An optical element provided on the optical path of the return path light between the objective lens and the light receiving element,
The optical element
A light separation unit for separating the outward light and the backward light;
A phase compensation unit that provides phase compensation to incident light;
The optical head is characterized in that the phase compensation unit is provided closer to the light receiving element than the light separation unit.

In the present invention, the optical element is
The surface of the phase compensator facing the light receiving element is inclined with respect to the optical axis of the return light between the objective lens and the light receiving element.

  The present invention also includes a diffusion angle adjusting element that is disposed between the optical element and the objective lens and adjusts the diffusion angle of light incident on the objective lens.

In the present invention, the phase compensation unit is a phase compensation glass having a plurality of divided regions.
Phase compensation glass
The refractive index of at least one divided region is different from the refractive index of other divided regions.

In the present invention, the direction in which the plurality of divided regions of the phase compensation glass are arranged is
It is characterized by being parallel to the radial direction of the optical recording medium in a recording or reproducing state.

In the present invention, the phase compensation unit is
A liquid crystal element having a plurality of divided regions;
Voltage application means for applying a voltage to each of the plurality of divided regions of the liquid crystal element to change the refractive index of each divided region;
The phase compensation amount given to each divided region with respect to the light incident on the divided region of the liquid crystal element is adjusted so that the spot of the light transmitted through the liquid crystal element is given a uniform phase change in the spot. Control means for controlling the operation of the voltage applying means for applying a voltage to the divided region of the element.

In the present invention, the liquid crystal element is
A transparent electrode is provided for each divided region.

  The present invention is also characterized in that the direction in which the plurality of divided regions of the liquid crystal element are arranged is parallel to the radial direction of the optical recording medium in a recording or reproducing state.

  In the invention, it is preferable that the light source emits laser light having a wavelength of 780 nm or less, and the objective lens has a numerical aperture NA of 0.45 or more.

  According to another aspect of the present invention, there is provided a disc reproducing apparatus including the optical head described above.

  According to the present invention, the optical head includes a light source that emits light, an objective lens that condenses forward light emitted from the light source on the optical recording medium, and return light that is emitted from the light source and reflected by the optical recording medium. And an optical element provided on the optical path of the return path light between the objective lens and the light receiving element and having a phase compensation unit. In such an optical head, the return light reflected by the optical recording medium is incident on the phase compensation unit of the optical element so that phase compensation is given to the incident light, and the crosstalk component due to the reflected light at the land of the optical recording medium. Since the error can be reduced by limiting the above, it is possible to prevent the reproduction characteristics from being deteriorated.

  Further, the optical element includes a light separation unit that separates the forward light and the return light, and a phase compensation unit that provides phase compensation to incident light, and the phase compensation unit receives light more than the light separation unit. Provided closer to the element. For this reason, it is not necessary to provide an optical separation element such as a beam splitter that separates the forward light and the backward light, guides the separated forward light to the optical recording medium side, and guides the backward light to the light receiving element side. Since a light separation element such as a beam splitter is large and expensive as an optical component, the optical head can be reduced in size and cost by adopting a configuration that does not require the use of the light separation element.

  According to the present invention, the surface of the optical element on the side that faces the light receiving element of the phase compensation unit is provided to be inclined with respect to the optical axis of the return light between the objective lens and the light receiving element. On the other hand, astigmatism can be generated, and an optical component for generating astigmatism such as a cylindrical lens becomes unnecessary. For this reason, the number of parts can be reduced and the optical head can be further reduced in size.

  In addition, according to the present invention, the optical head includes the diffusion angle adjusting element that is disposed between the optical element and the objective lens and adjusts the diffusion angle of light incident on the objective lens, thereby reducing the size of the optical head and improving the coupling efficiency. Can be planned.

  According to the invention, the phase compensation unit is a phase compensation glass having a plurality of divided regions, and the phase compensation glass has a refractive index of at least one divided region different from that of other divided regions. When diffused light enters the phase compensation glass, the incident angle of the incident light differs between the vicinity of the optical axis of the light spot and the periphery of the light spot, and the optical path length, which is the distance that the incident light travels through the phase compensation glass, is light. Since the difference between the vicinity of the optical axis of the spot and the vicinity of the periphery of the light spot is different, the amount of phase change given by transmitting through the phase compensation glass differs between the vicinity of the optical axis of the light spot and the vicinity of the periphery of the light spot. Although the phase change amount varies within the spot, by using a phase compensation glass having a plurality of divided regions, the refractive index in each divided region is made suitable, and the phase change amount in the light spot is reduced. Can be uniform.

  According to the invention, the direction in which the plurality of divided regions of the phase compensation glass are arranged is parallel to the radial direction of the optical recording medium in a recording or reproducing state. Of the light spots incident on the phase compensation glass, the light at the peripheral edge in the radial direction of the light spot does not contain an information reproduction signal. Accordingly, the incident angle of the critical portion between the portion including the information reproduction signal and the portion not including the information reproduction signal in the radial direction of the light spot is smaller than the incident angle of the peripheral portion in the tangential direction perpendicular to the radial direction. When phase compensation is applied in the radial direction, the difference in the amount of phase compensation to be applied in order to cause a uniform phase change in the light spot can be made smaller than when phase compensation is applied to. For this reason, it is preferable to provide phase compensation in the radial direction. By making the direction in which the divided regions are arranged parallel to the radial direction of the optical recording medium, the difference in the amount of phase compensation applied in the optical spot is reduced. In addition, the phase change in the light spot can be made uniform more easily.

  According to the invention, the phase compensation unit applies a voltage to the liquid crystal element having a plurality of divided regions and the plurality of divided regions of the liquid crystal element to change the refractive index of each divided region. By adjusting the voltage application means and the phase compensation amount given to each divided region with respect to the light incident on the divided region of the liquid crystal element, the spot of the light transmitted through the liquid crystal element is given a uniform phase change within the spot. And a control means for controlling the operation of the voltage applying means for applying a voltage to the divided region of the liquid crystal element. For this reason, the difference in the amount of phase change in the light spot caused by the incident angle of the light incident on the liquid crystal element can be reduced, and the reproduction characteristics of the optical recording medium can be further improved. Furthermore, when mounted on a disc reproducing apparatus having compatibility among a plurality of types of optical recording media, an optimum phase compensation amount can be given to any of the plurality of types of optical recording media. .

  According to the present invention, since the transparent electrode provided for each divided region is used as an electrode for applying a voltage to the liquid crystal element, it is possible to prevent a decrease in light intensity caused by blocking light with the electrode.

  Further, according to the present invention, the direction in which the plurality of divided regions of the liquid crystal element are arranged is parallel to the radial direction of the optical recording medium in the recording or reproducing state, and thus is uniform in the light spot as described above. It is possible to reduce the difference in the amount of phase compensation to be given to change the phase.

  According to the present invention, the light source emits a laser beam having a wavelength of 780 nm or less, and the objective lens has a numerical aperture NA of 0.45 or more. Therefore, a good information reproduction signal can be obtained according to various optical recording media. Obtainable.

  Further, according to the present invention, since the optical head according to any one of the above is provided, the crosstalk component caused by the reflected light at the land of the optical recording medium is generated without causing the problem of increase in cost and enlargement of the optical head. There is provided a disc reproducing apparatus capable of limiting and reducing errors and improving reproduction characteristics. Note that the disk reproducing device is not limited to only reproducing information recorded on the optical recording medium, and performs information recording on the optical recording medium and information recorded on the optical recording medium. Including.

  FIG. 1 is a side view showing a simplified configuration of an optical head 21 according to an embodiment of the present invention. The optical head 21 includes a semiconductor laser element 22, a grating 23, an optical element 24, a diffusion angle adjusting element 25, an objective lens 26, a Wollaston prism 27, and a photodetector 28.

  In the optical head 21 of the present embodiment, the optical element 24 is provided on the optical path of the return path light between the objective lens 26 and the photodetector 28, and is incident on the light separation unit 30 that separates the forward path light and the return path light. And a phase compensation glass 31 that is a phase compensation unit that imparts phase compensation to light.

  In the present invention, the “phase compensation amount” is the amount of phase change given to the incident light by the phase compensation unit, and the “phase change amount” is given by the phase compensation unit. This is the amount of change in the phase of the emitted light.

  The semiconductor laser element 22 is a light source that emits light. For example, when the optical recording medium 29 is a magneto-optical recording medium such as MD or Hi-MD or an optical recording medium such as CD (Compact Disk), the semiconductor laser element 22 emits laser light having a wavelength of 780 nm, When the recording medium 29 is an optical recording medium such as a DVD (Digital Versatile Disk), a laser beam having a wavelength of 630 to 690 nm is emitted, and the optical recording medium 29 is a light such as a Blu-ray disc (registered trademark). When the recording medium is used, blue laser light having a wavelength of 390 to 460 nm is emitted. The semiconductor laser element 22 is connected to an external circuit that supplies a drive current (not shown), and the intensity of the laser beam can be changed according to the amount of current from the external circuit. The light emitted from the semiconductor laser element 22 enters the grating 23.

  The grating 23 is a diffraction grating that separates light emitted from the semiconductor laser element 22 into 0th-order diffracted light, −1st-order diffracted light, and + 1st-order diffracted light. The laser light that has passed through the grating 23 enters the optical element 24.

  The optical element 24 includes a light separation unit 30 that separates forward light and return light, and a phase compensation glass 31 that provides phase compensation to incident light. In the optical element 24, the light separation unit 30 and the phase compensation glass 31 are integrally configured.

  As the light separation unit 30, for example, a half mirror can be used. The surface opposite to the side facing the phase compensation glass 31 of the light separating unit 30 is emitted from the semiconductor laser element 22 and is emitted from the optical axis of forward light incident on the light separating unit 30 and the semiconductor laser element 22, and optical recording is performed. It is provided so as to be inclined with respect to the optical axis of the return path light reflected by the medium 29 and incident on the light separation unit 30. In the light separation unit 30 of the present embodiment, the forward light emitted from the semiconductor laser element 22 is reflected and guided to the objective lens 26, and the return light emitted from the semiconductor laser element 22 and reflected by the optical recording medium 29 is transmitted. To do.

  The phase compensation glass 31 is provided closer to the photodetector 28 than the light separation unit 30. As the phase compensation glass 31, for example, an optical glass substrate having a phase compensation function can be used. The phase compensation glass 31 imparts phase compensation to the return light by transmitting and refracting the return light separated from the forward light by the light separation unit 30. A specific configuration of the phase compensation glass 31 will be described later. The forward light from the semiconductor laser element 22 that has entered the optical element 24 is reflected by the light separation unit 30 and enters the diffusion angle adjusting element 25.

  The diffusion angle adjustment element 25 is disposed between the optical element 24 and the objective lens 26 and adjusts the diffusion angle of light incident on the objective lens 26. As the diffusion angle adjusting element 25, for example, a collimating lens that makes incident light parallel light, a coupling lens that changes the diffusion angle of incident light, or the like can be used. Among these, a coupling lens that can reduce the size of the optical head 21 in the optical axis direction of the outgoing light and the objective lens 26 in the focus direction, and can improve the intensity of the outgoing light from the objective lens 26. Particularly preferred. The light whose diffusion angle is adjusted by the diffusion angle adjusting element 25 enters the objective lens 26.

  The objective lens 26 focuses the light emitted from the semiconductor laser element 22 on the optical recording medium 29. For example, when the optical recording medium 29 is a magneto-optical recording medium such as MD or Hi-MD or an optical recording medium such as CD, the objective lens 26 having a numerical aperture NA of 0.45 is used. Further, when the optical recording medium 29 is an optical recording medium such as a DVD, a medium having a numerical aperture NA of 0.6 is used. When the optical recording medium 29 is an optical recording medium such as a Blu-ray disc, the numerical aperture NA is used. That has a value of 0.85 is used.

  The objective lens 26 is held by an actuator (not shown) that can move in a focus direction that is the optical axis direction of incident light and a tracking direction that is parallel to the radial direction of the optical recording medium 29, and is emitted from the semiconductor laser element 22. The emitted outward light is condensed on the information recording surface of the optical recording medium 29, and a light spot is formed on the information recording surface. The light collected on the optical recording medium 29 is reflected by the information recording surface of the optical recording medium 29 to become return light, passes through the diffusion angle adjusting element 25, and passes through the light separating unit 30 of the optical element 24. The light enters the phase compensation glass 31 of the optical element 24. Here, the light condensed on the optical recording medium 29 by the objective lens 26 will be described.

  FIG. 2 is a schematic plan view showing how the light spot 41 is formed on the information recording surface of the optical recording medium 29. On the information recording surface of the optical recording medium 29, a guide groove-shaped groove 42 on which an information reproduction signal is recorded is formed. The three-dimensional XYZ axis shown in FIG. 2 is defined as follows. The direction perpendicular to the information recording surface (focus direction) of the optical recording medium 29 in the recording or reproducing state (focus direction) is the X-axis direction, the radial direction (tracking direction) of the optical recording medium 29 in the recording or reproducing state is the Y-axis direction, and light. The direction in which the groove 42 of the recording medium 29 extends and is orthogonal to the tracking direction (tangential direction) is defined as the Z-axis direction. The definition of the XYZ triaxial direction is commonly used throughout this specification.

  When reproducing information recorded on the optical recording medium 29, the optical head 21 irradiates the inside of the groove 42 with the light spot 41 of the laser light emitted from the semiconductor laser element 22, and the emitted laser light The information recorded in the groove 42 is read by the reflected light.

  When the optical recording medium 29 is MD, the track pitch 43 is 1.6 μm, and when the optical recording medium 29 is Hi-MD that realizes high-density recording, the track pitch 43 is 1.25 μm. When information is recorded on or reproduced from the optical recording medium 29 by the optical head 21, the light spot of the laser light emitted from the semiconductor laser element 22 and applied to the optical recording medium 29 is, for example, 1.6 μm in diameter. In this case, the light spot 41 protrudes from the groove 42.

  The light in the light spot region 41 a that protrudes from the groove 42 is reflected by the surface of the land 44 adjacent to the groove 42 and mixed into the light reflected by the groove 42. Such a phenomenon is called crosstalk. When other light is mixed in the light reflected by the groove 42, an electric signal converted by a photodetector 28 (to be described later) that receives the light, for example, an information reproduction signal (RF A large number of errors in the signal), leading to deterioration in reproduction characteristics.

  The optical element 24 of the optical head 21 of the present embodiment limits the crosstalk component from the land 44 by giving phase compensation to the return path light in order to prevent such deterioration of the reproduction characteristics, and an error is generated. A phase compensation glass 31 that is a phase compensation unit to be reduced is provided. Hereinafter, the configuration of the phase compensation glass 31 will be described.

  FIG. 3 is a plan view schematically showing the configuration of the phase compensation glass 31. The phase compensation glass 31 is a flat plate member having a rectangular shape when viewed from the plane, and is divided into a plurality of (three in the present embodiment) divided regions 31a, 31b, and 31c by dividing lines 51 and 52 extending in the Z-axis direction. A direction in which the plurality of divided regions 31a, 31b, and 31c are arranged is parallel to a Y-axis direction that is a radial direction of the optical recording medium 29 in a recording or reproducing state. In the present embodiment, the refractive indexes of the plurality of divided regions 31a, 31b, and 31c of the phase compensation glass 31 are different from each other, and the phase change of the light that enters the respective divided regions and is given phase compensation is the light The refractive indexes of the divided regions 31a, 31b, and 31c are set so as to be uniform within the spot.

  Here, a problem that occurs when diffused light enters the phase compensation glass having a uniform refractive index in the plane on which the incident light is incident will be described. When light enters such a phase compensation glass, if the incident angle of the incident light is different, the optical path length, which is the distance that the incident light travels through the phase compensation glass, is different, so the phase of the light transmitted through the phase compensation glass is different. The amount of change will be different. Such variation in the amount of phase change is not only a problem for a plurality of lights having different incident angles, but also when the incident light is diffuse light, the light near the optical axis of the light spot and the optical axis of the light spot are There is also a problem between the light near the periphery on both sides as the center.

  That is, when the diffused light is incident on the phase compensation glass, the incident angle of the incident light is different between the vicinity of the optical axis of the light spot and the peripheral edge of the light spot. The length differs between the vicinity of the optical axis of the light spot and the vicinity of the periphery of the light spot. In addition, if the optical path length differs between the vicinity of the optical axis of the light spot and the vicinity of the peripheral portion of the light spot, the amount of phase change imparted by transmitting through the phase compensation glass is near the optical axis of the light spot and the light spot. It differs between the vicinity of the periphery. For this reason, when phase compensation glass with a uniform refractive index in the plane on which incident light is incident is used, the polarization state of light near the periphery of the light spot changes from linearly polarized light to elliptically polarized light, and the phase in the light spot changes. Variation occurs in the amount of change.

  For such a problem, the phase compensation glass 31 of the present embodiment has a plurality of divided regions 31a, 31b, and 31c, and is incident on each divided region to provide phase compensation. Since the refractive index of each of the divided regions 31a, 31b, and 31c is set so that the phase change is uniform within the light spot, within the light spot of the light phase-compensated by the phase compensation glass 31. The amount of phase change can be made uniform.

  The phase compensation glass 31 can change the phase so that the polarization axis of the light adjusted to the linearly polarized light is parallel to the Y-axis direction that is the radial direction of the optical recording medium 29 in the recording or reproducing state. preferable. The reason will be described below.

  As shown in FIG. 2 described above, the phase compensation glass 31 is used to limit a crosstalk component due to light reflected by the surface of the land 44 adjacent to the groove 42. Here, when the information reproduction signal of the groove 42 is obtained, looking at the light spot 41, the information reproduction signal recorded in the groove 42 is included up to the peripheral portion of the light spot 41 in the Z-axis direction. On the other hand, when viewed in the Y-axis direction, the light spot region 41a in the vicinity of the peripheral portion of the light spot 41 is irradiated to the land 44, and no information reproduction signal is included. That is, when the light spot 41 is viewed in the Y-axis direction, the information reproduction signal exists only near the center of the light spot 41.

  Here, since the phase is a wave, the phase of the reflected light is divided into a P wave that is a wave in the Y-axis direction and an S wave that is a wave in the Z-axis direction. When the optical recording medium 29 is an MD, the phases of the reflected light from the optical recording medium 29 are in a state where both the P wave and the S wave are substantially aligned (SP = 0 °). However, when the optical recording medium 29 is Hi-MD, the reflected light from the optical recording medium 29 is in a state where the P wave is delayed by δ from the S wave (S−P = δ).

  When δ = 0 ° can be obtained by applying phase compensation by the phase compensation glass 31, optimum reproduction characteristics can be obtained even when the optical recording medium 29 is Hi-MD. There are two methods for setting δ = 0 ° in this way, a method of delaying an S wave that is a wave in the Z-axis direction by δ, and a method of advancing a P wave that is a wave in the Y-axis direction by δ, that is, the Y-axis. There is a method of delaying the P wave, which is a directional wave, by 2π−δ.

  As described above, the information reproduction signal recorded in the groove 42 is included up to the periphery of the light spot 41 in the Z-axis direction. Therefore, in the method of delaying the S wave, which is a wave in the Z-axis direction, by δ, it is necessary to give a phase change to the light at the peripheral edge incident on the phase compensation glass 31, and is provided in the optical head 21 of this embodiment. Even when the phase compensation glass 31 is used, a slight difference in the amount of phase change in the light spot occurs.

  On the other hand, in the Y-axis direction, the information reproduction signal recorded in the groove 42 is not included in the peripheral portion of the light spot 41. Therefore, in the method in which the P wave, which is a wave in the Y-axis direction, is advanced by δ, since the information reproduction signal is not included in the peripheral portion of the light incident on the phase compensation glass 31, the difference in phase change amount in the light spot The incident angle of the critical portion between the portion where the information reproduction signal is included and the portion where the information reproduction signal is not included in the Y-axis direction of the light spot is smaller than the incident angle of the peripheral portion of the light spot. As a signal, there is almost no difference in the amount of phase change.

  As described above, the incident angle of the critical portion between the portion including the information reproduction signal and the portion not including the information reproduction signal in the Y-axis direction of the light spot 41 is greater than the incident angle of the peripheral portion in the Z-axis direction perpendicular to the Y-axis direction. Is also small. Therefore, the difference in the amount of phase compensation to be applied in order to cause a uniform phase change in the light spot is smaller when the phase change is applied in the Y-axis direction than when the phase change is applied in the Z-axis direction. Therefore, it is preferable to give a phase change in the Y-axis direction of the optical recording medium 29, and the direction in which the divided regions 31a, 31b, 31c of the phase compensation glass 31 are arranged is parallel to the Y-axis direction of the optical recording medium 29. By doing so, it is possible to reduce the difference in the amount of phase compensation applied in the light spot and to make the phase change of the light spot more uniform.

  Further, the optical element 24 of the present embodiment is provided such that the surface of the phase compensation glass 31 facing the photodetector 28 is inclined with respect to the optical axis of the return light between the objective lens 26 and the photodetector 28. As a result, astigmatism can be generated for the return light from the optical recording medium 29 that is incident light on the phase compensation glass 31, and an optical component for generating astigmatism such as a cylindrical lens is provided. Since the configuration need not be used, the number of parts can be reduced and the optical head can be further reduced in size.

  The surface of the phase compensation glass 31 facing the photodetector 28 is inclined, so that light at one peripheral edge of the spot of incident light that is diffused light and light at the other peripheral edge opposite to the one peripheral edge. Although there is a possibility that the difference in the optical path length with respect to light may increase, the phase compensation glass 31 is divided as in this embodiment, and a suitable refractive index is set in each divided region, so that the phase compensation glass 31 is set. It is possible to prevent a difference in phase change amount from occurring in the light spot even if the light beams are inclined.

  The return light from the optical recording medium 29 that has passed through the phase compensation glass 31 as described above is subjected to phase change and astigmatism by the phase compensation glass 31 and is incident on the Wollaston prism 27.

  The Wollaston prism 27 reflects the return light from the optical recording medium 29 that is reflected by the optical recording medium 29 and separated by the light separation unit 30 of the optical element 24 and phase compensation and astigmatism are given by the phase compensation unit 31. It is an anisotropic element that is incident on the photodetector 28, and is disposed between the optical element 24 and the photodetector 28. The Wollaston prism 27 is a main signal used in a servo system for detecting incident light, for example, a focus error signal (FE signal) and a tracking error signal (TE signal), and an MO (Magneto-Optical) signal. The signals are separated into I and J signals used for (RF signal), and are made incident on the light receiving area of each signal provided in the photodetector 28.

  The photodetector 28 is a light receiving element that receives the return light reflected from the optical recording medium 29. The photodetector 28 converts the incident laser light into an electrical signal and outputs an FE signal, a TE signal, and an RF signal by performing an operation. The photodetector 28 is provided with a plurality of light receiving areas.

  FIG. 4 is a plan view schematically showing the configuration of a plurality of light receiving regions provided in the photodetector 28. The photodetector 28 includes, for example, light receiving areas A, B, C, and D in which light receiving areas divided into four equal-area rectangles are arranged in a matrix of 2 rows and 2 columns, and light receiving areas A to D. Two rectangular light receiving areas E and F arranged in the Y-axis direction on both sides and two rectangular light receiving areas I and J arranged in the Z-axis direction on both sides of the light receiving areas A to D are provided. . In the light receiving regions A to D, the zero-order diffracted light separated by the grating 23, which generates astigmatism by the phase compensation glass 31 and is used for the main signal separated by the Wollaston prism 27. The FE signal is output by the astigmatism method. In the light receiving regions E and F, light of −1st order diffracted light and + 1st order diffracted light separated by the grating 23 and used for the main signal separated by the Wollaston prism 27 is received, and the TE signal is detected. In the light receiving regions I and J, the 0th-order diffracted light separated by the grating 23 and used for the I and J signals separated by the Wollaston prism 27 is received, and the RF signal is detected.

The photodetector 28 receives the return light in each of the light receiving areas A to J, and outputs each electrical signal as shown in the following equation. In the following formula, a value represented by a signal detected from each light receiving area is represented by adding “S” to the head of the alphabet representing each light receiving area.
FE signal = (SA + SC) − (SB + SD)
TE signal = SE-SF
RF signal = SI-SJ

  The operation of the optical head 21 will be described below. The laser light emitted from the semiconductor laser element 22 passes through the grating 23 and is separated into 0th-order diffracted light, + 1st-order diffracted light, and −1st-order diffracted light, and is reflected by the light separation unit 30 of the optical element 24. The laser beam reflected by the light separation unit 30 spreads through the diffusion angle adjusting element 25, changes its angle, and is focused on the information recording surface of the optical recording medium 29 by the objective lens 26. The light condensed on the optical recording medium 29 is reflected by the optical recording medium 29, passes through the objective lens 26 and the diffusion angle adjusting element 25, passes through the light separating section 30 of the optical element 24, and is separated from the light separating section 30. The light is incident on the integrally formed phase compensation glass 31.

  The phase compensation glass 31 is divided into a plurality of parts, and the refractive index in each of the plurality of divided areas is different, so that the phase compensation that can reduce the difference in the amount of phase change in the light spot caused by the incident angle of light. A quantity is given to the incoming return light. Further, the surface of the phase compensation glass 31 facing the photodetector 28 is inclined with respect to the optical axis of the return light between the objective lens 26 and the photodetector 28, so that the incident light to the phase compensation glass 31 is provided. Astigmatism is imparted to.

  The return light to which the phase change and astigmatism are imparted by the phase compensation glass 31 is separated by the Wollaston prism 27 and received at a predetermined position of the photodetector 28. The photodetector 28 outputs each electric signal of the FE signal, the TE signal, and the RF signal using the received laser beam.

  As described above, in the optical head 21 of the present embodiment, the phase compensation glass 31 is divided into the plurality of regions 31a, 31b, and 31c having different refractive indexes, so that the phase compensation amount to be given to the incident light for each region. Therefore, the difference in the amount of phase change in the light spot can be reduced, and the reproduction characteristics of the optical recording medium 29 can be improved. Furthermore, since the phase compensation glass 31 is provided with an inclination, an optical component such as a cylindrical lens for generating astigmatism becomes unnecessary, and thus the optical head can be reduced in size.

  Such an optical head 21 is not limited to the above configuration, and various modifications can be made. In the optical head 21 of the present embodiment, the phase compensation glass 31 having a different refractive index with the dividing lines 51 and 52 as a boundary is used. However, the present invention is not limited to this. For example, the refractive index is within the plane of the phase compensation glass. A refractive index gradient glass or the like that changes may be used.

  FIG. 5 is a cross-sectional view showing a simplified configuration of the optical head 61 according to the second embodiment of the present invention. The optical head 61 of this embodiment is similar to the optical head 21 of the first embodiment described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

  The optical head 61 according to the second embodiment applies voltages to the liquid crystal element 63 having a plurality of divided regions and the plurality of divided regions of the liquid crystal element 63 as a phase compensation unit of the optical element 62. The voltage application means 64 for changing the refractive index of each divided region and the phase compensation amount given to each divided region with respect to the light incident on the divided region of the liquid crystal element 63 are adjusted, and the spot of the light transmitted through the liquid crystal element 63 is adjusted. Includes a control means 65 for controlling the operation of the voltage applying means 64 for applying a voltage to the divided region of the liquid crystal element 63 so that a uniform phase change is applied within the spot. And

  FIG. 6 is a plan view schematically showing the configuration of the liquid crystal element 63. The liquid crystal element 63 is provided integrally with the light separation unit 30 of the optical element 62 and is disposed closer to the photodetector 28 than the light separation unit 30. Further, the liquid crystal element 63 provided in the optical head 61 of the present embodiment is a flat plate-like member having a rectangular shape when viewed from above, and a plurality of (three in the present embodiment) are formed by the dividing lines 53 and 54 extending in the Z-axis direction. ) Are divided into divided areas 63a, 63b, 63c. The direction in which the plurality of divided regions 63a, 63b, and 63c are arranged is parallel to the Y-axis direction that is the radial direction of the optical recording medium 29 in the recording or reproducing state.

  The liquid crystal element 63 includes a transparent electrode connected to the voltage applying unit 64 for each of the divided regions 63a, 63b, and 63c, and another transparent electrode disposed so as to face the transparent electrode connected to the voltage applying unit 64. And a liquid crystal layer disposed between the pair of transparent electrodes. Such a liquid crystal layer and a transparent electrode are sealed with a glass substrate.

  A voltage is applied to the liquid crystal element 63 from the voltage applying means 64 through transparent electrodes provided in the divided regions 63a, 63b, and 63c. Therefore, the voltage application unit 64 is configured to apply different voltage values to the divided regions 63a, 63b, and 63c. By using a transparent electrode as an electrode provided in a plurality of divided regions of the liquid crystal element 63, light is not blocked by the electrode, so that a decrease in intensity of light passing through the liquid crystal element 63 can be prevented. In the liquid crystal element 63, a voltage is applied between the pair of transparent electrodes to change the refractive index of the liquid crystal layer, and the change in refractive index gives a phase change to incident light.

  The liquid crystal element 63 to which a voltage is applied by the voltage applying means 64 gives phase compensation to the incident light, and polarizes the incident light into substantially linearly polarized light. The voltage applying means for applying a voltage to each transparent electrode of the liquid crystal element 63 having the divided regions includes a power source (not shown) and PWM (Pulse Width Modulation). The operation of the voltage applying unit 64 is controlled by the control unit 65.

  The control means 65 adjusts the amount of phase compensation given to each of the divided areas with respect to the light incident on the divided areas 63a, 63b, 63c of the liquid crystal element 63, and the spot of the light transmitted through the liquid crystal element 63 is one in the spot. The operation of the voltage applying means 64 for applying a voltage to the divided regions 63a, 63b, 63c of the liquid crystal element 63 is controlled so that such a phase change is given. The reason for the difference in the phase change amount in the light spot of the diffused light incident on the liquid crystal element 63 and the method of adjusting the phase compensation amount so as to reduce the difference in the phase change amount will be described later.

  The control means 65 not only controls the operation of the voltage application means 64 so as to reduce the difference in phase change amount in the light spot, but also sets the phase compensation amount of the liquid crystal element 63 according to the type of the optical recording medium 29. The operation of the voltage applying means 64 is controlled so as to adjust. The control means 65 detects the type of the optical recording medium 29 and applies a predetermined voltage to each divided region of the liquid crystal element 63 according to the detected type of the optical recording medium 29. Depending on the type of the optical recording medium 29, the voltage to be applied to each divided region of the liquid crystal element 63, that is, the voltage with a refractive index that can give appropriate phase compensation to the incident light is tested in advance. Thus, it can be obtained for each type of optical recording medium 29 and stored in a memory 65a attached to the control means 65 in the form of table data or the like. The memory 65a is configured by, for example, an LSI (Large Scale Integration).

  The control means 65 is based on electrical signals obtained by the photodetector 28, for example, when using a magneto-optical recording medium as the optical recording medium 29, based on TOC (Table Of Contents) information recorded in advance on the magneto-optical recording medium. The type of the optical recording medium 29 is determined.

  Furthermore, although the liquid crystal element 63 has a problem that various characteristics such as its optical characteristics change due to temperature changes, the optical head 61 of this embodiment measures the surface temperature of the liquid crystal element 63 in the vicinity of the liquid crystal element 63. A temperature sensor (not shown) is provided, and changes in various characteristics accompanying changes in temperature of the liquid crystal element 63 are corrected using table data in which the temperature and voltage stored in advance in the memory 65a are associated.

  When the liquid crystal element is used as the phase compensation unit, the difference in the amount of phase change in the light spot of the diffused light incident on the liquid crystal element is further larger than when the phase compensation glass is used as the phase compensation unit. Hereinafter, when the liquid crystal element is used, the phase compensation amount is adjusted so that the difference in the phase change amount in the light spot of the diffused light is further increased and the difference in the phase change amount is reduced by the liquid crystal element 63 of the present embodiment. A method will be described.

  When light is incident on the liquid crystal element, the refractive index of the liquid crystal with respect to the incident light changes when the incident angle of the incident light changes due to the refractive index anisotropy of the liquid crystal constituting the liquid crystal element. In addition, when the incident angle of light incident on the liquid crystal element changes, the refraction of the light accompanying the change in the incident angle despite the same voltage applied to the liquid crystal element and the same refractive characteristics of the liquid crystal element itself. The rate change causes the light phase change amount to be different from the desired amount.

  Such a variation in the amount of phase change is not only a problem for a plurality of lights having different incident angles, but also when the incident light is diffuse light, the light near the optical axis of the light spot and the light spot There is also a problem with the light near the periphery on both sides with the optical axis as the center. In addition, if there is a difference between the refractive index of the liquid crystal near the center of the light spot and the refractive index of the liquid crystal near the periphery of the light spot due to the different incident angles, the phase near the center of the light spot is caused by the difference in refractive index. There is a difference between the amount of change and the amount of phase change near the periphery of the light spot.

Here, the difference between the phase change amount at the center of the light spot and the phase change amount at the peripheral portion of the light spot is expressed by the following equation (1). However, the “difference in refractive index” means the refractive index at the center of the light spot generated with the change in the incident angle even though the voltage applied to the liquid crystal element is the same and the refractive characteristics of the liquid crystal element itself are the same. And the refractive index of the periphery of the light spot.
(Difference in phase change)
= (Difference in refractive index) x (thickness of liquid crystal) x 360 / (wavelength of incident light) (1)

  As shown in the equation (1), if the variation in the phase change amount occurs in the same light spot, even if the optimum phase compensation amount near the center of the light spot is given to the entire light spot of the incident light that is the diffused light The phase change amount of the incident light at the periphery of the light spot becomes a phase change amount different from the optimum value.

  FIG. 7 shows the amount of phase change at each position in the radial direction of the light spot when the optimum phase compensation amount is uniformly applied to the entire incident light with respect to the diffused light incident on the liquid crystal element that is not divided. FIG. The liquid crystal element imparts an optimum phase compensation amount to the entire light spot at the optical axis center (center of light spot) of incident light that is diffused light. As a result, the incident light can be substantially linearly polarized near the center of the light spot of the incident light.

  However, as described above, even when the optimum phase compensation amount similar to that at the center of the light spot is given to the entire light spot, the incident angle of the incident light is the central portion of the optical axis at the periphery of the light spot of the diffused light. Therefore, the value is out of the optimum phase change amount. As described above, when the amount of phase change at the periphery of the light spot deviates from the optimum value, the polarization state of the light near the periphery of the light spot changes from linearly polarized light to elliptically polarized light.

  In order to reduce the variation in the amount of phase change in the light spot caused by the difference in the refractive index caused by the difference in the incident angle of light, the optical head 61 of the present embodiment has a structure as shown in FIG. A liquid crystal element 63 having a plurality of divided regions 63a, 63b, and 63c is used. The liquid crystal element 63 having the divided regions 63a, 63b, and 63c as shown in FIG. 6 has different voltage values applied to the transparent electrodes provided in the divided regions 63a, 63b, and 63c. The refractive index with respect to the incident light can be set to a different value for each of the regions 63a, 63b, and 63c, and the phase compensation amount applied to the light incident on the respective divided regions 63a, 63b, and 63c can be changed.

  FIG. 8 is a diagram showing the amount of phase compensation that the liquid crystal element 63 having a plurality of divided regions shown in FIG. 6 gives to incident light that is diffused light. In FIG. 8, the phase compensation amount imparted to the incident light in each of the divided regions 63a, 63b, and 63c is indicated by a solid line. In FIG. 8, a line 71 indicated by a two-dot chain line indicates a phase change amount when a uniform phase compensation amount is given in the light spot to the diffused light incident on the liquid crystal element that is not divided into a plurality of parts. .

  In the divided region 63a, a phase compensation amount larger than the phase compensation amount provided in the vicinity of the center of the light spot is given to one end side of the light spot peripheral portion where the actual phase change amount becomes smaller than the optimum value. In the divided region 63b, since the difference between the actual phase change amount and the optimum phase change amount is small, the phase compensation amount is not changed. In the divided region 63c, a phase compensation amount smaller than the phase compensation amount provided in the vicinity of the center of the light spot is applied to the other end side of the light spot peripheral edge where the actual phase change amount is larger than the optimum value.

  As described above, the voltage value applied to the transparent electrodes provided in the divided regions 63a, 63b, 63c in order to change the phase compensation amount in the divided regions 63a, 63b, 63c of the liquid crystal element 63 is, for example, in advance A value obtained by a test or the like and stored in a memory 65a provided in the control means 65 can be used.

  FIG. 9 is a diagram illustrating a phase change amount 72 when different phase compensation amounts are given to the divided light regions with respect to the diffused light incident on the liquid crystal element 63 having a plurality of divided regions. The liquid crystal element 63 is divided into a plurality of parts, and the phase compensation amount is changed by changing the applied voltage value from the voltage applying means 64 near the center and the periphery of the light spot, thereby optimizing the phase change amount in the light spot. The difference from the value can be reduced, and the difference in the amount of phase change in the light spot can be reduced.

  FIG. 10 shows an error rate during reproduction of the optical recording medium 29 when phase compensation is provided by a liquid crystal element that is not divided into a plurality of parts, and optical recording when phase compensation is provided by a liquid crystal element 63 having a plurality of divided regions. It is a figure which shows the error rate at the time of medium 29 reproduction | regeneration. When phase compensation is provided by a liquid crystal element that is not divided into a plurality (conventional), the error rate is white circles, and phase compensation is provided by a liquid crystal element 63 having a plurality of divided regions provided in the optical head 61 of this embodiment. The error rate in the case (invention) is indicated by a black circle. Note that the phase compensation amount indicated by the horizontal axis in the case of using the liquid crystal element 63 having a plurality of divided regions indicates the phase compensation amount provided in the divided region 63b. The error rate is a measurement of the number of errors that occurred per unit time. For measuring the error rate, MD was used as the optical recording medium 29.

  As shown in FIG. 10, the error rate when the phase change is applied by the liquid crystal element 63 having a plurality of divided regions in most of the phase compensation amount other than a certain range (about 90 ° to 120 °). This was much lower than the error rate when a phase change was applied by a liquid crystal element that was not divided into a plurality of parts. In this way, by dividing the liquid crystal element into a plurality of parts and appropriately selecting the voltage value to be applied to the liquid crystal element near the center and the periphery of the light spot, the amount of phase compensation in each divided region can be changed to change the inside of the light spot. It can be seen that the difference in the phase change amount in the optical recording medium 29 can be reduced and the reproduction characteristics of the optical recording medium 29 can be improved.

  Furthermore, by using the liquid crystal element 63 as the phase compensation unit, the phase compensation amount applied to the incident light according to the applied voltage from the voltage applying unit 64 can be set to an optimum value for each reproduction. For this reason, when the optical head 61 of this embodiment is mounted on, for example, a disc playback apparatus having compatibility between MD and Hi-MD, each time MD playback and Hi-MD playback are performed. In any case, an optimum phase compensation amount can be provided.

  The disk reproducing apparatus provided with the optical heads 21 and 61 of the present invention as described above can reduce the difference in phase change amount in the light spot caused by the incident angle of light, and can improve the reproduction characteristics of the optical recording medium 29. Further improvement can be achieved. The disk reproducing apparatus provided with the optical heads 21 and 61 of the present invention is not limited to the one that reproduces only the information recorded on the optical recording medium 29, and can record and record information on the optical recording medium 29. The information recorded on the optical recording medium 29 may be both reproduced.

It is a side view which simplifies and shows the structure of the optical head 21 which is one Embodiment of this invention. 3 is a schematic plan view showing a state where a light spot 41 is formed on an information recording surface of an optical recording medium 29. FIG. 2 is a plan view schematically showing a configuration of a phase compensation glass 31. FIG. 3 is a plan view schematically showing a configuration of a plurality of light receiving regions provided in the photodetector 28. FIG. It is sectional drawing which simplifies and shows the structure of the optical head 61 of the 2nd Embodiment of this invention. 4 is a plan view schematically showing a configuration of a liquid crystal element 63. FIG. FIG. 5 is a diagram showing the amount of phase change at each position in the radial direction of the light spot when an optimum phase compensation amount is uniformly applied to the entire incident light with respect to diffused light incident on a liquid crystal element that is not divided. is there. It is a figure which shows the phase compensation amount provided with respect to the incident light which is a diffused light by the liquid crystal element 63 which has several division area shown in FIG. It is a figure which shows the phase change amount 72 when giving different phase compensation amount for every division area with respect to the diffused light which injects into the liquid crystal element 63 which has the division area divided | segmented into plurality. Error rate when reproducing the optical recording medium 29 when phase compensation is provided by a liquid crystal element that is not divided into a plurality, and reproduction time when the optical recording medium 29 is reproduced when phase compensation is provided by a liquid crystal element 63 having a plurality of divided regions It is a figure which shows these error rates. It is a side view which shows roughly the structure of the optical head 1 disclosed by patent document 1. FIG. 2 is a side view schematically showing a configuration of an optical head 12 in which a liquid crystal element 13 is inclined. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21,61 Optical head 22 Semiconductor laser element 23 Grating 24,62 Optical element 25 Diffusion angle adjustment element 26 Objective lens 27 Wollaston prism 28 Photo detector 29 Optical recording medium 30 Light separation part 31 Phase compensation glass 63 Liquid crystal element 64 Voltage application means 65 Control means 65a Memory

Claims (10)

In an optical head for recording and / or reproducing information by irradiating light onto an optical recording medium,
A light source that emits light;
An objective lens for condensing the outward light emitted from the light source onto the optical recording medium;
A light receiving element that receives the return light emitted from the light source and reflected by the optical recording medium;
An optical element provided on the optical path of the return path light between the objective lens and the light receiving element,
The optical element
A light separation unit for separating the outward light and the backward light;
A phase compensation unit that provides phase compensation to incident light;
An optical head, wherein the phase compensation unit is provided closer to the light receiving element than the light separation unit. The optical element
2. The optical head according to claim 1, wherein a surface of the phase compensation unit facing the light receiving element is provided to be inclined with respect to the optical axis of the return light between the objective lens and the light receiving element.   3. The optical head according to claim 1, further comprising a diffusion angle adjusting element that is disposed between the optical element and the objective lens and adjusts a diffusion angle of light incident on the objective lens. The phase compensation unit is a phase compensation glass having a plurality of divided regions.
Phase compensation glass
The optical head according to claim 1, wherein a refractive index of at least one divided region is different from a refractive index of another divided region. The direction in which the plurality of divided regions of the phase compensation glass are arranged is
5. The optical head according to claim 4, wherein the optical head is parallel to a radial direction of the optical recording medium in a recording or reproducing state. The phase compensation unit
A liquid crystal element having a plurality of divided regions;
Voltage application means for applying a voltage to each of the plurality of divided regions of the liquid crystal element to change the refractive index of each divided region;
The phase compensation amount given to each divided region with respect to the light incident on the divided region of the liquid crystal element is adjusted so that the spot of the light transmitted through the liquid crystal element is given a uniform phase change in the spot. The optical head according to claim 1, further comprising a control unit that controls an operation of a voltage applying unit that applies a voltage to the divided region of the element. The liquid crystal element
The optical head according to claim 6, further comprising a transparent electrode for each divided region.   8. The optical head according to claim 6, wherein a direction in which the plurality of divided regions of the liquid crystal element are arranged is parallel to a radial direction of the optical recording medium in a recording or reproducing state.   The optical head according to claim 1, wherein the light source emits laser light having a wavelength of 780 nm or less, and the objective lens has a numerical aperture NA of 0.45 or more.   A disk reproducing apparatus comprising the optical head according to claim 1.

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