JP5120667B2 - Optical head device and optical information recording / reproducing device - Google Patents

Optical head device and optical information recording / reproducing device Download PDF

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JP5120667B2
JP5120667B2 JP2009511710A JP2009511710A JP5120667B2 JP 5120667 B2 JP5120667 B2 JP 5120667B2 JP 2009511710 A JP2009511710 A JP 2009511710A JP 2009511710 A JP2009511710 A JP 2009511710A JP 5120667 B2 JP5120667 B2 JP 5120667B2
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liquid crystal
crystal polymer
polymer layer
light
region
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JPWO2008132891A1 (en
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龍一 片山
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日本電気株式会社
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Priority to PCT/JP2008/055116 priority patent/WO2008132891A1/en
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    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0901Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
    • G11B7/0903Multi-beam tracking systems
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13Optical detectors therefor
    • G11B7/131Arrangement of detectors in a multiple array
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1367Stepped phase plates
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1381Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops

Description

  The present invention relates to an optical head device and an optical information recording / reproducing device for recording and reproducing with respect to an optical recording medium, and more particularly to an optical head for recording and reproducing with respect to an optical recording medium having a plurality of recording layers. The present invention relates to an apparatus and an optical information recording / reproducing apparatus. In addition, this application claims the priority based on the Japanese application number 2007-112390, and the disclosed content in the Japanese application number 2007-112390 is incorporated in this application by reference.

  In recordable optical recording media such as DVD-R and HD DVD-R, and rewritable optical recording media such as DVD-RW and HD DVD-RW, groove-shaped information tracks are formed in the recording layer. Yes. An optical head device and an optical information recording / reproducing device for recording and reproducing with respect to an optical recording medium are provided with a condensing spot for causing the condensing spot formed on the recording layer of the optical recording medium to follow the information track. And a function of detecting a track error signal representing a positional deviation from the information track. A push-pull method is generally used as a method for detecting a track error signal for a write-once type optical recording medium and a rewritable type optical recording medium. However, the track error signal by the push-pull method causes a large offset when the objective lens of the optical head device shifts in a direction perpendicular to the information track in order to follow the information track. This offset is called an offset due to lens shift, and causes deterioration in recording / reproducing characteristics. A differential push-pull method is known as a method for detecting a track error signal that does not cause an offset due to such a lens shift.

  In an optical head apparatus and an optical information recording / reproducing apparatus that detect a track error signal by a differential push-pull method, light emitted from a light source is divided into a main beam and two sub beams by a diffractive optical element. The main beam and the two sub beams are condensed on the recording layer of the optical recording medium by the objective lens. The reflected light of the main beam and the reflected light of the two sub beams reflected by the recording layer of the optical recording medium are received by the corresponding light receiving units of the photodetector. A main push-pull signal, which is a push-pull signal for the main beam, is detected based on an output from the main beam light-receiving unit that receives the reflected light of the main beam, and from the sub-beam light-receiving unit that receives the reflected light of the two sub beams. Based on the output, a sub push-pull signal that is a push-pull signal for the two sub beams is detected. From the difference between the main push-pull signal and the sub push-pull signal, a differential push-pull signal that is the source of the track error signal is obtained.

  Incidentally, as one method for increasing the recording capacity of the optical recording medium, there is a method of providing a plurality of recording layers on the optical recording medium. Optical recording media having two recording layers have already been put to practical use in DVD-R, HD DVD-R, and the like. When recording and reproducing with respect to such an optical recording medium having a plurality of recording layers using a conventional general optical head device, it is a layer that records and reproduces light emitted from a light source by an objective lens. When the light is focused on the target layer and the reflected light from the target layer is received by the photodetector, part of the reflected light from the non-target layer, which is a layer that does not perform recording or reproduction, also enters the photodetector as disturbance light. . When ambient light enters the light detector, the quality of the focus error signal, track error signal, and mark / space signal recorded on the target layer, which is detected based on the output from the light detector, decreases, and recording and playback are performed. May not be performed correctly.

  When the track error signal is detected by the differential push-pull method with respect to an optical recording medium having a plurality of recording layers, the influence of such disturbance light becomes particularly significant. When the main beam and the two sub beams are condensed on the target layer, and the reflected light of the main beam from the target layer and the reflected light of the two sub beams are received by the corresponding light receiving portions of the photodetector, the main beam from the non-target layer A part of the reflected light enters the sub-beam light receiving part as disturbance light. Since the reflected light of the main beam from the non-target layer is greatly spread on the photodetector, the ratio of incident light to the light receiving unit for the sub beam is small, but the amount of light of the main beam is larger than the amount of light of the two sub beams. The amount of light cannot be ignored. At this time, the reflected light and disturbance light of the two sub beams from the target layer interfere with each other on the sub beam light receiving unit. Here, when the distance between the target layer and the non-target layer changes, the phase difference between the reflected light of two sub beams from the target layer and the disturbance light changes. When the phase difference approaches 0 °, the intensity of light on the sub-beam light-receiving unit increases due to interference, and the output from the sub-beam light-receiving unit increases. On the other hand, when the phase difference approaches 180 °, the intensity of light on the sub-beam light-receiving unit becomes weak due to interference, and the output from the sub-beam light-receiving unit decreases. As a result, the sub push-pull signal and the differential push-pull signal are disturbed.

  From such a background, Japanese Patent Application Laid-Open No. 2005-203090 proposes an optical head device in which disturbance light is prevented from entering the sub-beam light receiving unit. FIG. 1 shows a main part of an optical head device described in Japanese Patent Application Laid-Open No. 2005-203090. Light emitted from the semiconductor laser 33 as a light source is split by the diffractive optical element 34 into a main beam that is 0th-order light and two sub-beams that are ± 1st-order diffracted light. The main beam and the two sub beams are incident on the polarization beam splitter 35 as P-polarized light and are almost 100% transmitted. The collimator lens 36 converts divergent light into parallel light, and almost 100% is transmitted through the diffractive optical element 37. The light is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 38, converted from parallel light to convergent light by the objective lens 39, and condensed on the recording layer of the disk 40 that is an optical recording medium. The reflected light of the main beam and the reflected light of the two sub beams reflected by the recording layer of the disk 40 are converted from divergent light to parallel light by the objective lens 39, and from the circularly polarized light to the forward path and the polarization direction by the quarter wavelength plate 38. Is converted into orthogonal linearly polarized light, and most of the light is transmitted through the diffractive optical element 37. The collimator lens 36 converts parallel light into convergent light, which is incident on the polarization beam splitter 35 as S-polarized light, and almost 100% is reflected. Astigmatism is given by the astigmatism lens 41 and received by the photodetector 42.

  FIG. 2 is a plan view of the diffractive optical element 37. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 40, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 39. The diffractive optical element 37 includes three regions 43a to 43c where diffraction gratings are formed. In the forward path from the semiconductor laser 33 to the disk 40, almost 100% of the light incident on the regions 43a to 43c of the diffractive optical element 37 and the light incident on the other regions are transmitted. On the other hand, in the return path from the disk 40 to the photodetector 42, almost 100% of light incident on the regions 43a to 43c of the diffractive optical element 37 is diffracted, and almost 100% of light incident on the other regions is diffracted. To Penetrate.

  FIG. 3 shows the pattern of the light receiving part of the photodetector 42 and the arrangement of the light spots on the photodetector 42. The photodetector 42 is provided in the middle of two focal lines of a lens system constituted by the collimator lens 36 and the astigmatism lens 41. The light spot 45a corresponds to the reflected light of the main beam, which is zero-order light from the diffractive optical element 34, and is separated by two dividing lines corresponding to the direction perpendicular to the direction of the information track of the disk 40 and the parallel direction. The light receiving portions 44a to 44d are formed on the four light receiving portions. The light spot 45b corresponds to the reflected light of the sub beam that is the + 1st order diffracted light from the diffractive optical element 34, and is separated by a dividing line corresponding to a direction perpendicular to the information track direction of the disk 40. 44f is formed on the two light receiving portions. The light spot 45c corresponds to the reflected light of the sub beam, which is the −1st order diffracted light from the diffractive optical element 34, and is separated by a dividing line corresponding to a direction perpendicular to the information track direction of the disk 40. It is formed on the two light receiving parts of the part 44h. Here, due to the action of the lens system constituted by the collimator lens 36 and the astigmatism lens 41, the light spots 45a to 45c are perpendicular to the information track direction of the disk 40 with respect to the light before entering the lens system. Intensity distributions in directions corresponding to different directions and parallel directions are interchanged. A main push-pull signal is detected based on outputs from the light receiving units 44a to 44d, and a sub push-pull signal is detected based on outputs from the light receiving units 44e to 44h. Further, the mark / space signal recorded on the disk 40 is detected based on the outputs from the light receiving portions 44a to 44d.

  A light spot 45d indicated by a broken-line circle in the drawing corresponds to the reflected light of the main beam from the non-target layer when the disk 40 is an optical recording medium having two recording layers. If a diffraction grating is not formed in the regions 43a to 43c of the diffractive optical element 37, almost 100% of the reflected light of the main beam from the non-target layer incident on the regions 43a, 43b, and 43c is transmitted, and the disturbance Light enters the light receiving unit 44a to the light receiving unit 44d, the light receiving unit 44e to the light receiving unit 44f, and the light receiving unit 44g to the light receiving unit 44h, respectively. However, since diffraction gratings are formed in the regions 43a to 43c of the diffractive optical element 37, almost 100% of the reflected light of the main beam from the non-target layer incident on the regions 43a to 43c is diffracted. The light does not enter the portion 44a to the light receiving portion 44h. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are not disturbed.

  However, in the optical head device described in Japanese Patent Application Laid-Open No. 2005-203090, when the disk 40 is an optical recording medium having two recording layers, the target layer incident on the regions 43a to 43c of the diffractive optical element 37 is used. The reflected light of the main beam from the beam is also almost 100% diffracted and does not enter the light receiving portions 44a to 44d. For this reason, the quality of the mark / space signal recorded on the target layer, which is detected based on the outputs from the light receiving unit 44a to the light receiving unit 44d, is deteriorated. Another light receiving portion that receives the reflected light of the main beam from the target layer that is incident and diffracted into the regions 43a to 43c of the diffractive optical element 37 is provided in the photodetector 42, and the light receiving portions 44a to 44d and the other light receiving portions are provided. It is also possible to detect the mark / space signal recorded in the target layer based on the output from the light receiving unit. However, as the number of light receiving parts used for detecting the mark / space signal increases, the number of current-voltage conversion circuits connected to the light receiving parts increases, and the noise generated there increases. Decreases.

  Japanese Patent Laid-Open No. 2005-276358 discloses an optical pickup device that records and reproduces information with respect to an optical disc, and includes a first diffractive portion, a first condenser lens, a second diffractive portion, and a second diffractive portion. An optical pickup device including a condenser lens and a light detector is disclosed. The first diffracting unit separates the reflected light from the optical disc into a first light beam and a second light beam. The first condenser lens collects the first and second light beams. The second diffracting unit diffracts the collected first and second light beams, respectively. The second condenser lens collects the diffracted first and second light beams. The light detection unit detects the tracking error signal based on the light intensity distributions of the first and second light beams incident from the second condenser lens. The photodetector includes first and second two-divided photodetectors, a push-pull signal generator, and an error signal detector. In the first and second two-divided photodetectors, the light detection region is divided in the track direction, and receives the first and second light beams, respectively. The push-pull signal generation unit outputs the first and second push-pull signals for the first and second light beams based on the light intensity difference between the light detection regions of the first and second two-split photodetectors. Generate each. A tracking error signal is detected from the error signal detector and the first and second push-pull signals. The first diffracting unit includes a phase difference adding unit that gives a phase difference to a part of the second light beam so that the amplitude of the second push-pull signal becomes zero.

  Japanese Patent Laid-Open No. 2006-244535 discloses an optical head device having an objective lens, a diffraction element, an optical element, a photodetector, and a signal processing circuit. The objective lens condenses light from the light source on any recording layer of a recording medium having at least two recording layers. The diffractive element causes a non-diffractive component that passes as it is and a ± first-order diffracted component around the light that passes through the objective lens and is collected on the recording layer of the recording medium. The optical element transmits light reflected by one of the recording layers of the recording medium captured by the objective lens, the first light flux that has passed through the center of the objective lens and the vicinity thereof, and the outside of the first light flux. Split into the second light flux that has passed. The photodetector has a plurality of detection regions, receives at least one of the first light flux and the second light flux separated by the optical element, and outputs an electrical signal corresponding to the intensity thereof. . The signal processing circuit removes the offset component of the component in the direction orthogonal to the guide groove unique to the recording surface of the recording medium from the output of the photodetector.

  An object of the present invention is to solve the above-described problems in an optical head device that performs recording and reproduction on an optical recording medium having a plurality of recording layers, even if the distance between the target layer and the non-target layer changes. It is an object of the present invention to provide an optical head device and an optical information recording / reproducing device in which a differential push-pull signal is not disturbed and the quality of a mark / space signal recorded on a target layer is not deteriorated.

  In an aspect of the present invention, the optical head device includes a diffractive optical element, an objective lens, a photodetector, a light separation unit, and a phase filter. The diffractive optical element generates a main beam and a sub beam group from the emitted light emitted from the light source. The objective lens collects the main beam and the sub beam group on the selected recording layer of the optical recording medium having a plurality of recording layers on which information tracks are formed. The photodetector receives the reflected light of the main beam and the reflected light of the sub beam group reflected by the selected recording layer. The light separation unit separates the optical path of the reflected light of the main beam and the reflected light of the sub beam group from the optical path of the main beam and the sub beam group. The phase filter is provided between the objective lens and the photodetector, and is a straight line that passes through the optical axis at least in a plane perpendicular to the optical axis of the reflected light from the optical recording medium and corresponds to the direction of the information track. It has the divided | segmented 1st area | region and 2nd area | region. This phase filter gives a phase difference of 180 ° between the reflected light from the optical recording medium that passes through the first region and the reflected light from the optical recording medium that passes through the second region.

  In another aspect of the present invention, an optical information recording / reproducing apparatus includes an optical head device and a differential push-pull signal calculation unit. The optical head device includes a diffractive optical element, an objective lens, a photodetector, a light separation unit, and a phase filter. The diffractive optical element generates a main beam and a sub beam group from the emitted light emitted from the light source. The objective lens collects the main beam and the sub beam group on the selected recording layer of the optical recording medium having a plurality of recording layers on which information tracks are formed. The photodetector receives the reflected light of the main beam and the reflected light of the sub beam group reflected by the selected recording layer. The light separation unit separates the optical path of the reflected light of the main beam and the reflected light of the sub beam group from the optical path of the main beam and the sub beam group. The phase filter is provided between the objective lens and the photodetector, and is a straight line that passes through the optical axis at least in a plane perpendicular to the optical axis of the reflected light from the optical recording medium and corresponds to the direction of the information track. It has the divided | segmented 1st area | region and 2nd area | region. This phase filter gives a phase difference of 180 ° between the reflected light from the optical recording medium that passes through the first region and the reflected light from the optical recording medium that passes through the second region. The differential push-pull signal calculation unit calculates a differential push-pull signal according to the output from the photodetector. The differential push-pull signal is a difference signal between the push-pull signal based on the main beam and the push-pull signal based on the sub beam group.

The objects, effects, and features of the present invention will become more apparent from the description of the embodiments in conjunction with the accompanying drawings.
FIG. 1 is a diagram showing a main part of a conventional optical head device. FIG. 2 is a plan view of a diffractive optical element used in a conventional optical head device. FIG. 3 is a diagram showing a pattern of a light receiving portion of a photodetector used in a conventional optical head device and an arrangement of light spots on the photodetector. FIG. 4 is a diagram showing the configuration of the optical head device according to the first embodiment of the present invention. FIG. 5 is a plan view of the photodetector according to the first embodiment of the present invention. 6A and 6B are a plan view and a cross-sectional view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 7 is a diagram showing the pattern of the light receiving part of the photodetector of the optical head device according to the first embodiment of the present invention and the arrangement of the light spots on the photodetector. 8A to 8C are a plan view and a cross-sectional view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 9 is a diagram showing the pattern of the light receiving portion of the photodetector of the optical head device according to the first embodiment of the present invention and the arrangement of the light spots on the photodetector. 10A to 10C are a plan view and a cross-sectional view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 11 is a diagram showing the pattern of the light receiving portion of the photodetector of the optical head device according to the first embodiment of the present invention and the arrangement of the light spots on the photodetector. 12A and 12B are diagrams showing an example of observation of a push-pull signal for an optical recording medium having two recording layers by a conventional general optical head device. 13A and 13B are diagrams showing an example of observation of a push-pull signal for an optical recording medium having two recording layers by the optical head device according to the first embodiment of the present invention. 14A to 14C are a plan view and a sectional view of the phase filter of the optical head device according to the first embodiment of the present invention. 15A to 15C are a plan view and a cross-sectional view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 16 is a plan view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 17 is a diagram showing the configuration of the optical head device according to the second embodiment of the present invention. 18A and 18B are a plan view and a sectional view of the phase filter of the optical head device according to the second embodiment of the present invention. 19A to 19C are a plan view and a cross-sectional view of a phase filter of an optical head device according to a second embodiment of the present invention. 20A to 20C are a plan view and a sectional view of the phase filter of the optical head device according to the second embodiment of the present invention. FIG. 21 is a plan view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 22 is a plan view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 23 is a plan view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 24 is a plan view of the phase filter of the optical head device according to the first embodiment of the present invention. FIG. 25 is a diagram showing a configuration of an optical information recording / reproducing apparatus according to the third embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 4 shows the configuration of the optical head device according to the first embodiment of the present invention. The optical head device 61 includes a semiconductor laser 1, a collimator lens 2, a diffractive optical element 3, a polarizing beam splitter 4, a quarter wavelength plate 5, an objective lens 6, a phase filter 11, a cylindrical lens 8, a convex lens 9, and a photodetector 10. It comprises. Light emitted from the semiconductor laser 1 that is a light source is converted from divergent light into parallel light by a collimator lens 2, and is split by a diffractive optical element 3 into a main beam that is zero-order light and two sub-beams that are ± first-order diffracted light. The The transmittance of the zero-order light in the diffractive optical element 3 is, for example, about 87.5%, and the diffraction efficiency of ± first-order diffracted light is, for example, about 5.1%. The main beam and the two sub beams are incident on the polarizing beam splitter 4 as the light separating means as P-polarized light and almost 100% are transmitted. The quarter-wave plate 5 converts the linearly-polarized light into circularly-polarized light. Is converted from parallel light into convergent light and condensed on the recording layer of the disk 7 which is an optical recording medium. Here, the 0th-order light from the diffractive optical element 3 is collected on a predetermined information track, and the + 1st-order diffracted light from the diffractive optical element 3 is intermediate between the predetermined information track and the information track adjacent to the outer periphery thereof. The -1st-order diffracted light from the diffractive optical element 3 is collected and collected in the middle between a predetermined information track and an information track adjacent to the inner periphery thereof. The reflected light of the main beam and the reflected light of the two sub beams reflected by the recording layer of the disk 7 are converted from diverging light to parallel light by the objective lens 6, and from the circularly polarized light to the forward path and the polarization direction by the quarter wavelength plate 5. Is converted into orthogonal linearly polarized light, is incident on the polarizing beam splitter 4 as S-polarized light, is reflected by almost 100%, passes through the phase filter 11, is given astigmatism by the cylindrical lens 8, and is collimated by the convex lens 9. Is converted into convergent light and received by the photodetector 10.

  FIG. 5 shows a plan view of the light receiving portion of the photodetector 10. The photodetector 10 is provided in the middle of two focal lines of a lens system constituted by the cylindrical lens 8 and the convex lens 9. The photodetector 10 includes three light receiving blocks that receive reflected light of the main beam and the sub beam, and each light receiving block has two dividing lines corresponding to a direction perpendicular to and parallel to the information track direction of the disk 7. It includes four light receiving parts separated by. Therefore, the light receiving block that receives the reflected light of the main beam that is the 0th order light from the diffractive optical element 3 includes the light receiving parts 13a to 13d, and the reflected light of the sub beam that is the + 1st order diffracted light from the diffractive optical element 3 is received. The light receiving blocks that receive light include light receiving portions 13e to 13h, and the light receiving blocks that receive the reflected light of the sub beam, which is the −1st order diffracted light from the diffractive optical element 3, include light receiving portions 13i to 13l.

  As the phase filter 11, any one of the phase filter 11a shown in FIGS. 6A and 6B, the phase filter 11b shown in FIGS. 8A to 8C, and the phase filter 11c shown in FIGS. 10A to 10C is used.

  6A is a plan view of the phase filter 11a, and FIG. 6B is a cross-sectional view of the phase filter 11a. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 7, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 11a has two regions, a region 15a to a region 15b, on the surface of the substrate. The thickness of the region 15a is thinner than that of the region 15b. When the wavelength of the semiconductor laser 1 is λ and the refractive index of the substrate is n, the difference h between the thickness of the region 15a and the thickness of the region 15b is h = 0.5λ / (n−1). Is set to At this time, a phase difference of 180 ° is given between the reflected light from the disc 7 that passes through the region 15a and the reflected light from the disc 7 that passes through the region 15b.

  FIG. 7 shows the arrangement of the light spots on the photodetector 10 when the phase filter 11a is used. The light spot 14a corresponds to the reflected light of the main beam, which is zero-order light from the diffractive optical element 3, and is formed on a light receiving block including the light receiving portions 13a to 13d. The light spot 14b corresponds to the reflected light of the sub beam which is the + 1st order diffracted light from the diffractive optical element 3, and is formed on the light receiving block including the light receiving portions 13e to 13h. The light spot 14c corresponds to the reflected light of the sub beam which is the −1st order diffracted light from the diffractive optical element 3, and is formed on the light receiving block including the light receiving portions 13i to 13l.

  Here, due to the action of the lens system constituted by the cylindrical lens 8 and the convex lens 9, the light spot 14a to the light spot 14c are perpendicular to the information track direction of the disk 7 with respect to the light before entering the lens system. The intensity distributions in the directions corresponding to the parallel directions are interchanged with each other. A main push-pull signal is detected based on outputs from the light receiving units 13a to 13d, and a sub push-pull signal is detected based on outputs from the light receiving units 13e to 13l. Further, a mark / space signal recorded on the disk 7 is detected based on outputs from the light receiving portions 13a to 13d.

  The light spot 14d indicated by a broken line in the figure corresponds to the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers. The phase filter 11a gives a 180 ° phase difference between the reflected light from the disk 7 that passes through the region 15a and the reflected light from the disk 7 that passes through the region 15b. Therefore, the reflected light of the main beam from the non-target layer that has entered the phase filter 11a is affected by diffraction in a straight line that separates the region 15a and the region 15b after transmission, and becomes a light spot 14d. The phase difference between the light transmitted through the region 15a and the light transmitted through the region 15b is close to 180 ° in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. For this reason, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track is weak.

  Here, the light receiving unit 13a to the light receiving unit 13l are located in the vicinity of a straight line that passes through the optical axis and corresponds to the direction of the information track. At this time, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13a to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are hardly disturbed.

  The reflected light of the main beam from the target layer incident on the phase filter 11a is also affected by diffraction on a straight line that separates the region 15a and the region 15b after transmission, and becomes a light spot 14a. The phase difference between the light transmitted through the region 15a and the light transmitted through the region 15b is close to 180 ° in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. For this reason, the intensity of the reflected light of the main beam from the target layer in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track is weak. However, the phase difference between the light transmitted through the region 15a and the light transmitted through the region 15b approaches 0 ° as the distance from the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track increases. Therefore, the intensity of the reflected light of the main beam from the target layer increases as the distance from the vicinity of the straight line corresponding to the direction of the information track passes through the optical axis.

  Here, a straight line passing through the optical axis and corresponding to the direction of the information track corresponds to a dividing line separating the light receiving portions 13a to 13b and the light receiving portions 13c to 13d. At this time, the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction although the intensity distribution changes. Therefore, the quality of the mark / space signal recorded on the target layer, which is detected based on the outputs from the light receiving units 13a to 13d, does not deteriorate.

  8A is a plan view of the phase filter 11b, and FIGS. 8B and 8C are cross-sectional views of the phase filter 11b. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 7, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 11b has ten regions 15c to 15l on the surface of the substrate. The thicknesses of the regions 15c, 15e, and 15g are smaller than the thicknesses of the regions 15d, 15f, and 15h. When the wavelength of the semiconductor laser 1 is λ and the refractive index of the substrate is n, the difference h between the thicknesses of the regions 15c, 15e, and 15g and the thicknesses of the regions 15d, 15f, and 15h is h = 0.5λ / (n−1). At this time, a phase difference of 180 ° is given between the reflected light from the disk 7 that passes through the areas 15c, 15e, and 15g and the reflected light from the disk 7 that passes through the areas 15d, 15f, and 15h. It is done.

  Note that the thicknesses of the regions 15i to 15l are the average of the thicknesses of the regions 15c, 15e, and 15g and the thicknesses of the regions 15d, 15f, and 15h. At this time, a 90 ° phase difference is given between the reflected light from the disk 7 that passes through the areas 15i to 15l and the reflected light from the disk 7 that passes through the areas 15c, 15e, and 15g. Furthermore, a phase difference of 90 ° is also given between the reflected light from the disk 7 that passes through the areas 15i to 15l and the reflected light from the disk 7 that passes through the areas 15d, 15f, and 15h.

  FIG. 9 shows the arrangement of the light spots on the photodetector 10 when the phase filter 11b is used. The light spot 14e corresponds to the reflected light of the main beam, which is zero-order light from the diffractive optical element 3, and is formed on a light receiving block including the light receiving portions 13a to 13d. The light spot 14f corresponds to the reflected light of the sub beam which is the + 1st order diffracted light from the diffractive optical element 3, and is formed on the light receiving block including the light receiving portions 13e to 13h. The light spot 14g corresponds to the reflected light of the sub beam that is the −1st order diffracted light from the diffractive optical element 3, and is formed on the light receiving block including the light receiving portions 13i to 13l.

  Here, due to the action of the lens system constituted by the cylindrical lens 8 and the convex lens 9, the light spot 14e to the light spot 14g are perpendicular to the information track direction of the disk 7 with respect to the light before entering the lens system. The intensity distributions in the directions corresponding to the parallel directions are interchanged with each other. A main push-pull signal and a sub push-pull signal are detected based on outputs from the light receiving unit 13a to the light receiving unit 13d and outputs from the light receiving unit 13e to the light receiving unit 13l, respectively. Further, a mark / space signal recorded on the disk 7 is detected based on outputs from the light receiving portions 13a to 13d.

  The light spot 14h indicated by a broken line in the figure corresponds to the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers. The phase filter 11b has a phase difference of 180 ° between the reflected light from the disk 7 that passes through the areas 15c, 15e, and 15g and the reflected light from the disk 7 that passes through the areas 15d, 15f, and 15h. give. Therefore, the reflected light of the main beam from the non-target layer incident on the phase filter 11b is transmitted at the boundary between the region 15c and the region 15d, the boundary between the region 15e and the region 15f, and the boundary between the region 15g and the region 15h. Under the influence of diffraction, the light spot becomes 14h. The light transmitted through the region 15c, the region 15e, and the region 15g and the light transmitted through the region 15d, the region 15f, and the region 15h interfere with each other, and the phase difference therebetween is a straight line corresponding to the direction of the information track through the optical axis. It is close to 180 ° in the vicinity. Therefore, in the portion where the light transmitted through the region 15c, the region 15e, and the region 15g and the light transmitted through the region 15d, the region 15f, and the region 15h interfere with each other, in the vicinity of a straight line that passes through the optical axis and corresponds to the information track direction. The intensity of the reflected light of the main beam from the non-target layer is weak.

  Here, the light receiving unit 13a to the light receiving unit 13d are located at portions where light transmitted through the region 15c and light transmitted through the region 15d interfere with each other in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. To do. The light receivers 13e to 13h are located in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track where light transmitted through the region 15e and light transmitted through the region 15f interfere with each other. The light receivers 13i to 13l are located in the vicinity of a straight line that passes through the optical axis and corresponds to the direction of the information track, where light transmitted through the region 15g and light transmitted through the region 15h interfere with each other. At this time, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13a to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are hardly disturbed.

  Further, the reflected light of the main beam from the target layer incident on the phase filter 11b is also affected by diffraction in a straight line separating the region 15c, the region 15e, the region 15g, the region 15d, the region 15f, and the region 15h after transmission. It becomes spot 14e. The phase difference between the light transmitted through the regions 15c, 15e, and 15g that interfere with each other and the light transmitted through the regions 15d, 15f, and 15h is a straight line that corresponds to the direction of the information track through the optical axis. It is close to 180 ° in the vicinity. Therefore, in the portion where the light transmitted through the region 15c, the region 15e, and the region 15g and the light transmitted through the region 15d, the region 15f, and the region 15h interfere with each other, in the vicinity of a straight line that passes through the optical axis and corresponds to the information track direction. The intensity of the reflected light of the main beam from the target layer is weak. However, the phase difference between the light transmitted through the regions 15c, 15e, and 15g that interfere with each other and the light transmitted through the regions 15d, 15f, and 15h is a straight line that passes through the optical axis and corresponds to the direction of the information track. As the distance from the vicinity increases, it approaches 0 °. Therefore, in the portion where the light transmitted through the region 15c, the region 15e, and the region 15g and the light transmitted through the region 15d, the region 15f, and the region 15h interfere with each other, from the vicinity of a straight line that passes through the optical axis and corresponds to the information track direction. As the distance increases, the intensity of the reflected light of the main beam from the target layer increases.

  Here, a straight line passing through the optical axis and corresponding to the direction of the information track corresponds to a dividing line separating the light receiving portions 13a to 13b and the light receiving portions 13c to 13d. At this time, the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction although the intensity distribution changes. Therefore, the quality of the mark / space signal recorded on the target layer, which is detected based on the outputs from the light receiving units 13a to 13d, does not deteriorate.

  10A is a plan view of the phase filter 11c, and FIGS. 10B and 10C are cross-sectional views of the phase filter 11c. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 7, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 11c has seven regions of a region 15m to a region 15s on the surface of the substrate. The thicknesses of the regions 15m and 15o are smaller than the thicknesses of the regions 15n and 15p. When the wavelength of the semiconductor laser 1 is λ and the refractive index of the substrate is n, the difference h between the thickness of the region 15m and the region 15o and the thickness of the region 15n and the region 15p is h = 0.5λ / ( n-1). At this time, a phase difference of 180 ° is given between the reflected light from the disk 7 that passes through the areas 15m and 15o and the reflected light from the disk 7 that passes through the areas 15n and 15p.

  The thicknesses of the regions 15q to 15s are the average of the thickness of the regions 15m and 15o and the thickness of the regions 15n and 15p. At this time, a phase difference of 90 ° is given between the reflected light from the disk 7 that passes through the areas 15q to 15s and the reflected light from the disk 7 that passes through the areas 15m and 15o. Further, a 90 ° phase difference is also given between the reflected light from the disk 7 that passes through the areas 15q to 15s and the reflected light from the disk 7 that passes through the areas 15n and 15p.

  FIG. 11 shows the arrangement of the light spots on the photodetector 10 when the phase filter 11c is used. The light spot 14i corresponds to the reflected light of the main beam, which is zero-order light from the diffractive optical element 3, and is formed on a light receiving block including the light receiving portions 13a to 13d. The light spot 14j corresponds to the reflected light of the sub beam which is the + 1st order diffracted light from the diffractive optical element 3, and is formed on the light receiving block including the light receiving portions 13e to 13h. The light spot 14k corresponds to the reflected light of the sub beam that is the −1st order diffracted light from the diffractive optical element 3, and is formed on the light receiving block including the light receiving portions 13i to 13l.

  Here, due to the action of the lens system constituted by the cylindrical lens 8 and the convex lens 9, the light spots 14i to 14k correspond to the intensity distribution in the direction perpendicular to the information track direction of the disk 7 and the parallel direction. The intensity distribution in the direction is switched with respect to the light before entering the lens system. A main push-pull signal is detected based on outputs from the light receiving units 13a to 13d, and a sub push-pull signal is detected based on outputs from the light receiving units 13e to 13l. Further, a mark / space signal recorded on the disk 7 is detected based on outputs from the light receiving portions 13a to 13d.

  The light spot 141 shown by a broken line in the figure corresponds to the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers. The phase filter 11c gives a phase difference of 180 ° between the reflected light from the disk 7 that passes through the areas 15m and 15o and the reflected light from the disk 7 that passes through the areas 15n and 15p. Therefore, the reflected light of the main beam from the non-target layer that has entered the phase filter 11c is affected by diffraction in a straight line that separates the region 15m, the region 15o from the region 15n, and the region 15p after transmission, and becomes a light spot 141. . The phase difference between the light transmitted through the regions 15m and 15o and the light transmitted through the regions 15n and 15p is close to 180 ° in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. . Therefore, in the part where the light transmitted through the region 15m and the region 15o and the light transmitted through the region 15n and the region 15p interfere with each other, the main from the non-target layer in the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track. The intensity of the reflected beam is weak.

  Here, the light receiving unit 13e to the light receiving unit 13h are located at portions where light transmitted through the region 15m and light transmitted through the region 15n interfere with each other in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. To do. The light receivers 13i to 13l are located in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track where light transmitted through the region 15o and light transmitted through the region 15p interfere with each other. At this time, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13e to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are hardly disturbed.

  Further, the reflected light of the main beam from the target layer incident on the phase filter 11c is also affected by diffraction at the boundary between the region 15m and the region 15n and the boundary between the region 15o and the region 15p after transmission, and becomes a light spot 14i. . The light transmitted through the regions 15m and 15o and the light transmitted through the regions 15n and 15p interfere with each other, and the phase difference therebetween is 180 in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. Close to °. Therefore, in the part where the light transmitted through the region 15m and the region 15o and the light transmitted through the region 15n and the region 15p interfere with each other, the main beam from the target layer in the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track. The intensity of reflected light is weak. However, the phase difference between the light transmitted through the region 15m and the region 15o and the light transmitted through the region 15n and the region 15p approaches 0 ° as the distance from the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track increases. Become. Therefore, in the part where the light transmitted through the region 15m and the region 15o and the light transmitted through the region 15n and the region 15p interfere with each other, the distance from the target layer increases as the distance from the vicinity of the straight line that passes through the optical axis and corresponds to the direction of the information track. The intensity of the reflected light from the main beam is increased. Here, a straight line passing through the optical axis and corresponding to the direction of the information track corresponds to a dividing line separating the light receiving portions 13a to 13b and the light receiving portions 13c to 13d. At this time, the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction although the intensity distribution changes. Therefore, the quality of the mark / space signal recorded on the target layer, which is detected based on the outputs from the light receiving units 13a to 13d, does not deteriorate.

  The levels of the voltage signals that are outputs from the light receiving units 13a to 13l of the photodetector 10 are represented by V13a to V13l, respectively. At this time, an astigmatism signal MAS for the main beam, an astigmatism signal SAS for the sub beam, a push-pull signal MPP for the main beam, a push-pull signal SPP for the sub beam, and a sum signal MSUM for the main beam are respectively given by the following equations.

MAS = (V13a + V13d)-(V13b + V13c)
SAS = (V13e + V13h + V13i + V13l) − (V13f + V13g + V13j + V13k)
MPP = (V13a + V13b)-(V13c + V13d)
SPP = (V13e + V13f + V13i + V13j) − (V13g + V13h + V13k + V13l)
MSUM = V13a + V13b + V13c + V13d

The differential astigmatism signal DAS that is the source of the focus error signal is
DAS = MAS + KFE x SAS (KFE is a constant)
Obtained from the operation. The differential push-pull signal DPP that is the source of the track error signal is
DPP = MPP-KTE × SPP (KTE is a constant)
Obtained from the operation. A reproduction signal which is a mark / space signal recorded on the disk 7 is obtained from a high-frequency component of MSUM.

  FIGS. 12A and 12B show examples of observation of push-pull signals obtained from an optical recording medium having two recording layers by a conventional general optical head device. FIG. 12A shows the main push-pull signal and the sub push-pull signal for the layer closer to the objective lens (first layer), and FIG. 12B shows the main push-pull signal for the layer farther from the objective lens (second layer). Signals and sub push-pull signals are shown. From the figure, it can be seen that the sub push-pull signal is disturbed.

  In contrast, FIGS. 13A and 13B show examples of observation of push-pull signals obtained from an optical recording medium having two recording layers by the optical head device of the present invention. FIG. 13A shows the main push-pull signal and the sub push-pull signal for the layer closer to the objective lens (first layer), and FIG. 13B shows the main push-pull signal for the layer farther from the objective lens (second layer) and A sub push-pull signal is shown. From the figure, it can be seen that the sub push-pull signal is not disturbed.

  In the first embodiment of the present invention, as the phase filter 11, the phase filter 11d shown in FIGS. 14A to 14C and the phase filter 11e shown in FIGS. 15A to 15C may be used.

  14A is a plan view of the phase filter 11d, and FIGS. 14B and 14C are cross-sectional views of the phase filter 11d. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 7, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 11d has eight regions of regions 18a to 18h on the surface of the substrate. The height of the region 18a, the region 18d, the region 18f, and the region 18g is lower than the height of the region 18b, the region 18c, the region 18e, and the region 18h. When the wavelength of the semiconductor laser 1 is λ and the refractive index of the substrate is n, the difference h between the height of the region 18a, the region 18d, the region 18f, and the region 18g and the height of the region 18b, the region 18c, the region 18e, and the region 18h is H = 0.5λ / (n−1). At this time, 180 ° between the reflected light from the disk 7 that passes through the areas 18a, 18d, 18f, and 18g and the reflected light from the disk 7 that passes through the areas 18b, 18c, 18e, and 18h. Is given.

  The reflected light of the main beam from the non-target layer that has entered the phase filter 11d is a straight line that separates the region 18e, the region 18a, the region 18c, the region 18g, the region 18f, the region 18b, the region 18d, and the region 18h after transmission. Influence of diffraction on a straight line separating the region 18b from the region 18c, the region 18d, a straight line separating the region 18e, the region 18f from the region 18a, and the region 18b, and a straight line separating the region 18c, the region 18d from the region 18g, and the region 18h. Receive. The phase difference between the light transmitted through the regions 18e, 18a, 18c, and 18g that interfere with each other and the light transmitted through the regions 18f, 18b, 18d, and 18h is the direction of the information track through the optical axis. It is close to 180 ° in the vicinity of the straight line corresponding to. For this reason, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track is weak. The phase difference between the light transmitted through the regions 18a and 18b and the light transmitted through the regions 18c and 18d is 180 ° in the vicinity of a straight line passing through the optical axis and corresponding to the direction orthogonal to the information track. Close to. For this reason, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of a straight line corresponding to the direction orthogonal to the information track passing through the optical axis is weak. The phase difference between the light transmitted through the regions 18e and 18f that interfere with each other and the light transmitted through the regions 18a and 18b is in the vicinity of a straight line that passes through the portion above the optical axis and corresponds to the direction orthogonal to the information track. Is close to 180 °. For this reason, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line corresponding to the direction orthogonal to the information track passing through the portion above the optical axis is weak. The phase difference between the light transmitted through the regions 18c and 18d that interfere with each other and the light transmitted through the regions 18g and 18h is in the vicinity of a straight line that passes through the portion below the optical axis and corresponds to the direction orthogonal to the information track. Is close to 180 °. Therefore, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line corresponding to the direction orthogonal to the information track passing through the portion below the optical axis is weak.

  Here, the light receiving unit 13a to the light receiving unit 13d are located in the vicinity of the intersection of a straight line corresponding to the direction of the information track passing through the optical axis and a straight line corresponding to the direction passing through the optical axis and orthogonal to the information track. The light receiving units 13e to 13h are located in the vicinity of the intersection of a straight line corresponding to the direction of the information track passing through the optical axis and a straight line corresponding to the direction passing through the portion above the optical axis and orthogonal to the information track. The light receiving units 13i to 13l are located in the vicinity of the intersection of a straight line that passes through the optical axis and corresponds to the direction of the information track, and a straight line that passes through a portion below the optical axis and corresponds to the direction orthogonal to the information track. At this time, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13a to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are hardly disturbed.

  Further, after the reflected light of the main beam from the target layer incident on the phase filter 11d is also transmitted, a straight line that separates the region 18e, the region 18a, the region 18c, the region 18g, the region 18f, the region 18b, the region 18d, and the region 18h, the region 18a Effects of diffraction on a straight line separating the region 18b from the region 18c and the region 18d, a straight line separating the region 18e, the region 18f from the region 18a and the region 18b, and a straight line separating the region 18c, the region 18d from the region 18g and the region 18h Receive. However, all the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction although the intensity distribution is changed. Therefore, the quality of the mark / space signal recorded on the target layer, which is detected based on the outputs from the light receiving units 13a to 13d, does not deteriorate.

  15A is a plan view of the phase filter 11e, and FIGS. 15B and 15C are cross-sectional views of the phase filter 11e. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 7, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 11e has six regions 18i to 18n on the surface of the substrate. The heights of the region 18i, the region 18l, and the region 18n are lower than the heights of the region 18j, the region 18k, and the region 18m. When the wavelength of the semiconductor laser 1 is λ and the refractive index of the substrate is n, the difference h between the heights of the regions 18i, 18l, and 18n and the heights of the regions 18j, 18k, and 18m is h = 0.5λ. / (N-1). At this time, a phase difference of 180 ° is given between the reflected light from the disk 7 that passes through the areas 18i, 18l, and 18n and the reflected light from the disk 7 that passes through the areas 18j, 18k, and 18m. .

  The reflected light of the main beam from the non-target layer incident on the phase filter 11e is a straight line that separates the region 18k, the region 18i, the region 18m, the region 18l, the region 18j, and the region 18n after transmission, the region 18k, the region 18l, and the region 18i. Are affected by diffraction on a straight line separating the region 18j, a straight line separating the region 18i, the region 18j, the region 18m, and the region 18n. The phase difference between the light transmitted through the regions 18k, 18i, and 18m that interfere with each other and the light transmitted through the regions 18l, 18j, and 18n is in the vicinity of a straight line that passes through the optical axis and corresponds to the information track direction. Is close to 180 °. For this reason, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track is weak. The phase difference between the light transmitted through the region 18k and the region 18l and the light transmitted through the region 18i and the region 18j that interfere with each other is in the vicinity of a straight line that passes through the portion above the optical axis and corresponds to the direction orthogonal to the information track Is close to 180 °. For this reason, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line corresponding to the direction orthogonal to the information track passing through the portion above the optical axis is weak. The phase difference between the light transmitted through the regions 18i and 18j and the light transmitted through the regions 18m and 18n is in the vicinity of a straight line corresponding to the direction perpendicular to the information track through the portion below the optical axis. Is close to 180 °. Therefore, the intensity of the reflected light of the main beam from the non-target layer in the vicinity of the straight line corresponding to the direction orthogonal to the information track passing through the portion below the optical axis is weak.

  Here, the light receiving unit 13a to the light receiving unit 13d are located in the vicinity of a straight line that passes through the optical axis and corresponds to the direction of the information track. The light receiving units 13e to 13h are located in the vicinity of the intersection of a straight line corresponding to the direction of the information track passing through the optical axis and a straight line corresponding to the direction passing through the portion above the optical axis and orthogonal to the information track. The light receiving units 13i to 13l are located in the vicinity of the intersection of a straight line that passes through the optical axis and corresponds to the direction of the information track, and a straight line that passes through a portion below the optical axis and corresponds to the direction orthogonal to the information track. At this time, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13a to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are hardly disturbed.

  Further, the reflected light of the main beam from the target layer incident on the phase filter 11e also passes through the straight line that separates the region 18k, the region 18i, the region 18m, the region 18l, the region 18j, and the region 18n, the region 18k, the region 18l, and the region 18i. Are affected by diffraction on a straight line separating the region 18j, a straight line separating the region 18i, the region 18j, the region 18m, and the region 18n. However, all the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction although the intensity distribution is changed. Therefore, the quality of the mark / space signal recorded on the target layer, which is detected based on the outputs from the light receiving units 13a to 13d, does not deteriorate.

  In the first embodiment of the present invention, the phase filter 11 f shown in FIG. 16 may be used as the phase filter 11.

  FIG. 16 is a plan view of the phase filter 11f. Here, the X direction and the Y direction in the figure correspond to a direction perpendicular to and parallel to the information track direction of the disc 7, respectively. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 11f has two liquid crystal polymer layers of a liquid crystal polymer layer 19a to a liquid crystal polymer layer 19b sandwiched between two substrates. The arrows in the figure indicate the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 19a to the liquid crystal polymer layer 19b. The longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 19a forms an angle of + 45 ° with respect to the X direction, and the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer 19b is −45 with respect to the X direction. It has an angle of °. The liquid crystal polymer layer 19a to the liquid crystal polymer layer 19b have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction. When the refractive index for a polarized component (abnormal light component) parallel to the longitudinal direction of the liquid crystal polymer is ne and the refractive index for a polarized component (ordinary light component) perpendicular to the longitudinal direction is no, ne is smaller than no. Big. When the wavelength of the semiconductor laser 1 is λ, the thickness t of the liquid crystal polymer layer 19a to the liquid crystal polymer layer 19b is set to be t = 0.5λ / (ne−no). That is, the liquid crystal polymer layer 19a to the liquid crystal polymer layer 19b function as a half-wave plate. The reflected light from the disk 7 enters the phase filter 11f as linearly polarized light in the Y-axis direction. At this time, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 19a and the reflected light from the disk 7 that passes through the liquid crystal polymer 19b both become linearly polarized light in the X-axis direction, and 180 ° between them. Is given.

  Furthermore, in the first embodiment of the present invention, a phase filter having eight liquid crystal polymer layers sandwiched between two substrates can be used as the phase filter 11. The eight liquid crystal polymer layers correspond to the eight regions of the region 18a to the region 18h of the phase filter 11d shown in FIGS. The longitudinal direction of the liquid crystal polymer in the regions corresponding to the region 18a, the region 18d, the region 18f, and the region 18g forms an angle of + 45 ° with respect to the X direction, and corresponds to the region 18b, the region 18c, the region 18e, and the region 18h. The longitudinal direction of the liquid crystal polymer in the region is -45 ° with respect to the X direction. The thickness t of the eight liquid crystal polymer layers is set to be t = 0.5λ / (ne−no). The reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. At this time, the reflected light from the disk 7 that transmits the liquid crystal polymer layer corresponding to the region 18a, the region 18d, the region 18f, and the region 18g, and the liquid crystal polymer layer corresponding to the region 18b, the region 18c, the region 18e, and the region 18h. All of the reflected light from the transmitted disk 7 is linearly polarized light in the X-axis direction, and a phase difference of 180 ° is given between them.

  In the first embodiment of the present invention, a phase filter having six liquid crystal polymer layers sandwiched between two substrates can also be used as the phase filter 11. The six liquid crystal polymer layers respectively correspond to the six regions of the region 18i to the region 18n of the phase filter 11e shown in FIGS. The longitudinal direction of the liquid crystal polymer in the region corresponding to the region 18i, the region 18l, and the region 18n forms an angle of + 45 ° with respect to the X direction, and the liquid crystal polymer in the region corresponding to the region 18j, the region 18k, and the region 18m. The longitudinal direction of this is at an angle of −45 ° with respect to the X direction. The thickness t of the six liquid crystal polymer layers is set to be t = 0.5λ / (ne−no). The reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. At this time, the reflected light from the disk 7 that transmits the liquid crystal polymer layer corresponding to the region 18i, the region 18l, and the region 18n, and the light from the disk 7 that transmits the liquid crystal polymer layer corresponding to the region 18j, the region 18k, and the region 18m. All the reflected lights are linearly polarized light in the X-axis direction, and a phase difference of 180 ° is given between them.

  In the optical head device according to the first embodiment of the present invention, the semiconductor laser 1 is used so that an optical recording medium of three kinds of standards of the CD standard, the DVD standard, and the HD DVD standard is used as the disk 7. Instead, a single or a plurality of semiconductor lasers that emit light of three types of wavelengths of 780 nm, 650 nm, and 400 nm corresponding to the respective standards may be used.

  When using optical recording media of three types of standards and using the phase filter 11a shown in FIGS. 6A and 6B as the phase filter 11, the difference h between the thickness of the region 15a and the thickness of the region 15b is: h = 4200 / (n−1) nm or h = 6200 / (n−1) nm. If h is set to be h = 4200 / (n−1) nm, h≈5.4λ / (n−1) for λ = 780 nm and h≈6 for λ = 650 nm. For 5λ / (n−1) and λ = 400 nm, h = 10.5λ / (n−1). At this time, the phase difference given between the reflected light from the disk 7 transmitting through the region 15a and the reflected light from the disk 7 transmitting through the region 15b is approximately 180 ° for λ = 780 nm and λ = 650 nm. Is approximately 180 ° for λ and 180 ° for λ = 400 nm. When h is set to be h = 6200 / (n−1) nm, h≈7.9λ / (n−1) for λ = 780 nm and h for λ = 650 nm. ≈9.5λ / (n−1), and for λ = 400 nm, h = 15.5λ / (n−1). At this time, the phase difference given between the reflected light from the disk 7 transmitting through the region 15a and the reflected light from the disk 7 transmitting through the region 15b is approximately 0 ° for λ = 780 nm and λ = 650 nm. Is approximately 180 ° for λ and 180 ° for λ = 400 nm. Since there is no optical recording medium having two recording layers in the CD standard, for λ = 780 nm, reflected light from the disk 7 that transmits the region 15a and reflected light from the disk 7 that transmits the region 15b The phase difference given during the period may be either 180 ° or 0 °. On the other hand, the DVD standard and the HD DVD standard include an optical recording medium having two recording layers. Therefore, for λ = 650 nm and λ = 400 nm, even if the distance between the target layer and the non-target layer changes, the differential push-pull signal is not disturbed, and the mark / space signal recorded in the target layer Therefore, the phase difference given between the reflected light from the disk 7 that transmits through the region 15a and the reflected light from the disk 7 that transmits through the region 15b needs to be 180 °. When h is set as described above, almost all of these conditions are satisfied.

  When an optical recording medium of three types of standards is used and the phase filter 11f shown in FIG. 16 is used as the phase filter 11, the thickness t of the liquid crystal polymer layer is t = 4200 / (ne-no) nm. Or it sets so that it may become t = 6200 / (ne-no) nm. If t is set to be t = 4200 / (ne−no) nm, t≈5.4λ / (ne−no) for λ = 780 nm and t≈6 for λ = 650 nm. For .lamda..lamda ./ (ne-no) and .lamda. = 400 nm, t = 10.5.lamda ./ (ne-no). At this time, the phase difference given between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 19a and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 19b is almost equal to λ = 780 nm. For 180 °, λ = 650 nm, it is approximately 180 °, and for λ = 400 nm, it is 180 °. If t is set to be t = 6200 / (ne−no) nm, t≈7.9λ / (ne−no) for λ = 780 nm and t for λ = 650 nm. ≈9.5λ / (ne−no), and for λ = 400 nm, t = 15.5λ / (ne−no). At this time, the phase difference given between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 19a and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 19b is almost equal to λ = 780 nm. It is approximately 180 ° for 0 ° and λ = 650 nm, and 180 ° for λ = 400 nm. Since the CD standard does not have an optical recording medium having two recording layers, for λ = 780 nm, the disc reflects light reflected from the disk 7 that transmits the liquid crystal polymer layer 19a and the liquid crystal polymer layer 19b. The phase difference given to the reflected light from 7 may be either 180 ° or 0 °. On the other hand, the DVD standard and the HD DVD standard include an optical recording medium having two recording layers. Therefore, for λ = 650 nm and λ = 400 nm, even if the distance between the target layer and the non-target layer changes, the differential push-pull signal is not disturbed, and the mark / space signal recorded in the target layer In order not to deteriorate the quality of the liquid crystal, the phase difference given between the reflected light from the disk 7 transmitting the liquid crystal polymer 19a and the reflected light from the disk 7 transmitting the liquid crystal polymer 19b needs to be 180 °. There is. When t is set as described above, almost all of these conditions are satisfied.

  FIG. 17 shows the configuration of an optical head device according to the second embodiment of the present invention. The optical head device 62 includes a semiconductor laser 1, a collimator lens 2, a diffractive optical element 3, a polarizing beam splitter 4, a phase filter 12, a quarter wavelength plate 5, an objective lens 6, a cylindrical lens 8, a convex lens 9, and a photodetector 10. It comprises. Light emitted from the semiconductor laser 1 that is a light source is converted from divergent light into parallel light by a collimator lens 2, and is split by a diffractive optical element 3 into a main beam that is zero-order light and two sub-beams that are ± first-order diffracted light. The The transmittance of the zero-order light in the diffractive optical element 3 is, for example, about 87.5%, and the diffraction efficiency of ± first-order diffracted light is, for example, about 5.1%. The main beam and the two sub beams are incident on the polarization beam splitter 4 which is a light separating means as P-polarized light, and almost 100% is transmitted, passes through the phase filter 12, and is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 5. Is converted from parallel light into convergent light by the objective lens 6 and condensed on the recording layer of the disk 7 which is an optical recording medium. Here, the 0th-order light from the diffractive optical element 3 is collected on a predetermined information track, and the + 1st-order diffracted light from the diffractive optical element 3 is intermediate between the predetermined information track and the information track adjacent to the outer periphery thereof. The -1st-order diffracted light from the diffractive optical element 3 is collected and collected in the middle between a predetermined information track and an information track adjacent to the inner periphery thereof. The reflected light of the main beam and the reflected light of the two sub beams reflected by the recording layer of the disk 7 are converted from diverging light to parallel light by the objective lens 6, and from the circularly polarized light to the forward path and the polarization direction by the quarter wavelength plate 5. Is converted into orthogonal linearly polarized light, transmitted through the phase filter 12, incident as S-polarized light on the polarization beam splitter 4, and almost 100% is reflected, given astigmatism by the cylindrical lens 8, and parallel light by the convex lens 9. Is converted into convergent light and received by the photodetector 10.

  As the phase filter 12, any one of the phase filter 12a shown in FIGS. 18A and 18B, the phase filter 12b shown in FIGS. 19A to 19C, and the phase filter 12c shown in FIGS. 20A to 20C is used.

  18A is a plan view of the phase filter 12a, and FIG. 18B is a cross-sectional view of the phase filter 12a. Here, the X direction and Y direction in the figure correspond to the direction perpendicular to and parallel to the information track direction of the disc 7, respectively, and the Z direction corresponds to the optical axis direction. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 12a includes a liquid crystal polymer layer sandwiched between a substrate 16a and a substrate 16b, and the liquid crystal polymer layer is divided into two liquid crystal polymer layers 17a to 17b. The arrows in the figure indicate the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17a to the liquid crystal polymer layer 17b. The longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17a is the Z-axis direction, and the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17b is the Y-axis direction. The liquid crystal polymer layer 17a to the liquid crystal polymer layer 17b have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction of the liquid crystal polymer. When the refractive index for the polarized component (abnormal light component) in the direction parallel to the longitudinal direction is ne and the refractive index for the polarized component (ordinary light component) in the direction perpendicular to the longitudinal direction is no, ne is larger than no. When the wavelength of the semiconductor laser 1 is λ, the thickness t of the liquid crystal polymer layer 17a to the liquid crystal polymer layer 17b is set to be t = 0.5λ / (ne−no). Since the light emitted from the semiconductor laser 1 enters the phase filter 12a as linearly polarized light in the X-axis direction, it becomes ordinary light for the liquid crystal polymer layer 17a and also becomes ordinary light for the liquid crystal polymer layer 17b. At this time, no phase difference is given between the outgoing light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17a and the outgoing light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17b. On the other hand, since the reflected light from the disk 7 enters the phase filter 12a as linearly polarized light in the Y-axis direction, it becomes ordinary light for the liquid crystal polymer layer 17a and becomes abnormal light for the liquid crystal polymer layer 17b. . At this time, a phase difference of 180 ° is given between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17a and the reflected light from the disk 7 that passes through the liquid crystal polymer 17b.

  When the phase filter 12a is used, the arrangement of the light spots on the photodetector 10 is the same as that shown in FIG. In this case, as described in FIG. 7, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13a to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the differential push-pull signal is hardly disturbed. In addition, since all the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction, the quality of the mark / space signal recorded on the target layer does not deteriorate.

  19A is a plan view of the phase filter 12b, and FIGS. 19B and 19C are cross-sectional views of the phase filter 12b. Here, the X direction and Y direction in the figure correspond to the direction perpendicular to and parallel to the information track direction of the disc 7, respectively, and the Z direction corresponds to the optical axis direction. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 12b includes a substrate 16a and a liquid crystal polymer layer sandwiched between the substrates 16b, and the liquid crystal polymer layer is divided into ten portions of a liquid crystal polymer layer 17c to a liquid crystal polymer layer 17l. The arrows in the figure indicate the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17c to the liquid crystal polymer layer 17l. The longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g is the Z-axis direction, and the liquid crystal polymer layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h are included. The longitudinal direction of the liquid crystal polymer is the Y-axis direction. The liquid crystal polymer layer 17c to the liquid crystal polymer layer 17l have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction. When the refractive index for the polarized component (abnormal light component) in the direction parallel to the longitudinal direction is ne and the refractive index for the polarized component (ordinary light component) in the direction perpendicular to the longitudinal direction is no, ne is larger than no. When the wavelength of the semiconductor laser 1 is λ, the thickness t of the liquid crystal polymer layer 17c to the liquid crystal polymer layer 17l is set to be t = 0.5λ / (ne−no).

  Since the light emitted from the semiconductor laser 1 enters the phase filter 12b as linearly polarized light in the X-axis direction, it becomes ordinary light with respect to the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g. The layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h are also ordinary light. At this time, the light emitted from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g, and the liquid crystal polymer layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h No phase difference is given between the transmitted light from the semiconductor laser 1 and the transmitted light. On the other hand, since the reflected light from the disk 7 enters the phase filter 12b as linearly polarized light in the Y-axis direction, it becomes ordinary light for the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g. The polymer layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h become abnormal light. At this time, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g and the liquid crystal polymer layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h are transmitted. A phase difference of 180 ° is given to the reflected light from the disk 7 to be played.

The longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17i to the liquid crystal polymer layer 17l is in the YZ plane, and the angle θ formed with the Z-axis direction is
tan θ = (ne / no) × [(ne + 3no) / (3ne + no)] 1/2
It is set to become. At this time, light emitted from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17i to the liquid crystal polymer layer 17l and from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g. Light emitted from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17i to the liquid crystal polymer layer 17l, and passes through the liquid crystal polymer layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h. No phase difference is given to the light emitted from the semiconductor laser 1 that performs the operation. On the other hand, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17i to the liquid crystal polymer layer 17l and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17c, the liquid crystal polymer layer 17e, and the liquid crystal polymer layer 17g. And the reflected light from the disk 7 that transmits the liquid crystal polymer layer 17i to the liquid crystal polymer layer 17l, and the disk 7 that transmits the liquid crystal polymer layer 17d, the liquid crystal polymer layer 17f, and the liquid crystal polymer layer 17h. A 90 ° phase difference is given to each of the reflected lights.

  When the phase filter 12b is used, the arrangement of the light spots on the photodetector 10 is the same as that shown in FIG. In this case, as described with reference to FIG. 9, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13a to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the differential push-pull signal is hardly disturbed. In addition, since all the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction, the quality of the mark / space signal recorded on the target layer does not deteriorate.

  20A is a plan view of the phase filter 12c, and FIGS. 20B and 20C are cross-sectional views of the phase filter 12c. Here, the X direction and Y direction in the figure correspond to the direction perpendicular to and parallel to the information track direction of the disc 7, respectively, and the Z direction corresponds to the optical axis direction. Further, a circle indicated by a broken line in the figure indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 12c includes a liquid crystal polymer layer sandwiched between a substrate 16a and a substrate 16b, and the liquid crystal polymer layer is divided into seven liquid crystal polymer layers 17m to 17s. The arrows in the figure indicate the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17m to the liquid crystal polymer layer 17s. The longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o is the Z axis direction, and the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17n and the liquid crystal polymer layer 17p is the Y axis direction. is there. The liquid crystal polymer layer 17m to the liquid crystal polymer layer 17s have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction. When the refractive index for the polarized component (abnormal light component) in the direction parallel to the longitudinal direction is ne and the refractive index for the polarized component (ordinary light component) in the direction perpendicular to the longitudinal direction is no, ne is larger than no. When the wavelength of the semiconductor laser 1 is λ, the thickness t of the liquid crystal polymer layer 17m to the liquid crystal polymer layer 17s is set to be t = 0.5λ / (ne−no).

  Since the emitted light from the semiconductor laser 1 enters the phase filter 12c as linearly polarized light in the X-axis direction, it becomes ordinary light for the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o, and the liquid crystal polymer layer 17n and the liquid crystal polymer Even the layer 17p becomes ordinary light. At this time, between the outgoing light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o and the outgoing light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17n and the liquid crystal polymer layer 17p. Is not given a phase difference. On the other hand, since the reflected light from the disk 7 enters the phase filter 12c as linearly polarized light in the Y-axis direction, it becomes ordinary light for the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o, and the liquid crystal polymer layer 17n and the liquid crystal The polymer layer 17p becomes extraordinary light. At this time, 180 light is reflected between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17n and the liquid crystal polymer layer 17p. A phase difference of ° is given.

The longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 17q to the liquid crystal polymer layer 17s is in the YZ plane, and the angle θ formed with the Z-axis direction is
tan θ = (ne / no) × [(ne + 3no) / (3ne + no)] 1/2
It is set to become. At this time, between the outgoing light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17q to the liquid crystal polymer layer 17s and the outgoing light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o. , And the emitted light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17q to the liquid crystal polymer layer 17s and the emitted light from the semiconductor laser 1 that passes through the liquid crystal polymer layer 17n and the liquid crystal polymer layer 17p. In any case, no phase difference is given. On the other hand, between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17q to the liquid crystal polymer layer 17s, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17m and the liquid crystal polymer layer 17o, and the liquid crystal Between the reflected light from the disk 7 that passes through the polymer layer 17q to the liquid crystal polymer layer 17s and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17n and the liquid crystal polymer layer 17p, both are 90 A phase difference of ° is given.

  When the phase filter 12c is used, the arrangement of the light spots on the photodetector 10 is the same as that shown in FIG. In this case, as described in FIG. 11, the reflected light of the main beam from the non-target layer hardly enters the light receiving unit 13e to the light receiving unit 13l due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the differential push-pull signal is hardly disturbed. In addition, since all the reflected light of the main beam from the target layer is incident on the light receiving unit 13a to the light receiving unit 13d regardless of the influence of diffraction, the quality of the mark / space signal recorded on the target layer does not deteriorate.

  In the second embodiment of the present invention, a phase filter having eight liquid crystal polymer layers sandwiched between two substrates can be used as the phase filter 12. The eight liquid crystal polymer layers correspond to the eight regions of the region 18a to the region 18h of the phase filter 11d shown in FIGS. The longitudinal direction of the liquid crystal polymer included in the liquid crystal polymer layer corresponding to the region 18a, the region 18d, the region 18f, and the region 18g is the Z-axis direction, and the liquid crystal polymer layer corresponding to the region 18b, the region 18c, the region 18e, and the region 18h. The longitudinal direction of the liquid crystal polymer contained in is the Y-axis direction. The thickness t of the eight liquid crystal polymer layers is set to be t = 0.5λ / (ne−no).

  Since the light emitted from the semiconductor laser 1 enters the phase filter as linearly polarized light in the X-axis direction, the normal light, the region 18b, and the region are applied to the liquid crystal polymer layers corresponding to the regions 18a, 18d, 18f, and 18g. The liquid crystal polymer layer corresponding to the region 18c, the region 18e, and the region 18h becomes normal light. At this time, the light emitted from the semiconductor laser 1 that passes through the liquid crystal polymer layer corresponding to the region 18a, the region 18d, the region 18f, and the region 18g, and the liquid crystal polymer corresponding to the region 18b, the region 18c, the region 18e, and the region 18h. No phase difference is given to the light emitted from the semiconductor laser 1 that passes through the layer. On the other hand, the reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. Therefore, ordinary light is applied to the liquid crystal polymer layers corresponding to the regions 18a, 18d, 18f and 18g, and extraordinary light is applied to the liquid crystal polymer layers corresponding to the regions 18b, 18c, 18e and 18h. It becomes. At this time, the reflected light from the disk 7 that passes through the liquid crystal polymer layer corresponding to the region 18a, region 18d, region 18f, and region 18g and the liquid crystal polymer layer corresponding to the region 18b, region 18c, region 18e, and region 18h. A phase difference of 180 ° is given to the reflected light from the disk 7 that passes through the disk.

  In the second embodiment of the present invention, a phase filter having six liquid crystal polymer layers sandwiched between two substrates can also be used as the phase filter 12. The six liquid crystal polymer layers respectively correspond to the six regions of the region 18i to the region 18n of the phase filter 11e shown in FIGS. The longitudinal direction of the liquid crystal polymer included in the liquid crystal polymer layer corresponding to the region 18i, the region 18l, and the region 18n is the Z-axis direction, and the liquid crystal polymer included in the liquid crystal polymer layer corresponding to the region 18j, the region 18k, and the region 18m. The longitudinal direction is the Y-axis direction. The thickness t of the six liquid crystal polymer layers is set to be t = 0.5λ / (ne−no).

  Since the light emitted from the semiconductor laser 1 enters the phase filter as linearly polarized light in the X-axis direction, the normal light, the region 18j, the region 18k, and the region are applied to the liquid crystal polymer layers corresponding to the regions 18i, 18l, and 18n. The liquid crystal polymer layer corresponding to 18 m becomes ordinary light. At this time, the emitted light from the semiconductor laser 1 that transmits the liquid crystal polymer layer corresponding to the region 18i, the region 18l, and the region 18n and the semiconductor laser that transmits the liquid crystal polymer layer corresponding to the region 18j, the region 18k, and the region 18m. No phase difference is given to the light emitted from 1. On the other hand, since the reflected light from the disk 7 is incident on the phase filter as linearly polarized light in the Y-axis direction, the liquid crystal polymer layers corresponding to the regions 18i, 18l, and 18n are ordinary light, regions 18j, regions 18k, The liquid crystal polymer layer corresponding to the region 18m becomes abnormal light. At this time, the reflected light from the disk 7 that transmits the liquid crystal polymer layer corresponding to the region 18i, the region 18l, and the region 18n and the disk 7 that transmits the liquid crystal polymer layer corresponding to the region 18j, the region 18k, and the region 18m. A phase difference of 180 ° is given to the reflected light.

  In the optical head device according to the second embodiment of the present invention, the semiconductor laser 1 is used so that an optical recording medium of three kinds of standards of the CD standard, the DVD standard, and the HD DVD standard is used as the disk 7. Instead, a single or a plurality of semiconductor lasers that emit light of three types of wavelengths of 780 nm, 650 nm, and 400 nm corresponding to the respective standards may be used.

  When optical recording media of three types of standards are used and the phase filter 12a shown in FIGS. 18A and 18B is used as the phase filter 12, the thickness t of the liquid crystal polymer layer 17a to the liquid crystal polymer layer 17b is t = 4200 / (ne-no) nm or t = 6200 / (ne-no) nm. If t is set to be t = 4200 / (ne−no) nm, t≈5.4λ / (ne−no) for λ = 780 nm and t≈6 for λ = 650 nm. For .lamda..lamda ./ (ne-no) and .lamda. = 400 nm, t = 10.5.lamda ./ (ne-no). At this time, the phase difference given between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17a and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 17b is almost equal to λ = 780 nm. For 180 °, λ = 650 nm, it is approximately 180 °, and for λ = 400 nm, it is 180 °. If t is set to be t = 6200 / (ne−no) nm, t≈7.9λ / (ne−no) for λ = 780 nm and t for λ = 650 nm. ≈9.5λ / (ne−no), and for λ = 400 nm, t = 15.5λ / (ne−no). At this time, the phase difference given between the reflected light from the disk 7 that transmits the liquid crystal polymer 17a and the reflected light from the disk 7 that transmits the liquid crystal polymer 17b is approximately 0 ° with respect to λ = 780 nm. Λ = 650 nm is approximately 180 °, and λ = 400 nm is 180 °. Since there is no optical recording medium having two recording layers in the CD standard, for λ = 780 nm, the reflected light from the disk 7 that transmits the liquid crystal polymer 17a and the disk 7 that transmits the liquid crystal polymer 17b are used. The phase difference given to the reflected light may be either 180 ° or 0 °. On the other hand, the DVD standard and the HD DVD standard include an optical recording medium having two recording layers. Therefore, for λ = 650 nm and λ = 400 nm, even if the distance between the target layer and the non-target layer changes, the differential push-pull signal is not disturbed, and the mark / space signal recorded in the target layer Therefore, the phase difference given between the reflected light from the disk 7 transmitting the liquid crystal polymer layer 17a and the reflected light from the disk 7 transmitting the liquid crystal polymer layer 17b is 180 °. There is a need to. When t is set as described above, almost all of these conditions are satisfied.

  In the optical head device according to the first embodiment of the present invention, instead of the semiconductor laser 1, an optical recording medium of three kinds of standards of the CD standard, the DVD standard, and the HD DVD standard is used as the disk 7. It is also possible to use a single or a plurality of semiconductor lasers that emit light of three wavelengths of wavelength 780 nm, wavelength 650 nm, and wavelength 400 nm corresponding to the respective standards, and use the phase filter 20 instead of the phase filter 11. . The phase filter 20 may be any of the phase filter 20a shown in FIG. 21, the phase filter 20b shown in FIG. 22, the phase filter 20c shown in FIG. 23, and the phase filter 20d shown in FIG.

  FIG. 21 is a plan view of the phase filter 20a. A circle indicated by a broken line in the drawing indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 20a has 20 liquid crystal polymer layers of a liquid crystal polymer layer 21a to a liquid crystal polymer layer 21t sandwiched between two substrates. The liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction of the liquid crystal polymer. When the refractive index for a polarized component (abnormal light component) parallel to the longitudinal direction of the liquid crystal polymer is ne and the refractive index for a polarized component (ordinary light component) perpendicular to the longitudinal direction is no, ne is smaller than no. Big. On the surfaces of the two substrates on the liquid crystal polymer layer 21a to liquid crystal polymer layer 21t side, the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21a for applying an AC voltage to each of the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t are provided. Electrodes corresponding to each of the molecular layers 21t are formed. When no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t is the Y-axis direction. On the other hand, when an AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t is Y−. A predetermined angle is formed with the Z-axis direction in the Z plane. As the effective value of the alternating voltage applied to the electrodes corresponding to the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t is larger, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t is Y−. The angle formed with the Z-axis direction in the Z plane is small.

  When the disk 7 is a CD standard optical recording medium and the semiconductor laser emits light having a wavelength of 780 nm, an AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t. At this time, no phase difference is given to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t. Since there is no optical recording medium having two recording layers in the CD standard, it is not necessary to give a phase difference to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21t.

  When the disk 7 is a DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 650 nm, the liquid crystal polymer layer 21a, the liquid crystal polymer layer 21g, the liquid crystal polymer layer 21i, the liquid crystal polymer layer 21k, the liquid crystal polymer layer An AC voltage having an effective value of Vd2 is applied to the electrode corresponding to the molecular layer 21m. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 21b, the liquid crystal polymer layer 21h, the liquid crystal polymer layer 21j, the liquid crystal polymer layer 21l, and the liquid crystal polymer layer 21n. An AC voltage having an effective value of Vd1 is applied to the electrodes corresponding to the liquid crystal polymer layer 21c to the liquid crystal polymer layer 21f and the liquid crystal polymer layer 21o to the liquid crystal polymer layer 21t. Here, Vd2 is the liquid crystal polymer layer 21a, the liquid crystal polymer layer 21g, the liquid crystal polymer layer 21i, the liquid crystal polymer layer 21k, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 21m, and the liquid crystal polymer layer. 21b, a liquid crystal polymer layer 21h, a liquid crystal polymer layer 21j, a liquid crystal polymer layer 21l, and a reflected light from the disk 7 that passes through the liquid crystal polymer layer 21n are set so as to give a phase difference of 180 °. The Vd1 is the reflected light from the disk 7 that transmits the liquid crystal polymer layer 21c to the liquid crystal polymer layer 21f and the liquid crystal polymer layer 21o to the liquid crystal polymer layer 21t, the liquid crystal polymer layer 21a, and the liquid crystal polymer layer 21g. The liquid crystal polymer layer 21i, the liquid crystal polymer layer 21k, and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 21m, the liquid crystal polymer layer 21c to the liquid crystal polymer layer 21f, and the liquid crystal polymer layer 21o to liquid crystal Reflected light from the disk 7 that passes through the polymer layer 21t and the liquid crystal polymer layer 21b, liquid crystal polymer layer 21h, liquid crystal polymer layer 21j, liquid crystal polymer layer 21l, and liquid crystal polymer layer 21n from the disk 7 that passes through the polymer layer 21t. The phase difference of 90 ° is set between the reflected light and the reflected light.

  The DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer interval is 55 μm. Considering the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers with a layer interval of 55 μm, the liquid crystal polymer layer 21a and the liquid crystal polymer layer 21b The positions are set so that the light receiving unit 13a to the light receiving unit 13d are positioned at portions where the light transmitted through the liquid crystal polymer layer 21a and the light transmitted through the liquid crystal polymer layer 21b interfere with each other. The positions of the liquid crystal polymer layer 21g, the liquid crystal polymer layer 21h, the liquid crystal polymer layer 21k, and the liquid crystal polymer layer 21l are such that the light that is transmitted through the liquid crystal polymer layer 21g and the liquid crystal polymer layer 21k by the light receiver 13e to 13h. And the liquid crystal polymer layer 21h and the light transmitted through the liquid crystal polymer layer 21l are set so as to be located at portions where they interfere with each other. The positions of the liquid crystal polymer layer 21i, the liquid crystal polymer layer 21j, the liquid crystal polymer layer 21m, and the liquid crystal polymer layer 21n are the light that the light receiving unit 13i to the light receiving unit 13l transmitted through the liquid crystal polymer layer 21i and the liquid crystal polymer layer 21m. And the liquid crystal polymer layer 21j and the light transmitted through the liquid crystal polymer layer 21n are set so as to be located at portions where they interfere with each other.

  When the disk 7 is an optical recording medium of the HD DVD standard and the semiconductor laser emits light having a wavelength of 400 nm, the liquid crystal polymer layer 21a, the liquid crystal polymer layer 21c, the liquid crystal polymer layer 21e, the liquid crystal polymer layer 21k, and the liquid crystal An AC voltage having an effective value of Vh2 is applied to the electrodes corresponding to the polymer layer 21m, the liquid crystal polymer layer 21o, and the liquid crystal polymer layer 21q. An alternating voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 21b, the liquid crystal polymer layer 21d, the liquid crystal polymer layer 21f, the liquid crystal polymer layer 21l, the liquid crystal polymer layer 21n, the liquid crystal polymer layer 21p, and the liquid crystal polymer layer 21r. Not. An AC voltage having an effective value of Vh1 is applied to the electrodes corresponding to the liquid crystal polymer layer 21g to the liquid crystal polymer layer 21j, the liquid crystal polymer layer 21s, and the liquid crystal polymer layer 21t. Here, Vh2 is transmitted through the liquid crystal polymer layer 21a, the liquid crystal polymer layer 21c, the liquid crystal polymer layer 21e, the liquid crystal polymer layer 21k, the liquid crystal polymer layer 21m, the liquid crystal polymer layer 21o, and the liquid crystal polymer layer 21q. Reflected light from the disk 7 and a liquid crystal polymer layer 21b, a liquid crystal polymer layer 21d, a liquid crystal polymer layer 21f, a liquid crystal polymer layer 21l, a liquid crystal polymer layer 21n, a liquid crystal polymer layer 21p, and a liquid crystal polymer layer 21r It is set so that a phase difference of 180 ° is given to the reflected light from the transmitting disk 7. Vh1 is a reflected light from the disk 7 that transmits the liquid crystal polymer layer 21g to the liquid crystal polymer layer 21j, the liquid crystal polymer layer 21s, and the liquid crystal polymer layer 21t, and the liquid crystal polymer layer 21a and the liquid crystal polymer layer 21c. The liquid crystal polymer layer 21e, the liquid crystal polymer layer 21k, the liquid crystal polymer layer 21m, the liquid crystal polymer layer 21o, and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 21q, the liquid crystal polymer layer 21g to the liquid crystal Reflected light from the disk 7 that passes through the polymer layer 21j, the liquid crystal polymer layer 21s, and the liquid crystal polymer layer 21t, the liquid crystal polymer layer 21b, the liquid crystal polymer layer 21d, the liquid crystal polymer layer 21f, and the liquid crystal polymer layer 21l. The liquid crystal polymer layer 21n, the liquid crystal polymer layer 21p, and the liquid crystal polymer layer 21r are set so as to give a 90 ° phase difference to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 21n.

  The HD DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer spacing is 25 μm. The position of the liquid crystal polymer layer 21a to the liquid crystal polymer layer 21f when the reflected light of the main beam from the non-target layer is considered when the disk 7 is an optical recording medium having two recording layers with a layer spacing of 25 μm. The light-receiving portions 13a to 13d pass through the liquid crystal polymer layer 21a, the liquid crystal polymer layer 21c, and the liquid crystal polymer layer 21e, and the liquid crystal polymer layer 21b, the liquid crystal polymer layer 21d, and the liquid crystal polymer layer 21f. It is set so that it may be located in the part which the light which permeate | transmitted mutually interferes. The positions of the liquid crystal polymer layer 21k, the liquid crystal polymer layer 21l, the liquid crystal polymer layer 21o, and the liquid crystal polymer layer 21p are such that the light that is transmitted through the liquid crystal polymer layer 21k and the liquid crystal polymer layer 21o by the light receiving unit 13e to 13h. And the liquid crystal polymer layer 21l and the light transmitted through the liquid crystal polymer layer 21p are set so as to be located at a portion where they interfere with each other. The positions of the liquid crystal polymer layer 21m, the liquid crystal polymer layer 21n, the liquid crystal polymer layer 21q, and the liquid crystal polymer layer 21r are as follows: the light transmitted through the liquid crystal polymer layer 21m and the liquid crystal polymer layer 21q by the light receiving unit 13i to the light receiving unit 13l. And the liquid crystal polymer layer 21n and the light transmitted through the liquid crystal polymer layer 21r are set so as to be located at portions where they interfere with each other.

  FIG. 22 is a plan view of the phase filter 20b. A circle indicated by a broken line in the drawing indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 20b has 15 liquid crystal polymer layers of a liquid crystal polymer layer 22a to a liquid crystal polymer layer 22o sandwiched between two substrates. The liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction of the liquid crystal polymer. When the refractive index for a polarized component (abnormal light component) parallel to the longitudinal direction of the liquid crystal polymer is ne and the refractive index for a polarized component (ordinary light component) perpendicular to the longitudinal direction is no, ne is smaller than no. Big. The liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o side surfaces of the two substrates have a liquid crystal polymer layer 22a to a liquid crystal high layer for applying an AC voltage to each of the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o. Electrodes corresponding to each of the molecular layers 22o are formed. When no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o is the Y-axis direction. On the other hand, when an AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o is Y−. A predetermined angle is formed with the Z-axis direction in the Z plane. As the effective value of the alternating voltage applied to the electrodes corresponding to the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o is larger, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o is Y. -The angle formed with the Z-axis direction in the Z plane is small.

  When the disk 7 is a CD standard optical recording medium and the semiconductor laser emits light having a wavelength of 780 nm, an AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o. At this time, no phase difference is given to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o. Since there is no optical recording medium having two recording layers in the CD standard, it is not necessary to give a phase difference to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22o.

  When the disk 7 is a DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 650 nm, the liquid crystal polymer layer 22a, the liquid crystal polymer layer 22c, the liquid crystal polymer layer 22e, and the liquid crystal polymer layer 22g are supported. An AC voltage having an effective value of Vd2 is applied to the electrode. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 22b, the liquid crystal polymer layer 22d, the liquid crystal polymer layer 22f, and the liquid crystal polymer layer 22h. An AC voltage having an effective value of Vd1 is applied to the electrodes corresponding to the liquid crystal polymer layers 22i to 22o. Here, Vd2 is the liquid crystal polymer layer 22a, the liquid crystal polymer layer 22c, the liquid crystal polymer layer 22e, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 22g, the liquid crystal polymer layer 22b, and the liquid crystal polymer layer. It is set so that a phase difference of 180 ° is given to the reflected light from the disk 7 that passes through 22d, the liquid crystal polymer layer 22f, and the liquid crystal polymer layer 22h. Vd1 is reflected light from the disk 7 that passes through the liquid crystal polymer layer 22i to the liquid crystal polymer layer 22o, the liquid crystal polymer layer 22a, the liquid crystal polymer layer 22c, the liquid crystal polymer layer 22e, and the liquid crystal polymer layer 22g. Between the reflected light from the disk 7 that passes through the liquid crystal polymer layer 22i to the liquid crystal polymer layer 22o, and the reflected light from the disk 7, the liquid crystal polymer layer 22b, the liquid crystal polymer layer 22d, and the liquid crystal polymer. Both are set so that a phase difference of 90 ° is given to the light reflected from the disk 7 that passes through the layer 22f and the liquid crystal polymer layer 22h.

  The DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer interval is 55 μm. Considering the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers with a layer spacing of 55 μm, the liquid crystal polymer layer 22a, the liquid crystal polymer layer 22b, The positions of the liquid crystal polymer layer 22e and the liquid crystal polymer layer 22f are as follows. It is set so as to be located in a portion where the light transmitted through 22f interferes with each other. The positions of the liquid crystal polymer layer 22c, the liquid crystal polymer layer 22d, the liquid crystal polymer layer 22g, and the liquid crystal polymer layer 22h are as follows. And the light transmitted through the liquid crystal polymer layer 22d and the liquid crystal polymer layer 22h are positioned so as to interfere with each other.

  When the disk 7 is an optical recording medium of the HD DVD standard and the semiconductor laser emits light having a wavelength of 400 nm, it corresponds to the liquid crystal polymer layer 22e, the liquid crystal polymer layer 22g, the liquid crystal polymer layer 22i, and the liquid crystal polymer layer 22k. An AC voltage having an effective value of Vh2 is applied to the electrode. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 22f, the liquid crystal polymer layer 22h, the liquid crystal polymer layer 22j, and the liquid crystal polymer layer 22l. An AC voltage having an effective value Vh1 is applied to the electrodes corresponding to the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22d and the liquid crystal polymer layer 22m to the liquid crystal polymer layer 22o. Here, Vh2 is the reflected light from the disk 7 that transmits the liquid crystal polymer layer 22e, the liquid crystal polymer layer 22g, the liquid crystal polymer layer 22i, and the liquid crystal polymer layer 22k, the liquid crystal polymer layer 22f, and the liquid crystal polymer layer. It is set so that a phase difference of 180 ° is given to the reflected light from the disk 7 that passes through 22h, the liquid crystal polymer layer 22j, and the liquid crystal polymer layer 22l. Vh1 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22d and the liquid crystal polymer layer 22m to the liquid crystal polymer layer 22o, the liquid crystal polymer layer 22e, and the liquid crystal polymer layer 22g. Between the liquid crystal polymer layer 22i and the reflected light from the disk 7 that transmits the liquid crystal polymer layer 22k, the liquid crystal polymer layer 22a to the liquid crystal polymer layer 22d and the liquid crystal polymer layer 22m to the liquid crystal polymer layer 22o are transmitted. 90 ° between the reflected light from the disk 7 and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 22f, the liquid crystal polymer layer 22h, the liquid crystal polymer layer 22j, and the liquid crystal polymer layer 22l. The phase difference is set to be given.

  The HD DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer spacing is 25 μm. Considering the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers with a layer spacing of 25 μm, the liquid crystal polymer layer 22e, the liquid crystal polymer layer 22f, and the liquid crystal The positions of the polymer layer 22i and the liquid crystal polymer layer 22j are as follows: the light transmitted through the liquid crystal polymer layer 22e and the liquid crystal polymer layer 22i, the liquid crystal polymer layer 22f, and the liquid crystal polymer layer 22j. It is set so that it is located in the part which the light which permeate | transmitted mutually interferes. The positions of the liquid crystal polymer layer 22g, the liquid crystal polymer layer 22h, the liquid crystal polymer layer 22k, and the liquid crystal polymer layer 22l are such that the light receiving portions 13i to 13l are transmitted through the liquid crystal polymer layer 22g and the liquid crystal polymer layer 22k. And the light transmitted through the liquid crystal polymer layer 22h and the liquid crystal polymer layer 22l are set so as to be located in a portion where they interfere with each other.

  FIG. 23 is a plan view of the phase filter 20c. A circle indicated by a broken line in the drawing indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 20c has twelve liquid crystal polymer layers of a liquid crystal polymer layer 23a to a liquid crystal polymer layer 23l sandwiched between two substrates. The liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction of the liquid crystal polymer. When the refractive index for a polarized component (abnormal light component) parallel to the longitudinal direction of the liquid crystal polymer is ne and the refractive index for a polarized component (ordinary light component) perpendicular to the longitudinal direction is no, ne is smaller than no. Big. The liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l side of the two substrates have liquid crystal polymer layer 23a to liquid crystal high layer for applying an AC voltage to each of the liquid crystal polymer layer 23a to liquid crystal polymer layer 23l. Electrodes corresponding to each of the molecular layers 231 are formed. When no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l is the Y-axis direction. On the other hand, when an AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l is Y−. A predetermined angle is formed with the Z-axis direction in the Z plane. As the effective value of the alternating voltage applied to the electrodes corresponding to the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l is larger, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l is Y. -The angle formed with the Z-axis direction in the Z plane is small.

  When the disk 7 is a CD standard optical recording medium and the semiconductor laser emits light having a wavelength of 780 nm, no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l. At this time, no phase difference is given to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l. Since there is no optical recording medium having two recording layers in the CD standard, it is not necessary to give a phase difference to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l.

  When the disk 7 is a DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 650 nm, the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer An AC voltage having an effective value of Vd2 is applied to the electrodes corresponding to the molecular layer 23j and the liquid crystal polymer layer 23k. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l. Here, Vd2 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23j, and the liquid crystal polymer layer 23k. Between the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23i, and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23l. A phase difference of 180 ° is set.

  The DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer interval is 55 μm. Considering the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers with a layer interval of 55 μm, the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l The position is set as follows. The positions of the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23d are such that the light receiving portions 13a to 13d are located at portions where light transmitted through the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23d interferes with each other. Is set. Further, the positions of the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23e, and the liquid crystal polymer layer 23i are as follows: light transmitted through the liquid crystal polymer layer 23a and light transmitted through the liquid crystal polymer layer 23b. The light receiving portions 13e to 13h are located at portions where the light transmitted through the liquid crystal polymer layer 23e and the liquid crystal polymer layer 23i and the light transmitted through the liquid crystal polymer layer 23f and the liquid crystal polymer layer 23j interfere with each other. Is set as follows. The positions of the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23k, the liquid crystal polymer layer 23h, and the liquid crystal polymer layer 23l are as follows: In the portion where the light transmitted through the liquid crystal polymer layer 23d, the light transmitted through the liquid crystal polymer layer 23g and the liquid crystal polymer layer 23k, and the light transmitted through the liquid crystal polymer layer 23h and the liquid crystal polymer layer 23l interfere with each other. The light receiving units 13i to 13l are set to be positioned.

  When the disc 7 is an optical recording medium of the HD DVD standard and the semiconductor laser emits light having a wavelength of 400 nm, the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, and the liquid crystal An AC voltage having an effective value of Vh2 is applied to the electrodes corresponding to the polymer layer 23j and the liquid crystal polymer layer 23k. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l. Here, Vh2 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23j, and the liquid crystal polymer layer 23k. Between the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23i, and the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23l. A phase difference of 180 ° is set.

  The HD DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer spacing is 25 μm. The position of the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l when the reflected light of the main beam from the non-target layer is considered when the disk 7 is an optical recording medium having two recording layers with a layer spacing of 25 μm. Is set as follows. The positions of the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23h are: the light transmitted through the liquid crystal polymer layer 23a and the liquid crystal polymer layer 23e, the light transmitted through the liquid crystal polymer layer 23b and the liquid crystal polymer layer 23f, and the liquid crystal. The light receiving portions 13a to 13d are positioned at portions where the light transmitted through the polymer layer 23c and the liquid crystal polymer layer 23g and the light transmitted through the liquid crystal polymer layer 23d and the liquid crystal polymer layer 23h interfere with each other. Is set. The positions of the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23j are the liquid crystal polymer layer 23a and the liquid crystal polymer layer 23e. , The light transmitted through the liquid crystal polymer layer 23b and the liquid crystal polymer layer 23f, the light transmitted through the liquid crystal polymer layer 23i, and the light transmitted through the liquid crystal polymer layer 23j interfere with each other. The light receiving units 13e to 13h are set so as to be positioned. The positions of the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23k, and the liquid crystal polymer layer 23l are the liquid crystal polymer layer 23c and the liquid crystal polymer layer 23g. , The light transmitted through the liquid crystal polymer layer 23d and the liquid crystal polymer layer 23h, the light transmitted through the liquid crystal polymer layer 23k, and the light transmitted through the liquid crystal polymer layer 23l interfere with each other. The light receiving units 13i to 13l are set to be positioned.

  FIG. 24 is a plan view of the phase filter 20d. A circle indicated by a broken line in the drawing indicates a circle having a diameter corresponding to the effective diameter of the objective lens 6. The phase filter 20d has ten liquid crystal polymer layers of a liquid crystal polymer layer 23m to a liquid crystal polymer layer 23v sandwiched between two substrates. The liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v have uniaxial refractive index anisotropy in which the direction of the optical axis is the longitudinal direction of the liquid crystal polymer. When the refractive index for a polarized component (abnormal light component) parallel to the longitudinal direction of the liquid crystal polymer is ne and the refractive index for a polarized component (ordinary light component) perpendicular to the longitudinal direction is no, ne is smaller than no. Big. On the surfaces of the two substrates on the liquid crystal polymer layer 23m to liquid crystal polymer layer 23v side, the liquid crystal polymer layer 23m to the liquid crystal high layer for applying an AC voltage to each of the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v are provided. Electrodes corresponding to each of the molecular layers 23v are formed. When no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v is the Y-axis direction. On the other hand, when an AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v is Y−. A predetermined angle is formed with the Z-axis direction in the Z plane. As the effective value of the AC voltage applied to the electrodes corresponding to the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v is larger, the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v is Y. -The angle formed with the Z-axis direction in the Z plane is small.

  When the disk 7 is a CD standard optical recording medium and the semiconductor laser emits light having a wavelength of 780 nm, an AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v. At this time, no phase difference is given to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v. Since there is no optical recording medium having two recording layers in the CD standard, it is not necessary to give a phase difference to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v.

  When the disc 7 is a DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 650 nm, the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23t, the liquid crystal polymer layer An AC voltage having an effective value of Vd2 is applied to the electrode corresponding to the molecular layer 23v. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u. Here, Vd2 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23t, and the liquid crystal polymer layer 23v, and the liquid crystal polymer layer. 23n, a liquid crystal polymer layer 23o, a liquid crystal polymer layer 23q, a liquid crystal polymer layer 23s, and a reflected light from the disk 7 that passes through the liquid crystal polymer layer 23u are set to give a phase difference of 180 °. The

  The DVD standard optical recording medium includes an optical recording medium having two recording layers, and the standard value of the layer interval is 55 μm. Considering the reflected light of the main beam from the non-target layer when the disk 7 is an optical recording medium having two recording layers with a layer spacing of 55 μm, the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v The position is set as follows. The positions of the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23p and the liquid crystal polymer layer 23s to the liquid crystal polymer layer 23t are the light transmitted through the liquid crystal polymer layer 23m, the light transmitted through the liquid crystal polymer layer 23n, and the liquid crystal. The light receiving portions 13e to 13h are positioned at portions where the light transmitted through the polymer layer 23o and the liquid crystal polymer layer 23s and the light transmitted through the liquid crystal polymer layer 23p and the liquid crystal polymer layer 23t interfere with each other. Is set. The positions of the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23q to the liquid crystal polymer layer 23r, and the liquid crystal polymer layer 23u to the liquid crystal polymer layer 23v are as follows: In a portion where the light transmitted through the liquid crystal polymer layer 23n, the light transmitted through the liquid crystal polymer layer 23q and the liquid crystal polymer layer 23u, and the light transmitted through the liquid crystal polymer layer 23r and the liquid crystal polymer layer 23v interfere with each other. The light receiving units 13i to 13l are set to be positioned.

  When the disk 7 is an HD DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 400 nm, the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23t, and the liquid crystal An AC voltage having an effective value of Vh2 is applied to the electrode corresponding to the polymer layer 23v. An AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u. Here, Vh2 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23t, and the liquid crystal polymer layer 23v, and the liquid crystal polymer layer. 23n, a liquid crystal polymer layer 23p, a liquid crystal polymer layer 23r, a liquid crystal polymer layer 23s, and a reflected light from the disk 7 that passes through the liquid crystal polymer layer 23u are set to give a phase difference of 180 °. The

  The HD DVD standard includes an optical recording medium having two recording layers, and the standard value of the layer spacing is 25 μm. The position of the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v when the reflected light of the main beam from the non-target layer is considered when the disk 7 is an optical recording medium having two recording layers with a layer spacing of 25 μm. Is set as follows. The positions of the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23t are the light transmitted through the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23o, and the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23p, The light receiving portions 13e to 13h are positioned at portions where the light transmitted through the liquid crystal polymer layer 23r, the light transmitted through the liquid crystal polymer layer 23s, and the light transmitted through the liquid crystal polymer layer 23t interfere with each other. Is set. The positions of the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23o to the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23r, and the liquid crystal polymer layer 23u to the liquid crystal polymer layer 23v are as follows. The light transmitted through the liquid crystal polymer layer 23o and the liquid crystal polymer layer 23q, the light transmitted through the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23p and the liquid crystal polymer layer 23r, and the light transmitted through the liquid crystal polymer layer 23u. And the light receiving portions 13i to 13l are set in portions where the light transmitted through the liquid crystal polymer layer 23v interferes with each other.

  In the optical head device according to the first embodiment of the present invention, when no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l as the phase filter 20c, the liquid crystal polymer layer 23a to A phase filter in which the longitudinal direction of the liquid crystal polymer contained in the liquid crystal polymer layer 23l forms an angle of + 45 ° or −45 ° with respect to the X direction can also be used.

  When the disk 7 is a CD standard optical recording medium and the semiconductor laser emits light having a wavelength of 780 nm, no AC voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l. At this time, no phase difference is given to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a to the liquid crystal polymer layer 23l.

  When the disk 7 is a DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 650 nm, the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer An AC voltage having an effective value of Vd3 is applied to the electrodes corresponding to the molecular layer 23j and the liquid crystal polymer layer 23k. An AC voltage having an effective value of Vd4 is applied to the electrodes corresponding to the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l. The The reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. Here, Vd3 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23j, and the liquid crystal polymer layer 23k. The phase difference of 180 ° is set between the extraordinary light component and the ordinary light component. Also, Vd4 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l. The phase difference of 540 ° is set between the extraordinary light component and the ordinary light component. However, the extraordinary light component and the ordinary light component are the polarization component in the direction parallel to the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer and the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer, respectively. It is a polarization component in a direction perpendicular to. At this time, the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23j, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23k, and the liquid crystal height The reflected light from the disk 7 that passes through the molecular layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l is all in the X-axis direction. It becomes linearly polarized light, and a phase difference of 180 ° is given between them.

  When the disc 7 is an optical recording medium of the HD DVD standard and the semiconductor laser emits light having a wavelength of 400 nm, the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, and the liquid crystal An AC voltage having an effective value of Vh3 is applied to the electrodes corresponding to the polymer layer 23j and the liquid crystal polymer layer 23k. An AC voltage having an effective value of Vh4 is applied to the electrodes corresponding to the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l. The The reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. Here, Vh3 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23j, and the liquid crystal polymer layer 23k. The phase difference of 180 ° is set between the extraordinary light component and the ordinary light component. Further, Vh4 is the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l. The phase difference of 540 ° is set between the extraordinary light component and the ordinary light component. However, the extraordinary light component and the ordinary light component are the polarization component in the direction parallel to the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer and the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer, respectively. It is a polarization component in a direction perpendicular to. At this time, the liquid crystal polymer layer 23a, the liquid crystal polymer layer 23d, the liquid crystal polymer layer 23e, the liquid crystal polymer layer 23h, the liquid crystal polymer layer 23j, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23k, the liquid crystal height Reflected light from the disk 7 that passes through the molecular layer 23b, the liquid crystal polymer layer 23c, the liquid crystal polymer layer 23f, the liquid crystal polymer layer 23g, the liquid crystal polymer layer 23i, and the liquid crystal polymer layer 23l is all in the X-axis direction. It becomes linearly polarized light, and a phase difference of 180 ° is given between them.

  In the optical head device according to the first embodiment of the present invention, when no alternating voltage is applied to the electrodes corresponding to the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v as the phase filter 20d, the liquid crystal polymer layer 23m to A phase filter in which the longitudinal direction of the liquid crystal polymer layer 23v forms an angle of + 45 ° or −45 ° with respect to the X direction can also be used.

  When the disk 7 is a CD standard optical recording medium and the semiconductor laser emits light having a wavelength of 780 nm, an AC voltage is not applied to the electrodes corresponding to the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v. At this time, no phase difference is given to the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m to the liquid crystal polymer layer 23v.

  When the disc 7 is a DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 650 nm, the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23t, the liquid crystal polymer layer An AC voltage having an effective value of Vd3 is applied to the electrode corresponding to the molecular layer 23v. Further, an AC voltage having an effective value of Vd4 is applied to the electrodes corresponding to the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u. The reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. Here, Vd3 is an extraordinary light component and ordinary light of reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23t, and the liquid crystal polymer layer 23v. It is set so that a phase difference of 180 ° is given to the component. Vd4 is an abnormal light component and an ordinary light component of the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u. Is set so that a phase difference of 540 ° is given between the two. However, the extraordinary light component and the ordinary light component are the polarization component in the direction parallel to the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer and the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer, respectively. It is a polarization component in a direction perpendicular to. At this time, the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23t, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23v, the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23 Reflected light from the disk 7 that passes through the molecular layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u is all linearly polarized in the X-axis direction, and 180 ° between them. A phase difference is given.

  When the disk 7 is an HD DVD standard optical recording medium and the semiconductor laser emits light having a wavelength of 400 nm, the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23t, and the liquid crystal An AC voltage having an effective value of Vh3 is applied to the electrode corresponding to the polymer layer 23v. An AC voltage having an effective value of Vh4 is applied to the electrodes corresponding to the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u. The reflected light from the disk 7 enters the phase filter as linearly polarized light in the Y-axis direction. Here, Vh3 is the extraordinary light component and ordinary light of the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23t, and the liquid crystal polymer layer 23v. Vh4 is set to give a phase difference of 180 ° between the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u. Is set so that a phase difference of 540 ° is given between the extraordinary light component and the ordinary light component of the reflected light from the disk 7 that passes through the disk. However, the extraordinary light component and the ordinary light component are the polarization component in the direction parallel to the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer and the projection onto the surface perpendicular to the longitudinal optical axis of the liquid crystal polymer, respectively. It is a polarization component in a direction perpendicular to. At this time, the liquid crystal polymer layer 23m, the liquid crystal polymer layer 23o, the liquid crystal polymer layer 23q, the liquid crystal polymer layer 23t, the reflected light from the disk 7 that passes through the liquid crystal polymer layer 23v, the liquid crystal polymer layer 23n, the liquid crystal polymer layer 23 Reflected light from the disk 7 that passes through the molecular layer 23p, the liquid crystal polymer layer 23r, the liquid crystal polymer layer 23s, and the liquid crystal polymer layer 23u is linearly polarized in the X-axis direction, and is 180 ° between them. A phase difference is given.

  In the optical head device according to the second embodiment of the present invention, instead of the semiconductor laser 1, an optical recording medium of three kinds of standards, CD standard, DVD standard and HD DVD standard, is used as the disk 7. It is also possible to use a single or a plurality of semiconductor lasers that emit light of three wavelengths of wavelength 780 nm, wavelength 650 nm, and wavelength 400 nm corresponding to the respective standards, and use the phase filter 20 instead of the phase filter 12. . The phase filter 20 may be any of the phase filter 20a shown in FIG. 21, the phase filter 20b shown in FIG. 22, the phase filter 20c shown in FIG. 23, and the phase filter 20d shown in FIG.

  When the disk 7 is a CD standard optical recording medium, no AC voltage is applied to the electrodes corresponding to each liquid crystal polymer. Since the outgoing light from the semiconductor laser 1 enters the phase filter 20 as linearly polarized light in the X-axis direction, no phase difference is given to the outgoing light from the semiconductor laser that passes through each liquid crystal polymer. On the other hand, since the reflected light from the disk 7 enters the phase filter 20 as linearly polarized light in the Y-axis direction, no phase difference is given to the reflected light from the disk 7 that passes through each liquid crystal polymer.

  When the disc 7 is a DVD standard optical recording medium, an AC voltage is applied to electrodes corresponding to some liquid crystal polymers, and no AC voltage is applied to electrodes corresponding to some liquid crystal polymers. Since the light emitted from the semiconductor laser enters the phase filter 20 as linearly polarized light in the X-axis direction, the light emitted from the semiconductor laser 1 that passes through the liquid crystal polymer to which an AC voltage is applied to the corresponding electrode, and the corresponding electrode No phase difference is given to the light emitted from the semiconductor laser 1 that passes through the liquid crystal polymer to which no AC voltage is applied. On the other hand, since the reflected light from the disk 7 enters the phase filter 20 as linearly polarized light in the Y-axis direction, it corresponds to the reflected light from the disk 7 that transmits the liquid crystal polymer to which the AC voltage is applied to the corresponding electrode. A phase difference of 180 ° is given to the reflected light from the disk 7 that transmits the liquid crystal polymer to which no AC voltage is applied to the electrodes.

  When the disc 7 is an HD DVD standard optical recording medium, an AC voltage is applied to electrodes corresponding to some liquid crystal polymers, and no AC voltage is applied to electrodes corresponding to some liquid crystal polymers. Since the emitted light from the semiconductor laser 1 enters the phase filter 20 as linearly polarized light in the X-axis direction, the emitted light from the semiconductor laser that transmits the liquid crystal polymer to which an AC voltage is applied to the corresponding electrode No phase difference is given to the light emitted from the semiconductor laser that passes through the liquid crystal polymer to which no AC voltage is applied. On the other hand, the reflected light from the disk 7 is incident on the phase filter 20 as linearly polarized light in the Y-axis direction. A phase difference of 180 ° is given to the reflected light from the disk 7 that transmits the liquid crystal polymer to which no alternating voltage is applied to the electrode. An electrode to which an AC voltage is applied when the disc 7 is a DVD standard optical recording medium is different from an electrode to which an AC voltage is applied when the disc 7 is an HD DVD standard optical recording medium. Also, an electrode to which no AC voltage is applied when the disk 7 is a DVD standard optical recording medium is different from an electrode to which no AC voltage is applied when the disk 7 is an HD DVD standard optical recording medium.

  In the first and second embodiments of the present invention, when the disk 7 is a read-only optical recording medium such as a DVD-ROM or HD DVD-ROM, a differential push is used as a method for detecting a track error signal. The pull method is not used. Therefore, an AC voltage is not applied to the electrodes corresponding to each liquid crystal polymer, and a phase difference is not given to the reflected light from the disk 7 that transmits each liquid crystal polymer. When the disk 7 is a write-once optical recording medium such as DVD-R or HD DVD-R, a differential push-pull method is used as a method for detecting a track error signal. Therefore, an alternating voltage is applied to the electrodes corresponding to some liquid crystal polymers, and no alternating voltage is applied to the electrodes corresponding to some liquid crystal polymers. It is also possible to give a 180 ° phase difference between the reflected light from the disk 7 that passes through the former and the reflected light from the disk 7 that passes through the latter.

  In the first and second embodiments of the present invention, the disk 7 is an optical recording medium having two recording layers. If the optical path length from the objective lens 6 to the phase filter 20 is long, the layer closer to the objective lens (first layer) is the target layer and the layer farther from the objective lens (second layer) is the target layer. In some cases, the diameter of the reflected light of the main beam from the non-target layer at the position of the phase filter 20 is different. Therefore, an electrode to which an AC voltage is applied when the layer closer to the objective lens (first layer) is the target layer according to the diameter of the reflected light of the main beam from the non-target layer at the position of the phase filter 20. When the layer far from the objective lens (second layer) is the target layer, the electrode to which the AC voltage is applied is different, and the layer closer to the objective lens (first layer) is the target layer. In some cases, an electrode to which no AC voltage is applied may be different from an electrode to which no AC voltage is applied when the layer farther from the objective lens (second layer) is the target layer.

  FIG. 25 shows the configuration of an optical information recording / reproducing apparatus according to the third embodiment of the present invention. In the present embodiment, the optical head device 61, the controller 24, the modulation circuit 25, the recording signal generation circuit 26, the semiconductor laser drive circuit 27, the amplification circuit 28, the reproduction signal processing circuit 29, the demodulation circuit 30, and the error shown in FIG. A signal generation circuit 31 and an objective lens drive circuit 32 are provided. Circuits from the modulation circuit 25 to the objective lens driving circuit 32 are controlled by the controller 24.

  When recording data on the disk 7, the modulation circuit 25 modulates data to be recorded on the disk 7 in accordance with a modulation rule. The recording signal generation circuit 26 generates a recording signal for driving the semiconductor laser 1 according to the recording strategy based on the signal modulated by the modulation circuit 25. The semiconductor laser drive circuit 27 drives the semiconductor laser 1 by supplying a current corresponding to the recording signal to the semiconductor laser 1 based on the recording signal generated by the recording signal generation circuit 26. On the other hand, when reproducing data from the disk 7, the semiconductor laser drive circuit 27 supplies a constant current to the semiconductor laser 1 so that the power of the emitted light from the semiconductor laser 1 becomes constant, thereby supplying the semiconductor laser 1. Drive.

  The amplifier circuit 28 amplifies a voltage signal that is an output from each light receiving unit of the photodetector 10. When reproducing data from the disc 7, the reproduction signal processing circuit 29 generates a reproduction signal, which is a mark / space signal recorded on the disc 7, based on the voltage signal amplified by the amplification circuit 28, waveform equalization, Perform binarization. The demodulation circuit 30 demodulates the signal binarized by the reproduction signal processing circuit 29 according to a demodulation rule. The error signal generation circuit 31 generates a focus error signal and a track error signal for driving the objective lens 6 based on the voltage signal amplified by the amplification circuit 28. The objective lens driving circuit 32 supplies the current corresponding to the focus error signal and the track error signal to an actuator (not shown) based on the focus error signal and the track error signal generated by the error signal generation circuit 31 to cause the objective lens 6 to move. To drive. In addition to this, the present embodiment includes a positioner control circuit and a spindle control circuit. The positioner control circuit moves the entire optical head device excluding the disk 7 in the radial direction of the disk 7 by a motor (not shown), and the spindle control circuit rotates the disk 7 by a motor (not shown).

  The optical information recording / reproducing apparatus includes an optical head device 62, a controller, a modulation circuit, a recording signal generation circuit, a semiconductor laser driving circuit, an amplification circuit, a reproduction signal processing circuit, a demodulation circuit, an error signal generation circuit, an objective shown in FIG. The structure which comprises a lens drive circuit may be sufficient.

  When the phase filter 20 is used as the phase filter of the optical information recording / reproducing apparatus according to the third embodiment of the present invention, the optical information recording / reproducing apparatus supplies alternating current to the electrodes corresponding to the liquid crystal polymers of the phase filter 20. It further includes a phase filter drive circuit that drives the phase filter 20 by applying a voltage.

  As described above, when the optical recording medium is an optical recording medium having a plurality of recording layers, the phase filter transmits the reflected light from the optical recording medium that transmits the first area and the optical recording that transmits the second area. If no phase difference is given to the reflected light from the medium, the reflected light of the main beam from the non-target layer incident on the phase filter is diffracted in a straight line separating the first region and the second region after transmission. A part of the reflected light of the main beam from the non-target layer is incident on the sub-beam light receiving unit as disturbance light. However, since the phase filter gives a phase difference of 180 ° between the reflected light from the optical recording medium that passes through the first region and the reflected light from the optical recording medium that passes through the second region, The reflected light of the main beam from the incident non-target layer is affected by diffraction in a straight line separating the first region and the second region after transmission. Of the reflected light of the main beam from the non-target layer, the light transmitted through the first region passes through the second region across the plane including the optical axis and the straight line as it propagates due to diffraction along the straight line. Spreads in the direction of the transmitted light and interferes with the light transmitted through the second region. Similarly, of the reflected light of the main beam from the non-target layer, the light transmitted through the second region is diffracted in the straight line, and propagates through the first plane across the plane including the optical axis and the straight line as it propagates. It spreads toward the light transmitted through the region and interferes with the light transmitted through the first region. The phase difference between the light transmitted through the first region and the light transmitted through the second region that interfere with each other is close to 180 ° in the vicinity of a straight line that passes through the optical axis and corresponds to the direction of the information track. In the portion where the light transmitted through the first region and the light transmitted through the second region interfere with each other, the reflected light of the main beam from the non-target layer in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track The strength of is weak. Here, the sub-beam light receiving unit is located in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track where light transmitted through the first region and light transmitted through the second region interfere with each other. To position. At this time, the reflected light of the main beam from the non-target layer hardly enters the sub-beam light receiving portion due to the influence of diffraction. Therefore, even if the distance between the target layer and the non-target layer changes, the sub push-pull signal and the differential push-pull signal are hardly disturbed.

  Further, the reflected light of the main beam from the target layer incident on the phase filter is also affected by diffraction on a straight line separating the first region and the second region after transmission. The phase difference between the light transmitted through the first region and the light transmitted through the second region that interfere with each other is close to 180 ° in the vicinity of a straight line that passes through the optical axis and corresponds to the direction of the information track. In the portion where the light transmitted through the first region and the light transmitted through the second region interfere with each other, the reflected light of the main beam from the target layer in the vicinity of a straight line passing through the optical axis and corresponding to the direction of the information track. The strength is weak. However, the phase difference between the light transmitted through the first region and the light transmitted through the second region is 0 ° as it moves away from the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track. Therefore, at the part where the light transmitted through the first area and the light transmitted through the second area interfere with each other, the distance from the target layer increases as the distance from the vicinity of the straight line passing through the optical axis and corresponding to the direction of the information track increases. The intensity of the reflected light from the main beam is increased. At this time, all the reflected light of the main beam from the target layer is incident on the main beam light receiving unit regardless of the influence of diffraction, although the intensity distribution changes. Therefore, the quality of the mark / space signal recorded on the target layer, which is detected based on the output from the main beam light receiving unit, does not deteriorate.

  According to the present invention, in recording and reproduction with respect to an optical recording medium having a plurality of recording layers, even if the distance between the target layer and the non-target layer of the optical recording medium changes, the differential push-pull signal is not disturbed, In addition, it is possible to provide an optical head device and an optical information recording / reproducing device in which the quality of the mark / space signal recorded in the target layer does not deteriorate. This is because the reflected light of the main beam from the non-target layer incident on the phase filter is hardly incident on the light receiving part for the sub beam due to diffraction, and the reflected light of the main beam from the target layer incident on the phase filter. This is because all of the light is incident on the light receiving portion for main beam regardless of the influence of diffraction.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims (21)

  1. A diffractive optical element that generates a main beam and a sub beam group from outgoing light emitted from a light source;
    Condensing means for condensing the main beam and the sub beam group on the selected recording layer of an optical recording medium having a plurality of recording layers on which information tracks are formed;
    A light detection means for receiving the reflected light of the main beam and the reflected light of the sub beam group reflected by the selected recording layer;
    A light separating means for separating the reflected light of the main beam and the reflected light of the sub beam group from the optical path of the main beam and the sub beam group;
    Corresponding to the direction of the information track passing through the optical axis at least in part in a plane perpendicular to the optical axis of the reflected light from the optical recording medium, provided between the condensing means and the light detecting means. A phase filter having a first region and a second region divided by a straight line,
    The phase filter gives a phase difference of 180 ° between reflected light from the optical recording medium that passes through the first region and reflected light from the optical recording medium that passes through the second region. Optical head device.
  2. The optical head device according to claim 1, wherein the phase filter is provided between the light separation unit and the light detection unit.
  3. The phase filter has a first half-wave plate in the first region and a second half-wave plate in the second region,
    The direction of the optical axis of the first half-wave plate forms an angle of + 45 ° with respect to the polarization direction of incident light,
    The optical head device according to claim 2, wherein the direction of the optical axis of the second half-wave plate forms an angle of −45 ° with respect to the polarization direction of incident light.
  4. The phase filter is provided between the light collecting means and the light separating means,
    Between the light transmitted through the first region and the light transmitted through the second region, 0 ° for linearly polarized light in a predetermined direction, and for linearly polarized light in a direction orthogonal to the predetermined direction Gives a phase difference of 180 °,
    Outgoing light from the light source enters the phase filter as linearly polarized light in the predetermined direction, and reflected light from the optical recording medium enters the phase filter as linearly polarized light in a direction orthogonal to the predetermined direction. The optical head device according to claim 1.
  5. The first area is divided into first to third small areas that are in contact with the straight line and are spaced apart from each other by first and second intermediate areas;
    The second region is divided into fourth to sixth small regions that are in contact with the straight line and spaced apart from each other by the first and second intermediate regions,
    The phase filter is
    Between the reflected light from the optical recording medium that passes through the first and second intermediate regions and the reflected light from the optical recording medium that passes through the first to third small regions. Give the phase difference,
    Between the reflected light from the optical recording medium that passes through the first and second intermediate regions and the reflected light from the optical recording medium that passes through the fourth to sixth small regions The optical head device according to claim 1, wherein a phase difference is given.
  6. The first region is divided into first and second small regions that are in contact with the straight line and are spaced apart from each other by an intermediate region;
    The second region is divided into third and fourth small regions that are in contact with the straight line and are spaced apart from each other by the intermediate region;
    The phase filter is
    Providing a 90 ° phase difference between the reflected light from the optical recording medium that passes through the intermediate region and the reflected light from the optical recording medium that passes through the first and second small regions;
    The phase difference of 90 ° is given between the reflected light from the optical recording medium that transmits through the intermediate region and the reflected light from the optical recording medium that transmits through the third and fourth small regions. 2. An optical head device according to 1.
  7. The first area is divided into first to fourth small areas that are bounded by first to third straight lines corresponding to a direction orthogonal to the information track,
    The second region is divided into fifth to eighth small regions bounded by the first to third straight lines,
    The phase filter transmits the reflected light from the optical recording medium that transmits the first, third, sixth, and eighth small areas, and the second, fourth, fifth, and seventh small areas. The optical head device according to claim 1, wherein a phase difference of 180 ° is given to the reflected light from the optical recording medium.
  8. The first area is divided into first to third small areas that are bounded by first and second straight lines corresponding to a direction orthogonal to the information track,
    The second region is divided into fourth to sixth subregions bounded by the first and second straight lines,
    The phase filter includes reflected light from the optical recording medium that transmits the first, third, and fifth small regions, and the optical recording medium that transmits the second, fourth, and sixth small regions. The optical head device according to claim 1, wherein a phase difference of 180 ° is provided between the reflected light and the reflected light.
  9. The light source comprises a single or a plurality of light sources that selectively emit light of a plurality of wavelengths,
    The phase filter has a reflected light from the optical recording medium that transmits the first region and the optical recording medium that transmits the second region with respect to at least one of the plurality of wavelengths. The optical head device according to claim 1, wherein a phase difference of 180 ° is given to the reflected light from the optical head device.
  10. The phase filter is
    A first state that gives a phase difference of 180 ° between reflected light from the optical recording medium that passes through the first region and reflected light from the optical recording medium that passes through the second region; ,
    A second state that does not give a phase difference between the reflected light from the optical recording medium that passes through the first region and the reflected light from the optical recording medium that passes through the second region. The optical head device according to claim 1, wherein the first state and the second state can be switched.
  11. The phase filter is
    A first liquid crystal polymer layer provided in the first region;
    A first electrode for applying an alternating voltage to the first liquid crystal polymer layer;
    A second liquid crystal polymer layer provided in the second region;
    The optical head device according to claim 10, further comprising: a second electrode that applies an alternating voltage to the second liquid crystal polymer layer.
  12. The phase filter has a plurality of small regions,
    A first state in which the first region includes a first small region group of the plurality of small regions, and the second region includes a second small region group of the plurality of small regions;
    The first region includes a third small region group different from the first small region group among the plurality of small regions, and the second region is the second small region group among the plurality of small regions. The optical head device according to claim 1, comprising: a second state including a fourth small region group different from the first state and being capable of switching between the first state and the second state.
  13. The phase filter includes a plurality of liquid crystal polymer layers provided in each of the plurality of small regions, and a plurality of electrodes that apply an alternating voltage to each of the plurality of liquid crystal polymer layers. Optical head device.
  14. A diffractive optical element that generates a main beam and a sub beam group from outgoing light emitted from a light source;
    Condensing means for condensing the main beam and the sub beam group on the selected recording layer of an optical recording medium having a plurality of recording layers on which information tracks are formed;
    A light detection means for receiving the reflected light of the main beam and the reflected light of the sub beam group reflected by the selected recording layer;
    A light separating means for separating the reflected light of the main beam and the reflected light of the sub beam group from the optical path of the main beam and the sub beam group;
    Corresponding to the direction of the information track through the optical axis at least part of the plane perpendicular to the optical axis of the reflected light from the optical recording medium. A phase filter having a first region and a second region divided by a straight line,
    The phase filter produces a phase difference of 180 ° between the reflected light from the optical recording medium that passes through the first region and the reflected light from the optical recording medium that passes through the second region. An optical head device to give,
    Differential push-pull signal calculation means for calculating a differential push-pull signal, which is a difference between a push-pull signal based on the main beam and a push-pull signal based on the sub-beam group, in accordance with an output from the light detection means; An optical information recording / reproducing apparatus.
  15. The phase filter is
    A first state that gives a phase difference of 180 ° between reflected light from the optical recording medium that passes through the first region and reflected light from the optical recording medium that passes through the second region; ,
    A second state that does not give a phase difference between the reflected light from the optical recording medium that passes through the first region and the reflected light from the optical recording medium that passes through the second region. ,
    The optical information recording / reproducing apparatus according to claim 14, further comprising phase filter driving means for switching the state of the phase filter to the first state or the second state.
  16. The phase filter is
    A first liquid crystal polymer layer provided in the first region;
    A first electrode for applying an alternating voltage to the first liquid crystal polymer layer;
    A second liquid crystal polymer layer provided in the second region;
    A second electrode for applying an alternating voltage to the second liquid crystal polymer layer,
    The optical information recording / reproducing apparatus according to claim 15, wherein the phase filter driving unit supplies an AC voltage to the first and second electrodes.
  17. The optical information recording according to claim 15 or 16, wherein the phase filter driving means switches the state of the phase filter to the first state or the second state according to the type of the optical recording medium. Playback device.
  18. The phase filter has a plurality of small regions,
    A first state in which the first region includes a first small region group of the plurality of small regions, and the second region includes a second small region group of the plurality of small regions;
    The first region includes a third small region group different from the first small region group among the plurality of small regions, and the second region is the second small region group among the plurality of small regions. And a second state including a different fourth subregion group,
    The optical information recording / reproducing apparatus according to claim 14, further comprising phase filter driving means for switching the state of the phase filter to the first state or the second state.
  19. The phase filter includes a plurality of liquid crystal polymer layers provided in each of the plurality of small regions, and a plurality of electrodes that apply an alternating voltage to each of the plurality of liquid crystal polymer layers,
    The optical information recording / reproducing apparatus according to claim 18, wherein the phase filter driving unit supplies an AC voltage to the plurality of electrodes.
  20. The optical information recording according to claim 18 or claim 19, wherein the phase filter driving means switches the state of the phase filter to the first state or the second state according to the type of the optical recording medium. Playback device.
  21. The phase filter driving means switches the state of the phase filter to the first state or the second state according to a target layer to be recorded or reproduced among the plurality of recording layers. The optical information recording / reproducing apparatus according to claim 19.
JP2009511710A 2007-04-20 2008-03-19 Optical head device and optical information recording / reproducing device Expired - Fee Related JP5120667B2 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
JP2007112390 2007-04-20
JP2007112390 2007-04-20
PCT/JP2008/055116 WO2008132891A1 (en) 2007-04-20 2008-03-19 Optical head device and optical information recoding/reproducing device
JP2009511710A JP5120667B2 (en) 2007-04-20 2008-03-19 Optical head device and optical information recording / reproducing device

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Application Number Priority Date Filing Date Title
JP2009511710A JP5120667B2 (en) 2007-04-20 2008-03-19 Optical head device and optical information recording / reproducing device

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009087423A (en) * 2007-09-28 2009-04-23 Sony Optiarc Inc Optical pickup apparatus, optical recording medium driving apparatus, and signal recording/reproducing method
JP2009223937A (en) * 2008-03-14 2009-10-01 Ricoh Co Ltd Optical pickup and optical information processing device using the same

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JP2005063595A (en) * 2003-08-18 2005-03-10 Sony Corp Optical pickup and disk drive device
JP2005203090A (en) * 2004-01-14 2005-07-28 Samsung Electronics Co Ltd Optical pickup
WO2007043663A1 (en) * 2005-10-14 2007-04-19 Matsushita Electric Industrial Co., Ltd. Optical head
JP2007257750A (en) * 2006-03-24 2007-10-04 Hitachi Media Electoronics Co Ltd Optical pickup and optical disk device
JP2008021339A (en) * 2006-07-10 2008-01-31 Pioneer Electronic Corp Optical pickup and information device

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JPWO2008132891A1 (en) 2010-07-22

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