WO2009122987A1 - 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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Publication number
WO2009122987A1
WO2009122987A1 PCT/JP2009/055992 JP2009055992W WO2009122987A1 WO 2009122987 A1 WO2009122987 A1 WO 2009122987A1 JP 2009055992 W JP2009055992 W JP 2009055992W WO 2009122987 A1 WO2009122987 A1 WO 2009122987A1
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WO
WIPO (PCT)
Prior art keywords
plurality
beam group
optical
light
recording
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PCT/JP2009/055992
Other languages
French (fr)
Japanese (ja)
Inventor
片山 龍一
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日本電気株式会社
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Priority to JP2008-090180 priority Critical
Priority to JP2008090180 priority
Application filed by 日本電気株式会社 filed Critical 日本電気株式会社
Publication of WO2009122987A1 publication Critical patent/WO2009122987A1/en

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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/32Holograms used as optical elements
    • 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
    • G11B7/004Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • 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
    • G11B7/083Disposition or mounting of heads or light sources relatively to record carriers relative to record carriers storing information in the form of optical interference patterns, e.g. holograms
    • 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
    • G11B7/1398Means for shaping the cross-section of the beam, e.g. into circular or elliptical cross-section
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03HHOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00Holographic processes or apparatus using light, infra-red or ultra-violet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/30Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique discrete holograms only
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03HHOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00Holographic processes or apparatus using light, infra-red or ultra-violet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04Processes or apparatus for producing holograms
    • G03H1/0402Recording geometries or arrangements
    • G03H2001/0415Recording geometries or arrangements for recording reflection holograms
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03HHOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2223/00Optical components
    • G03H2223/19Microoptic array, e.g. lens array
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03HHOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2225/00Active addressable light modulator
    • G03H2225/30Modulation
    • G03H2225/31Amplitude only

Abstract

Light emitted from a laser (3) is divided into a plurality of beams by a micro lens array (5). Each of the beams is possible to be independently modulated by a spatial light modulator (6). The beams are each divided by a polarized beam splitter (10a) into reflected light and transmitted light, which are opposed to each other. The opposed reflected and transmitted light from the polarized beam splitter (10a) are collected at the same position within the recording layer of a disk (2a) and are made interfere with each other, forming a very small diffraction grating at the light collection position. This makes it possible to record information in parallel.

Description

Optical head device and optical information recording / reproducing device

The present invention relates to an optical head device and an optical information recording / reproducing apparatus for recording / reproducing information three-dimensionally with respect to an optical recording medium.

As one of the technologies for increasing the capacity of optical recording media, information is recorded and reproduced three-dimensionally on the optical recording medium using not only the in-plane dimension of the optical recording medium but also the thickness dimension. There is a three-dimensional recording / reproducing technique. As a three-dimensional recording / reproducing technique, there are a bit-type three-dimensional recording technique and a page-type hologram recording technique. In the bit-type three-dimensional recording technology, information is recorded by converging two opposing beams at the same position in the recording layer of the optical recording medium to cause interference to form a minute diffraction grating at the converging position. Is done. Information is reproduced by condensing one of the two beams in the recording layer of the optical recording medium and detecting the reflected light from the diffraction grating. In the page-type hologram recording technique, the intensity distribution in the cross section of the signal light of the signal light and the reference light, which are two beams, is modulated according to the recording information, and then the two beams enter the recording layer of the optical recording medium. Information is recorded by making it enter and interfering and forming a hologram in the position where two beams overlap. Information is reproduced by making reference light of the two beams enter the recording layer of the optical recording medium and detecting the intensity distribution in the cross section of the diffracted light from the hologram modulated according to the reproduction information. The size of the diffraction grating in the bit type three-dimensional recording is smaller than the size of the hologram in the page type hologram recording. For this reason, bit-type three-dimensional recording has characteristics such as a wider tolerance against wavelength fluctuations of the light source than page-type hologram recording. As such a bit-type optical head device for three-dimensional recording, “Drive System for Micro-Reflector Recording Employing Blue Laser Diode” (International Symposium on Optical Memory. There is a head device.

FIG. 1 shows the configuration of the optical head device. The light emitted from the semiconductor laser 43a passes through the convex lens 44a and is converted from divergent light into parallel light, partly transmitted through the beam splitter 45a, and partly reflected by the beam splitter 45a.

When recording information on the disk 42, the light transmitted through the beam splitter 45a is reflected by the interference filter 46 and is condensed in the recording layer of the disk 42 by the objective lens 49a. On the other hand, the light reflected by the beam splitter 45a passes through the shutter 48, a part thereof is reflected by the beam splitter 45b, is reflected by the mirror 47, and is condensed in the recording layer of the disk 42 by the objective lens 49b. The light transmitted through the beam splitter 45a and the light reflected by the beam splitter 45a are condensed and interfered at the same position in the recording layer of the disk 42, and a minute diffraction grating is formed at the condensing position. .

When information is reproduced from the disk 42, the light transmitted through the beam splitter 45a is collected in the recording layer of the disk 42, but the light reflected by the beam splitter 45a is blocked by the shutter 48 and does not travel toward the disk 42. . The light condensed in the recording layer of the disk 42 is reflected by the diffraction grating formed at the condensing position, passes through the objective lens 49a in the reverse direction, and is reflected by the interference filter 46. A part of the light reflected by the interference filter 46 is reflected by the beam splitter 45a and condensed on the light receiving part of the photodetector 50a by the convex lens 44b.

Here, the diffraction grating has bit data information. The converging position of the light transmitted through the beam splitter 45a and the light reflected by the beam splitter 45a is moved in the thickness direction of the recording layer, and the diffraction grating is formed in multiple layers not only in the in-plane direction of the recording layer but also in the thickness direction. By forming, three-dimensional recording / reproduction can be performed.

When the convex lens 44c and the photodetector 50b record information on the disk 42, the light reflected by the beam splitter 45a with respect to the condensing position of the light transmitted through the beam splitter 45a in the recording layer of the disk 42 is recorded. It is used to detect the deviation of the light collection position. Further, the semiconductor laser 43b, the convex lens 44d, the beam splitter 45c, the convex lens 44e, and the photodetector 50c are used to detect a shift in the condensing position of the light emitted from the semiconductor laser 43b with respect to the reference position of the disk 42.

This optical head device is an optical head device for bit-type three-dimensional recording. In bit-type three-dimensional recording, one diffraction grating is formed by one recording. Here, bit data included in one diffraction grating corresponds to one bit. On the other hand, in page-type hologram recording, one hologram is formed by one recording. Here, page data included in one hologram corresponds to a plurality of bits. That is, the bit type three-dimensional recording has a problem that the data transfer speed is lower than that of the page type hologram recording.

Japanese Patent Application Laid-Open No. 2006-79702 discloses a recording / reproducing apparatus in which a plurality of light beams can be selectively incident on an objective lens based on a recording signal to form an arbitrary recording pattern. This recording / reproducing apparatus includes a condenser lens, a light selection element, and an objective lens. The condensing lens condenses light from a plurality of light sources. The light selection element is disposed in the vicinity of the condensing point of the light condensed by the condensing lens, and selectively transmits or reflects light based on the recording signal. The objective lens collects the transmitted or reflected light beam on the recording medium.

JP-A-11-133845 discloses a method for duplicating an optical information recording medium on which information is recorded using holography. Recording is performed on the recorded optical information recording medium and the unrecorded optical information recording medium in a state where the recorded optical information recording medium on which information is recorded and the unrecorded optical information recording medium on which information is not recorded are superimposed. Reference light is irradiated so that reproduction light is generated from each hologram of the finished optical information recording medium. An interference pattern due to the interference between the reproduction light generated from each hologram by the reference light irradiation and the reference light is recorded on the unrecorded optical information recording medium. As a result, the information recorded on the recorded optical information recording medium is copied to the unrecorded optical information recording medium, and the optical information recording medium is duplicated.

Japanese Patent Publication No. 11-513817 discloses an apparatus for generating a two-dimensional array of modulated light beams. The apparatus includes a light source, a first lens, a two-dimensional holographic beam splitter, and a two-dimensional modulator array to generate a two-dimensional array of diffraction limited light beams. The light source generates light, and the first lens collimates this light into a light beam. A two-dimensional holographic beam splitter creates a two-dimensional array composed of a plurality of diffraction limited light beams as the light beam passes. The two-dimensional modulator array modulates a plurality of light beams independently. A plurality of modulated light beams are created by the modulator to produce a two-dimensional array of modulated diffraction limited light beams.

Japanese Patent Application Laid-Open No. 2002-123948 discloses an optical information recording apparatus that records information on an optical information recording medium having an information recording layer on which information is recorded using holography. This optical information recording apparatus includes information light generating means, recording reference light generating means, and a recording optical system. The information light generating means generates information light carrying information to be recorded. The recording reference light generating means generates recording reference light. The recording optical system is generated by the information light generated by the information light generating means and the recording reference light generating means so that information is recorded on the information recording layer by an interference pattern due to interference between the information light and the recording reference light. The information recording layer is irradiated with the recorded recording reference light while being converged so as to have the smallest diameter at the same position coaxially from opposite surfaces to the information recording layer. These branched reference lights enter the holographic recording medium through the branched reference optical paths having different optical path lengths from the beam splitter to the holographic recording medium and at different angles. Each branch reference optical path has a difference between the optical path length and the optical path length of any one of the plurality of branched object optical paths, which is shorter than the coherence distance of the laser beam, and the difference between the optical path lengths of the other branched object optical paths. However, it is longer than the coherence distance.

Japanese Patent Application Laid-Open No. 2005-70341 discloses a holographic recording method that forms interference fringes by causing interference between reference light and modulated object light in a holographic recording medium. The object light and the reference light are branched into the same number of branched object lights and branched reference lights, respectively. These branched object lights are modulated by different reflective spatial light modulators, and the optical path lengths from the beam splitter including the optical paths before and after the reflective spatial light modulator to the holographic recording medium are different from each other. The reflected light from the reflective spatial light modulator is integrated on the same optical path through the object optical path, and is incident on the holographic recording medium.

Japanese Patent Application Laid-Open No. 2005-172956 discloses a holographic memory reproducing method. The holographic recording medium has a plurality of recording areas in the surface direction of the recording layer, and a hologram is formed for each recording area. The holographic recording medium is irradiated with a reproduction light beam, and information is reproduced from the hologram. The reproduction light beam emitted from the light source is used as a plurality of divided beams, the same number of recording areas are simultaneously irradiated, and the diffracted light from the plurality of recording areas is simultaneously received, so that information is read out collectively.

An object of the present invention is to provide an optical head device and an optical information recording / reproducing device having a high data transfer rate.

In an aspect of the present invention, an optical head device of the present invention performs recording and reproduction of information on an optical recording medium having a recording layer, a single light source, beam group generation means, a spatial light modulator, An aperture, a beam group dividing means, and an objective lens are provided. The beam group generation unit generates an output beam group including a plurality of beams from the output light from the light source. The spatial light modulator has a modulation layer including a plurality of pixels capable of independently modulating each of the plurality of beams included in the outgoing beam group. The opening is provided in the Fourier plane for the modulation layer. The beam group dividing means divides the outgoing beam group into a first outgoing beam group and a second outgoing beam group when information is recorded on the optical recording medium. The objective lens collects each of the plurality of beams included in the first outbound beam group and each of the plurality of beams included in the second outbound beam group at the same position in the recording layer so as to face each other. Shine.

In another aspect of the present invention, an optical information recording / reproducing apparatus of the present invention includes the above-described optical head device, a light source driving circuit for driving a light source, and a spatial light modulator driving circuit for driving a spatial light modulator. Have.

According to the present invention, it is possible to increase the data transfer speed while maintaining the characteristics of bit-type three-dimensional recording such as a wide tolerance for wavelength variation of the light source.

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 the configuration of a related three-dimensional recording / reproducing optical head device. FIG. 2 is a diagram showing a configuration of the optical head device according to the first embodiment of the present invention. 3A to 3B are diagrams for explaining the operation of the spatial light modulator that combines a transmissive liquid crystal optical element and a polarizer in the optical head device according to the embodiment of the present invention. 4A to 4B are diagrams for explaining the operation of the spatial light modulator in which the reflective liquid crystal optical element and the polarization beam splitter are combined in the optical head device according to the embodiment of the present invention. 5A to 5B show a plurality of pixels included in the modulation layer provided in the liquid crystal optical element in a plane perpendicular to the optical axis of the liquid crystal optical element used in the optical head device according to the embodiment of the present invention. FIG. 6A to 6B are diagrams showing optical paths of an incident beam to the disk and a reflected beam from the disk in the optical head device according to the first embodiment of the present invention. FIG. 7 is a diagram showing the configuration of the optical information recording / reproducing apparatus according to the first embodiment of the present invention. FIG. 8 is a diagram showing the configuration of the optical head device according to the second embodiment of the present invention. 9A to 9B are diagrams showing optical paths of an incident beam to the disk and a reflected beam from the disk in the optical head device according to the second embodiment of the present invention. FIG. 10 is a diagram showing a configuration of an optical information recording / reproducing apparatus according to the second embodiment of the present invention.

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

FIG. 2 shows the configuration of the optical head device according to the first embodiment of the present invention. The optical head 1a records information on the disk 2a which is an optical recording medium, and reproduces the information recorded on the disk 2a. The optical head 1a includes a laser 3, convex lenses 4a to 4f and 4k, a microlens array 5, a spatial light modulator 6, a variable wavelength plate 7, openings 9a and 9b, a polarizing beam splitter 10a, mirrors 11a to 11f, and a quarter wavelength. Plates 12a and 12b, objective lenses 13a and 13b, and an image sensor 14 are provided. The laser 3 as a light source is a single mode semiconductor laser that emits light having a wavelength of 405 nm. The light emitted from the laser 3 enters the convex lens 4a as divergent light, passes through the convex lens 4a and is converted from divergent light to parallel light, and passes through the microlens array 5 to convert parallel light into a plurality of convergent lights. Then, the light is condensed as a plurality of condensing spots in a modulation layer including a plurality of pixels of the spatial light modulator 6. Each condensing position of the plurality of condensing spots corresponds to each of the plurality of pixels. Here, the microlens array 5 corresponds to a beam group generation unit, and a plurality of lights condensed as a plurality of focused spots correspond to an outgoing beam group. The plurality of lights enter the convex lens 4 b as a plurality of divergent lights, pass through the convex lens 4 b, are converted from the plurality of divergent lights to a plurality of parallel lights, and enter the variable wavelength plate 7. The variable wavelength plate 7 has the effect of a quarter wavelength plate with respect to incident light when recording information on the disk 2a, which is an optical recording medium, and changes to incident light when information is reproduced from the disk 2a, which is an optical recording medium. On the other hand, it has the effect of a half-wave plate.

When recording information on the disk 2a, a plurality of light incident on the variable wavelength plate 7 is transmitted through the variable wavelength plate 7 and converted from a plurality of linearly polarized light into a plurality of circularly polarized light. About 50% of each of the converted plurality of circularly polarized lights is reflected as an S-polarized component by the polarizing beam splitter 10a, and about 50% of each of the plurality of circularly polarized lights is transmitted through the polarizing beam splitter 10a as a P-polarized light component. Here, the variable wavelength plate 7 and the polarization beam splitter 10a correspond to beam group dividing means. The plurality of lights reflected by the polarization beam splitter 10a and the plurality of lights transmitted through the polarization beam splitter 10a correspond to a first outbound beam group and a second outbound beam group, respectively.

The plurality of lights reflected by the polarization beam splitter 10a are transmitted through the aperture 9a, transmitted through the convex lens 4c, converted from a plurality of parallel lights to a plurality of convergent lights, and collected as a plurality of condensed spots in the vicinity of the mirror 11a. To be lighted. The plurality of lights are reflected by the mirror 11a and the mirror 11c, enter the convex lens 4e as a plurality of diverging lights, pass through the convex lens 4e, are converted from the plurality of diverging lights to a plurality of parallel lights, and are reflected by the mirror 11e. Is done. The reflected light passes through the quarter-wave plate 12a and is converted from a plurality of linearly polarized light into a plurality of circularly polarized lights, and is transmitted through the objective lens 13a and converted from a plurality of parallel lights into a plurality of convergent lights. The light is condensed as a plurality of condensing spots in the recording layer 2a.

On the other hand, the plurality of lights transmitted through the polarization beam splitter 10a are transmitted through the aperture 9b, transmitted through the convex lens 4d, converted from a plurality of parallel lights to a plurality of convergent lights, and are formed as a plurality of condensed spots near the mirror 11b. Focused. The plurality of lights are reflected by the mirror 11b and the mirror 11d, enter the convex lens 4f as a plurality of diverging lights, pass through the convex lens 4f, are converted from the plurality of diverging lights to a plurality of parallel lights, and are reflected by the mirror 11f. Is done. The reflected light is transmitted through the quarter-wave plate 12b and converted from a plurality of linearly polarized light to a plurality of circularly polarized lights, and transmitted through the objective lens 13b and converted from a plurality of parallel lights to a plurality of convergent lights. The light is condensed as a plurality of condensing spots in the recording layer 2a.

Each of the plurality of lights reflected by the polarization beam splitter 10a and each of the plurality of lights transmitted through the polarization beam splitter 10a are condensed at the same position in the recording layer of the disk 2a and interfere with each other. A minute diffraction grating is formed at each condensing position. Here, the rear focal position of the convex lens 4b coincides with the front focal position of the convex lenses 4c and 4d. The rear focal positions of the convex lenses 4e and 4f and the front focal positions of the objective lenses 13a and 13b coincide with each other.

Each of the plurality of condensed spots formed in the modulation layer of the spatial light modulator 6 corresponds to each of the plurality of condensed spots formed in the recording layer of the disk 2a. That is, the modulation layer of the spatial light modulator 6 and the recording layer of the disk 2a are optically connected to the convex lenses 4b, 4c, and 4e and the objective lens 13a, and to the convex lenses 4b, 4d, and 4f, and the objective lens 13b. In a conjugate position. In FIG. 2, the number of the plurality of condensing spots formed in the modulation layer of the spatial light modulator 6 and the number of the plurality of condensing spots formed in the recording layer of the disk 2a are all five. is there.

The modulation layer of the spatial light modulator 6 is at the front focal position of the convex lens 4b. The openings 9a and 9b are at the rear focal position of the convex lens 4b. That is, the openings 9 a and 9 b are provided in the Fourier plane with respect to the modulation layer of the spatial light modulator 6. A plurality of principal rays corresponding to a plurality of condensing spots formed in the modulation layer of the spatial light modulator 6 intersect at one point at the rear focal position of the convex lens 4b. Therefore, by providing the openings 9a and 9b at this position, it is possible to make the beam diameters of a plurality of lights having a plurality of focused spots as object points all equal. As a result, the numerical apertures of the objective lenses 13a and 13b for each of the plurality of lights can be all made equal. That is, the size of the plurality of diffraction gratings formed at the plurality of condensing positions in the recording layer of the disk 2a can be all made equal. Note that the position of the aperture need not be the rear focal position of the convex lens 4b as long as it is the Fourier plane of the modulation layer of the spatial light modulator 6. For example, instead of the openings 9a and 9b, the rear focal position of the convex lens 4b and the convex position of the convex lens 4b and the rear focal position of the convex lens 4d and 4f, respectively. An opening may be provided at an optically conjugate position.

On the optical path of the outgoing beam group and the first outgoing beam group from the spatial light modulator 6 to the incident surface on the objective lens 13a side of the disk 2a, the reflecting surface of the polarizing beam splitter 10a, the reflecting surface of the mirror 11a, and the mirror 11c There are a total of four reflecting surfaces, the reflecting surface and the reflecting surface of the mirror 11e. At this time, a plurality of focused spots are formed in the modulation layer of the spatial light modulator 6 and in the recording layer of the disk 2a. Of these plurality of focused spots, the light having the focused spot located at points a and b (see FIG. 2) in the modulation layer of the spatial light modulator 6 as an object point is the spatial light modulator 6. Then, the light passes through an optical path from the disk 2a to the incident surface on the objective lens 13a side, and becomes a light having a focused spot positioned at points A and B (see FIG. 2) in the recording layer of the disk 2a as image points.

On the other hand, in the optical path of the outgoing beam group and the second outgoing beam group from the spatial light modulator 6 to the incident surface on the objective lens 13b side of the disk 2a, the reflecting surface of the mirror 11b, the reflecting surface of the mirror 11d, and the mirror 11f There are a total of three reflective surfaces. At this time, a plurality of focused spots are formed in the modulation layer of the spatial light modulator 6 and in the recording layer of the disk 2a. Of these plurality of focused spots, the light having the focused spot located at points a and b (see FIG. 2) in the modulation layer of the spatial light modulator 6 as an object point is the spatial light modulator 6. Through the optical path from the disk 2a to the entrance surface on the objective lens 13b side, the light is focused on the condensing spots at points A and B (see FIG. 2) in the recording layer of the disk 2a.

As described above, the number of reflecting surfaces in the optical path of the outgoing beam group and the first outgoing beam group from the spatial light modulator 6 to the incident surface on the objective lens 13a side of the disk 2a, and the spatial light modulator 6 to the disk 2a. The difference between the number of reflecting surfaces in the optical path of the outgoing beam group and the second outgoing beam group up to the incident surface on the objective lens 13b side is an odd number. Thereby, the same condensing spot formed in the modulation layer of the spatial light modulator 6 among the plurality of lights included in the first outbound beam group and the plurality of lights included in the second outbound beam group. The light having the object point is the light having the same focused spot formed in the recording layer of the disk 2a as the image point.

On the other hand, when information is reproduced from the disk 2a, the plurality of lights incident on the variable wavelength plate 7 are transmitted through the variable wavelength plate 7 to change the polarization direction by 90 °, and each of the plurality of linearly polarized light beams is a polarized beam. The light is incident on the splitter 10a as S-polarized light and almost 100% is reflected. Here, the plurality of lights reflected by the polarization beam splitter 10a correspond to the forward beam group.

The plurality of lights reflected by the polarization beam splitter 10a pass through the convex lens 4c, are converted from a plurality of parallel lights to a plurality of convergent lights, and are collected as a plurality of focused spots in the vicinity of the mirror 11a. The plurality of lights are reflected by the mirror 11a and the mirror 11c, enter the convex lens 4e as a plurality of diverging lights, pass through the convex lens 4e, are converted from the plurality of diverging lights to a plurality of parallel lights, and are reflected by the mirror 11e. Is done. The reflected light passes through the quarter-wave plate 12a and is converted from a plurality of linearly polarized light into a plurality of circularly polarized lights, and is transmitted through the objective lens 13a and converted from a plurality of parallel lights into a plurality of convergent lights. The light is condensed as a plurality of condensing spots in the recording layer 2a. The plurality of lights are reflected by a plurality of diffraction gratings formed at a plurality of condensing positions, are incident on the objective lens 13a as a plurality of diverging lights, pass through the objective lens 13a, and are emitted from the plurality of diverging lights. Converted to parallel light. The converted light passes through the quarter-wave plate 12a, is converted from a plurality of circularly polarized light into a plurality of linearly polarized light, is reflected by the mirror 11e, passes through the convex lens 4e, and is converted from a plurality of parallel lights into a plurality of convergent lights. , Reflected by the mirror 11c, and condensed as a plurality of condensing spots in the vicinity of the mirror 11a. The plurality of lights are reflected by the mirror 11a, enter the convex lens 4c as a plurality of diverging lights, pass through the convex lens 4c, and are converted from the plurality of diverging lights to a plurality of parallel lights. Nearly 100% is transmitted as P-polarized light to the polarizing beam splitter 10a. The plurality of lights that have passed through the polarization beam splitter 10a are converted from a plurality of parallel lights to a plurality of convergent lights through the convex lens 4k, and are used as a plurality of condensing spots in a light receiving layer including a plurality of pixels of the image sensor 14. Focused. Each condensing position of the plurality of condensing spots corresponds to each of the plurality of pixels. Here, the image sensor 14 corresponds to a photodetector, and a plurality of lights condensed as a plurality of condensing spots correspond to a return beam group.

Each of the plurality of condensing spots formed in the light receiving layer of the image sensor 14 corresponds to each of the plurality of condensing spots formed in the recording layer of the disk 2a. That is, the light receiving layer of the image sensor 14 and the recording layer of the disk 2a are optically connected to the objective lens 13a and the convex lenses 4e, 4c, and 4k and to the objective lens 13b and the convex lenses 4f, 4d, and 4k. It is in a conjugate position. In FIG. 2, the number of the plurality of condensing spots formed in the light receiving layer of the image sensor 14 and the number of the plurality of condensing spots formed in the recording layer of the disk 2a are all five. The light receiving layer of the image sensor 14 is at the rear focal position of the convex lens 4k. The openings 9a and 9b are at the front focal position of the convex lens 4k. That is, the openings 9 a and 9 b are provided on the Fourier plane with respect to the light receiving layer of the image sensor 14.

Here, each of the plurality of diffraction gratings has bit data information. A plurality of condensing positions of the plurality of lights reflected by the polarization beam splitter 10a and the plurality of lights transmitted through the polarization beam splitter 10a are moved in the thickness direction of the recording layer, so that the thickness of the recording layer as well as the in-plane direction is increased. By forming a plurality of diffraction gratings in multiple layers in the direction, three-dimensional recording / reproduction can be performed in parallel.

The variable wavelength plate 7 is configured to sandwich a liquid crystal layer between two substrates. Electrodes for applying a voltage to the liquid crystal layer are formed on the surface of the two substrates on the liquid crystal layer side. The liquid crystal has a uniaxial refractive index anisotropy. The thickness of the liquid crystal layer is determined so that the phase difference between the polarization component in the direction parallel to the optical axis and the polarization component in the direction perpendicular to the optical axis generated in the light transmitted through the liquid crystal layer is π. . When the voltage V is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is an intermediate direction parallel to the direction perpendicular to the optical axis of the incident light. At this time, the variable wave plate 7 has the effect of a quarter wave plate. When no voltage is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is a direction perpendicular to the optical axis of the incident light. At this time, the variable wavelength plate 7 has the effect of a half-wave plate.

As the spatial light modulator 6, a spatial light modulator 6a in which a transmissive liquid crystal optical element and a polarizer are combined, and a spatial light modulator 6b in which a reflective liquid crystal optical element and a polarizing beam splitter are combined can be used.

With reference to FIGS. 3A to 3B, the operation of the spatial light modulator 6a in which a transmissive liquid crystal optical element and a polarizer are combined will be described. FIG. 3A shows the operation of the spatial light modulator 6a when recording information on the disc 2a, and FIG. 3B shows the operation of the spatial light modulator 6a when reproducing information from the disc 2a. The spatial light modulator 6 a includes a transmissive liquid crystal optical element 15 a and a polarizer 16. The modulation layer including a plurality of pixels of the spatial light modulator 6a is provided in the liquid crystal optical element 15a. Here, the light emitted from the laser 3 is linearly polarized light in a direction perpendicular to the paper surface. This light passes through the microlens array 5 and is condensed as a plurality of condensing spots in the modulation layer. 3A to 3B, the number of the plurality of focused spots formed in the modulation layer is five.

The polarizer 16 functions to transmit almost 100% of linearly polarized light in a direction parallel to the paper surface and reflect almost 100% of linearly polarized light in a direction perpendicular to the paper surface. When recording information on the disk 2a, the pixel representing the bit data “1” changes the polarization direction of the incident light by 90 °, and the pixel representing the bit data “0” does not change the polarization state of the incident light. Light that has a focused spot formed in the pixel representing the bit data “1” as an object point passes through the pixel, changes its polarization direction by 90 °, and becomes linearly polarized light in a direction parallel to the paper surface to the polarizer 16. Incident light is transmitted almost 100%. On the other hand, light having a focused spot formed in the pixel representing the bit data “0” as an object point is transmitted through the pixel without changing its polarization state, and linearly polarized in the direction perpendicular to the paper surface to the polarizer 16. And almost 100% is reflected.

In FIG. 3A, of the five focused spots, three are formed in the pixel representing the bit data “1”, and two are formed in the pixel representing the bit data “0”. Three lights having an object point of each of the three focused spots formed in the pixel representing the bit data “1” are transmitted through the polarizer 16 to become beams 17a, 17c, and 17e. On the other hand, when information is reproduced from the disk 2a, all the pixels change the polarization direction of the incident light by 90 °. Light that has a focused spot formed in the pixel as an object point passes through the pixel and changes its polarization direction by 90 °, and is incident on the polarizer 16 as linearly polarized light in a direction parallel to the paper surface. To Penetrate. In FIG. 3B, the five lights having the object points of the five focused spots are transmitted through the polarizer 16 to become beams 17a, 17b, 17c, 17d, and 17e.

4A to 4B, the operation of the spatial light modulator 6b in which the reflective liquid crystal optical element and the polarization beam splitter are combined will be described. 4A shows the operation of the spatial light modulator 6b when information is recorded on the disc 2a, and FIG. 4B shows the operation of the spatial light modulator 6b when information is reproduced from the disc 2a. The spatial light modulator 6b includes a reflective liquid crystal optical element 15b and a polarizing beam splitter 10d. The modulation layer including the plurality of pixels of the spatial light modulator 6b is provided in the liquid crystal optical element 15b. Here, the light emitted from the laser 3 is linearly polarized light in a direction perpendicular to the paper surface. This light is transmitted through the microlens array 5, is incident on the polarizing beam splitter 10d as S-polarized light, is almost 100% reflected, and is condensed as a plurality of condensing spots in the modulation layer. 4A to 4B, the number of the plurality of focused spots formed in the modulation layer is five.

When recording information on the disk 2a, the pixel representing the bit data “1” changes the polarization direction of the incident light by 90 °, and the pixel representing the bit data “0” does not change the polarization state of the incident light. Light having a focused spot formed in the pixel representing the bit data “1” as an object point is reflected by the pixel, the polarization direction changes by 90 °, and enters the polarization beam splitter 10d as P-polarized light, and is approximately 100. % Is transmitted. On the other hand, light having a focused spot formed in the pixel representing the bit data “0” as an object point is reflected without change in the polarization state at the pixel, and is incident on the polarization beam splitter 10d as S-polarized light. 100% is reflected.

In FIG. 4A, three of the five focused spots are formed in a pixel representing bit data “1”, and two are formed in a pixel representing bit data “0”. Three lights having each of the three focused spots formed in the pixel representing the bit data “1” as object points are transmitted through the polarization beam splitter 10d to become beams 17a, 17c, and 17e. On the other hand, when information is reproduced from the disk 2a, all the pixels change the polarization direction of the incident light by 90 °. Light that has a focused spot formed in the pixel as an object point is reflected by the pixel, the polarization direction changes by 90 °, enters the polarization beam splitter 10d as P-polarized light, and almost 100% is transmitted. In FIG. 4B, the five lights whose object points are the five focused spots are transmitted through the polarizing beam splitter 10d to become beams 17a, 17b, 17c, 17d, and 17e.

5A to 5B show the arrangement of a plurality of pixels included in the modulation layer provided in the liquid crystal optical elements 15a and 15b in a plane perpendicular to the optical axis of the liquid crystal optical elements 15a and 15b. FIG. 5A shows an arrangement of a plurality of pixels when information is recorded on the disk 2a, and FIG. 5B shows an arrangement of a plurality of pixels when information is reproduced from the disk 2a. In FIGS. 5A to 5B, a plurality of pixels are arranged in a two-dimensional form of 5 rows and 5 columns, and the number thereof is 25. Here, each of the five focused spots in FIGS. 3A to 3B and FIGS. 4A to 4B is formed in the pixels 18a, 18b, 18c, 18d, and 18e in FIGS. 5A to 5B.

The liquid crystal optical elements 15a and 15b are configured so that a ferroelectric liquid crystal layer as a modulation layer is sandwiched between two substrates. Electrodes for applying a voltage to the ferroelectric liquid crystal layer are formed on the surface of the two substrates on the ferroelectric liquid crystal layer side. One electrode is a two-dimensionally divided pattern electrode corresponding to a plurality of pixels, and the other electrode is a full surface electrode. A voltage can be independently applied to the ferroelectric liquid crystal layer corresponding to each of the plurality of pixels. The ferroelectric liquid crystal has a uniaxial refractive index anisotropy, and an arrow in the figure indicates the direction of the optical axis of the ferroelectric liquid crystal layer. Here, the thickness of the ferroelectric liquid crystal layer in the liquid crystal optical element 15a is the phase difference between the polarization component in the direction parallel to the optical axis and the polarization component in the direction perpendicular to the optical axis generated in the light transmitted through the pixel. Is determined to be π. Further, the thickness of the ferroelectric liquid crystal layer in the liquid crystal optical element 15b is the phase difference between the polarization component in the direction parallel to the optical axis and the polarization component in the direction perpendicular to the optical axis, which occurs in the light reflected by the pixel. Is determined to be π. The light incident on the ferroelectric liquid crystal layer is linearly polarized light in the horizontal direction in the figure.

When recording information on the disk 2a, a positive voltage is applied to the ferroelectric liquid crystal layer corresponding to the pixel representing the bit data “1”, and the ferroelectric liquid crystal layer corresponding to the pixel representing the bit data “0”. A negative voltage is applied to. At this time, the direction of the optical axis of the ferroelectric liquid crystal corresponding to the pixel representing the bit data “1” is the 45 ° direction in the figure, and the optical axis of the ferroelectric liquid crystal corresponding to the pixel representing the bit data “0” is The direction is the horizontal direction in the figure. Light incident on the ferroelectric liquid crystal layer corresponding to the pixel representing the bit data “1” is transmitted through the pixel in the liquid crystal optical element 15a and the polarization direction is changed by 90 °, and reflected by the pixel in the liquid crystal optical element 15b. As a result, the polarization direction is changed by 90 ° and emitted from the ferroelectric liquid crystal layer. On the other hand, the light incident on the ferroelectric liquid crystal layer corresponding to the pixel representing the bit data “0” is transmitted through the pixel without changing the polarization state in the liquid crystal optical element 15a, and the pixel in the liquid crystal optical element 15b. The light is reflected without changing its polarization state and is emitted from the ferroelectric liquid crystal layer. Pixels 18a, 18c, and 18e represent bit data “1”, and pixels 18b and 18d represent bit data “0”. The three lights whose object points are the pixels 18a, 18c, and 18e are beams 17a, 17c, and 17e in FIG. 3A or 4A, respectively.

On the other hand, when information is reproduced from the disk 2a, a positive voltage is applied to the ferroelectric liquid crystal layer corresponding to all the pixels. At this time, the direction of the optical axis of the ferroelectric liquid crystal corresponding to all the pixels is the 45 ° direction in the figure. The light incident on the ferroelectric liquid crystal layer corresponding to the pixel passes through the pixel in the liquid crystal optical element 15a and changes its polarization direction by 90 °, and is reflected by the pixel in the liquid crystal optical element 15b and has a polarization direction of 90 °. Changes and emerges from the ferroelectric liquid crystal layer. The five lights whose object points are the pixels 18a, 18b, 18c, 18d, and 18e are beams 17a, 17b, 17c, 17d, and 17e in FIG. 3B or 4B.

6A to 6B show optical paths of an incident beam to the disk 2a and a reflected beam from the disk 2a when information is recorded on the disk 2a and information is reproduced from the disk 2a. The disk 2a is configured so that the recording layer 19a is sandwiched between the substrate 22a and the substrate 22b. Glass or the like is used as the material for the substrates 22a and 22b. As a material of the recording layer 19a, a photopolymer or the like is used. About 50% of the beams 17a, 17c, and 17e in FIG. 3A or FIG. 4A are reflected by the polarization beam splitter 10a to become beams 25a, 25c, and 25e shown in FIG. 6A, respectively. Further, the other approximately 50% passes through the polarization beam splitter 10a to become beams 26a, 26c, and 26e shown in FIG. 6A, respectively. Further, almost 100% of the beams 17a, 17b, 17c, 17d, and 17e shown in FIG. 3B or FIG. 4B are reflected by the polarization beam splitter 10a, and the beams 25a, 25b, 25c, 25d, and FIG. 25e. Here, the surface of the substrate 22a on the objective lens 13a side and the surface of the substrate 22b on the objective lens 13b side correspond to a first incident surface and a second incident surface, respectively.

FIG. 6A shows an optical path of an incident beam on the disk 2a when information is recorded on the disk 2a. As shown in FIG. 6A, the beams 25a, 25c, and 25e enter the objective lens 13a as parallel light and are condensed in the recording layer 19a. The beams 26a, 26c, and 26e are incident on the objective lens 13b as parallel light and are condensed in the recording layer 19a. The beams 25a and 26a are focused on the focusing point 23a, the beams 25c and 26c are focused on the focusing point 23b, and the beams 25e and 26e are focused on the focusing point 23c and interfere with each other. A minute diffraction grating is formed. Thus, the state where the diffraction grating is formed corresponds to the bit data “1”, and the state where the diffraction grating is not formed corresponds to the bit data “0”. The diffraction gratings formed at the condensing points 23a, 23b, and 23c shown in FIG. 6A correspond to the diffraction gratings 24a, 24b, and 24c shown in FIG. 6B.

FIG. 6B shows an optical path of an incident beam to the disk 2a and an optical path of a reflected beam from the disk 2a when information is reproduced from the disk 2a. As shown in FIG. 6B, the beams 25a, 25b, 25c, 25d, and 25e enter the objective lens 13a as parallel light and are condensed in the recording layer 19a. The beams 25a, 25c, and 25e are reflected by the diffraction gratings 24a, 24b, and 24c formed at the condensing points, respectively, are emitted from the objective lens 13a as parallel light, and reverse the same optical path as the beams 25a, 25c, and 25e. The light is received by a corresponding pixel among a plurality of pixels included in the light receiving layer of the image sensor 14. On the other hand, the beams 25b and 25d are not reflected because the diffraction grating is not formed at the condensing point, and are not received by the corresponding pixels among the plurality of pixels included in the light receiving layer of the image sensor 14. As described above, the state where the pixel receives the beam corresponds to the bit data “1”, and the state where the pixel does not receive the beam corresponds to the bit data “0”. When the liquid crystal optical elements 15a and 15b shown in FIGS. 5A to 5B are used, 25 channels of parallel recording / reproduction can be performed in the plane of the recording layer 19a.

Note that the optical head device according to the first embodiment of the present invention can include means for detecting and correcting the deviation of the light collection position. One of them is an optical system for detecting a deviation of one condensing position with respect to one condensing position of two beams opposed to each other when information is recorded on the disk 2a and a means for correcting the deviation. It is. Further, an optical system for detecting the deviation of the beam condensing position with respect to the reference position of the disk 2a and means for correcting the deviation can be provided.

FIG. 7 shows the configuration of an optical information recording / reproducing apparatus equipped with the above-described optical head 1a. The optical information recording / reproducing apparatus includes an optical head 1a, a positioner 27a, a spindle 28, a controller 29, a laser drive circuit 30, a modulation circuit 31, a recording signal generation circuit 32, a spatial modulator drive circuit 33, an amplification circuit 34, and reproduction signal processing. A circuit 35, a demodulation circuit 36, a variable wavelength plate drive circuit 37, an objective lens drive circuit 38, a positioner drive circuit 40, and a spindle drive circuit 41 are provided. The optical head 1a is mounted on a positioner 27a. The disk 2 a is mounted on the spindle 28. A laser drive circuit 30 which is a light source drive circuit, a circuit from the modulation circuit 31 to the spatial light modulator drive circuit 33, a circuit from the amplification circuit 34 to the demodulation circuit 36, a variable wavelength plate drive circuit 37, an objective lens drive circuit 38, a positioner The drive circuit 40 and the spindle drive circuit 41 are controlled by the controller 29.

When recording information on the disk 2a and reproducing information from the disk 2a, the laser drive circuit 30 applies constant power to the laser 3 so that the power of the emitted light from the laser 3 in the optical head 1a is constant. A current is supplied to drive the laser 3.

The modulation circuit 31 modulates a signal input from the outside as recording data according to a modulation rule when recording information on the disk 2a. The recording signal generation circuit 32 generates a recording signal for driving the spatial light modulator 6 in the optical head 1 a based on the signal modulated by the modulation circuit 31. The spatial light modulator drive circuit 33 drives the spatial light modulator 6. When recording information on the disk 2a, the spatial light modulator drive circuit 33 records on the ferroelectric liquid crystal layer, which is a modulation layer corresponding to each pixel, based on the recording signal generated by the recording signal generation circuit 32. A voltage corresponding to the signal is supplied to drive the spatial light modulator 6. Thereby, light having a pixel representing the bit data “1” as an object point among a plurality of pixels included in the modulation layer of the spatial light modulator 6 is generated, and the pixel representing the bit data “0” is defined as the object point. No light is generated. On the other hand, when reproducing information from the disk 2a, the spatial light modulator drive circuit 33 is configured so that light having all the pixels included in the modulation layer of the spatial light modulator 6 as object points is generated. The spatial light modulator 6 is driven by supplying a constant voltage to the ferroelectric liquid crystal layer which is the modulation layer corresponding to the pixel.

The amplifying circuit 34 amplifies the voltage signal output from each of the plurality of pixels included in the light receiving layer of the image sensor 14 in the optical head 1a when reproducing information from the disk 2a. The reproduction signal processing circuit 35 performs generation, waveform equalization, and binarization of a reproduction signal recorded in the form of a diffraction grating on the disk 2a based on the voltage signal amplified by the amplifier circuit 34. The demodulation circuit 36 demodulates the signal binarized by the reproduction signal processing circuit 35 according to a demodulation rule, and outputs it as reproduction data to the outside.

When recording information on the disk 2a, the variable wavelength plate driving circuit 37 applies a voltage V to the liquid crystal layer of the variable wavelength plate 7 so that the variable wavelength plate 7 in the optical head 1a has the effect of a quarter wavelength plate. Is applied. When reproducing information from the disk 2a, the variable wavelength plate driving circuit 37 applies a voltage to the liquid crystal layer of the variable wavelength plate 7 so that the variable wavelength plate 7 in the optical head 1a has the effect of a half wavelength plate. Do not apply.

The objective lens drive circuit 38 supplies current to an actuator (not shown) to drive the objective lenses 13a and 13b in the optical head 1a in the optical axis direction. Thereby, when information is recorded on the disk 2a and when information is reproduced from the disk 2a, a plurality of light converging positions of a plurality of lights in the recording layer of the disk 2a move in the thickness direction of the recording layer.

Positioner drive circuit 40 supplies current to a motor (not shown) to move positioner 27a on which optical head 1a is mounted in the radial direction of disk 2a. As a result, when information is recorded on the disk 2a and when information is reproduced from the disk 2a, a plurality of light converging positions of a plurality of lights in the recording layer of the disk 2a move in the radial direction of the disk 2a. The spindle drive circuit 41 supplies current to a motor (not shown) to rotate the spindle 28 on which the disk 2a is mounted. Accordingly, when information is recorded on the disk 2a and when information is reproduced from the disk 2a, a plurality of light converging positions of a plurality of lights in the recording layer of the disk 2a move in the tangential direction of the disk 2a.

FIG. 8 shows a configuration of an optical head device according to the second embodiment of the present invention. The optical head 1b records information on the disk 2b which is an optical recording medium, and reproduces the information recorded on the disk 2b. The optical head 1b includes a laser 3, convex lenses 4a, 4b, 4g to 4k, a microlens array 5, a spatial light modulator 6, a variable wavelength plate 7, a beam splitter 8, an aperture 9c, polarizing beam splitters 10b and 10c, a mirror 11g, 11h, an objective lens 13c, and an image sensor 14. The laser 3 as a light source is a single mode semiconductor laser, and emits light having a wavelength of 405 nm. The light emitted from the laser 3 enters the convex lens 4a as divergent light, passes through the convex lens 4a and is converted from divergent light to parallel light, and passes through the microlens array 5 to convert parallel light into a plurality of convergent lights. Then, the light is condensed as a plurality of condensing spots in a modulation layer including a plurality of pixels of the spatial light modulator 6. Each condensing position of the plurality of condensing spots corresponds to each of the plurality of pixels. Here, the microlens array 5 corresponds to a beam group generation unit, and a plurality of lights condensed as a plurality of focused spots correspond to an outgoing beam group. The plurality of lights enter the convex lens 4 b as a plurality of divergent lights, pass through the convex lens 4 b, are converted from the plurality of divergent lights to a plurality of parallel lights, and enter the variable wavelength plate 7. The variable wavelength plate 7 has the effect of a ¼ wavelength plate with respect to incident light when recording information on the disk 2b, which is an optical recording medium, and changes to incident light when information is reproduced from the disk 2b, which is an optical recording medium. On the other hand, it has the effect of all wave plates.

When recording information on the disk 2b, a plurality of lights incident on the variable wavelength plate 7 are transmitted through the variable wavelength plate 7 and converted from a plurality of linearly polarized lights to a plurality of circularly polarized lights. 8 is reflected. About 50% of each of the reflected plurality of circularly polarized light passes through the polarizing beam splitter 10b as a P-polarized component, and about 50% of each of the plurality of circularly polarized light is reflected by the polarizing beam splitter 10b as an S-polarized component. Here, the variable wavelength plate 7 and the polarization beam splitter 10b correspond to a beam group splitting unit. The plurality of lights transmitted through the polarization beam splitter 10b and the plurality of lights reflected by the polarization beam splitter 10b correspond to a first outbound beam group and a second outbound beam group, respectively.

The plurality of lights transmitted through the polarizing beam splitter 10b are transmitted through the convex lens 4g, converted from a plurality of parallel lights to a plurality of convergent lights, and collected as a plurality of focused spots. The plurality of lights enter the convex lens 4i as a plurality of divergent lights, pass through the convex lens 4i, are converted from the plurality of divergent lights into convergent lights close to a plurality of parallel lights, and are reflected by the mirror 11h. Each of the plurality of linearly polarized light enters the polarizing beam splitter 10c as P-polarized light and almost 100% is transmitted. The plurality of lights transmitted through the polarizing beam splitter 10c are transmitted from the objective lens 13c and converted from convergent lights close to a plurality of parallel lights to a plurality of convergent lights, and collected as a plurality of condensed spots in the recording layer of the disk 2b. To be lighted.

On the other hand, the plurality of lights reflected by the polarization beam splitter 10b are reflected by the mirror 11g, pass through the convex lens 4h, converted from a plurality of parallel lights to a plurality of convergent lights, and collected as a plurality of focused spots. . The plurality of lights enter the convex lens 4j as a plurality of diverging lights, pass through the convex lens 4j, and are converted from a plurality of diverging lights to diverging lights close to a plurality of parallel lights, and each of the plurality of linearly polarized lights is a polarized beam. It enters the splitter 10c as S-polarized light and almost 100% is reflected. The plurality of lights reflected by the polarization beam splitter 10c are transmitted through the objective lens 13c and converted from diverging lights close to a plurality of parallel lights to a plurality of convergent lights, and as a plurality of condensed spots in the recording layer of the disk 2b. Focused. Each of the plurality of lights transmitted through the polarization beam splitter 10b and each of the plurality of lights reflected by the polarization beam splitter 10b are condensed at the same position in the recording layer of the disk 2b and interfere with each other. A minute diffraction grating is formed at each light position. Here, the rear focal position of the convex lens 4b coincides with the front focal position of the convex lenses 4g and 4h, and the rear focal position of the convex lenses 4i and 4j coincides with the front focal position of the objective lens 13c.

Each of the plurality of focused spots formed in the modulation layer of the spatial light modulator 6 corresponds to each of the plurality of focused spots formed in the recording layer of the disk 2b. That is, the modulation layer of the spatial light modulator 6 and the recording layer of the disk 2b are optically connected to the convex lenses 4b, 4g, 4i and the objective lens 13c, and to the convex lenses 4b, 4h, 4j and the objective lens 13c. In a conjugate position. In FIG. 8, the number of the plurality of condensing spots formed in the modulation layer of the spatial light modulator 6 and the number of the plurality of condensing spots formed in the recording layer of the disk 2b are all five. is there. The modulation layer of the spatial light modulator 6 is at the front focal position of the convex lens 4b, and the opening 9c is at the rear focal position of the convex lens 4b. That is, the opening 9 c is provided in the Fourier plane with respect to the modulation layer of the spatial light modulator 6.

The plurality of principal rays corresponding to the plurality of condensing spots formed in the modulation layer of the spatial light modulator 6 intersect at one point at the rear focal position of the convex lens 4b. Therefore, by providing the opening 9c at this position, it is possible to make all the beam diameters of a plurality of lights having a plurality of focused spots as object points equal. As a result, all the numerical apertures of the objective lens 13c for each of the plurality of lights can be made equal, and the sizes of the plurality of diffraction gratings formed at the plurality of condensing positions in the recording layer of the disk 2b are all made equal. be able to. Note that the position of the opening 9c is not necessarily the rear focal position of the convex lens 4b as long as it is the Fourier plane of the modulation layer of the spatial light modulator 6. For example, instead of the opening 9c, a position that is optically conjugate with the rear focal position of the convex lens 4b with respect to the convex lenses 4g and 4i, and a position with the rear focal position of the convex lens 4b with respect to the convex lenses 4h and 4j are optically coupled with each other. An opening may be provided at a position conjugate to the.

The outgoing beam group from the spatial light modulator 6 to the incident surface of the disk 2b and the optical path of the first outgoing beam group have two reflecting surfaces in total, the reflecting surface of the beam splitter 8 and the reflecting surface of the mirror 11h. At this time, a plurality of condensed spots are formed in the modulation layer of the spatial light modulator 6 and in the recording layer of the disk 2b. Of these plurality of focused spots, light having focused spots located at points a and b (see FIG. 8) in the modulation layer of the spatial light modulator 6 is the spatial light modulator 6. The light passes through the optical path from the incident surface of the disk 2b to the incident surface of the disk 2b, and becomes a light having a focused spot located at points A and B (see FIG. 8) in the recording layer of the disk 2b as image points.

On the other hand, on the optical path of the outgoing beam group and the second outgoing beam group from the spatial light modulator 6 to the incident surface of the disk 2b, there are a reflecting surface of the beam splitter 8, a reflecting surface of the polarizing beam splitter 10b, and a reflecting surface of the mirror 11g. There are a total of four reflecting surfaces of the polarizing beam splitter 10c. At this time, a plurality of condensed spots are formed in the modulation layer of the spatial light modulator 6 and in the recording layer of the disk 2b. Of these plurality of focused spots, light having focused spots located at points a and b (see FIG. 8) in the modulation layer of the spatial light modulator 6 is the spatial light modulator 6. The light passes through the optical path from the incident surface of the disk 2b to the incident surface of the disk 2b, and becomes a light having a focused spot located at points A and B (see FIG. 8) in the recording layer of the disk 2b as image points.

Thus, the number of reflecting surfaces in the optical path of the outgoing beam group and the first outgoing beam group from the spatial light modulator 6 to the incident surface of the disk 2b, and the outgoing light from the spatial light modulator 6 to the incident surface of the disk 2b. The difference between the number of reflection surfaces in the optical path of the beam group and the second forward beam group is an even number. As a result, the same focused spot formed in the modulation layer of the spatial light modulator 6 among the plurality of lights included in the first outbound beam group and the plurality of lights included in the second outbound beam group The light that becomes the object point becomes light that has the same focused spot formed in the recording layer of the disk 2b as the image point.

On the other hand, when reproducing information from the disk 2b, a plurality of lights incident on the variable wavelength plate 7 are transmitted through the variable wavelength plate 7 without changing the polarization state, and about 50% of each light is transmitted by the beam splitter 8. Reflected. Each of the reflected linearly polarized light is incident on the polarizing beam splitter 10b as P-polarized light and almost 100% is transmitted. Here, the plurality of lights transmitted through the polarization beam splitter 10b correspond to the forward beam group. The plurality of lights that have passed through the polarization beam splitter 10b are transmitted through the convex lens 4g, converted from a plurality of parallel lights to a plurality of convergent lights, and collected as a plurality of focused spots. The plurality of lights enter the convex lens 4i as a plurality of diverging lights, pass through the convex lens 4i, are converted from the plurality of diverging lights into convergent lights close to a plurality of parallel lights, and are reflected by the mirror 11h. Each of the reflected plurality of linearly polarized light enters the polarizing beam splitter 10c as P-polarized light and almost 100% is transmitted. The plurality of lights transmitted through the polarizing beam splitter 10c are transmitted from the objective lens 13c and converted from convergent lights close to a plurality of parallel lights to a plurality of convergent lights, and collected as a plurality of condensed spots in the recording layer of the disk 2b. Be lit.

The plurality of lights are reflected by a plurality of diffraction gratings formed at a plurality of condensing positions, are incident on the objective lens 13c as a plurality of diverging lights, pass through the objective lens 13c, and are transmitted from the plurality of diverging lights. It is converted into divergent light that is close to parallel light. Each of the converted plurality of linearly polarized light enters the polarizing beam splitter 10c as P-polarized light and almost 100% is transmitted. The plurality of lights that have passed through the polarization beam splitter 10c are reflected by the mirror 11h, are transmitted through the convex lens 4i, are converted from divergent light that is close to the plurality of parallel lights, into a plurality of convergent lights, and are collected as a plurality of condensed spots. The The plurality of lights enter the convex lens 4g as a plurality of divergent lights, pass through the convex lens 4g and converted from the plurality of divergent lights to a plurality of parallel lights, and each of the plurality of linearly polarized lights is applied to the polarization beam splitter 10b. Nearly 100% is transmitted as polarized light. About 50% of each of the plurality of lights transmitted through the polarization beam splitter 10b is transmitted through the beam splitter 8 and transmitted through the convex lens 4k to be converted from a plurality of parallel lights into a plurality of convergent lights. The light is condensed as a plurality of light condensing spots in the light receiving layer including the pixels. Each condensing position of the plurality of condensing spots corresponds to each of the plurality of pixels. Here, the image sensor 14 corresponds to a photodetector, and a plurality of lights condensed as a plurality of condensing spots correspond to a return beam group.

Each of the plurality of condensing spots formed in the light receiving layer of the image sensor 14 corresponds to each of the plurality of condensing spots formed in the recording layer of the disk 2b. That is, the light receiving layer of the image sensor 14 and the recording layer of the disk 2b are optically connected to the objective lens 13c and the convex lenses 4i, 4g, and 4k, and to the objective lens 13c and the convex lenses 4j, 4h, and 4k. It is in a conjugate position. In FIG. 8, the number of the plurality of condensing spots formed in the light receiving layer of the image sensor 14 and the number of the plurality of condensing spots formed in the recording layer of the disk 2b are all five. The light receiving layer of the image sensor 14 is at the rear focal position of the convex lens 4k, and the opening 9c is at the front focal position of the convex lens 4k. That is, the opening 9 c is provided in the Fourier plane with respect to the light receiving layer of the image sensor 14.

Here, each of the plurality of diffraction gratings has bit data information. A plurality of condensing positions of a plurality of lights transmitted through the polarization beam splitter 10b and a plurality of lights reflected by the polarization beam splitter 10b are moved in the thickness direction of the recording layer, so that the thickness of the recording layer as well as the in-plane direction is increased. By forming a plurality of diffraction gratings in multiple layers in the direction, three-dimensional recording / reproduction can be performed in parallel.

The variable wavelength plate 7 is configured to sandwich a liquid crystal layer between two substrates. Electrodes for applying a voltage to the liquid crystal layer are formed on the surface of the two substrates on the liquid crystal layer side. The liquid crystal contained in the liquid crystal layer has uniaxial refractive index anisotropy. The thickness of the liquid crystal layer is determined so that the phase difference between the polarization component in the direction parallel to the optical axis and the polarization component in the direction perpendicular to the optical axis generated in the light transmitted through the liquid crystal layer is π. . When the voltage V is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is an intermediate direction parallel to the direction perpendicular to the optical axis of the incident light. At this time, the variable wave plate 7 has an effect of a quarter wave plate. When a voltage of 2 V is applied to the liquid crystal layer, the direction of the optical axis of the liquid crystal layer is parallel to the optical axis of incident light. At this time, the variable wave plate 7 has the effect of a full wave plate.

In the optical head device according to the second embodiment of the present invention, similarly to the optical head device according to the first embodiment of the present invention, a transmissive liquid crystal optical element and a polarization are used as the spatial light modulator 6. It is possible to use a spatial light modulator 6a in which a child is combined and a spatial light modulator 6b in which a reflective liquid crystal optical element and a polarization beam splitter are combined. The spatial light modulator 6a that combines a transmissive liquid crystal optical element and a polarizer operates as shown in FIGS. 3A to 3B. The spatial light modulator 6b in which the reflective liquid crystal optical element and the polarization beam splitter are combined operates as shown in FIGS. 4A to 4B. The plurality of pixels included in the modulation layer provided in the liquid crystal optical element in the plane perpendicular to the optical axis of the liquid crystal optical element are the same as those shown in FIGS. 5A to 5B.

9A to 9B show optical paths of an incident beam to the disk 2b and a reflected beam from the disk 2b when information is recorded on the disk 2b and information is reproduced from the disk 2b. FIG. 9A shows an optical path of an incident beam to the disk 2b when information is recorded on the disk 2b. FIG. 9B shows an optical path of an incident beam to the disk 2b and a reflected beam from the disk 2b when information is reproduced from the disk 2b. The disk 2b is configured to sandwich the recording layer 19b, the quarter-wave plate layer 20, and the reflective layer 21 in this order between the substrate 22c and the substrate 22d. Glass or the like is used as the material of the substrates 22c and 22d. As a material for the recording layer 19b, a photopolymer or the like is used. A liquid crystal or the like is used as the material of the quarter-wave plate layer 20. Aluminum or the like is used as the material of the reflective layer 21. About 50% of the beams 17a, 17c, and 17e in FIG. 3A or 4A are transmitted through the polarization beam splitter 10b in FIG. 8 to become beams 25f, 25h, and 25j in FIG. 9A, respectively. The other approximately 50% is reflected by the polarization beam splitter 10b in FIG. 8 to become the beams 26f, 26h, and 26j in FIG. 9A, respectively. Further, almost 100% of the beams 17a, 17b, 17c, 17d, and 17e in FIG. 3B or FIG. 4B are transmitted through the polarization beam splitter 10b in FIG. 8, and the beams 25f, 25g, 25h, 25i, and 25j in FIG. It becomes.

In FIG. 9A, beams 25f, 25h, and 25j are incident on the objective lens 13c as convergent light whose polarization direction is parallel to the plane of the paper, and are condensed on the way toward the reflective layer 21 in the recording layer 19b. Is done. The beams 26f, 26h, and 26j are incident on the objective lens 13c as diverging light whose polarization direction is perpendicular to the plane of the paper, pass through the recording layer 19b, pass through the quarter-wave plate layer 20, and pass through the circle. It is converted into polarized light and reflected by the reflective layer 21. The reflected circularly polarized light passes through the quarter-wave plate layer 20 and is converted into linearly polarized light whose polarization direction is parallel to the paper surface, and is condensed on the way to the side opposite to the reflective layer 21 in the recording layer 19b. The The beam 25f and the beam 26f are condensed at the condensing point 23d, the beam 25h and the beam 26h are condensed at the condensing point 23e, and the beam 25j and the beam 26j are condensed at the condensing point 23f. A minute diffraction grating is formed at the light spot. Thus, the state where the diffraction grating is formed corresponds to the bit data “1”, and the state where the diffraction grating is not formed corresponds to the bit data “0”. The diffraction gratings 24d, 24e, and 24f in FIG. 9B are respectively formed at the condensing points 23d, 23e, and 23f in FIG. 9A.

In FIG. 9B, beams 25f, 25g, 25h, 25i, and 25j enter the objective lens 13c as convergent light whose polarization direction is parallel to the plane of the paper, and travel toward the reflective layer 21 in the recording layer 19b. It is condensed on the way. The beams 25f, 25h, and 25j are reflected by the diffraction gratings 24d, 24e, and 24f formed at the condensing points, respectively, and are emitted from the objective lens 13c as divergent light whose polarization direction is parallel to the paper surface, and are emitted from the objective lens 13c. , 25h, 25j, and the same optical path as in the opposite direction, and light is received by the corresponding pixels among the plurality of pixels included in the light receiving layer of the image sensor 14. On the other hand, the beams 25g and 25i are not reflected because the diffraction grating is not formed at the condensing point, and are not received by the corresponding pixels among the plurality of pixels included in the light receiving layer of the image sensor 14. As described above, the state where the pixel receives the beam corresponds to the bit data “1”, and the state where the pixel does not receive the beam corresponds to the bit data “0”. When the liquid crystal optical elements 15a and 15b shown in FIGS. 5A to 5B are used, 25 channels of parallel recording / reproducing can be performed in the plane of the recording layer 19b.

It should be noted that the optical head device according to the second embodiment of the present invention can also include means for detecting and correcting the deviation of the condensing position. One of them is an optical system for detecting a deviation of one of two condensing positions when recording information on the disk 2b and a means for correcting the deviation. It is. In addition, an optical system for detecting the deviation of the beam condensing position with respect to the reference position of the disk 2b and means for correcting the deviation can be provided.

FIG. 10 shows a configuration of an optical information recording / reproducing apparatus equipped with the above-described optical head 1b. The optical information recording / reproducing apparatus includes an optical head 1b, a positioner 27b, a spindle 28, a controller 29, a laser drive circuit 30, a modulation circuit 31, a recording signal generation circuit 32, a spatial modulator drive circuit 33, an amplification circuit 34, and reproduction signal processing. A circuit 35, a demodulation circuit 36, a variable wavelength plate drive circuit 37, a convex lens drive circuit 39, a positioner drive circuit 40, and a spindle drive circuit 41 are provided. The optical head 1b is mounted on the positioner 27b. The disk 2b is mounted on the spindle 28. A laser drive circuit 30 that is a light source drive circuit, a circuit from the modulation circuit 31 to the spatial light modulator drive circuit 33, a circuit from the amplification circuit 34 to the demodulation circuit 36, a variable wavelength plate drive circuit 37, a convex lens drive circuit 39, and a positioner drive The circuit 40 and the spindle drive circuit 41 are controlled by the controller 29.

When recording information on the disk 2b and reproducing information from the disk 2b, the laser drive circuit 30 applies constant power to the laser 3 so that the power of the emitted light from the laser 3 in the optical head 1b is constant. A current is supplied to drive the laser 3.

The modulation circuit 31 modulates a signal input from the outside as recording data according to a modulation rule when recording information on the disk 2b. The recording signal generation circuit 32 generates a recording signal for driving the spatial light modulator 6 in the optical head 1 b based on the signal modulated by the modulation circuit 31. The spatial light modulator drive circuit 33 drives the spatial light modulator 6. When recording information on the disk 2b, the spatial light modulator drive circuit 33 records on the ferroelectric liquid crystal layer, which is a modulation layer corresponding to each pixel, based on the recording signal generated by the recording signal generation circuit 32. A voltage corresponding to the signal is supplied to drive the spatial light modulator 6. Thereby, light having a pixel representing the bit data “1” as an object point among a plurality of pixels included in the modulation layer of the spatial light modulator 6 is generated, and the pixel representing the bit data “0” is defined as the object point. No light is generated. On the other hand, when reproducing information from the disk 2b, the spatial light modulator driving circuit 33 is configured so that light having all pixels included in the modulation layer of the spatial light modulator 6 as object points is generated. The spatial light modulator 6 is driven by supplying a constant voltage to the ferroelectric liquid crystal layer which is the modulation layer corresponding to the pixel.

The amplifying circuit 34 amplifies the voltage signal output from each of the plurality of pixels included in the light receiving layer of the image sensor 14 in the optical head 1b when reproducing information from the disk 2b. The reproduction signal processing circuit 35 performs generation, waveform equalization, and binarization of a reproduction signal recorded in the form of a diffraction grating on the disk 2b based on the voltage signal amplified by the amplifier circuit 34. The demodulation circuit 36 demodulates the signal binarized by the reproduction signal processing circuit 35 according to a demodulation rule, and outputs it as reproduction data to the outside.

When recording information on the disk 2b, the variable wavelength plate driving circuit 37 applies a voltage V to the liquid crystal layer of the variable wavelength plate 7 so that the variable wavelength plate 7 in the optical head 1b has the effect of a quarter wavelength plate. Is applied. When reproducing information from the disk 2b, the variable wavelength plate drive circuit 37 applies a voltage of 2V to the liquid crystal layer of the variable wavelength plate 7 so that the variable wavelength plate 7 in the optical head 1b has the effect of all wavelength plates. To do.

The convex lens drive circuit 39 supplies current to an actuator (not shown) to drive the convex lenses 4i and 4j in the optical head 1b in the optical axis direction. Accordingly, when information is recorded on the disk 2b and when information is reproduced from the disk 2b, a plurality of light converging positions of a plurality of lights in the recording layer of the disk 2b move in the thickness direction of the recording layer.

Positioner drive circuit 40 supplies current to a motor (not shown) to move positioner 27b on which optical head 1b is mounted in the radial direction of disk 2b. Thereby, when information is recorded on the disk 2b and when information is reproduced from the disk 2b, a plurality of light converging positions of a plurality of lights in the recording layer of the disk 2b move in the radial direction of the disk 2b. The spindle drive circuit 41 supplies a current to a motor (not shown) to rotate the spindle 28 on which the disk 2b is mounted. As a result, when information is recorded on the disk 2b and when information is reproduced from the disk 2b, a plurality of condensing positions of a plurality of lights in the recording layer of the disk 2b move in the tangential direction of the disk 2b.

As described above, the optical head device and the optical information recording / reproducing device of the present invention divide the light emitted from the light source into a plurality of beams that can be independently modulated, and divide each of the plurality of beams into two beams. Information is recorded in parallel by converging the two opposed beams to the same position in the recording layer of the optical recording medium to cause interference and forming a minute diffraction grating at the converging position. . That is, a plurality of diffraction gratings are formed by one recording. Here, the bit data included in the plurality of diffraction gratings corresponds to a plurality of bits. Therefore, it is possible to increase the data transfer speed while maintaining the characteristics of the bit type three-dimensional recording such as a wide tolerance against the wavelength variation of the light source. At that time, the numerical apertures of the objective lenses for the plurality of beams are all equalized by the action of the apertures provided in the optical system, and the sizes of the plurality of diffraction gratings formed at the condensing positions are all equal.

According to the present invention, it is possible to increase the data transfer speed while maintaining the characteristics of bit-type three-dimensional recording such as a wide tolerance for wavelength variation of the light source.

The present invention has been described above with reference to the embodiments, but 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.

Note that this application claims priority based on Japanese Application No. 2008-090180, and the disclosure in Japanese Application No. 2008-090180 is incorporated by reference into this application.

Claims (8)

  1. An optical head device for recording and reproducing information with respect to an optical recording medium having a recording layer,
    A single light source,
    Beam group generation means for generating an output beam group including a plurality of beams from the output light from the light source;
    A spatial light modulator having a modulation layer including a plurality of pixels capable of independently modulating each of the plurality of beams included in the output beam group;
    An opening provided in a Fourier plane for the modulation layer;
    Beam group dividing means for dividing the outgoing beam group into a first outgoing beam group and a second outgoing beam group when recording information on the optical recording medium;
    Each of the plurality of beams included in the first outbound beam group and each of the plurality of beams included in the second outbound beam group are opposed to each other and condensed at the same position in the recording layer. And an objective lens.
  2. The beam group dividing means has a function of dividing the outgoing beam group into the first outgoing beam group and the second outgoing beam group, and passes the outgoing beam group into a single outgoing beam group. Can be switched between functions,
    When reproducing information from the optical recording medium, the beam group splitting means passes the exit beam group into the single forward beam group,
    The objective lens focuses each of a plurality of beams included in the single forward beam group in the recording layer,
    The optical head device according to claim 1, further comprising a photodetector that receives a return beam group generated by the single outgoing beam group being reflected by the recording layer.
  3. The optical head device according to claim 1, wherein the beam group generation unit includes a microlens array.
  4. The lens system including the objective lens is provided between the modulation layer and the recording layer, and the modulation layer and the recording layer are in an optically conjugate position with respect to the lens system. The optical head device according to any one of claims 1 to 3.
  5. The lens is provided between the modulation layer and the opening, and the modulation layer and the opening are at a front focal position and a rear focal position of the lens, respectively. 2. An optical head device according to 1.
  6. As the optical recording medium, an optical recording medium having a first incident surface and a second incident surface parallel to the recording layer and sandwiching the recording layer is used.
    When recording information on the optical recording medium, the first outgoing beam group and the second outgoing beam group are incident on the optical recording medium from the first incident surface and the second incident surface, respectively. Collected in the recording layer,
    The number of reflecting surfaces in the optical path of the outgoing beam group and the first forward beam group from the spatial light modulator to the first incident surface; and the number of reflective surfaces from the spatial light modulator to the second incident surface. The optical head device according to any one of claims 1 to 5, wherein a difference between the number of reflecting surfaces in the optical path of the outgoing beam group and the second outgoing beam group is an odd number.
  7. As the optical recording medium, an optical recording medium having an incident surface parallel to the recording layer and a reflective layer located on the opposite side of the incident surface across the recording layer is used,
    When recording information on the optical recording medium, the first forward beam group is incident on the optical recording medium from the incident surface and is condensed on the way to the reflective layer side in the recording layer,
    The second outward beam group is incident on the optical recording medium from the incident surface, passes through the recording layer, is reflected by the reflective layer, and is condensed on the way to the incident surface side in the recording layer. And
    The number of reflecting surfaces in the optical path of the outgoing beam group and the first forward beam group from the spatial light modulator to the incident surface, the outgoing beam group from the spatial light modulator to the incident surface, and the first The optical head device according to any one of claims 1 to 5, wherein the difference between the number of reflection surfaces in the optical path of the two forward beam groups is an even number.
  8. An optical head device according to any one of claims 1 to 7,
    A light source driving circuit for driving the light source;
    An optical information recording / reproducing apparatus comprising: a spatial light modulator driving circuit that drives the spatial light modulator.
PCT/JP2009/055992 2008-03-31 2009-03-25 Optical head device and optical information recording/reproducing device WO2009122987A1 (en)

Priority Applications (2)

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JP2008090180 2008-03-31

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