WO2007026588A1

WO2007026588A1 - Optical pickup device and hologram recording/reproducing system

Info

Publication number: WO2007026588A1
Application number: PCT/JP2006/316547
Authority: WO
Inventors: Masakazu Ogasawara
Original assignee: Pioneer Corporation
Priority date: 2005-08-30
Filing date: 2006-08-17
Publication date: 2007-03-08
Also published as: JPWO2007026588A1

Abstract

An optical pickup device for recording or reproducing information in and from a hologram record carrier includes a light source; a spatial light modulator, which is composed of a center area arranged on an optical axis and an annular area arranged to surround the center area, spatially separates components passing through the center area from those passing through the annular area, generates reference beams and signal beams and propagates the beams coaxially in the same direction; an objective lens, which is arranged on an optical axis, projects the signal beams and the reference beams coaxially toward a hologram recording layer, and collects the reference beams and the signal beams at different focal points; an image detecting means which receives beams returned from the hologram recording layer; and an aberration correcting device, which is composed of a center correcting area arranged on an optical axis and an annular peripheral area arranged to surround the center correcting area, and has at least one of the center correcting area and the annular peripheral area composed of a transmissive liquid crystal device provided with a plurality of transparent electrodes which correct the wavefront aberration of a passing luminous flux that partially changes the phase of the wavefront of the passing luminous flux.

Description

Technical field of optical pick-up device and photogram recording / reproducing system

The present invention relates to a record carrier on which information is recorded or reproduced optically, such as an optical disk and a light field, and more particularly to a hologram record carrier having a hologram recording layer capable of recording or reproducing information by irradiation with a light beam. The present invention relates to an optical pick-up device and a holographic recording / reproducing system. Background technology.

In order to record high-density information, attention is being paid to a photogram that can record secondary charge data at high density. The feature of this hologram is that the wavefront of light carrying recorded information is recorded as a change in refractive index in volume on a recording medium made of a photosensitive material such as a photorefractive material. By performing multiplex recording on the hologram record carrier, the food recording capacity can be dramatically increased. As a structure, a recording medium in which a substrate, an information recording layer, and a reflective layer are formed in this order is known.

For example, conventionally, in an information recording apparatus for recording a hologram by coaxially irradiating a short-wavelength writing object light and a reference light on a thin film recording layer to record a hologram, circularly polarized objects having different rotation directions from each other There is a technique (see Japanese Patent Publication No. 2 0 0 2-5 1 3 9 8 1) that performs polarization hologram recording by condensing light and reference light onto a recording medium with the same lens. Such polarization holographic recording consists of two plane waves with mutually orthogonal polarizations. The object light and reference light are converted into clockwise circularly polarized light and counterclockwise circularly polarized light using a quarter-wave plate, and one polarization hologram is recorded by interference in these recording media. At the time of reproduction, reference light for reading having a wavelength longer than that at the time of recording is used, and reproduction is performed by a separate reproduction optical system. In the reproduction optical system, a special half-wave plate having a central aperture is provided, and the reproduction light is obtained from the polarization hologram by irradiating the central reference light. Since the reproduction light spreads due to the long-wavelength reference light, it passes through the half-wave plate around the aperture, so that the polarization direction changes and is separated by the polarization beam splitter, and the transmitted reproduction light is detected. Is done. Therefore, in the technology disclosed in JP 200.2-513981, it is necessary to switch between the writing and reading wavelength light sources and the optical system during recording and reproduction, and the reflected light sometimes does not return from the recording medium during recording. Another optical system that performs positioning servo control between the irradiation light and the recording medium is required. Further, in the technique of JP-T-2002-513981, since the reference light is parallel light in the recording medium, shift multiplex recording cannot be performed. -Furthermore, conventionally, the information light is converged and irradiated so as to have the smallest diameter on the boundary surface between the hologram recording layer and the protective layer of the recording medium and reflected by the reflective layer. At the same time, the recording reference light is protected from the hologram recording layer and the protective layer. Recording was performed on the hologram recording layer by converging so as to be the smallest diameter before the boundary surface of the eyelid and irradiating it with divergent light to cause interference (Japanese Patent Laid-Open No. 11-311938). Issue gazette).

Furthermore, in the recording optical system, the information light is converged on the reflection layer, the recording reference light is defocused on the reflection layer, and the conjugate focal point of the recording reference light is from the boundary surface between the substrate and the information recording layer. There is also a technique for irradiating a recording reference beam so that it is positioned on the substrate side (see Japanese Patent Application Laid-Open No. 2004-171611). Disclosure of the invention

In order to record the refractive index as a volume change on the recording medium in the prior art, the diffraction pattern spacing may change due to the shrinkage of the recording medium due to the shrinkage of the recording medium, and the diffraction efficiency during reproduction may decrease. There is a problem that the playback signal contains distortion. Conventional recording media, particularly polymer-based photosensitive materials, have a large rate of change in expansion and contraction due to light irradiation, but no countermeasures have been taken in the prior art.

Further, examples of objective lens configurations in a mode in which recording and reproduction are performed from one side of the recording layer in the prior art, for example, the techniques disclosed in Japanese Patent Laid-Open Nos. 11-31.1938 and 2004-171611 are shown in FIGS. 1 and 2, respectively. Show.

In any technique, during recording, as shown in the figure, the reference light and the signal light are guided to the objective lens OB so as to overlap each other on the same axis. The reference light and signal light after passing through the objective lens OB are set to have different focal lengths.

In Fig. 1), the signal light is condensed (focal point P) at the position where the reflective layer is to be arranged, and the reference light is condensed before the focal point P (focal point P 1). In Fig. 2 (a), the signal light is focused (focused) at the position where the reflective layer should be placed, and the reference light is focused before focus P (focused P2). In either case, the reference light and signal light collected by the objective lens OB are always in a state of interference on the optical axis. Therefore, as shown in FIGS. 1 (b) and 2 (b), when the reflection layer is arranged at the position of the focal point P of the signal light and the recording medium is arranged between the objective lens and the reflection layer, the reference light and The signal light passes back and forth through the recording medium for hologram recording. During reproduction, the reference light passes back and forth through the recording medium, and the reflected reference light returns to the objective lens OB together with the reproduction light. As shown in FIG. 3, the holograms to be specifically recorded are hologram recording A (reflecting reference light and reflected signal light) and hologram recording B (incident reference light and reflected signal light) in any technique. ), Hologram recording C (reflecting reference light and incident signal light), and hologram recording D (incident reference light and incident signal light). Also, the hologram to be reproduced is hologram recording A (read by reflected reference light), hologram recording B (read by incident reference light), hologram recording C (read by incident reference light), hologram recording There are four types, D (read out by the incident reference light).

Therefore, in these conventional techniques, all the light rays in the recording layer (incident light and reflected light of the reference light and incident light and reflected light of the information light) interfere with each other, so that a plurality of holograms are recorded and reproduced. End up. This is, for example, as described in paragraph (0 0 9 6) (0 0 9 7) of Japanese Patent Application Laid-Open No. 2 00 4-1 7 1 6 11. In the conventional method, when a hologram is recorded on a hologram record carrier having a reflecting surface, four holograms are recorded due to the interference of the four beams of incident reference light, signal light, reflected reference light, and signal light. Therefore, the performance of the hologram recording layer was used unnecessarily. Therefore, when reproducing information, the reference light is reflected by the reflection layer of the hologram record carrier, so that it is necessary to separate the reproduced light from the reproduced hologram. For this reason, the read performance of the reproduction signal is deteriorated.

In addition, since the conventional method requires many optical components for generating and merging the reference light and the signal light, it is desired to reduce the size of the apparatus.

Therefore, the problem to be solved by the present invention includes an optical pick-up apparatus and a holographic apparatus for hologram recording / reproduction that enable stable recording or reproduction. An example is to provide a video recording / playback system.

The optical pick-up apparatus of the present invention is an optical pick-up apparatus for recording or reproducing information on a hologram record carrier having a hologram recording layer that stores therein an optical interference pattern of reference light and signal light as a diffraction grating.

A light source that generates interfering light, and a central region disposed on an optical axis of the coherent light and an annular region disposed so as to surround the central region, the coherent light A spatial light modulator that spatially separates the pass component of the central region and the pass component of the annular region to generate a reference light and a signal light and propagates them in the same direction on the same axis;

An objective lens optical system that is arranged on an optical axis and irradiates the signal light and the reference light toward the hologram recording layer on the same axis and collects the reference light and the signal light at different focal points; An image detecting means that receives light returning from the hologram recording layer via the objective lens optical system when the hologram recording layer is irradiated with the reference light,

A central correction region disposed on the optical axis and an annular peripheral region disposed so as to surround the central correction region, at least one of the central correction region and the annular peripheral region being a phase of a wavefront of a passing light beam And an aberration correction device comprising a transmissive liquid crystal device having a plurality of transparent electrodes for correcting wavefront aberration of the passing light flux that partially changes the light flux.

The hologram recording / reproducing system of the present invention records or reproduces information on a hologram record carrier that stores therein the optical interference pattern of reference light and signal light as a diffraction grating. A hologram recording / reproducing system,

Light generating means for generating, from coherent light, reference light, and signal light obtained by modulating the coherent light according to recording information,

One of the reference light and the signal light is on the optical axis, and the other is annularly formed around the one, spatially separated from each other and propagated coaxially in the same direction, via the objective lens optical system, Interference means for condensing the reference light and the signal light at different focal points on an optical axis, and interfering the reference light and the signal light;

A hologram record carrier having a hologram recording layer located on the focal side close to the objective lens optical system among the different focal points;

A reflective layer located on the focal side far from the objective lens optical system among the different focal points;

An image detecting means disposed on the optical axis and receiving light returning from the hologram recording layer through the objective lens optical system when the hologram recording layer is irradiated with the reference light; A central correction region and an annular peripheral region disposed so as to surround the central correction region, and at least one of the central correction region and the annular peripheral region partially includes the phase of the wavefront of the passing light beam. An aberration correction device comprising a transmission-type liquid crystal device having a plurality of transparent electrodes for correcting wavefront aberration of the passing light flux that is changed in accordance with a correction voltage when information is recorded or reproduced on each of the plurality of transparent electrodes An aberration correction liquid crystal drive circuit for supplying

According to the above configuration, even when distortion, thickness error, inclination, etc. occur in the hologram record carrier, etc., the transparent electrode in the aberration correction device performs correction according to the aberration. The phase difference is suitable for canceling aberrations in the transmitted wavefront because the applied correction voltage can give the liquid crystal a refractive index change according to the divided electrode pattern. (Aberration) can be given. By providing the phase difference, it is possible to reduce the aberration generated in the passing light due to the tilt and thickness error of the hologram record carrier and the refractive index error of the hologram record carrier. Holodarum recording Since the appropriate reference beam can be obtained regardless of the physical error of the carrier, holographic recording can be performed well. An error signal obtained by a tilt sensor or the like provided separately can be used for the tilt of the hologram record carrier disk. Brief Description of Drawings

1 to 3 are schematic partial sectional views showing a hologram record carrier for explaining conventional hologram recording.

FIG. 4 is a configuration diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on the hologram record carrier according to the embodiment of the present invention.

FIG. 5 is a front view seen from the optical axis of the spatial light modulator of the pick-up according to the embodiment of the present invention. '

FIG. 6 is a front view seen from the optical axis of the spatial light modulator of the pick-up according to another embodiment of the present invention.

FIG. 7 is a schematic sectional view showing the objective lens module of the pickup according to the embodiment of the present invention.

FIG. 8 is a schematic sectional view showing a hologram recording carrier and an objective lens module for explaining hologram recording according to an embodiment of the present invention. FIG. 9 is a schematic partial sectional view showing a hologram recording carrier for explaining the hologram recording of the embodiment according to the present invention.

FIG. 10 is a schematic sectional view showing a hologram recording carrier and an objective lens for explaining hologram reproduction according to an embodiment of the present invention.

FIG. 11 is a schematic cross-sectional view showing a hologram record carrier and objective lens module for explaining hologram recording of another embodiment according to the present invention.

FIG. 12 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording of another embodiment according to the present invention. ,

FIG. 13 is a schematic cross-sectional view showing an objective lens module of a pick-up / pump according to another embodiment of the present invention.

14 and 15 are schematic cross-sectional views showing a bifocal lens of an objective lens of a pickup according to another embodiment of the present invention. FIG. 16 is a schematic sectional view showing an objective lens module of a pickup according to another embodiment of the present invention. '' FIG. 17 is a schematic sectional view showing a hologram record carrier and an objective lens module for explaining hologram recording of another embodiment according to the present invention.

FIG. 18 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording of another embodiment according to the present invention.

FIG. 19 is a schematic cross-sectional view showing a hologram record carrier and objective lens for explaining hologram reproduction according to another embodiment of the present invention.

FIG. 20 is a schematic sectional view showing a hologram record carrier and objective lens module for explaining hologram recording of another embodiment according to the present invention. FIG. 21 is a schematic partial sectional view showing a hologram record carrier for explaining hologram recording according to another embodiment of the present invention.

FIG. 22 is a schematic sectional view showing an objective lens module of a pick-up according to another embodiment of the present invention.

Figure? 3 and 24 are schematic sectional views showing a bifocal lens of an objective lens of a pick-up according to another embodiment of the present invention.

FIG. 25 is a perspective view of an aberration correction liquid crystal panel of the pick-up aberration correction apparatus according to the embodiment of the present invention. .

FIG. 26 is a perspective view of an aberration correction liquid crystal panel of a pickup aberration correction apparatus according to another embodiment of the present invention. .

FIG. 27 is a partial sectional view taken along line XX in FIG.

FIG. 28 is a partially cutaway perspective view of an aberration correction apparatus for pick-up according to another embodiment of the present invention. .

FIG. 29 is a schematic partial sectional view showing a hologram record carrier according to an embodiment of the present invention.

FIG. 30 is a front view as seen from the optical axis of a spatial light modulator of another embodiment according to the present invention.

FIG. 31 is a partial cross-sectional view taken along line XX in FIG. 26 illustrating the polarization state. FIG. 32 is a configuration diagram showing an outline of pick-up of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention. .

FIG. 33 is a block diagram showing a schematic configuration of the hologram apparatus according to the embodiment of the present invention. FIG. 34 is a configuration diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.

FIGS. 35 and 36 are schematic cross-sectional views showing a hologram record carrier and an objective lens module in a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention. FIG. 37 is a flowchart showing a recording method in a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention.

FIGS. 38 and 39 are flowcharts showing a reproducing method in a hologram apparatus for recording / reproducing information on a hologram record carrier according to another embodiment of the present invention. FIG. 40 is a configuration diagram showing an outline of a pickup of a hologram apparatus for recording / reproducing information on a hologram record carrier of another embodiment according to the present invention.

FIG. 41 is a front view seen from the optical axis of the polarization spatial light modulator of the pickup according to another embodiment of the present invention. Detailed Description of the Invention.

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

FIG. 4 shows a schematic configuration of a pickup 23 for recording or reproducing the hologram record carrier 2. .

Pickups 2 and 3 consist of a laser light source LD for recording and reproduction of holograms, a collimator-evening lens CL, a transmissive spatial light modulator SLM, a polarization beam splitter PBS, an imaging lens ML, an image sensor IS and its drive system. (Not shown), including transmissive aberration correction liquid crystal panel LCP and objective lens module OBM. Objective lens Yule BM, etc. are placed on the optical axis of the light beam from the laser light source LD in the housing (not shown). The wavelength of the laser light source LD is a wavelength at which a translucent photosensitive material capable of preserving the optical interference pattern of the hologram record carrier 2 reacts. The collimator lens CL converts coherent light from the laser light source LD into parallel light.

Fig. 5 is a front view of the spatial light modulator S L M irradiated within the parallel beam diameter as seen from the optical axis. The spatial light modulator S L M is divided into a central region L C C R including the optical axis and an annular region L C P R not including the surrounding optical axis in the vicinity of the optical axis. In the central region L C C R, the penetration loss is made of a transparent material, and no modulation is given to the light beam passing therethrough. The transparent annular region LCPR is a function of electrically shielding a part of incident light for each pixel in a liquid crystal panel with an analyzer having a plurality of pixel electrodes divided into a matrix, or transmitting completely. Thus, it has a function of making it unmodulated. As shown in FIG. 4, the annular region L C PR modulates the parallel light from the collimator overnight lens C L according to the recording information. That is, when the light passes through the spatial light modulator SLM, the light beam is concentrically separated into the spatially modulated signal light 'S B and the non-spatial reference light RB.

This spatial modulator SLM is connected to the spatial light modulator horse motion circuit 26 and has a distribution based on the page data to be recorded (information pattern of two-dimensional data such as bright and dark dot patterns on a plane). The light beam is modulated and transmitted to generate signal light S Β.

Further, as shown in FIG. 6, the entire spatial light modulator SL is used as a transmissive matrix liquid crystal display device, and its control circuit 26 uses an annular region LCPR for displaying a predetermined pattern of page data to be recorded. Inside the center area LCCR unmodulated light It can also be configured to display transparent areas. The central region LCCR can also be used as a phase modulation light transmission region, and phase modulation reference light may be generated.

As described above, the spatial light modulator SLM is composed of the central region LCCR arranged on the optical axis of the coherent light and the annular region LCPR arranged so as to surround the central region LCCR. The reference component and the signal component are generated by spatially separating the passing component and the passing component of the annular region, and propagated coaxially. The central region LCCR and the annular region L C PR generate reference light and signal light, but the central region LCCR can generate signal light and the annular region LC PR can generate reference light. .

As an example of the spatial light modulator, a reflective liquid crystal panel or a DMD can be used in addition to the transmissive type. In the reflective spatial light modulator, the central region LCCR and the surrounding light are also similar to the transmissive type. It includes an annular region LCPR that does not include an axis, and its action separates the light flux from the central region and the annular region.

<Objective lens optics> ■

The objective lens module OBM shown in FIG. 4 belongs to an objective lens optical system that irradiates signal light and reference light toward the hologram recording carrier 2 coaxially and collects the reference light RB and the signal light SB at different focal points. .

FIG. 7 is a schematic sectional view of an example of the objective lens module 0 BM. The objective lens module OBM is a convex lens optical element CVX that is fixed by a hollow holder (not shown) and has a convex lens with the optical axis as the coaxial and a convex lens with a diameter smaller than that of the objective lens OB. Consists of. The convex lens optical element CVX consists of a central region CR (convex lens) including the optical axis and an annular region PR (transmission parallel plate) around it. Consists of. As shown in Fig. 8 (a), the objective lens module OBM collects the light passing through the central region CR at the near focal point nP on the near side and the light passing through the annular region PR into the far focal point fP far away. Collect light. The short-distance focal point n P is the combined focal point of the objective lens 0 B and the convex lens optical element c VX, and the long-distance focal point f P is the focal point of the objective lens OB.

At the time of hologram recording, as shown in FIG. 8 (a), the reference light RB and the signal light SB around the optical axis from the spatial light modulator SLM are coaxially spaced apart from each other. The objective lens module is guided to OBM. The spatial light modulator propagates the reference light RB to the central region C on the optical axis and the signal light SB having a circular cross section to the annular region PR around the reference light RB spatially separated from each other and transmitted coaxially. . The objective lens module 0 B M refracts the reference light RB and the signal light SB in the central region CR and the annular region PR, respectively. Therefore, even after passing through the objective lens, the reference light RB and the signal light SB are spatially separated, the reference light RB is collected at the short-distance focal point nP near the objective lens B, and the signal light SB is farther than the short-distance focal point. Since the light is focused on the far focus, interference occurs at a distance farther than the short focus nP.

As shown in Fig. 8 (b), the reflective layer 5 is disposed at the position of the short-distance focal point nP of the reference light RB, and the hologram recording layer 7 is used as a recording medium between the objective lens module BM and the reflective layer 5. To place. The signal light SB having an annular cross section is reflected by the reflection layer 5 and collected at the symmetrical position of the long-distance focal point f P, and the reference light RB is reflected by the reflective layer 5 in front of the long-distance focal point f P (short-distance focal point nP). The Therefore, the signal light SB reflected and converged in the opposite propagation directions and the reference light RB interfere with each other in the annular region near the optical axis. Has a hologram recording layer located between the near focus n P and the far focus f P If the holographic record carrier is used, the reference light RB and the signal light SB are spherical waves that propagate in directions opposite to each other. Hologram Recorded as HG. Therefore, the hologram recording layer 7 needs to have a film thickness sufficient to generate an optical interference pattern by crossing and interfering with the reflected signal light and reference light. As shown in FIG. 9, the holograms to be recorded specifically are hologram recording A (reflected and diverging reference light and reflected and converged signal light), hologram recording B (incident converging reference light and Signal light reflected and converged). There are also two types of holograms to be reproduced: hologram record A (read out with reflected reference light) and hologram record B (read out with incident reference light).

Therefore, in the hologram reproduction system for reproducing information from such a hologram record carrier, as shown in FIG. 10, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is supplied to the short-range focus n. When the hologram HG of the hologram recording layer is transmitted while being converged on P. (reflection layer 5), normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG. From the objective lens, which is also a part of the detection means, the reproduction light and the phase conjugate wave can be guided to the photodetector. In other hologram recording / reproducing systems, the reflection layer 5 is not disposed at the position of the short-distance focal point η Β of the reference beam R 、, but the long-distance focal point of the signal beam SB as shown in FIG. The hologram recording carrier 2 is arranged so that the hologram recording layer 7 is between the objective lens module Ο Β Μ and the reflection layer 5. The signal light S 環状 having an annular cross section is focused and reflected by the reflection layer 5, and the reference light; Β is collected and diverged from the reflection layer 5 (near focal point η Ρ) and reflected by the reflection layer 5. Is done. This place In the case of the reflection layer 5, the reference light RB is defocused and the signal light SB is in focus. Therefore, if the hologram recording layer 7 is disposed away from the reflection layer 5 so that only the reflected reference light RB and the signal light SB intersect, the signal light SB and the reference in the opposite propagation directions are arranged. The optical RB component causes interference in an annular region near the optical axis. As shown in Fig. 12, the holograms that are specifically recorded are hologram record A (reflected and diverged reference light and reflected and diverged signal light), and hologram record C (reflected and diverged reference light). 2 types of signal light that converges on incident light. There are also two types of holograms to be reproduced. In the hologram reproduction system in this case, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is irradiated to the reflection layer 5 in the same defocused state as during recording, so that the hologram recording layer When the hologram HG is transmitted, normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG in the same optical path.

It should be noted that the objective lens module 0BM of another modified example has a transmissive diffractive optical element DOE having a convex lens function on the optical axis in front of the objective lens OB, instead of the convex lens optical element, as shown in FIG. It can also be configured by arranging them coaxially. Further, as shown in FIG. 14, the objective lens OB and the transmissive diffractive optical element DOE having a convex lens function can be integrated. By constructing the objective lens module OBM as a bifocal lens OB 2 with a Fresnel lens surface or a diffraction grating DOE formed coaxially on the refracting surface (central region CR), the reference beam RB The focal lengths of the signal light SB can be made different from each other. Furthermore, as shown in FIG. 15, the convex lens portion CVX is integrated with the objective lens so that a step is provided at the boundary between the central region CR and the annular region PR, and the aspherical lenses have different curvatures. The objective lens module OBM may be configured as the bifocal lens OB2. Furthermore, a modification of the bifocal lens is one in which an annular diffraction grating is provided in the central region CR and a convex lens portion is left around it, but conversely, an annular diffraction grating is provided in the annular region PR. It is also possible to leave a convex lens part on the surface.

In the above embodiment, the signal light around the reference light is irradiated so as to be in a defocused state on the reflection layer, when the focus of the signal light is farther than the objective lens than the focus of the reference light. As described above, this defocus state can be achieved even when the focus of the signal light is in front of the focus of the reference light. For example, FIG. 16 shows a configuration example of an objective lens optical system according to another embodiment. .

The objective lens module of Fig. 16. The OBM is a convex lens that is fixed by a hollow holder (not shown) and whose optical axis is the coaxial objective lens OB and a concave lens that is smaller in diameter than the objective lens 〇 B. Concave lens optical element CCV. The concave lens optical element CCV is composed of a central region CR (concave lens) including the optical axis and a surrounding annular region PR (transmission parallel plate). As shown in Fig. 1'7 (a), the objective lens module OBM collects the light passing through the center region CR at the far focal point f P far away, and passes the light passing through the annular region P toward the near focal point P. To collect light. The far focus f P is the composite focus of the objective lens B and the concave lens optical element C C V, and the short focus n P is the focus of the objective lens OB. .

At the time of hologram recording, first, the coherent reference light RB around the optical axis and the reference light RB around the optical axis according to the recording information by the spatial light modulator coaxial with the objective lens module OBM. The signal light SB obtained by the modulation is generated. As shown in Fig. 17 (a), the reference light RB and the signal light SB are coaxial and are mutually spaced. It is guided to the objective lens module OBM in a state where it is far away. The objective lens module OBM refracts the reference light RB and the signal light SB in the central region CR and the annular region PR, respectively. Therefore, even after passing through the objective lens, the reference light RB and the signal light SB are spatially separated, and the signal light SB is collected at the short-distance focal point n P near the objective lens OB, and the reference light RB is far from the short-distance focal point. Focused at the distance focus. At the time of hologram recording, first, a coherent reference light RB and a signal light SB obtained by modulating the reference light RB according to the recording information are generated.

Then, the reference light RB and the signal light SB are guided to the objective lens module O B M so as to be coaxially spaced apart from each other. That is, as shown in Fig.1.7 (a), the reference light RB is spatially separated from each other into the central region CR on the optical axis and the signal light SB into the annular region PR around the reference light RB. To propagate coaxially. Even after passing through the objective lens, the reference light RB and the signal light SB are spatially separated, and the signal light SB is collected at the near focus n P close to the objective lens module OBM, and the reference light RB is far away from the near focus. Focused at the focal point fP. '

As shown in Fig. 17 (b), the reflective layer 5 is arranged at the position of the long-distance focal point fP of the reference light RB, and the hologram recording layer 7 is arranged between the objective lens module OBM and the reflective layer 5. . The signal light SB having an annular cross-section is collected and diverged before the reflection layer 5 (short-distance focal point n P) and is reflected by the reflection layer 5, and the reference light RB is focused and reflected by the reflection layer 5. . Therefore, since the signal light SB having the annular cross section is condensed before the reflection layer 5, it becomes a defocus in the reflection layer 5, and the reflected signal light SB does not cross the reference light RB and does not interfere with it. Since the intersection angle between the incident signal light SB and the reference light RB can be made relatively large, the multiplexing interval can be reduced. As shown in Fig. 18, the holograms that are specifically recorded are hologram recording C (reflected and divergent reference light and incident convergent signal light), and hologram record D (incident and convergent reference light and incident convergent). Signal light). There are two similar types of holograms to be reproduced.

Therefore, in the hologram reproducing system for reproducing information from such a hologram record carrier, as shown in FIG. 19, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is supplied to the reflecting layer 5 ( When the hologram HG of the hologram recording layer is transmitted while converging to the far-distance focal point (f P), re-normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG. The reproduction light and the phase conjugate wave can be guided to the photodetector by the object lens module O B M which is also a part of the detection means.

In other hologram recording / reproducing systems, the reflective layer 5 is arranged at the position of the long-distance focal point f P of the reference beam RB, and the hologram recording layer 7 is not arranged between the objective lens module OBM and the reflective layer 5. As shown in FIG. 20, a reflection layer 5 is arranged at the position of the short-distance focal point nP of the signal light SB that has passed through the annular region PR, and the hologram recording carrier 2 has a hologram recording layer 7 that has an objective lens module. Place it so that it is between the OBM and the reflective layer 5. The signal light SB having an annular cross-section is focused and reflected by the reflection layer 5, and the reference light RB is reflected by the reflection layer 5 and collected at a symmetrical position of the long-distance focal point fP. In this case, in the reflection layer 5, the reference light RB is defocused and the signal light SB is in focus. As shown in Fig. 21, there are two types of holograms that can be specifically recorded: hologram recording B (incident reference light and reflected signal light) and hologram recording C (incident reference light and incident signal light). is there. There are also two types of holograms to be reproduced. In the hologram reproduction system in this case, only the reference light RB is supplied to the central region CR of the objective lens module OBM, and the reference light RB is irradiated to the reflection layer 5 in the same defocused state as that during recording, so that the hologram recording layer When the hologram HG is transmitted, normal reproduction light and phase conjugate wave reproduction light can be generated from the hologram HG in the same optical path.

Furthermore, another modified example of the bifocal objective lens module OBM has a transmission type diffractive optical element D0E having a concave lens function at the center as shown in FIG. By using an objective lens module, the focal lengths of the reference light RB and the signal light SB can be made different from each other. Also, as shown in Fig. 23, the objective lens OB and the transmission type diffractive optical element DOE are integrated (Fresnel lens surface or diffraction grating D having a concave lens action formed coaxially in the central region CR of the refractive surface). (It has E) The bifocal lens OB 2 makes it possible to make the reference light RB and the signal light SB have different focal lengths. Also, instead of the lens-integrated diffraction grating, as shown in Fig. 24, the concave lens portion CCV is integrated, and a step is provided at the boundary between the central region CR and the annular region PR. The objective lens module OBM may be configured as the focus lens OB2.

According to the configuration in which the reference light and the signal light are propagated and irradiated so that the other is separated and surrounded by a coaxial axis, the overlap of the reference light and the signal light can be limited to some extent at the time of incidence.

In the embodiment shown in FIGS. 8 and Γ 7, the reference light focused on the reflective layer can be used as a light beam for detecting a spot error. In addition, as shown in Figure 11 and Figure 20. In this embodiment, the reference light is generated in the center and the signal light is generated in the outer annular region. If this is modified to generate the signal light in the central region and the reference light in the outer annular region, It is possible to use the reference light having an annular cross-section that is focused on the reflective layer as a light beam for detecting a servo error.

According to the embodiment and the modification described above, during hologram recording, the interfering signal light and reference light are limited, so that extra holograms are not recorded and reproduced. In addition, since the reference light RB and the signal light SB are spherical waves propagating in directions opposite to each other, their crossing angle can be made relatively large, so that shift multiplexing is possible, and the multiplexing interval can be reduced. . ,

Polarized beam splitter PBS, imaging lens ML, and image sensor IS placed on the optical axis in Fig. 4 return from the hologram record carrier 2 through the objective lens module OBM when the hologram recording layer is irradiated with the reference light. It functions as an image detection means that receives light. The image sensor I S. is a photoelectric conversion element consisting of an array of C CD (charge coupled device) and CMO S (complementary metal oxide semiconductor device).

The transmission type aberration correction liquid crystal panel LCP in FIG. 4 includes a central correction area PLCCR arranged on the optical axis and an annular peripheral area PLCPR arranged so as to surround the central correction area PLCCR, and at least one of them passes through the central correction area PLCCR. This is a transmissive liquid crystal device that includes a plurality of transparent electrodes that partially change the phase of the wavefront of the light beam to correct the wavefront aberration of the passing light beam.

Figure 25 shows an aberration-corrected liquid crystal panel LCP consisting of a transmissive liquid crystal device. Aberration correction The liquid crystal panel LCP is connected to the aberration correction liquid crystal drive circuit L CPD, and is composed of an annular peripheral region PLCPR and a central correction region P LCCR therein.

As shown in FIGS. 25 and 26, in the aberration-correcting liquid crystal panel LCP, a fluid transparent liquid crystal composition 11 is sandwiched between two glass substrates 12a and 12b, and the periphery of the substrate is sealed. It has a stopped structure. On the inner surfaces of both glass substrates 12a and 12b, there are transparent electrode layers (1 3 ai, 13 a) (1 3 b) for applying voltage to the liquid crystal made of indium tin oxide, etc. Alignment films 1.4 a and 14 b that define the orientation (orientation) of are stacked in order. In the aberration-corrected liquid crystal panel LCP, the orientation of the liquid crystal changes according to the potential difference generated in the liquid crystal, and the refractive index changes according to the voltage, thereby changing the phase of the wavefront passing through the liquid crystal. Therefore, it tries to cancel out the aberration of the passing light.

The central correction area PLCCR through which only the reference light is transmitted has a split electrode shape corresponding to the aberration generated in the reference light. The electrode division shape of the central correction area PLC CR can take a spherical aberration correction pattern, a coma aberration correction pattern, and an astigmatism correction pattern, which will be described later. It can also be configured. For example, at least one of the opposite electrode layers of the central correction region PLCCR is divided into a plurality of transparent electrodes as a phase adjustment unit, and each of the plurality of transparent electrodes corresponds to the distribution shape of the aberration generated in the reference light. By adopting a configuration in which a voltage is applied, the aberration of the reference light transmitted through the aberration-correcting liquid crystal panel LCP can be corrected. In Fig. 26, the transparent electrode 13b is a common electrode, but the transparent electrode 13a in the annular peripheral region PLCPR and the multiple transparent electrodes 13ai (i = l, 2, 3) in the central correction region PLC C inside it , — ′) And are applied independently by the aberration correction liquid crystal drive circuit LC PD. FIG. 27 is a plan view of an electrode pattern schematically showing an example of the structure of the central correction area PLCCR of the aberration correction liquid crystal panel LCP for correcting spherical aberration. As shown in Fig. 27 (a), the central correction area PLCCR is divided by a gap within the effective diameter of the incident reference light beam in correspondence with the distribution of spherical aberration generated in the hologram record carrier 2, and A plurality of concentric (annular) transparent electrodes 13 a 1, 13 a 2, 13 a 3, 13 a 4, 13 a 5, 13 a 6 and 13 a 7 are included. The width of each of the transparent electrodes 13 a 1 to 13 a 7 can be varied in order to change the phase of the wavefront corresponding to the distribution of spherical aberration, but may be configured equally. FIG. 27 shows a case where the central correction region PLC CR has seven transparent electrodes, but the number of electrodes may be two or more. When the correction voltage V i (i = l, 2, 3, 4, 5, 6, 7) is applied to the transparent electrode 13 a l_13 a 7 via the lead line, it depends on the electric field generated by the correction voltage V i. Thus, the refractive index alignment of the liquid crystal molecules in each part in the liquid crystal layer 11 changes. As a result, the phase of the wavefront of light passing through the liquid crystal layer 11 changes due to the birefringence of the liquid crystal layer 11. In other words, the wavefront of the reference light passing through can be controlled by the correction voltage V i applied to the liquid crystal layer 11. As shown in Fig. 27 (b), the voltage waveform of the correction voltage V i from the reference voltage applied to the transparent electrode 13 al — 13 a 7 on the diameter of the central correction region LCCR is shown. By applying a correction voltage according to the distribution shape of the spherical aberration to be corrected to the electrode pattern, it is possible to cancel the spherical aberration caused by the thickness non-uniformity of the light transmission protective layer of the hologram record carrier. Correction is made to suppress spherical aberration.

Therefore, when the recording layer shrinks due to hologram recording or the refractive index changes. In this case, it is considered that an axially symmetric aberration is generated, and in that case, spherical aberration and defocus aberration are generated. In such a case, the aberration correction of the reference light is realized by applying a previously stored spherical aberration correction amount or the like as a correction voltage to the aberration correction liquid crystal panel LCP, and a reference having the same wavefront as that at the time of recording. Since it can be reproduced with light, a good reproduction signal can be obtained. -FIG. 28 is a plan view schematically showing an example of the structure of the central correction area PLC CR of the aberration correction liquid crystal panel LCP for correcting coma. Figure 28 (a) shows the transparent electrode pattern for correcting coma in the central correction area PLCCR. Central correction area Four divided transparent electrodes 13 all, 13 a 12, 13 a 13, 13 a 1 4 for changing the phase of the wavefront within the effective diameter of the reference beam incident on the PLCCR Are separated by a gap and are electrically separated. The pairs of the transparent electrodes 13 a 11, 13 a 12 and the transparent electrodes 13 al 3, 13 a 14 are arranged symmetrically with respect to the diameter of the central correction region PL CCR. That is, in the coma aberration correcting transparent electrode pattern, the central correction area PLCCR is arranged as an inner and outer area divided by a gap including the straight line or symmetrical to the diameter perpendicular to the optical axis. The positive liquid crystal driving circuit supplies a correction voltage corresponding to the coma aberration to be corrected. When a positive voltage is applied to the divided transparent electrode with respect to the reference voltage, a potential difference is generated between the transparent electrode 13 b and the liquid crystal orientation changes according to the potential difference to change the refractive index. Therefore, the phase of the wavefront of the reference light component passing through the transparent electrode is advanced. Conversely, when a negative voltage with respect to the reference voltage is applied to the divided transparent electrode, the phase of the wavefront of the reference light component passing through the transparent electrode is delayed. Therefore, symmetrically arranged transparent electrodes 13 all, 13 a 12 and transparent electrodes 13 al 3, 13 al 4 As shown in Fig. 28 (b), the central correction area PLCCR is tilted with respect to the optical axis by applying a correction voltage having a voltage waveform corresponding to the distribution shape of the coma aberration to be corrected. It is possible to cancel out the coma caused by, and to correct the coma. ·

Therefore, when the recording layer is inclined with respect to the light beam by hologram recording, the aberration of the reference light can be corrected based on the quality of the reproduction signal. Evaluate the quality of the reproduced signal based on the SNR or error rate of the reproduced image and compensate for the best result; determine the E voltage. By applying the correction voltage to the aberration correction liquid crystal panel L C P, the aberration correction of the reference light is realized, and the reproduction can be performed with the reference light having the same wavefront as that at the time of recording, so that a good reproduction signal can be obtained.

In addition, the aberration correction liquid crystal panel LCP is connected to the annular peripheral area PLCPR and the central correction area PLCCR in the same state by the connected aberration correction liquid crystal drive circuit LCPD. It can be controlled to have different polarization action states in the region.

The aberration correction liquid crystal panel LCP, for example, performs a fei rotation of the polarization plane of the signal light that passes through the annular region and the reference light that passes through the central region ′, and switches the rotation angle between hologram recording and playback. It can be controlled by the aberration correction liquid crystal drive circuit LCPD. The aberration correction liquid crystal drive circuit LCPD and the aberration correction liquid crystal panel LCP are systems that can rotate the polarization direction of the annular region light beam part of the light beam emitted from the laser light source and the central region light beam part inside it by a predetermined angle, for example 90 degrees. is there.

A liquid crystal is a substance that shows an intermediate phase between a solid and a liquid in which the molecule is elongated and the position and the direction of its axis are both regular and irregular. Generally natural (no mark In the applied electric field), a plurality of liquid crystal molecules are arranged with gentle regularity in the major axis direction. When a liquid crystal molecule is brought into contact with an alignment film in which a plurality of micro grooves in a certain direction are carved by rubbing or the like, the molecular axis of liquid crystal molecules has a property of changing the alignment along the grooves. Therefore, in a TN (Twisted Nematic) type liquid crystal, the orientation of each micro-groove is 90 degrees, and the two alignments are arranged in parallel at a predetermined interval. The liquid crystal molecules are arranged so that they are gradually twisted from one alignment film to the other alignment film and rotated 90 degrees (helical alignment). When light is passed through the liquid crystal from one alignment film to the other alignment film in a state where the liquid crystal molecules are twisted, light is transmitted along the gaps where the liquid crystal molecules are arranged. For example, linearly polarized light parallel to the liquid crystal molecular axis near one alignment film becomes linearly polarized light parallel to the liquid crystal molecular axis near the other alignment film, and its vibration plane (polarization plane) is twisted 90 degrees. (Transmits off without applying voltage J).

On the other hand, when a voltage is applied between the opposing transparent electrodes sandwiching the liquid crystal, the liquid crystal molecules change from the direction along the alignment film to the vertical direction and line up along the electric field. As the liquid crystal molecules stand upright from the alignment film and the orientation of the liquid crystal molecules changes, as shown in Fig. 26, for example, the polarization plane of the linearly polarized transmitted light (parallel to the plane of the paper) does not rotate. Transmits in a state (ON state with the same voltage applied).

In order to obtain a liquid crystal panel that combines multiple functions as described above, an alignment film is set so that liquid crystal molecules are aligned in parallel in the region used for aberration correction, while in the region used for polarization. An alignment film is set so as to achieve TN alignment. For example, in the facing alignment films 14 a and 14 b of the aberration-correcting liquid crystal panel LCP shown in FIG. 26, one alignment film 14 b is placed in a uniform direction (indicated by the broken line in FIG. 25). (Indicated by arrows) In the other alignment film 14a, the circumferential area PLCPR and the central correction area PLCCR are separated from each other, and in the annular surrounding area PLCPR, the direction is 90 degrees with respect to the rubbing direction of the alignment film 14b. (Indicated by a solid double-directional arrow in Fig. 25) and in the central correction area PLCCR rubbing in parallel to the rubbing direction of the alignment film 14b (indicated by a solid double-directional arrow in Fig. 25) To do. In this way, the liquid crystal molecules can be set in parallel in the central correction region PLCCR used for aberration correction, while the TN alignment can be set in the annular peripheral region PLCPR used for polarization. ,

Holographic record carrier>

An example of the Holodaram record carrier 2 in FIG. 4 is shown in FIG. The hologram record carrier 2 includes a reflective layer 5, a separation layer 6, a hologram recording layer 7, and a protective layer 8 laminated on the substrate 3 in the film thickness direction.

The photogram recording layer 7 stores the optical interference pattern by the coherent reference light R B and the signal light S B for recording inside as a diffraction grating (hologram). The hologram recording layer 7 includes, for example, a light-transmitting photosensitive material capable of storing an optical interference pattern such as a photopolymer, a light anisotropic material, a photorefractive material, a hole burning material, or a photochromic material. Used.

The substrate 3 supporting each film is made of, for example, glass, or polycarbonate, amorphous polyolefin, polyimide, PET, PEN, PES, or an ultraviolet curable acrylic resin.

The separation layer 6 and the protective layer 8 are made of a light transmissive material, and play a role of flattening the laminated structure and protecting the hologram recording layer and the like. When the substrate 3 is a disc, the track can be formed spirally or concentrically on the center of the circular substrate, or in the form of a plurality of divided spiral arcs. When the substrate 3 is in the shape of a force, the track may be formed in parallel on the substrate. Further, even in the case of the rectangular card substrate 3, the track may be formed in a spiral shape, a spiral arc shape, or a concentric shape on the center of gravity of the substrate, for example.

The recording / reproducing operation of this embodiment shown in FIG. 4 will be described.

In the recording operation, as shown in FIG. 4 (a), the laser light from the laser light source LD polarized in parallel with the paper is converted into a parallel light beam by the collimator lens CL, and then passes through the spatial light modulator SLM. Thus, the light beam including the optical axis is divided into the annular cross-section light flux surrounding the light beam, and the light beam including the optical axis is generated as the reference light RB and the circular cross-section light beam as the signal light SB. The reference light RB and the signal light SB are coaxially passed through the polarization beam splitter PBS and the aberration correction liquid crystal panel LCP, and are converged on the hologram record carrier 2 by the objective lens module BM. During hologram recording, the area through which only the reference light RB of the aberration correction LCD panel LCP passes (center correction area PLC CR) and the area through which only the signal light SB passes (the annular surrounding area PLCPR0 is turned on, and the signal light SB The polarization state of the reference light RB is set so as to be the same (parallel to the paper surface), so that it is recorded in the hologram recording layer 7 of the hologram record carrier 2 due to the interference of the signal light SB and the reference light RB. The central correction area PLC CR and the annular peripheral area PLC PR are all set to the on state and the aberration correction of the reference light may be performed, but may not be performed. Thus, the effect of aberration is considered to be small. In the reproduction operation, as shown in FIG. 4 (b), only the light beam including the optical axis (reference light RB) is generated by the spatial light modulator SLM from the light beam in the polarization direction parallel to the paper surface. When the light is condensed on the hologram record carrier 2 via the polarizing beam splitter PBS and the aberration correction liquid crystal panel LCP via the objective lens module OBM, the reproduction light having the polarization parallel to the paper surface is reconstructed. During reproduction, a correction voltage corresponding to the distribution shape of the aberration generated in the reference light is applied to the plurality of divided transparent electrodes of the phase adjustment section of the aberration correction liquid crystal panel LCP, and the central correction area PLCCR is turned on to make a ring shape. Set so that the polarization state of the transmitted light that passes through the surrounding area PLCPR and the transmitted light that passes through the central correction area PLC CR differ by approximately 90 °. The reproduction light reproduced by the reference light RB is the same divergent and convergent light beam as the signal light at the time of recording and has a polarization direction parallel to the paper surface, but the reproduction light passes through the annular polarization region PLCPR of the polarizing liquid crystal panel LCP. Therefore, the polarizing action of the polarizing liquid crystal panel LCP causes the polarization direction to be perpendicular to the paper surface. On the other hand, the reference light RB is reflected by the reflective layer 5 while being parallel to the paper surface, and is not subjected to the polarization action at the aberration-correcting liquid crystal panel LCP. Therefore, since the polarization direction of the reference light RB reflected by the reflective layer 5 and the reproduced light to be reproduced differs during reproduction, it can be separated by the polarization beam splitter PBS, and the reference light RB is received on the detector that receives the reproduced light. Reproduction SN is improved because no light enters.

Aberration correction LCD panel LCP makes polarized light perpendicular to the paper (the aberration correction LCD panel LCP rotates the polarization direction of the transmitted light beam by 90 degrees), and the component reflected by polarization beam splitting PBS enters image sensor IS. To do. The image sensor IS sends an output corresponding to the image formed with the reproduction light to a reproduction signal detection processing circuit (not shown), and performs processing to reproduce the page data. Thus, in a pickup used for hologram recording, the hologram recording light beam is divided into a light beam including the optical axis in the vicinity of the optical axis (reference light) and an annular cross-section light beam (signal light) surrounding it. It has an objective lens optical system (lens group) having different focal lengths for the light and the reference light, and further has an aberration correction liquid crystal panel LCP arranged between the spatial light modulator SLM and the objective lens OB. The aberration-correcting liquid crystal panel LCP has a central correction area PLCCR and an annular peripheral area PLCPR, and the divided shapes are a light beam (reference light) including the optical axis to be transmitted and an annular cross-section light beam (signal) surrounding it. It substantially matches the cross-sectional shape of (light).

The above-mentioned aberration-correcting liquid crystal panel LCP uses the split transparent electrode of the central correction area PLCCR for reference light that should be corrected for wavefront aberration depending on the voltage application state, and the light flux that passes through the annular peripheral area PLCPR is used for signal light. Although described, as a modification, the configuration of the aberration correction liquid crystal panel LCP and the spatial light modulator S LM does not propagate the reference light on the optical axis and the signal light around it, but conversely. It is also possible to propagate the signal light by generating the reference light around the optical axis. In this case, as shown in FIG. 30, the entire spatial light modulator SLM is a transmission matrix liquid crystal display device, and the control circuit 26 controls the central area LCCR for displaying a predetermined pattern of page data to be recorded. It can also be configured to display an unmodulated light transmission region of the annular region LCPR around it. The non-modulated light transmission region of the annular region LCPR can be formed from a transparent material. Furthermore, as shown in FIG. 31, in the annular peripheral region P LCPR of the aberration correction liquid crystal panel LCP, a spherical electrode for correcting spherical aberration, a transparent electrode pattern for correcting coma aberration 13 ai, etc. The transparent electrode pattern 13aa is formed in the central correction area PLCCR for transmission of light. That is, the configuration can be the same as that shown in FIG. 26 except that the transparent electrode patterns in the central correction area PLCRC and the annular surrounding area PLCPR are replaced.

Also in this modified example, the aberration correction liquid crystal panel L CP ensures that the polarization state of the signal light SB and the reference light RB is the same in the hologram recording layer 7 during holographic recording, and is approximately 90 ° between each other during reproduction. It can be different. Therefore, the aberration-correcting liquid crystal panel LCP has the same polarized light transmission state in both areas during hologram recording by the aberration-correcting liquid crystal driving circuit LCPD, or the central correction area PLCCR of the aberration-correcting liquid crystal panel LCP during reproduction, for example. In the annular peripheral region P LCP R, the wavefront aberration correction voltage can be applied and turned on in the annular peripheral region P LCP R, so that both regions can have different polarization action states. In this case, as shown in FIG. 32 (a), the parallel light beam that has passed through the spatial light modulator SLM is divided into the signal light SB (light beam including the optical axis) and the reference light beam RB of the annular cross-section light beam that surrounds it. As a result, the reference beam RB of the annular cross section is subjected to wavefront aberration and passes through the polarization beam splitting PBS and the aberration correcting liquid crystal panel LCP. The recording operation (Fig. 32 (a)) and the reproducing operation (Fig. 32 (b)) are the same as the above example except that the propagation position is different between the reference light and the signal light. Even in this modification, the configuration of the objective lens module OBM as shown in FIGS. 8 to 24 can be applied.

According to the present embodiment described above, since the reference light RB reflected at the time of reproduction is separated or does not form an image, only the reproduction light from the program necessary for signal reproduction because the reference light RB does not reach the image sensor IS. Can be received. As a result, regeneration SN is improved and stable Can do life.

The servo control is not shown, but for example, a track is provided on the reflective layer 5, and the reference light RB is collected as a spot on the track, and a servo optical system including an objective lens that guides the reflected light to the photodetector is used. This is possible by driving the objective lens optical system overnight according to the detected servo error signal. That is, the reference light RB light beam irradiated from the objective lens is used so as to be in focus when the reflection layer 5 is positioned at the position of the beam waist.

As another embodiment, a hologram apparatus will be described as a hologram recording / reproducing system of the present invention for recording and reproducing information on a disc-shaped hologram record carrier.

FIG. 33 is a block diagram of an example of a hologram device.

The hologram device includes a spindle motor 2. 2 that rotates a disk of the hologram record carrier 2 on a turntable, a pickup 2 3 that reads a signal from the hologram record carrier 2 by a light beam, and holds the pickup in a radial direction (X direction). Moved pickup drive unit 24, light source drive circuit 25, spatial light modulator drive circuit 26, reproduction light signal detection circuit 27, servo signal processing circuit 28, focus servo circuit 29, xy direction movement servo Circuit 30, Pickup position detection circuit 31 connected to the pickup drive unit 24 to detect the position signal of the pickup 31, Slider servo circuit 3 2 connected to the pickup drive unit 24 and supplying a predetermined signal thereto, Spindle motor 2 2 is connected to 2 to detect the rotation speed signal of the spindle motor 3 3, the hologram connected to the rotation speed detection section Times to generate a rotational position signal of the recording carrier 2 A shift position detection circuit 34, an aberration correction liquid crystal drive circuit LCPD, and a spindle servo circuit 35 connected to the spindle motor 22 and supplying a predetermined signal thereto are provided.

The hologram apparatus has a control circuit 37, which includes a light source drive circuit 25, a spatial light modulator drive circuit 26, a reproduction light signal detection circuit 27, a servo signal processing circuit 28, and a focus circuit. Po circuit 29, xy-direction moving support circuit 30, pickup position detection circuit 31, slider service circuit 3 2, speed detector 3 3, rotation position detection circuit 34, aberration correction liquid crystal drive circuit LCPD and spindle service circuit 3 5 It is connected to the. Based on the signals from these circuits, the control circuit 37 is used to control focus servo control related to pick-up, X and y direction movement servo control, and playback position (positions in the X and y directions) via these drive circuits. Control and so on. The control circuit 37 consists of a microcomputer equipped with various memories and controls the entire device. It controls the operation input by the user from the operation unit (not shown) and the current operation status of the device. In response to this, it generates various control signals and is connected to a display (not shown) that displays the operating status to the user.

Hologram recording / reproducing laser light source L D 1 ί The connected light source driving circuit 25 adjusts the output of the laser light source L D 1 so that the intensity of both emitted light beams is strong during hologram recording and weak during reproduction.

Further, the control circuit 37 executes processing such as encoding of data to be recorded from the outside inputted from outside, and supplies a predetermined signal to the spatial light modulator driving circuit 26 to control the recording sequence of the hologram. . The control circuit 37 is configured to perform demodulation and error correction processing based on the read signal from the reproduction light signal detection circuit 27 connected to the image sensor IS. By doing this, the data recorded on the hologram record carrier is restored. Further, the control circuit 37 reproduces the information data by performing decoding processing on the restored data, and outputs this as reproduction information data. The control circuit 37 includes a convergence correction unit 40 and discriminates the aberration of the reference light based on the signal received from the reproduction light signal detection circuit 27 and according to Z or a predetermined processing procedure. Further, the control circuit 37 determines each correction voltage V i of the phase adjustment unit (transparent electrode) of the aberration correction liquid crystal panel LCP based on the aberration of the reference light. The control circuit 37 supplies each control signal representing the correction voltage V i to the aberration correction liquid crystal drive circuit LCPD for driving the aberration correction liquid crystal panel LCP. The aberration correction liquid crystal drive circuit LCPD generates a drive voltage (correction voltage) to be applied to the aberration correction liquid crystal panel LCP according to the control signal, and supplies the drive voltage to the aberration correction liquid crystal panel LCP.

Furthermore, the control circuit 37 controls to form holograms at predetermined intervals so that holograms to be recorded can be recorded at predetermined intervals (multiple intervals).

In the support signal processing circuit 28, a focusing drive signal is generated from the focus error signal and is supplied to the focus support circuit 29 via the control circuit 37. In response to the I-segment motion signal, the vocus servo circuit 29 drives the focusing part of the objective lens driving part 36 (see Fig. 35) mounted on the pickup 23, and the focusing part is used as a hologram record carrier. Operates to adjust the focal position of the illuminated light spot.

Further, in the support signal processing circuit 28, X and y direction movement drive signals are generated and supplied to the xy direction movement support circuit 30. The xy direction moving support circuit 30 is mounted on the pickup 23 according to the X and y direction moving drive signals. The objective lens drive unit 3 6 (see Fig. 35) is driven. Therefore, the objective lens is driven by an amount corresponding to the drive current by drive signals in the X, y, and z directions, and the position of the light spot irradiated on the hologram record carrier is displaced. As a result, the hologram formation time can be secured while keeping the relative position of the light spot relative to the moving hologram record carrier at the time of recording. ·

The control circuit 37 generates a slider drive signal based on the position signal from the operation unit or pick-up position detection circuit 31 and the X-direction movement error signal from the servo signal processing circuit 28, and generates this slider drive circuit 3 Supply to 2. The slider support circuit 32 moves the pickup 23 in the radial direction of the disk through the pickup drive unit 24 according to the drive current generated by the slider drive signal.

The rotation speed detector 33 detects a frequency signal indicating the current rotation frequency of the spindle motor 22 that rotates the hologram record carrier 2 on a turntable, and generates a rotation speed signal indicating the corresponding spindle rotation speed. The rotation position detection circuit 3 4 is supplied. The rotational position detection circuit 3 4 generates a rotational position signal and supplies it to the control circuit 37. The control circuit 37 generates a spindle drive signal, supplies it to the spindle support circuit 35, controls the spindle motor 22 (rotates and drives the hologram record carrier 2).

Kukou Pickup>

FIG. 34 shows the schematic configuration of the pickup 23.

The pickup 23 includes a hologram recording optical system, a hologram reproducing optical system, and a servo control system. These systems are arranged in the housing (not shown) except for the objective lens module BM and its drive system. Laser light source LD for hologram recording / reproduction 1, Collimator overnight lens CL 1, Spatial light modulator SLM, Polarization beam splitter PB S, 4 f Lens fd and fe and image sensor IS are arranged in a straight line, mirror MR, 1/4 wavelength plate 1Z4, 4 f Lens fc, polarization beam split PBS, aberration correction liquid crystal panel LCP, objective lens module OBM are arranged on a straight line, and these linear array parts are arranged orthogonally by polarization beam splitter PBS. _ <Hologram recording optical system>

Hologram recording optical system: Hologram recording / reproducing laser light source LD 1, collimator lens. CL 1, transmissive spatial light modulator SLM, polarization beam splitter PBS, aberration correction liquid crystal panel LCP, 4 f lens fc, mirror MR Including 1/4 wavelength plate 1Z4, and objective lens module OBM.

The light emitted from the laser light source LD 1 is converted into parallel light by the collimator lens CL 1 and enters the spatial light modulator SLM and the polarization beam splitter PBS in this order. The polarization direction of the parallel light is a direction perpendicular to the paper surface. The spatial light modulator S.LM that displays the page data to be recorded in the central area uses the light beam transmitted through the central area including the optical axis as the unmodulated reference light RB, and the surrounding annular light beam as the signal light SB. The polarization beam splitter PBS is arranged so that the incident spatially separated reference light RB and signal light SB are both reflected by the polarizing film (S-polarized light) and incident on the 4 f lens fc. Yes. This 4 f lens fc is a lens for forming an image at the focal position of the objective lens OB (focal length f ob on the optical axis). Since it is difficult to place the spatial light modulator SLM at the focal position of the objective lens OB, the distance from the spatial light modulator SLM to the 4 f lens c is the focal length of the 4 f lens c. The 4 f lens fc passes through the 1 Z4 wave plate 1 Z4 λ and is converted into circularly polarized light. It is arranged so that it is reflected by the mirror MR and incident on the 1 Z4 wave plate 1/4 λ again. As a result, the reference light RB and the signal light SB from the 1/4 wavelength plate 1/4 λ are incident on the polarization beam splitter PBS again with the polarization direction parallel to the paper surface, but the polarization direction is horizontal to the paper surface. (P-polarized light), transmitted through the polarization beam splitter PBS. The reference light RB and the signal light SB are imaged again at the focal position of the 4: f lens: fc, which is equivalent to the presence of the spatial light modulator S.LM at this image position. At this focal position, an aberration correcting liquid crystal panel LCP is placed, and the focal position of the objective lens OB of the objective lens module OBM is matched. The aberration correction liquid crystal panel, LCP, has the TN type orientation of the aberration correction liquid crystal panel LCP. ,

As shown in FIG. 35, in the objective lens module OBM, the concave lens optical element CCV is arranged so that the concave lens action acts only on the reference light RB, and the reference light RB is combined with the action of the objective lens OB to achieve the original objective. It is set so that the focal point is farther than the focal point of the lens OB, and the signal light SB is focused on the focal point of the objective lens OB without receiving the lens action. The eye-to-eye position of the objective lens module OB with respect to the hologram recording carrier 2 is controlled so that the focal point of the objective lens 0 B of the signal light S B is located on the wavelength selective reflection layer 5 of the hologram recording carrier 2.

As shown in Fig. 34, the hologram reproduction optical system consists of a hologram recording / reproduction laser light source LD1, a collimator lens CL 1, a spatial light modulator SLM, a polarization beam splitter PBS, an aberration correction liquid crystal panel LCP, and an objective lens module OBM. 4 f lens fc, fd and fe, mirror MR, quarter wave plate 1Z4 λ, and image sensor IS. In this optical system, the 4 f lenses fd and fe and the image sensor IS The optical parts except for are common to the hologram recording optical system.

As shown in FIG. 34, the 4 f lens f d of the hologram reproducing optical system is arranged at a position where the focal point coincides with the focal position of the objective lens OB through the polarization beam splitter P B S. In addition, a 4 f lens e with the same focal length as the 4 f lens ί d is placed above the optical axis at a distance twice that of the focal point from the 4 f lens ί d. This constitutes the system optical system. Since it is difficult to place the image sensor IS at the focal point of the objective lens OB on which the reproduced image from the reproduced light from the hologram record carrier 2 is formed, the image sensor IS that receives the reproduced light has its light receiving surface. Is positioned at the focal point of the 4 f lens fe, and the reconstructed image is imaged on the light receiving surface of the image sensor IS to obtain a reconstructed signal. By reproducing this, the recorded signal can be reproduced.

Hologram record carrier>

As shown in FIG. 3.5, the hologram record carrier 2 includes a protective layer 8, a hologram recording layer 7, a separation layer 6, a wavelength selective reflection layer 5, a second separation layer 4, as viewed from the reference light incident side. The support guide layer 9 and the substrate 3 onto which the address and track structure are transferred. This wavelength-selective reflection layer 5 is made of a dielectric laminate that transmits the support beam SVB ^ and reflects only the reflection wavelength band including the wavelengths of the reference light and signal light. In the service guide layer 9, a service group or a pin is formed as a service mark T such as a plurality of tracks that extend without being separated from each other. Further, the pitch PX (so-called track pitch) of the servo mark T of the servo guide layer 9 is set as a predetermined distance determined from the multiplicity of the hologram HG recorded above the spot of the signal light and the reference light. The width of the Serpo Mark T is from the optical spot of the SVB SVB It is appropriately set according to the output of the photodetector that receives the reflected light, for example, a push-pull signal. Positioning on the hologram record carrier 2 for performing hologram recording / reproduction by following the servo beam SVB on the support mark T of the support guide layer 9 of the hologram record carrier 2 of the hologram record carrier 2 shown in FIG. 35 (focus support, xy Do direction service). By playing back a focus track, a pre-recorded guide track such as a group or pit, and a signal, you can perform a track spot support.

Servo control system>

The servo control system is also φ for controlling the position of the objective lens module OBM with respect to the hologram record carrier 2 (moving in the xyz direction). As shown in Fig. 34, the second laser light source that emits the hypobeam SVB Includes LD 2, adjustment lens CL 2, half mirror MR, dichroic prism DP, polarizing beam splitter PBS, objective lens module OBM, force pulling lens AS, and photodetector PD. The second laser light source LD 2 is assumed to have a wavelength different from that of the recording raw laser (suppo beam SVB). The servo beam SVB is light having a wavelength insensitive to the hologram recording layer 7 other than the sensitive wavelength bands of the signal light and the reference light.

The servo control system is coupled to the hologram reproducing optical system by a dichroic prism DP disposed between the 4 f lens fc and fe in the 4 ί optical system. That is, the second laser light source LD 2 so that the hypobeam SVB from the second laser light source LD 2 is reflected by the half mirror MR, reflected by the dichroic prism DP, and combined with the light beam of the reproducing optical system. 2, Adjustment lens CL 2, Half mirror MR, Dichroic prism DP are arranged. The control lens CL 2 is combined with the detection system 4 f lens 4 fd, so that the servo beam SVB It is set to be parallel light before BM.

As shown in FIG. 35, in the objective lens module OBM, the diameter (d a) of the hypobeam S VB is set to be equal to or smaller than the diameter (db) of the light beam of the reference light RB. Therefore, the relationship between the outer diameter (d c) and inner diameter (dd) of the signal light SB and these diameters is d c> dd> db≥d a. Here, if the recording guide structure such as recording interval (multiple interval) and track pitch is wider (larger) than that of ordinary optical discs, the aberration of the servo beam SVB and the beam diameter of the hypo beam SVB are small. The lower the numerical aperture NA, the less the reading is affected. As shown in FIG. 34, since the polarization direction of the servo beam S V B is set perpendicular to the paper surface, the servo beam S VB is incident on the objective lens module OBM without being affected by the aberration correcting liquid crystal panel L C P.

As shown in FIG. 35, in the objective lens module OBM, in combination with the concave lens optical element CC V and the objective lens OB, the servo beam SVB is condensed farther than the wavelength selective reflection layer 5 of the hologram recording carrier 2, that is, It is set together with the hologram recording carrier 2 so as to be focused on the support guide layer 9 that has passed through the wavelength selective reflection layer 5 ′ and formed the servo mark T. In this ^f this, the concave lens optical element CCV is not aberration Sapobimu SVB its wavelength in combination with the objective lens OB, so as to focus on the server Pogaido layer 9 is set.

The servo beam S V B passes through the wavelength selective reflection layer 5, reaches the service guide layer 9, and is reflected by the service guide layer 9.

Servo beam reflected by the support guide layer 9 and returned via the objective lens module OBM The reflected light of the SVB is polarized light split PBS or PBS as shown in 34. Then, the dichroic prism DP reaches the half mirror MR through the same optical path as the forward path, and enters the photodetector PD via the servo signal generation optical system.

In the photodetector PD, a focus sap signal can be obtained, for example, by an astigmatism method using a cylindrical lens, etc., and a push-pull tracking error signal etc. can be obtained by reading a servo mark T formed on the sap guide layer 9. You can also get It can also read address signals formed by pit trains.

In this way, the servo control condenses the servo beam SVB as a light spot on the rack on the servo guide layer 9 through the objective lens module OBM, and guides the reflected light to the photodetector PD. The objective lens module OBM is driven by the objective lens drive unit 36 according to the signal detected there.

As shown in FIG. 35, since the wavelength selective reflection layer 5 is closer to the objective lens OB side (light irradiation side) than the servo guide layer 9, the signal light and the reference light are reflected. Since signal light and reference light are not diffracted by the servo structure (Servo Mark T), the influence of the diffracted light is reduced, and hologram reproduction with good SN is possible.

The light emitted from the laser light source LD 1 is converted into parallel light by the collimator lens CL 1 and is incident on the spatial light modulator SLM and the polarization beam splitter PBS in this order. At the time of recording, the page data to be recorded in the annular area is displayed, and the parallel light divided into the reference light RB and the signal light SB by the spatial light modulator SLM that is not modulated in the central area is Each is reflected by the polarization beam splitter PBS, reflected by the 14 wavelength plate 1 Z 4 λ and the mirror MR, and again returns to the polarization beam splitter PBS to be transmitted therethrough. The transmitted reference light RB and signal light SB enter the aberration correction liquid crystal panel LCP. During recording, the same voltage is applied to the transparent electrodes of the central correction area P LCC R and the annular peripheral area P LCP of the aberration correction liquid crystal panel LCP shown in FIG. Therefore, no polarization action occurs in the aberration-correcting liquid crystal panel LCP, the transmitted signal light SB and reference light RB do not receive the polarization action, and their polarization directions (parallel to the paper surface) do not change. ,

The signal light S B and the reference light RB transmitted through the aberration correction liquid crystal panel L C P are incident on the objective lens module O BM with the same polarization direction. Since the signal light SB is not affected by the concave lens optical element CCV, it is collected at the focal point of the original objective lens OB, and the reference light RB is condensed further away from the focal point due to the concave lens action. -Since the wavelength selective reflection layer 5 of the hologram record carrier 2 is set to reflect the light beam having the wavelength of the recording / reproducing laser, the signal light SB is condensed on the wavelength selective reflection layer 5 and reflected. Is done. On the other hand, the reference light RB is reflected by the wavelength selective reflection layer 5 in a defocused state. A region where the signal light SB and the incident reference light RB overlap is generated, and interference between the reference light RB and the signal light SB occurs in this region. By arranging the hologram recording layer 7 in this region (region where the reference light RB and the signal light SB overlap with each other on the objective lens side from the focal point of the signal light SB), the hologram recording layer 7 A hologram is recorded in 7.

During reproduction, as shown in FIG. 36, the light emitted from the laser light source LD 1 is shielded by the annular region of the spatial light modulator SLM, and only the light beam including the optical axis is transmitted unmodulated in the central region. Illumination RB is generated. Follow the same optical path as when recording, and let the reference beam RB reach the central correction area PLCCR of the aberration correction LCD panel CP. Here, an aberration correction liquid crystal panel is applied to a plurality of divided transparent electrodes of the CP phase adjustment unit, and a correction voltage corresponding to the distribution shape of the aberration generated in the reference light is applied, and the annular peripheral region PLCPR is turned off (voltage application is not performed). Do not) and leave the central correction area PLCC on. Since the reference light RB is incident on the hologram recording layer 7 with the polarization direction being parallel to the paper surface, the reproduced light to be reproduced has the same divergence and convergent light beam as the signal light at the time of recording and has a polarization direction parallel to the paper surface. Therefore, the reproduction light is transmitted through the aberration correction liquid and the annular peripheral region PLCPR of the crystal panel LCP, so that the polarization direction is perpendicular to the paper surface due to the polarization effect. On the other hand, the reference light RB is reflected by the wavelength-selective reflection layer 5 while being parallel to the paper surface, but has no polarization action in the liquid crystal, so the polarization direction differs from that of the reproduction light. Therefore, since the polarization of the reproduction light is changed, it is reflected by the polarization beam splitter PBS perpendicular to the paper surface, but the signal light SB is transmitted therethrough. The separated reproduction light forms an image on the light receiving surface of the image sensor IS through the 4 f lenses fd and fe of the detection system to obtain a reproduction image, and the image sensor IS outputs a reproduction signal.

Hologram Recording / Reproducing Method> In the present embodiment of FIG. 34, a hologram recording / reproducing method will be described. When the aberration correction amount determined at the time of hologram recording and the polarization of the reproduction light is changed, hologram recording is performed according to the flowchart shown in FIG.

First, after the hologram record carrier is loaded in the device, the focus / tracking (zx direction) and spindle spindles are operated, and the focal point of the objective lens acquires the predetermined servo mark position information of the hologram record carrier. (Step S 1) Move the pickup to the recording area so that it matches the position (Step S2). Next, the position support (y direction) is operated so that the light beam and the recording layer 7 are relatively stationary (step S3).

Next, when irradiating the hologram recording carrier with the reference light and the signal light, the correction voltage for correcting the reference light aberration is not applied (step S 4), and the central correction region P of the aberration correction liquid crystal panel L CP is applied. The same electric power is applied to the transparent electrodes of the LCC R. and the annular peripheral region P LCP to turn it on (step S5). 'Then, a predetermined amount of information data to be recorded is supplied to the spatial light modulator, the output of the laser light is increased, and the hologram recording carrier is irradiated with signal light and reference light to perform hologram recording. Open (Step S6). Next, it is determined whether or not the information data has been recorded (step S7). If it is a continuation, the process returns to step S2, and if the recording is completed, the process ends.

If the aberration correction amount is fixed at the time of hologram reproduction and the polarization of the reproduction light is changed, the hologram is reproduced as shown in Fig. 38:

First, after the hologram recording carrier is loaded into the apparatus, the focus Z tracking (zx direction) and the spindle support are operated so that the focal point of the objective lens is the predetermined position information on the hologram record carrier. Acquire it (Step S 1 1), and move the pickup to the playback area to match the position (Step S 12).

Next, the position support (y direction) is operated so that the light beam and the recording layer 7 are relatively stationary (step S13).

Next, when the hologram recording carrier is irradiated with only the reference light, a correction voltage for correcting the reference light aberration is applied to correct the aberration in the reference light region (step S14). simultaneous In addition, since the central correction area PLCCR of the aberration correction liquid crystal panel LCP is turned on and the annular surrounding area PLCP (signal light area) is turned off (step S 15), the reproduction light can be separated by polarization. In this reference light aberration correction, the state change caused by the recording / recording of the recording layer 7 is recorded in the memory of the control circuit 37 in advance, and the aberration correction unit 40 drives the aberration correction liquid crystal according to the corresponding aberration correction amount. This is output to the circuit LCPD, and the aberration correction liquid crystal panel LCP corrects the aberration of the reference light. Here, in particular, a problem peculiar to the hologram record carrier, for example, aberration due to shrinkage of the hologram record carrier or change in refractive index is corrected. Therefore, it is effective when the amount of change in the refractive index of the recording layer after recording is anticipated depending on the characteristics of the recording layer of the hologram record carrier.

Next, the output of the laser beam is increased and the hologram record carrier is irradiated with only the reference beam to start hologram reproduction (step S 16). -Next, it is determined whether or not the reproduction of the information data is continued (step S 1 7).

If it is not necessary to change the polarization of the reproduction light in the processes shown in FIGS. 37 and 38, the steps S5 and S15 are omitted, and all the aberration correction liquid crystal panels LCP are kept on. You just have to.

When the aberration correction amount is determined by the quality of the playback signal during playback of the program, the playback of the hologram is performed according to the flowchart shown in Fig. 39.

First, steps S21 to S23 are executed in the same manner as the recording process shown in FIG.

Next, the hologram record carrier is irradiated with only the reference light of the low-power laser beam to Start playback (step S24).

Next, a correction voltage for correcting the reference light aberration is applied, and aberration correction is performed in the reference light region (step S 25).

Next, the SNR or error rate of the reproduced image is acquired in order to evaluate the quality of the reproduction signal based on the aberration correction amount (step S26). For example, in the page data recorded on the recording layer 7, the pixel that transmits the incident light of the spatial light modulator SLM is represented by white level as “1”, and the pixel that blocks the incident light is represented as black by “0”. Since it is recorded as expressed by level, the SNR of the reproduced image is calculated by the following formula. .

SNR- ₍

ψ {10 ₂ )

(Where ml is the average light intensity at the black level, m 2 is the average light intensity at the white level, σ 1 is the standard deviation of the black level, and σ 2 is the standard deviation of the white level.)

Next, an optimum correction value search is performed based on whether the SNR 'or error rate of the acquired image exceeds a predetermined value recorded in the memory of the control circuit 37 (step). S 27). If the acquired value is less than the predetermined value, continue to step S24 and

(

If the obtained value exceeds the predetermined value, the search ends, and the process proceeds to the next to determine the reference light aberration correction value (step S 28).

Next, while correcting the aberration in the reference light region based on the reference light aberration correction value, the output of the laser light is increased and only the reference light is irradiated onto the hologram record carrier to start hologram reproduction (step S 2 9).

Next, it is determined whether or not playback of the information item is continued (step S 3 0), and If there is, return to step S 2 2, and if playback ends, end.

Here, the aberration caused by the shrinkage and the change in refractive index peculiar to the hologram record carrier is corrected according to the recording state of the hologram record carrier, so that it is effective for reproducing various hologram record carriers. Also, if the hologram reading quality is reduced due to the shrinkage of the hologram record carrier, etc., the wavefront control of the reference light seems to be effective. Is expected to occur. Therefore, it is effective to prevent the aberration correction effect of the liquid crystal from acting on the servo beam. .

As described above, the transparent electrode of the aberration correction liquid crystal panel LCP has a division suitable for performing correction according to the aberration when distortion, thickness error, inclination, etc. occur in a hologram record carrier or the like. Therefore, the aberration correction of the reference light can be performed.

As described above, in the prior art, the reference light for holographic recording is a parallel light beam. However, in this embodiment, the signal light and the reference light are diverged or converged so as to make the focal point positions different by a specific objective lens module. In addition, a specific aberration correction device such as an aberration correction liquid crystal panel is used to switch the polarization state during recording and reproduction. Also, in this objective lens module, a specific optical element combined with the objective lens is used to collect light with no aberration on the servo layer of the hologram record carrier using a servo beam that uses a wavelength different from the recording / reproducing laser wavelength. Is set to Furthermore, in the prior art, it is necessary to change the optical system for recording and reproduction, but in this embodiment, the same effect can be obtained by controlling the voltage applied to the aberration correction liquid crystal panel.

In the prior art, since the reference beam is a parallel beam, shift multiplex recording is not possible. The recording capacity was low. However, in this embodiment, a high-quality reproduction signal can be obtained by making the reference beam RB the convergent beam and enabling shift multiplexing. This is particularly effective when the wavefront of the reference light at the time of recording differs from the wavefront of the reference light at the time of reproduction due to shrinkage of the hologram recording layer or a change in refractive index after recording. In addition, since the aberration is removed by the combination of the optical element and the objective lens at the wavelength of the hypo beam SVB, the reproduction of the hypo signal can be performed satisfactorily.

Furthermore, space can be saved by arranging the combined optical path of the servo beam in the 4f system of the detection system, and a synthetic prism can be arranged in the condensing system, so the effective diameter of the prism, etc. can be reduced. can do.

Other Pickup Variations>

Figure 40 shows the configuration of another pickup. '

This pickup removes the mirror MR, the quarter wave plate Ι 74 λ, and the 4 f lens fc in the pickup shown in Fig. 34, and instead of the transmissive spatial light modulator SLM at these positions, a reflection type The polarization spatial light modulator PSLM is placed, and the light beam from the hologram light source LD 1 for hologram recording / reproduction is incident on the polarization spatial light modulator PSLM via the polarization beam splitter PB 'S and the reflected light is used. Other than the above, the same as Pickup 2 3 above. Therefore, the recording / reproducing operation is performed in the same manner as the pickup 23 described above.

As shown in FIG. 41, the polarization spatial light modulator PSLM is divided into a central region A including the optical axis and a spatial light modulation region B not including the surrounding optical axis in the vicinity of the optical axis. LCOS (Liquid Crystal On Silicon) equipment. The reflected light beam is polarized by 90 degrees, and the polarization spatial light modulator PSLM reflects the light beam. At that time, the light beam is coaxially separated into the spatially modulated signal light SB in the spatial light modulation region B and the non-spatial reference light RB in the central region A.

The polarization spatial light modulator PSLMM has a function of electrically polarizing part of incident light for each pixel in a liquid crystal panel having a plurality of pixel electrodes divided in a matrix. This polarization spatial light modulator PSLM is connected to the spatial light modulator driving circuit 26, and modulates the polarization of the light flux so that it has a distribution based on the page to be recorded from now on—the signal light of the annular cross section. Generate SB. In addition, the polarization spatial light modulator PSLM can maintain the same polarization by incidence and reflection, and if it is controlled to be in the reflection state while maintaining the modulation state only in the spatial light modulation region Β, the polarization beam splitter PBS It can function as a shirt evening in combination with the objective lens module OBM.

Claims

The scope of the claims

1. An optical pickup device that records or reproduces information on a hologram record carrier having a hologram recording layer that stores therein an optical interference pattern of reference light and signal light as a diffraction grating,

¾ a light source that generates coherent light,

The center region disposed on the optical axis of the coherent light and the annular region disposed so as to surround the center region, the coherent light passing component of the center region and the annular region A spatial light modulator that spatially separates the passing component of the signal to generate reference light and signal light and propagates them in the same direction on the same axis;

An objective lens optical system that is disposed on an optical axis and irradiates the signal light and the reference light toward the hologram recording layer on the same axis and collects the reference light and the signal light at different focal points;

An image detecting means for receiving light returning from the hologram recording layer via the objective lens optical system when the hologram recording layer is irradiated with the reference light,

'' It consists of a central correction region arranged on the optical axis and an annular peripheral region arranged so as to surround the central correction region, and at least one of the central correction region and the annular peripheral region is the wavefront of the passing light flux. And an aberration correction device comprising a transmissive liquid crystal device including a plurality of transparent electrodes for correcting wavefront aberration of the passing light flux that partially changes the phase.

2. The spatial light modulator comprises a transmissive matrix liquid crystal display device, 2. The optical pick-up device according to claim 1, wherein the central region is made of a through opening or a transparent material.

3. The spatial light modulator comprises a transmissive matrix liquid crystal display device, the central region also comprises a transmissive matrix liquid crystal display device, and the central region is in a transmissive state during recording. Item 1. An optical pick-up device according to item 1.

4. The center correction region is composed of the transmissive liquid crystal device, and corrects wavefront aberration of the passing light beam at least during recording and during reproduction. Optical pick-up device.

5. The optical pick-up humiliation according to claim 4, wherein the wavefront aberration of the passing light beam is corrected only during reproduction.

6. The optical pick-up device according to claim 1, wherein the spatial light modulator is formed of a transmissive matrix liquid crystal display device, and the annular region is formed of a through opening or a transparent material.

7. The spatial light modulator is formed of a transmissive matrix liquid crystal display device, the annular region is also formed of a transmissive matrix liquid crystal display device, and the annular region is in a light transmissive state during recording. Item 1. An optical pick-up device according to item 1.

8. The annular peripheral region is composed of the transmissive liquid crystal device, and corrects wavefront aberration of the passing light beam at least during recording and during reproduction. Optical pick-up device.

9. The optical pick-up device according to claim 8, wherein the wavefront aberration of the passing light beam is corrected only during reproduction.

1 0. The aberration correction device passes through the central correction region and the annular peripheral region. The optical pickup device according to any one of claims 1 to 9, wherein the rotation angles of the polarization planes are made different from each other. '

1 1. The objective lens optical system is a bifocal lens having a convex or concave lens, a Fresnel lens surface having a convex or concave lens action, or a diffraction grating, which is formed integrally with a condensing lens and coaxially formed on a refractive surface thereof. The optical pick-up device according to claim 1, wherein the optical pick-up device is provided.

1 2. The objective lens optical system comprises: a condensing lens and a convex or concave lens arranged coaxially with the condensing lens, or a transmissive optical element having a convex or concave, Fresnel lens surface or diffraction grating having a lens action. The optical pick-up device according to claim 1, wherein

13. The optical pickup device according to claim 1, wherein the plurality of transparent electrodes are arranged in a concentric pattern around the optical axis.

1 4. The plurality of transparent electrodes are arranged in a pattern of inner and outer regions that are symmetrical with respect to a straight line perpendicular to the optical axis and divided by a gap including the straight line. ~ 1 Optical pick-up device described in 2

15. A hologram recording / reproducing system for recording / reproducing information on / from a hologram recording carrier that stores therein an optical interference pattern of reference light and signal light as a diffraction grating.

From the coherent light, a reference light, a signal light obtained by modulating the coherent light according to the recording information, and a light generating means for generating

Either the reference light or the signal light is on the optical axis, and the other is around the one The reference light and the signal light are condensed at different focal points on the optical axis via the objective lens optical system, and are spatially separated from each other and transmitted coaxially in the same direction. And interference means for interfering with the signal light,

A hologram recording carrier having a hologram recording layer located on the focal side near the objective lens optical system among the different focal points;

A reflection layer located on the focal side far from the objective lens optical system;

An image detecting means disposed on the optical axis and receiving light from the hologram recording layer via the objective lens optical system when the hologram recording layer is irradiated with the reference light; and

A central correction region disposed on the optical axis and an annular peripheral region disposed so as to surround the central correction region, and at least one of the central correction region and the annular peripheral region is a wavefront of a passing light flux. An aberration correction device including a transmission type liquid crystal device including a plurality of transparent electrodes for correcting wavefront aberration of the passing light flux that partially changes the phase; and when information is recorded on or reproduced from each of the plurality of transparent electrodes And a aberration correction liquid crystal driving circuit for supplying a correction voltage to the hologram recording / reproducing system.

16. The hologram recording layer is sufficient that either one of the reference light or the signal light is defocused on the reflection layer and reflected so as to intersect with the other to generate a diffraction grating. 16. The hologram recording / reproducing system according to claim 15, wherein the hologram recording / reproducing system has a film thickness.

17. The hologram record carrier is formed as an integrated body in which a separation layer is laminated between the hologram recording layer and the reflective layer. 16. The hologram recording / reproducing system according to any one of 6 above.

18. The aberration correction device has a function of making the rotation angles of the polarization planes different at the time of recording or reproducing information, and the aberration correction liquid crystal driving circuit is connected to the central correction region with respect to the aberration correction device. 2. The hologram recording / reproducing system according to claim 1, wherein the rotation angle of the polarization plane of the passing component in the annular peripheral region is controlled to be different from each other.

19. The plurality of transparent electrodes are arranged in a concentric pattern around the optical axis, and the aberration correction liquid crystal driving circuit supplies a correction voltage corresponding to the spherical aberration to be corrected. The hologram recording / reproducing system according to any one of claims 15 to 18.

The plurality of transparent electrodes are arranged in a pattern of inner and outer regions that are symmetrical with respect to a straight line perpendicular to the optical axis and divided by a gap including the straight line, and the aberration correction liquid crystal driving circuit includes: The hologram recording / reproducing system according to claim 15, wherein a correction voltage corresponding to coma aberration to be corrected is supplied. '