WO2006118036A1 - Method and device for recording/reproducing hologram - Google Patents

Abstract

A hologram device is provided with a supporting section which mountably holds a recording medium, which has a hologram recording layer wherein an optical interference fringe due to coherent signal beam and reference beam is kept as diffraction grating, so that a reflection layer is positioned on a side opposite to the beam irradiated plane of the hologram recording layer; a light source for generating the coherent reference beam; a signal beam generating section which includes a spatial light modulator arranged on an optical axis and generates the signal beam by modulating the reference beam corresponding to recording information; and an interference section which irradiates the hologram recording layer with the signal beam and the reference beam and forms the diffraction grating by optical interference fringe inside the hologram recording layer. The hologram device includes a rotation inversion mask which is arranged in an optical path of the reference beam and partially blocks the reference beam; and an objective lens coaxially arranged with the rotation inversion mask for collecting the passed through reference beam on the reflection layer.

Description

 TECHNICAL FIELD Field of the Invention

 The present invention relates to a recording medium on which optical information recording or information reproduction is performed, such as an optical disk or a light field, and more particularly to hologram recording / reproduction of a recording medium having a hologram recording layer capable of recording or reproducing information by irradiation with a light beam. The present invention relates to a method and an apparatus. Background art

 Holograms that can record two-dimensional data at high density are attracting attention for high-density information recording. 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 hologram multiplex recording on the recording medium, the recording capacity can be dramatically increased. As a structure, a recording medium is known in which a substrate, a hologram recording layer, and a reflection layer are formed in this order.

 For example, conventionally, the information light is converged and irradiated so as to have the smallest diameter on the boundary surface between the hologram layer and the protective layer of the recording medium and reflected by the reflective layer. At the same time, the recording reference light is reflected by the hologram layer and the protective layer. Recording on the hologram recording medium by converging so that it has the smallest diameter on the front side of the boundary surface and irradiating as divergent light and causing interference

(See Japanese Patent Laid-Open No. 11-311 938).

Furthermore, in the recording optical system, the information light is converged on the reflective layer, and the recording reference There is also a technology for irradiating the recording reference light so that the light is defocused on the reflective layer and the conjugate focal point of the recording reference light is located on the substrate side of the boundary surface between the substrate and the hologram recording layer. (See Japanese Patent Laid-Open No. 2 0 0 4-1 7 1 6 1 1). Disclosure of the invention

 For example, an object lens configuration of an aspect in which recording / reproduction is performed from one side of a hologram recording layer of a recording medium in Japanese Patent Application Laid-Open Nos. 1-11 3 1 1 9 3 8 and 2 0 4 -1 7 1 6 1 1 Examples are shown in Figs. 1 and 2, respectively.

 In any conventional technique, as shown in the figure, during recording, the reference light and the signal light are coaxially guided to the objective lens OB so that they overlap each other. The light always interferes on the optical axis. When a reflective layer is placed at the focal point P of the signal light and the recording medium is placed between the objective lens and the reflective layer, the reference light and the signal light pass back and forth through the recording medium to perform hologram recording. Is called. 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 specifically recorded in the recording medium are holograms A (recording interference between reflected reference light and reflected signal light), holograms, B (recording of interference between incident reference light and reflected signal light), hologram C (recording interference between reflected reference light and incident signal light), hologram D (incident There are four types of recordings where the interference between the reference beam and the incident signal beam is recorded. In addition, the reproduction light obtained from the recording medium during the reproduction process is also reproduced light from the hologram A (read out by the reflected reference light), holo Reproduction light from Gram B (read out with incident reference light), reproduction light from hologram (read out with reflected reference light), reproduction light from hologram D (read out with incident reference light) 4 It is a kind.

 Thus, in these prior arts, all the light rays in the hologram recording layer

Since (incident reference light and reflected light and information light incident and reflected light) interfere with each other, a plurality of holograms are recorded and reproduced. This is, for example, disclosed in JP

This is as described in paragraph (0 0 9 6) (0 0 9 7) of the publication No. 4-1 7 1 6 11.

 In the conventional method, when a hologram is recorded on a recording medium having a reflecting surface, four holograms are recorded by four-way interference between the incident reference light and signal light and the reflected reference light and signal light. As a result, the performance of the hologram recording layer was wasted. Also, when reproducing information, reproduced light and phase conjugate reproduced light appear simultaneously, and they are mixed and detected by the same detector, so the read performance of the reproduced signal is degraded.

 In addition, since many optical components are required to generate and merge the reference light and signal light, it is desired to reduce the size of the apparatus.

 Thus, an example of the problem to be solved by the present invention is to provide a hologram recording / reproducing method and a hologram apparatus that enable stable recording or reproduction.

The hologram recording apparatus according to claim 1, wherein a recording medium having a hologram recording layer that stores therein optical interference fringes by coherent signal light and reference light as a diffraction grating is provided on a light irradiation surface of the hologram recording layer. Wear so that the reflective layer is located on the opposite side A support part for holding freely;

 A light source that generates coherent reference light;

 A signal light generation unit including a spatial light modulator that is arranged on the optical axis and generates the signal light by modulating the reference light according to recording information;

 A hologram recording apparatus comprising: an interference unit configured to irradiate the hologram recording layer with the signal light and the reference light to form a diffraction grating by optical interference fringes inside the hologram recording layer;

 An anti-reflective mask disposed in the optical path of the reference light and partially blocking the reference light; an objective lens disposed coaxially with the anti-reflective mask and condensing the reference light that has passed through the reflective layer; It is characterized by including these.

 The hologram reproducing device according to claim 17 is a hologram reproducing device for reproducing information from a recording medium having a hologram recording layer in which optical interference fringes by reference light and signal light are stored as diffraction gratings.

 A support unit that holds the recording medium so that the reflective layer is positioned on the opposite side of the light irradiation surface of the hologram recording layer;

 A light source that generates coherent reference light;

 An anti-reflection mask comprising a light-shielding region and a light-transmitting region which are anti-symmetric about the optical axis of the reference light, which is disposed in the optical path of the reference light and partially blocks the reference light;

 The reference light is condensed on the reflection layer so as to pass through the anti-reflection mask and the diffraction grating of the hologram recording layer to generate reproduction light from the diffraction grating, and the reproduction light is received. An objective lens;

And an image sensor for detecting the received reproduction light. The hologram recording method according to claim 22 is a hologram recording method for recording information on a recording medium having a hologram recording layer in which optical interference fringes by reference light and signal light are stored as diffraction gratings.

 Generating a coherent reference beam;

 Disposing an anti-reflection mask consisting of a light-shielding region and a light-transmitting region that are anti-symmetric about the optical axis of the reference light, which partially shields the reference light, in the optical path of the reference light; Disposing a reflective layer on the opposite side of the light irradiation surface; and reflecting the reference light so as to pass through the hologram recording layer while passing through the light-transmitting region of the anti-reflection mask and converging by the objective lens. Irradiating the layer and reflecting on the reflective layer, and

 In the step of reflecting on the reflection layer, signal light obtained by modulating the reference light according to recording information is caused to interfere with the reference light in the hologram recording layer to form a diffraction grating. Features.

 The hologram reproducing method according to claim 23 is a hologram reproducing method for reproducing information from a recording medium having a hologram recording layer in which optical interference fringes by reference light and signal light are stored as diffraction gratings.

 Generating a coherent reference beam;

Disposing an anti-reflection mask consisting of a light-shielding region and a light-transmitting region that are anti-symmetric about the optical axis of the reference light, which partially shields the reference light, in the optical path of the reference light; A step of disposing a reflective layer on the opposite side of the light irradiation surface; and passing through the photogram recording layer while allowing the reference light to pass through the translucent region of the anti-reflection mask and to be converged by the objective lens. Irradiate the reflective layer and Generating reproduction light from the diffraction grating;

 Guiding the reproduction light to the image sensor through the objective lens. Brief Description of Drawings

 1 and 2 are schematic partial cross-sectional views showing an optical system and a recording medium for explaining conventional hologram recording.

 FIG. 3 is a schematic partial sectional view showing a recording medium for explaining conventional hologram recording.

 FIG. 4 is a schematic configuration diagram showing an optical system and a recording medium for explaining the recording / reproducing apparatus of the embodiment according to the present invention.

 FIG. 5 is a schematic configuration diagram showing an optical system and a recording medium for explaining a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 6 is a schematic partial sectional view showing a recording medium according to another embodiment of the present invention. 7A to 7D are front views showing a reversal mask in the recording / reproducing apparatus according to the embodiment of the present invention.

 FIG. 13 is a schematic partial sectional view for explaining hologram recording / reproduction according to the embodiment of the present invention.

 FIG. 14 is a schematic partial cross-sectional view showing a recording medium for explaining hologram recording of an embodiment according to the present invention.

FIG. 15 is a schematic partial sectional view showing an optical system for explaining hologram recording / reproduction according to an embodiment of the present invention. ' FIGS. 16A and 16B are front views showing a reversal mask in a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 17 is a schematic configuration diagram showing an optical system and a recording medium for explaining a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 18 is a front view showing a spatial light modulator in a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 19 is a schematic configuration diagram showing an optical system and a recording medium for explaining a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 20 is a front view showing a spatial light modulator in a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 21 is a schematic configuration diagram showing an optical system and a recording medium for explaining a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 22 is a front view showing a spatial light modulator in a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 23 is a schematic configuration diagram showing an optical system and a recording medium for explaining a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 24 is a front view showing a spatial light modulator in a recording / reproducing apparatus according to another embodiment of the present invention.

 FIG. 25 is a partial sectional view showing a liquid crystal element in a recording / reproducing apparatus according to another embodiment of the present invention.

FIG. 26 is a front view as seen from the optical axis of the spatial light modulator in the recording / reproducing apparatus according to another embodiment of the present invention. ' FIG. 27 is a schematic configuration diagram showing an optical system and a recording medium for explaining a recording / reproducing apparatus according to another embodiment of the present invention.

 28A to 28C are front views showing a spatial light modulator in a recording / reproducing apparatus according to another embodiment of the present invention. Detailed Description of the Invention

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

FIG. 4 shows a configuration example of the optical system of the hologram recording / reproducing apparatus in the present embodiment. The hologram recording / reproducing apparatus uses a recording medium 2 having a hologram recording layer 7 that stores optical interference fringes as a diffraction grating inside the coherent signal light SB and reference light RB, as opposed to the light irradiation surface of the hologram recording layer 7. A support portion (not shown) that is detachably held is provided so that the reflective layer 5 is positioned on the side. The hologram recording / reproducing apparatus is roughly composed of a hologram recording and reproducing optical system. These systems share the objective lens 0B and include an objective lens drive system and a servo error detection system (not shown). It is out. The hologram recording / reproducing optical system consists of a laser light source LD that generates coherent light for hologram recording and reproduction, a collimator lens CL, first and second half mirrors HM 1 and HM 2, and transmissive spatial light modulation. SLM, anti-reverse mask RIM, objective lens 0B, imaging lens ML, CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor Device), etc. Placed in. The anti-reverse mask RIM belonging to the reference light generation unit is composed of a light-shielding region SR and a light-transmitting region TR that are anti-symmetric about the optical axis of the reference light RB that partially blocks the reference light RB. I can arrange it. ' The spatial light modulator SLM belonging to the signal light generation unit is arranged on the optical axis and modulates the reference light RB according to the recording information to generate the signal light SB. The transmissive spatial light modulator SLM is a function of electrically shielding a part of incident light for each pixel by a liquid crystal panel having a plurality of pixel electrodes divided in a matrix, or is not transmitted and transmitted. It has a function to make a modulation state. This spatial light modulator SLM is connected to a spatial light modulator driving circuit (not shown), 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 signal beam SB is generated by modulating and transmitting the light flux as if it has.

 The objective lens OB of the interference unit condenses the reference light R B that is disposed coaxially with the anti-reflection mask R I M and passes through the reflection layer 5. The objective lens OB is set so that the reference light RB forms a spot without aberration on the reflection layer 5 of the recording medium. On the other hand, since the signal light S B is subjected to the action of the spatial light modulator S L M, it forms a spot that is wider than the reference light R B. A hologram (diffraction grating) is formed inside the hologram recording layer 7 by the interference fringes of these lights.

 In the configuration example of FIG. 4, the laser light from the light source D is divided into the optical paths of the signal light SB and the reference light RB by the first half mirror HM 1 and the second light passes through the anti-reflection mask RIM and the spatial light modulator SLM, respectively. The beams are merged by the half mirror HM 2 and irradiated coaxially in the hologram recording layer 7 so as to overlap with the reference beam RB.

In addition, the hologram recording / reproducing apparatus omits the second half mirror HM 2 and the optical path of the reference light RB so that the signal light SB overlaps the reference light RB in the hologram recording layer 7 as shown in FIG. It can be configured to be illuminated from the outside. If the optical path of the signal light SB and the reference light RB are completely separated, any of the optical paths of the reference light RB An anti-rotation mask R IM can be placed at some place.

 FIG. 6 shows an example of the recording medium 2. The recording medium 2 includes a reflective layer 5, a separation layer 6, a hologram recording layer 7, and a protective layer 8 stacked on the substrate 3 in the film thickness direction. Note that the reflective layer 5 may be separated from the hologram recording layer 7 and configured as a separate body.

 For the hologram recording layer 7, for example, a light-transmitting photosensitive material capable of storing optical interference fringes such as a photopolymer, a light anisotropic material, a photorefractive material, a hole burning material, and a photochromic material is used.

 The substrate 3 supporting each of the above films is made of, for example, glass, polycarbonate, amorphous polyolefin, polyimide, PET, PEN, PES or other plastics, UV curable acrylic resin, or the like.

 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.

 Anti-rotation mask R I M is a light-dark pattern that is anti-rotation in the optical path of the effective diameter of reference beam RB.

It has a light-shielding region SR and a light-transmitting region TR (when the image is rotated 180 degrees around the optical axis, the pattern is inverted from light to dark). In other words, the anti-rotation mask RIM having strict anti-rotation symmetry means that the light shielding region SR and the light transmitting region TR are arranged around the optical axis of the reference light RB.

When a rotation operation rotating by (2m-1) is performed, the light shielding area has a pattern that overlaps the light transmitting area, and the light transmitting area overlaps the light shielding area. Where m is an integer such as 1, 2, 3, 4, 5, 6. As m increases, the light-shielding pattern becomes finer, and the effect of diffraction effects at the boundary of the light-shielding Z light-transmitting region occurs.

7A to 7D are front views showing examples of anti-rotation mask RIM with m == 1. FIG. 8 is a front view showing an example of an antisymmetric anti-rotation mask RIM with m = 2.

 FIG. 9 is a front view showing an example of the anti-rotation mask R I M of m = 3.

 FIG. 10 is a front view showing an example of an antisymmetric anti-rotation mask R I M with m = 4.

 FIG. 11 is a front view showing an example of an antisymmetric anti-rotation mask R I M with m = 5.

 FIG. 12 is a front view showing an example of an antisymmetric anti-rotation mask R I M with m = 6.

 In the hologram recording method, as shown in FIG. 4, the light source LD generates the reference light RB, and the antireflection mask RIM is partially blocked by the antireflection mask RIM arranged in the optical path of the reference light RB. The reflection layer 5 is irradiated so as to pass through the hologram recording layer 7 through the light transmission region TR, converged by the objective lens OB. The signal light SB modulated according to the recording information and the reference light RB are caused to interfere with each other in the hologram recording layer 7 to form a diffraction grating.

 In the hologram reproducing method, the divergent coherent light emitted from the laser light source LD is converted into a parallel light beam by the collimator lens CL, and is condensed as the reference light RB on the recording medium 2 by the objective lens OB via the half mirror HM. Is done. Reproduced light is generated from the diffraction grating of the hologram recording layer and is reflected by the third half mirror HM 3 through the objective lens OB. Reproduced light is imaged on the image sensor IS by the imaging lens ML. As described above, the generation of the reference beam RB to the irradiation of the reflective layer 5 is the same as that in the photogram recording method, and the reproduction beam is generated from the diffraction grating by the irradiation, and the reproduction beam is transmitted through the objective lens B. To the image sensor IS to reproduce information by photoelectric conversion. In this embodiment, normal playback is performed if playback is performed with the same anti-reverse mask R I M as during recording.

As shown in Fig.13, the objective is selected by placing the anti-reverse mask RIM in the reference beam path. In the optical path space between the lens OB and the reflective layer 5, either the light from the objective lens B to the reflective layer 5 (bound light) or the light from the reflective layer 5 to the objective lens OB (return light) Only one of them will exist. Further, when the anti-rotation mask RIM having a strict anti-rotation symmetry is used, either light is always present in the irradiated portion of the recording medium 2, and there is no place where the light is not irradiated. As shown in Fig. 14, the hologram pair E due to interference between the incident reference light and the incident signal light and interference between the incident reference light and the reflected signal light, or interference between the reflected reference light and the incident signal light, and Depending on the location of the recording layer 7, any pair of hologram pairs F due to interference between the reflected reference light and the reflected signal light is recorded alternatively.

 By placing the anti-rotation mask R I M in this way, the problem of recording two holograms (uselessly) is solved.

 If the anti-reflection mask RIM is placed in the same way during reproduction, the same reference light RB as that when the hologram is recorded is irradiated, so that only normal reproduction light appears, and phase-shared reproduction light does not appear.

In another embodiment, the light shielding region SR and the light transmitting region TR of the anti-rotation mask RIM shown in FIG. 4 are provided with inversion means INV that inverts or rotates 180 degrees around the optical axis, so Phase conjugation reproduction can be achieved by reversing the light-blocking region SR and the light-transmitting region TR) of the anti-mask RIM or by rotating it 180 degrees around the optical axis. During playback, it is possible to switch between normal playback and phase conjugate playback and to prevent two playback lights from returning to the image sensor IS at the same time. The anti-rotation mask RIM can be composed of a fixed plate-like body, but this is composed of a transmissive liquid crystal element, and at the time of writing, the liquid crystal element shows a light shielding region SR and a light transmissive region TR. It can also be controlled to be in a state.

 As shown in Fig. 15, when the anti-rotation mask RIM is rotated 180 degrees from the recording state (in which light and dark are reversed), all locations between the objective lens B and the reflective layer 5 are shown. The direction of the reference beam is reversed. Where there has been a “light for going”, there is a “light for return” and where there has been a “light for return” there is “light for going”. When reproduction is performed in this state, only phase conjugate reproduction light appears, and normal reproduction light does not appear. In addition, it is possible to select normal reproduction or phase conjugate reproduction by switching the anti-reflection mask R I M in two states during reproduction by the inversion means. If the objective lens OB is an ideal lens (for example, a Fourier transform lens), a light beam emitted from a point on the page data of the spatial light modulator forms an image on a point on the image plane of the image sensor IS. However, an actual objective lens is affected by lens aberration and MTF characteristics, resulting in image blurring. This is even more conspicuous when the numerical aperture NA of the objective lens OB is large or when the image height (distance from the optical axis of the dot on the page) is large.

 When the pattern of the spatial light modulator SLM is recorded as a hologram, the pattern of the spatial light modulator SLM corresponds to page data. In this case, a hologram is formed by interfering with the reference light RB between the objective lens OB and the reflecting layer 5. Since the reproduced light appears as if there is a page dew in the original location, the optical path of the reproduced light is the same as that of the actual objective lens during recording, and the influence of the aberration of the objective lens B and the MTF is affected. The received image is blurred on the image sensor IS.

On the other hand, in the phase conjugate reproduction, the reproduced light appears so as to return back to the optical path of the original signal light SB. Therefore, the original page regardless of the performance of the objective lens 〇B The same image as the data can be formed. Therefore, if the NA of the objective lens OB to be used is large, or if there is a part where the spatial light modulator SLM has a large pattern and a large image height, the performance of the objective lens 0B can be improved by using phase conjugate reproduction. Good reproduction images can be obtained without any restrictions. However, since the phase conjugate reproduction light is inferior to the normal reproduction light in the SN ratio, it is preferable to use only the normal reproduction light if reproduction with a good SN ratio is desired. You can choose between normal playback and phase-conjugate playback depending on whether you want the SN ratio or imaging performance.

 As is clear from the above description, the shape of the anti-rotation mask RIM is not strictly anti-rotation-symmetric, and the shading area SR illustrated in FIG. 16A has a slightly smaller area than the translucent area TR. Even if the shape conforms to anti-rotation symmetry (quasi-anti-anti-symmetry), it is possible to greatly reduce the area where “bound reference light” and “return reference light” exist simultaneously in the medium. The effect of the present invention to reduce the influence of a simple hologram can be obtained. In addition, when the light-shielding region SR illustrated in Fig. 16B has a slightly larger area than the light-transmitting region TR, a region where no reference light exists in the medium is generated. And “returning reference beam” can be realized, and the effect of the present invention can be obtained. Therefore, in the shape of the anti-rotation mask RIM, the areas of the light-shielding region SR and the light-transmitting region TR are strictly equal, and these areas can be increased or decreased if the optical paths of incident light and reflected light in the medium are limited. Can do.

 Other embodiments include the following.

For example, as shown in FIG. 17, only the outer peripheral part of the laser beam from the light source LD is modulated so that the outer peripheral part is signal light SB and the inner peripheral part on the optical axis is unmodulated reference light RB. Can do. In this case, as shown in FIG. 18, the spatial light modulator SLM is arranged around the transmission central region TCR arranged on the optical axis that allows the reference light RB to pass through without modulation, and around the transmission central region TCR. A spatial light modulation annular region SLMRR composed of a transmissive matrix liquid crystal device that modulates the reference light RB according to information and generates the signal light SB spatially separated from the reference light RB. In this embodiment, since the optical axis and the vicinity thereof become the reference light RB, the anti-reflection mask RIM that acts only on the inner periphery may be disposed at any location so as not to affect the signal light s. . In other words, the anti-reflection mask RIM is arranged so as to partially block only the reference light RB passing through the transmission central region TCR without blocking the signal light SB. Further, the transmission central region TCR can be formed of a through opening or a transparent material. Further, the transmissive central region TCR is composed of a transmissive liquid crystal element, and is controlled so that the liquid crystal element is in a translucent state during recording. On the other hand, as shown in FIG. 19, the spatial light modulator SLM and the anti-rotation mask RIM may be integrally formed, and the other configuration may be the same as the example of FIG. In this case, as shown in FIG. 20, the spatial light modulator SLM is arranged around the central mask region CMR as the anti-rotation mask RIM and the central mask region CMR and modulates the reference light RB according to the recording information. And a spatial light modulation annular region SLMRR composed of a transmissive matrix liquid crystal device that generates signal light SB spatially separated from the reference light RB. The central mask area CMR can be composed of a fixed plate, but the central mask area CMR is composed of a transmissive liquid crystal element, and the liquid crystal element displays the light shielding area SR and the translucent area TR during recording. It can also be controlled as is.

Contrary to the examples of FIGS. 17 and 19, a configuration in which the inner peripheral portion is the signal light SB and the outer peripheral portion is the reference light RB can be employed. For example, as shown in Fig. 21, the laser beam from the light source LD Only the inner peripheral part of the signal can be modulated so that the inner peripheral part is the signal light SB and the outer peripheral part is the unmodulated reference light RB. In this case, as shown in FIG. 22, the spatial light modulator SLM is a transmissive matrix liquid crystal device arranged on the optical axis that modulates the reference light RB in accordance with the recording information and generates the signal light SB. Spatial light modulation central region SLM CR consisting of and a transmission annular region TRR arranged around the spatial light modulation central region S LMC R and spatially separated from the signal light SB through the reference light RB without modulation. Consists of. The anti-rotation mask RIM is arranged so as to partially block only the reference light RB passing through the transmission annular region TRR without blocking the signal light SB. The transmissive annular region TRR consists of a through-opening or a transparent material. Further, the transmissive annular region TRR can be constituted by a transmissive liquid crystal element and can be controlled so that the liquid crystal element is in a light-transmitting state during recording. Further, as shown in FIG. 23, the spatial light modulator SLM and the anti-rotation mask RIM may be integrally formed, and the other configuration may be the same as the example of FIG. In this case, as shown in FIG. 24, the spatial light modulator SLM modulates the reference light RB in accordance with the recording information and passes it to generate a transmission light matrix liquid crystal disposed on the optical axis. It consists of a spatial light modulation central region SLMCR consisting of a device and an annular mask region RMR as a reversal mask RIM arranged around the spatial light modulation central region SLMCR. The annular mask area RMR is composed of a transmissive liquid crystal element, and the liquid crystal element is in a state where the annular mask area RM R displays the light shielding area SR and the light transmitting area TR during recording.

As shown in FIG. 25, the liquid crystal device portion of the spatial light modulator SLM or anti-rotation mask RIM—body-type spatial light modulator SLM is composed of a transmissive liquid crystal element, which consists of a pair of opposing polarizing plates 80 liquid crystal layer 83 (crystal molecules) sandwiched between transparent electrodes 81 a and 81 b and alignment films 82 a and 82 b sequentially formed on the inner surfaces of a and 80 b. Layer). The transparent electrodes 8 1 a and 8 1 b have one or more pairs of electrode shapes according to the shape of the anti-rotation mask RIM. As shown in FIG. 26, the spatial light modulator SLM as a whole is a transmissive matrix liquid crystal device, and its control circuit 26 displays a predetermined pattern, for example, an inner central region A and an outer peripheral region B on its outer periphery. Each can also be configured to display an anti-reflection mask area and a page data area. To switch between normal playback and phase conjugate playback during playback, the anti-rotation mask RIM is rotated 180 degrees around the optical axis. If a liquid crystal element is used, the same effect can be obtained only by electrical switching.

 Liquid crystal molecules have the property of rotating the polarization plane of light (rotation) only at the part where voltage is applied. The amount of rotation of the polarization plane varies depending on the thickness of the liquid crystal layer and the magnitude of the applied voltage. It is assumed that the polarization of the portion where voltage is applied between the transparent electrodes 8 1 a and 8 1 b is set to rotate 90 degrees. It is assumed that the polarization state of the light passing through the polarizing plate 80 a is linearly polarized light (referred to as A-polarized light) parallel to the paper surface.

 The polarizing plate 80 a is a polarizing plate that allows only the A polarized light to pass therethrough, and the polarizing plate 80 b is the same.

 A voltage is applied to the liquid crystal layer 83 only by a certain electrode pair, and the polarization plane is rotated by 90 degrees only for the light passing through this portion, and linearly polarized light perpendicular to the paper surface (referred to as B-polarized light). It becomes.

 Since the polarizing plate 80 b facing thereafter passes only the A-polarized light, only the light from the other electrode pair passes, and the other light is blocked.

The liquid crystal element as a whole acts as an anti-rotation mask RIM that shields light only from a portion to which a voltage is applied. ' For example, if the anti-reverse mask RIM of the pattern in Fig. 7C is realized with liquid crystal, the electrode pattern is made to correspond to the white and shaded portions, and voltage is applied only to the shaded portions. The shaded area is the light shielding region SR.

 In order to switch between normal playback and phase conjugate playback during playback, instead of rotating the anti-reverse mask RIM by 180 degrees, a voltage is applied to the white area and no voltage is applied to the shaded area. The shaded area is translucent and the other areas are light-shielded. Optically, this is the same as turning the entire anti-rotation mask RIM 180 degrees around the optical axis. The incident side polarizing plate (in this example, polarizing plate 80a) may be omitted. Furthermore, by arranging the polarizing plate to rotate 90 degrees around the optical axis, it is possible to transmit only the part to which voltage is applied (the other part is shielded). In this way, the same effect can be obtained only by electrical switching without physically rotating the anti-rotation mask RIM.

In still another embodiment, the embodiment shown in FIGS. 17 to 24 (the signal light SB and the reference light RB are propagated separately along the optical axis at the inner and outer circumferences of the effective diameter of the laser beam from the light source LD. As shown in Fig. 27, it is possible to use a QSLM with an anti-reverse mask integrated spatial light modulator that divides the luminous flux into the first to fourth quadrants as viewed from the optical axis. As shown in FIG. 28A, during recording, signal light SB is generated in a state in which a page data pattern for modulating the reference light RB is displayed in the first and third quadrants Ql and Q3 according to the recording information. The fourth quadrant Q2 and Q4 are used as the reference beam RB (however, the second quadrant Q2 is shielded). At this time, the second and fourth quadrants Q2 and Q4 corresponding to the reference beam RB become antisymmetric. As shown in Figure 28B, during playback, the first to third quadrants Q1 to Q3 are shielded, and the reference light is in the same light transmission state (fourth quadrant Q4) as during recording. As shown in Fig. 28 C, phase conjugate reproduction is possible by reversing the brightness and darkness during recording (fourth quadrant Q4 is light-shielded and second quadrant is translucent). Become. As described above, according to the present embodiment, at the time of hologram recording, only one of the outgoing reference light and the reflected reference light interferes with the signal light SB, and therefore an extra hologram can be recorded. Absent. Also, during reproduction, only normal reproduction or phase conjugate reproduction can be performed, and normal reproduction light and phase conjugate reproduction light are not mixed on the detector, so that good reproduction can be performed. I can do it.

Claims

The scope of the claims 1. A recording medium having a hologram recording layer in which optical interference fringes due to coherent signal light and reference light are stored as diffraction gratings is placed so that the reflection layer is positioned on the opposite side of the light irradiation surface of the hologram recording layer. In addition, a support portion that is detachably held, a light source that generates coherent reference light,  A signal light generation unit including a spatial light modulator that is arranged on the optical axis and generates the signal light by modulating the reference light according to recording information;  A hologram recording apparatus comprising: an interference unit configured to irradiate the hologram recording layer with the signal light and the reference light to form a diffraction grating by optical interference fringes inside the hologram recording layer;  An anti-reflective mask disposed in the optical path of the reference light and partially blocking the reference light; an objective lens disposed coaxially with the anti-reflective mask and condensing the reference light that has passed through the reflective layer; A hologram recording apparatus comprising:  2. The anti-rotation mask performs a rotation operation (m is a positive integer) that rotates the light-shielding region and the light-transmitting region about the optical axis of the reference light by πΖ (2 m-1). 2. The hologram recording apparatus according to claim 1, further comprising: a pattern in which the light shielding region is a light transmitting region and the light transmitting region is a light shielding region.  3. The hologram recording apparatus according to claim 2, wherein the m is 6 or less. 4. The spatial light modulator includes a transmission center region disposed on an optical axis that allows the reference light to pass through without modulation, and is disposed around the transmission center region and corresponds to recorded information. And a spatial light modulation annular region composed of a transmissive matrix liquid crystal device that modulates the reference light and generates the signal light spatially separated from the reference light. 4. The hologram recording device according to any one of 3.  5. The hologram recording apparatus according to claim 4, wherein the transmission central region is made of a through-opening or a transparent material.  6. The hologram recording apparatus according to claim 4, wherein the transmission central region is made of a transmission type liquid crystal element, and the liquid crystal element is in a light transmitting state during recording.  7. The anti-rotation mask is arranged so as to partially block only the reference light passing through the transmission central region without blocking the signal light. Hologram recording device.  8. The spatial light modulator is disposed around the central mask region as the anti-rotation mask and around the central mask region and modulates the reference light according to recording information to spatially separate the reference light from the reference light. 4. The hologram recording device according to claim 1, further comprising: a spatial light modulation annular region formed of a transmission type matrix liquid crystal device that generates the separated signal light.  9. The hologram recording apparatus according to claim 8, wherein the central mask region is formed of a transmissive liquid crystal element, and the liquid crystal element displays the light-shielding region and the light-transmitting region during recording. , 10. The spatial light modulator is a spatial light modulation center comprising a transmissive matrix liquid crystal device arranged on an optical axis for modulating and passing the reference light according to recording information and generating the signal light. An area, and a transparent bowl-shaped area disposed around the spatial light modulation central area and spatially separated from the signal light by allowing the reference light to pass through unmodulated. The photogram recording device according to any one of claims 1 to 3, wherein the photogram recording device comprises:  11. The hologram recording apparatus according to claim 10, wherein the transmission annular region is made of a through opening or a transparent material.  12. The hologram recording apparatus according to claim 10, wherein the transmissive annular region is formed of a transmissive liquid crystal element, and the liquid crystal element is in a light-transmitting state during recording.  13. The anti-rotation mask is arranged so as to partially block only the reference light passing through the transmission annular region without blocking the signal light. 1. The hologram recording device according to 1.  1 4. The spatial light modulator is a spatial light modulation center comprising a transmissive matrix liquid crystal device arranged on an optical axis for modulating and passing the reference light according to recorded information and generating the signal light. 4. The hologram recording apparatus according to claim 1, wherein the hologram recording apparatus includes an area and an annular mask area as the anti-reflection mask arranged around the spatial light modulation central area.  15. The hologram recording according to claim 14, wherein the annular mask area is made of a transmissive liquid crystal element, and the liquid crystal element displays the light shielding area and the light transmitting area during recording. apparatus. 16. The spatial light modulator is in a state of displaying the light-shielding region and the light-transmitting region as the anti-rotation mask, and displays a pattern for modulating the reference light according to recording information in the light-transmitting region. 4. The hologram recording apparatus according to claim 1, wherein the hologram recording apparatus is in a state of being performed. ' 17. A hologram reproducing apparatus for reproducing information from a recording medium having a hologram recording layer in which optical interference fringes due to reference light and signal light are stored inside as a diffraction grating,  A support unit that holds the recording medium so that the reflective layer is positioned on the opposite side of the light irradiation surface of the hologram recording layer;  A light source that generates coherent reference light;  An anti-reflection mask comprising a light-shielding region and a light-transmitting region which are anti-symmetric about the optical axis of the reference light, which is disposed in the optical path of the reference light and partially blocks the reference light;  The reference light is condensed on the reflection layer so as to pass through the anti-reflection mask and the diffraction grating of the hologram recording layer to generate reproduction light from the diffraction grating, and the reproduction light is received. An objective lens;  A hologram reproducing apparatus, comprising: an image sensor that detects the reproduced light received.  18. The hologram reproducing apparatus according to claim 17, wherein the anti-rotation mask includes the same light-shielding area and light-transmitting area as in recording.  19. The hologram reproduction according to claim 17, wherein the anti-rotation mask is a light-transmitting area where the light-shielding area is recorded, and a light-shielding area is the light-transmitting area when recording. apparatus.  20. The anti-rotation mask is formed of a transmissive liquid crystal element, and the liquid crystal element displays the light-shielding region and the light-transmitting region during reproduction. Hologram playback device. 2 1. Has a step to reverse the light shielding region and the light transmitting region of the anti-mask. The hologram reproducing apparatus according to claim 17 or 20, wherein  2. A hologram recording method for recording information on a recording medium having a hologram recording layer in which optical interference fringes by reference light and signal light are stored inside as a diffraction grating,  Generating a coherent reference beam;  A step of disposing an anti-reflection mask comprising a light-shielding region and a light-transmitting region that are anti-symmetric about the optical axis of the reference light that partially shields the reference light; and a hologram recording layer comprising: Disposing a reflective layer on the opposite side of the light irradiation surface; and reflecting the reference light so as to pass through the hologram recording layer while passing through the light-transmitting region of the anti-reflection mask and converging by the objective lens. Irradiating the layer and reflecting on the reflective layer, and  In the step of reflecting by the reflection layer, signal light obtained by modulating the reference light according to recording information is caused to interfere with the reference light in the hologram recording layer, thereby forming a diffraction grating. A hologram recording method.  2 3. A hologram reproducing method for reproducing information from a recording medium having a hologram recording layer in which optical interference fringes due to reference light and signal light are stored inside as a diffraction grating,  Generating a coherent reference beam; A step of disposing an anti-reflection mask comprising a light-shielding region and a light-transmitting region that are anti-symmetric about the optical axis of the reference light that partially shields the reference light; and a hologram recording layer comprising: A step of disposing a reflective layer on the opposite side of the light irradiation surface; and passing the reference light through the translucent region of the anti-reflection mask and collecting it by the objective lens. Irradiating the reflective layer so as to pass through the hologram recording layer while being bundled to generate reproduction light from the diffraction grating;  Guiding the reproduction light to the image sensor through the objective lens.  24. The hologram reproducing method according to claim 23, wherein in the step of generating the reproduction light, the anti-reflection mask is composed of the same light shielding area and light transmission area as in recording.  25. The hologram reproduction method according to claim 23, wherein, in the step of generating the reproduction light, the light shielding area and the light transmission area of the anti-reflection mask are reversed from those during recording.