JP2007114388A - Hologram recording and reproducing device, and hologram recording and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording and reproducing device that can be reduced in cost for volume hologram recording, and can apply spherical wave shift multiplexing method. <P>SOLUTION: The hologram recording and reproducing device 1 is equipped with a SLM (spatial light modulator) 11 and a lens 12 (signal light irradiating means) to irradiate a recording medium D with signal light, a galvanomirror 13 and a relay lens optical system 14 (reference light irradiating means) for irradiating the recording medium D with a reference light, and an imaging element 16 (detecting means) for detecting the reproduced light outgoing from the recording medium, when the recording medium D is irradiated with reference light from the relay lens optical system 14, the recording medium D, disposed in a reversed position in such a manner that the back face of the recording face of the recording medium D is placed at the position where the recording face of the recording medium D irradiated with reference light is placed upon recording phase information, by irradiating the recording medium D with the signal light from the lens 12 and the reference light from the relay lens optical system 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hologram recording / reproducing apparatus and a hologram recording / reproducing method for reproducing digital information recorded on a recording medium by volume hologram recording.

  In recent years, optical information recording media such as optical disks are becoming popular in information recording. In addition, research and development of next-generation optical information recording media aiming at higher speed and larger capacity is being actively conducted. Techniques for increasing the recording capacity of an optical disk include shortening the wavelength of recording / reproducing light, increasing the NA (numerical aperture) of an objective lens in a recording / reproducing optical system, increasing the number of recording marks, or volume hologram recording. . In particular, volume hologram recording can record information not only in the in-plane recording but also in the thickness direction of the medium, so that a high speed and a dramatic increase in capacity can be expected.

  As a method for performing this volume hologram recording, a method using an angle multiplexing optical system is known (see Non-Patent Document 1). Here, a conventional method of performing volume hologram recording will be described with reference to FIG. FIG. 6 is an explanatory diagram for explaining volume hologram recording by a conventional angle multiplexing optical system, (a) is a configuration diagram showing the configuration of a conventional angle multiplexing optical system, and (b) is a volume hologram on a recording medium. Schematic diagram schematically showing the optical path and wavefront of the signal light and the reference light when recording, (c) is the optical path and wavefront of the reference light applied to the recording medium on which the interference fringes are recorded in (b) FIG. 5 is a schematic diagram schematically showing an optical path and a wavefront of reproduction light generated at this time. In FIG. 6, the optical path of the laser beam during recording is schematically indicated by a solid line, the optical path during reproduction is schematically indicated by a broken line, and the traveling direction is indicated by an arrow.

  As shown in FIG. 6A, the angle multiplexing optical system 100 records the digital information as a hologram by irradiating the recording medium D with the signal light and the reference light, and irradiating the recording medium D with the reference light for recording. The reproduced digital information is reproduced. The angle multiplexing optical system 100 includes an SLM 101, an FTL 102, a galvano mirror 103, a relay lens optical system 104, an FTL 105, and an image sensor 106.

  The angle multiplexing optical system 100 generates signal light indicating digital information by an SLM (Spatial Light Modulator) 101, and optically Fourier-converts the signal light by an FTL (Fourier Transform Lens; Fourier Transform Lens) 102. The recording medium D is converted and irradiated. The FTL 102 includes a plurality of optical elements (not shown) (see Non-Patent Document 2), and can suppress aberrations to a minimum. At the same time, as shown in FIG. 6B, the reference light is irradiated to the position where the signal light in the recording medium D passes from another angle. Then, interference fringes (not shown) are generated inside the recording medium D, and volume hologram recording is performed by transferring the interference fringe distribution to the recording medium D in the form of a refractive index distribution or the like.

  As shown in FIG. 6A, the reference light is reflected by the galvanometer mirror 103, passes through two lenses constituting the relay lens optical system 104 (or 4f optical system), and irradiates the recording medium D. Is done. Then, by rotating the galvanometer mirror 103, the incident angle of the reference light with respect to the recording medium D can be changed and irradiated. Here, the reference light applied to the recording medium D is a plane wave.

  On the other hand, at the time of reproduction, only the reference light is irradiated without irradiating the recording medium D with the signal light. At this time, when the galvano mirror 103 is rotated and the reference light having the same condition (irradiation angle or the like) as when digital information is recorded as a hologram is irradiated, reproduction light is generated from the recording medium D by diffraction. Then, as shown in FIG. 6 (c), the reproduction light has the same optical path and wavefront as the signal light irradiated during recording passes through the recording medium D, and travels in the same direction. Further, as shown in FIG. 6A, the reproduction light passes through the FTL 105 and is optically inverse Fourier transformed. Then, page data is photographed by the image sensor 106. Digital information is reproduced by decoding the page data with a computer or the like (not shown).

  In the volume hologram recording by the angle multiplexing optical system 100, the signal light of another page data is applied to the same location in the recording medium D while variously changing the conditions of the reference light such as the incident angle, wavelength, and phase pattern. Since it has the feature of being capable of multiplex recording, it is expected as a recording method capable of storing digital information at high density.

  Further, as a method for performing volume hologram recording, a method using a phase conjugate wave has been proposed (see Non-Patent Document 3 and Non-Patent Document 4). Here, a method of performing volume hologram recording using conventional phase conjugation will be described with reference to FIGS. FIG. 7 is a configuration diagram showing the configuration of a conventional angle multiplexing optical system using phase conjugation. FIG. 8 is an explanatory diagram for explaining light at the time of recording and reproduction by an angle multiplexing optical system using conventional phase conjugation, and (a) is a signal light and reference light when performing volume hologram recording on a recording medium. FIG. 4B is a schematic diagram schematically showing the wavefront of the reference light that is irradiated onto the recording medium on which the interference fringes are recorded in FIG. 5A, and the wavefront of the reproduction light generated at this time. It is the schematic diagram shown. In FIG. 7, the optical path of the laser beam during recording is schematically indicated by a solid line, the optical path during reproduction is schematically indicated by a broken line, and the traveling direction is indicated by an arrow.

  As shown in FIG. 7, the angle multiplexing optical system 100A includes relay lens optical systems 104A and 110A on both sides of the recording medium D, and irradiates the recording medium D with signal light and reference light to provide digital information. Digital information is reproduced by recording as a hologram and irradiating the recording portion of the recording medium D with the reference light from the direction opposite to the direction in which the reference light was irradiated during recording. The angle multiplexing optical system 100A includes an SLM 101, a galvano mirror 103A, a relay lens optical system 104A, an image sensor 106A, lenses 107A and BS 108A, a galvano mirror 109A, a relay lens optical system 110A, and mirrors 111A and 111A.

  The angle multiplexing optical system 100A generates signal light indicating digital information by the SLM 101, condenses the signal light by the lens 107A, and irradiates the recording medium D. At the same time, the reference light reflected by the galvano mirror 103A and passed through the relay lens optical system 104A is irradiated from another angle to the position where the signal light in the recording medium D passes, as shown in FIG. The Then, interference fringes (not shown) are generated inside the recording medium D, and volume hologram recording is performed.

  On the other hand, at the time of reproduction, the reference light reflected by the galvanometer mirror 109A and passed through the relay lens optical system 110A is irradiated from the direction opposite to the traveling direction of the reference light passed through the relay lens optical system 104A. At this time, due to diffraction, signal light is generated in a backward direction compared to the time of recording. Then, as shown in FIG. 8B, the reproduction light has the same wavefront as the light irradiated on the recording medium D as the signal light irradiated at the time of recording, and travels in the opposite direction (phase conjugate wave). ) Further, as shown in FIG. 7, the reproduced light passes through the lens 107A, and its optical path is changed by the BS (beam splitter) 108A. Then, the reproduction light enters the image sensor 106A, and page data of the reproduction light is captured by the image sensor 106A. Digital information is reproduced by decoding the page data with a computer or the like (not shown).

  In the angle multiplexing optical system 100A using the phase conjugate wave, an inexpensive lens such as a convex lens can be used without using an FTL with strictly designed imaging performance for the following reason. That is, at the time of recording, a hologram is recorded on the recording medium D in a state where aberration is generated with respect to the signal light, but at the time of reproduction, reproduction light is generated in the reverse direction as if the signal light is retracted, This has the effect of canceling out this aberration.

  Furthermore, there is disclosed an angle multiplexing optical system using phase conjugation that eliminates the relay lens optical system by using four galvanometer mirrors (see Non-Patent Document 5).

Further, a spherical wave shift multiplexing method is disclosed as another multiplexing method for volume hologram recording (see Non-Patent Document 6). In this spherical wave shift multiplexing system, the reference light is used as a spherical wave, and the recording position is moved little by little to multiplex record the signal light of another page data.
HJ Coufal, et al, "Holographic Data Storage", Springer, pp.243 “Latest Optical Technology Handbook”, Asakura Shoten, p. 458 TK Gaylord, et al, "Analysis and Applications of Optical Diffraction by Gratings", Proc.IEEE, Vol.73, pp.894-937, May 1985 K. Curtis, et al, "High Density Holographic Storage", ISOM'04 Technical Digest, pp.35 K. Anderson, et al, "High speed holographic data storage at 100Gbit / in2", ISOM / ODS 2005 Conference Program and Technical Digest, ThE2, Fig.3 GJ Steckman, et al, "Storage density of shift-multiplexed holographic memory", Applied Optics, Vol.40, No.20, pp.3387-3394, 2000

  However, in volume hologram recording by an angle multiplexing optical system that does not use phase conjugation, in order to record and reproduce digital information without error, a two-dimensional image on the SLM is highly accurate without causing aberration or distortion on the image sensor. It is necessary to form an image. If an inexpensive single lens (such as a plano-convex lens or a biconvex lens) or a two-group lens (such as an achromatic lens) is used instead of FTL, the distortion of the page data image on the image sensor becomes significant. It is necessary to design a lens so as to satisfy image characteristics and use an FTL composed of a multi-group lens. Further, since the size of the recording area is determined by the size of the Nyquist area on the optical Fourier transform surface, it is desirable that the FTL has a high numerical aperture. However, since a high numerical aperture FTL is expensive, there is a problem that the cost of the apparatus cannot be reduced.

  In addition, volume hologram recording by an angle multiplexing optical system using phase conjugation requires two galvano mirror driving units and two relay lens optical systems, or four galvano mirror driving units. High accuracy was required, which caused cost increase. Furthermore, no example has been reported in which the spherical wave shift multiplexing method is applied to volume hologram recording using a phase conjugate wave.

  The present invention has been made to solve the above-described problems of the prior art, and can be reduced in volume hologram recording, and can also be applied to a spherical wave shift multiplex system and hologram recording / reproducing apparatus. It aims to provide a method.

  In order to solve the above problem, the hologram recording / reproducing apparatus according to claim 1, irradiates a recording medium with signal light and reference light, records information indicated by the signal light as light phase information, and A hologram recording / reproducing apparatus for reproducing information indicated by signal light, comprising: signal light irradiating means for irradiating the recording medium with the signal light; reference light irradiating means for irradiating the recording medium with the reference light; When recording the phase information by irradiating the recording medium with the signal light from the signal light irradiation means and the reference light from the reference light irradiation means, the recording surface of the recording medium irradiated with the reference light is recorded. Detection means for detecting reproduction light emitted from the recording medium when the reference light from the reference light irradiation means is irradiated to the recording medium transposed so that the back surface of the recording surface comes to a position; With It was constructed.

  According to such a configuration, the hologram recording / reproducing apparatus records information on the recording medium as a hologram by irradiating the irradiation surface of the recording medium with the signal light and the reference light. At this time, if an FTL having high-precision imaging characteristics is not used, a hologram is recorded on the recording medium in a state of aberration, but the reference light is applied to the rear surface of the irradiated surface of the recording medium that is transposed during reproduction. , A phase conjugate optical system is configured, and a phase conjugate wave can be emitted as reproduction light and detected. As a result, the hologram recording / reproducing apparatus can perform volume hologram recording of information on the recording medium by one reference light irradiation means, reproduce the recorded information, and emit the reproduced light of phase conjugate wave with less aberration be able to.

  In the hologram recording / reproducing method according to claim 2, the signal light irradiating means for irradiating the recording medium with signal light, the reference light irradiating means for irradiating the recording medium with reference light, and only the reference light is irradiated. The hologram recording / reproducing apparatus is provided with a detecting means for detecting reproducing light emitted when the recording medium is irradiated with the signal light and the reference light, and the information indicated by the signal light is converted into light. A hologram recording / reproducing method for recording as phase information and reproducing information indicated by the signal light, wherein the recording medium is irradiated with the signal light from the signal light irradiation means and the reference light from the reference light irradiation means And the reference light on the recording medium transposed so that the back surface of the recording surface comes to the position of the recording surface of the recording medium irradiated with the reference light in the recording step. A reproduction step of irradiating the reference light from the morphism means, characterized in that it comprises a detection step for detecting a reproduction beam the reference beam is emitted from the recording medium when irradiated in the regeneration step, the.

  According to this method, in the recording step, the irradiation surface of the recording medium is irradiated with signal light and reference light to record information on the recording medium as a hologram, and in the reproducing step, the irradiation surface of the transposed recording medium is recorded. By irradiating the back surface with the reference light, the phase conjugate wave of the signal light is emitted as the reproduction light, and the reproduction light can be detected by the detection step. As a result, volume hologram recording of information on a recording medium and reproduction of recorded information on a recording medium by a hologram recording / reproducing apparatus including one reference light irradiation means, and reproduced light of a phase conjugate wave with less aberration Can be emitted.

The hologram recording / reproducing apparatus and hologram recording / reproducing method according to the present invention have the following excellent effects.
According to the first and second aspects of the present invention, the reproduction light of the phase conjugate wave that can cancel out the aberration is generated. Therefore, the hologram recording / reproduction device is placed on each optical path of the signal light and the reproduction light. It is not necessary to provide an expensive FTL, and instead, a single lens or a two-group lens that can be obtained at low cost even with a high numerical aperture can be used. Furthermore, the hologram recording / reproducing apparatus does not need to include a plurality of reference light irradiation means. Therefore, it is possible to reduce the cost and size of the hologram recording / reproducing apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Configuration of Hologram Recording / Reproducing Apparatus (First Embodiment)]
First, the configuration of a hologram recording / reproducing apparatus 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram schematically showing the configuration of a hologram recording / reproducing apparatus according to the first embodiment of the present invention. In FIG. 1, the optical path of the laser beam during recording is schematically indicated by a solid line, the optical path during reproduction is schematically indicated by a broken line, and the traveling direction is indicated by an arrow.

  The hologram recording / reproducing apparatus 1 performs volume hologram recording on a recording medium D, and further reproduces digital information recorded by volume hologram using phase conjugation. Here, the hologram recording / reproducing apparatus 1 multiplex-records another page data to the same location in the recording medium D (angle multiplexing method) while changing the incident angle of the reference light to the recording medium D. . The hologram recording / reproducing apparatus 1 includes an SLM 11, a lens 12, a galvano mirror 13, a relay lens optical system 14, a lens 15, and an image sensor 16.

  Here, a case where the hologram to be recorded is a transmission hologram will be described. A coherent laser beam emitted from a laser light source (not shown) is enlarged by a spatial filter (not shown) and split into two beams by a beam splitter (not shown). The light was incident on the SLM 11 and the galvanometer mirror 13. In this case, a DPSS (Diode Pump Solid State) laser that oscillates a laser beam having a wavelength of 532 nm is used as the laser light source.

  Further, here, a recording medium D using a photoreactive organic material having high sensitivity and high stability is used as the hologram recording material. In this recording medium D, a photoreactive organic material is filled in a gap between two glass substrates (not shown) having a thickness of 1.1 mm, and the material thickness is 1.0 mm. The material thickness is preferably 0.5 to 5.0 mm. Furthermore, the thickness of the glass substrate is preferably about 0.1 to 2.0 mm. The thickness of the two glass substrates may or may not be the same. In addition to the glass substrate, a substrate made of an organic material such as a polycarbonate substrate (not shown) can also be used.

  The SLM 11 receives a laser beam and digital information and generates signal light indicating the digital information. The SLM 11 is configured by, for example, a liquid crystal display panel or a DMD (digital mirror device). Here, when digital information for volume hologram recording is input to the SLM 11, the SLM 11 modulates the digital information and arranges it in two dimensions to form page data. Each pixel of the SLM 11 is binary digital information on the page data. Accordingly, light is spatially modulated by transmitting or blocking a laser beam emitted from a laser light source (not shown).

  Here, it is assumed that the SLM 11 is configured by a transmissive liquid crystal panel, and signal light indicating page data configured by modulating random digital information by a 2: 4 modulation method is generated. Here, the page data will be described with reference to FIG. 2 (refer to FIG. 1 as appropriate). FIG. 2 is a schematic diagram schematically illustrating an example of page data generated by the SLM. The page data P is image data composed of light and dark areas p, p,... Corresponding to each pixel of the SLM 11. The hologram recording / reproducing apparatus 1 can record or reproduce the page data P on the recording medium D at a time.

  Returning to FIG. 1, the description will be continued. The lens 12 condenses the signal light emitted from the SLM 11 and irradiates the recording portion of the recording medium D. Here, the lens 12 is made of a plano-convex lens (single lens). The lens 12 only needs to be able to collect the signal light so as to irradiate the signal light onto the recording medium D with a small area. For example, the lens 12 may be a biconvex lens or a two-group lens such as an achromatic lens.

  The galvanometer mirror 13 reflects a laser beam (reference light) emitted from a laser light source (not shown), and changes the entrance angle of the reference light to the relay lens optical system 14 to be described later. Here, the galvanometer mirror 13 is provided on the optical path of the reference light. The galvanometer mirror 13 has an inclination adjusting means (not shown) that adjusts the inclination of the incident reference light with respect to the traveling direction. By changing the inclination by the inclination adjusting means, the angle of entry into the recording medium D can be changed. Can be changed.

  The relay lens optical system 14 irradiates the recording medium D with the reference light reflected by the galvanometer mirror 13. Here, the relay lens optical system 14 (also referred to as a 4f optical system) is composed of two lenses, and on the recording medium D, a position intersecting with the signal light emitted from the lens 12 or a hologram to be reproduced is recorded. A plane wave reference beam is condensed and irradiated to the position.

  Note that the galvanometer mirror 13 and the relay lens optical system 14 irradiate the recording medium D with reference light while changing the incident angle when recording and reproducing digital information by the angle multiplexing method. It functions as (reference light irradiation means). This angle changing means may be composed of a plurality of galvanometer mirrors (not shown) as described in Non-Patent Document 5, or may be constructed by Fai H. Mok, “Angle-multiplexed storage of 5000 holograms in lithium. niobate ", OPTICS Letters, Vol.18, No.11, June 1, 1993, composed of an AOD (acousto-optic device; not shown) and a lens (not shown). It is also good to do.

  The lens 15 converges the reproduction light emitted from the recording medium D and emits it to the image sensor 16. The lens 15 is composed of the same optical system as the lens 12, and here is composed of the same plano-convex lens (single lens) as the lens 12. The lenses 12 and 15 are arranged symmetrically with the central plane of the recording medium D as the symmetry plane S.

  The image sensor (detection unit) 16 captures page data of the reproduction light incident from the lens 15. The page data is output to a computer (not shown) or the like and decoded to reproduce digital information.

  Here, referring to FIG. 3 (refer to FIG. 1 as appropriate), the direction of the recording medium D irradiated with the reference light during recording and reproduction, and the signal light and the reproduction light will be described. FIG. 3 is a schematic diagram schematically showing the direction of the recording medium irradiated with the reference light and the signal light, the reference light, and the reproduction light. FIG. 3A shows the direction of the recording medium during recording, the signal light, FIG. 5B is a schematic diagram schematically showing the direction of the recording medium during reproduction, and the wavefronts of the reference light and the reproduction light. In FIG. 3, optical paths and wavefronts of the signal light, the reference light, and the reproduction light are schematically shown.

  At the time of recording, the recording medium D is irradiated with the signal light emitted from the lens 12 and the reference light emitted from the relay lens optical system 14. In FIG. 3A, the signal light and the reference light are irradiated from the surface (recording surface) A side of the recording medium D. A hologram is recorded in a region surrounded by points a, b, c, and d.

  At the time of reproduction, as shown in FIG. 3B, the recording medium D is transposed so that the surface B, which is the back surface of the surface A, comes to the position of the surface A. Then, the reference light emitted from the relay lens optical system 14 is applied to the surface B of the recording medium D. Then, reproduction light is generated by the hologram recorded in the region surrounded by the points a, b, c, and d.

  At this time, the area surrounded by the points a, b, c, and d of the recording medium D is irradiated with the reference light from the opposite direction to that during recording. Therefore, the reproduction light becomes a phase conjugate wave. Here, since the lens 12 and the lens 15 made of the same optical system are arranged symmetrically with respect to the symmetry plane S, the aberration included in the signal light applied to the recording medium D during recording is reproduced light. However, the aberration can be canceled by allowing the reproduction light to pass through the optical system having the same configuration as the signal light during recording in the opposite direction. As a result, the hologram recording / reproducing apparatus 1 can reproduce digital information with almost no influence of aberration, and can stably perform information recording / reproducing.

  Since the aberration can be canceled out, the hologram recording / reproducing apparatus 1 can use a plano-convex lens or the like for the lens 12 and the lens 15 without using an FTL that has strictly designed the imaging performance. Such lenses 12 and 15 are inexpensive even with a high numerical aperture. Furthermore, in order to transpose the recording medium D, it is not necessary to provide a plurality of galvanometer mirrors 13 and relay lens optical systems 14, and it is not necessary to provide a beam splitter. As a result, the hologram recording / reproducing apparatus 1 can be reduced in size and cost.

  Note that the transposition of the recording medium D may be performed by a user, for example. At this time, the hologram recording / reproducing apparatus 1 can realize a phase conjugate optical system by simply mounting the recording medium D in the opposite direction during recording and reproduction, and is a special additional component compared with a conventional apparatus that does not use phase conjugation. The effect of canceling out the aberration of the lens 12, which is an advantage of phase conjugation, can be used. Further, the hologram recording / reproducing apparatus 1 holds a recording medium D, and recording medium holding means (not shown) that holds the recording medium D by transposing and holding the recording medium D based on a command from a user, a signal from a computer (not shown), or the like. It is good also as providing. In addition, the signal light irradiation means described in the claims corresponds to the SLM 11 and the lens 12.

[Operation of Hologram Recording / Reproducing Device (First Embodiment)]
Next, with reference to FIG. 1, an operation of recording / reproducing digital information by the hologram recording / reproducing apparatus 1 according to the first embodiment of the present invention will be described.

  First, an operation in which the hologram recording / reproducing apparatus 1 performs volume hologram recording of digital information on the recording medium D will be described. The hologram recording / reproducing apparatus 1 sets the tilt of the galvanometer mirror 13 by tilt adjusting means (not shown).

(Recording step)
Then, the hologram recording / reproducing apparatus 1 generates signal light indicating digital information by the SLM 11, collects the signal light by the lens 12, and irradiates the recording portion of the recording medium D. At the same time, the hologram recording / reproducing apparatus 1 reflects the reference light emitted from a laser light source (not shown) by the galvanometer mirror 13 and emits the reference light from the lens 12 in the recording medium D by the relay lens optical system 14. Irradiate the position that intersects the signal light. Then, the interference fringes between the signal light and the reference light are recorded on the recording medium D as a hologram.

  Next, an operation in which the hologram recording / reproducing apparatus 1 reproduces digital information recorded in a volume hologram on the recording medium D will be described. First, the back surface of this surface comes to the position of the surface (recording surface) irradiated with the reference light when the recording medium D is transposed from the recording state and the digital information to be reproduced is volume hologram recorded. Installed. Then, the hologram recording / reproducing apparatus 1 sets the inclination of the galvano mirror 13 by an inclination adjusting means (not shown). Here, the tilt adjusting means adjusts the galvanometer mirror 13 so that the optical path coincides with that when the recording medium D is irradiated with the reference light when the digital information to be reproduced is recorded on the volume hologram and the approach direction is opposite. Set the tilt.

(Playback step)
Subsequently, the hologram recording / reproducing apparatus 1 reflects the reference light emitted from a laser light source (not shown) by the galvanometer mirror 13 and reproduces the reference light on the recording medium D by the relay lens optical system 14. Irradiate to the position where the hologram indicating is recorded. Then, reproduced light that is a phase conjugate wave of the signal light is generated by the hologram recorded on the recording medium D.

  Then, the hologram recording / reproducing apparatus 1 converges the reproduction light by the lens 15. At this time, the reproduction light passes through the lens 15 to cancel out aberration.

(Playback step)
Subsequently, the hologram recording / reproducing apparatus 1 images the page data indicated by the reproduction light by the imaging element 16. The captured page data is decoded by a computer (not shown) or the like, and digital information is reproduced.

[Configuration of Hologram Recording / Reproducing Device (Second Embodiment)]
Next, the configuration of a hologram recording / reproducing apparatus 1A according to the second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram schematically showing the configuration of the hologram recording / reproducing apparatus according to the second embodiment of the present invention. In FIG. 4, the optical path of the laser beam during recording is schematically indicated by a solid line, the optical path during reproduction is schematically indicated by a broken line, and the traveling direction is indicated by an arrow.

  As shown in FIG. 4, the hologram recording / reproducing apparatus 1A performs volume hologram recording on a recording medium D, and further reproduces the recorded digital information using phase conjugation. Here, the hologram recording / reproducing apparatus 1A performs multiplex recording by the spherical wave shift multiplex method.

  The hologram recording / reproducing apparatus 1A includes a lens 17A instead of the galvanometer mirror 13 and the relay lens optical system 14 of the hologram recording / reproducing apparatus 1 (see FIG. 1). Since the configuration other than the lens 17A in the hologram recording / reproducing apparatus 1A is the same as that shown in FIG. 1, the same reference numerals are given and description thereof is omitted.

  The lens (reference light irradiation means) 17A collects a laser beam (reference light) emitted from a laser light source (not shown) and irradiates the recording medium D. Here, the lens 17A is made of a biconvex lens (single lens). The lens 17A only needs to be able to collect the reference light, and may be, for example, a diffractive optical element such as a Fresnel zone plate, a diffraction grating, or a hologram lens.

  This lens 17A irradiates the reference light of the spherical wave at the position where the signal light emitted from the lens 12 intersects the recording medium D or the position where the hologram to be reproduced is recorded. Further, the position of the lens 17A is changed in the optical axis direction of the reference light by a lens position changing unit (not shown). As a result, the position where the reference light is collected during recording and during reproduction can be shifted in the optical axis direction.

  Here, reference light at the time of recording and reproduction will be described with reference to FIG. 5 (refer to FIG. 4 as appropriate). FIG. 5 is a schematic diagram schematically showing reference light during recording and reproduction, (a) is a schematic diagram schematically showing reference light irradiated during recording, and (b) is irradiated during reproduction. It is a schematic diagram which shows a reference beam typically. In FIG. 5, the optical path and wavefront of the reference light are schematically shown, and the optical path and wavefront of the signal light and the reproduction light are not shown.

  At the time of recording, the recording medium D is irradiated with the signal light emitted from the lens 12 and the spherical wave reference light emitted from the lens 17A. In FIG. 5A, the reference light is collected on the front side of the surface A (recording surface) of the recording medium D and irradiated with the signal light. A hologram is recorded in a region surrounded by points a, b, c, and d.

  At the time of reproduction, as shown in FIG. 5B, the recording medium D is transposed so that the surface B, which is the back surface of the surface A, comes to the position of the surface A. Then, the reference light emitted from the lens 17A is applied to the surface B of the recording medium D. At this time, since the recording medium D is transposed, the position of the lens 17A is moved in the optical axis direction to satisfy the hologram reproduction condition. In FIG. 5B, the lens position changing means (not shown) brings the lens 17A closer to the recording medium D on the optical axis of the reference light, and the spherical wave reference light is moved behind the surface A that has passed the recording medium D. Collect light. Then, reproduction light is generated by the hologram recorded in the region surrounded by the points a, b, c, and d.

  As a result, the area surrounded by the points a, b, c, and d of the recording medium D is irradiated with reference light having the same wavefront from the opposite direction to that during recording. Therefore, the reproduction light becomes a phase conjugate wave, and the aberration of the reproduction light can be canceled. As a result, the hologram recording / reproducing apparatus 1A can perform reproduction using phase conjugation, and can obtain stable recording / reproducing performance that is hardly affected by aberration. The spherical wave can be generated by refracting or diffracting a plane wave with a lens (not shown) or a diffractive optical element (not shown).

  The hologram recording / reproducing apparatus 1 or 1A according to the present invention has been described above, but the present invention is not limited to this. For example, a DMD may be used for the SLM 11. The recording medium D may be made of a photorefractive crystal instead of a photosensitive organic material. Further, a blue-violet laser light source may be used as the laser light source. Further, as a modulation method, page data is configured by modulation by a modulation method other than 2: 4 modulation method, for example, 3:16 modulation method, NRZ (Non-Return to Zero) method, or differential code method. It is good as well.

  Furthermore, it may be in the form of a reflection hologram. Further, another multiplexing scheme such as peritropic multiplexing or phase code multiplexing may be employed, or a polytopic scheme combining the angle multiplexing scheme and the shift multiplexing scheme may be employed.

1 is a configuration diagram schematically showing a configuration of a hologram recording / reproducing apparatus according to a first embodiment of the present invention. It is a schematic diagram which shows typically the example of the page data produced | generated by SLM of the hologram recording / reproducing apparatus which is 1st embodiment in this invention. In the hologram recording / reproducing apparatus according to the first embodiment of the present invention, a schematic diagram schematically showing the direction of the recording medium irradiated with the reference light, the signal light, the reference light, and the reproducing light, (a) FIG. 5B is a schematic diagram schematically showing the direction of the recording medium at the time of recording and the wavefronts of the signal light and the reference light. FIG. 5B schematically shows the direction of the recording medium at the time of reproduction and the wavefronts of the reference light and the reproducing light. It is a schematic diagram shown. It is the block diagram which showed typically the structure of the hologram recording / reproducing apparatus which is 2nd embodiment in this invention. In the hologram recording / reproducing apparatus according to the second embodiment of the present invention, a schematic diagram schematically showing reference light at the time of recording and reproduction, (a) schematically shows the reference light irradiated at the time of recording. Schematic diagram (b) is a schematic diagram schematically showing reference light irradiated during reproduction. Explanatory drawing for demonstrating the volume hologram recording by the angle multiplexing optical system which does not use the conventional phase conjugation, (a) is a block diagram which shows the structure of the angle multiplexing optical system which does not use the conventional phase conjugation, (b) Schematic diagram schematically showing optical paths and wavefronts of signal light and reference light when performing volume hologram recording on the recording medium, (c) is a reference for irradiating the recording medium on which interference fringes are recorded in (b) It is the schematic diagram which showed typically the optical path and wavefront of light, and the optical path and wavefront of reproduction | regeneration light produced | generated in this case. It is a block diagram which shows the structure of the angle multiplexing optical system using the conventional phase conjugation. Explanatory drawing for demonstrating the light at the time of recording and reproduction | regeneration by the angle multiplexing optical system using the conventional phase conjugation, (a) is a schematic diagram of the wavefront of the signal light and the reference light when performing volume hologram recording on the recording medium (B) schematically shows the wavefront of the reference light applied to the recording medium on which the interference fringes are recorded in (a) and the wavefront of the reproduction light generated at this time. It is a schematic diagram.

Explanation of symbols

1, 1A Hologram recording / reproducing device 11 SLM
12 Lens 13 Galvano mirror 14 Relay lens optical system 15 Lens 16 Image sensor (detection means)
17A lens (reference light irradiation means)

Claims (2)

A hologram recording / reproducing device that irradiates a recording medium with signal light and reference light, records information indicated by the signal light as light phase information, and reproduces the information indicated by the signal light,
Signal light irradiation means for irradiating the recording medium with the signal light;
Reference light irradiating means for irradiating the recording medium with the reference light;
The recording surface of the recording medium irradiated with the reference light when the phase information is recorded by irradiating the recording medium with the signal light from the signal light irradiation means and the reference light from the reference light irradiation means Detecting means for detecting reproduction light emitted from the recording medium when the reference light from the reference light irradiating means is applied to the recording medium transposed so that the back surface of the recording surface is positioned at ,
A hologram recording / reproducing apparatus comprising: Signal light irradiation means for irradiating the recording medium with signal light, reference light irradiation means for irradiating the recording medium with reference light, and detection means for detecting reproduction light emitted when only the reference light is irradiated Using the hologram recording / reproducing device provided, the recording medium is irradiated with the signal light and the reference light, information indicated by the signal light is recorded as light phase information, and information indicated by the signal light is recorded. A hologram recording / reproducing method for reproducing,
A recording step of irradiating the recording medium with the signal light from the signal light irradiation means and the reference light from the reference light irradiation means;
Reproduction of irradiating the reference light from the reference light irradiating means onto the recording medium transposed so that the back surface of the recording surface comes to the position of the recording surface of the recording medium irradiated with the reference light in this recording step Steps,
A detection step of detecting reproduction light emitted from the recording medium when the reference light is irradiated in the reproduction step;
A hologram recording / reproducing method comprising:

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