JP2000242156A - Device and method for recording and reproducing hologram - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make recordable and reproducible a large capacity of data by performing multiple recording while restraining the lowering of diffraction efficiency as much as possible. SOLUTION: Plural holograms are multiply recorded on a 1st hologram recording medium 8 by using the same reference light while changing the incident angle of object light every time one hologram is recorded, and a plurality of holograms multiply recorded on the medium 8 are reproduced all together. By setting the reproducing light as the object light, the multiply recorded hologram constituted by superposing plural holograms as one hologram is multiply recorded on a 2nd recording medium 18 by using different reference light. Then, a desired multiply recorded hologram is selectively reproduced from among a plurality of multiply recorded holograms multiply recorded on the medium 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram recording / reproducing apparatus for recording data on a hologram recording medium or reproducing data recorded on a hologram recording medium by utilizing an interference effect between an object beam and a reference beam. The present invention relates to a hologram recording / reproducing method.

[0002]

2. Description of the Related Art Conventionally, object light and reference light modulated according to data to be recorded interfere with each other in a hologram recording medium exhibiting a large photorefractive effect. A hologram recording / reproducing method for reproducing data recorded on a hologram recording medium by reproducing the data recorded on the hologram recording medium by recording the data as a fringe and making the reading light incident on the hologram recording medium on which the data is recorded at the same incident angle as the reference light has been proposed. ing.

In this hologram recording / reproducing method,
For example, light transmitted through a spatial light modulator such as a liquid crystal display panel (LCD) and modulated in accordance with data for one image displayed on the spatial light modulator enters the hologram recording medium as object light as object light. Therefore, data for one image is recorded on the hologram recording medium at one time as one hologram. Then, also at the time of reproduction, reproduction is performed in units of holograms including the data of one image. Therefore, this hologram recording / reproducing method is characterized in that higher-speed data access is possible, for example, as compared with a recording / reproducing method using an optical disk, which is relatively high-speed accessible, as a recording medium. Have.

In this hologram recording / reproducing method, for example, a large number of holograms are recorded on one hologram recording medium in a superimposed manner by changing an incident angle of a reference beam every time one hologram is recorded. Multiple recording is possible. Therefore, this hologram recording / reproducing method has a feature that data can be recorded at a very high density.

[0005] In view of the above, the hologram recording / reproducing method has attracted attention as a recording / reproducing method which satisfies the improvement in recording density and the speeding up of data access required with the development of the information industry in recent years.

[0006]

By the way, in this hologram recording / reproducing method, multiplex recording for realizing high-density recording is limited by a decrease in diffraction efficiency caused by erasure during recording or reproduction. That is, when performing multiplex recording, the hologram previously recorded on the hologram recording medium is erased when recording the subsequent hologram,
Diffraction efficiency is slightly reduced. Further, the diffraction efficiency of each hologram recorded on the hologram recording medium by the multiplex recording is slightly lowered even by exposure at the time of reproduction. In addition, the diffusion of electrons due to dark current causes a decrease in diffraction efficiency over time in the long term.

As described above, when the diffraction efficiency of each hologram multiplex-recorded on the hologram recording medium is reduced due to erasure or the like, the S / N ratio at the time of reproduction gradually decreases.

The diffraction efficiency η _writw (t) at the time of recording each hologram recorded on the hologram recording medium is given by the following equation (1).
Given by

Η _writw (t) = η ₀ · (1−e ⁻ α ^It ) (1) where α is a time constant at the time of recording, I is a spatial average light intensity, and t is a time at the time of recording. Is the time when is set to 0, η ₀ is the saturation diffraction efficiency.

The diffraction efficiency η _read (t) for reproducing each multiplexed hologram or for erasing a previously recorded hologram by irradiating light for recording a subsequent hologram is given by the following equation. Given by (2).

[0011] _{η read (t) = η 1} · e - α 'It ··· (2) where, α' is the time constant of the time playback (or erased), I is the average of the light intensity, η ₁ is the initial Diffraction efficiency.

From the above equations, it can be seen that the diffraction efficiency of each hologram recorded on the hologram recording medium decreases exponentially by reproduction (see "Photorefractive Nonlinear Optics", P. YEH, published by Maruzen). ). At this time,
It is known that when multiple recording is performed so that the diffraction efficiencies of all holograms are equal, the final diffraction efficiency of each hologram is inversely proportional to the square of the number of recordings ("System meter").
ic for holographic memory system ", Fai H. Mok, Geo
ffrey W. Burr and Demetri Psaltis, OpticsLetters,
21, pp. 896, 1996).

For example, when 1,000 holograms are recorded with the same intensity, the diffraction efficiency of each hologram is reduced to about 10 ^-6 compared to the case where one hologram is recorded.

As described above, when the diffraction efficiency decreases, the S / N ratio at the time of reproduction decreases. If the decrease in the S / N ratio during reproduction is large, the signal component is buried in noise, and reproduction becomes impossible. Therefore, in order to ensure reproducible diffraction efficiency, it is necessary to limit the number of holograms recorded on the hologram recording medium,
This has been a factor limiting the recording capacity of data recorded on the hologram recording medium.

Therefore, in the hologram recording / reproducing method, it is possible to increase the data recording capacity by performing the multiplex recording while minimizing the reduction in the diffraction efficiency. It is considered one of the issues for widespread use.

As a means for performing multiplex recording while minimizing the reduction in diffraction efficiency, a method has been proposed in which a multiplexed hologram is used as a master and the hologram is multiplex-recorded on another hologram (see “Multiplot”).
le multiple-exposure hologram ”, Kristina M. Johnso
n, Mark Armstrong, Lambertus Hesselink, and Joseph
W. Goodman, Applied Optics, 24, pp. 4467-4472, 1985
reference).

This method will be described below. First, m holograms are recorded on a first hologram recording medium using a common reference beam. Then, m holograms recorded on the first hologram recording medium are collectively reproduced, and the reproduced light is recorded on the second hologram recording medium as object light. Next, the m holograms are again recorded on the first hologram recording medium, and are copied and recorded on the second hologram recording medium using the same reference light as when the first m holograms were recorded. . The above procedure is repeated n times. As a result, (n × m) holograms are multiplex-recorded on the second hologram recording medium.

If this hologram is reproduced, (n)
Since (xm) holograms are superimposed and reproduced, (nxm) layer images can be superimposed and displayed simultaneously. For example, if a three-dimensional tomographic image is recorded using this method, the entire three-dimensional object can be displayed three-dimensionally.

At this time, the diffraction efficiency can be increased by a factor of m as compared with the case where recording is performed according to a normal recording schedule. That is, when m holograms are recorded on the first hologram recording medium, the diffraction efficiency of each hologram becomes 1 / m ² . However, at the time of copying to the second hologram recording medium, since the m holograms are recorded as one hologram, the total diffraction efficiency of the m holograms is 1 / n ² . Therefore, assuming that all the m holograms have the same diffraction efficiency, when the second hologram is reproduced, the diffraction efficiency per one hologram is 1 / m, and the final diffraction efficiency per one hologram is , 1 / (m × n ² ). On the other hand, when (n × m) holograms are multiplex-recorded according to a normal recording schedule, the diffraction efficiency is 1 / (m ² × n ² ). Therefore, by copying the hologram by the above method,
It can be seen that the diffraction efficiency has increased m times.

However, as described above, this method has been proposed for the purpose of displaying a three-dimensional image by superposing cross sections, and collectively collectively record holograms recorded on the first hologram recording medium. In order to reproduce the holograms, a common reference beam is used when recording each hologram on the first hologram recording medium. At the time of reproduction, all the holograms are reproduced simultaneously in a superimposed state, and each hologram is reproduced one by one. Cannot be separated. Therefore, this method is difficult to apply to applications other than the special uses as described above, and has not essentially solved the above-mentioned problems.

Accordingly, an object of the present invention is to provide a hologram recording / reproducing apparatus and a hologram recording / reproducing method capable of performing multiplex recording while minimizing a decrease in diffraction efficiency and recording / reproducing a large amount of data. .

[0022]

In order to solve the above problems, the hologram recording / reproducing apparatus according to the present invention uses the same reference light while changing the incident angle of the object light every time one hologram is recorded. First recording means for multiplex-recording a plurality of holograms on a first hologram recording medium using the first hologram recording medium;
First reproducing means for collectively reproducing a plurality of holograms multiplex-recorded on the first hologram recording medium by the first recording means, and a plurality of holograms collectively reproduced by the first reproducing means Second recording in which a plurality of holograms formed by superimposing the plurality of holograms and forming one hologram are multiplex-recorded on a second recording medium by using different reference lights, using reproduction light of the hologram as object light. Means, and second reproducing means for selectively reproducing a desired multiplexed hologram from a plurality of multiplexed holograms multiplex-recorded on the second hologram recording medium by the second recording means.

According to this hologram recording / reproducing apparatus, a plurality of holograms are multiplex-recorded on the first recording medium by the first recording means. At this time, each hologram is recorded on the first hologram recording medium using the same reference light while varying the incident angle of the object light.

A plurality of holograms multiplex-recorded on the first hologram recording medium by the first recording means are collectively reproduced by the first reproducing means. That is, the first reproducing means outputs the read light to the first hologram recording medium at the same incident angle as the reference light used when the first recording means records a plurality of holograms on the first hologram recording medium. By being incident, a plurality of holograms multiplex-recorded on the first hologram recording medium are collectively reproduced.

The plurality of holograms which are collectively reproduced by the first reproducing means are in a state where each hologram is superimposed. Then, the multiple recording hologram in which the plurality of holograms are superimposed to form one hologram is recorded again on the second hologram recording medium by the second recording means. That is, the second recording means uses, as object light, reproduction light of a plurality of holograms (multiplexed recording holograms) collectively reproduced by the first reproducing means, and uses the multiple recording hologram as a second hologram recording medium. Record again. Then, the second recording means multiplex-records a plurality of multiplexed holograms on the second recording medium using different reference beams.

The multiple recording holograms multiplex-recorded on the second hologram recording medium by the second recording means are selectively reproduced by the second reproducing means. That is, for example, when a plurality of multiplexed recording holograms are multiplex-recorded on the second hologram recording medium by angle multiplexing, the second reproducing unit selects a desired incident angle of the readout light to thereby obtain a desired angle. Regenerate the multiplex recording hologram.

It is preferable that the hologram recording / reproducing apparatus according to the present invention includes hologram extracting means for extracting a desired hologram from a plurality of holograms constituting the multiplexed hologram reproduced by the second reproducing means. . As the hologram extracting means, for example, the second
And a multiplexed hologram reconstructed by the second reconstructing means, by extracting a desired hologram by filtering the reconstructed light of the multiplexed hologram reconstructed by the reconstructing means on the Fourier plane of the image using a spatial aperture. It is conceivable to extract a desired hologram by selectively transmitting or reflecting the reproduction light of the recording hologram by an element having an angle dependency.

The hologram recording / reproducing apparatus according to the present invention uses a rewritable hologram recording material such as a photorefractive crystal as the first hologram recording medium, and uses a hologram recording medium as the second hologram recording medium. It is desirable to use a hologram recording material such as a polymer that can be recorded only once.

Also, in the hologram recording / reproducing apparatus according to the present invention, the first recording means is a microlens comprising a spatial light modulator and a plurality of microlenses arranged corresponding to each pixel of the spatial light modulator. An array is provided, and a spot on a focal plane of each microlens is separated by changing an incident angle of light incident on the spatial light modulator, and one image displayed on the spatial light modulator is divided into a plurality of images. Multiple recording is performed on the first recording medium as a plurality of holograms, and the second reproducing unit reproduces a multiplex recording hologram formed by superimposing a plurality of holograms obtained by dividing one image displayed on the spatial light modulator. You may make it.

In this case, the multiplexed hologram reproduced by the second reproducing means is displayed as one image by the display means, for example. Alternatively, a desired hologram is extracted from a plurality of holograms constituting the multiplexed hologram by the hologram extracting means.

In order to solve the above-mentioned problems, the hologram recording / reproducing method according to the present invention changes a plurality of holograms by using the same reference light while changing the incident angle of the object light every time one hologram is recorded. A first step of multiplex-recording the holograms on the first hologram recording medium, and a second step of collectively reproducing a plurality of holograms multiplex-recorded on the first hologram recording medium in the first step. The multiplexed hologram formed by superimposing the plurality of holograms to form one hologram using the reproduction light of the plurality of holograms collectively reproduced in the second step as object light using a different reference light. A third step of multiplex-recording a plurality of sheets on the second recording medium, and multiplexing a plurality of sheets multiplex-recorded on the second hologram recording medium in the third step Of recorded hologram it is characterized by undergoing a fourth step of reproducing selectively the desired multiple recording holograms.

According to the hologram recording / reproducing method, in the first step, a plurality of holograms are multiplex-recorded on the first recording medium. At this time, each hologram is
Recording is performed on the first hologram recording medium using the same reference light while changing the incident angle of the object light.

In the first step, a plurality of holograms multiplex-recorded on the first hologram recording medium are
Are reproduced collectively in the step. That is, in the second step, the readout light is incident on the first hologram recording medium at the same incident angle as the reference light used when recording a plurality of holograms on the first hologram recording medium in the first step. Thereby, a plurality of holograms multiplex-recorded on the first hologram recording medium are reproduced collectively.

The plurality of holograms reproduced collectively in the second step are in a state where each hologram is superimposed. Then, the multiple recording hologram in which the plurality of holograms are superimposed into one hologram is recorded again in the second hologram recording medium in the third step. That is, in the third step, the reproduction light of a plurality of holograms (multiple recording holograms) collectively reproduced by the first reproducing means is used as object light, and the multiple recording hologram is used as the second hologram recording medium. Record again. And the third
In the step (2), multiple holograms are multiplex-recorded on the second recording medium using different reference beams.

The multiple holograms multiplex-recorded on the second hologram recording medium in the third step are selectively reproduced in the fourth step. That is, in the fourth step, for example, when a plurality of multiplexed recording holograms are multiplex-recorded on the second hologram recording medium by angle multiplexing, the desired multiplexing is performed by selecting the incident angle of the reading light. Regenerate the recorded hologram.

The hologram recording / reproducing method according to the present invention desirably includes a fifth step of extracting a desired hologram from a plurality of holograms constituting the multiplexed hologram reproduced in the fourth step. . In the fifth step, for example, a desired hologram is extracted by filtering the reproduction light of the multiplexed hologram reproduced in the fourth step on the Fourier plane of the image using a spatial aperture, or It is possible to extract a desired hologram by selectively transmitting or reflecting the reproduction light of the multiplexed hologram reproduced by the second reproducing means by an element having an angle dependency.

In the hologram recording / reproducing method according to the present invention, a rewritable hologram recording material such as a photorefractive crystal is used as the first hologram recording medium, and a hologram recording medium is used as the second hologram recording medium. It is desirable to use a hologram recording material such as a polymer that can be recorded only once.

Further, in the hologram recording / reproducing method according to the present invention, in the first step, a microlens array comprising a spatial light modulator and a plurality of microlenses arranged corresponding to each pixel of the spatial light modulator. The spot on the focal plane of each microlens is separated by changing the angle of incidence of the light incident on the spatial light modulator, and one image displayed on the spatial light modulator is divided into a plurality of images. Multiplex recording on the first recording medium as one hologram,
In a fourth step, the 1 displayed on the spatial light modulator
A multiplexed hologram formed by superposing a plurality of holograms obtained by dividing an image may be reproduced.

In this case, the multiplexed hologram reproduced in the fourth step is displayed as, for example, one image. Alternatively, in the fifth step, a desired hologram is extracted from a plurality of holograms forming the multiplexed hologram.

[0040]

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

FIG. 1 shows an example of the configuration of a hologram recording / reproducing apparatus to which the present invention is applied. The hologram recording / reproducing apparatus 1 shown in FIG. 1 includes a light source 2 which emits laser light having a sufficiently narrow wavelength width and high coherence. A collimator lens 3 for converting the laser light into parallel light is provided on an optical path of the laser light emitted from the light source 2, and a collimator lens 3 for branching the optical path of the laser light converted into parallel light by the collimator lens 3. One beam splitter 4 is provided. The first beam splitter 4 transmits, for example, a part of the laser light converted into the parallel light by the collimator lens 3 and reflects the other part to bend the optical path by, for example, about 90 degrees. The optical path of the laser light is branched.

A first shutter 5 for switching ON / OFF of the laser light is provided on the optical path of the laser light whose optical path is reflected by the first beam splitter 4, and the traveling direction of the laser light. And a first beam deflector 6 for controlling the first beam deflector. The first beam deflector 6 controls the traveling direction of the laser light by deflecting the incident laser light at a predetermined deflection angle and transmitting or reflecting the laser light. For example, an acousto-optic deflector or an electro-optic deflection And a galvanomirror. Note that the first beam deflector 6 may deflect the laser light in a one-dimensional direction or may deflect the laser light in a two-dimensional direction.

On the optical path of the laser beam whose traveling direction is controlled by the first beam deflector 6, a spatial light modulator 7 and a first hologram recording medium 8 are provided.
Further, between the first beam deflector 6 and the spatial light modulator 7, lenses 9 and 10 for projecting the emission surface of the first beam deflector 6 to the spatial light modulator 7 are provided. . In the example shown in FIG. 1, the focal length of both the lens 9 and the lens 10 is set to F in consideration of a case where the emission surface of the first beam deflector 6 is projected onto the spatial light modulator 7 at the same magnification. One beam deflector 7 is disposed on the focal plane of the lens 9 and the spatial light modulator 7 is disposed on the focal plane of the lens 10 so that the distance between the lenses 9 and 10 is 2F.

Here, from the relationship of Lagrange Helmholtz, the product of the incident light and the incident angle on each surface is constant, so that when the light beam is enlarged, the deflection angle of the beam is reduced. Conversely, to increase the beam deflection angle, the beam diameter must be reduced. Therefore, if necessary, it is desirable to set the projection magnification and the emission diameter of the emitted light beam from the first beam deflector 7 to appropriate values.

The spatial light modulator 7 is composed of, for example, a transmission type liquid crystal display (LCD) and displays an image corresponding to an image signal on a display unit. The spatial light modulator 7 transmits the laser beam emitted from the first beam deflector 6 through the display unit, and modulates the laser beam according to the image displayed on the display unit.

In the hologram recording / reproducing apparatus 1, as described above, the laser light reflected by the first beam splitter 4, deflected by the first beam deflector 6, and then modulated by the spatial light modulator 7 is used. Object light.

Between the spatial light modulator 7 and the first hologram recording medium 8, a lens for Fourier transforming the object light modulated according to the image displayed on the display unit of the spatial light modulator 7 11 are provided. In the example shown in FIG. 1, the focal length of the lens 11 is f, and the spatial light modulator 7 and the first hologram recording medium 8 are arranged on the focal plane of the lens 11, respectively. Here, the center of the first hologram recording medium 8 is used as a position reference.

The object light modulated by the spatial light modulator 7 after being deflected by the first beam deflector 6 is transmitted through the lens 11 to be Fourier-transformed, and the first object light is disposed near the Fourier plane. Hologram recording medium 8
At an incident angle corresponding to the deflection angle of the first beam deflector 6.

On the other hand, on the optical path of the laser beam transmitted through the first beam splitter 4, there are provided a folding mirror 12 for reflecting the laser beam and bending the optical path by about 90 degrees, and a reflecting mirror 12 for reflecting the laser beam. And a second beam splitter 13 for splitting the optical path of the laser light having the bent laser beam. The second beam splitter 13 transmits, for example, a part of the laser light reflected by the return mirror 12, reflects the other part, and bends the optical path of the laser light by, for example, about 90 degrees. The optical path is branched.

A second shutter 14 for switching ON / OFF of the laser light is disposed on the optical path of the laser light reflected by the second beam splitter 13 and bent. On the optical path of the laser beam transmitted through the second beam splitter 13, a third shutter 15 for switching ON / OFF of the laser beam is provided.

In the hologram recording / reproducing apparatus 1, when the second shutter 14 is opened, the laser light reflected by the second beam splitter 13 and having the optical path bent is used as the reference light as the above-mentioned reference light. The light is incident on the first hologram recording medium 8 at a predetermined incident angle.

Therefore, the hologram recording / reproducing apparatus 1 emits laser light from the light source 2 in a state where the first shutter 5 and the second shutter 14 are opened and the third shutter 15 is closed. The object light modulated by the light modulator 7 and incident on the first hologram recording medium 8 at an incident angle corresponding to the deflection angle of the first beam deflector 6 and the first hologram recording medium 8 at a predetermined incident angle The incident reference light is caused to interfere in the first hologram recording medium 8, and the image displayed on the spatial light modulator 7 can be recorded on the first hologram recording medium 8 as a hologram.

Hologram recording / reproducing apparatus 1 according to the present invention
In the recording process described above, the same reference is performed while changing the angle of incidence of the object light transmitted through the spatial light modulator 7 on the first hologram recording medium 8 by changing the deflection angle of the first beam deflector 6. This is repeatedly performed using light, and a plurality of holograms are multiplex-recorded on the first hologram recording medium 8. Hereinafter, this recording process is referred to as a first step.

The recording schedule in the first step of the hologram recording / reproducing apparatus 1 is set such that all “pages” multiplex-recorded on the first hologram recording medium 8 have the same diffraction efficiency during reproduction. .

For the sake of convenience, in the following description, 1 is recorded on the first hologram recording medium 8.
Each hologram is called a “page”, and each of these “pages” is multiplex-recorded on the first hologram recording medium using the same reference light, so that the plurality of “pages”
Will be referred to as a “chapter”.

All "pages" multiplex-recorded on the first hologram recording medium 8 in the first step are recorded using the same reference light, as described above. Therefore, the hologram recording / reproducing apparatus 1 irradiates the first hologram recording medium 8 with the same light as the reference light used when recording each “page” as readout light. All the "pages" of the recorded "chapter" can be reproduced collectively. Hereinafter, this reproduction process is referred to as a second step.

On the optical path of the reproduced light reproduced in the second step, lenses 16 and 17 for Fourier transforming the reproduced light, and the reproduced light transmitted through the lenses 16 and 17 are incident as object light. A second hologram recording medium 18 is provided. In the example shown in FIG. 1, the focal lengths of the lenses 16 and 17 are both f, the first hologram recording medium 8 is located on the focal plane of the lens 16, and the second hologram recording medium 18 is And the distance between the lens 16 and the lens 17 is 2f
I am trying to be. Here, the center of the second hologram recording medium 18 is used as a position reference.

In the second step, all the “pages”, ie, “chapters” reproduced from the first hologram recording medium 8 are Fourier-transformed by the lens 16, so that the reproduction image plane which is the focal plane of the lens 16 is obtained. A reproduced image of the “chapter” is reproduced. The reproduced images of the “chapter” reproduced on this reproduced image plane are in a state where the reproduced images of all the “pages” constituting the “chapter” are superposed coherently and interfere with each other. “Page” cannot be determined and read.

Hologram recording / reproducing apparatus 1 according to the present invention
A Fourier transform is again performed by the lens 17 on the reproduced image of the “chapter” reproduced on the reproduced image plane, and the Fourier-transformed image is used as the object light. The light is incident on the medium 18 at a predetermined angle.

On the other hand, the second beam splitter 1
A second beam deflector 19 for controlling the traveling direction of the laser light is disposed on the optical path of the laser light transmitted through the laser beam 3. Like the first beam deflector 4, the second beam deflector 19 controls the traveling direction of the laser beam by deflecting the incident laser beam at a predetermined deflection angle and transmitting or reflecting the laser beam. For example, it is composed of an acousto-optic deflector, an electro-optic deflector, a galvanomirror and the like. However, the second beam deflector 19
Is used as a means for changing the incident angle of the reference light in order to record the “chapter” on the second hologram recording medium 18 by angle multiplexing, and therefore cannot deflect the laser light in the two-dimensional direction. It is necessary to deflect in a one-dimensional plane including the optical axis. If the reference beam is scanned in the direction perpendicular to the plane created by the reference beam and the object beam, degeneration occurs,
This is because multiple holograms are reproduced at the same time (see "Photorefractive Nonlinear Optics", P. Yeh, Maruzen). However, this is not the case when fractal multiplexing is performed, and the laser beam can be deflected also in a direction perpendicular to the plane formed by the reference beam and the object beam, but not so much multiplicity can be obtained and the reproduced image cannot be obtained. Is shifted in the direction perpendicular to the plane formed by the reference light and the object light, it is necessary to move a light receiver such as a CCD or use a large CCD.

In the hologram recording / reproducing apparatus 1 according to the present invention, the light is transmitted through the second beam splitter 13 and
The laser beam whose traveling direction is controlled by the beam deflector 19 is used as the reference beam as the second beam deflector 19.
Is incident on the second hologram recording medium 18 at an incident angle corresponding to the deflection angle of the second hologram.

Therefore, the hologram recording / reproducing apparatus 1 closes the first shutter 5 and opens the second and third shutters 14 and 15, and emits a laser beam from the light source 2, thereby obtaining the first hologram. Each “page” multiplex-recorded on the recording medium 8, that is, “chapter” is reproduced,
The reproduced light is made to be incident on the second hologram recording medium 18 at a predetermined incident angle as object light, and the laser light transmitted through the second beam splitter 13 is deflected by a second beam deflector 19, and is deflected by the second beam deflector 19. Incident on the second hologram recording medium 18 as reference light at the corresponding incident angle,
These lights interfere with each other in the second hologram recording medium 18, and a multiplexed hologram in which all the “pages” constituting the “chapter” are superimposed on the second hologram recording medium 18 as one hologram. Can be recorded.

The hologram recording / reproducing apparatus 1 according to the present invention
Is a multi-recording hologram in which all the “pages” constituting the “chapter” are superimposed through the above recording process as one hologram.
8 and then return to the first step again and
A new “page” is multiplex-recorded on the first hologram recording medium 8 to form a new “chapter” on the first hologram recording medium 8. At this time, before recording a new “chapter” on the first hologram recording medium 8, all “pages” of the old “chapter” recorded on the first hologram recording medium 8 are irradiated with light or heated. You may make it erase | eliminate using a means.

When a new "chapter" is recorded on the first hologram recording medium 8, this "chapter" is reproduced in a second step. Then, the reproduced image of the “chapter” is made to enter the second hologram recording medium 18 again as object light. At this time, by changing the deflection angle by the second beam deflector 19, the second
The angle of incidence on the hologram recording medium 18 is different from that at the time of the previous “chapter” recording, and a new “chapter” is set as the first “chapter”.
Is recorded on the hologram recording medium 18. By repeating this procedure, a plurality of “chapter” is recorded on the second recording medium 18 by so-called angle multiplex recording. Hereinafter, this recording process is referred to as a third step.

The hologram recording / reproducing apparatus 1 controls each “chapter” multiplex-recorded on the second hologram recording medium 18.
Are set to have the same diffraction efficiency during reproduction.

For the sake of convenience, in the following description, a “chapter” composed of “pages” multiplex-recorded with the same reference light will be described in the second hologram recording medium 18 for each “chapter”. The entire hologram multiplexed and recorded using different reference beams will be referred to as a “book”.

In the third step, to reproduce a desired “chapter” from a “book” in which a plurality of “chapters” are multiplex-recorded on the second hologram recording medium 18, the first shutter 5 and the When recording a “chapter” to be reproduced by emitting a laser beam from the light source 2 with the second shutter 14 closed and the third shutter 15 opened, adjusting the deflection angle by the second beam deflector 19 In this case, the same light as the reference light used in step (b) may be incident on the second hologram recording medium 18 as read light. Hereinafter, this reproduction process is referred to as a fourth step.

On the optical path of the reproduced light reproduced in the fourth step, lenses 20 and 21 for Fourier transforming the reproduced light are provided. In the example shown in FIG. 1, the focal lengths of the lenses 20 and 21 are both f, and the second
Is located on the focal plane of the lens 20, and the distance between the lens 20 and the lens 21 is 2f.

In the fourth step, if the “chapter” selectively reproduced from the second hologram recording medium 18 is subjected to Fourier transform by the lens 20, the “chapter” selected as the reproduction image plane which is the focal plane of the lens 20 is obtained. The reproduced image of "chapter" is reproduced. However, as described above, the reproduced images of the “chapter” reproduced on this reproduced image plane are in a state where the reproduced images of all the “pages” constituting the “chapter” are superposed coherently and interfere with each other. Therefore, each “page” cannot be determined and read from this image.

Therefore, the hologram recording / reproducing apparatus 1 according to the present invention performs the Fourier transform on the reproduced image of the “chapter” reproduced on the reproduced image plane again by the lens 21, and focuses the Fourier-transformed image on the focal point of the lens 21. Playback is performed on a playback image plane that is a surface. Here, the reproduction image plane which is the focal plane of the lens 21 is a Fourier transform plane of the spatial light modulator 7. Therefore, parallel rays in different directions on the surface of the spatial light modulator 7 are condensed at different points on the reproduced image plane. More specifically, since the spatial light modulator 7 generally has a shape in which each pixel has a rectangular aperture in most cases, the reproduced image reproduced on the reproduced image plane has diffracted light spread vertically and horizontally. Take a diffraction pattern.

Hologram recording / reproducing apparatus 1 according to the present invention
Is provided with a hologram extracting means 22 for filtering out a diffracted light of a specific “page” component, including the vertical and horizontal positive and negative primary lights of the reproduced image, on a reproduced image plane which is a focal plane of the lens 21. Then, a desired “page” is extracted from the “chapter” reproduced on the reproduction image plane by the hologram extraction means 22. Hereinafter, the process of extracting the desired “page” is referred to as a fifth step.

The hologram extracting means 22 used in the fifth step may be, for example, an aperture having a movable opening. That is, by using this aperture, only the desired “page” component from the diffraction pattern of the entire “chapter” is transmitted through the opening, and the diffracted light of the other “page” is blocked. The diffracted light of the “page” component transmitted through the lens is subjected to the Fourier transform again by the lens 23 disposed on the optical path, thereby obtaining the “page”.
Can be restored to the rear focal plane of the lens 23.

Then, on the rear focal plane of the lens 23,
If a detector array 24 such as a CCD is provided, the data of the “page” extracted by the hologram extracting means 22 can be read.

Here, as the aperture having a movable opening, for example, a liquid crystal shutter array 3 as shown in FIG.
It is conceivable to use 0. The liquid crystal shutter array 30 has a large number of shutter arrays each including an array of liquid crystal cells 31 arranged on a filter surface.
The liquid crystal cell 31 is similar to a liquid crystal cell used for a display panel or the like, and is formed by sandwiching liquid crystal between two transparent substrates coated with an alignment film and a transparent electrode. Each of the liquid crystal cells 31 is provided with a transistor element or a wiring capable of driving each part independently.
The liquid crystal shutter array 30 can individually control the light transmittance of each liquid crystal cell 31 by externally applying an electric signal to each liquid crystal cell 31. Here, the opening of each liquid crystal cell 31 has a shape and a size capable of spatially selecting only the diffracted light of a specific “page”.

Using this liquid crystal shutter array 30,
By increasing only the transmittance of the liquid crystal cell 31 in a portion corresponding to a desired “page” and decreasing the transmittance of the liquid crystal cell 31 in other portions, as shown in FIG. 3, the diffraction pattern of the entire “chapter” can be obtained. Only the desired “page” component is transmitted through the corresponding portion of the liquid crystal cell 31 through the opening of the liquid crystal cell 31 and the other “page” diffracted light is blocked, and only the desired “page” is selected. And can be played. Various operation principles of each liquid crystal cell 31 constituting the liquid crystal shutter array 30 can be considered, and various elements known as a spatial light modulator, for example, a reflection type liquid crystal display, a light writing type light valve, A micromachine such as a micromirror array using a microfabrication technique can be used.

As the aperture having a movable opening, in addition to the above-described liquid crystal shutter array 30 that electrically moves the opening, for example, a shutter device that mechanically moves the opening may be used. It may be.

As the hologram extracting means 22 used in the fifth step, for example, as shown in FIG. 4, an aperture 40 having a fixed opening and a beam for changing the traveling direction of light, such as a galvanomirror, are used. A combination with the deflecting means 41 is conceivable. In this case, instead of the lens 20, a lens 42 for converting the reproduction light into parallel light is provided on the optical path of the reproduction light reproduced in the fourth step. Then, the beam deflecting unit 41 is disposed on the optical path of the reproduction light converted into the parallel light by the lens 42. By this beam deflecting means 41, the diffraction patterns of all the "pages" belonging to the "chapter" are scanned on the focal plane of the lens 21 arranged at the subsequent stage. Then, the aperture 4 is placed on the focal plane of the lens 21 where the diffraction patterns of all the “pages” belonging to the “chapter” are scanned.
0 is provided.

The aperture 40 is provided with, for example, a central portion of an opening 43 that transmits only the diffracted light of one “page” selected from the diffraction pattern of the entire “chapter”. The aperture 40 blocks all the diffracted lights of the “page” other than the selected “page”. Therefore, the tail hologram extracting unit 22 transmits only the desired “page” component from the diffraction pattern of the entire “chapter” deflected by the beam deflecting unit 41 through the opening 43 of the aperture 40. , Only the desired “page” can be extracted from the “chapter”.

The hologram extracting means 22 may have a configuration other than the above example as long as it can extract only a desired “page” from the “chapter”. A configuration in which the above examples are combined may be adopted.

FIG. 5 is an enlarged view of a portion from the spatial light modulator 7 to the detector array 24 of the hologram recording / reproducing apparatus 1 according to the present invention. 6A to 6G show the intensity distribution of the laser beam on each of the surfaces (a) to (g) in FIG.
(G) schematically shows this.

In this hologram recording / reproducing apparatus 1,
The laser beam transmitted through the spatial light modulator 7 has a pattern as shown in FIG. 6A on the (a) plane in FIG. The object light incident on the first hologram recording medium 8 is shown in FIG.
The pattern is as shown in FIG. The reproduction light (object light) transmitted through the lens 16 has a pattern as shown in FIG. 6C on the (c) plane in FIG. The object light incident on the second hologram recording medium 18 is shown in FIG.
FIG. 6D shows a pattern on the surface. Also, the reproduction light transmitted through the lens 20 is shown in FIG.
It becomes a pattern like The reproduction light transmitted through the lens 21 has a pattern as shown in FIG. 6F on the (f) plane in FIG. The reproduction light incident on the detector array 24 has a pattern as shown in FIG. 6 (g) on the (g) plane in FIG.

Here, since the object light (or reproduction light) of each “page” constituting the “chapter” is a ray having a different incident angle, its Fourier plane (b) plane, (d)
The plane and the (f) plane show spatially separated diffraction patterns. The (c) plane, which is the reproduced image plane of “chapter” recorded on the first hologram recording medium 8, and the (f), the reproduced image plane of “chapter” recorded on the second hologram recording medium 18. On the surface, since all the “pages” belonging to the “chapter” are reproduced, a pattern in which all the “pages” are superposed coherently is observed. And
In the hologram recording / reproducing apparatus 1 according to the present invention, only the desired “page” is extracted from the reproduced image of the “chapter” by the hologram extracting means 22, and only the component of the “page” is incident on the detector array 24. Therefore, in the (g) plane, only the selected one “page” is observed.

Therefore, in the hologram recording / reproducing apparatus 1 according to the present invention, the first hologram recording medium 8 temporarily stores information as a buffer memory, and the second hologram recording medium 18 functions as a main memory. Become. Here, when m “pages” are recorded on the first hologram and are copied n times on the second hologram, that is, when n “pages” each including m “pages” are recorded.
When "chapter" is set to 1 "book", 1 "book" is (n
× m) Consists of “pages”. At this time, 1 "page"
The diffraction efficiency per unit is 1 / (n ² × m). Since the diffraction efficiency when holograms are multiplex-recorded in a normal recording schedule is 1 / (n ² × m ² ), the holograms are recorded and reproduced by the hologram recording and reproducing apparatus 1 according to the present invention, so that each hologram is recorded. Diffraction efficiency can be increased by a factor of m as compared with the case where multiplex recording is performed with a normal recording schedule.

More specifically, for example, when 1000 holograms are multiplex-recorded according to a normal recording schedule, the diffraction efficiency of one hologram is 10 ⁻⁶ , whereas the hologram recording and reproduction according to the present invention is performed. By the device 1, 1000 as 100 “pages” and 10 “chapter”
When recording and reproducing one hologram, the diffraction efficiency of one hologram is 10 ^-4 . Therefore, as described above, using the hologram recording / reproducing apparatus 1 according to the present invention, 100
It can be seen that by recording / reproducing 0 holograms, the diffraction efficiency of one hologram can be made 100 times that in the case of multiplex recording with a normal recording schedule.

(Example Using Microlens Array) Next, a hologram recording / reproducing apparatus having a microlens array in which a plurality of microlenses are arranged corresponding to each pixel of the spatial light modulator 7 will be described. In the following description, the same components as those of the hologram recording / reproducing apparatus 1 described above are denoted by the same reference numerals, and detailed description will be omitted.

When a microlens array is used in the hologram recording / reproducing device, the spot on the focal plane of each microlens is separated by changing the incident angle of the light incident on the spatial light modulator 7, and the spatial light modulator 7 Can be divided into a plurality of images.

When a microlens array is used as in this example, the principle of the hologram recording / reproducing apparatus 1 described above is applied to each pixel of the spatial light modulator 7.
Therefore, in the case of extracting a specific “page” in this example, filtering by the hologram extracting means 22 may be performed in pixel units on the image plane of the microlens array.

FIG. 7 shows a configuration example of a hologram recording / reproducing apparatus using a microlens array. Here, the first
Only the portion that performs recording and reproduction on the hologram recording medium 8 will be described with reference to the drawings.

The hologram recording / reproducing apparatus 5 shown in FIG.
At 0, the laser light emitted from the light source 2 is converted into parallel light by the collimator lens 3 and then converted into the first light.
The optical path is branched by the beam splitter 4. In the example shown in FIG. 7, the laser beam reflected by the first beam splitter 4 is reflected by the folding mirror 12 and is incident on the first hologram recording medium 8 as a reference beam at a predetermined incident angle. I do. Although not shown here, a reference beam to be incident on the second hologram recording medium is obtained by disposing a second beam splitter on the optical path of the laser beam reflected by the return mirror 12. be able to.

The laser beam transmitted through the first beam splitter 4 is applied to a first beam deflector 6 such as a galvanomirror.
Is deflected at a predetermined deflection angle, and the traveling direction is controlled. The laser beam whose traveling direction is controlled by the first beam deflector 6 enters the spatial light modulator 7 at an incident angle different for each “page”. The laser light modulated according to the image displayed on the spatial light modulator 7 is used as the object light.

In this hologram recording / reproducing apparatus 50, the microlens array 5
1 is provided. Therefore, the object light transmitted through the spatial light modulator 7 and modulated according to the image displayed on the spatial light modulator 7 is condensed by a microlens element different for each pixel of the spatial light modulator 7. You. The spot of each microlens element is Fourier-transformed by the lens 11 and is incident on the first hologram recording medium 8 as object light. Thereby, the object light condensed by the microlens element and the reference light incident on the first hologram recording medium 8 at a predetermined angle of incidence
The image of the spot converged by the microlens element in the hologram recording medium 8
Can be recorded in the first hologram recording medium 8.

The hologram recording / reproducing apparatus 50 performs the above recording process by changing the angle of deflection of the laser beam incident on the spatial light modulator 7 by changing the angle of deflection by the first beam deflector 6. Is repeatedly performed by using the hologram recording method.

The hologram recording / reproducing apparatus 50 using the microlens array 51 has the following features as compared with the hologram recording / reproducing apparatus 1 described above. That is, a reproduced image obtained by performing Fourier transform on the reproduced light of the hologram recorded on the first hologram recording medium 8 by the hologram recording / reproducing device 50 again is an image on the focal plane of the microlens array 51. Accordingly, if the angular interval of the laser beams incident on the spatial light modulator 7 when recording different “pages” is made sufficiently large, FIGS.
As shown in (1), each pixel can be separated on the reproduced image plane. If a detector array such as a CCD is arranged on this reproduced image plane, a high-definition image can be reproduced.

However, a reproduced image obtained by subjecting the reproduced light of the hologram recorded on the first hologram recording medium 8 to Fourier transform again by the hologram recording / reproducing device 50 using the microlens array 51 is shown in FIG. As shown, pixels of different "pages" are adjacent images,
Pixels on the same "page" will be periodically distributed. Therefore, in order to reproduce the original “page”, the “chapter” image recorded on the first hologram recording medium 8 is collectively reproduced in the same manner as the hologram recording / reproducing apparatus 1 described above, and hardware or This image is rearranged into the original "page" by performing electrical signal processing by software.

Conversely, data to be recorded at the time of recording may be processed so that a desired reproduced image is finally obtained. If the recording data is processed so as to finally obtain a desired reproduction image, the hologram recording / reproduction device 50 can be used as an image display device. The display device disclosed in Japanese Patent Application Laid-Open No. 7-36040 has a problem that high-speed operation is required for the spatial light modulator because all pixels cannot be displayed simultaneously. However, since the hologram recording / reproducing apparatus 50 can simultaneously display all “pages” included in the “chapter”, it appropriately displays a high-definition image without operating the spatial light modulator 7 at high speed. It is possible. Further, since the hologram recording / reproducing device 50 can increase the number of pixels of the spatial light modulator 7 by a number of “pages”, it can be used for a high-definition still image display device or a display of a three-dimensional image.

Next, a case will be described in which a hologram recorded on the first hologram recording medium 8 by the hologram recording / reproducing apparatus 50 using the microlens array 51 is extracted and reproduced one by one for each "page". . FIG. 12 shows a portion of the hologram recording / reproducing apparatus 50 from the spatial light modulator 7 to the detector array 24.
The hologram recording / reproducing apparatus 50 includes a microlens array 52 instead of the lens 21 used in the hologram recording / reproducing apparatus 1 described above.
Is used.

As described above, in the hologram recording / reproducing apparatus 50, the image of the spot transmitted through the spatial light modulator 7 and condensed for each pixel of the spatial light modulator 7 by the microlens array 51 is represented by “ The page is recorded on the first hologram recording medium 8. By repeating the above recording process using the same reference light while changing the incident angle of the laser light incident on the spatial light modulator 7, a plurality of “pages” are recorded on the first hologram recording medium 8.
Are multiplex-recorded.

By causing the same light as the reference light used at the time of recording to enter the first hologram recording medium 8 as readout light, all “pages” multiplex-recorded on the first hologram recording medium 8, that is, The images of the "chapter" are reproduced collectively. Then, after the reproduction light passes through the lens 16 and the lens 17, it enters the second hologram recording medium 18 as object light.

By causing the object light and the reference light to interfere with each other in the second hologram recording medium 18, a “chapter” is copied and recorded on the second hologram recording medium 18.
By repeating the above-mentioned recording process using a reference beam whose incident angle and the like are changed for each reproduction “chapter”, a plurality of “chapters” are formed on the second hologram recording medium 18 by a multiplexing method such as angle multiplexing. Are multiplex-recorded.

When reproducing a desired “chapter” from the second hologram recording medium, the same light as the reference light used for recording the “chapter” is read out to the second hologram recording medium 18. Make it incident. As a result, a desired “chapter” is collectively reproduced from the second hologram recording medium 18. This reproduced light is passed through a lens 20
, The images of all the “pages” included in the “chapter” are superimposed and reproduced on the focal plane of the lens 20.

The hologram reproducing device 50 uses the lens 2
The microlens array 52 that focuses on the reproduction image plane at the focal plane of 0 converts each spot of this reproduction image into parallel light traveling at a different angle for each “page”. The micro lens array 52 is arranged such that each lens element corresponds to one pixel of the spatial light modulator 7 on a one-to-one basis. Therefore, the reproduction light of each hologram formed as the object light with the light incident on the spatial light modulator 7 at different incident angles is:
Each will have a different direction of travel.

The hologram recording / reproducing apparatus 50 is provided with an angle-dependent reflection or transmission filter (angle-dependent filter 53) on the optical path of the reproduction light of each hologram. Then, the hologram recording / reproducing device 50 selectively reflects or transmits the reproduced light of each hologram by the angle-dependent filter 53 so as to extract only a component having one traveling direction from the reproduced light of each hologram. ing.

The component of the reproduction light extracted by the angle dependent filter 53 is a component of one “page”. The component of this one “page” transmits through the lens 23 to form an image on the exit surface of the microlens.
The data of the “page” extracted by the angle-dependent filter 53 is read by the detector array 24 such as a CCD arranged on the image plane.

The hologram recording / reproducing apparatus 50 repeats the above-mentioned reproducing process, for example, by rotating the angle-dependent filter 53 or by changing the selected angle of the angle-dependent filter 53, thereby obtaining the “chapter”. Desired “pages” can be separated and taken out one after another.

Here, as the angle-dependent filter 53, an optical element based on principles such as total reflection, Bragg diffraction, interference in multiple reflection in a thin film, and fine structure with a wavelength or less can be used. Examples of the optical element using Bragg diffraction include an acousto-optic element and a volume hologram. In addition, a diffraction grating or a photonic crystal having a structure equal to or less than the wavelength has a resonant diffraction efficiency or transmittance at a specific wavelength and a specific incident angle, and can be used. In addition, it is also possible to use a plurality of these in combination.

(Other Modifications) In the hologram recording / reproducing apparatus 1 and the hologram recording / reproducing apparatus 50 described above, two hologram recording media, the first hologram recording medium 8 and the second hologram recording medium 18, are used. However, the hologram recording / reproducing apparatus according to the present invention is not limited to the above example, and may use two or more hologram recording media. For example,
The hologram recording / reproducing device can improve the recording speed when a plurality of first hologram recording media 8 are installed in parallel. Also, the hologram recording / reproducing device
By arranging the hologram recording media in series and repeating copying and recording, the diffraction efficiency can be improved.

The hologram recording / reproducing apparatus 1 described above
In the hologram recording / reproducing apparatus 50, the same light is used as the reference light when recording the hologram on the first hologram recording medium 8. However, the hologram recording / reproducing apparatus according to the present invention is not limited to the above example. The present invention is not limited to this. Similar to the normal angle multiplex recording, each “page” is recorded with a different reference light, and the same light as the reference light is read out at the same time as the first hologram recording medium 8.
And all holograms may be collectively reproduced. In this case, a means for generating a plurality of different reference beams is required, which complicates the structure. However, with such a configuration, only a specific page can be selectively used as the second page.
Can be copied and recorded on the hologram 18.

Further, the first hologram recording medium 8 and the second
The hologram recording media 18 need not be the same material, and various hologram recording materials can be combined. For example, as the first hologram recording medium 8 or the second hologram recording medium 18, Pr: LiNbO
3, non-destructive reproduction can be realized by so-called two-wavelength gate recording by using a material capable of two-wavelength recording such as Pr: LiTaO3 and irradiating a short-wavelength light beam only during recording (USP). 5665493 Bai et al, YS Bai an
d R. Kachru, Phys. Rev. Lett, 78, 2944, 1997). When a photopolymer is used as the hologram recording medium, a hologram that is stable for a long period and can be stored for a long period can be recorded. Therefore, as the material of the first hologram recording medium 8, a material such as a photorefractive crystal, which is not suitable for long-term storage but has high diffraction efficiency and high recording sensitivity, is used.
If a material that can be stored for a long period of time, such as a photopolymer, is used as the material of No. 8, a hologram recording / reproducing system that can take advantage of the advantages while compensating for the disadvantages of the two materials can be constructed.

In particular, when a photopolymer is used as the hologram recording medium, it is effective to make the hologram recording medium into a disk shape as shown in FIG. By processing a hologram recording medium into a disk structure similar to that of an optical disk and rotating the hologram recording medium, another hologram can be written at different positions on the hologram recording medium, and handling is easy. Also, for multiplexing, without using a beam deflector such as a beam deflector,
This can be substituted by rotating the disk.
When multiplex recording is performed on a hologram recording medium having such a shape, shift multiplex recording or peristlographic multiplex recording is effective.

A hologram recording / reproducing apparatus 60 shown in FIG.
Uses a bulk-shaped photorefractive crystal as the first hologram recording medium 8. Then, holograms are multiplex-recorded by angle multiplexing on the first hologram recording medium 8 made of the photorefractive crystal. Further, the hologram recording / reproducing device 60
As the second hologram recording medium 18, a layer formed by applying a photopolymer in a layer form on a disk surface is used. Then, holograms are multiplex-recorded on the second hologram recording medium 18 in the form of a disk by shift multiplexing. The other configuration of the hologram recording / reproducing device 60 is almost the same as that of the hologram recording / reproducing device 1 described above, and thus the same components are denoted by the same reference numerals and description thereof will be omitted.

The hologram recording / reproducing apparatus 1 described above
In the hologram recording / reproducing apparatus 50, the case where the angle multiplexing method is used as the multiplex recording method of the second hologram recording medium 18 has been described, but the hologram recording / reproducing apparatus according to the present invention is not limited to the above example. Instead, other multiplex recording methods may be used. That is,
In addition to shift multiplexing, peristrophic multiplexing, phase code multiplexing, and the like, which are considered to be variations of the angle multiplexing method, wavelength multiplexing, spatial multiplexing, fractal multiplexing, etc. Can be used for hologram recording. Also, a multiplexing method combining some of these may be adopted. However, in the case of using the wavelength multiplexing method, it is necessary to use a different wavelength for each “chapter” when recording the hologram on the first hologram recording medium 8 in order to reproduce using the same reference light.

It is known that if conjugate light having the same wavefront as the reference light during recording and propagating in the opposite direction is used as the reference light during hologram reproduction, the object light is also reproduced in the opposite direction. The hologram recording / reproducing apparatus according to the present invention may reproduce the first hologram recording medium 8 or the second hologram recording medium 18 using this phenomenon (phase conjugate).

FIG. 14 shows an example of the configuration of a hologram recording / reproducing apparatus using phase conjugation. The hologram recording / reproducing apparatus 70 shown in FIG. 14 emits a laser beam having a sufficiently narrow wavelength width and high coherence from a light source 71. The laser light emitted from the light source 71 passes through the collimator lens 72 and is converted into parallel light, and then the first beam splitter 73
Incident on. A part of the laser beam incident on the first beam splitter 73 is
Through the first beam splitter 73.
Is reflected by

The laser beam transmitted through the first beam splitter 73 enters a second beam splitter 74 disposed on the optical path. Then, a part of the laser light incident on the second beam splitter 74 is transmitted through the second beam splitter 74, and the other part is reflected by the second beam splitter 74.

The laser beam transmitted through the second beam splitter 74 is incident on a third beam splitter 75 provided on the optical path. Then, a part of the laser light that has entered the third beam splitter 75 is transmitted through the third beam splitter 75, and the other part is reflected by the third beam splitter 75.

The laser beam transmitted through the third beam splitter 75 is incident on the spatial light modulator 77 after its traveling direction is controlled by the first beam deflector 76. Then, the light passes through the spatial light modulator 77 and passes through the spatial light modulator 7.
Light modulated according to the image displayed in 7 is used as object light. This object light passes through the fourth beam splitter 78 and is subjected to Fourier transform by the lens 79, after which the first
Incident on the first hologram recording medium 80 at an incident angle corresponding to the deflection angle of the beam deflector 76 of FIG.

On the other hand, the laser light reflected by the second beam splitter 74 is reflected by the first mirror 81 and the second mirror 82 and is incident on the first hologram recording medium 80 at a predetermined incident angle. As a result, the object light and the reference light interfere with each other in the first hologram recording medium 80, and a hologram (“page”) is recorded on the first hologram recording medium 80.

The hologram recording / reproducing apparatus 70 repeats the above recording process using the same reference light while changing the incident angle of the object light, and
A plurality of “pages” are multiplex-recorded on 0.

Here, the laser beam reflected by the third beam splitter 75 is incident on the first hologram recording medium 80 after being reflected by the third mirror 83 and the fourth mirror 84. Since this laser light is a conjugate light having the same wavefront as the reference light and propagating in the opposite direction, if the conjugate light of the reference light is used as the reading light, a plurality of multiplexed recordings on the first hologram recording medium 80 are performed. “Pages” (“chapter”) are collectively reproduced, and the reproduced light is emitted from the side of the first hologram recording medium 80 where the object light is incident.

This reproduction light is subjected to Fourier transform by the lens 79, reflected by the fourth beam splitter 78, and enters the fifth beam splitter 85. Then, the reproduction light transmitted through the fifth beam splitter 85 is
After being Fourier-transformed by the lens 86, the light enters the second hologram recording medium 87 at a predetermined incident angle as object light.

On the other hand, the traveling direction of the laser beam reflected by the first beam splitter 73 is controlled by the second beam deflector 88, and the second beam deflector 88
Incident on the second hologram recording medium 87 as reference light at an incident angle corresponding to the deflection angle due to As a result, the object light and the reference light interfere with each other in the second hologram recording medium 87, and the “chapter” read out from the first hologram recording medium 80 collectively is converted into the second hologram recording medium 87.
Is recorded.

The hologram recording / reproducing apparatus 70 repeats the above recording process while changing the incident angle of the reference light, and converts a plurality of “chapter” read one after another from the first hologram recording medium 80 into an angle. The data is copied and recorded on the second hologram recording medium 87 by a multiplexing method such as multiplexing.

The laser beam incident on the second hologram recording medium 80 as reference light is applied to the second hologram recording medium 8.
After passing through 0, the light is reflected by a fifth mirror 89 disposed on the optical path. Then, the laser light reflected by the fifth mirror 89 enters the second hologram recording medium 87 again. This laser light is conjugate light having the same wavefront as the reference light and propagating in the opposite direction. Therefore, if this laser light is used as the reading light, the hologram multiplexed and recorded on the second hologram recording medium 87 is selectively reproduced, and the reproduced light is applied to the side of the second hologram recording medium 87 on which the object light is incident. Will be emitted.

This reproduction light is Fourier-transformed by the lens 86, and then enters the fifth beam splitter 85. Then, the reproduction light reflected by the fifth beam splitter 85 is again Fourier-transformed by the lens 90, and then enters the hologram extraction means 91. Then, only a specific “page” component is extracted from the “chapter” read from the second hologram recording medium 87 by the hologram extracting means 91.

The light of the specific “page” component extracted by the hologram extracting means 91 is again subjected to Fourier transform by the lens 92, and then the light from the detector array 9 such as a CCD is detected.
3 is received. Thereby, from among the “chapter” read from the second hologram recording medium 87,
The desired “page” data can be read.

In the above, an example in which a hologram is recorded as a Fourier hologram has been described. However, the hologram recording / reproducing apparatus according to the present invention is not limited to the above example. May be configured to record another hologram. In the above, an example of recording and reproducing a transmission hologram has been described. However, the hologram recording and reproducing apparatus according to the present invention is not limited to this example, and is configured to record and reproduce a reflection hologram. You may.

The technique of the present invention is not only applied to information recording / reproducing devices and image display devices, but can be widely applied to other devices utilizing the principle of hologram recording / reproducing. For example, the method of the present invention can be applied to a correlation computer, an optical computer such as an associative memory, an optical interconnection, a hologram printer, a holographic interferometer, a holographic optical element, and the like.

[0128]

According to the hologram recording / reproducing apparatus of the present invention, the holograms multiplex-recorded on the first hologram recording medium by the first recording means are collectively reproduced by the first reproducing means. The multiple recording holograms reproduced at one time are multiplex-copied and recorded on the second hologram recording medium by the second recording means, so that the final diffraction efficiency per hologram is multiplexed on the first hologram recording medium. It can be multiplied by the multiplex number when recording. As a result, a decrease in diffraction efficiency due to multiplex recording of holograms can be avoided, the S / N ratio can be improved, and the amount of recorded information can be increased.

According to this hologram recording / reproducing apparatus, the holograms multiplex-recorded on the first hologram recording medium by the first recording means are collectively reproduced by the first reproducing means. Reconstructed hologram 1
The amount of information included per sheet is large, and the access speed is improved.

According to this hologram recording / reproducing apparatus, the holograms multiplex-recorded on the first hologram recording medium by the first recording means are collectively reproduced by the first reproducing means. A lot of spatial information can be displayed. Therefore, this hologram recording / reproducing apparatus can be used as a display device for a high-definition still image or a three-dimensional image.

According to the hologram recording / reproducing method according to the present invention, the holograms multiplex-recorded on the first hologram recording medium in the first step are collectively reproduced in the second step, and the collective reproduction is performed. In the third step, the multiple multiplexed holograms
Hologram recording medium, the final diffraction efficiency per hologram can be multiplied by the number of multiplexed holograms recorded on the first hologram recording medium. As a result, a decrease in diffraction efficiency due to multiplex recording of holograms can be avoided, the S / N ratio can be improved, and the amount of recorded information can be increased.

Further, according to the hologram recording / reproducing method, the holograms multiplex-recorded on the first hologram recording medium in the first step are collectively reproduced in the second step. The amount of information contained in one hologram is large, and the access speed is improved.

According to the hologram recording / reproducing method, the holograms multiplex-recorded on the first hologram recording medium in the first step are collectively reproduced in the second step. Since spatial information can be displayed, a high-definition still image or a three-dimensional image can be displayed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one configuration example of a hologram recording / reproducing apparatus according to the present invention.

FIG. 2 is a plan view showing a liquid crystal shutter array used as hologram extracting means.

FIG. 3 is a schematic diagram for explaining how a desired hologram component is extracted using the liquid crystal shutter array.

FIG. 4 is a schematic diagram showing an example in which an aperture having a fixed opening as a hologram extracting unit and a beam deflecting unit are used in combination.

FIG. 5 is an enlarged schematic view showing a portion from a spatial light modulator to a detector array of the hologram recording / reproducing apparatus according to the present invention.

6A and 6B are diagrams showing the intensity distribution of laser light on the planes (a) to (g) in FIG. 5, where FIG. 6A shows a pattern on the plane (a) in FIG. 5, and FIG. FIG. 5C shows a pattern on the plane (c) in FIG. 5, FIG. 5C shows a pattern on the plane (d) in FIG. 5, and FIG. 5E shows a pattern on the plane (e) in FIG. 5) shows a pattern on the (f) plane in FIG. 5, and FIG.
(G) shows the pattern on the (g) plane in FIG.

FIG. 7 is a schematic diagram showing a portion for performing recording and reproduction on a first hologram recording medium of a hologram recording and reproduction apparatus using a microlens array.

FIG. 8 is a schematic diagram illustrating a manner in which a spot of each pixel of a spatial light modulator is separated on a reproduction image plane by a microlens array.

FIG. 9 is a side view showing a manner in which spots of respective pixels of the spatial light modulator are separated on a reproduced image plane by a microlens array.

FIG. 10 is a plan view showing a state of a reproduced image plane in FIG. 9;

FIG. 11 is a diagram showing a reproduced image obtained from reproduction light of a hologram recorded on a first hologram recording medium by a hologram recording / reproducing apparatus using a microlens array.

FIG. 12 is a schematic diagram showing a portion from a spatial light modulator to a detector array of a hologram recording / reproducing apparatus using a microlens array.

FIG. 13 is a schematic diagram showing a hologram recording / reproducing apparatus using a bulk-shaped photorefractive crystal as a first hologram recording medium, and using a layer obtained by applying a photopolymer in a layer on a disk surface as a second hologram recording medium FIG.

FIG. 14 is a schematic diagram illustrating a configuration example of a hologram recording / reproducing apparatus using phase conjugation.

[Explanation of symbols]

Reference Signs List 1 hologram recording / reproducing device, 2 light source, 6 first beam deflector, 7 spatial light modulator, 8 first hologram recording medium, 18 second hologram recording medium, 19
A second beam deflector, 22 hologram extracting means,
24 detector array

Claims (16)

[Claims] 1. A first recording means for multiplex-recording a plurality of holograms on a first hologram recording medium using the same reference light while changing the incident angle of object light every time one hologram is recorded. A first reproducing means for collectively reproducing a plurality of holograms multiplex-recorded on the first hologram recording medium by the first recording means; and a collective reproduction by the first reproducing means. The multiplexed recording hologram formed by superimposing the plurality of holograms and forming one hologram is used as object light with the reproduced light of the plurality of holograms as object light. 2 recording means, and a desired multiple recording hologram is selectively selected from a plurality of multiple recording holograms multiplex-recorded on the second hologram recording medium by the second recording means. A hologram recording / reproducing apparatus comprising: a second reproducing means for reproducing. 2. A hologram recording apparatus according to claim 1, further comprising hologram extraction means for extracting a desired hologram from a plurality of holograms constituting the multiplexed hologram reproduced by said second reproduction means. Playback device. 3. The hologram extraction means extracts a desired hologram by filtering the reproduction light of the multiplexed hologram reproduced by the second reproduction means on the Fourier plane of the image using a spatial aperture. 3. The hologram recording / reproducing apparatus according to claim 2, wherein: 4. The hologram extracting means extracts a desired hologram by selectively transmitting or reflecting reproduction light of a multiplexed recording hologram reproduced by the second reproducing means by an element having an angle dependency. 3. The hologram recording / reproducing apparatus according to claim 2, wherein: 5. The hologram recording material according to claim 1, wherein a rewritable hologram recording material is used as said first hologram recording medium, and a hologram recording material which can be recorded only once is used as said second hologram recording medium. Hologram recording and reproducing device. 6. The first recording means includes a spatial light modulator and a microlens array in which a plurality of microlenses are arranged corresponding to each pixel of the spatial light modulator.
The spot on the focal plane of each of the microlenses is separated by changing the incident angle of the light incident on the spatial light modulator, and one image displayed on the spatial light modulator is divided into a plurality of images to form a plurality of images. Multiplex-recording on the first recording medium as the hologram, and the second reproducing means forms a multiplex-recorded hologram formed by superimposing a plurality of holograms obtained by dividing one image displayed on the spatial light modulator. The hologram recording / reproducing apparatus according to claim 1, wherein the hologram is reproduced. 7. The hologram recording / reproducing apparatus according to claim 6, further comprising display means for displaying a multiplexed hologram reproduced by the second reproducing means as one image. 8. A hologram recording apparatus according to claim 6, further comprising hologram extraction means for extracting a desired hologram from a plurality of holograms constituting the multiplexed hologram reproduced by said second reproduction means. Playback device. 9. A first step of multiplex-recording a plurality of holograms on a first hologram recording medium using the same reference light while changing the incident angle of object light every time one hologram is recorded; A second step of collectively reproducing a plurality of holograms multiplex-recorded on the first hologram recording medium in the first step, and a plurality of holograms collectively reproduced in the second step. A third step of multiplex-recording a plurality of holograms formed by superimposing the plurality of holograms to form one hologram on a second recording medium using different reference beams, using the hologram reproduction light as object light; In the third step, a desired multiple-recording hologram is selected from a plurality of multiple-recording holograms multiplex-recorded on the second hologram recording medium. And a fourth step of selectively reproducing the hologram. 10. The hologram recording according to claim 9, further comprising a fifth step of extracting a desired hologram from a plurality of holograms constituting the multiplexed hologram reproduced in the fourth step. Playback method. 11. The fifth step is to extract a desired hologram by filtering the reproduction light of the multiplexed hologram reproduced in the fourth step on the Fourier plane of the image using a spatial aperture. The hologram recording / reproducing method according to claim 10, wherein: 12. The fifth step extracts a desired hologram by selectively transmitting or reflecting the reproduction light of the multiplexed hologram reproduced in the fourth step by an element having an angle dependency. The hologram recording / reproducing method according to claim 10, wherein: 13. The hologram recording material according to claim 9, wherein a rewritable hologram recording material is used as said first hologram recording medium, and a hologram recording material which can be recorded only once is used as said second hologram recording medium. Hologram recording / reproduction method. 14. The spatial light modulator according to claim 1, wherein in the first step, a spatial light modulator and a microlens array in which a plurality of microlenses are arranged corresponding to each pixel of the spatial light modulator are used. The spot on the focal plane of each of the microlenses is separated by changing the incident angle of light incident on the microlens, and one image displayed on the spatial light modulator is divided into a plurality of images to form a plurality of holograms. Multiplex recording on one recording medium; and reproducing, in the fourth step, a multiplex recording hologram in which a plurality of holograms obtained by dividing one image displayed on the spatial light modulator are superimposed. The hologram recording / reproducing method according to claim 9, wherein 15. The hologram recording / reproducing method according to claim 14, wherein the multiplexed hologram reproduced in the fourth step is displayed as one image. 16. The hologram recording according to claim 14, further comprising a fifth step of extracting a desired hologram from a plurality of holograms constituting the multiplexed hologram reproduced in the fourth step. Playback method.