JP4214601B2 - Hologram recording / reproducing apparatus and hologram recording / reproducing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hologram recording / reproducing apparatus and a hologram recording / reproducing method for recording data on a hologram recording medium using an interference effect between an object beam and a reference beam, or reproducing data recorded on a hologram recording medium.
[0002]
[Prior art]
Conventionally, by causing object light modulated according to data to be recorded and reference light to interfere in a hologram recording medium that expresses a large photorefractive effect, data is recorded on the hologram recording medium as interference fringes, Further, there has been proposed a hologram recording / reproducing method for reproducing data recorded on a hologram recording medium by causing reading light to enter the hologram recording medium on which data is recorded at the same incident angle as that of the reference light.
[0003]
In this hologram recording / reproducing system, for example, light that is modulated in accordance with data for one image displayed on the spatial light modulator by passing through the spatial light modulator such as a liquid crystal display panel (LCD) is an object. Since it enters the hologram recording medium as light, data for one image is recorded on the hologram recording medium as a single hologram at a time. Even at the time of reproduction, reproduction is performed in units of holograms including the data for one image. Therefore, this hologram recording / reproducing system has a feature that, for example, higher-speed data access is possible even when compared with a recording / reproducing system using an optical disc that can be accessed at a relatively high speed as a recording medium. Have.
[0004]
In this hologram recording / reproducing system, for example, so-called multiple recording is performed in which a large number of holograms are recorded on one hologram recording medium by changing the incident angle of the reference light every time one hologram is recorded. Is possible. Therefore, this hologram recording / reproducing system 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 been attracting attention as a recording / reproducing method that satisfies the improvement in recording density and the speeding up of data access required with the recent development of the information industry.
[0006]
[Problems to be solved by the invention]
By the way, in this hologram recording / reproducing system, multiplex recording that realizes high-density recording is limited by a decrease in diffraction efficiency caused by erasing during recording or reproduction. That is, when performing multiplex recording, the hologram previously recorded on the hologram recording medium is erased when a subsequent hologram is recorded, and the diffraction efficiency is somewhat reduced. In addition, the diffraction efficiency of each hologram recorded on the hologram recording medium by multiplex recording is somewhat reduced by exposure during reproduction. In addition, the long-term diffraction efficiency decreases due to the diffusion of electrons due to dark current.
[0007]
As described above, when holograms multiplexed and recorded on the hologram recording medium have a reduced diffraction efficiency due to erasure or the like, the S / N ratio during reproduction gradually decreases.
[0008]
Diffraction efficiency η when recording each hologram recorded on the hologram recording medium _writw (T) is given by the following equation (1).
[0009]
η _writw (T) = η ₀ ・ (1-e ^- α ^It (1)
Here, α is a time constant during recording, I is a spatial average light intensity, t is a time when the recording time is 0, η ₀ Is the saturation diffraction efficiency.
[0010]
Also, the diffraction efficiency η when reproducing each hologram recorded in multiple recording or when erasing the previously recorded hologram by light irradiation when recording a subsequent hologram _read (T) is given by the following equation (2).
[0011]
η _read (T) = η ₁ ・ E ^- α ^'It ... (2)
Where α ′ is the time constant during reproduction (or erasure), I is the average light intensity, η ₁ Is the initial diffraction efficiency.
[0012]
From the above formulas, 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” by P. YEH, published by Maruzen). At this time, when multiple recording is performed so that the diffraction efficiencies of all holograms are equal, it is known that the final diffraction efficiency of each hologram is inversely proportional to the square of the number of recorded sheets ("System metric for holographic memory system"). Fai H. Mok, Geoffrey W. Burr and Demetri Psaltis, Optics Letters, 21, pp. 896, 1996).
[0013]
For example, when 1000 holograms are recorded with the same intensity, the diffraction efficiency of each hologram is 10 compared to when one hologram is recorded. ^-6 To a degree.
[0014]
As described above, when the diffraction efficiency is lowered, the S / N ratio at the time of reproduction is lowered. If the S / N ratio is greatly reduced during reproduction, the signal component is buried in noise, making reproduction impossible. Therefore, in order to ensure reproducible diffraction efficiency, it is necessary to limit the number of holograms recorded on the hologram recording medium, which is a factor that limits the recording capacity of data recorded on the hologram recording medium. It was.
[0015]
Therefore, in the hologram recording / reproducing system, it is possible to increase the data recording capacity by performing multiplex recording while suppressing the decrease in diffraction efficiency as much as possible. It is considered as one of the issues to make it happen.
[0016]
As a means for performing multiplex recording while suppressing a decrease in diffraction efficiency as much as possible, a method has been proposed in which a multiplex recorded hologram is used as a master and the hologram is further recorded in another hologram (“Multiple multiple-exposure hologram”). ”, Kristina M. Johnson, Mark Armstrong, Lambertus Hesselink, and Joseph W. Goodman, Applied Optics, 24, pp. 4467-4472, 1985).
[0017]
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 as object light on the second hologram recording medium. Next, m holograms are recorded again on the first hologram recording medium, and this is copied and recorded on the second hologram recording medium using the same reference light as when the first m holograms were recorded. . Repeat the above procedure n times. As a result, (n × m) holograms are multiplexed and recorded on the second hologram recording medium.
[0018]
If this hologram is reproduced, (n × m) holograms are superimposed and reproduced simultaneously, so that (n × m) layer images can be superimposed and displayed simultaneously. If, for example, a solid slice is recorded using this method, the whole solid can be displayed three-dimensionally.
[0019]
The diffraction efficiency at this time can be increased by a factor of m as compared with the case of recording with a normal recording schedule. That is, if m holograms are recorded on the first hologram recording medium, the diffraction efficiency of each hologram is 1 / m. ² become. However, when 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 It becomes. Therefore, if all the holograms of m have the same diffraction efficiency, when the second hologram is reproduced, the diffraction efficiency per hologram is 1 / m, and the final diffraction efficiency per sheet is , 1 / (m × n ² ). On the other hand, the diffraction efficiency when (n × m) holograms are multiplexed and recorded with a normal recording schedule is 1 / (m ² × n ² ). Therefore, it can be seen that the diffraction efficiency is increased by m times by copying the hologram by the above method.
[0020]
However, as described above, this method has been proposed for the purpose of displaying a three-dimensional image by superimposing cross sections, and reproduces holograms recorded in a multiplexed manner on the first hologram recording medium. Therefore, a common reference beam is used when recording each hologram on the first hologram recording medium, and at the time of reproduction, all holograms are reproduced in a superimposed state and separated one by one. It is not possible. Therefore, this method is difficult to apply for purposes other than the special uses described above, and has not yet solved the above-mentioned problem essentially.
[0021]
SUMMARY OF THE INVENTION An object of the present invention is to provide a hologram recording / reproducing apparatus and a hologram recording / reproducing method capable of performing multi-recording while minimizing a decrease in diffraction efficiency and recording / reproducing a large amount of data.
[0022]
[Means for Solving the Problems]
In order to solve the above-described problem, the hologram recording / reproducing apparatus according to the present invention uses the same reference light to change the number of holograms to the first while changing the incident angle of the object light every time one hologram is recorded. First recording means for performing multiple recording on the hologram recording medium, and first reproducing means for collectively reproducing a plurality of holograms multiplexed and recorded on the first hologram recording medium by the first recording means, Using the reproduction light of a plurality of holograms collectively reproduced by the first reproduction means as object light, the multiple recording hologram formed by superimposing the plurality of holograms into one hologram is used with different reference lights. A second recording means for multiple recording on the second recording medium; and a plurality of multiple recording holograms recorded on the second hologram recording medium by the second recording means. And a second reproducing means for reproducing selectively the desired multiple recording holograms of.
[0023]
According to this hologram recording / reproducing apparatus, a plurality of holograms are multiplexed and 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.
[0024]
The 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 reading 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 entering, a plurality of holograms multiplexed and recorded on the first hologram recording medium are collectively reproduced.
[0025]
The plurality of holograms reproduced together by the first reproducing means are in a state in which the holograms are superimposed. Then, the multiple recording hologram formed by superimposing the plurality of holograms into 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 (multiple recording holograms) collectively reproduced by the first reproducing means, and uses the multiple recording hologram as the second hologram recording medium. Record again. The second recording means multiplex-records a plurality of multiplex recording holograms on the second recording medium using different reference beams.
[0026]
A plurality of multiplexed recording holograms multiplexed and 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 multiplex recording holograms are multiplexed and recorded on the second holographic recording medium by angle multiplexing, the second reproducing means selects a desired incident angle of the readout light, thereby Play back multiple recording holograms.
[0027]
The hologram recording / reproducing apparatus according to the present invention preferably includes a hologram extracting means for extracting a desired hologram from a plurality of holograms constituting the multiplex recording hologram reproduced by the second reproducing means. As this hologram extraction means, for example, a desired hologram can be extracted by filtering the reproduction light of the multiplex recording hologram reproduced by the second reproduction 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 multiple recording hologram reproduced by the second reproducing means with an element having an angle dependency.
[0028]
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 photopolymer or the like as the second hologram recording medium. It is desirable to use a hologram recording material that can be recorded only once.
[0029]
In the hologram recording / reproducing apparatus according to the present invention, 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 microlens 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. A hologram is multiplexed and recorded on the first recording medium, and the second reproducing means reproduces a multiplexed recording hologram formed by superimposing a plurality of holograms obtained by dividing one image displayed on the spatial light modulator. May be.
[0030]
In this case, the multiplex recording 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 multiplex recording hologram by the hologram extracting means.
[0031]
Further, in order to solve the above-described problem, the hologram recording / reproducing method according to the present invention uses a single reference beam to change a plurality of holograms while changing the incident angle of the object beam every time one hologram is recorded. A first step of multiplex recording on the first hologram recording medium; a second step of collectively reproducing a plurality of holograms multiplex-recorded on the first hologram recording medium in the first step; The second recording is performed on the multiple recording hologram formed by superimposing the plurality of holograms into one hologram using the reproduction light of the plurality of holograms reproduced in a batch in the step as object light, using different reference lights. A third step of multiple recording on a medium, and a plurality of multiple recording holograms that are multiplexed and recorded on a second hologram recording medium in the third step It is characterized in that through the fourth step of reproducing selectively the desired multiple recording holograms of.
[0032]
According to this hologram recording / reproducing method, in the first step, a plurality of holograms are multiplexed and recorded on the first recording medium. 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.
[0033]
The plurality of holograms multiplexed and recorded on the first hologram recording medium in the first step are reproduced in a lump in the second step. That is, in the second step, the reading light is incident on the first hologram recording medium at the same incident angle as the reference light used when a plurality of holograms are recorded on the first hologram recording medium in the first step. Thus, a plurality of holograms multiplexed and recorded on the first hologram recording medium are collectively reproduced.
[0034]
The plurality of holograms collectively reproduced in the second step are in a state in which the holograms are superimposed. Then, the multiple recording hologram formed by superimposing the plurality of holograms into one hologram is recorded again on 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 this multiple recording hologram is used as the second hologram recording medium. Record again. In the third step, a plurality of multiplex recording holograms are multiplexed and recorded on the second recording medium using different reference beams.
[0035]
A plurality of multiplex recording holograms multiplexed and 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 multiplexed and recorded on the second hologram recording medium by angle multiplexing, the desired multiplexing is selected by selecting the incident angle of the readout light. Play the recorded hologram.
[0036]
The hologram recording / reproducing method according to the present invention preferably undergoes a fifth step of extracting a desired hologram from a plurality of holograms constituting the multiplex recording hologram reproduced in the fourth step. In this fifth step, for example, a desired hologram is extracted by filtering the reproduction light of the multiplex recording hologram reproduced in the fourth step on the Fourier plane of the image using a spatial aperture, or It is conceivable to extract a desired hologram by selectively transmitting or reflecting the reproduction light of the multiplex recording hologram reproduced by the second reproducing means with an element having angle dependency.
[0037]
The hologram recording / reproducing method 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 photopolymer or the like as the second hologram recording medium. It is desirable to use a hologram recording material that can be recorded only once.
[0038]
The hologram recording / reproducing method according to the present invention uses, 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. 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, and one image displayed on the spatial light modulator is divided into a plurality of images to generate a plurality of holograms In the fourth step, a multiplex recording hologram formed by superimposing a plurality of holograms obtained by dividing one image displayed on the spatial light modulator may be reproduced in the fourth step. Good.
[0039]
In this case, the multiplex recording hologram reproduced in the fourth step is displayed as one image, for example. Alternatively, in the fifth step, a desired hologram is extracted from a plurality of holograms constituting the multiple recording hologram.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0041]
A configuration example of a hologram recording / reproducing apparatus to which the present invention is applied is shown in FIG. The hologram recording / reproducing apparatus 1 shown in FIG. 1 includes a light source 2 that emits laser light having a sufficiently narrow wavelength width and high coherence. On the optical path of the laser light emitted from the light source 2, a collimator lens 3 that converts the laser light into parallel light, and a first optical path for branching the optical path of the laser light converted into parallel light by the collimator lens 3. 1 beam splitter 4 is provided. The first beam splitter 4 transmits, for example, a part of the laser light converted into parallel light by the collimator lens 3 and reflects the other part to bend the optical path thereof by, for example, about 90 degrees. The optical path of the laser beam is branched.
[0042]
On the optical path of the laser beam reflected by the first beam splitter 4 and whose optical path is bent, the first shutter 5 for switching ON / OFF of the laser beam and the traveling direction of the laser beam are controlled. A first beam deflector 6 is provided. The first beam deflector 6 controls the traveling direction of the laser beam by deflecting the incident laser beam with a predetermined deflection angle and transmitting or reflecting the laser beam, for example, an acousto-optic deflector or an electro-optic deflector. It consists of a container, galvanometer mirror, etc. 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.
[0043]
A spatial light modulator 7 and a first hologram recording medium 8 are disposed on the optical path of the laser light whose traveling direction is controlled by the first beam deflector 6. 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 onto the spatial light modulator 7 are disposed. . In the example shown in FIG. 1, considering the case where the exit surface of the first beam deflector 6 is projected onto the spatial light modulator 7 at the same magnification, the focal lengths of the lens 9 and the lens 10 are both F, 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 lens 9 and the lens 10 is 2F.
[0044]
Here, because of the Lagrange-Helmholtz relationship, the product of the incident light on each surface and the incident angle is constant, so that when the light beam is enlarged, the deflection angle of the beam is reduced. On the other hand, if the deflection angle of the beam is to be increased, the beam diameter must be reduced. Therefore, if necessary, it is desirable to set the projection magnification and the exit diameter of the exit beam from the first beam deflector 7 to appropriate values.
[0045]
The spatial light modulator 7 is composed of, for example, a transmissive liquid crystal display (LCD) or the like, and displays an image corresponding to the image signal on the display unit. The spatial light modulator 7 transmits the laser light emitted from the first beam deflector 6 through the display unit, and modulates the laser light according to the image displayed on the display unit.
[0046]
In the hologram recording / reproducing apparatus 1, as described above, the laser beam reflected by the first beam splitter 4 and deflected by the first beam deflector 6 and then modulated by the spatial light modulator 7 is converted into object light. Is done.
[0047]
Between the spatial light modulator 7 and the first hologram recording medium 8, a lens 11 for Fourier transforming the object light modulated in accordance with the image displayed on the display unit of the spatial light modulator 7 is arranged. It is installed. 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 respectively disposed on the focal plane of the lens 11. Here, the center of the first hologram recording medium 8 is used as a position reference.
[0048]
The object light that has been deflected by the first beam deflector 6 and then modulated by the spatial light modulator 7 is Fourier-transformed by passing through the lens 11 and is disposed in the vicinity of the Fourier plane. 8 is incident at an incident angle corresponding to the deflection angle by the first beam deflector 6.
[0049]
On the other hand, on the optical path of the laser beam that has passed through the first beam splitter 4, a reflection mirror 12 that reflects this laser beam and bends the optical path by about 90 degrees and is reflected by the folding mirror 12, and the optical path is folded. And a second beam splitter 13 for branching the optical path of the laser light. The second beam splitter 13 transmits, for example, a part of the laser light reflected by the folding mirror 12 and reflects the other part and bends the optical path thereof by, for example, about 90 degrees to Branch the optical path.
[0050]
On the optical path of the laser beam reflected by the second beam splitter 13 and having its optical path bent, a second shutter 14 for switching ON / OFF of the laser beam is disposed. A third shutter 15 for switching ON / OFF of the laser light is disposed on the optical path of the laser light transmitted through the second beam splitter 13.
[0051]
In the hologram recording / reproducing apparatus 1, when the second shutter 14 is opened, the laser beam reflected by the second beam splitter 13 and whose optical path is bent is used as the reference light. The light is incident on the hologram recording medium 8 at a predetermined incident angle.
[0052]
Therefore, the hologram recording / reproducing apparatus 1 emits laser light from the light source 2 with the first shutter 5 and the second shutter 14 opened and the third shutter 15 closed, thereby producing a spatial light modulator. 7 and the object beam incident on the first hologram recording medium 8 at an incident angle corresponding to the deflection angle by the first beam deflector 6 and the reference incident on the first hologram recording medium 8 at a predetermined incident angle The light can be 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.
[0053]
The hologram recording / reproducing apparatus 1 according to the present invention performs the above recording process by changing the deflection angle of the first beam deflector 6 to the first hologram recording medium 8 of the object light transmitted through the spatial light modulator 7. A plurality of holograms are multiplexed and recorded on the first hologram recording medium 8 by repeatedly using the same reference light while changing the incident angle. Hereinafter, this recording process is referred to as a first step.
[0054]
In the hologram recording / reproducing apparatus 1, the recording schedule in the first step is set so that each “page” multiplexedly recorded on the first hologram recording medium 8 has the same diffraction efficiency at the time of reproduction.
[0055]
For convenience of explanation, in the following explanation, each hologram recorded on the first hologram recording medium 8 is called a “page”, and each “page” has the same reference light. A multiplex recording hologram in which a plurality of “pages” are overlapped by being multiplex-recorded on the first hologram recording medium using the above will be referred to as a “chapter”.
[0056]
As described above, all “pages” multiplexed and recorded on the first hologram recording medium 8 in the first step are recorded using the same reference light. Therefore, when the hologram recording / reproducing apparatus 1 causes the same light as the reference light used when each “page” is recorded to enter the first hologram recording medium 8 as readout light, the hologram recording / reproducing apparatus 1 enters the first hologram recording medium 8. All “pages” of the recorded “chapter” can be played back together. Hereinafter, this reproduction process is referred to as a second step.
[0057]
On the optical path of the reproduction light reproduced in the second step, lenses 16 and 17 for Fourier transforming the reproduction light and the reproduction light transmitted through the lenses 16 and 17 are incident as object light. A 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 the lens 17. The distance between the lens 16 and the lens 17 is 2f. Here, the center of the second hologram recording medium 18 is used as a position reference.
[0058]
In the second step, if all the “pages” reproduced from the first hologram recording medium 8, that is, “chapter” are Fourier-transformed by the lens 16, the “chapter” becomes the reproduction image plane that is the focal plane of the lens 16. Are reproduced. The reproduced image of “chapter” reproduced on this reproduced image plane is a state in which the reproduced images of all “pages” constituting “chapter” are coherently superimposed and interfere with each other. The “page” cannot be determined and read.
[0059]
In the hologram recording / reproducing apparatus 1 according to the present invention, the reproduction image of the “chapter” reproduced on the reproduction image plane is Fourier-transformed by the lens 17 again, and the Fourier-transformed image is used as object light in the vicinity of the Fourier plane. The incident light is incident on the second hologram recording medium 18 disposed at a predetermined angle.
[0060]
On the other hand, 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 second beam splitter 13 described above. Similar to the first beam deflector 4, the second beam deflector 19 controls the traveling direction of the laser beam by deflecting the incident laser beam with a predetermined deflection angle and transmitting or reflecting it. For example, an acousto-optic deflector, an electro-optic deflector, a galvanometer mirror or the like is included. However, since 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, the laser beam is transmitted in a two-dimensional direction. However, it is necessary to deflect in a one-dimensional plane including the object optical axis. If the reference beam is scanned in the direction perpendicular to the plane formed by the reference beam and the object beam, degeneration occurs and multiple holograms are reproduced simultaneously (“Photorefractive Nonlinear Optics”, P. Yeh , See Maruzen). However, this is not the case when fractal multiplexing is performed, and the laser beam can be deflected in a direction perpendicular to the plane formed by the reference beam and the object beam. Is shifted in a direction perpendicular to the plane formed by the reference light and the object light, it is necessary to take measures such as moving a light receiver such as a CCD or using a large CCD.
[0061]
In the hologram recording / reproducing apparatus 1 according to the present invention, the laser beam that has passed through the second beam splitter 13 and whose traveling direction is controlled by the second beam deflector 19 is used as reference light by the second beam deflector 19. The light is incident on the second hologram recording medium 18 at an incident angle corresponding to the deflection angle.
[0062]
Therefore, the hologram recording / reproducing apparatus 1 closes the first shutter 5, opens the second and third shutters 14, 15, and emits laser light from the light source 2, whereby the first hologram recording medium 8. Each “page”, that is, “chapter”, recorded in a multiplexed manner is reproduced as object light and incident on the second hologram recording medium 18 at a predetermined incident angle and transmitted through the second beam splitter 13. The laser beam thus deflected is deflected by the second beam deflector 19 and is incident on the second hologram recording medium 18 at an incident angle corresponding to the deflection angle, and these lights are incident on the second hologram recording medium 18. Second hologram recording with multiple recording holograms made by overlapping all “pages” constituting “chapter” as one hologram It can be recorded in the body 18.
[0063]
The hologram recording / reproducing apparatus 1 according to the present invention, through the above recording process, uses the second hologram recording medium 18 as a single hologram of a multiple recording hologram formed by superimposing all “pages” constituting a “chapter”. Then, the process returns to the first step again to multiplex-record a new “page” on the first hologram recording medium 8 and 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 using a means.
[0064]
When a new “chapter” is recorded on the first hologram recording medium 8, this “chapter” is reproduced in the second step. Then, the reproduction image of this “chapter” is incident on 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 incident angle of the reference light to the second hologram recording medium 18 is made different from that in the previous “chapter” recording, and a new “chapter” is added. Recording is performed on one 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.
[0065]
In the hologram recording / reproducing apparatus 1, the recording schedule in the third step is set so that each “chapter” multiplexed and recorded on the second hologram recording medium 18 has the same diffraction efficiency at the time of reproduction.
[0066]
For convenience of explanation, in the following explanation, a “chapter” composed of “pages” that are multiplexed and recorded with the same reference light is changed to a different reference light for each “chapter” on the second hologram recording medium 18. The entire hologram that is multiplexed and recorded using is called a “book”.
[0067]
In order to reproduce a desired “chapter” among the “books” in which a plurality of “chapter” is recorded on the second hologram recording medium 18 in the third step, the first shutter 5 and the second shutter Used when recording a “chapter” to be reproduced by emitting laser light from the light source 2 with the shutter 14 closed and the third shutter 15 open, adjusting the deflection angle by the second beam deflector 19 The same light as the reference light may be incident on the second hologram recording medium 18 as readout light. Hereinafter, this reproduction process is referred to as a fourth step.
[0068]
Lenses 20 and 21 for Fourier transforming the reproduced light are disposed on the optical path of the reproduced light reproduced in the fourth step. In the example shown in FIG. 1, the focal lengths of the lenses 20 and 21 are both f, the second hologram recording medium 18 is located on the focal plane of the lens 20, and the distance between the lens 20 and the lens 21 is 2f. I am doing so.
[0069]
In the fourth step, if the “chapter” selectively reproduced from the second hologram recording medium 18 is Fourier-transformed by the lens 20, the “chapter” selected on the reproduced image plane that is the focal plane of the lens 20 is obtained. A reproduced image is reproduced. However, as described above, the reproduction image of the “chapter” reproduced on this reproduction image plane is a state in which the reproduction images of all “pages” constituting the “chapter” are coherently superimposed and interfere with each other. Therefore, it is impossible to distinguish and read out each “page” from this image.
[0070]
Therefore, the hologram recording / reproducing apparatus 1 according to the present invention Fourier-transforms the reproduced image of the “chapter” reproduced on the reproduced image plane by the lens 21, and the Fourier-transformed image is the focal plane of the lens 21. Playback on the playback image plane. Here, the reproduction image plane which is the focal plane of the lens 21 is the Fourier transform plane of the spatial light modulator 7. Accordingly, parallel rays in different directions on the surface of the spatial light modulator 7 are condensed at different points on the reproduced image plane. Specifically, since the spatial light modulator 7 generally has a rectangular aperture in the shape of each pixel, the reproduced image reproduced on the reproduced image plane has diffracted light spread vertically and horizontally. Take a diffraction pattern.
[0071]
The hologram recording / reproducing apparatus 1 according to the present invention filters the diffracted light of a specific “page” component, including up to the positive and negative primary lights in the vertical and horizontal directions of the reproduced image, on the reproduced image plane that is the focal plane of the lens 21. A hologram extracting unit 22 is provided to extract a desired “page” from the “chapter” reproduced on the reproduction image plane by the hologram extracting unit 22. Hereinafter, the process of extracting the desired “page” is referred to as a fifth step.
[0072]
As the hologram extraction means 22 used in the fifth step, for example, an aperture whose opening is movable can be considered. That is, by using this aperture, only the desired “page” component is transmitted through the aperture from the entire diffraction pattern of the “chapter”, and the diffracted light of the other “page” is blocked, and the aperture is blocked. The diffracted light of the “page” component transmitted therethrough is Fourier-transformed again by the lens 23 disposed on the optical path, so that the image of the “page” can be restored to the rear focal plane of the lens 23. it can.
[0073]
If a detector array 24 such as a CCD is disposed on the rear focal plane of the lens 23, the “page” data extracted by the hologram extracting means 22 can be read.
[0074]
Here, for example, a liquid crystal shutter array 30 as shown in FIG. 2 may be used as an aperture whose opening is movable. The liquid crystal shutter array 30 is formed by arranging a large number of shutter arrays including an array of liquid crystal cells 31 on a filter surface. The liquid crystal cell 31 is the same as the liquid crystal cell used for a display panel or the like, and is obtained by sandwiching liquid crystal between two transparent substrates coated with an alignment film and a transparent electrode. Each of these liquid crystal cells 31 is provided with transistor elements and wirings that can drive each part independently. The liquid crystal shutter array 30 can individually control the light transmittance of each liquid crystal cell 31 by applying an electrical signal to each liquid crystal cell 31 from the outside. Here, the opening of each liquid crystal cell 31 has a shape and size capable of spatially selecting only a specific “page” of diffracted light.
[0075]
If only the transmittance of the liquid crystal cell 31 corresponding to the desired “page” is increased and the transmittance of the liquid crystal cell 31 of the other portion is lowered using the liquid crystal shutter array 30, as shown in FIG. , By transmitting only the desired “page” component from the diffraction pattern of the entire “chapter” through the opening of the liquid crystal cell 31 corresponding to this, and blocking the diffracted light of the other “page” Only the desired “page” can be selected and played back. The operation principle of each liquid crystal cell 31 constituting the liquid crystal shutter array 30 may be various, and various elements known as spatial light modulators such as a reflective liquid crystal display, an optical writing light valve, A micromachine such as a micromirror array using a microfabrication technique can be used.
[0076]
Further, as an aperture whose opening is movable, for example, a shutter device that mechanically moves the opening may be used in addition to the one that electrically moves the opening as in the liquid crystal shutter array 30 described above. Good.
[0077]
Further, 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 deflecting means 41 that makes the traveling direction of light such as a galvanometer mirror variable. A combination of these can be considered. In this case, on the optical path of the reproduction light reproduced in the fourth step, a lens 42 for converting the reproduction light into parallel light is provided instead of the lens 20. Then, a beam deflection unit 41 is disposed on the optical path of the reproduction light converted into parallel light by the lens 42. The beam deflecting means 41 scans the diffraction patterns of all “pages” belonging to “chapter” on the focal plane of the lens 21 disposed in the subsequent stage. An aperture 40 is disposed on the focal plane of the lens 21 where the diffraction patterns of all “pages” belonging to “chapter” are scanned.
[0078]
The aperture 40 is provided with, for example, an opening 43 that transmits only the diffracted light of one “page” selected from the diffraction pattern of the entire “chapter”. The aperture 40 is configured to block all diffracted light of “page” other than the selected “page”. Accordingly, the tail hologram extracting means 22 transmits only the desired “page” component from the diffraction pattern of the entire “chapter” deflected by the beam deflecting means 41 through the opening 43 of the aperture 40. , Only a desired “page” can be extracted from “chapter”.
[0079]
The hologram extracting unit 22 may be configured other than the above-described example as long as it can extract only a desired “page” from the “chapter”. You may be set as the structure combined.
[0080]
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 is shown in an enlarged manner in FIG. Moreover, the intensity distribution of the laser beam on each of the surfaces (a) to (g) in FIG. 5 is schematically shown in FIGS.
[0081]
In this hologram recording / reproducing apparatus 1, the laser light transmitted through the spatial light modulator 7 has a pattern as shown in FIG. 6A on the surface (a) in FIG. Further, the object light incident on the first hologram recording medium 8 has a pattern as shown in FIG. 6B on the surface (b) in FIG. Further, the reproduction light (object light) transmitted through the lens 16 has a pattern as shown in FIG. 6C on the surface (c) in FIG. Further, the object light incident on the second hologram recording medium 18 has a pattern as shown in FIG. 6D on the surface (d) in FIG. The reproduction light transmitted through the lens 20 has a pattern as shown in FIG. 6E on the (e) plane in FIG. Further, the reproduction light transmitted through the lens 21 has a pattern as shown in FIG. 6F on the (f) plane in FIG. Further, the reproduction light incident on the detector array 24 has a pattern as shown in FIG. 6G on the (g) plane in FIG.
[0082]
Here, since the object light (or reproduction light) of each “page” constituting the “chapter” is a light beam having a different incident angle, the Fourier plane (b) plane, (d) plane, (f) In the plane, spatially separated diffraction patterns are shown. Further, (c) is a reproduction image plane of the “chapter” recorded on the first hologram recording medium 8 and (f) is a reproduction image plane of the “chapter” recorded on the second hologram recording medium 18. On the surface, since all “pages” belonging to “chapter” are reproduced, a pattern in which all “pages” are coherently superimposed is observed. In the hologram recording / reproducing apparatus 1 according to the present invention, only a desired “page” is extracted from the reproduced image of “chapter” by the hologram extracting means 22, and only the component of this “page” is detected by the detector array 24. Therefore, only the selected “page” is observed on the (g) plane.
[0083]
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 serves as a main memory. Here, when m “pages” are recorded on the first hologram and copied to the second hologram n times, that is, n “chapter” consisting of m “pages” is defined as 1 “book”. 1 “book” is composed of (n × m) “pages”. At this time, the diffraction efficiency per “page” is 1 / (n ² Xm). The diffraction efficiency when multiple holograms are recorded with a normal recording schedule is 1 / (n ² × m ² Therefore, by recording and reproducing holograms with the hologram recording / reproducing apparatus 1 according to the present invention, the diffraction efficiency of each hologram can be increased to m times that when multiple recording is performed according to a normal recording schedule.
[0084]
Specifically, for example, when 1000 holograms are multiplexed and recorded with a normal recording schedule, the diffraction efficiency of one hologram is 10 ^-6 On the other hand, when 1000 holograms are recorded and reproduced as 100 “pages” and 10 “chapter” by the hologram recording / reproducing apparatus 1 according to the present invention, the diffraction efficiency of one hologram is 10 ^-Four It becomes. Therefore, by recording and reproducing 1000 holograms as described above using the hologram recording / reproducing apparatus 1 according to the present invention, the diffraction efficiency of one hologram is 100 times that obtained when multiple recording is performed according to a normal recording schedule. You can see that
[0085]
(Example using microlens array)
Next, a hologram recording / reproducing apparatus provided with 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 thereof is omitted.
[0086]
When a microlens array is used in the hologram recording / reproducing apparatus, the spot on the focal plane of each microlens is separated by changing the incident angle of light incident on the spatial light modulator 7 and displayed on the spatial light modulator 7. One image can be divided into a plurality of images.
[0087]
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, when a specific “page” is extracted in this example, filtering by the hologram extracting means 22 may be performed in units of pixels on the image plane of the microlens array.
[0088]
One structural example of a hologram recording / reproducing apparatus using a microlens array is shown in FIG. Here, only the portion for recording / reproducing with respect to the first hologram recording medium 8 will be described.
[0089]
In the hologram recording / reproducing apparatus 50 shown in FIG. 7, the laser light emitted from the light source 2 is converted into parallel light by the collimator lens 3, and then the optical path is branched by the first 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. To do. Although not shown here, reference light to be incident on the second hologram recording medium is obtained by disposing the second beam splitter on the optical path of the laser light reflected by the folding mirror 12. be able to.
[0090]
The laser beam that has passed through the first beam splitter 4 is deflected at a predetermined deflection angle by a first beam deflector 6 such as a galvanometer mirror, and the traveling direction is controlled. The laser light whose traveling direction is controlled by the first beam deflector 6 is incident on the spatial light modulator 7 at a different incident angle for each “page”. The laser beam modulated according to the image displayed on the spatial light modulator 7 is used as object light.
[0091]
In this hologram recording / reproducing apparatus 50, a microlens array 51 is disposed on the emission side of the spatial light modulator 7. Accordingly, the object light that has been transmitted through the spatial light modulator 7 and modulated according to the image displayed on the spatial light modulator 7 is condensed by a different microlens element for each pixel of the spatial light modulator 7. The 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. As a result, the object light collected by the microlens element interferes with the reference light incident on the first hologram recording medium 8 at a predetermined incident angle in the first hologram recording medium 8, and the microlens element The image of the spot condensed by the above can be recorded on the first hologram recording medium 8 as a “page”.
[0092]
The hologram recording / reproducing apparatus 50 performs 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 by changing the deflection angle by the first beam deflector 6. Repeatedly, a plurality of “pages” are multiplexed and recorded on the first hologram recording medium 8.
[0093]
The hologram recording / reproducing apparatus 50 using the microlens array 51 has the following characteristics as compared with the hologram recording / reproducing apparatus 1 described above. In other words, the reproduced image obtained by Fourier transforming the reproduced light of the hologram recorded on the first hologram recording medium 8 by the hologram recording / reproducing apparatus 50 is an image of the focal plane of the microlens array 51. Therefore, if the angular interval of the laser light incident on the spatial light modulator 7 is set sufficiently large when recording different “pages”, each pixel is separated on the reproduced image plane as shown in FIGS. If a detector array such as a CCD is disposed on the reproduction image plane, a high-definition image can be reproduced.
[0094]
However, a reproduced image obtained by performing Fourier transform again on the hologram reproduction light recorded on the first hologram recording medium 8 by the hologram recording / reproducing apparatus 50 using the microlens array 51 is as shown in FIG. This is an image in which pixels of different “pages” are adjacent to each other, and pixels of the same “page” are periodically distributed. Therefore, in order to reproduce the original “page”, similar to the hologram recording / reproducing apparatus 1 described above, the “chapter” images recorded on the first hologram recording medium 8 are reproduced in batch, This image is rearranged to the original “page” by performing electrical signal processing with software.
[0095]
Conversely, data to be recorded at the time of recording may be processed so that a desired reproduced image is finally obtained. In this way, if the recording data is processed so that a desired reproduced image is finally obtained, this hologram recording / reproducing apparatus 50 can be used as an image display apparatus. The display device disclosed in Japanese Patent Laid-Open No. 7-36040 has a problem that high speed operation is required for the spatial light modulator because all the 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, the hologram recording / reproducing apparatus 50 can increase the number of pixels of the spatial light modulator 7 by “page” several times, so that it can be used for a high-definition still image display apparatus or a three-dimensional image display.
[0096]
Next, a case where 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 for each “page” will be described. A portion from the spatial light modulator 7 to the detector array 24 of the hologram recording / reproducing apparatus 50 is shown in FIG. In this hologram recording / reproducing apparatus 50, a microlens array 52 is provided in place of the lens 21 used in the hologram recording / reproducing apparatus 1 described above, and an angle-dependent filter 53 is used as the hologram extracting means 22. It is characterized by having.
[0097]
As described above, in this hologram recording / reproducing apparatus 50, an image of a spot that is transmitted through the spatial light modulator 7 and condensed by the microlens array 51 for each pixel of the spatial light modulator 7 is referred to as a “page”. It is recorded on the first hologram recording medium 8. Then, the above recording process is repeated using the same reference light while changing the incident angle of the laser light incident on the spatial light modulator 7, whereby a plurality of “pages” are recorded on the first hologram recording medium 8. Are recorded multiple times.
[0098]
By making the same light as the reference light used at the time of recording enter the first hologram recording medium 8 as a readout light, all “pages” that are multiplexed and recorded on the first hologram recording medium 8, that is, “chapters”. Images are played back together. The reproduced light passes through the lens 16 and the lens 17 and then enters the second hologram recording medium 18 as object light.
[0099]
By making the object light and the reference light interfere with each other in the second hologram recording medium 18, “chapter” is copied and recorded on the second hologram recording medium 18. The above-described recording process is repeated using reference light whose incident angle has been changed for each reproduction “chapter”, whereby a plurality of “chapter” is recorded on the second hologram recording medium 18 by a multiplexing method such as angle multiplexing. Are recorded multiple times.
[0100]
When reproducing a desired “chapter” from the second hologram recording medium, the same light as the reference light used for recording the “chapter” is incident on the second hologram recording medium 18 as readout light. Thereby, desired “chapter” is collectively reproduced from the second hologram recording medium 18. When the reproduction light is Fourier transformed by the lens 20, all “page” images included in the “chapter” are superimposed on the focal plane of the lens 20 and reproduced.
[0101]
The hologram reproducing device 50 converts each spot of the reproduced image into parallel light traveling at different angles for each “page” by the microlens array 52 which is focused on the reproduced image plane on the focal plane of the lens 20. The microlens array 52 is arranged so 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 with the light incident on the spatial light modulator 7 at different incident angles as the object light has different traveling directions.
[0102]
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 apparatus 50 selectively reflects or transmits the reproduction light of each hologram by the angle-dependent filter 53 so that only the component having one traveling direction is extracted from the reproduction light of each hologram. ing.
[0103]
The component of the reproduction light extracted by the angle-dependent filter 53 is one “page” component. This one “page” component is transmitted through the lens 23 to form an image of the exit surface of the microlens. Then, the “page” data extracted by the angle-dependent filter 53 is read by the detector array 24 such as a CCD disposed on the image plane.
[0104]
The hologram recording / reproducing apparatus 50 repeats the above reproduction process by, for example, rotating the angle-dependent filter 53 or changing the selected angle of the angle-dependent filter 53 to change the desired value in the “chapter”. The “pages” can be separated and taken out one after another.
[0105]
Here, as the angle-dependent filter 53, an optical element using principles such as total reflection, Bragg diffraction, interference in a multiple reflection thin film, and a fine structure with a wavelength or less can be used. Examples of optical elements using Bragg diffraction include acousto-optic elements and volume holograms. In addition, a diffraction grating or a photonic crystal having a structure of a wavelength or less has resonance diffraction efficiency and transmittance for a specific wavelength and a specific incident angle, which can be used. Of these, a plurality may be used in combination.
[0106]
(Other variations)
In the hologram recording / reproducing apparatus 1 and the hologram recording / reproducing apparatus 50 described above, two hologram recording media of the first hologram recording medium 8 and the second hologram recording medium 18 are used. The hologram recording / reproducing apparatus is not limited to the above example, and two or more hologram recording media may be used. For example, the hologram recording / reproducing apparatus can improve the recording speed when a plurality of first hologram recording media 8 are installed in parallel. Further, the hologram recording / reproducing apparatus can improve the diffraction efficiency by repeating hologram recording media by arranging hologram recording media in series.
[0107]
In the hologram recording / reproducing apparatus 1 and the hologram recording / reproducing apparatus 50 described above, the same light is used as the reference light at the time of hologram recording on the first hologram recording medium 8, but the hologram according to the present invention is used. The recording / reproducing apparatus is not limited to the above example, and each “page” is recorded with a different reference light, and the same light as the reference light is simultaneously read as reading light, as in the normal angle multiplex recording. It may be incident on the first hologram recording medium 8 and all holograms may be reproduced collectively. In this case, since a means for generating a plurality of different reference beams is required, the structure is complicated. With such a configuration, only a specific page is selectively copied and recorded on the second hologram 18. be able to.
[0108]
Further, the first hologram recording medium 8 and the second hologram recording medium 18 do not need to 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, a material capable of two-wavelength recording such as Pr: LiNbO3, Pr: LiTaO3 is used, and a short wavelength light beam is irradiated only during recording. It is also possible to realize non-destructive reproduction by so-called two-wavelength gate recording (see USP 5665493 Bai et al, YS Bai and R. Kachru, Phys. Rev. Lett, 78, 2944, 1997). In addition, when a photopolymer is used as the hologram recording medium, a hologram that is stable for a long time and can be stored for a long time can be recorded. Therefore, as a material for the first hologram recording medium 8, a material such as a photorefractive crystal having high diffraction efficiency and high recording sensitivity is used, even if it is not suitable for long-term storage, and a material for the second hologram recording medium 18 is used. If a material that can be stored for a long time, such as a photopolymer, is used, a hologram recording / reproducing system that makes use of the advantages of the two materials while compensating for each other can be constructed.
[0109]
In particular, when a photopolymer is used as the hologram recording medium, it is effective to change the shape of the hologram recording medium to a disk shape as shown in FIG. By processing the hologram recording medium into a disk structure similar to that of an optical disk and rotating it, another hologram can be written at different positions on the hologram recording medium and handling is easy. Further, for multiplexing, this can be substituted by rotating the disk without using beam deflecting means such as a beam deflector. When multiplex recording is performed on a hologram recording medium having such a shape, shift multiplex recording or peritropic multiplex recording is effective.
[0110]
The hologram recording / reproducing apparatus 60 shown in FIG. 13 uses a bulk photorefractive crystal as the first hologram recording medium 8. Then, holograms are multiplexed and recorded on the first hologram recording medium 8 made of the photorefractive crystal by angle multiplexing. The hologram recording / reproducing apparatus 60 uses a second hologram recording medium 18 in which a photopolymer is applied in a layered manner on the disk surface. Then, holograms are multiplexed and recorded on the disk-shaped second hologram recording medium 18 by shift multiplexing. Since the other configuration of the hologram recording / reproducing apparatus 60 is almost the same as that of the hologram recording / reproducing apparatus 1 described above, the same components are denoted by the same reference numerals and description thereof is omitted.
[0111]
In the hologram recording / reproducing apparatus 1 and the hologram recording / reproducing apparatus 50 described above, the case of using the angle multiplexing method as the multiplex recording method of the second hologram recording medium 18 has been described. The apparatus is not limited to the above example, and other multiple recording methods may be used. That is, in addition to the shift multiplexing method, the peritropic multiplexing method, the phase code multiplexing method, and the like, which are considered to be modifications of the angle multiplexing method, the wavelength multiplexing method, the spatial multiplexing method, the fractal multiplexing method, etc. 18 can be used for hologram recording. Moreover, you may employ | adopt the multiplexing system which combined some of these. However, in the case of using the wavelength multiplexing method, it is necessary to use a different wavelength for each “chapter” at the time of hologram recording on the first hologram recording medium 8 in order to perform reproduction using the same reference light.
[0112]
Further, it is known that the object light is also reproduced in the opposite direction when the conjugate light that has the same wavefront as the reference light at the time of recording and propagates in the opposite direction is used as the reference light at the time of hologram reproduction. 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 by utilizing this phenomenon (phase conjugation).
[0113]
An example of the configuration of a hologram recording / reproducing apparatus using phase conjugation is shown in FIG. The hologram recording / reproducing apparatus 70 shown in FIG. 14 emits laser light 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 enters the first beam splitter 73. A part of the laser light incident on the first beam splitter 73 is transmitted through the first beam splitter 73 and the other part is reflected by the first beam splitter 73.
[0114]
The laser light transmitted through the first beam splitter 73 is incident on a second beam splitter 74 disposed on the optical path. 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.
[0115]
The laser light transmitted through the second beam splitter 74 is incident on a third beam splitter 75 disposed on the optical path. A part of the laser light incident on 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.
[0116]
The laser light 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, light that has passed through the spatial light modulator 77 and is modulated according to the image displayed on the spatial light modulator 77 is used as object light. The object light passes through the fourth beam splitter 78, is Fourier-transformed by the lens 79, and then enters the first hologram recording medium 80 at an incident angle corresponding to the deflection angle by the first beam deflector 76.
[0117]
On the other hand, the laser beam reflected by the second beam splitter 74 is reflected by the first mirror 81 and the second mirror 82 and enters the first hologram recording medium 80 at a predetermined incident angle. As a result, the object light and the reference light interfere in the first hologram recording medium 80, and a hologram (“page”) is recorded on the first hologram recording medium 80.
[0118]
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 multiplexly records a plurality of “pages” on the first hologram recording medium 80.
[0119]
Here, the laser beam reflected by the third beam splitter 75 is reflected by the third mirror 83 and the fourth mirror 84 and then enters the first hologram recording medium 80. Since this laser light is conjugate light having the same wavefront as that of the reference light and propagating in the opposite direction, if the conjugate light of this reference light is used as readout light, a plurality of multiplex recordings on the first hologram recording medium 80 are performed. The “page” (“chapter”) is reproduced at once, and this reproduced light is emitted from the side of the first hologram recording medium 80 where the object light is incident.
[0120]
The reproduced light is Fourier transformed by the lens 79, reflected by the fourth beam splitter 78, and incident on the fifth beam splitter 85. Then, after the reproduction light transmitted through the fifth beam splitter 85 is Fourier-transformed by the lens 86, it enters the second hologram recording medium 87 at a predetermined incident angle as object light.
[0121]
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 hologram recording is performed at an incident angle corresponding to the deflection angle by the second beam deflector 88. The light enters the medium 87 as reference light. 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 is copied to the second hologram recording medium 87. To be recorded.
[0122]
The hologram recording / reproducing apparatus 70 repeatedly performs 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 multiplex or the like. Copy and record on the second hologram recording medium 87 by the multiplexing method.
[0123]
The laser light incident as the reference light on the second hologram recording medium 80 is reflected by the fifth mirror 89 disposed on the optical path after passing through the second hologram recording medium 80. Then, the laser beam reflected by the fifth mirror 89 is incident on the second hologram recording medium 87 again. This laser light is conjugate light that has the same wavefront as the reference light and propagates in the opposite direction. Therefore, if this laser beam is used as the readout beam, the hologram recorded in a multiplexed manner on the second hologram recording medium 87 is selectively reproduced, and this reproduced beam is incident on the side on which the object beam of the second hologram recording medium 87 is incident. It will be emitted from.
[0124]
The reproduced 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 subjected to Fourier transform again by the lens 90 and then enters the hologram extraction means 91. The hologram extracting unit 91 extracts only a specific “page” component from the “chapter” read from the second hologram recording medium 87.
[0125]
The light of a specific “page” component extracted by the hologram extracting means 91 is subjected to Fourier transform again by the lens 92 and then received by a detector array 93 such as a CCD. As a result, data of a desired “page” can be read from the “chapter” read from the second hologram recording medium 87.
[0126]
In the above, an example of recording a hologram 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, and other examples such as an image hologram, a Fresnel hologram, etc. It may be configured to record a hologram. Further, the example of recording / reproducing a transmission hologram has been described above. However, the hologram recording / reproducing apparatus according to the present invention is not limited to this example, and is configured to record / reproduce a reflection hologram. May be.
[0127]
Further, the method of the present invention is not applied only to the information recording / reproducing apparatus and the image display apparatus, but can be widely applied to other apparatuses utilizing the principle of hologram recording / reproducing. For example, the method of the present invention can be applied to a correlation calculator, 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]
【The invention's effect】
According to the hologram recording / reproducing apparatus of the present invention, the holograms multiplexed and recorded on the first hologram recording medium by the first recording means are collectively reproduced by the first reproducing means, and the collectively reproduced multiplexed data are reproduced. Since a plurality of recording holograms are multiplexed and recorded on the second hologram recording medium by the second recording means, the multiplexing when the final diffraction efficiency per hologram is multiplexed and recorded on the first hologram recording medium The number can be doubled. As a result, it is possible to avoid a decrease in diffraction efficiency due to multiplex recording of holograms, improve the S / N ratio, and increase the amount of recorded information.
[0129]
Further, according to this hologram recording / reproducing apparatus, the holograms multiplexed and recorded on the first hologram recording medium by the first recording means are reproduced collectively by the first reproducing means, so that they are reproduced at a time. The amount of information contained per hologram is large, and the access speed is improved.
[0130]
Further, according to this hologram recording / reproducing apparatus, since the holograms multiplexed and recorded on the first hologram recording medium by the first recording means are reproduced collectively by the first reproducing means, a large amount of space can be obtained at one time. Information can be displayed. Therefore, this hologram recording / reproducing apparatus can be used as a display apparatus for high-definition still images and three-dimensional images.
[0131]
Further, according to the hologram recording / reproducing method of the present invention, the holograms that are multiplexed and recorded on the first hologram recording medium in the first step are reproduced in a lump in the second step, and this lump-reproduced multiplexed Since a plurality of recording holograms are multiplexed and recorded on the second hologram recording medium in the third step, the number of recording holograms when the final diffraction efficiency per hologram is multiplexed and recorded on the first hologram recording medium Can be doubled. As a result, it is possible to avoid a decrease in diffraction efficiency due to multiplex recording of holograms, improve the S / N ratio, and increase the amount of recorded information.
[0132]
Further, according to this hologram recording / reproducing method, the holograms multiplexed and recorded on the first hologram recording medium in the first step are reproduced collectively in the second step, so that the hologram 1 reproduced at a time The amount of information contained per sheet is large, and the access speed is improved.
[0133]
In addition, according to this hologram recording / reproducing method, the holograms multiplexed and recorded on the first hologram recording medium in the first step are reproduced collectively in the second step. Can be displayed, so that a high-definition still image or three-dimensional image can be displayed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a 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 extraction means.
FIG. 3 is a schematic diagram illustrating 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 an aperture fixed 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.
6 is a diagram showing an intensity distribution of laser light on the planes (a) to (g) in FIG. 5, (a) showing a pattern on the (a) plane in FIG. 5, and (b) in FIG. (B) shows a pattern on the plane, (c) shows a pattern on the (c) plane in FIG. 5, (d) shows a pattern on the (d) plane in FIG. 5, and (e) shows (e) in FIG. ) Surface pattern, (f) shows the pattern on the (f) surface in FIG. 5, and (g) shows the pattern on the (g) surface in FIG.
FIG. 7 is a schematic diagram showing a portion for recording / reproducing with respect to a first hologram recording medium of a hologram recording / reproducing apparatus using a microlens array.
FIG. 8 is a schematic diagram for explaining how the spot of each pixel of the spatial light modulator is separated on the reproduced image plane by the microlens array.
FIG. 9 is a side view showing a state where spots of each pixel of the spatial light modulator are separated on the reproduced image plane by the microlens array.
10 is a plan view showing a state of a reproduction image plane in FIG. 9. FIG.
FIG. 11 is a view showing a reproduced image obtained from the reproduced light of the hologram recorded on the first hologram recording medium by the hologram recording / reproducing apparatus using the 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 photorefractive crystal as a first hologram recording medium and a layer formed by applying a photopolymer in a layered manner on a disk surface as a second hologram recording medium. FIG.
FIG. 14 is a schematic diagram showing a configuration example of a hologram recording / reproducing apparatus using phase conjugation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hologram recording / reproducing apparatus, 2 Light source, 6 1st beam deflector, 7 Spatial light modulator, 8 1st hologram recording medium, 18 2nd hologram recording medium, 19 2nd beam deflector, 22 Hologram extraction means, 24 Detector array

Claims (16)

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 the object light each time one hologram is recorded;
First reproducing means for collectively reproducing a plurality of holograms multiplexed and recorded on the first hologram recording medium by the first recording means;
Using the reproduction light of a plurality of holograms collectively reproduced by the first reproduction means as object light, the multiple recording hologram formed by superimposing the plurality of holograms into a single hologram using different reference lights A second recording means for performing multiple recording on a second recording medium;
And a second reproducing means for selectively reproducing a desired multiplex recording hologram among a plurality of multiplex recording holograms multiplex-recorded on the second hologram recording medium by the second recording means. Hologram recording / reproducing apparatus. 2. The hologram recording / reproducing apparatus according to claim 1, further comprising hologram extracting means for extracting a desired hologram from a plurality of holograms constituting the multiplex recording hologram reproduced by the second reproducing means. The hologram extraction means extracts a desired hologram by filtering the reproduction light of the multiplex recording hologram reproduced by the second reproduction means on the Fourier plane of the image using a spatial aperture. The hologram recording / reproducing apparatus according to claim 2. The hologram extraction means extracts a desired hologram by selectively transmitting or reflecting the reproduction light of the multiplex recording hologram reproduced by the second reproduction means by an element having an angle dependency. The hologram recording / reproducing apparatus according to claim 2. 2. The hologram recording / reproducing apparatus according to claim 1, wherein a rewritable hologram recording material is used as the first hologram recording medium, and a hologram recording material capable of recording only once is used as the second hologram recording medium. . 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, and light incident on the spatial light modulator. The spot on the focal plane of each of the microlenses is separated by changing the incident angle of the first lens, and one image displayed on the spatial light modulator is divided into a plurality of images as a plurality of holograms. Multiplex recording and
2. The hologram recording according to claim 1, wherein the second reproducing means reproduces a multiplex recording hologram formed by superimposing a plurality of holograms obtained by dividing one image displayed on the spatial light modulator. Playback device. 7. The hologram recording / reproducing apparatus according to claim 6, further comprising display means for displaying the multiplex recording hologram reproduced by the second reproducing means as one image. 7. The hologram recording / reproducing apparatus according to claim 6, further comprising hologram extracting means for extracting a desired hologram from a plurality of holograms constituting the multiplex recording hologram reproduced by the second reproducing means. 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 the object light every time one hologram is recorded;
A second step of collectively reproducing a plurality of holograms recorded in a multiplexed manner on the first hologram recording medium in the first step;
Using the reproduced light of the plurality of holograms collectively reproduced in the second step as object light, the multiple recording hologram formed by superimposing the plurality of holograms into one hologram is obtained using different reference lights. A third step of multiple recording on the two recording media;
And a fourth step of selectively reproducing a desired multiplex recording hologram among a plurality of multiplex recording holograms multiplex-recorded on the second hologram recording medium in the third step. Recording and playback method. 10. The hologram recording / reproducing method according to claim 9, wherein a fifth step of extracting a desired hologram from a plurality of holograms constituting the multiplex recording hologram reproduced in the fourth step is performed. The fifth step is characterized in that a desired hologram is extracted by filtering the reproduction light of the multiple recording 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. In the fifth step, a desired hologram is extracted by selectively transmitting or reflecting the reproduction light of the multiplexed recording hologram reproduced in the fourth step by an element having an angle dependency. The hologram recording / reproducing method according to claim 10. 10. The hologram recording / reproducing method according to claim 9, wherein a rewritable hologram recording material is used as the first hologram recording medium, and a hologram recording material capable of recording only once is used as the second hologram recording medium. . In the first step, using 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 light incident on the spatial light modulator is The spot on the focal plane of each microlens is separated by changing the incident angle, and one image displayed on the spatial light modulator is divided into a plurality of images to form a plurality of holograms on the first recording medium. Multiplex recording,
10. The hologram recording / reproducing according to claim 9, wherein, in the fourth step, a multiplex recording hologram obtained by superimposing a plurality of holograms obtained by dividing one image displayed on the spatial light modulator is reproduced. Method. 15. The hologram recording / reproducing method according to claim 14, wherein the multiplex recording hologram reproduced in the fourth step is displayed as one image. 15. The hologram recording / reproducing method according to claim 14, further comprising a fifth step of extracting a desired hologram from a plurality of holograms constituting the multiplex recording hologram reproduced in the fourth step.

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