JP2002207412A - Holographic recording method and device for the same, holographic reproducing method and device for the same as well as holographic recording and reproducing method and device for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a holographic reproducing device which permits use of a high-numerical aperture lens by using conjugation reading-out and is capable of reproducing images recorded with high resolution. SOLUTION: The holographic reproducing device has a holographic recording medium 35, an image element 45, such as the lens, a detector 60, conjugation reading-out beam forming means 44 for forming a conjugation reading-out beam 42 and signal reproducing means 63 for reproducing the signal detected by the detector 60 to digital data. The recording medium 35 is irradiated from the image element 45 with the conjugation reading-out beam 42 emitted form reference beam providing means 43 for reproduction. As a result, the real image 57 is formed between the recording medium 35 and the image element 45. The signal beam 50 rebuilt by the image element 45 is imaged on the detector 60. The information detected by the detector 60 is reproduced to the original digital data recorded at the recording medium 35 by the signal reproducing means 63.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for storing and reproducing data using a hologram, and more particularly, to recording a hologram on a holographic recording medium,
The present invention relates to a method and an apparatus for reading a hologram.

[0002]

2. Description of the Related Art A hologram is obtained by adding a reference wavefront to a wavefront reflected or transmitted from an object, and recording the intensity distribution of interference fringes generated by causing the wavefronts to interfere with each other on a recording material (photosensitive material). The general principle of a hologram will be described with reference to FIGS.

FIG. 1 is a block diagram of an apparatus showing an operation of recording data on a hologram. In FIG. 1, light having good coherence from a light source passes through a half mirror and is applied to a target object (object). Diffracted light (signal wave) transmitted through the object is transmitted from the same light source through the half mirror and the mirror. A hologram is formed by causing the interference with the reference wave directly obtained and recording the interference fringes on the photosensitive material.

FIG. 2 is a block diagram of an apparatus for reading data from a hologram on which data has been recorded by the above method. FIG.
In the above, when the hologram is irradiated with another light wave (reproduction illumination light), the reproduction light corresponding to the signal wave is emitted from the hologram by the diffracted light, and the image of the object can be reproduced. In the case of an opaque object, the reflected light becomes a signal wave.
For a target object having a dimensional structure, a three-dimensional image is reproduced.

Various uses of such a hologram are being studied. Hereinafter, an outline of a holographic memory using a hologram as a memory will be described. When data is recorded in the holographic memory, the digital data is converted into a two-dimensional light and dark dot pattern, and this is stored as an object in a hologram by adding an appropriate reference wave. When reading data from the holographic memory, irradiating the same hologram with the same wave as the reference wave,
Since the original dot pattern image is reproduced from the hologram, the image is detected by a photodetector arranged in a two-dimensional matrix, and the signal detected by the electronic circuit is processed. Can be played.

In principle, such a holographic memory has the advantages of short access time, suitable for high-density recording, and high redundancy. However, there are many problems to be overcome when the holographic memory is put into practical use.

In a data storage / readout system (architecture) using a hologram, usually, a large number of data are stored in at least one or a plurality of locations in a storage medium (holographic recording medium, holographic memory) using a hologram. Contains page data.

[0008] Data of different pages can be multiplexed into a single location in the holographic recording medium by changing the characteristics of the reference beam used to store the hologram, eg, the angle of incidence or wavelength of the reference beam. As a multiplexing method, typically, a two-dimensional spatial light modulator (SLM: Spatial Ligh) such as a liquid crystal display panel is used.
The information to be recorded is imprinted into a single beam (t Modulator).

In order to read out the stored hologram, a desired hologram is searched (irradiated) using a read reference beam having the same characteristics as the reference beam used for storage, and the hologram is reconstructed from the hologram. Retrieve the optical information of the data page. The optical information is detected by using a two-dimensional detection array device, and further subjected to signal processing and read out as digital data.

[0010]

SUMMARY OF THE INVENTION The holographic memory described above, however, encounters many of the limitations described below.

[0011] The recording density of each data page in a hologram is limited by the pixel size and pitch specified by an optical modulator (SLM) used for data recording and a two-dimensional detection array device used for reading data. Therefore, in order to compensate for the limitation and realize a holographic recording medium (holographic memory) with high density recording, it is necessary to multiplex a large number of holograms at each location of the holographic recording medium. Become. However, the volume occupied by each hologram in the holographic recording medium depends on the multiplexing method used for data recording and the spatial location in the holographic recording medium and the amount of overlapping locations. Changes according to the effective number of holograms multiplexed at each position in the holographic recording medium. Both of these factors, i.e., the multiplexing method and the amount of location overlap, are different for different holograms in the holographic recording medium and for different pixels in one hologram in the holographic recording medium. This leads to uneven strength. As a result of the non-uniform intensity, complex compensation techniques are required to reduce the likelihood of read errors when reading data from a holographic recording medium. If the spatial locations do not overlap in the holographic storage medium, the dynamic range is lost in the unused material located between the discrete locations in the holographic storage medium.

As another disadvantage, there is not yet a feasible method for reproducing data at high speed in a holographic recording medium in which data is recorded as a hologram by such a holographic recording / reproducing apparatus. Each hologram must be recorded continuously for each multiplexed page and at each spatial location in the holographic recording medium. In such a case, in order to obtain a hologram of uniform intensity, a very complicated irradiation operation must be repeated at each location.

The present inventor has filed Japanese Patent Application No. 11-310394.
No. (filing date, July 1, 1999) proposes a new holographic recording / reproducing method that overcomes the above disadvantages. However, Japanese Patent Application No. 11-310
The reading method proposed in Japanese Patent No. 394 has a problem that the quality of an image read from the hologram is reduced when the thickness of the hologram recording medium is large.

Further, when the thickness of the holographic recording medium is large, there are disadvantages in that the irradiation conditions of the reference light beam are restricted and the size of the apparatus becomes large due to the spatial limitation between the optical elements.

An object of the present invention is to overcome the above-mentioned disadvantages of the reading method proposed in Japanese Patent Application No. 11-310394, as well as to overcome the above-mentioned disadvantages, and to provide a more practical holographic recording / reproducing method. And to provide the device. The object of the present invention will be described below more specifically.

A first object of the present invention is to limit only the optical resolution without being limited by the resolution of an optical modulator (SLM) used for recording data and a two-dimensional detection array device used for reading data. Holographic recording, and / or that the pixel size can be defined to increase the density of the data page to be read
It is an object of the present invention to provide a reproducing method (hereinafter abbreviated as a holographic recording / reproducing method) and an apparatus therefor.

A second object of the present invention is to provide a holographic recording / reproducing method and apparatus capable of reconstructing a hologram with high reliability even if the hologram has a large thickness.

A third object of the present invention is to provide an image element for reading out an image on the same side as an image element such as a lens without enlarging a space through which a reference light beam irradiated to the hologram passes or a range of the reference light beam. It is another object of the present invention to provide a holographic recording / reproducing method and apparatus which can use an image element having a large numerical aperture.

A fourth object of the present invention is to provide a holographic recording / reproducing method and apparatus capable of reproducing at a high spatial frequency in a read image even when the recording material of the hologram is double refracted. is there.

[0020]

According to a first aspect of the present invention, there is provided a parallel light emitting means for emitting parallel light, and a spatial light modulating means for modulating the parallel light emitted from the parallel light emitting means. , A first surface and a second surface opposite to the first surface, and the spatial light modulating means is located at a position facing the spatial light modulating means such that the light modulated by the spatial light modulating means is received by the first surface. A holographic recording medium arranged in parallel with
Recording holographic recording medium comprising: a holographic recording medium having recording reference light emitting means for irradiating a second surface of the holographic recording medium opposite to the first surface receiving the modulated light with recording reference light; A holographic recording device configured to record, as a hologram, an interference fringe generated by causing the modulated light irradiated on the second surface to interfere with the recording reference light irradiated on the second surface.

[0021] Preferably, the recording reference light emitting means changes an incident angle of the recording reference light on the second surface of the holographic recording medium. Also preferably,
The recording reference light emitting means changes the wavelength of the recording reference light. More preferably, the recording reference light emitting means changes the wavelength of the recording reference light and the angle of incidence on the second surface of the holographic recording medium.

Preferably, the spatial light modulating means is configured as a disk-shaped flat plate, the holographic recording medium is configured as a disk-shaped flat plate, and the spatial light modulating means and the holographic recording medium are rotated. Driven by driving means, the parallel light emitting means and the recording reference light emitting means are mounted on a radial direction moving means capable of moving in the radial direction of the holographic recording medium, and the spatial light modulating means is The parallel light is modulated according to digital data to be recorded on the holographic recording medium.

According to a second aspect of the present invention, the parallel light is modulated according to data to be recorded on the holographic recording medium, and the modulated light is irradiated on the first surface of the holographic recording medium, The second surface of the holographic recording medium opposite to the first surface receiving the modulated light is irradiated with the recording reference light, and the modulated light and the recording reference light interfere with each other in the holographic recording medium. A holographic recording medium that forms a hologram corresponding to the data to be recorded on the holographic recording medium.

[0024] Preferably, the wavelength of the reference light for recording applied to the second surface of the holographic recording medium and / or the angle of incidence on the second surface of the holographic recording medium is changed.

According to a third aspect of the present invention, the parallel light is modulated according to data to be recorded on the holographic recording medium, and the modulated light is irradiated on the first surface of the holographic recording medium, The second surface of the holographic recording medium opposite to the first surface receiving the modulated light is irradiated with the recording reference light, and the modulated light and the recording reference light interfere with each other in the holographic recording medium. A holographic reproduction device that reads the hologram from the holographic recording medium on which the hologram corresponding to the data to be recorded is recorded and reproduces the data,
Reproduction reference light emitting means for irradiating a conjugate readout light conjugate to the recording reference light on the first surface of the holographic recording medium, and a real image is formed on the first surface side of the holographic recording medium. An imaging means arranged on the first surface side of the holographic recording medium at a predetermined distance from the holographic recording medium, and a position where the signal light reconstructed by the imaging means is refocused. Arranged,
A holographic playback device comprising: a detector for detecting the signal light reconstructed from the above.

Preferably, the reproducing reference light emitting means changes the wavelength of the conjugate read light and / or the angle of incidence on the first surface of the holographic recording medium.

Preferably, the holographic recording medium is configured as a disk-shaped flat plate, and the reproducing reference light emitting means and the reproducing reference light emitting means are mounted on a radial direction moving means capable of moving in the radial direction of the holographic recording medium. Have been.

According to a fourth aspect of the present invention, parallel light is modulated in accordance with data to be recorded on a holographic recording medium, and the modulated light is irradiated on a first surface of the holographic recording medium, The second surface of the holographic recording medium opposite to the first surface receiving the modulated light is irradiated with the recording reference light, and the modulated light and the recording reference light interfere with each other in the holographic recording medium. A holographic reproduction method for reading out the hologram from the holographic recording medium on which the hologram corresponding to the data to be recorded is recorded and reproducing the data,
(A) irradiating the first surface of the holographic recording medium with a conjugate reading light conjugate with the recording reference light, and (b) forming a real image on the first surface side of the holographic recording medium. A hologram image from the holographic recording medium is formed by an image forming means arranged on the first surface side of the holographic recording medium at a predetermined distance from the holographic recording medium; A holographic reproduction method is provided, comprising detecting the signal light with a detector arranged at a position where the signal light reconstructed by the means is refocused.

Preferably, the wavelength of the conjugate readout light is
And / or a first holographic recording medium.
Change the angle of incidence on the surface.

According to a fifth aspect of the present invention, there is provided a holographic recording / reproducing method for recording information on a hologram on a holographic recording medium and reading information from the hologram on the holographic recording medium. Various steps, that is, (a) irradiating a selected spot on the holographic recording medium with a signal light and a recording reference light modulated using data to record a hologram on the holographic recording medium;
(B) generating a read reference light having a substantially conjugate relationship with the recording reference light beam, and (c) irradiating the hologram with the generated read reference light to generate a holographic part. It is reconstructed as a real image on the same side as the read detection device arranged at a certain distance from the recording medium, and as a result, the real image and the read detection device to be sufficiently separated from the holographic recording medium A holographic recording / reproducing method is provided, comprising steps for positioning an imaging means therebetween.

Preferably, the method further comprises the step of moving the read reference light with respect to the holographic recording medium.

Preferably, the hologram is recorded on the holographic recording medium by changing the incident angle of the recording reference light applied to the holographic recording medium with respect to each of a plurality of holograms. The hologram is reconstructed by irradiating the reading light at the same angle as the incident angle used for recording.

Preferably, the plurality of holograms have different wavelengths of the signal light and different wavelengths of the recording reference light applied to the holographic recording medium with respect to each hologram of the plurality of holograms. The hologram is recorded on the graphic recording medium, and the hologram is reconstructed by changing the wavelength of the read reference light.

According to a sixth aspect of the present invention, data is recorded over substantially the entire surface of a disk-shaped holographic recording medium as a single continuous hologram, and as a result, the data portion is A holographic recording / reproducing method that can be reconstructed by irradiating an appropriate reading reference beam, comprising the following steps:
(A) irradiating a selected spot on the holographic recording medium with a plane wave of signal light and recording reference light modulated using data, and recording a hologram by the interference fringes; Generating conjugate read reference light having substantially the same properties as light, and (c) illuminating the hologram with the read reference light to reconstruct the data portion as an image. A holographic recording / reproducing method is provided.

Preferably, the method further comprises the step of moving the read reference light with respect to the holographic recording medium.

Preferably, a plurality of holograms are recorded on the holographic recording medium by making incident angles of the recording reference light applied to the holographic recording medium different from the holograms of the plurality of holograms. Each hologram is reconstructed by irradiating the readout light beam at the same angle as the incident angle used for recording.

Preferably, the plurality of holograms have different wavelengths of the signal light and different wavelengths of the recording reference light applied to the holographic recording medium for each hologram of the plurality of holograms. A different hologram is recorded on the holographic recording medium and reconstructed by changing the wavelength of the read reference light beam.

Preferably, the information on the data is:
The tangential edge within the substantially circular track pattern of the disc-shaped holographic recording medium
Encoded as a transition.

According to a seventh aspect of the present invention, data is recorded over substantially the entire surface of a holographic recording medium having a substantially disk shape as a single continuous hologram, and as a result, a portion of the data is recorded. Is a holographic recording / reproducing method that can be reconstructed by irradiating an appropriate reading reference beam. The holographic recording / reproducing method includes the following steps: (a) a signal light modulated using data; And irradiating a selected spot on the holographic recording medium with a plane wave of the recording reference light to record a hologram, and (b) generating a conjugate read reference light having substantially conjugate characteristics with the recording reference light. And (c) illuminating the hologram with the conjugate reference light, so that the data portion is It is reconstructed in a recording medium as an image,
A holographic recording / reproducing method including steps is provided.

Preferably, the method further comprises a step of moving the read reference beam with respect to the holographic recording medium to reconstruct different portions of the data on the holographic recording medium.

Preferably, a plurality of holograms are recorded on the holographic recording medium by making the incident angles of the recording reference light irradiating the holographic recording medium different for each of the plurality of holograms, Each hologram is reconstructed by irradiating the reading light at the same angle as the incident angle used for the recording.

Preferably, the plurality of holograms differ in the wavelength of the signal light and the wavelength of the recording reference light applied to the holographic recording medium for each hologram of the plurality of holograms. Different holograms recorded on the holographic recording medium, by changing the wavelength of the read reference light,
Different holograms are reconstructed.

Preferably, the information on the data is:
The tangential edge within the substantially circular track pattern of the disc-shaped holographic recording medium
It is encoded as a transition, so that the disc-shaped holographic recording medium is read out in substantially the same way as an optical disc.

According to an eighth aspect of the present invention, there is provided a hologram reading device, comprising: means for generating a coherent collimated plane wave; at least one light detecting device; and a substantially disk-shaped device having a pre-stored hologram. The holographic recording medium, wherein the hologram is recorded in a substantially continuous manner across the surface of the holographic recording medium, a disk-shaped holographic recording medium, the holographic recording medium And a means for moving the plane wave.

Preferably, the means for generating the coherent collimator plane wave is adjustable in wavelength.

Preferably, the means for generating the coherent collimator plane wave has a plurality of light sources having different wavelengths.

More preferably, the apparatus further comprises means for changing the angle of the plane wave light beam.

The present invention can record and read holograms in a manner that reconstructs the hologram area by scanning the reference beam over the hologram area. In particular, by using conjugate readout, a lens with a high numerical aperture can be used, while reproducing the recorded image with high resolution, while allowing space for the readout reference beam to pass through the lens.

In the present invention, multiple holograms can be recorded in the same amount of recording material by applying a multiplexing technique for angles and wavelengths.

The memory configuration of the present invention is suitable for a disk-shaped recording medium. In the special case of a disc-shaped recording medium, the additional features and benefits of the present invention can be provided by the presence of a readout mechanism that exists for optical discs. This allows data to be read continuously rather than at discrete locations on the disk.

[0051]

DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the reproducing method and apparatus will be described with reference to the accompanying drawings.

First Embodiment A first embodiment of the present invention will be described with reference to FIG. FIG.
FIG. 1 is a partial configuration diagram of a holographic recording device suitable for recording on a hologram according to a first embodiment of the present invention. FIG. 3 shows the holographic recording device of the present invention.
1 illustrates the principal parts of the present invention for recording data on a holographic recording medium. The holographic recording device illustrated in FIG.
And Spatial Light Modulator (SLM)
Or) a data pattern 25, an incident light beam providing unit 21, a data converting unit 23, and a recording reference beam providing unit 33.

The holographic recording medium 35 is made of a photosensitive material, for example, a photosensitive polymer or a photorefractive crystal, and data is recorded on the holographic recording medium 35 as a hologram.

In this embodiment, the spatial light modulator or the data pattern 25 placed in parallel with the holographic recording medium 35 at a position separated from the holographic recording medium 35 by a distance d is a transmission type modulator such as a liquid crystal panel. A three-dimensional spatial light modulator. The incident light beam providing means (or coherent light source) 21 emits a plane wave light to the two-dimensional spatial light modulator 25. Preferably, the incident light beam providing means 21 is a coherent (coherent) plane wave, for example,
A laser light source that emits laser light.

The data converting means 23 modulates the digital data to be recorded as a hologram on the holographic recording medium 35 with the coherent plane light beam 10 emitted from the incident light beam providing means 21 in the two-dimensional spatial light modulator 25. The data is converted into two-dimensional modulation data 15 and output to a two-dimensional spatial light modulator 25 such as a liquid crystal panel.

A two-dimensional spatial light modulator 25 such as a liquid crystal display panel modulates the coherent plane light beam 10 according to a modulation signal from the data conversion means 23 to generate a modulated diffraction signal beam 20, The light is irradiated on the front surface (first surface) of the graphic recording medium 35. Specifically,
The two-dimensional spatial light modulator 25 outputs a coherent planar light beam 10 according to the two-dimensional modulation data 15 as a signal beam 20 which is indicated by light and dark.

The recording reference beam providing means 33 irradiates the recording reference beam 30 to the second surface of the holographic recording medium 35 to which the modulated signal beam 20 is irradiated, opposite to the first surface. Reference beam providing means 33 for recording
Preferably, the angle of incidence of the recording reference beam 30 on the second surface of the holographic recording medium 35 can be changed, and / or the wavelength of the recording reference beam 30 can be changed. . The reason is that, by changing the condition of the recording reference beam 30 that interferes with the signal beam 20 modulated in the holographic recording medium 35, multiple recording can be performed at the same location.

Hereinafter, the operation of the holographic recording apparatus illustrated in FIG. 3 will be briefly described. The data converter 23 converts digital data to be recorded in the form of a hologram on the holographic recording medium 35 into a two-dimensional bright and dark dot pattern, and converts the two-dimensional modulated data 15 converted into two-dimensional information into a two-dimensional It is applied to the spatial light modulator 25. The two-dimensional spatial light modulator 25 is a coherent plane light beam 1 emitted from the incident light beam providing means 21.
0 is modulated (diffracted) according to the two-dimensional modulation data 15. As a result, the modulated signal beam 20 is emitted from the two-dimensional spatial light modulator 25 to the holographic recording medium 35.

A modulated signal beam 20 is applied to the first surface (front) of a holographic recording medium 35 made of a photosensitive material such as a photosensitive polymer or a photorefractive crystal. The second surface (rear surface) of the holographic recording medium 35 opposite to the front surface irradiated with 20 is irradiated with the recording reference beam 30 emitted from the recording reference beam providing means 33. As a result, the signal beam 20 modulated inside the holographic recording medium 35 and the recording reference beam 30 interfere. The interference fringes generated by the interference are recorded on the holographic recording medium 35 as a hologram.

The configuration of the holographic recording device illustrated in FIG. 3 is compared with the general configuration illustrated in FIG.
In the configuration illustrated in FIG. 1, the reference wave is applied to the hologram from the same side as the signal wave is applied to the hologram. Therefore, in the configuration of FIG. 1, an interval is required between the target object and the hologram such that the reference wave enters the hologram at a predetermined angle. In particular, as described later, when the incident angle of the reference wave with respect to the hologram is made different, it is necessary to make the interval between the object (corresponding to the spatial light modulator or the data pattern 25 in FIG. 3) and the hologram sufficiently large. . In contrast, the holographic recording device illustrated in FIG.
Is incident from the side facing the modulated signal beam 20. Therefore, there is no need to provide an interval between the spatial light modulator or the data pattern 25 and the holographic recording medium 35 for irradiating the holographic recording medium 35 with the recording reference beam 30 at a predetermined angle θ. As a result, the holographic recording device illustrated in FIG. 3 can reduce the distance d between the spatial light modulator or data pattern 25 and the holographic recording medium 35, and can reduce the size of the holographic recording device. There is an advantage. Even when the angle of incidence of the recording reference beam 30 on the holographic recording medium 35 is changed, FIG.
The holographic recording device of the first embodiment does not have the restrictions as in the holographic recording device of FIG.

However, in the holographic recording apparatus of the present embodiment illustrated in FIG. 3, the holographic recording medium 35 has a material and a structure (reflection) suitable for recording a hologram from both the front and back sides. (Geometric configuration).

FIG. 4 shows a readout method proposed in Japanese Patent Application No. 11-310394 for reconstructing (reproducing) a hologram recorded on the holographic recording medium 35 in the holographic recording apparatus illustrated in FIG. FIG. 2 is a configuration diagram of an apparatus suitable for forward reading of a hologram, that is, a holographic reproducing apparatus, by a method.

The holographic reproducing apparatus illustrated in FIG. 4 includes a holographic recording medium 35 on which the hologram illustrated in FIG. 3 is recorded, an image element 45 for converting a hologram such as a lens into two-dimensional image information, 45 and a detector 60 such as a two-dimensional array detector for detecting the two-dimensional image information generated at 45, respectively.
It is arranged at a distance of d2. The holographic reproducing apparatus irradiates the holographic recording medium 35 with a forward read beam 40 having the same characteristics as the recording reference beam 30 illustrated in FIG. 3, for example, the same shape, the same angle and the same wavelength. It has a reproducing reference beam providing means 43 for generating. The holographic reproducing device has a signal reproducing means 63 for performing signal processing for reproducing a signal detected by the detector 60 into digital data. Distance d in front of the holographic recording medium 35
A virtual image 55 is formed at a position separated by 0.

The forward read beam 40 is emitted from the reproducing reference beam providing means 43 and irradiates the holographic recording medium 35. Forward read beam 4
0 is reconstructed (reproduced) in the holographic recording medium 35 by irradiating the holographic recording medium 35 with the signal beam 50 passing through the image element 45.
Goes towards the detector 60 and refocuses the image on the detector 60. That is, the reconstructed signal beam 5
0 travels in the same direction as the modulated signal beam 20 in the holographic recording device illustrated in FIG.

In the holographic reproducing apparatus illustrated in FIG. 4, if the hologram recorded on the holographic recording medium 35 contains a pattern with a high spatial frequency, a large numerical aperture (NA) is used as an image element 45 such as a lens. Must be used. This limits the range of the incident angle of the forward read beam 40 incident on the holographic recording medium 35. That is, the holographic reproducing device of FIG. 4 has a configuration in which the range in which the incident angle of the forward read beam 40 to the holographic recording medium 35 is changed is limited.

In the holographic reproducing apparatus shown in FIG. 4, the modulated signal beam 20 is irradiated from the front and the recording reference beam 30 is irradiated from the rear as described with reference to FIG. Graphic recording medium 3
As the thickness of the image element 45 increases, the thickness of the image element 45 increases by that thickness.
Since the substantial distance d1 between the holographic recording medium 35 and the holographic recording medium 35 is reduced,
There is a disadvantage that the substantial distance d1 for inserting the forward read beam 40 for irradiating the holographic recording medium 35 from between the image element 5 and the image element (lens) 45 is reduced.

The holographic reproducing apparatus of the present embodiment described with reference to FIG. 5 improves the disadvantage of the holographic reproducing apparatus illustrated in FIG. FIG. 5 is a schematic configuration diagram of a holographic reproducing apparatus according to an embodiment of the present invention for reconstructing (reproducing) a hologram. The holographic reproducing device illustrated in FIG. 5 includes a holographic recording medium 35, an image element 45 such as a lens, and a detector 60 such as a two-dimensional detection array device, which are arranged at intervals d11 and d12, respectively. I have. The holographic reproducing apparatus further includes a conjugate read beam generating means 44 for generating a conjugate read beam 42, and a detector 6
There is a signal reproducing means 63 for reproducing the signal detected at 0 into digital data.

The conjugate read beam 42 emitted from the reproduction reference beam providing means 43 is applied to the holographic recording medium 35 from the image element 45 side. As a result, the holographic recording medium 35 and the image element 45
Between the holographic recording medium 35 and the distance d1
A real image 57 is formed at a position separated by three. The signal beam 50 reconstructed by the image element 45 forms an image on the detector 60. The information detected by the detector 60 is reproduced by the signal reproducing means 63 into the original digital data recorded on the holographic recording medium 35.

In the holographic reproducing apparatus shown in FIG. 5, the conjugate read beam 42 is used for the recording reference beam 30 in the holographic recording apparatus shown in FIG.
The hologram stored in the holographic recording medium 35 is irradiated from the opposite direction. In the specific case where the recording reference beam 30 described with reference to FIG. 3 is a plane wave, the conjugate read beam 42
A simple counter-propagating plane wave (counter pr
opagation plain wave).

The holographic recording medium 3 is irradiated with the conjugate read beam 42 to the holographic recording medium 35.
The light emitted from 5 is propagated toward an image element (lens) 45. The propagation direction of the light is the modulated signal beam 2 used for recording the hologram illustrated in FIG.
This is the direction opposite to the propagation direction of 0.

The light emitted from the holographic recording medium 35 is converted into a reconstructed signal beam 50 in the image element 45. The propagation direction of the reconstructed signal beam 50 is also opposite to the propagation direction of the modulated signal beam 20 used for recording the hologram illustrated in FIG.

The reconstructed signal beam 50 is applied to the detector 6
It is refocused on 0 to form a real image 57.

The signal detected by the detector 60 is converted into data corresponding to the original digital data before the signal reproducing means 63 records it on the holographic recording medium 35.

The device configuration of the holographic reproducing device illustrated in FIG. 4 and the holographic reproducing device illustrated in FIG. 5 will be compared. In the holographic reproducing device illustrated in FIG. 5, since the real image 57 is formed on the front surface of the holographic recording medium 35, the virtual image 55 in the holographic reproducing device illustrated in FIG.
Is formed behind the holographic recording medium 35, the distance d11 between the image element 45 and the holographic recording medium 35 is different from the forward reading beam 40 in the holographic reproducing apparatus illustrated in FIG. Is longer than the distance d1 between the image element 45 and the holographic recording medium 35 when. As described above, the holographic reproducing apparatus of the present embodiment illustrated in FIG. 5 can secure a large distance d11 between the image element 45 and the holographic recording medium 35, and thus does not suffer from the obstacle caused by the image element 45, By changing the angle of incidence, the holographic recording medium 35 can be irradiated with the conjugate read beam 42. This is advantageous when the multiplexed hologram is read out by changing the incident angle of the conjugate readout beam 42 variously when multiplexing is performed at one location of the hologram.

FIG. 3 illustrates a holographic recording apparatus according to a first embodiment of the present invention, and FIG.
Although the holographic reproducing apparatus according to the embodiment has been illustrated, a holographic recording / reproducing apparatus can be assembled by integrating them. In that case, the spatial light modulator or data pattern 25 illustrated in FIG.
Is the image element 45 and the detector 60 illustrated in FIG.
Note that it is located on the same side as That is, when the holographic recording / reproducing method is configured by combining the holographic recording device of FIG. 3 and the holographic reproducing device of FIG. 5, as described with reference to FIG. This means that related elements can be arranged on the upper surface side. As a result, the configuration of the holographic recording / reproducing apparatus can be simplified.

The holographic reproducing apparatus illustrated in FIG. 5 illustrates a reflection geometric reproducing method in which the conjugate read beam 42 is reflected on the holographic recording medium 35. However, the same advantage as described above is obtained in the case of transmission recording. Applied. In the case of the transmissive type, the enlarged space d11 between the image element 45 and the holographic recording medium 35 indicates that the transmitted light is not captured by the readout image element 45 (not affected by the image element 45). A)
to be certain. The transmitted light interferes with the refracted light from the holographic recording medium 35.

The portion of the reconstructed spatial light modulator or data pattern 25 is the area around the same traverse coordinates as the center of the illumination spot of the conjugate read beam 42 on the holographic recording medium 35. Moving the holographic recording medium 35 or the conjugate read beam 42 relative to each other in the traverse direction is a different part of the spatial light modulator or data pattern 25 to be reconstructed.

An advantageous device configuration of the above-described embodiment of the present invention is that any large page can be recorded as one hologram, where a fraction of the information in the hologram is restored. The reading light in a small part of the hologram for the purpose.
This means that the amount of data recorded on each hologram is larger than that of a conventional holographic recording / reproducing apparatus,
It reduces overall recording time and reduces the complexity of the recording procedure required, thereby facilitating achieving uniformity within each hologram and across different holograms.

The device configuration of the present invention is particularly suitable for a disk-shaped memory. This is because it records a continuous hologram over the entire area of the disk, but moves a narrow read beam across the surface of the disk to access a specific disk location. However, in the case of an apparatus configuration using a disk as a substrate, the complexity that arises from reading data from a rotating disk is that the read head is fixed for all the rotational positions of the disk and the radial read of the read head is fixed. It is required to maintain position.

FIGS. 6 and 7 are block diagrams of a device according to a second preferred embodiment of the present invention integrated with the first embodiment of the hologram type disk. FIG. 6 is a diagram showing a configuration of a holographic recording device that can be implemented practically.

The holographic recording device illustrated in FIG. 6 is a disk-shaped spatial light modulator or data pattern 2.
5, a disk-shaped holographic recording medium 35,
The disk-shaped beam shaping elements 131 are arranged at intervals (distances) d21 and d22, respectively. The collimated signal beam 110 is modulated by a disc-shaped spatial light modulator or data pattern 25,
The modulated signal beam 20 approaches the spatial light modulator or data pattern 25 substantially parallel to the disk-shaped spatial light modulator or data pattern 25 so as to best capture the modulated signal beam 20. The light enters the disk-shaped holographic recording medium 35 provided. To allow reconstruction of the hologram to maintain a fixed position with respect to the read reference beam 130 with the disc rotated, a donut-shaped symmetric reference beam must be provided. This means that reference beam 1
A lens, an optical element for refraction, provided in a path of 30;
Alternatively, this is achieved by a beam shaping element 131 such as a hologram. The reference beam 132 shaped by the beam shaping element 131 is substantially a plane wave and is incident at the same radial angle over the surface of the disk.

FIG. 7 is a diagram showing a modification of the device configuration shown in FIG. In this embodiment, the disk-shaped spatial light modulator or data pattern 25 and the disk-shaped holographic recording medium 35 are simultaneously rotated by a motor-driven rotary spindle (spindle motor) 138. The reference beam 130 is a holographic recording medium 35
The holographic recording medium 35 is irradiated at a predetermined angle only along the stripe-shaped (striped) recording area 134 in FIG. A modulated signal beam 20 from a spatial light modulator or data pattern 25 also illuminates the same striped recording area 134. The spindle motor 138 controls the spatial light modulator or data pattern 2 during recording.
5 and the holographic recording medium 35 are rotated 360 degrees together to efficiently form a single continuous hologram over the surface of the holographic recording medium 35. Recording is not performed continuously, but rather in incremental steps.

FIG. 8 is a block diagram of an apparatus according to a second preferred embodiment of the present invention for reading data from a disk-shaped holographic recording medium 35 recorded by one of the above-described methods. This device uses a spindle motor 138
And a disk-shaped holographic recording medium 35 rotated by a spindle motor, and a radial direction moving mechanism 143 located above the disk-shaped holographic recording medium 35 opposite to the spindle motor 138.
Further, the radial moving mechanism 143 includes a read head 142 and a detector 60 such as a two-dimensional detection array.
And an image element 45 such as a lens, and a laser light source 95 that emits coherent (coherent) laser light.
The holographic recording medium 35 is mounted facing the surface of the holographic recording medium 35. That is, the read head 142 is located above the surface of the holographic recording medium 35. The holographic recording medium 35 is a spindle motor 138
And the reading head 142 can access all the tangential positions of the holographic recording medium 35. The read head 142 is held by the radial movement mechanism 143. Radial movement mechanism 1
Reference numeral 43 denotes, for example, a sliding track or a rotatable arm.
2 allows the holographic recording medium 35 to move to different radial positions. The read head 142 includes the laser light source 95 and the image element 45.
And a detector 60, and these elements are arranged at appropriate positions to realize the reading described in the first embodiment of the present invention. All locations in the holographic recording medium 35 rotate the holographic recording medium 35 and the read head 14
2 can be accessed in the radial direction by the radial moving mechanism 143, or by combining both.

For both recording and reading, a plurality of holograms can be multiplexed (multiplexed). An example of such multiplexing is multiplexing angles or wavelengths. This means that during recording the recording reference beam 30 or reference beam 130
By changing the incident angle or wavelength of each hologram. Then, in the readout device, an additional element that can change the beam angle or the wavelength is added in order to read out different holograms.

Although the description of the above embodiments is specific, these specific descriptions do not limit the scope of the present invention, but rather exemplify preferred embodiments of the present invention. I want to understand. Therefore, the present invention can take various modifications.

For example, what is illustrated in FIGS.
Although the case where the modulated signal beam 20 and the recording reference beam 30 are incident from opposite sides of the holographic recording medium 35 is illustrated, the method of the present invention uses the modulated signal beam 20 and the recording reference beam 30. 30 can be applied to the same side of the holographic recording medium 35. Also, the conjugate read beam 42 is not required for this memory device configuration. Even if a sufficient space (spacing) is already maintained, the present invention can of course be applied.

The spatial light modulator or data pattern 25 may be a transmissive element or a reflective element.
It can take the form of appropriate information. For example, in the case of a disk-shaped hologram recording medium, a circular track pattern coded at a location of a transition of an edge of a data pattern is recorded instead of a binary on / off pixel state in a normal array. obtain. This means that the data pattern recorded on the hologram recording medium can be read out by a method similar to the method of reading out the pits of the optical disk. When multiple holograms are multiplexed, the data pattern can be obtained by using appropriate means such as an electrically controllable spatial light modulator such as a liquid crystal display or by having different ones between recordings It can be changed by replacing the pattern.

The holographic recording medium 35 of the present invention can have any suitable shape and dimensions.

The image element 45 such as a lens may be a single element or an image processing device having a plurality of elements.

Any suitable mechanism can be used to scan the conjugate read beam 42 over the surface of the holographic recording medium 35 to read different portions of the recorded hologram.

As described above, the scope of the present invention should not be limited by the embodiments described with reference to the accompanying drawings, and the present invention is described in the appended claims of the present invention. Inventions and their equivalents.

[0092]

As is apparent from the above, the hologram readout method of the present invention provides a method of restoring a hologram recorded at high density using a large numerical aperture for readout to a high resolution. A sufficient space (distance) is provided between the hologram recording medium and an image element such as a lens through which the beam passes.

The present invention makes it possible to use a hologram recording medium having a large thickness without reducing the resolution.

According to the present invention, by irradiating a narrow read beam to a desired data location in a hologram recording medium, a continuous hologram is stored over the surface of a large hologram recording medium, and the method is compatible with a method of partially reading data. it can.

The method of the present invention has the additional benefit that both recording and reading operations are performed by simple optics.

According to the present invention, a large-capacity memory can be quickly read. The reason is that the large page size per page and the high data density allow recording large amounts of data in a few holograms.

The present invention also allows for a simple recording procedure due to the small amount of holograms and the uniformity of the recording process across each data page.

The present invention provides a hologram disc that is compatible with existing optical data readout mechanisms.

In the present invention, when the hologram recording medium is double refraction, it is possible to appropriately focus a read image that cannot be obtained by using the conjugate read for the forward read.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of recording data on a hologram.

FIG. 2 is a diagram illustrating a principle of reading data from a hologram;

FIG. 3 is a partial configuration diagram of a hologram-type recording / reproducing apparatus suitable for recording on a hologram as the first embodiment of the present invention.

FIG. 4 is a configuration diagram of an apparatus suitable for reading a hologram forward.

FIG. 5 is a configuration diagram of an apparatus suitable for reading a conjugate of a hologram.

FIG. 6 is a configuration diagram of a branch device for recording a disk-sized hologram over the surface of a hologram recording medium using a beam shaping element.

FIG. 7 is a configuration diagram of an apparatus for recording a radial stripe on a disk, revising a data pattern of the hologram recording medium, and continuously recording a hologram over the surface of the disk-shaped hologram recording medium.

FIG. 8 is a configuration diagram of an apparatus suitable for reading a hologram portion from a disk-shaped hologram recording medium according to an embodiment of the present invention.

[Explanation of symbols]

10. Coherent parallel incident light beam 15 Two-dimensional converted signal 20 Modulated signal beam 21 Incident light beam providing means 23 Data converting means 25 Two-dimensional spatial light modulator or two-dimensional Data pattern 30 Recording reference beam 33 Recording reference beam providing means 35 Holographic recording medium 40 Forward reading beam 42 Conjugate reading beam 43 Reproducing reference beam providing means 44 Conjugate Read beam providing means 45 image element (lens) 50 reconstructed signal beam 55 virtual image 57 actual image 60 detector 63 signal reproducing means 95 laser light source 110 Collimated signal beam 130 Reference beam 131 Beam shaping element 132 By reference beam 134 · striped recording area 138 · spindle motor 142 ... read head 143 · radial movement mechanism

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/006 G11B 7/006 7/12 7/12 F term (Reference) 2H049 AA25 AA34 AA56 AA57 AA69 CA01 CA05 CA20 CA28 2K008 AA04 BB04 BB05 BB06 CC01 CC03 DD03 DD12 DD23 EE01 EE04 FF07 FF17 HH06 HH18 HH26 HH28 5D090 AA01 BB04 BB12 DD01 KK06 KK14 5D119 AA22 BA01 BB03 FA05 KA03 LB01

Claims (37)

[Claims] 1. A parallel light emitting means for emitting parallel light, a spatial light modulating means for modulating parallel light emitted from the parallel light emitting means, and a first surface and a second surface opposite to the first surface. A holographic recording medium disposed parallel to the spatial light modulating means at a position facing the spatial light modulating means so as to receive the light modulated by the spatial light modulating means on a first surface; Recording reference light emitting means for irradiating a second surface of the recording medium opposite to the first surface receiving the modulated light with recording reference light, wherein the holographic recording medium is irradiated on the first surface. A holographic recording device configured to record, as a hologram, an interference fringe generated by causing the modulated light to interfere with the recording reference light applied to the second surface. 2. The holographic recording apparatus according to claim 1, wherein said recording reference light emitting means changes an incident angle of said recording reference light on a second surface of said holographic recording medium. 3. The holographic recording apparatus according to claim 1, wherein said recording reference light emitting means changes a wavelength of said recording reference light. 4. The holographic recording apparatus according to claim 1, wherein the recording reference light emitting means changes a wavelength of the recording reference light and an incident angle on the second surface of the holographic recording medium. . 5. The spatial light modulating means is configured as a disk-shaped flat plate, the holographic recording medium is configured as a disk-shaped flat plate, and the spatial light modulating means and the holographic recording medium are rotationally driven. The parallel light emitting means and the recording reference light emitting means,
The holographic recording medium is mounted on radial moving means movable in the radial direction, and the spatial light modulating means modulates the parallel light according to digital data to be recorded on the holographic recording medium. Item 2. The holographic recording device according to Item 1. 6. A method for modulating parallel light according to data to be recorded on a holographic recording medium, irradiating the modulated light onto a first surface of the holographic recording medium, and a first surface receiving the modulated light. Irradiates the second surface of the opposite holographic recording medium with a recording reference light, and causes the modulated light and the recording reference light to interfere with each other in the holographic recording medium in accordance with the data to be recorded. A holographic recording method, comprising the steps of recording on the holographic recording medium that forms a hologram. 7. The holographic recording method according to claim 6, wherein an incident angle of the recording reference light applied to the second surface of the holographic recording medium is changed. 8. The holographic recording method according to claim 6, wherein the wavelength of the recording reference light applied to the second surface of the holographic recording medium is changed. 9. The hologram according to claim 6, wherein the wavelength of the reference light for recording applied to the second surface of the holographic recording medium and the angle of incidence on the second surface of the holographic recording medium are changed. Graphic recording method. 10. A holographic recording medium for modulating parallel light according to data to be recorded on the holographic recording medium, irradiating the modulated light onto a first surface of the holographic recording medium, and a first surface receiving the modulated light. Irradiates the second surface of the opposite holographic recording medium with a recording reference light, and causes the modulated light and the recording reference light to interfere with each other in the holographic recording medium in accordance with the data to be recorded. A holographic reproducing apparatus for reading out the hologram from the holographic recording medium on which the hologram is recorded and reproducing the data, and conjugate reading conjugate with the recording reference light on a first surface of the holographic recording medium. A reproduction reference light emitting means for irradiating light, and the holographic recording medium so that a real image is formed on the first surface side of the holographic recording medium. Imaging means arranged on the first surface side of the holographic recording medium at a predetermined distance from the recording medium, and a signal light reconstructed by the imaging means is disposed at a position where the signal light is refocused. And a detector for detecting the signal light reconstructed as described above. 11. The holographic reproducing apparatus according to claim 10, wherein said reproducing reference light emitting means can change an incident angle of said conjugate readout light on a first surface of said holographic recording medium. 12. The holographic reproducing apparatus according to claim 10, wherein said reproducing reference light emitting means can change a wavelength of said conjugate reading light. 13. The holographic reproducing apparatus according to claim 10, wherein said reproducing reference light emitting means can change a wavelength of said conjugate read light and an incident angle on said first surface of said holographic recording medium. . 14. The holographic recording medium is configured as a disk-shaped flat plate, and the reproducing reference light emitting means and the reproducing holographic recording medium are mounted on a radial direction moving means capable of moving in the radial direction of the holographic recording medium. The holographic playback device according to claim 10, wherein: 15. A holographic recording medium for modulating parallel light according to data to be recorded on the holographic recording medium, irradiating the modulated light to a first surface of the holographic recording medium, and a first surface for receiving the modulated light. Irradiates the second surface of the opposite holographic recording medium with a recording reference light, and causes the modulated light and the recording reference light to interfere with each other in the holographic recording medium in accordance with the data to be recorded. A holographic reproduction method for reading out the hologram from the holographic recording medium on which the hologram is recorded and reproducing the data, comprising: Illuminating the holographic recording medium with a predetermined distance so that a real image is formed on the first surface side of the holographic recording medium; The holographic image from the holographic recording medium is formed by the image forming means arranged on the first surface side of the holographic recording medium while keeping the signal light, and the signal light reconstructed by the image forming means is refocused. A holographic reproduction method comprising: detecting the signal light with a detector disposed at a position. 16. The holographic reproducing method according to claim 15, wherein an incident angle of the conjugate read light on the first surface of the holographic recording medium can be changed. 17. The holographic reproduction method according to claim 15, wherein the wavelength of the conjugate readout light can be changed. 18. The holographic reproducing method according to claim 15, wherein a wavelength of the conjugate read light and an incident angle on the first surface of the holographic recording medium are changed. 19. A holographic recording / reproducing method for recording information on a hologram on a holographic recording medium and reading information from the hologram on the holographic recording medium, comprising the following steps: A hologram is recorded on the holographic recording medium by irradiating a selected spot on the holographic recording medium with the signal light and the recording reference light modulated by using (b), and (b) substantially conjugate with the recording reference light beam. (C) irradiating the hologram with the generated read reference light, and a portion of data generated by the hologram is disposed at a certain distance from the holographic recording medium. It is reconstructed as a real image on the same side as the readout detection device, so that the real image and the B graphics comprising the stages to position the imaging means between said read detector to be sufficiently separated from the recording medium, the holographic recording and reproducing method. 20. The holographic recording / reproducing method according to claim 19, further comprising the step of moving the read reference light with respect to the holographic recording medium. 21. A hologram is recorded on the holographic recording medium by changing an incident angle of the recording reference light applied to the holographic recording medium with respect to each of a plurality of holograms. 20. The holographic recording / reproducing method according to claim 19, wherein the hologram is reconstructed by irradiating the readout light at the same angle as the incident angle used for the holographic recording. 22. The holographic apparatus according to claim 19, wherein the plurality of holograms have different wavelengths of the signal light and different wavelengths of the recording reference light applied to the holographic recording medium for each hologram of the plurality of holograms. The holographic recording / reproducing method according to claim 19, wherein the hologram is recorded on a recording medium, and the hologram is reconstructed by changing the wavelength of the read reference light. 23. The holographic recording / reproducing method according to claim 19, wherein said holographic recording medium has a substantially rotatable disk shape. 24. Data is recorded over substantially the entire surface of a disk-shaped holographic recording medium as a single continuous hologram, and as a result, the data portion is irradiated with an appropriate reading reference beam. A reconstructable holographic recording / reproducing method, comprising the following steps: (a) A plane wave of a signal light and a recording reference light modulated using data is selected on a holographic recording medium. To record a hologram using the interference fringes; (b) generate a conjugate readout reference beam having substantially the same characteristics as the recording reference beam; and (c) use the readout reference beam to generate the hologram. Holographic recording / reproducing method comprising the steps of: 25. The holographic recording / reproducing method according to claim 24, further comprising moving the read reference light with respect to the holographic recording medium. 26. A plurality of holograms are recorded on the holographic recording medium by making the incident angles of the recording reference light applied to the holographic recording medium different from the holograms of the plurality of holograms. 26. The holographic recording / reproducing method according to claim 24, wherein each hologram is reconstructed by irradiating the readout light beam at the same angle as the incident angle used for recording. 27. The holographic apparatus according to claim 27, wherein the plurality of holograms differ in the wavelength of the signal light and the wavelength of the recording reference light applied to the holographic recording medium for each hologram of the plurality of holograms. The holographic recording / reproducing method according to claim 24, wherein a different hologram is reconstructed by changing the wavelength of the read reference light beam recorded on the recording medium. 28. The holographic recording / reproducing apparatus according to claim 24, wherein the information on the data is encoded as a tangential edge transition in a substantially circular track pattern of the disk-shaped holographic recording medium. Method. 29. Data is recorded over substantially the entire surface of a holographic recording medium having a substantially disk shape as a single continuous hologram, and as a result, the data portion is irradiated with an appropriate reading reference beam. Holographic recording and playback method that can be reconstructed by
The holographic recording / playback method is as follows:
That is, (a) irradiating a selected spot on the holographic recording medium with a plane wave of signal light and recording reference light modulated using data to record a hologram; Generating a conjugate read reference beam having substantially conjugate properties; and (c) irradiating the hologram with the conjugate reference beam, so that the data portion is reproduced as an image on the holographic recording medium. A holographic recording / reproducing method that has various steps to be built. 30. The holographic recording medium according to claim 29, further comprising moving the read reference light with respect to the holographic recording medium so that different portions of the data are reconstructed on the holographic recording medium. Recording and playback method. 31. A plurality of holograms are recorded on the holographic recording medium by making incident angles of the recording reference light irradiating the holographic recording medium different for each of the holograms. 30. The holographic recording / reproducing method according to claim 29, wherein the hologram is reconstructed by irradiating the readout light at the same angle as the incident angle used for the recording. 32. The holographic apparatus according to claim 31, wherein the plurality of holograms have different wavelengths of the signal light and different wavelengths of the recording reference light applied to the holographic recording medium for each hologram of the plurality of holograms. 30. The holographic recording / reproducing method according to claim 29, wherein different holograms recorded on the recording medium are reconstructed by changing the wavelength of the reference light for reading, so that different holograms are reconstructed. 33. The information relating to the data is encoded as tangential edge transitions in a substantially circular track pattern of the disc-shaped holographic recording medium, so that the disc-shaped holographic recording medium is encoded. 30. The holographic recording / reproducing method according to claim 29, wherein is read out in substantially the same manner as an optical disc. 34. A holographic readout device comprising: a means for generating a coherent collimated plane wave; at least one photodetector; and a holographic recording medium having a pre-stored hologram. The hologram is recorded in a substantially continuous manner across the surface of the holographic recording medium, a disk-shaped holographic recording medium, and means for moving the plane wave with respect to the holographic recording medium, A holographic playback device comprising: 35. The holographic reproducing apparatus according to claim 34, wherein the means for generating the coherent collimator plane wave has an adjustable wavelength. 36. The holographic reproducing apparatus according to claim 34, wherein the means for generating the coherent collimator plane wave has a plurality of light sources having different wavelengths. 37. The holographic reproducing apparatus according to claim 34, further comprising means for changing an angle of said plane wave light beam.