JP2005122814A - Hologram recording and reproducing device and method, and phase address code creating method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfactorily keep the S/N of reproduced data by reducing cross talk even if light phase modulation is not performed in an ideal state. <P>SOLUTION: When the light phase modulation is performed to be deviated from the ideal state, one part of an element constituting a matrix becomes equivalent to the case in which a phase address code is created based on the Hadamard matrix deviated from an original value. In this equivalent Hadamard matrix, as a code using elements of especially a first column and a first row contributes largely as a function causing cross talk when multiplex-recorded data is reproduced, the phase address code is created on the basis of residual elements in which the first column (or the first row) is eliminated from the Hadamard matrix by a control part 28, a phase modulation pattern created from the phase address code is displayed on a spatial light phase modulator 22 and reference light is light-phase-modulated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hologram recording / reproducing apparatus and a hologram recording / reproducing method for recording / reproducing a hologram by a phase modulation multiplexing method, and more particularly to a method and program for creating a phase address code for optical phase modulation of reference light.

  In recent years, holographic technology has been rapidly developed for the practical use of holographic memory, which is attracting attention as a candidate for powerful storage that competes with next-generation and next-generation optical discs. Thus, a hologram recording / reproducing system for recording / reproducing a large amount of data has been proposed.

  In this hologram storage recording / reproducing system, as shown in FIG. 7, the coherent laser light emitted from the laser light source 2 enters the beam splitter 6 through the shutter 4 and is branched into the signal light 100 and the reference light 200. The The signal light 100 is incident on the spatial light modulator 10 via the mirror 8, and the signal light is intensity-modulated by the spatial light modulator 10 displaying the data page. The modulated signal light is focused on the hologram recording medium 14 by the lens 12. On the other hand, since the reference light 200 irradiates the hologram recording medium 14 via the mirror 16, the signal light 100 and the reference light 200 are overlapped in the hologram recording medium 14, and the interference fringes formed as a result are holograms. It is recorded as a fine density pattern on the recording medium 14.

  In order to reproduce the data recorded on the hologram recording medium 14, the same reproduction light as the reference light 200 is incident on the hologram recording medium 14, thereby diffracted light corresponding to the interference fringes recorded on the hologram recording medium 14. And the diffracted light is focused on an image sensor 20 such as a CCD or CMOS by a lens (inverse Fourier lens) 18. The image sensor 20 photoelectrically converts the received diffracted light, and the obtained light reception signal is analyzed and reproduced as image data.

  By the way, the storage capacity of the holographic memory is determined by the volume recording density while the storage capacity of the optical disk is determined by the surface recording density. When recording data in a holographic manner, recording data is not directly recorded on the hologram recording medium 14, but interference fringes between the signal light and the reference light are recorded. Therefore, 1 Mbyte is recorded in one hologram (data page). It is also possible to allocate the data. When the multiplex recording of this data page is repeated using the volume of the hologram recording medium, a large capacity exceeding several hundreds of Gbytes can be realized. Normal volume hologram multiplexing does not fix the reference beam for each data page, records some interference fringes at the same location or almost the same location with some change, and between different reference beams (reproduced beams) This is realized by giving Bragg selectivity. Typical multiplexing methods include angle multiplexing, shift multiplexing, wavelength multiplexing, phase modulation multiplexing, and the like.

  Focusing on the phase modulation multiplexing method among the above multiplexing methods, this phase modulation multiplexing method is greatly different from other methods, such as mechanically changing the angle of the reference beam in the optical system, Rather than shifting the recording medium, all optical components remain fixed, and the reference light is optically phase-modulated with a spatial light modulator to generate reference light having various phases. This is a method of multiplex recording data in the same recording area (spot) of a hologram recording medium by interfering with light. One of the causes of reducing the S / N ratio of reproduced data by using this light phase characteristic. There is an advantage that a certain crosstalk can be greatly reduced.

  All the literatures related to the hologram memory using the phase modulation multiplexing method reported so far are only about the case where a one-dimensional spatial light phase modulator is used. A report of 180 multiplexing in an experiment using a one-dimensional phase modulator was made by Denz et al. In 1998 (see Non-Patent Document 1, for example).

  In the phase modulation multiplex method, the conditions imposed on the actual optical system to realize multiplex recording without crosstalk are that the reference light has uniform brightness and accurately reproduces the quadrature phase modulation code as described later. Is subject to phase modulation. This condition does not change whether the spatial light phase modulator is one-dimensional or two-dimensional, but in any case, the uniform irradiation with the reference light becomes more difficult as the size of the spatial light phase modulator increases. In addition, since the parallelism of the light wave varies depending on the region of the reference light due to the aberration of the lens, the code orthogonality is not satisfied.

The advantage of making the spatial light phase modulator two-dimensional is that the multiplicity can be increased efficiently. When displaying a phase modulation pattern (phase address pattern) on a spatial light phase modulator, even if the pattern is displayed with a finer pitch than a certain resolution, the selectivity does not work between those patterns, so different data pages Cannot be played independently. The limit of resolution is determined by the Bragg condition, but what is actually recorded as a hologram is a speckle pattern formed by a diffuser incorporated in the optical system of the reference light. Therefore, it actually depends on the resolution of the spatial light phase modulator. Therefore, once the resolution is determined, the size of the spatial light phase modulator must be increased in order to increase the multiplicity. For example, in order to ensure the same multiplicity, 1 is required. The horizontal dimension (width) of the two-dimensional spatial light phase modulator is a square multiple of the two-dimensional case. As described above, the larger the display area of the spatial light phase modulator, the more optically unfavorable conditions increase. Therefore, it is clear that the display with a two-dimensional pattern is more advantageous.
C. Denz, Kai-Oliver Muller, Thorsten Heimann, and Theo Tschudi, “Volume Holographic Storage Demonstrator Based on Phase-Coded Multiplexing”, IEEE J. Sel. Top. Quantum Electron. 4, 832 (1998)

  As described above, in the phase modulation multiplexing system, it is advantageous to use a two-dimensional spatial light phase modulator with less optical burden. In order to optically modulate the reference light with the two-dimensional spatial light phase modulator, a phase modulation pattern corresponding to the phase address code is created, and the reference light is emitted by the spatial light phase modulator on which the phase modulation pattern is displayed. Phase modulation. As a result, reference light that is optically phase-modulated for each phase modulation pattern is generated, and interference fringes of each reference light and signal light are multiplexed and recorded in the same recording area. At this time, if the reference light that irradiates the phase modulation pattern displayed on the spatial light phase modulator is parallel light and the brightness thereof is not uniform, modulation of the reference light is not performed with binary values of 0 or π, and orthogonality Is lost, crosstalk increases, and the S / N ratio of the reproduced data is deteriorated. However, it is difficult to generate reference light with uniform brightness using parallel light, due to aberrations in the optical system and non-uniformity in the brightness of the laser light that is the light source, and optical phase modulation deviates from the ideal state. Therefore, it was impossible to avoid the above problem.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to achieve crosstalk even when optical phase modulation is not performed in an ideal state when data is multiplexed and recorded by the phase modulation multiplexing method. Is to provide a hologram recording / reproducing apparatus, a hologram recording / reproducing method, a phase address code generating method, and a program that can maintain a good S / N ratio of reproduced data.

  In order to achieve the above object, the present invention provides a hologram recording apparatus for recording on a hologram recording medium interference fringes generated by causing a first light beam spatially modulated by recording data to interfere with a second light beam. , Phase address code creating means for creating a phase address code based on the remaining elements obtained by removing either the first column or the first row of the unitary matrix, and a phase generated from the created phase address code Optical phase modulation means for optically phase-modulating the second light beam by a modulation pattern, and interference fringes between the second light beam modulated by the optical phase and the first light beam modulated by the spatial light. Multiple recording is performed in the same area of the hologram recording medium.

  As described above, in the hologram recording apparatus of the present invention, when the optical phase modulation is performed out of the ideal state, when a phase address code is created from a unitary matrix, for example, a Hadamard matrix, elements constituting the matrix This is equivalent to the case where the phase address code is created based on the Hadamard matrix in which a part of is deviated from the original value. In this equivalent Hadamard matrix, the elements of the first column and the first row contribute greatly as an effect of generating crosstalk when reproducing the data recorded in multiple recording. Therefore, the first column (or the first row) from the Hadamard matrix. If the phase modulation multiplex recording is performed by creating a phase address code based on the remaining elements from which the phase is removed and optically phase-modulating the second light beam with the phase modulation pattern generated from the phase address code, the reproduction data Crosstalk can be reduced, and the S / N ratio of the reproduced data can be maintained well.

  The present invention also relates to a hologram reproducing apparatus for reproducing data by reading out diffracted light generated by irradiating a light beam onto a hologram recording medium on which interference fringes are recorded, and receiving the light by a light receiving element. Phase address code generating means for generating a phase address code based on the remaining elements from which either the first column or the first row of the matrix is removed, and a phase modulation pattern generated from the generated phase address code And an optical phase modulation means for optical phase modulating the optical beam, and irradiating the hologram recording medium with the optical phase modulated optical beam to obtain the diffracted light.

  Thus, in the hologram reproducing apparatus of the present invention, a phase address code is created based on the remaining elements obtained by removing either the first column or the first row from the Hadamard matrix, which is a kind of unitary matrix, and this phase By optically phase-modulating the light beam (reproduction light) with the phase modulation pattern generated from the address code, the same reproduction light as the reference light at the time of recording is generated, and this is irradiated onto the hologram recording medium, thereby Data with good S / N with reduced talk can be reproduced.

  The present invention is also a hologram recording method for recording interference fringes generated by causing a first light beam spatially modulated by recording data to interfere with a second light beam on a hologram recording medium, wherein the unitary matrix A step of creating a phase address code based on the remaining elements from which either the first column or the first row is removed, and the second light by a phase modulation pattern generated from the created phase address code And optically phase-modulating the beam, and multiple-recording interference fringes of the optical phase-modulated second light beam and the spatial light-modulated first light beam in the same region of the hologram recording medium It is characterized by that.

  As described above, in the hologram recording method of the present invention, when the optical phase modulation is performed out of the ideal state, when a phase address code is created from a unitary matrix, for example, a Hadamard matrix, the elements constituting the matrix This is equivalent to the case where the phase address code is created based on the Hadamard matrix in which a part of is deviated from the original value. In this Hadamard matrix, the first column (or first row) is removed from the Hadamard matrix because the elements of the first column and the first row greatly contribute to the effect of generating crosstalk when data recorded in multiple recording is reproduced. A phase address code is created based on the remaining elements, and the second light beam is optically phase-modulated by the phase modulation pattern generated from the phase address code. Talk can be reduced, and the S / N ratio of the reproduced data can be kept good.

  The present invention also relates to a hologram reproduction method for reproducing data by reading out a diffracted light generated by irradiating a light beam onto a hologram recording medium on which interference fringes are recorded, and receiving the light by a light receiving element. A step of generating a phase address code based on the remaining elements obtained by removing either the first column or the first row of the matrix; and the light beam by a phase modulation pattern generated from the generated phase address code. And diffracting light to obtain the diffracted light by irradiating the hologram recording medium with the optical phase-modulated light beam.

  Thus, in the hologram reproducing method of the present invention, a phase address code is created based on the remaining elements obtained by removing either the first column or the first row from the Hadamard matrix, which is a kind of unitary matrix, and this phase By optically phase-modulating the light beam (reproduction light) with the phase modulation pattern generated from the address code, the same reproduction light as the reference light at the time of recording is generated, and this is irradiated onto the hologram recording medium, thereby Data with good S / N with reduced talk can be reproduced.

  The present invention is also a method for creating a phase address code for generating a phase modulation pattern to be displayed on the optical phase modulator when the optical beam is optically phase modulated by the optical phase modulator, the matrix size m Generating a Hadamard matrix, removing one of the first column or the first row of the generated Hadamard matrix, and the Hadamard from which either the first column or the first row is removed Creating a phase modulation address code from the remaining elements of the matrix.

  Thus, in the phase address code creation method of the present invention, a phase modulation address code is created from the remaining elements of the Hadamard matrix from which either the first column or the first row is removed, and is generated from this phase modulation address code. If the phase modulation pattern is used, if the reference light is optically phase-modulated, phase modulation multiplexing with little crosstalk can be performed even if the optical phase modulation is shifted from an ideal state.

  The present invention is also a program for creating a phase address code for generating a phase modulation pattern to be displayed on the optical phase modulator when the optical beam is optically phase modulated by the optical phase modulator, the matrix size m A function of generating a Hadamard matrix, a function of removing either the first column or the first row of the generated Hadamard matrix, and a Hadamard from which one of the first column or the first row is removed And a function of creating a phase modulation address code from the remaining elements of the matrix.

  As described above in detail, according to the present invention, a phase address code is generated based on the remaining elements obtained by removing the first column (or first row) from the Hadamard matrix, and is generated from this phase address code. By displaying the phase modulation pattern on the optical phase modulator and modulating the reference light (reproduced light) with this optical phase modulator, the reference light is deviated from the parallel light or its brightness is not uniform. Thus, even if the optical phase modulation deviates from the ideal state, the crosstalk can be reduced and the S / N ratio of the reproduced data can be maintained well. Also, phase modulation multiplex recording with good S / N can be performed even if the accuracy of an optical system that generates parallel reference light with uniform brightness is reduced.

  Even if optical phase modulation is not performed in an ideal state when data is multiplexed and recorded by phase modulation multiplexing, the purpose of reducing the crosstalk and maintaining a good S / N ratio of the reproduced data is based on the Hadamard matrix. A phase address code is created based on the remaining elements from which the first column (or first row) is removed, and a phase modulation pattern generated from the phase address code is displayed on the optical phase modulator. This was realized by optical phase modulation of the reference beam (reproduced beam).

  FIG. 1 is a block diagram showing a configuration of a hologram recording / reproducing apparatus according to an embodiment of the present invention. However, the same parts as in the conventional example will be described using the same reference numerals. The hologram recording / reproducing apparatus includes a laser light source 2, a shutter 4, a beam splitter 6, a mirror 8, a spatial light modulator 10, a signal light lens (Fourier lens) 10, a hologram recording medium 14, a mirror 16, and a lens (inverse Fourier lens). 18, an image pickup device 20 such as a CCD, a two-dimensional spatial light phase modulator (hereinafter simply referred to as a phase modulator) 22, a lenslet array 24, and a reference light (or reproduction light) lens (Fourier lens) 26 Configured. However, the hologram recording medium in the claims corresponds to the hologram recording medium 14, the optical phase modulation means corresponds to the spatial light phase modulator 22, and the light receiving element corresponds to the imaging element 20.

  As the two-dimensional phase modulator 22, PPMX8267 manufactured by Hamamatsu Photonics is used, and its performance is as follows: input signal XGA level, number of control pixels of about 590000 (pixels), effective screen size 20 × 20 mm, phase modulation amount 2π or more It is.

  FIG. 2 is a block diagram showing a configuration of a signal processing system of the hologram recording / reproducing apparatus shown in FIG. In the signal processing system, a control unit 28 such as a personal computer controls opening / closing of the shutter 4, display control of a data page of the spatial light modulator 10, and a two-dimensional phase modulator 22 having a phase modulation pattern corresponding to a phase address code described later. Display control and control for reproducing image data from the light reception signal of the image sensor 20. However, the phase address code creating means in the claims corresponds to the control unit 28.

  Next, the operation of the present embodiment will be described. First, the control unit 28 displays a data page to be recorded on the spatial light modulator 10 and displays a phase modulation pattern on the two-dimensional phase modulator 22 and then opens the shutter 4. As a result, the coherent laser light emitted from the laser light source 2 enters the beam splitter 6 through the shutter 4 and branches into the signal light (first light beam) 100 and the reference light (second light beam) 200. Is done. The signal light 100 is incident on the spatial light modulator 10 via the mirror 8, and the signal light is intensity-modulated by the spatial light modulator 10 displaying the data page. The intensity-modulated signal light is condensed on the hologram recording medium 14 by the lens 12.

  On the other hand, the reference beam 200 is incident on the two-dimensional phase modulator 22 via the mirror 16 and is optically phase-modulated (hereinafter simply referred to as phase modulation), and then the hologram via the lenslet array 24 and the lens 26. The light is condensed on the recording medium 14 so as to overlap the signal light 100. As a result, the signal light 100 and the reference light 200 are overlapped in the recording area of the hologram recording medium 14, and the interference fringes formed as a result are recorded on the hologram recording medium 14 as a fine dense pattern.

  In order to reproduce the data recorded on the hologram recording medium 14, the same reproduction light as the reference light 200 is incident on the hologram recording medium 14, thereby diffracted light corresponding to the interference fringes recorded on the hologram recording medium 14. And the diffracted light is focused on the image sensor 20 such as a CCD or CMOS by the lens 18. The image sensor 20 photoelectrically converts the received diffracted light, and the received light signal obtained is analyzed by the control unit 28 and reproduced as image data.

  Here, the phase modulation pattern displayed on the two-dimensional phase modulator 22 that modulates the reference light 200 will be described in more detail with reference to FIG. The phase modulator 22 displays a phase modulation pattern for optical phase modulation of the reference light 200 as shown in FIG. The reference beam 200 enters the phase modulator 22 as a plane wave, and is optically phase-modulated according to the recording multiplicity by the phase modulation pattern.

  Thereafter, the reference light 200 having the respective phases is incident on the same region of the hologram recording medium 14 by the lens 26, undergoes intensity modulation by the spatial light modulator 10, and interferes with the signal light 100 incident by the lens 12. Form stripes. When reproducing a data page that has been phase-modulated and multiplexed, the reproduction light that is optically phase-modulated with the same phase modulation pattern as that used to record each data page is reproduced at the same angle as the recording. When incident on the recording medium 14, the corresponding data page can be reproduced independently from the same recording area.

  By the way, when data pages are multiplexed and recorded in one recording area of the hologram recording medium 14 by the phase modulation multiplexing method, the situation where there is no crosstalk between the data pages is expressed by the following equation (1).

  In this equation (1), the phase address of the reference beam 200 used for recording the i-th data page is indicated by a χ · χ * unitary matrix. N columns (or rows) which are orthogonal to each other are obtained from the matrix of the equation (1), and the matrix element corresponds to the phase term of the phase address code, which is a phase address code capable of maximum multiplexing (N multiplexing) and Become.

  This phase address code is generally generated using a Walsh-Hadamard matrix (H-matrix). This H-matrix includes the same number of 1s and -1 except for elements on two sides of the matrix, and the H-matrix is generated by the following algorithm.

  Here, if 1 of each element of the H-matrix represented by Expression (2) is associated with modulation 0 and −1 is associated with modulation π, a phase orthogonal address code satisfying Expression (1) is obtained.

  In the case of the phase modulation multiplexing method, as described above, among the light waves diffracted according to the Bragg condition, extra light waves contributing to crosstalk are weakened by interference and disappear. By this principle, multiple recording of data is possible, and the S / N ratio can be dramatically improved as compared with other multiplexing systems.

  Next, the correspondence relationship between the orthogonal code (phase address code) obtained by the H-matrix and the phase modulation pattern displayed by the phase modulator 22 will be described. The simplest method for associating the orthogonal code with the display pattern of the phase modulator 22 is to divide the reference beam 200 into a two-dimensional lattice and to divide the multiplicity into N, and to associate one element of the orthogonal code with each cell. is there. In the case of H-matrix H (4), it is expressed as shown in equation (3), and the phase address code is (φi1, φi2, φi3, φi4).

  Phase modulation patterns are created corresponding to the phase address codes φ1, φ2, φ3, and φ4 shown on the right side of the equation (3). With these phase modulation patterns, the phase address codes are allocated in a two-dimensional plane. Therefore, as shown in FIG. 4A, the phase modulation pattern is obtained by dividing the display surface of the phase modulator 22 into four, and each divided portion has a pattern in which 0 corresponds to −π. FIG. 4B shows an actual phase modulation pattern, where 0 is black and −π is white. In FIG. 4B, the phase modulation patterns corresponding to the phase address codes φ1, φ2, φ3, and φ4 are indicated by P1, P2, P3, and P4, respectively.

  Therefore, the control unit 28 displays the phase modulation pattern P1 shown in FIG. 4B on the phase modulator 22, and also displays the data page data D1 (not shown) on the spatial light modulator 10, which is described above. As described above, the data page data D1 is hologram-recorded in the recording area of the hologram recording medium 14. Next, the control unit 28 displays the phase modulation pattern P2 shown in FIG. 4B on the phase modulator 22, and also displays the data page data D2 on the spatial light modulator 10, so that the hologram recording medium 14 Data page data D2 is holographically recorded in the same recording area as described above. By repeating this, four pages of data from the data page data D1 to D4 are phase-modulated and multiplexed recorded in the same recording area of the hologram recording medium 14.

  At the time of reproduction, phase modulation patterns P1 to P2 are sequentially displayed on the phase modulator 22 to generate reproduction light that is the same as the reference light 200, and irradiating the reproduction light onto the recording area of the hologram recording medium 14 The data page data D1 to D4 can be read and reproduced sequentially.

  As described above, multiplexing without crosstalk is realized using an orthogonal code when the optical phase modulation by the phase modulator 22 is performed with binary values of 0 or π. Although the modulation accuracy by the phase modulator 22 has been improved, it is unavoidable that the ideal performance is slightly deviated from the ideal performance due to the unevenness of the brightness of the reference light 300 and the aberration of the optical system. There will be a lot of talk.

  Considering this situation, a method for improving crosstalk by using only the first column (or first row) of a matrix when generating an orthogonal code from an H-matrix will be described. The reason for this will be described using H (4) shown in the following equation (4).

  Here, it is assumed that the reference light 200 is modulated by the phase modulator 22 so that the region to be modulated by π is uniformly shifted from π by δ. Then, the H-matrix is rewritten as shown in the following equation (5).

  When the same calculation as in the equation (1) is performed using the equation (5), the result shown in the equation (6) is obtained.

  The orthogonality of this matrix is as shown in Equation (6), and it can be seen that crosstalk is particularly strong in the first column (or the first row) with respect to the diagonal component necessary for the reproduction signal. .

  When calculating how much the crosstalk actually becomes, when the optical phase modulation is ideally performed, if the same calculation as the expression (1) is performed using the expression (4), the following expression (7) ) Is obtained, and when the accuracy of optical phase modulation is poor, δ = 0.3 is set in equation (5), and using this, calculation similar to equation (1) is performed to obtain equation (8).

  Here, the reproduced image data corresponding to Expression (7) is shown in FIG. 5A, and the reproduced image data corresponding to Expression (8) is shown in FIG. 5B. In FIG. 5A, it can be seen that there is no crosstalk, the diagonal components are white and the remaining components are all black, and there is no crosstalk. On the other hand, in FIG. 5B, the diagonal component is white and the remaining components are all gray and black, which indicates that there is crosstalk. In addition, it can be seen that the gray portion is a portion where the crosstalk is large and corresponds to the first column (or the first row) of Expression (8).

  In general, the crosstalk component in the H-matrix that can be m-multiplexed is shown in the portion excluding the diagonal component of Equation (9).

  In equation (9), the crosstalk of the terms in the first column (or the first row) is proportional to δ, as compared to the fact that the crosstalk of the terms other than the first column (or the first row) is effective at δ2. And increase. Therefore, crosstalk can be reduced if the terms in the first column (or first row) are not used. Therefore, if these terms are not used as the phase address code in advance, even if the optical phase modulation deviates from the ideal state, the crosstalk in the phase modulation multiplex recording can be reduced. This effect has been confirmed. Although the case where the phase shift is uniform (δ = constant) is considered here, the first column (or the first row) is also used when there is a random phase shift around a certain average shift amount. Use of the phase address code excluding the row) is effective in reducing crosstalk.

  FIG. 6 is a flowchart showing a procedure for creating a phase address code by the control unit 28. First, when a matrix size m corresponding to the maximum multiplicity at the time of phase modulation multiplex recording is designated and inputted (step S1), an m × m Hadamard matrix H (m) represented by equation (9) is generated. (Step S2), the elements in the first column are removed from the created Hadamard matrix H (m) (Step S3). The second column, third column,..., M-th column of the Hadamard matrix H (m) from which the elements of the first column are removed are set as address codes φ1, φ2,..., Φm−1 (step S4), and the phase modulation address Codes (φ1, φ2,..., Φm−1) are created (step S5).

  Thereafter, the control unit 28 creates a phase modulation pattern corresponding to the phase address code (φ1, φ2,..., Φm−1) by the same method as described with reference to FIG. 4 and sequentially displays it on the phase modulator 22. The same phase modulation multiplex recording as described above is performed.

According to the present embodiment, a phase address code is created from each element obtained by removing the first column (or first row) of the Hadamard matrix, and a phase modulation pattern corresponding to the created phase address code is generated. By performing optical phase modulation of the reference light by the two-dimensional phase modulator 22 displaying the phase modulation pattern and performing phase modulation multiplex recording / reproduction, the optical phase is caused by unevenness in the brightness of the reference light 200 or aberration of the optical system. Even if the modulation is performed out of the ideal state, multiplex recording / reproduction with reduced crosstalk can be performed. Therefore, phase modulation multiplex recording / reproduction with good S / N can be performed even if the accuracy of an optical system that generates parallel reference light with uniform brightness is moderated. Can be increased efficiently without imposing a burden on the device.

  The procedure for creating the phase address code shown in FIG. 6 of the present embodiment can be implemented by programming it as a phase address code creating program and causing it to be executed by a computer. At this time, the phase address code creating program can be supplied to the computer through a disk-type storage medium such as a flexible disk or a hard disk, various memories such as a semiconductor memory or a card-type memory, or various program storage media such as a communication network.

  In addition, the present invention is not limited to the above-described embodiment, and can be implemented in various other forms in specific configurations, functions, operations, and effects without departing from the gist thereof.

It is the block diagram which showed the structure of the hologram recording / reproducing apparatus which concerns on one embodiment of this invention. FIG. 2 is a block diagram showing a configuration of a signal processing system of the hologram recording / reproducing apparatus shown in FIG. 1. FIG. 2 is a perspective view illustrating an operation of a two-dimensional phase modulator that optically modulates the reference light illustrated in FIG. 1. It is explanatory drawing which showed the production | generation method of the phase modulation pattern displayed on the two-dimensional phase modulator shown in FIG. It is a figure explaining the difference in crosstalk when the orthogonality of H-matrix is hold | maintained, and the case where orthogonality is not hold | maintained. 3 is a flowchart showing a procedure for creating a phase address code by the control unit of FIG. 2. It is the schematic which showed the structural example of the recording / reproducing system of the conventional hologram storage.

Explanation of symbols

  2 ... Laser light source, 4 ... Shutter, 6 ... Beam splitter, 8, 16 ... Mirror, 10 ... Spatial light modulator, 12 ... Signal light lens (Fourier lens), 14 ... Hologram recording medium , 18... Lens (inverse Fourier lens), 20... Imaging element, 22... Spatial light phase modulator, 24... Lenslet array, 26. .

Claims (12)

A hologram recording apparatus that records interference fringes generated by causing a first light beam spatially modulated by recording data to interfere with a second light beam on a hologram recording medium,
Phase address code creating means for creating a phase address code based on the remaining elements obtained by removing either the first column or the first row of the unitary matrix;
Optical phase modulation means for optically phase-modulating the second light beam with a phase modulation pattern generated from the created phase address code,
A hologram recording apparatus, wherein interference fringes of the optical phase-modulated second light beam and the spatial light-modulated first light beam are multiplexed and recorded in the same region of the hologram recording medium.   The hologram recording apparatus according to claim 1, wherein the unitary matrix is a Hadamard matrix.   2. The hologram recording apparatus according to claim 1, wherein the optical phase modulation means includes an optical phase modulator that displays a two-dimensional phase modulation pattern. A hologram reproducing apparatus for reproducing data by reading out a diffracted light generated by irradiating a light beam onto a hologram recording medium on which interference fringes are recorded, by receiving the light with a light receiving element,
Phase address code creating means for creating a phase address code based on the remaining elements obtained by removing either the first column or the first row of the unitary matrix;
Optical phase modulation means for optically phase-modulating the light beam with a phase modulation pattern generated from the created phase address code,
A hologram reproducing apparatus characterized in that the diffracted light is obtained by irradiating the hologram recording medium with the optical phase-modulated light beam.   The hologram reproducing apparatus according to claim 4, wherein the unitary matrix is a Hadamard matrix.   5. The hologram reproducing apparatus according to claim 4, wherein the optical phase modulation means includes an optical phase modulator that displays a two-dimensional phase modulation pattern. A hologram recording method for recording interference fringes generated by causing a first light beam spatially modulated by recording data to interfere with a second light beam on a hologram recording medium,
Creating a phase address code based on the remaining elements from which either the first column or the second row of the unitary matrix is removed;
Optically phase-modulating the second light beam with a phase modulation pattern generated from the generated phase address code,
A hologram recording method, wherein interference fringes of the optical phase-modulated second light beam and the spatial light-modulated first light beam are multiplexed and recorded in the same region of the hologram recording medium.   The hologram recording method according to claim 7, wherein the unitary matrix is a Hadamard matrix. A hologram reproduction method for reproducing data by reading out diffracted light generated by irradiating a light beam onto a hologram recording medium on which interference fringes are recorded, by receiving the light with a light receiving element,
Creating a phase address code based on the remaining elements from which either the first column or the first row of the unitary matrix is removed;
Optical phase modulation of the light beam with a phase modulation pattern generated from the generated phase address code,
A hologram reproducing method, wherein the diffracted light is obtained by irradiating the hologram recording medium with the optical phase-modulated light beam.   The hologram reproduction method according to claim 9, wherein the unitary matrix is a Hadamard matrix. A method of creating a phase address code for generating a phase modulation pattern to be displayed on the optical phase modulator when optical phase modulation of the light beam is performed by the optical phase modulator,
Generating a Hadamard matrix of matrix size m;
Removing either the first column or the first row of the generated Hadamard matrix;
Creating a phase modulation address code from the remaining elements of the Hadamard matrix from which either the first column or the first row has been removed;
A phase address code creating method comprising: A program for creating a phase address code for generating a phase modulation pattern to be displayed on the optical phase modulator when an optical beam is optically phase modulated by an optical phase modulator,
A function for generating a Hadamard matrix of matrix size m,
A function of removing either the first column or the first row of the generated Hadamard matrix;
A function of creating a phase modulation address code from the remaining elements of the Hadamard matrix from which either the first column or the first row is removed;
A program for creating a phase address code, characterized in that a computer is realized.

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