JP2005135531A - Hologram recording reproducing device, hologram recording reproducing method, method for creating address code, and program for creating address code - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To well maintain a S/N ratio of reproduced data by reducing crosstalk among multiple recorded data even if optical phase modulation of reference light deviates from an ideal state. <P>SOLUTION: When different recording data are recorded in a multiplexed manner on a same spot using phase modulation multiplexing, in recording the recording data, a phase modulation pattern created from a phase address code different from a phase address code used when reference light 200 was subjected to optical phase modulation by a spatial phase modulator 18 is indicated on the spatial phase modulator 18 to be subjected to optical phase modulation and then emitted to a hologram recording medium 14, thereby the recording data are read out by an image sensor 16 and thus reproduction data are obtained. Accordingly, even if operation of the spatial phase modulator 18 deviates from an ideal condition, crosstalk components included in the reproduction data are reduced, therefore reproduction data having a good S/N ratio is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hologram recording / reproducing apparatus and method, and more particularly to an address code creating method and an address code creating program for reducing crosstalk noise in phase multiplex recording / reproducing.

  In recent years, holographic data storage systems that record and reproduce large amounts of data using hologram technology have been proposed. In this hologram recording / reproducing system, for example, signal light including recording data generated by spatial light modulation means such as a liquid crystal element and reference light set corresponding to the signal light are applied to a hologram recording medium at a predetermined angle. A recording system that records interference fringes generated by signal light and reference light on a hologram recording medium by irradiation, and reproduction corresponding to a dense pattern by irradiating reproduction illumination light (hereinafter referred to as illumination light) to the hologram medium It is configured to have a reproduction system that generates light, receives the light by a light receiving element such as a CCD image sensor, analyzes the light, and reproduces the data. A hologram per spatial light modulator recorded in this way is called a page.

  FIG. 5A is a schematic configuration diagram showing a recording system of a conventional holographic data storage system. Light emitted from a coherent light source (for example, a laser light source) 2 is split into a signal light 100 and a reference light 200 by a beam splitter 4, and the signal light 100 is modulated by a spatial light modulator 6 displaying desired data. Irradiated onto the hologram recording medium 10 via the lens 8. On the other hand, the reference light 200 is also irradiated to the same area as the signal light through the lens 12, and interference fringes resulting from the interference between the signal light 100 and the reference light 200 are recorded on the recording medium 10.

  FIG. 5B is a schematic configuration diagram showing a reproduction system of a conventional holographic data storage system. At the time of reproduction, the hologram recording medium 10 is irradiated from the same direction as the reference light through the lens 12 with the same reproduction illumination light 300 as the recording reference light generated from the light source 2 similar to that at the time of recording. The reproduction light (diffracted light) 400 is generated by the interference fringes recorded in the image 10, and this is detected by the image sensor 16 through the lens 14, whereby reproduction data can be obtained.

  In the holographic data storage system as described above, a technique called multiple recording is used to improve recording density. This is different from conventional recording in that a large number of independent pages are recorded in one place. Typical examples of such multiplex recording methods are angle multiplex recording, shift multiplex recording, phase code multiplex recording, and the like.

  Angle multiplexing is for recording and reproducing a large number of independent pages in one place by changing the angle of the reference beam. Shift multiplex performs multiplex recording by shifting the recording position little by little. In phase multiplexing, when recording one page, recording is performed by simultaneously applying reference light from various directions. At this time, a phase change is given to the reference light from each direction. By combining this phase change in various ways, a large number of independent pages are recorded and reproduced at one place.

  Here, when an optical disk is taken as an example of the hologram recording medium 10, one page of data (= number of spatial light modulator pixels) can be recorded in one recording spot by one hologram recording. Further, the recording spot can be overwritten by the multiplicity. Therefore, the storage capacity of the entire optical disk can be obtained by considering the number of recording spots on the entire disk and recording capacity = number of spatial light modulator pixels × spot number × multiplicity.

When this multiplex recording is performed, noise becomes a problem. When the multiplicity is increased, not only the originally recorded page pattern but also a phenomenon that a portion that should be reproduced in black originally becomes brighter. There are several causes of noise, such as crosstalk between different pages, and scattering noise caused by materials (for example, see Non-Patent Document 1). This crosstalk is a phenomenon in which pages that should originally be independent are overlapped and reproduced. In a simple example, when the angle change amount of the reference light between each page is not sufficient in angle multiplexing, crosstalk noise is remarkably generated. In this case, the problem of crosstalk noise can be solved by taking a sufficient amount of angle change, and the same can be done for shift multiplexing.
Holographic Data Storage: HJCoufal, D.Psaltis, GTSincerbox ED: Springer: p.63-88 Fundamental Noise Sources in Volume Holographic Storage)

  As described above, the multiplex recording of the hologram by the phase multiplexing method does not require mechanical control for addressing each page, and is advantageous in improving the transfer rate and has a merit that the noise level is reduced. However, it is thought that if the phase modulation degree in the phase modulator used in the phase multiplexing system takes an ideal value, the crosstalk can be suppressed considerably. It deviates from the value, crosstalk occurs, and the S / N ratio of the reproduction data deteriorates. Moreover, since the concept of taking a sufficient amount of change is not valid in phase multiplexing, there is currently no suitable method for suppressing the occurrence of crosstalk and improving the S / N ratio of reproduced data.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to reduce crosstalk between multiple recorded data even if the optical phase modulation of the reference light deviates from an ideal state. Another object of the present invention is to provide a hologram recording / reproducing apparatus, a hologram recording / reproducing method, an address code creating method, and an address code creating program capable of maintaining a good S / N ratio of reproduced data.

  In order to achieve the above object, the present invention 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. A hologram recording / reproducing apparatus for reproducing data by receiving diffracted light generated by irradiating a third light beam by receiving it with a light receiving element, wherein the second light beam is generated from a phase address code. First phase modulation means for optical phase modulation using a modulation pattern, and a phase modulation pattern generated from a phase address code different from the phase address code used when optically modulating the second light beam during recording of the recording data And second phase modulation means for optical phase modulating the three light beams, and using the phase-modulated second light beam The recording data is recorded as the interference fringes on the hologram recording medium, and the hologram recording medium is irradiated with the phase-modulated third light beam to reproduce the same recording data as the recording data. To do.

  As described above, in the hologram recording / reproducing apparatus of the present invention, when different recording data is multiplexed and recorded on the same spot by phase modulation multiplexing, the second light beam (reference light) is optically phase modulated when recording the recording data. In order to obtain a reproduction data by reading out the recording data by irradiating the hologram recording medium with a third light beam (illumination light) by a phase modulation pattern generated from an address code different from the address code, Even if optical phase modulation is performed with a deviation from the ideal value, the crosstalk component included in the reproduction data can be reduced, and therefore reproduction data with a good S / N ratio can be obtained.

  Further, the present invention records interference fringes generated by causing the first light beam spatially modulated by the recording data to interfere with the second light beam on the hologram recording medium, and the third light is recorded on the hologram recording medium. A hologram recording and reproducing method for reproducing data by reading out diffracted light generated by irradiating a beam with a light receiving element and reproducing the data by using a phase modulation pattern generated from a phase address code. A phase modulation step, and a third light beam is optically phase-modulated by a phase modulation pattern generated from a phase address code different from the phase address code used when the second light beam is optically phase-modulated when recording the recording data. And the recording data as the interference fringes using the phase-modulated second light beam. Recorded on beam recording medium, characterized by comprising a step of reproducing the same recording data and by irradiating the recording data of the third light beam the phase modulation in the holographic recording medium.

  As described above, the hologram recording / reproducing method of the present invention is used when the second light beam (reference light) is optically phase-modulated when recording data is recorded when multiple recording data is recorded in the same spot by phase modulation multiplexing. In order to obtain a reproduction data by reading out the recording data by irradiating the hologram recording medium with a third light beam (illumination light) by a phase modulation pattern generated from an address code different from the address code, Even if optical phase modulation is performed with a deviation from the ideal value, the crosstalk component included in the reproduction data can be reduced, and therefore reproduction data with a good S / N ratio can be obtained.

  The present invention also relates to a method for generating an address code used when optical phase modulation of a light beam is performed, the step of generating a square matrix having a matrix size of m rows and m columns, and a specific row of the generated matrix. A step of removing, a step of creating an address code for reproduction by extracting each row of the matrix from which the specific row has been removed, and two or more types of sums of zero for each address code for reproduction And a step of creating an address code for recording by applying a coefficient.

  As described above, in the address code generation method of the present invention, a specific row of an m × m square matrix is removed, and each row of the matrix is extracted to generate a reproduction address code. An address code for recording is created by multiplying each element of the code by two or more types of coefficients with a total sum of zero. Thereafter, interference fringes are recorded on the hologram recording medium by interfering with the reference light that has been optically phase-modulated using the recording address code and the signal light that has been spatially modulated according to the recording data, and the reproducing address code is recorded. By irradiating the hologram recording medium with illumination light that has been optically phase-modulated and reproducing the same data as the recorded data, even if the optical phase modulation is deviated from the ideal value, The talk component can be reduced, and therefore reproduction data with a good S / N ratio can be obtained.

  The present invention is also a program for creating an address code for use in optical phase modulation of a light beam, which removes a specific row of the generated matrix and a function of generating an m × m square matrix. A function, a function of creating a first address code from the matrix from which the particular row has been removed, and a second address by multiplying each element of the first address code by two or more types of coefficients whose sum is zero. And a function of creating an address code for a computer.

According to the present invention, when different recording data is multiplexed and recorded on the same spot by phase modulation multiplexing, the address code used for optical phase modulation of the reference light at the time of recording the recording data and the optical phase modulation of the illumination light at the time of reproduction are performed. By reading out the same playback data as the recorded data using different address codes, the crosstalk contained in the playback data can be reduced even if the optical phase modulation of the reference light deviates from the ideal state. Thus, the S / N ratio of the reproduction data can be kept good.
As a result of the disappearance of the crosstalk noise, the multiplicity of recording data by the phase modulation multiplexing method can be increased, and the storage capacity of the hologram recording medium can be increased correspondingly.
In addition, the above effect can be achieved without making the apparatus complicated and expensive, since it is only necessary to devise coding at the time of recording of the phase modulator originally included in the reference light without performing new optical phase modulation on the signal light side. Can be obtained.
Furthermore, the effect that the crosstalk component can be reduced even if the optical phase modulation deviates from the ideal value means that the demand for the accuracy of the phase modulator can be relaxed. Price can be achieved. For the same reason, tolerance for various instabilities becomes loose, and the degree of freedom in device design can be improved.

  Even if the optical phase modulation of the reference beam deviates from the ideal state, the same spot is used by phase modulation multiplexing for the purpose of reducing the crosstalk between multiplexed data and maintaining a good S / N ratio of the reproduced data. When recording different recording data, the address code used for optical phase modulation of the reference light during recording of the recording data is different from the address code used for optical phase modulation of the illumination light during reproduction. This is realized by reading the same playback data.

  FIG. 1 is a configuration diagram showing a configuration of a hologram recording / reproducing apparatus according to the first embodiment of the present invention. The hologram recording / reproducing apparatus includes a laser light source 2, a beam splitter 4, a spatial light modulator 6, a lens (Fourier transform lens) 8, a hologram recording medium 10, a lens 12, a lens (inverse Fourier transform lens) 14, an image sensor 16, and a space. A phase modulator (hereinafter referred to as a phase modulator) 18, a lenslet array 20, and a control unit 22 are configured. However, the hologram recording medium in the claims corresponds to the hologram recording medium 10, and the first and second phase modulation means correspond to the spatial phase modulator 18.

  Next, the operation of the present embodiment will be described. First, the control unit 22 displays a data page to be recorded on the two-dimensional spatial light modulator 6 and displays a phase modulation pattern on the two-dimensional phase modulator 18. Thereafter, the coherent laser light emitted from the laser light source 2 enters the beam splitter 4 and is branched into a signal light (first light beam) 100 and a reference light (second light beam) 200, and the signal light. 100 is incident on the spatial light modulator 6. The signal light 100 is intensity-modulated by the spatial light modulator 6 displaying the data page, and the intensity-modulated signal light is condensed on the hologram recording medium 10 by the lens 8.

  On the other hand, the reference light 200 is incident on the two-dimensional phase modulator 18 and is optically phase-modulated here, and then collected on the hologram recording medium 10 via the lenslet array 20 and the lens 12 so as to overlap the signal light 100. Lighted. As a result, the signal light 100 and the reference light 200 are overlapped at the recording spot of the hologram recording medium 10, and the interference fringes formed as a result are recorded on the hologram recording medium 10 as a fine dense pattern.

  In order to reproduce the data recorded on the hologram recording medium 10, the same illumination light as the reference light 200 is optically spatially phase-modulated by the phase modulator 18 and incident on the hologram recording medium 10. Data is reproduced as diffracted light (hereinafter referred to as reproduction light) corresponding to the recorded interference fringes, and this reproduction light is condensed on an image sensor 16 such as a CCD or CMOS by the lens 14. The image sensor 16 photoelectrically converts the received diffracted light, and the received light signal obtained is analyzed by the control unit 22 and reproduced as image data.

    Here, in the above operation, the phase modulator 18 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 18 as a plane wave, and is optically phase-modulated according to the recording multiplicity by the phase modulation pattern. On the other hand, the data pattern is displayed on the spatial light modulator 6 by the control unit 22 as shown in FIG. 2, and the signal light 100 is intensity-modulated by the data pattern. The signal light 100 subjected to intensity modulation by the spatial light modulator 6 is incident on the hologram recording medium 10 by the lens 8, and the reference light 200 optically phase-modulated by the phase modulator 18 at the same time is the same as that of the hologram recording medium 10 by the lens 12. By entering the region, the signal light 100 and interference fringes are formed.

  When reproducing a data page recorded in phase modulation multiplex, a phase modulation pattern different from the phase modulation pattern used to record each data page (this different phase modulation pattern, ie, a different address code should be used) This is a feature of the present embodiment. This will be described later.) When the illumination light that has been optically phase-modulated in 9 is incident on the hologram recording medium 10 at the same angle as that during recording, it corresponds from the same recorded spot Data pages can be played independently.

  Next, the phase modulation multiplexing operation in the hologram recording / reproducing apparatus will be described in detail. The phase modulator 18 is given a phase of φ1 = (φ11, φ12,..., Φ1N), the optical phase of the reference light 200 is modulated, and this interferes with the signal light 100 whose intensity is modulated by the spatial light modulator 6 The fringes are recorded on the hologram recording medium 10 as shown in FIG. Thereafter, a phase of φj = (φj1, φj2,..., ΦjN) is applied to the spatial light modulator 6 to irradiate the hologram recording medium 10 with the illumination light that has been optically phase-modulated and reproduced as shown in FIG. Assume that light 400 is obtained.

  The amplitude ratio between the reproduction light 400 and the signal light 100 reproduced at this time is expressed by the following equation (1).

However, χ _lm in the equation (1) is defined as χ _lm = e ^iφ _lm . ^Expressing this in the form of a matrix, when (χ _lm ) = (e ^iφlm ), the matrix A representing the reproduction amplitude is expressed by the following equation (2).

  Hereinafter, the matrix χ is referred to as a phase code matrix, and A is referred to as a reproduction amplitude matrix. The meaning of this matrix A is as follows. First, Equation (2) is rewritten as shown in Equation (3) below.

In equation (3), when recording is performed with φl and playback is performed with φm, it can be seen that the playback amplitude is a _lm . From this, it can be understood that the diagonal component of the matrix A is a signal and the other components are crosstalk noise. That is, the matrix χ is required to satisfy χ · χ * = En (where En is an n × n unit matrix).

  Further, considering the case of multiple recording, φ1, φ2, φ3,... Are multiplexed during recording. In the normal method, reproduction is performed with φl during reproduction. In this case, the reproduction amplitude is a1l + a2l + a3l +. ,..., All +, and the S / N ratio is expressed by the following equation (4).

As an example of the phase code matrix χ, a Hadamard matrix is known. The 4 × 4 Hadamard matrix H ⁽⁴⁾ is expressed by the following equation (5).

The matrix of this equation (5) is H ⁽⁴⁾ × H ^{(4) *} = E ₄ and has the necessary characteristics for the phase code matrix.

  If the ideal Hadamard code as described above can be generated, reproduction with considerably less crosstalk is possible, but the actual operation of the phase modulator 18 has a deviation from the ideal state as described above. That is, when the 1 component of the phase code matrix is considered as a reference, in order to produce the −1 component, the phase of the light needs to be modulated by π by the phase modulator 18. However, in practice, there is always a deviation from π modulation, which causes crosstalk noise.

  Hereinafter, this situation will be described in detail. First, it is assumed that a phase shift by π + α by a phase modulator 18 is shifted by π + α. When this phase shift is reflected in the Hadamard matrix of the equation (5), the following equation (6) is obtained.

  When the reproduction amplitude matrix A in such a case is calculated, it can be seen that the following equation (7) is obtained.

  In this equation (7), the diagonal component is a signal for reproduction and the other components are crosstalk components. Moreover, it can be seen that among these crosstalk components, the first column (or first row) component is large. Therefore, it can be seen that the S / N ratio increases when the address code (1, 1, 1, 1) is excluded from the Hadamard matrix of Equation (6). When this code (1, 1, 1, 1) is excluded, the S / N ratio for each address code is calculated using equation (4), and is expressed by the following equation (8).

  When this equation (8) is generalized in the case of a 2m matrix, the following equation (9) is obtained.

  When the S / N ratio is calculated in the matrix of the equation (9) by the same method as described above, it is expressed by the equation (10).

  From this equation (10), it can be seen that the S / N ratio decreases because the denominator term increases as the multiplicity 2m increases. This is because the noise level reproduced by each code = m (1-Cosα) is added together and reproduced, and if the noises cancel each other out, the noise level can be greatly reduced. it can.

  There has been an idea in the past to cancel noises by changing the phase between pages, but this is to change the phase of the signal light 100. When the phase multiplexing method is used, the reference light 200 is used. In addition, it is necessary to provide not only the signal light 100 but also a phase modulator for changing the phase, which complicates the apparatus and increases costs.

  In this respect, in the present embodiment, the phase modulator 18 on the reference light side has an effect of reducing not only the page addressing but also the noise level at the same time. Usually, the same phase is used for recording and reproduction. Where the code matrix is used, the above functions are realized by using different phase code matrices for recording and reproduction. Hereinafter, a phase multiplexing method using different phase code matrices for recording and reproduction will be described.

Consider a case where different phase code matrices are used during recording and playback. At this time, assuming that the recording phase code matrix is χ _record and the reproduction phase code matrix is χ _read , the reproduction amplitude matrix A is expressed as shown in the following equation (11).

Here, as a specific example of χ _record and χ _read , consider a phase code matrix as shown in the following equation (12).

The regeneration phase code matrix chi _read is the same as the 4 × 4 Hadamard matrix when there is a phase shift α, which came out earlier, the recording phase code matrix chi _record is chi _read, row by row - e ^{iγ multiplied} by. Physically, it is easy to understand when considering the case of γ = 0 (that is, one multiplied by −1 for each row). In this case, every time each page is recorded, the phase of the reference light is changed by 180 degrees for recording. For this reason, during reproduction, noises cancel each other and the S / N ratio increases. The above matrix is a matrix that assumes a shift of γ from the ideal state of 180 degrees. Actually, when the reselection amplitude matrix is calculated, the following equation (13) is obtained.

  In general, in the case of a 2 m × 2 m matrix, the S / N ratio when a phase difference of π + γ is alternately given to each row can be calculated similarly, and the above-described codes (1, 1, 1,..., 1, 1 In the state excluding), the following equation (14) is obtained.

  When there is no cancellation as described above, S / N = 2 / m (1-Cos α). Therefore, when γ is small, that is, when cancellation is close to the ideal 180 degrees, S / N It can be seen that the ratio is greatly improved.

The recording phase code matrix χ _record described above is created by the control unit 22 in the apparatus of FIG. 1, and the creation procedure is as shown in the flowchart of FIG. 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). Next, the sign is inverted every other row of the created recording phase code matrix H (m) to create a temporary reproduction phase code matrix χ _record (step S3).

Thereafter, the elements in the first column are removed from the recording phase code matrix χ _record (step S4), and the address codes φ1, φ2,..., Φm from the remaining second column, third column,. −1 (step S5), a phase code matrix (φ1, φ2,..., Φm−1) is created from these address codes φ1, φ2 _,. Is completed (step S6).

On the other hand, the reproduction phase code matrix χ _read is the m × m Hadamard matrix H (m) generated in step S2, but the first column element is removed from the computational recording phase code matrix χ _record . Therefore, the element of the first column of the Hadamard matrix H (m) is removed in the same manner as when the recording phase code matrix is created, and the address code is created from the remaining elements to obtain the final reproduction phase. Create a code matrix χ _read .

The control unit 22 displays the phase modulation pattern created from, for example, the address code in the first column of the recording phase code matrix χ _record on the phase modulator 18 and optically modulates the reference beam 200, and corresponds to this and the recording data. Then, interference fringes with the spatial light modulated signal light are recorded on the hologram recording medium 10. Thereafter, the phase modulation pattern created from the address code in the first column of the reproduction phase code matrix χ _read is displayed on the phase modulator 18, and the illumination light 300 is optically phase-modulated. By irradiating the hologram recording medium 10, the recording data is read as reproduction light.

  At this time, the reproduction light has the information in the first row of Expression (13), and in this example, the diagonal component 4 is the target reproduction information, and the other components are crosstalk components. However, as described above, the sum of the crosstalk components is small with respect to the target reproduction information, and thus a reproduction signal with a good S / N ratio (see Expression (14)) can be obtained from the image sensor 16.

  According to the present embodiment, the address code used when optically modulating the reference light 200 by the phase modulator 18 is different from the address code used when optically modulating the illumination light 300 by the phase modulator 18. Thus, it is possible to reduce the crosstalk component included in the reproduction signal that occurs when the phase modulation by the phase modulator 18 deviates from the ideal value, and to greatly improve the S / N ratio of the reproduction signal. As a result of the reduction of the crosstalk noise, the multiplicity of recording data by the phase modulation multiplexing method can be increased, and the storage capacity of the hologram recording medium 10 can be increased.

  Further, since it is only necessary to devise coding at the time of recording of the phase modulator 18 originally included in the reference light 200 side without performing new phase modulation on the signal light 100 side, the apparatus is complicated and expensive. The above effect can be obtained.

  Furthermore, the effect that the crosstalk component can be reduced even when the phase modulation deviates from the ideal value, on the contrary, means that the demand for the accuracy of the phase modulator 18 can be relaxed. The price can be reduced. For the same reason, the tolerance for various instabilities becomes loose, so that the merit in the system configuration can be increased.

Although the Hadamard matrix is used for χ _read in the above embodiment, any matrix satisfying χ · χ * = E _n as described above may be used. Furthermore, it does not matter if the off-diagonal component of χ · χ * is zero. In this case, however, the absolute values of the diagonal components are all preferably close. Otherwise, the intensity of the reproduction light will vary greatly from page to page. Here, the absolute value is because the diagonal component is generally a complex number representing the amplitude of the reproduction light, and the square of the absolute value is the intensity.

In the above embodiment, χ _record is generated by alternately applying −1 to the row of χ _read . However, it is not always necessary to alternately apply χ _record . If the number of -1 and 1 is equal as a whole, the same effect can be obtained.

Furthermore, in the above embodiment, examples of 1 and −1 have been shown. However, at an arbitrary angle θ, θ and θ + π may be applied to the row of χ _read and χ _record may be generated as shown in equation (15). Good, similar effects can be obtained. Note that the two types of coefficients applied to the row of χ _read from the equation (15) are e ^iθ and −e ^iθ , and the ratio is −1.

  Next, a method for creating a phase code matrix according to the second embodiment of the present invention will be described. However, since the configuration of this example is the same as that of the first embodiment described above, the description of the configuration and operation of each unit having the same configuration will be omitted, and the characteristic part of the operation will be described below.

This embodiment differs from the first embodiment in which the recording phase code matrix χ _record is created by multiplying the reproduction phase code matrix χ _read by two values (for example, 1 and −1) for each row. , Χ _read rows are applied with various values to create a recording phase code matrix χ _record . However, in this case, it is desirable that the sum of the values applied to the rows of the reproduction phase code matrix χ _read is zero. A specific creation method using the 8 × 8 Hadamard matrix Η ⁽⁸⁾ represented by the equation (13) as the reproduction phase code matrix χ _read will be described below.

However, since the spatial light modulation on the reference light 200 by the phase modulator 18 of Expression (16) is not performed as ideal, it actually deviates from a phase of exactly -1. The deviation amount α is used as the reproduction phase code matrix χ _read as described above. In this case, χ _read is expressed as shown in equation (17).

In the present embodiment, a matrix obtained by multiplying each row of the equation (17) by a coefficient (a, b, c, d, e, f, g, h) is used as the recording phase code matrix χ _record , which is expressed by the equation ( 18).

  When the reproduction amplitude matrix A is obtained from Expressions (17) and (18), Expression (19) is obtained.

  In this equation (19), except for the diagonal component and the code (1, 1, 1, 1, 1, 1, 1, 1) portion (that is, the first line), all are the same, and the coefficient is applied. You can see that there is only. For example, paying attention to the second column, the sum of the noise components is N = 4 × (c + d + e + f + g + h) (1−Cos (α)). Therefore, in order to reduce noise, it is desirable to bring a set such that c + d + e + f + g + h = 0. The same applies to the other columns. Actually, there is no pair that becomes zero in all columns, but when the size of the Hadamard matrix is large, there is no practical problem if it is approximately zero.

This embodiment also records the recording data by optical phase modulation of the reference light using the phase address code created from the recording phase code matrix χ _record created from the playback phase code matrix χ _read , and the playback phase during playback By reproducing the data by optical phase modulation of the illumination light using the address code, the same effect as that of the first embodiment can be obtained.

  The procedure for creating the phase address code of the above embodiment can be implemented by programming it as a phase address code creating program and causing the computer to execute it. 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. For example, in the embodiment described above, a reproduction phase code matrix is first created, and a coefficient is applied to each element of the reproduction phase code matrix to create a recording phase code matrix. However, reverse this, first create a recording phase code matrix, multiply each element of this recording phase code matrix by a coefficient, create a reproduction phase code matrix, and create it from the recording phase code matrix By recording the recorded data by optical phase modulation of the reference light using the address code, and reproducing the data by optical phase modulating the illumination light using the address code created from the reproduction phase code matrix at the time of reproduction, The same effect as the above embodiment can be obtained.

1 is a configuration diagram showing a configuration of a hologram recording / reproducing apparatus according to a first embodiment of the present invention. It is a perspective view explaining operation | movement of the optical phase modulator shown in FIG. It is a figure explaining the phase modulation multiplex recording / reproducing operation by the hologram recording / reproducing apparatus shown in FIG. 3 is a flowchart showing a procedure for creating a recording and reproduction phase code matrix by the control unit 22 shown in FIG. 1. It is a schematic block diagram explaining the structure of the conventional hologram recording / reproducing apparatus.

Explanation of symbols

  2 ... Laser light source, 4 ... Beam splitter, 6 ... Spatial light modulator, 8, 12, 14 ... Lens, 10 ... Hologram recording medium, 16 ... Image sensor, 18 ... Spatial phase modulator, 20: Lenslet array, 22: Control unit.

Claims (15)

By recording on the hologram recording medium interference fringes generated by causing the first light beam spatially modulated by the recording data to interfere with the second light beam, and irradiating the hologram recording medium with the third light beam. A hologram recording / reproducing apparatus that reads out and reproduces data by receiving generated diffracted light with a light receiving element,
First phase modulation means for optically phase-modulating the second light beam with a phase modulation pattern generated from a phase address code;
Second phase modulation means for optical phase modulating the third light beam by a phase modulation pattern generated from a phase address code different from the phase address code used when optical phase modulation of the second light beam was performed when recording the recording data And
The recording data is recorded on the hologram recording medium as the interference fringes using the phase-modulated second light beam, and the recording is performed by irradiating the hologram recording medium with the phase-modulated third light beam. A hologram recording / reproducing apparatus for reproducing recorded data identical to data.   2. The hologram recording / reproducing apparatus according to claim 1, wherein the first and second phase modulation means include an optical phase modulator for displaying a two-dimensional phase modulation pattern.   2. The hologram recording / reproducing apparatus according to claim 1, wherein the first and second phase modulation means are also used as the same phase modulation means.   2. The hologram recording / reproducing apparatus is separate from a hologram recording apparatus that records recording data on the hologram recording medium and a hologram reproducing apparatus that reproduces the recording data from the hologram recording medium. The hologram recording / reproducing apparatus as described.   2. The hologram recording according to claim 1, wherein interference fringes of the optical phase-modulated second light beam and the spatial light-modulated first light beam are multiplexed and recorded on the same spot of the hologram recording medium. Playback device. By recording on the hologram recording medium interference fringes generated by causing the first light beam spatially modulated by the recording data to interfere with the second light beam, and irradiating the hologram recording medium with the third light beam. A hologram recording / reproducing method for reading out and reproducing data by receiving generated diffracted light with a light receiving element,
Optical phase modulating the second light beam with a phase modulation pattern generated from a phase address code;
Optical phase modulation of the third light beam by a phase modulation pattern generated from a phase address code different from the phase address code used when optically modulating the second light beam during recording of the recording data;
Recording the recording data on the hologram recording medium as the interference fringes using the phase-modulated second light beam;
Irradiating the hologram recording medium with the phase-modulated third light beam to reproduce the same recording data as the recording data;
A hologram recording / reproducing method comprising: A method for creating an address code used for optical phase modulation of a light beam,
Generating a square matrix of matrix size m rows m columns;
Removing specific rows of the generated matrix;
Creating an address code for reproduction by extracting each row of the matrix from which the particular row has been removed;
A step of creating an address code for recording by multiplying each address code for reproduction by two or more types of coefficients with a total sum of zero;
A method for generating an address code, comprising:   8. The address code generating method according to claim 7, wherein the matrix has a non-diagonal component of zero given by χ · χ *, where χ is the matrix.   8. The address code generation method according to claim 7, wherein the matrix is a unitary matrix.   8. The method of creating an address code according to claim 7, wherein there are two types of coefficients.   11. The address code generating method according to claim 10, wherein the ratio of the values of the two types of coefficients is -1.   11. The address code generation method according to claim 10, wherein the two types of coefficients are 1 and -1.   The interference light is recorded on the hologram recording medium by interfering with the reference light optically phase-modulated using the address code for recording and the signal light optically spatially modulated according to the recording data, and the address code for reproduction is recorded. 8. The address code generating method according to claim 7, wherein the recorded data is reproduced by irradiating the hologram recording medium with illumination light that has been optically phase-modulated.   A record address code is created by extracting each row of the matrix from which a specific row of the generated m-row m-column square matrix is removed, and the sum is zero for each address code for recording 2 8. A method for creating an address code according to claim 7, wherein a reproduction address code is created by multiplying more than types of coefficients. A program for creating an address code used for optical phase modulation of a light beam,
a function to generate an m × m square matrix;
A function to remove a specific row of the generated matrix;
Creating a first address code from the matrix with the particular row removed;
A function of creating a second address code by multiplying each element of the first address code by two or more types of coefficients with a total sum of zero;
An address code creating program characterized by causing a computer to realize the above.

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