JP2007250076A - Data recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data recording and reproducing device in which interference between codes is reduced based on a pattern of a phase modulation mask. <P>SOLUTION: The device is provided with a space light amplitude modulator 20 space-modulating amplitude, a phase modulation mask 30 modulating a phase, and an interference optical part 40 recording interference in a medium M. Further, the device is provided with an image sensor 50 taking out reproduction light from the medium M and photographing it, and a signal processing means 60 signal-processing a photographed digital image, wherein a space filter performed in the signal processing means 60 reduces interference between codes by changing a filter property based on space positions of respective pixels, and an error rate is improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a data recording / reproducing apparatus, and more particularly to a data recording / reproducing apparatus using holographic.

  In recent years, the use of multimedia has progressed, and the data handled has increased. In order to record this large amount of data, various researches have been made on recording devices using holography (hereinafter referred to as “hologram memory”). Since this hologram memory can record and reproduce two-dimensional page data at a time, it is said that the data transfer speed is high, and that the storage capacity can be increased by using the technique of multiplex recording. Yes.

The hologram memory has a disturbance factor having a property different from that of an optical disk apparatus that records and reproduces information on a medium such as a DVD. Among them, ISI (Inter Symbol Interference) is greatly different in characteristics between DVD and hologram memory. The ISI of the hologram memory will be described with reference to FIG.
FIG. 12 shows a spatial light amplitude modulator 101 that spatially modulates the amplitude of coherent (coherent) light, and spatially modulates the amplitude of the coherent light emitted from the upper part of the drawing and receives it by the image sensor 102. The principle until the output value of the image sensor 102 is obtained is shown. This spatial light amplitude modulator is composed of cells that transmit light and cells that block light, and has a two-dimensional array represented by n rows and m columns. In FIG. 12, there is a case where there is one cell that transmits light (a cell in which only cell A is transmitted, which is described as “ON is isolated” in the drawing), and a case where two cells are adjacent (“ON is adjacent” in the drawing). For the cell A and B described), the electric field amplitude waveform, electric field power waveform, and image sensor output value are compared. The image sensor 102 is composed of photoelectric conversion elements, and the image sensor output value in each cell is obtained by integrating the output values of components received by the pixels in each cell. As can be seen from the figure, the image sensor output of each cell is affected by whether the adjacent cell is a shielded cell or a transparent cell. This has a characteristic different from the ISI generated in the conventional optical disk apparatus.

  Conventionally, as one means for reducing the influence of the ISI, there is a method of applying a “modulation code” having a small amount of data “1” to an adjacent cell of data “1” (corresponding to a light transmitting cell). For example, a code called 1-4 code (1 Light Bit on 4 Cells Coding) is data “1” for only one of four cells and data “0” for the remaining three (corresponding to cells that block light). ). This code is characterized in that “1” is reduced in a cell adjacent to the cell “1”, and the influence of ISI can be suppressed (see, for example, Patent Document 1).

  Further, as another means for reducing the influence of the ISI, there is a method using a “phase modulation mask”. This phase modulation mask is a phase modulator having a cell interval matched with the spatial light amplitude modulator, and can change the phase of light for each cell. As an effective phase modulation mask phase pattern, four values of 0, π / 2, π, and 3π / 2 are used as illustrated in FIG. 13, and the phase difference between adjacent vertical and horizontal cells is π / 2. There is a so-called “pseudo-random diffuser plate 103” with restrictions.

Here, the effect of the pseudo random diffusion plate 103 will be described. FIG. 14 shows a principle diagram in which the amplitude of the coherent light is spatially modulated by the spatial light amplitude modulator 101 and photographed by the image sensor 102 through the pseudo-random diffuser plate 103. It differs from FIG. 12 described above in that it has a pseudo-random diffuser plate 103.
As can be seen from FIG. 14, even if the spatial modulation cell A is the same data “1”, the image sensor is affected by the integration depending on whether the adjacent cell B is the data “1” or the data “0”. The output of 102 changes. However, comparing FIG. 12 with FIG. 14, the image sensor output of the cell A clearly changes less in FIG. In FIG. 14, since there is a phase shift of π / 2 between adjacent cells, the adjacent cells A and B in which the electric field power is the sum of the electric field power of the cell A and the electric field power of the cell B are adjacent cells. This is because the influence of ISI is reduced even if is ON. Thus, by using the pseudo-random diffuser plate 103, the influence of ISI can be reduced (for example, see Patent Document 2).

Further, the pseudo random diffuser plate 103 has other effects. That is, the power at the focal point of the 0th-order light of the diffracted light generated by the grating structure of the spatial light amplitude modulator 101 can be reduced. When the coherent light is collected by the lens, the light is collected at one point, and when the data is recorded on the medium at the focal point, the medium may be burned, and there is a possibility that the data cannot be recorded / reproduced. If a random diffuser plate is used in addition to the pseudo-random diffuser plate 103, the power of the 0th-order light at the focal point can be reduced and media burn-in can be prevented.
Japanese Patent Laid-Open No. 9-197947 (page 1-8, FIG. 1) JP-A-1-302376 (page 2-4, FIG. 4)

  By the way, in the conventional configuration, the pseudo random diffuser plate has a constraint to rotate the phase between adjacent cells in the horizontal and vertical directions by π / 2, but the phase relationship with the diagonally adjacent cells is the same phase or π It is a random pattern that rotates. In this case, the influence of ISI between diagonally adjacent cells cannot be reduced or deteriorated.

  The present invention has been made in view of the above circumstances, and performs the phase adjustment of light not only in horizontally and vertically adjacent cells but also in ISI between diagonally adjacent cells, and thereby affects the influence of diagonally adjacent cells. An object of the present invention is to provide a data recording / reproducing apparatus that can be removed.

  The data recording / reproducing apparatus of the present invention includes a spatial light amplitude modulator that spatially modulates the amplitude of coherent light, and a phase of the light that has been spatially modulated by the spatial light amplitude modulator. A phase modulation mask to be modulated, and a reference beam for recording the information on a medium by an interference pattern of the light whose phase is spatially modulated by the phase modulation mask, or for taking out reproduction light from the medium and reading the information An interference optical unit that is incident on the medium; an image sensor that photoelectrically converts the reproduction light; and a signal processing unit that reads binary information from a digital image output from the image sensor. A means for correcting the digital image to an appropriate spatial position; and a digital image corrected by the alignment means. A spatial filter for filtering, and binarization means for binarizing the filtered digital image, the spatial filter corresponding to a pixel adjacent to a target pixel to which a current filter is applied. The filter characteristics of the spatial filter are changed according to the phase of the modulation mask.

  Further, the data recording / reproducing apparatus of the present invention includes a phase modulation mask that spatially modulates the phase of coherent light, and the amplitude of the coherent light whose phase is spatially modulated by the phase modulation mask. The information is recorded on the medium by the spatial light amplitude modulator to be modulated and the interference pattern of the coherent light whose amplitude is spatially modulated by the spatial light amplitude modulator, or the reproduction light is taken out from the medium to obtain the information. An interference optical unit for making a reference light for reading incident on the medium, an image sensor for photoelectrically converting the reproduction light, a signal processing unit for reading binary information from a digital image output from the image sensor, The signal processing means includes an alignment means for correcting the digital image to an appropriate spatial position, and correction by the alignment means. A spatial filter for filtering the filtered digital image, and binarization means for binarizing the filtered digital image, wherein the spatial filter is a pixel adjacent to the pixel of interest to which the current filter is applied. The filter characteristic of the spatial filter is changed according to the phase of the phase modulation mask corresponding to.

  In the data recording / reproducing apparatus of the present invention, the modulation pattern of the phase modulation mask is a pseudo-random pattern in which the phase of pixels adjacent in the vertical and horizontal directions of the pixel of interest is rotated by π / 2. It is a feature.

  In the data recording / reproducing apparatus of the present invention, the spatial filter is configured to perform the attention for each phase of the phase modulation mask in four pixels obliquely adjacent to the attention pixel to which the current filter is applied. The filter coefficient for determining the filter characteristic of the spatial filter is changed based on the determination as to whether the phase is the same as the phase of the pixel.

  Further, in the data recording / reproducing apparatus of the present invention, the signal processing unit reproduces the modulation pattern of the spatial light amplitude modulator from the digital image corrected to an appropriate spatial position by the alignment unit. Provisional judging means for binarizing to “0” or “1”, wherein the spatial filter includes the phase modulation mask in four pixels diagonally adjacent to the target pixel to which the current filter is applied. Whether the phase of the pixel of interest is the same as the phase of the pixel of interest, and whether each of the outputs of the provisional determination means at four diagonally adjacent pixels is “1”. Based on this, the filter coefficient for determining the filter characteristic is changed.

  In the data recording / reproducing apparatus of the present invention, the spatial filter is configured to perform the attention for each phase of the phase modulation mask in four pixels obliquely adjacent to the attention pixel to which the current filter is applied. The filter coefficient for determining the filter characteristic of the spatial filter is changed according to the number of pixels having the same phase as the pixel phase.

  According to the data recording / reproducing apparatus of the present invention, it is possible to eliminate the influence due to the phase of light such as ISI between diagonally adjacent cells. Therefore, a data recording / reproducing apparatus that can improve the bit error rate can be provided.

Hereinafter, embodiments of the data recording / reproducing apparatus of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows the configuration of a data recording / reproducing apparatus according to the present embodiment. This data recording / reproducing apparatus records and reproduces information on a medium M. A spatial light amplitude modulator 20, a phase modulation mask 30, an interference optical unit 40, an image sensor 50, and a signal processing means 60.

  The recording / reproducing light generation unit 10 generates two coherent lights (coherent light) necessary for forming a hologram, and emits one of the coherent lights to the spatial light amplitude modulator 20, while the other one. Two coherent lights are output to the interference optical unit 40 as reference lights. The spatial light amplitude modulator 20 performs spatial modulation of the amplitude corresponding to the data to be written on the object light from the recording / reproducing light generation unit 10. The phase modulation mask 30 performs spatial modulation of the phase of the object light input from the spatial light amplitude modulator 20 to the phase modulation mask 30. The image sensor 50 outputs a digital image by photoelectric conversion. Note that the arrangement order of the spatial light amplitude modulator 20 and the phase modulation mask 30 may be reversed from the present embodiment.

Next, the operation of the data recording / reproducing apparatus of this embodiment will be described.
One of the two coherent lights generated by the recording / reproducing light generation unit 10 is applied to the spatial light amplitude modulator 20, and the spatial light amplitude modulator 20 has a light amplitude space corresponding to information to be written. Modulate. The light whose amplitude is spatially modulated is input to the phase modulation mask 30 to perform spatial modulation of the phase of the light. The light that has been spatially modulated by the phase modulation mask 30 is input as signal light to the interference optical unit 40 for recording an interference pattern on the medium M, where it is applied to the medium M by interference with reference light described later. Data is recorded.

  In the present embodiment, as described above, of the two lights generated by the recording / reproducing light generation unit 10, spatial modulation is performed using one of the lights and the signal light is used, and the other is used as the reference light. A method of recording a hologram on the medium M by making light interfere with each other is adopted. Further, when reproducing the recorded hologram, only the reference light has to be input to the interference optical unit 40. Thereby, the diffracted light from the medium M is read as reproduction light. That is, the reproduction light from the medium M is irradiated to the image sensor 50, and the image sensor 50 outputs a digital image by photoelectric conversion. The digital image is binarized by the signal processing means 60.

Next, the recording / reproducing light generation unit 10 will be described in detail with reference to FIG.
The recording / reproducing light generation unit 10 changes the optical path, a laser light source 11 that is a coherent light source, a prism beam splitter 12 such as a polarization beam splitter (PBS) that divides the laser beam into two, a collimator 13 that forms parallel light, and the like. In order to achieve this, a pair of two mirrors 14 are provided.

  Since the coherent light emitted from the laser light source 11 records information as a hologram using the interference action of the two lights, the bandwidth of the wavelength is very narrow. A laser beam that is coherent light emitted from the laser light source 11 is input to the prism beam splitter 12 and split into two beams. One of the divided beams is expanded in laser diameter by the collimator 13 and output to the spatial light amplitude modulator 20 to form object light (becomes signal light). The other of the divided beams is irradiated onto the mirror 14 to change the traveling direction of the beam as reference light. The light output from the mirror 14 is output to the interference optical unit 40 as reference light.

  The spatial light amplitude modulator 20 that spatially modulates the amplitude of light and the cell that is the element of the minimum modulation interval of the phase modulation mask 30 that spatially modulates the phase of light correspond one-to-one and are installed close to each other. ing. In addition, the order of incidence of light on the spatial light amplitude modulator 20 and the phase modulation mask 30 (that is, the arrangement of the two optical elements) may be switched. This is because even if the order of incidence of light is changed, the output light becomes exactly the same light and does not affect the performance. In the present embodiment, both of these are installed close to each other, but it is also possible to install both at the front focal point and the rear focal point of the relay lens using a relay lens.

The spatial light amplitude modulator 20 is composed of a liquid crystal panel or the like, and can set data “1” that is transmitted and data “0” that is blocked for each cell. As long as the light amplitude can be spatially modulated, a DMD (Digital Micromirror Device) or the like may be used, and the present invention is not limited by the configuration of the spatial light amplitude modulator 20.
The modulation pattern of the spatial light amplitude modulator 20 changes depending on information to be written. In the present embodiment, the 1-4 code (1 Light Bit on 4 Cells Coding) described in [Background Art] is used as the modulation code. FIG. 3 shows an encoding method of the 1-4 code. As described above, the 1-4 code is a constraint code in which only one of the four cells is data “1” and the remaining three are data “0”. As shown in FIG. 3, the encoding is performed by extracting 2-bit data to be encoded from the information sequence by the information acquisition unit 91 and converting it into 4-bit data according to the encoding table by the encoding unit 92. It is. Two-dimensional modulation data that is two-dimensional data is generated by combining a plurality of 4-bit data.

  The phase modulation mask 30 uses the four modulation patterns 0, π / 2, π, and 3π / 2 as described in [Background Art], and has a constraint that the phase of adjacent vertical and horizontal cells is π / 2. A random diffuser is used. The phase modulation mask 30 of this embodiment is made of glass or the like, and rotates the phase for each cell depending on the thickness of the glass for each cell. The phase modulation mask 30 may be a liquid crystal element or the like as long as it can spatially modulate the phase of light. Further, the present invention is not limited by the configuration of the phase modulation mask 30.

  Next, FIG. 4 shows the two-dimensional modulation data and the electric field power of the reproduction light when the data is recorded / reproduced. 4A shows the two-dimensional modulation data, FIG. 4B shows the electric field power of the reproduction light when there is no pseudorandom diffuser, and FIG. 4C shows the reproduction when there is a pseudorandom diffuser. The electric field power of light is shown respectively. Here, R1 and R2 indicate appropriate comparison regions focused arbitrarily in an oblique direction.

  FIG. 4C using a pseudo random diffuser as the phase modulation mask 30 is less affected by ISI than in the case of FIG. You can see that there is no variation. The modulation pattern of the phase modulation mask 30 has a predetermined fixed pattern. 4B and 4C are binary images obtained by applying error diffusion, and are actually multi-valued images.

  Therefore, as shown in FIG. 4C, better reproduction light can be obtained by using a pseudo-random diffuser. However, when comparing the region R1 and the region R2 in FIG. 4C, the electric field power has a different shape in spite of the same diagonally adjacent “1” data. This is due to the influence of ISI of diagonally adjacent cells. Here, sharing one side of the square is “vertical and horizontal adjacency”, sharing only one corner of the square and not sharing the side is “diagonal adjacency”.

By using a pseudo-random diffuser plate as the phase modulation mask 30, the influence of ISI adjacent in the horizontal and vertical directions can be reduced, but the influence of diagonally adjacent ISI cannot be reduced. 5A and 5B show the phase arrangement pattern of the pseudo random diffuser plate 31 corresponding to the region R1 and the region R2 in FIG. 4A, respectively, and FIGS. 4A and 4B show intersymbol interference patterns of electric field power when using the pseudo-random diffuser plate 31 shown in FIGS.
Cell I and cell J diagonally adjacent to region R1 have both phases of 0 and the same phase, and cells K and cell L diagonally adjacent to region B have phases of 0 and π and are rotated by π. I understand. That is, there is a difference between observing the electric field power by adding the electric fields in the same phase and observing the power by adding the electric fields in the opposite phase. Due to this influence, the value corresponding to the “1” data varies, and the possibility of an error increases. The object of the present invention is to eliminate the influence of such a phase of light. The influence of this obliquely adjacent ISI can be reduced by a spatial filter described later.

  Next, the interference optical unit 40 is an optical system that records light on the medium M by causing the light (object light) modulated by the spatial light amplitude modulator 20 and the phase modulation mask 30 to interfere with the reference light during recording. In the present embodiment, one of the two lights generated by the recording / reproducing light generation unit 20 is used as a reference light, and the other is used to generate a signal light (object light) to irradiate the spatial light amplitude modulator 20 and a phase modulation mask. By using the light output from 30 as signal light (object light), the medium M is caused to generate two-beam interference due to these two lights.

Next, FIG. 6 shows a principle diagram of recording and reproduction of interference with the medium M.
The interference optical unit 40 includes a Fourier transform lens 41 and an aperture 43. The signal light collected by the Fourier transform lens 41 is applied to the medium M. Further, the reference light is also applied to the medium M, and an interference pattern of these two lights is recorded on the medium M. At this time, the aperture 43 restricts the aperture on the Fourier plane constructed by the Fourier transform lens 41, thereby removing high frequency components. The medium M is made of a material such as a photoreactive polymer and can record a light interference pattern.

At the time of reproduction, the medium M is irradiated with only the reference light, and the diffracted light is inverse Fourier transformed by the inverse Fourier transform lens 42, and this light can be read from the medium M as reproduction light.
That is, the image sensor 50 photoelectrically converts the reproduction light read from the medium M to generate a digital image, and this digital image is input to the signal processing means 60. The signal processing means 60 performs rough adjustment, alignment, spatial filtering, and binarization of the luminance amplitude (luminance magnitude) and DC offset on the digital image.

Next, the configuration of the signal processing means 60 is shown in FIG.
The signal processing means 60 includes a memory 62, a memory interface 61, an amplitude detection means 63, an amplitude adjustment means 64, a coordinate detection means 65, a resampling means 66, a spatial filter 67, and a filter coefficient setting means 68. A phase pattern storage unit 69 and a binarization unit 70.

  The digital image output from the image sensor 50 is stored in the memory 62 via the memory interface 61. At this time, the amplitude detection means 63 detects the amplitude and DC offset of the digital image. The digital image stored in the memory 62 is input to the amplitude adjusting unit 64 via the memory interface 61.

The amplitude adjusting unit 64 adjusts the amplitude of the digital image detected by the amplitude detecting unit 63 and the DC offset so as to have predetermined values. The digital image whose amplitude and DC offset are adjusted by the amplitude adjusting unit 64 is input to the coordinate detecting unit 65.
The coordinate detection means 65 calculates appropriate coordinates by detecting the position of position detection data called “markers” included in the digital image. Usually, the pixel pitch of the image sensor 50 does not correspond one-to-one with the cell pitch of the spatial light amplitude modulator 20. This is because one pixel may not be sensed for one cell due to the effects of lens aberration, medium tilt, and the like. If one pixel cannot be sensed for one cell, the original image cannot be reproduced by the sampling theorem, and the number of errors increases. In order to prevent this, oversampling of, for example, 1.5 pixels is performed on one cell. The coordinate detection means 65 and the resampling means 66 described later align the sampling that has been shifted due to the influence of aberration or the like or due to oversampling so as to correspond to one pixel with respect to one cell. The detection means 65 and the resampling means 66 are combined to constitute an alignment means.

  The resampling unit 66 resamples the digital image with appropriate coordinates detected by the coordinate detection unit 65. That is, the resampling means 66 implements resampling at appropriate coordinates by interpolating using a Nyquist filter (a filter whose amplitude frequency characteristics are flat in the pass band). . By re-sampling in this way, the image of the digital image and the cell that is an element of the minimum modulation interval of the spatial light amplitude modulator have a one-to-one correspondence. The digital image of appropriate coordinates obtained by the resampling means 66 is stored again in the memory 62 via the memory interface 61. An appropriately sampled digital image stored in the memory 62 is input to the spatial filter 67 via the memory interface 61.

  The spatial filter 67 is a filter for equalizing a digital image. Digital image equalization refers to filtering the spatial frequency characteristics of a digital image to predetermined characteristics so that data can be easily read. The digital image filtered by the spatial filter 67 is stored again in the memory 62 via the memory interface 61. The spatial filter 67 can be realized by a two-dimensional FIR filter (Finite Impulse Response Filter). The “filter coefficient” that determines the characteristics of the spatial filter 67 that equalizes the digital image is set from the filter coefficient calculation means 68.

  Here, a configuration example of the spatial filter 67 is shown in FIG. FIG. 8 is a diagram showing a 5 × 5 tap spatial filter 67, and A1 to E5 indicate tap input positions on the digital image. S_A1 to S_E5 are tap inputs, and the magnitude of the luminance of the pixel existing at the position A1 on the digital image is the tap input of S_A1. C_A1 to C_E5 are tap coefficients. By multiplying both of them and adding all of them, a filter output of one pixel is generated. When C3 is the center tap and the input is the target pixel, a filter output of the coordinate of the target pixel is obtained.

The filter coefficient setting unit 68 sets a filter coefficient for determining the characteristics of the spatial filter 67 to the spatial filter 67 based on the output of the phase pattern storage unit 69. The phase pattern storage means 69 stores the phases of the phase modulation mask 30 in order.
For example, as shown in FIG. 9, the spatial filter 67 scans the rows in order starting from the upper left pixel of the digital image (DI) while filtering the rows toward the right, and then lowers the rows one line to the left. Repeat scanning from right to right. When scanning while filtering to the lower right pixel, the phase information of the pixel to be scanned is stored in the order from the upper left to the lower right, and the phase pattern storage means 69 sequentially outputs it. The phase information of the pixels is a pattern of the phase modulation mask 30, and this pattern is fixed as described above. Although the phase pattern storage means 69 stores the phases of the phase modulation mask 30 in order, a sequence generation formula for generating the phase of the phase modulation mask 30 may be configured. The circuit scale can be reduced.
The filter coefficient setting unit 68 stores an optimum filter coefficient for the phase pattern between the diagonally adjacent pixels, and outputs the filter coefficient according to the phase pattern output from the phase pattern storage unit 69.

  In this way, the filter coefficient calculation means 68 sets the “filter coefficient” that determines the characteristics of the spatial filter 67 that equalizes the digital image. The filter coefficient setting unit 68 stores an optimum filter coefficient for the phase pattern between diagonally adjacent pixels, and outputs an optimum filter coefficient according to the phase pattern output from the phase pattern storage unit 69. To do.

Therefore, next, a method for optimizing the filter coefficient stored in the filter coefficient setting means 68 will be described.
There are several methods for optimizing the filter coefficient. In this embodiment, an LMS (Least Mean Square) algorithm is used. The formula for calculating the optimum filter coefficient by this LMS algorithm is shown in the following [Equation 1]. Where h (n + 1) is the next learned filter coefficient vector, h (n) is the current filter coefficient vector, μ is the step gain parameter, e (n) is the current equalization error, and u (n) is the filter. ^T (n) is the current equalization target value, and u ^T (n) is the transpose of the filter tap input vector.

When the filter coefficient is calculated from the above equation [1] by LMS, the filter coefficient h (n) approaches the optimum value h0. The equalization error e (n) decreases. The tap input vector of the u (n) filter is the tap input of the spatial filter 67 described above. The product h (n) u ^T (n) of the current filter coefficient vector h (n) and the transposed u ^T (n) of the tap input vector indicates the output of the spatial filter 67 described above.

Here, a filter coefficient setting method for removing the influence of ISI adjacent to the diagonal, which has been a problem in the past, will be described.
As described above, the electric field power differs in shape depending on whether the phase between the diagonally adjacent cells is the same phase or the opposite phase. Therefore, the optimum filter coefficient differs depending on whether the phase between the diagonally adjacent cells is the same phase or the opposite phase. Ideally
1. The filter coefficient when the current pixel and the diagonally adjacent cells are all in antiphase,
2. Filter coefficient when only the upper left neighbor cell is in phase,
3. Filter coefficient when only the upper right adjacent cell is in phase,
4). Filter coefficient when only the lower left neighbor cell is in phase,
5). Filter coefficient when only the lower right neighbor cell is in phase,
6). The filter coefficient when it is in phase with the two pixels in the upper left and upper right adjacent cells,
7). The filter coefficient when it is in phase with the two pixels in the lower left and lower right adjacent cells,
8). The filter coefficient when it is in phase with the two pixels in the upper left and lower left adjacent cells,
9. The filter coefficient when it is in phase with the two pixels in the upper right and lower right adjacent cells,
10. The filter coefficient when it is in phase with the two pixels in the upper left and lower right adjacent cells,
11. The filter coefficient when it is in phase with the two pixels in the upper right and lower left adjacent cells,
12 The filter coefficient when it is in phase with the three pixels in the upper left, upper right, and lower left adjacent cells,
13. The filter coefficient when it is in phase with the three pixels in the upper left, upper right, and lower right adjacent cells,
14 Filter coefficients when they are in phase with the three pixels in the upper left, lower left, lower right adjacent cells,
15. Filter coefficients when they are in phase with the three pixels in the upper right, lower right, and lower left adjacent cells,
16. Filter coefficients when all diagonally adjacent cells are in phase,
It is preferable to prepare optimum filter coefficients for each of the 16 patterns.

  When LMS is used, coefficient learning for each phase pattern between diagonally adjacent cells can be easily performed. For example, in a method for obtaining a Wiener solution, which is another coefficient learning method, the input is handled as a set of vectors, and therefore, the coefficients cannot be learned separately for each phase pattern. However, since the LMS is an algorithm that gradually learns the coefficients based on the tap input and the equalization target value, the coefficient of each pattern depends on the phase pattern corresponding to the luminance of the pixel that is the tap input. Can be learned separately.

  A specific learning method of the filter coefficient is, for example, by operating the LMS algorithm only when the pixel of the center tap to which the filter is currently applied and its diagonally adjacent cells are all in antiphase, and the filter coefficient; h ( n + 1) is calculated and updated. For other phase patterns, the filter coefficient h (n + 1) is not updated. In this way, it is possible to obtain the optimum filter coefficient when the adjacent cells are all in the reverse phase pattern.

Furthermore, a method for reducing the influence of ISI between diagonally adjacent pixels will be described with reference to FIG.
When scanning is performed as shown in FIG. 9 and the center tap C3 of the spatial filter 67 shown in FIG. 8 is at the position of coordinates (x, y), the phase at that position is determined from the phase pattern of the phase modulation mask 30. It is 0 as shown in FIG. The phase of the upper left coordinate (x-1, y-1) is π, the upper right is π, the lower left is 0, and the lower right is 0. That is, at this time, with respect to the center tap C3, the upper left and upper right are in opposite phases, and the lower left and lower right are in phase. The filter coefficient setting unit 68 includes a peripheral pixel information detection unit (not shown) that detects this pattern. The peripheral pixel information detection unit (not shown) has the phase pattern sequentially output from the phase pattern storage unit 69 as described above. It is detected which of the 16 patterns (1 to 16) of the diagonally adjacent cells matches.

  Next, the filter coefficient setting unit 68 outputs to the spatial filter 67 the filter coefficient obtained in advance that is optimal for the pattern detected by the peripheral pixel information detection unit (not shown). As described above, it is possible to reduce the influence of ISI between diagonally adjacent pixels by performing spatial filtering using optimum filter coefficients depending on the phase relationship between diagonally adjacent cells.

The filtered digital image is input from the memory 62 to the binarization means 70 via the memory interface 61. The binarizing means 70 binarizes the digital image and outputs binary data. The binary data is demodulated by a modulation code decoder (not shown), corrected by an error correction means (not shown), and then transferred to the host.
In order to reduce the influence of ISI between diagonally adjacent pixels, an optimum filter coefficient may be set for each in-phase number or in-phase number of diagonally adjacent pixels, and in this case, the number of patterns decreases. Therefore, the circuit scale can be reduced.

  Note that the resampling means 66 and the spatial filter 67 of the present invention can be configured by the aforementioned FIR filter (Finite Impulse Response Filter). It is well known that cascaded FIR filters can be made into one filter by convolving filter coefficients. Therefore, the circuit scale can be reduced by using a single filter. The present invention can be applied to, for example, a two-dimensional barcode as long as it uses two-dimensional data, that is, a spatial filter 67 for facilitating binarization of an image.

  As described above, in this embodiment, the influence of ISI between diagonally adjacent pixels can be reduced by optimizing the filter coefficient of the spatial filter 67 based on the phase relationship between diagonally adjacent cells. be able to. Therefore, the quality of the digital image is improved and the bit error rate is improved.

(Second Embodiment)
Next, a second embodiment of the data recording / reproducing apparatus of the present invention will be described.
The data recording / reproducing apparatus of this embodiment includes signal processing means 80 (shown in FIG. 11) different from the signal processing means 60 in the data recording / reproducing apparatus of the first embodiment shown in FIGS. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals to avoid redundant description.

  The signal processing means 80 of this embodiment is different from the signal processing means 60 described in the first embodiment in that a provisional determination means 81 and a second filter coefficient setting means 82 are provided.

  Among these, the temporary determination unit 81 temporarily determines whether each pixel of the digital image sampled at an appropriate position is “1” or “0”. This temporary determination means 81 determines “1” or “0” based on a threshold value set from a register (not shown). The threshold value is set in a register (not shown) by calculating the center of the amplitude adjusted by the amplitude adjusting means 64. The temporary determination means 81 may perform a soft determination using 1-4 codes to determine “1” or “0”. In this case, a temporary determination with higher accuracy than the former is possible.

  On the other hand, the second filter coefficient setting unit 82 sets the characteristics of the spatial filter 67 based on the pattern of the output of the phase pattern storage unit 69 and the output of the temporary determination unit 81.

Next, the operation of the signal processing unit 80 of the present embodiment will be briefly described.
The digital image output from the image sensor 50 is subjected to amplitude adjustment by the amplitude adjusting unit 64 and resampling by the resampling unit 66 through the memory interface 61 and the memory 62, and is sampled at an appropriate position. And stored in the memory 62.

Next, spatial filtering is performed on the stored digital image using an optimum filter coefficient to reduce the influence of ISI between diagonally adjacent pixels.
Here, a filter coefficient setting method for removing the influence of the obliquely adjacent ISI will be described.
As described above, the electric field power differs in shape depending on whether the phase between the diagonally adjacent cells is the same phase or the opposite phase. Therefore, the optimum filter coefficient differs depending on whether the phase between the diagonally adjacent cells is the same phase or the opposite phase. Ideally, it is preferable to consider the optimum filter coefficient for each of the 16 patterns described above, whether the current pixel and the upper left, upper right, lower left, and lower right pixels are in phase.

  In addition, the influence of the diagonally adjacent ISI varies depending on whether the diagonally adjacent pixel is “1” or “0”. Therefore, 16 patterns are considered in which each of the upper left, upper right, lower left, and lower right pixels is data “1” or data “0”. Therefore, ideally, coefficients of 16 × 16 = 256 patterns are prepared. When LMS is used, coefficient learning for each pattern can be easily performed.

The specific learning method of the filter coefficient is, for example, that the pixel at the center tap to which the filter is currently applied and its diagonally adjacent cells are all in reverse phase, and further, the temporary determination means 81 determines that the upper left is “1”. Only when the LMS algorithm is operated, the filter coefficient; h (n + 1) is calculated and updated. For other phase patterns, the filter coefficient h (n + 1) is not updated. In this way, it is possible to obtain the optimum filter coefficient when the adjacent cells are all in the opposite phase and the upper left is “1”.
As described above, by performing spatial filtering using the optimum filter coefficient according to the phase relationship and the size relationship between the diagonally adjacent pixels, it is possible to reduce the influence of ISI between the diagonally adjacent pixels.

  Next, the digital image that has been filtered to reduce the influence of ISI between diagonally adjacent pixels is input from the memory 62 to the binarization means 70 via the memory interface 61. The binarizing means 70 binarizes the digital image and outputs binary data. The binary data is demodulated by a modulation code decoder (not shown), corrected by an error correction means (not shown), and then transferred to the host.

Note that an optimum filter coefficient may be set for each in-phase number or opposite-phase number of diagonally adjacent pixels. In this case, the number of patterns is reduced, so that the circuit scale can be reduced. Further, an optimum filter coefficient may be set for each “1” number or “0” number of diagonally adjacent pixels. In this case, the number of patterns is reduced, so that the circuit scale can be reduced.
The present invention can be applied to, for example, a two-dimensional barcode as long as it uses two-dimensional data, that is, a spatial filter 67 for facilitating binarization of an image. Further, since the resampling means 66 and the spatial filter 67 of the present invention can be constituted by FIR filters, it is possible to make one filter by convolving the filter coefficients of both, and in this way, The circuit scale can be reduced.

  As described above, in the present embodiment, the filter coefficient of the spatial filter 67 is optimized based on the phase relationship between the diagonally adjacent cells and the data of the diagonally adjacent cells being “1” or “0”. As a result, the influence of ISI between diagonally adjacent pixels can be reduced. Therefore, the quality of the digital image is improved and the bit error rate is improved.

  The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the invention.

  The data recording / reproducing apparatus according to the present invention can reduce the influence of ISI due to the pseudo-random diffusion plate and is useful as a large-capacity storage device.

The block diagram of the data recording / reproducing apparatus in the 1st Embodiment of this invention 1 is a configuration diagram of a recording / reproducing light generation unit according to a first embodiment of the present invention. FIG. 4 is a diagram for explaining 1-4 encoding and two-dimensional modulation data in the first embodiment of the present invention. (A) Two-dimensionally modulated two-dimensionally modulated recording data in the first embodiment of the present invention, (B) is the electric field power of reproduction light obtained when the reproduction is performed, and (C) is a pseudo-random diffuser plate Explanatory drawing which shows the electric field power of reproduction | regeneration light obtained when reproducing | regenerating with the data recording / reproducing apparatus which concerns on the 1st Embodiment of this invention which has (A) and (B) show the phase arrangement patterns of the pseudo-random diffuser plate corresponding to the regions R1 and R2 in FIG. 4 (A), respectively, and (C) and (D) show the same. The intersymbol interference pattern of the electric field power at the time of using the pseudo-random diffuser plate of (A) and (B) is shown. The block diagram of the interference optical part in the 1st Embodiment of this invention The block diagram of the signal processing means in the 1st Embodiment of this invention Explanatory drawing which shows application of the spatial filter with respect to the planar cell in the 1st Embodiment of this invention Explanatory drawing which shows an example of the order of filtering in the 1st Embodiment of this invention (A) is explanatory drawing which shows the coordinate of the cell adjacent to the center cell in the 1st Embodiment of this invention, (B) is explanatory drawing which shows the phase of the phase modulation mask corresponding to the coordinate of a cell The block diagram of the signal processing means in the 2nd Embodiment of this invention (A) is an explanatory diagram showing the principle from the spatial light amplitude modulator to spatially modulating the amplitude of coherent light, receiving it by the image sensor, and obtaining the output value of the image sensor, (B) at that time Explanatory drawing showing how the waveform and output change due to the influence from adjacent cells Explanatory drawing which shows the phase for every cell of a pseudo-random diffuser (A) is explanatory drawing which shows the waveform and output when a pseudorandom diffuser is attached to the spatial light amplitude modulator of FIG. 12 (A), and (B) is the waveform and output due to the influence from the adjacent cells at that time. Explanatory diagram showing how the change occurs

Explanation of symbols

10 Recording / reproducing light generator 11 Laser light source (coherent light source)
DESCRIPTION OF SYMBOLS 12 Prism beam splitter 13 Collimator 14 Mirror 20 Spatial light amplitude modulator 30 Phase modulation mask 40 Interference optical part 41 Fourier transform lens 42 Inverse Fourier transform lens 43 Aperture 50 Image sensor 60 Signal processing means 61 Memory interface 62 Memory 63 Amplitude detection means 64 Amplitude adjustment means 65 Coordinate detection means 66 Resampling means 67 Spatial filter 68 Filter coefficient setting means (peripheral pixel information detection means)
69 phase pattern storage means 70 binarization means 81 provisional judgment means 82 second filter coefficient setting means DI digital image M medium

Claims (6)

A spatial light amplitude modulator that spatially modulates the amplitude of coherent light;
A phase modulation mask for spatially modulating the phase of the light whose amplitude is spatially modulated by the spatial light amplitude modulator;
Interferometric optics that records the information on a medium by the interference pattern of the light whose phase is spatially modulated by the phase modulation mask, or makes the reference light incident on the medium to extract the reproduction light from the medium and read the information And
An image sensor for photoelectrically converting the reproduction light;
Signal processing means for reading out binary information from the digital image output from the image sensor;
With
The signal processing means includes
Alignment means for correcting the digital image to an appropriate spatial position;
A spatial filter for filtering the digital image corrected by the alignment means;
Binarization means for binarizing the filtered digital image;
With
The data recording / reproducing apparatus, wherein the spatial filter changes a filter characteristic of the spatial filter according to a phase of the phase modulation mask corresponding to a pixel adjacent to a target pixel to which a filter is currently applied. A phase modulation mask that spatially modulates the phase of coherent light;
A spatial light amplitude modulator that spatially modulates the amplitude of the coherent light whose phase is spatially modulated by the phase modulation mask;
The information is recorded on the medium by the interference pattern of the coherent light whose amplitude is spatially modulated by the spatial light amplitude modulator, or reference light for reading out the reproduction light from the medium and reading the information to the medium. An interference optical unit to be incident;
An image sensor for photoelectrically converting the reproduction light;
Signal processing means for reading out binary information from the digital image output from the image sensor;
With
The signal processing means includes
Alignment means for correcting the digital image to an appropriate spatial position;
A spatial filter for filtering the digital image corrected by the alignment means;
Binarization means for binarizing the filtered digital image;
With
The data recording / reproducing apparatus, wherein the spatial filter changes a filter characteristic of the spatial filter according to a phase of the phase modulation mask corresponding to a pixel adjacent to a target pixel to which a filter is currently applied.   3. The data recording / reproducing apparatus according to claim 1, wherein the modulation pattern of the phase modulation mask is a pseudo-random pattern in which the phase of pixels adjacent in the vertical and horizontal directions of the pixel of interest is rotated by π / 2.   Whether the spatial filter is in phase with the phase of the pixel of interest for each of the phases of the phase modulation mask in four pixels diagonally adjacent to the pixel of interest to which the filter is currently applied The data recording / reproducing apparatus according to claim 1, wherein a filter coefficient for determining a filter characteristic of the spatial filter is changed based on the determination. The signal processing unit binarizes the digital image corrected to an appropriate spatial position by the alignment unit into “0” or “1” so as to reproduce the modulation pattern of the spatial light amplitude modulator. Provisional judging means to
Whether the spatial filter is in phase with the phase of the pixel of interest for each of the phases of the phase modulation mask in four pixels diagonally adjacent to the pixel of interest to which the filter is currently applied And a filter coefficient for determining a filter characteristic is changed based on whether or not each of the outputs of the provisional determination means at four pixels adjacent obliquely is “1”. The data recording / reproducing apparatus according to any one of the above.   The spatial filter is the number of pixels that are in phase with the phase of the pixel of interest for each of the phases of the phase modulation mask in four pixels diagonally adjacent to the pixel of interest to which the filter is currently applied. The data recording / reproducing apparatus according to claim 1, wherein a filter coefficient for determining a filter characteristic of the spatial filter is changed by.