JP2009104699A - Recording compensation method and device for hologram memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a real optical system, that a high-frequency signal is not transmitted well during recording or reproducing, nonlinear characteristics different in recording characteristic are caused by two-dimensional data to be recorded, a high-density recording is not stably recorded if only a recording optical system is improved, though the performance of the optical system is improved or the improvement is tried by recording codes to improve recording characteristics in hologram recording. <P>SOLUTION: The recording compensation method for hologram memory is characterized in that first recording data is generated based on two-dimensional input data to be recorded two-dimensionally, recording compensation data emphasizing a high-frequency component is calculated based on the two-dimensional input data, and then the first recording data and the recording compensation data are recorded into a medium. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a recording compensation method for recording data on a hologram recording apparatus. The present invention also relates to a recording compensation device for recording data on a hologram recording device.

  In recent years, in order to improve the recording characteristics by hologram recording, the performance of the optical system has been improved, or improvement by recording codes has been attempted. However, further improvement by these methods has become difficult. Therefore, the signal light representing the binary digital data as a light and dark image and the reference light are Fourier transformed, the direct current component of the Fourier transformed signal light is attenuated, and the signal light and the reference light with the attenuated direct current component are transmitted as light. A hologram is recorded by simultaneously irradiating a recording medium. This is to improve the dynamic range by inserting an attenuation filter in the optical system to cut the DC component, and to improve the sensitivity of the medium for recording even if the signal quality is suppressed. .

  In addition, when multiple recording fringes of signal light and reference light are recorded on a single layer hologram recording material, data is stored in a layer including two locations near the front and near the back in the thickness direction of the hologram recording material. A method of performing multi-layer recording in which a book is formed in two layers in a hologram recording material by multiplex recording is recorded.

  Furthermore, in the light modulation means for outputting the signal light modulated by the information data written to the holographic medium, and the information data string written by the light modulation means, each information data is encoded by performing sum conversion with the immediately preceding information data. Coding means for writing and information writing means for writing the information data of the information data string to the holographic medium by the reference light. However, only coding for conversion based on the previous data is written. .

In addition, a modulation code composed of the central bit and the peripheral bits of the central bit and a multi-bit feature amount code expressing a feature amount extracted according to the bit pattern of the modulation code are associated in advance. The bit string data to be recorded is divided into the plurality of bits, each of the divided plurality of bits is encoded into the modulation code associated with the feature code represented by the plurality of bits, and the code Based on each of the modulated modulation codes, the spatial light modulator has an encoding processing unit that forms modulated image data for setting the two-dimensional grayscale image pattern. It is known that an encoding process is performed in which a recording code is changed by a central bit and peripheral bits of the central bit.
Japanese Patent Publication No. 2007-172682 Japanese Patent Publication No. 2007-25417 Japanese Patent Publication No. 2006-216148 Japanese Patent Publication No. 2006-179079

  If the DC component of the two-dimensional signal is suppressed and the AC component is emphasized, the signal light intensity resulting from the two-dimensional recording signal becomes strong. However, if the AC component is simply emphasized, the two-dimensional information is emphasized differently depending on the information to be recorded, and the non-linear characteristic that the reproduction characteristics differ depending on the information to be recorded occurs. In emphasis, the signal may not be reproduced correctly. Further, in order to optically perform Fourier transform, a high-precision optical system is required separately, and the apparatus becomes large.

  In addition, if the modulation code is designed to improve the recording / reproducing characteristics by using the encoding by the modulation code, a code that deteriorates the characteristics of the medium is not used. Although it can be stabilized by the modulation code, there is a problem that high density recording which is the original purpose cannot be achieved.

  Further, even if surrounding bit information is used as a modulation method, a code that also deteriorates the characteristics of the medium is not used. Although it can be stabilized by the modulation code, there is a problem that high density recording which is the original purpose cannot be achieved.

  In order to record two-dimensional data, a precise optical system that does not cause distortion of the two-dimensional image is necessary, but the optical system becomes large. On the other hand, it is necessary to reduce the size of the optical system for use in a recording apparatus. Therefore, there is a problem that both miniaturization and stable recording cannot be realized.

  In order to solve the above problems and achieve the object, the hologram memory recording compensation method and apparatus of the present invention are configured as follows.

  In the hologram memory recording compensation method, the first step of creating the first recording data based on the input data to be recorded, and the calculation of the recording compensation data in which the high frequency component is emphasized based on the input data And a step of recording the first recording data of the first step and the recording compensation data of the second step.

  In the hologram memory recording compensation apparatus, the first means for creating the first recording data based on the input data to be recorded and the recording compensation data in which the high frequency component is emphasized based on the input data And means for integrating the first recording data created by the first means and the recording compensation data created by the second means.

  By adopting the above-described configuration, it becomes possible to record everything that has been processed in the reproduction system in the conventional system without distortion in the recording system, and more stable recording and reproduction can be realized. Calculations show that using the present invention shows a 17% improvement in signal-to-noise ratio, which proves effective in improving recording distortion. Therefore, the nonlinear characteristics during recording can be compensated according to the two-dimensional data to be recorded, and high-density two-dimensional data can be stably recorded and reproduced. Further, compensation of the optical system is simplified, and a small and low-cost optical system can be realized.

  In the recording device of the hologram memory, the recording compensation data in which the high frequency component is emphasized is calculated based on the data to be recorded, and the base data and the recording compensation data are recorded on the medium. Data recording with a small amount of data is realized, and a large amount of data is recorded in the hologram memory.

  FIG. 1 shows a configuration of a recording compensation apparatus for a hologram recording apparatus according to the present invention. According to the present invention, the recording compensation apparatus takes a two-dimensional input signal to be recorded as an input 1 and divides it into two signals by a dividing circuit 10. The divided signal is shaped by the high-frequency emphasis filter 11 so that each element of the two-dimensional input signal can be recorded correctly. Further, the original two-dimensional signal is transmitted as it is by the delay circuit 12. The outputs of the high frequency emphasis filter 11 and the delay circuit 12 are combined with a signal by a combining circuit 13. The two-dimensional input signal to be recorded as the output 2 of the coupling circuit 13 and the signal from the high-frequency emphasis filter 11 are output in time series. According to the present invention, in a recording apparatus for holograms, compensation data is generated from the two-dimensional input signal to be recorded together with the two-dimensional input signal to be recorded, and is recorded together. A device is provided.

  With reference to FIG. 2 and FIG. 3, the configuration and operation of a high-frequency emphasis filter as the main object of the present invention will be described. The two-dimensional data 20 is separated as data 22 by a dividing circuit. Further, the high-frequency emphasis filter 21 extracts the compensation data 23 of the two-dimensional data 20. In the high-frequency emphasis filter shown in FIG. 3, calculation is performed based on the value of the pixel Ix, y of interest in the two-dimensional data 31 and the values of the surrounding eight pixels. In the computing unit 32, the basic output O (x, y) is obtained by multiplying the pixel by the coefficient of interest and subtracting the sum of the surrounding pixels. In the comparator 33, compensation data can be obtained by binarizing the basic output O (x, y) based on a fixed threshold value. Compensation data is obtained for all pixels of the two-dimensional data. For the edge pixel, the calculation is performed with the pixel value set to 0 for a portion where there are no surrounding pixels.

  In FIG. 3, the determination is made for the surrounding eight pixels, but the determination may be made for four pixels in the vertical and horizontal directions. Moreover, you may judge about right diagonal and left diagonal. Furthermore, considering the distance from the pixel, if we consider 12 peripheral pixels with 1 pixel vertically, 1 pixel below, 1 pixel on the right, 1 pixel on the right, and 1 pixel on the left, It becomes possible to suppress the influence.

  In FIG. 3, 5 is used as the coefficient to be multiplied by the center pixel. However, the optimum coefficient and threshold value for the system can be determined by performing recording and reproduction on the medium and performing a test together with the threshold value. This is a good example of the optimum recording compensation.

  An example of recording and reproduction according to the present invention will be described with reference to FIGS. A two-dimensional image to be recorded is input to the two-dimensional image input unit 42. The two-dimensional image input unit 42 is called a spatial light modulator and modulates the object light 41 with a two-dimensional image that is an input signal. The object light 31 modulated by the two-dimensional image input unit 42 is condensed on the recording medium 45 by the first optical system 43. The recording medium 45 is irradiated with reference light 44 emitted from the same light source as the object light 41 at the same time as the object light 41. Interference fringes due to the reference beam 44 and the object beam 41 are formed in the recording medium 45. In order to multiplex-record as a hologram, it is a good example to change the angle of the reference beam 44, change the light condensing characteristic, or move the position of the medium. At the time of signal reproduction, only the reference light 44 is irradiated, and the signal from the interference fringe formed in the recording medium is reproduced by the two-dimensional image reproduction unit 47 using the second optical system 46. The two-dimensional image reproduction unit 47 is preferably a two-dimensional element made of CCD, CMOS, or the like.

  FIG. 5 shows a time schedule for recording. In conventional recording, recording is performed by setting a two-dimensional signal to be recorded in the two-dimensional image input unit 42 and irradiating the object beam 31 and the reference beam 34 for a certain period of time. In the present application, after the first data 51 is set and recorded in the two-dimensional image input unit 42, the second data 52 is set in the two-dimensional image input unit 42 and recorded as compensation data. When the first data 51 and the second data 52 are recorded, a signal is recorded using the same reference beam 34. By doing so, the compensation data can be recorded as interference fringes in the medium, so that the high frequency component can be emphasized and recorded as compared with the conventional case. Although FIG. 5 shows an example in which the compensation data is recorded later, the compensation data may be recorded first.

  In the present invention, the reason why high-frequency components are recorded with emphasis is that the first optical system 43 attenuates the high-frequency components, and interference in a two-dimensional image occurs when recording at a high density. It is to suppress the influence of non-linearity of the medium. In these cases, since the high frequency portion is basically attenuated, compensation data is recorded in order to emphasize it. As a result, the influence of the above disturbance is suppressed, and the signal of each pixel can be accurately reproduced.

  Compared to the case where recording compensation is not performed in the case where recording compensation is performed in FIG. 6 and the case where recording compensation is not performed, when recording compensation is performed, a signal is strongly reproduced at an isolated pixel and a pixel at the end of a bright portion. It can be seen that the present invention is effective.

  FIG. 7 shows the improvement characteristics of the signal-to-noise ratio (SNR). Here, the signal (s) is defined as the difference between the average reproduction intensity of the bright signal 1 and the average reproduction intensity of the dark signal 0. Further, it is defined that the square root of the standard deviation of the bright signal 1 and the square of the standard deviation of the dark signal 0 are added as noise (N) and the square root thereof is taken. In this way, the relationship between the signal-to-noise ratio (SNR) and the exposure time of compensation data is shown. Note that the exposure time of the compensation data is shown normalized by the exposure time of the original data to be recorded. Thus, it can be seen that it is a good example that the recording time of compensation data is set to zero or more and 0.4 or less compared to the exposure time of compensation data. Further, it can be seen that optimum compensation can be performed from 0.15 to 0.25, and good recording and reproduction can be performed.

  FIG. 8 shows the improvement characteristics of the signal-to-noise ratio (SNR) when the characteristics of the optical system are changed. Here, the effect of the present invention when the cut-off frequency fc of the spatial frequency of the optical system is changed is shown. Here, the cut-off frequency fc indicates the transfer characteristic of the high frequency component of the optical system, and gives an upper limit for signal transmission. Further, in FIG. 8, normalization is performed with the frequency of the pixel pitch of the pixels. From FIG. 8, even if the cut-off frequency fc changes, recording the compensation data improves the signal-to-noise ratio (SNR) by about 17%, and the effect when the high recording density is performed is large. It can be seen that the invention is effective.

  FIG. 2 shows an example using a binary signal. However, when the two-dimensional image input unit in FIG. 4 can output gradation in analog, the intensity of the compensation data is set when the intensity of the data 22 is 1. It is a good example to add by setting 0 to 0.4 or less. Thereby, recording can be performed by one recording exposure. Further, when the intensity of the data 22 is 1, it is more preferable that the intensity of the compensation data is set to 1.5 to 2.5 and added. Thereby, stable recording can be realized by one recording exposure.

  The recording compensation method for the hologram memory will be described with reference to FIG. In the input 91 of the two-dimensional input data to be recorded in two dimensions, the signal to be recorded by the apparatus is received in accordance with the size of the two-dimensional image input unit. In creation 92 of the first recording data based on the two-dimensional input data, the first recording data obtained by copying the two-dimensional input data as it is is output. Further, in the calculation 93, the recording compensation data in which the high frequency component is emphasized based on the two-dimensional input data is used to create recording compensation data for recording compensation based on the value of each pixel of the two-dimensional data and its surrounding values. . The first recording data holding 94 holds the first recording data created by the creation 92 of the first recording data based on the two-dimensional input data. Further, in the integration 95, the first recording data and the recording compensation data are arranged so that the recording compensation data comes after the first recording data. In step 96 of recording the integrated data, after recording the first recording data using the reference light, the recording compensation data is recorded using the same reference light. This makes it possible to realize recording that emphasizes high-frequency components.

  With reference to FIGS. 2 and 3, a compensation method using a high-frequency emphasis filter as a main object of the present invention will be described. The two-dimensional data 20 is separated as data 22 by a dividing circuit. Further, the high-frequency emphasis filter 21 extracts the compensation data 23 of the two-dimensional data 20. In the high-frequency emphasis filter shown in FIG. 3, calculation is performed based on the value of the pixel Ix, y of interest in the two-dimensional data 31 and the values of the surrounding eight pixels. In the computing unit 32, the basic output O (x, y) is obtained by multiplying the pixel by the coefficient of interest and subtracting the sum of the surrounding pixels. In the comparator 33, compensation data can be obtained by binarizing the basic output O (x, y) based on a fixed threshold value. Compensation data is obtained for all pixels of the two-dimensional data. For the edge pixel, the calculation is performed with the pixel value set to 0 for a portion where there are no surrounding pixels.

  In FIG. 3, the determination is made for the surrounding eight pixels, but the determination may be made for four pixels in the vertical and horizontal directions. Moreover, you may judge about right diagonal and left diagonal. Furthermore, considering the distance from the pixel, if we consider 12 peripheral pixels with 1 pixel vertically, 1 pixel below, 1 pixel on the right, 1 pixel on the right, and 1 pixel on the left, It becomes possible to suppress the influence.

  In FIG. 3, 5 is used as the coefficient to be multiplied by the center pixel. However, the optimum coefficient and threshold value for the system can be determined by performing recording and reproduction on the medium and performing a test together with the threshold value. This is a good example of the optimum recording compensation.

  When the threshold value is set to 0, it is a good example to set the coefficient to be multiplied to the center pixel from 1 to 5, and this can emphasize isolated and edge data.

  In the above embodiment, an example in which the recording time of the recording compensation data is determined in advance has been described. However, a process for selecting the recording time of the recording compensation data with the smallest reproduction error from the error characteristics of the reproduction signal may be provided. In this way, it is possible to suppress characteristic fluctuations due to differences in reproduction conditions.

  The present invention has been shown by way of example in which a normal 4f two-dimensional image is recorded. However, the present invention is also effective when recording one bit in a medium three-dimensionally using a hologram called a micro-hologram.

  In the micro-hologram, the high-frequency component is generated based on the first step of making the data to be recorded two-dimensional input data having a two-dimensional arrangement on the medium and the two-dimensional input data created in the first step. The second step of creating emphasized recording compensation data, and the data of the first step are added to the recording compensation data of the second step by a coupling circuit. In this way, it is possible to provide a method for recording the data for recording compensation together with the data in the order of forming the micro-holograms.

  A good example of combining the data with the compensation data is to increase the intensity of the laser to be recorded to more than 1 and 1.4 times when the compensation data is valid. Thereby, the high frequency component can be emphasized and recorded, and attenuation of the high frequency component at the time of recording and reproduction can be compensated.

  In addition, when the compensation data is valid, it is a good example to increase the recording laser intensity from 1 to 1.4 times. As a result, high-frequency components can be emphasized and recorded, and attenuation of the high-frequency components during recording and reproduction can be sufficiently compensated.

  In the micro-hologram, in the first step of converting the data to be recorded into two-dimensional input data having a two-dimensional arrangement on the medium, recording is already performed in the medium on the layer below or above the area to be recorded. Read the data that has been recorded, and read the relationship with the data recording layer. Data for recording compensation may be calculated by combining the data to be recorded in the second step and the recorded data.

  In this case as well, it is only necessary to calculate the adjacent pixel as the lower layer in which the region is close from the in-plane as shown in FIG. Therefore, in this case, the peripheral pixels may be determined by adding 8 pixels to 9 pixels in the lower layer in the case of FIG. Furthermore, when considering the upper layer, the adjacent layer may be calculated as a pixel for the upper layer whose region is close to the surface as shown in FIG. Therefore, in this case, the surrounding pixels may be determined by adding 8 pixels to 9 pixels in the upper layer in the case of FIG. Also, when considering the upper layer and the lower layer, the adjacent layers may be calculated as pixels for the upper layer and the lower layer whose regions are close to each other as shown in FIG. Therefore, in this case, the surrounding pixels may be determined by adding 8 pixels to 9 pixels in the upper layer and 9 pixels in the lower layer in the case of FIG.

  In micro-holograms, it is conceivable that the medium is rotated in the form of a disk. Also in this case, if the high frequency is emphasized using the method of FIG. 3, it can be used without any problem.

  In the micro-hologram, the high-frequency component is generated on the basis of the first means to make the data to be recorded two-dimensionally arranged in a two-dimensional configuration on the medium and the two-dimensional input data created by the first means. The second means for creating emphasized recording compensation data, and the data of the first means are added to the recording compensation data of the second step by a coupling circuit. In this way, it is possible to provide an apparatus for recording data for recording compensation together with data in the order in which micro-holograms are formed.

  As described above, according to the hologram memory recording compensation method and apparatus of the present invention, in the hologram memory recording apparatus, based on the data to be recorded, the recording compensation data in which the high frequency component is emphasized is calculated, By recording the basic data and the recording compensation data in time series, it is possible to record recording data with less distortion on the medium.

  Specifically, for each element of binary two-dimensional data to be recorded “1” or “0”, subtraction with the data of the elements around the element from the element of interest, using a threshold value for the numerical value, This creates binary two-dimensional data for recording compensation. The created recording compensation data is recorded subsequent to the original data.

  In addition, this invention is not limited to the said embodiment, In the implementation stage, it can change variously in the range which does not deviate from a summary. In addition, the embodiments may be appropriately combined as much as possible, and in that case, the combined effect can be obtained. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effect described in the column of the effect of the invention Can be obtained as an invention.

  According to the present invention, the following hologram memory recording compensation method and apparatus can be provided.

(1) A hologram memory recording compensation method capable of recording without distortion in a hologram memory recording system and capable of realizing more stable recording.

(2) A hologram memory recording compensation apparatus that can record without distortion in the hologram memory recording system and can realize more stable recording.

The figure which shows the structure of the recording compensation apparatus of the hologram memory of this invention The figure which shows the composition of the high frequency emphasis filter The figure which shows the detailed composition of the high frequency emphasis filter The figure which shows the recording / reproducing structure to the medium The figure which shows the recording schedule of this invention The figure which shows the example of the reproduction | regeneration image of this invention Diagram showing normalized recording time and signal-to-noise ratio Diagram showing normalized frequency and signal-to-noise ratio The figure which shows the structure of the recording compensation method of the hologram memory of this invention

Explanation of symbols

1 input 2 output 10 dividing circuit 11 high-frequency emphasis filter 12 delay circuit 20 two-dimensional data 21 high-frequency emphasis filter 22 data 23 compensation data 31 detector pixel (x, y)
32 arithmetic unit 33 comparator 41 object light 42 two-dimensional image input unit 43 first optical system 44 reference light 45 recording medium 46 second optical system 47 two-dimensional image reproduction unit

Claims (2)

  In the hologram memory recording compensation method, the first step of creating the first recording data based on the input data to be recorded, and the calculation of the recording compensation data in which the high frequency component is emphasized based on the input data 2. A hologram memory recording compensation method comprising: a step 2, and a step of recording the first recording data of the first step and the recording compensation data of the second step.   In the hologram memory recording compensation apparatus, the first means for creating the first recording data based on the input data to be recorded and the recording compensation data in which the high frequency component is emphasized based on the input data 2. A hologram memory recording compensation apparatus comprising: means 2; and means for integrating the first recording data created by the first means and the recording compensation data created by the second means .

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