JP2007004926A - Method, device and program for reproducing optical information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method, a device and a program for reproducing optical information, capable of performing accurate reproduction by executing sure and correct adaptation equalization processing even when an aberration generated by the uneven thickness, the surface wobbling or the eccentricity of an optical information recording medium causes data rotation, bending, distortion or intercode interference. <P>SOLUTION: In an optical information recording medium equipped with an information recording layer in which information is recorded by using holography, a known pattern is recorded as a recording pattern of a specific page or block with respect to a certain reference light, and a data pattern is recorded with respect to another reference light. For the reproducing signal of the known patten, and the known pattern, transmission characteristics are obtained by subtracting calculation results obtained by 2-dimensional discrete Fourier transform (S1 to S3), and the influence of transmission characteristics is eliminated from the reproducing signal of the data pattern by subtracting the transmission characteristics from the 2-dimensional discrete Fourier transform of the reproducing signal of the data pattern (S4 and S5). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical information reproducing method, an optical information reproducing apparatus, and a recording medium, and in particular, optical information reproduction for optically reproducing recorded information from an optical information recording medium having an information recording layer on which information is recorded using holography. The present invention relates to a method, an optical information reproducing apparatus, and an optical information reproducing program used for the optical information reproducing apparatus.

  Holographic recording, in which information is recorded on a recording medium using holography, is generally performed by superimposing light having image information and reference light inside the recording medium, and forming the interference fringes formed at that time on the recording medium. Done by writing. At the time of reproducing the recorded information, the image information is reproduced by diffraction by interference fringes by irradiating the recording medium with reference light.

  In recent years, volume holography, particularly digital volume holography, has been developed and attracted attention for practical use for ultra-high density optical recording. Volume holography is a method of writing interference fringes in three dimensions by actively utilizing the thickness direction of the recording medium. Increasing the thickness increases the diffraction efficiency and increases the recording capacity using multiple recording. There is a feature that can be planned. Digital volume holography is a computer-oriented holographic recording method that uses a recording medium and a recording method similar to those of volume holography, but restricts image information to be recorded to a binarized digital pattern.

  In this digital volume holography, for example, image information such as an analog picture is once digitized, developed into two-dimensional digital pattern information (also referred to as page data), and recorded as image information. At the time of reproduction, the digital pattern information is read and decoded so that the original image information is restored and displayed. As a result, even if the S / N ratio (signal to noise ratio) is somewhat poor at the time of reproduction, the original information is reproduced very faithfully by performing differential detection or encoding binary data and performing error correction. It becomes possible.

  Such two-dimensional digital pattern information includes a positioning synchronization code (hereinafter referred to as “sync code” or “sync code”) used in pattern detection. This Sync code is matched with a Sync code provided on an image detector composed of a CCD (Charge Coupled Devise) or CMOS (Complementary Metal Oxide Semiconductor). Then, positioning is performed so that both Sync codes coincide with each other, and a reproduced image is detected.

  FIG. 7 shows an example of a two-dimensional digital pattern (page data). In FIG. 7, a plurality of large rectangular marks are Sync codes, which are used for alignment on an image detector such as a CCD or CMOS.

  Template matching is known as one method for matching two images (see, for example, Non-Patent Document 1). In template matching, a desired image pattern can be efficiently detected from certain image information. However, in this template matching, it is necessary to calculate the maximum correlation value using a predetermined formula. This formula calculates a correlation value indicating the similarity between a certain pattern in the reproduced image and the template image. The correlation value is calculated for all coordinate positions in the reproduced image in one area provided by dividing the entire page data into a plurality of parts, so that the calculation amount is enormous and image detection is performed quickly. It is a problem to realize.

  Therefore, in order to solve this problem, in an apparatus for reproducing information from an optical information recording medium having an information recording layer on which information is recorded using holography, the above-mentioned information recording layer is irradiated with reproduction reference light. The detection means for detecting the reproduction light generated by the operation is set so that all the sync codes (Sync codes) for positioning the reproduction image included in the reproduction light have the same pixel value, from the XY plane. In this search range, either one of the components is fixed, the correlation value in the other direction is obtained, then the correlation value in the fixed direction is obtained, and all correlation values obtained in the search range are obtained. There is known an optical information reproducing apparatus in which the largest one is set as a position where matching is achieved (see, for example, Patent Document 1).

  According to the conventional optical information reproducing apparatus described in Patent Document 1, by introducing a Sync code having the same pixel value, the amount of calculation for calculating the correlation value is reduced, and further the correlation value is calculated. In this case, the X direction or the Y direction is fixed, and one of the searches is performed, and after that, the other search is performed to simplify the calculation, thereby reducing the calculation processing time. I am trying.

"Introduction to Computer Image Processing", published by Soken Publishing, June 1, 1986, p. 149-151 JP 2004-310957 A

  However, in the conventional optical information reproducing apparatus described in Patent Document 1, even if the SYNC code position is found, in order to extract actual recording data bits, distortion and rotation of a two-dimensional digital pattern (page data) are performed. Cannot be handled, and the position in bit units cannot be specified. In particular, in an actual system, aberrations caused by thickness unevenness, surface blurring, decentration, and the like of an optical disk that is an optical information recording medium are generated as rotation, curvature, and distortion of data.

  In such a state, in order to efficiently reduce the rotation, curvature, distortion, and intersymbol interference of data, it is desirable to perform adaptive equalization processing, that is, equalizer (EQ) processing. In particular, it is important to perform two-dimensional EQ processing or three-dimensional (including page direction) EQ processing.

  In order to efficiently perform two-dimensional EQ, it is desirable to perform equalization adaptively according to the aberration. However, if the error rate is bad, the input signal is provisionally determined and an ideal Since there are many errors in the provisional determination for outputting the value (target value), the EQ characteristic cannot be converged to the correct target value. In particular, in recording / reproducing on a holographic medium, since it is sensitive to parameters of the holographic medium or the optical system, there is a high possibility that the EQ characteristic cannot be converged to a correct target value.

  The present invention has been made in view of the above points, and even when aberrations caused by thickness unevenness, surface blurring, decentration, etc. of optical information recording media are caused by data rotation, curvature, distortion, or intersymbol interference. An object of the present invention is to provide an optical information reproducing method, an optical information reproducing apparatus, and an optical information reproducing program capable of reliably performing correct adaptive equalization processing and performing accurate reproduction.

In the present invention, in order to achieve the above object, the reproduction reference light is irradiated to the optical information recording medium including the information recording layer on which information is recorded using holography, and the reproduction reference light is irradiated. In an optical information reproducing method for reproducing information generated by detecting reproduction light generated by the information recording layer, the information recording layer irradiated with the reproduction reference light of the optical information recording medium has a recording pattern of a specific page or block. A known pattern is recorded for the first reference light, and a data pattern is recorded for the second reference light.
A first calculation result is obtained by performing two-dimensional discrete Fourier transform on a reproduction signal of a known pattern obtained by collecting reproduction light generated in the information recording layer by being irradiated with the first reference light. A first step, a second step of obtaining a second calculation result obtained by performing a two-dimensional discrete Fourier transform on the known pattern recorded on the optical information recording medium, and a first calculation result Obtained by collecting the reproduction light generated in the information recording layer by irradiating the second reference light with the third step of obtaining the first subtraction value by subtracting the first and second calculation results A fourth step of obtaining a third calculation result by performing two-dimensional discrete Fourier transform on the reproduced signal of the data pattern, and subtracting the first subtraction value from the third calculation result, Re-establishing data patterns that have had their effects removed A fifth step of obtaining a second subtraction value as a signal, and a sixth step of performing two-dimensional inverse discrete Fourier transform on the second subtraction value and detecting data from the calculation result, To do.

  In the present invention, by subtracting the first calculation result and the second subtraction result obtained by two-dimensional discrete Fourier transform of the reproduction signal of the known pattern and the recording signal of the known pattern, respectively, the optical information recording medium Since the first subtraction value indicating the characteristics of the reproduction system (transmission system) can be obtained, this is subtracted from the third calculation result obtained by performing the two-dimensional discrete Fourier transform on the reproduction signal of the data pattern. Thus, it is possible to obtain the second subtraction value that is a reproduction signal of the data pattern from which the influence of the transmission system is removed.

In order to achieve the above object, in the second invention, reproduction reference light is irradiated to an optical information recording medium having an information recording layer on which information is recorded using holography, and the reproduction reference is provided. In an optical information reproduction method for reproducing information by detecting reproduction light generated by light irradiation, a specific page or block is provided on an information recording layer irradiated with reproduction reference light of an optical information recording medium. As the recording pattern, a known pattern having an isolated waveform is recorded for the first reference light, and a data pattern is recorded for the second reference light.
A first calculation result is obtained by performing two-dimensional discrete Fourier transform on a reproduction signal having a known pattern of an isolated waveform obtained by collecting reproduction light generated in the information recording layer by irradiation with the first reference light. And a two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the second reference light. A second step of obtaining a second calculation result, and a subtraction value that is a reproduction signal of the data pattern from which the influence of the transmission system is removed by subtracting the first calculation result from the second calculation result. And a fourth step of performing two-dimensional inverse discrete Fourier transform on the subtracted value and detecting data from the calculation result.

  In the present invention, since the known pattern is an isolated waveform, the first calculation result including the influence of the reproduction system (transmission system) obtained by two-dimensional discrete Fourier transform on the reproduction signal of the known pattern of the isolated waveform is obtained. By subtracting from the second calculation result obtained by performing the two-dimensional discrete Fourier transform on the reproduction signal of the data pattern, the reproduction signal of the data pattern from which the influence of the transmission system is removed can be obtained.

  Here, discrete cosine transform may be performed instead of the two-dimensional discrete Fourier transform in the first or second invention, and discrete cosine inverse transform may be performed instead of the two-dimensional inverse discrete Fourier transform.

In order to achieve the above object, an optical information reproducing apparatus of the present invention irradiates an optical information recording medium having an information recording layer on which information is recorded using holography with reproduction reference light. In an optical information reproducing apparatus that reproduces information by detecting reproduction light generated by irradiation with reproduction reference light, an information recording layer irradiated with reproduction reference light on an optical information recording medium has a specific information recording layer. As a page or block recording pattern, a known pattern is recorded for the first reference light, and a data pattern is recorded for the second reference light,
A first calculation result is obtained by performing two-dimensional discrete Fourier transform on a reproduction signal of a known pattern obtained by collecting reproduction light generated in the information recording layer by being irradiated with the first reference light. A first computing means, a second computing means for obtaining a second computing result obtained by performing a two-dimensional discrete Fourier transform on the known pattern recorded on the optical information recording medium, The third calculation means for obtaining the first subtraction value by subtracting the calculation result and the second calculation result, and collecting the reproduction light generated in the information recording layer by irradiating the second reference light A fourth calculation means for obtaining a third calculation result by performing two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained in this manner, and subtracting the first subtraction value from the third calculation result , Re-retrieval of data patterns from which transmission system effects have been removed A fifth calculating means for obtaining a second subtraction value as a signal, and a detecting means for detecting data based on a calculation result obtained by performing a two-dimensional inverse discrete Fourier transform on the second subtraction value. Features. In the present invention, similarly to the first invention, it is possible to obtain the second subtraction value that is a reproduction signal of the data pattern from which the influence of the transmission system is removed.

In order to achieve the above object, an optical information reproducing apparatus of the present invention irradiates an optical information recording medium having an information recording layer on which information is recorded using holography with reproduction reference light. In an optical information reproducing apparatus that reproduces information by detecting reproduction light generated by irradiation with reproduction reference light, an information recording layer irradiated with reproduction reference light on an optical information recording medium has a specific information recording layer. As a page or block recording pattern, a known pattern having an isolated waveform is recorded for the first reference light, and a data pattern is recorded for the second reference light,
A first calculation is performed by performing a two-dimensional discrete Fourier transform on a reproduction signal of a known pattern, which is an isolated waveform obtained by collecting reproduction light generated in the information recording layer by being irradiated with the first reference light. Two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained by collecting the reproduction light generated in the information recording layer by irradiating the second reference light with the first calculation means for obtaining the result The second calculation means for obtaining the second calculation result, and the subtraction value which is a reproduction signal of the data pattern from which the influence of the transmission system is removed by subtracting the first calculation result from the second calculation result And a detection means for detecting data based on a calculation result obtained by performing a two-dimensional inverse discrete Fourier transform on the subtracted value.

  In the present invention, since the known pattern is an isolated waveform as in the second invention, the influence of the reproduction system (transmission system) obtained by two-dimensional discrete Fourier transform on the reproduction signal of the known pattern of the isolated waveform. The data pattern reproduction signal from which the influence of the transmission system is removed by subtracting the first calculation result including the second calculation result obtained by performing the two-dimensional discrete Fourier transform on the data pattern reproduction signal. Can be obtained.

  In order to achieve the above object, the optical information reproducing program of the present invention irradiates an optical information recording medium having an information recording layer on which information is recorded using holography with a reproduction reference beam, Each step of the optical information reproducing method according to any one of the first to third inventions for reproducing information by detecting reproduction light generated by irradiation with reproduction reference light is executed by a computer. It is characterized by making it.

  According to the present invention, the first calculation result and the second subtraction result obtained by performing two-dimensional discrete Fourier transform or cosine transform on the reproduction signal of the known pattern and the recording signal of the known pattern, respectively, are subtracted. After obtaining the first subtraction value indicating the characteristics of the reproduction system (transmission system) of the information recording medium, this is subtracted from the third calculation result obtained by two-dimensional discrete Fourier transform on the reproduction signal of the data pattern. As a result, the second subtraction value, which is the reproduction signal of the data pattern from which the influence of the transmission system has been removed, is obtained, so that the thickness of the optical information recording medium on the actual system, surface blurring, eccentricity, etc. Even when data rotation, curvature, distortion, or intersymbol interference caused by the generated aberration occurs in the reproduction signal of the data pattern, the data can be reliably detected without causing the adaptive equalization process to diverge.

  In addition, according to the present invention, since the known pattern is an isolated waveform, a reproduction signal of the data pattern from which the influence of the transmission system is removed can be obtained with a small number of calculation steps, so that accurate data detection can be performed quickly. Can do.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of an optical information reproducing apparatus according to the present invention, and FIG. 2 is a configuration diagram of an example of a pickup device in FIG. The configuration of the optical information reproducing apparatus according to the present embodiment will be described with reference to FIG. 1. An optical information reproducing apparatus 10 according to the present embodiment includes a spindle 21 to which an optical information recording medium (here, an optical disk) 1 is attached, A spindle motor 22 for rotating the spindle 21 and a pickup for irradiating the optical information recording medium 1 with reproduction reference light, detecting the reproduction light, and reproducing the information recorded on the optical information recording medium 1 A device 23 and a drive device 24 that can move the pickup device 23 in the radial direction of the optical information recording medium 1 are provided.

  Further, the optical information reproducing apparatus 10 detects the focus error signal FE, the tracking error signal TE and the reproduction signal RF from the output signal of the pickup apparatus 23, and the pickup apparatus based on the focus error signal FE. A focus servo that controls the focus of the light beam on the optical information recording medium 1 by moving the objective lens in the optical information recording medium 1 in the thickness direction, and the objective in the pickup device 23 based on the tracking error signal TE. A focus / tracking servo circuit 26 that performs tracking servo for moving and controlling the lens so that the irradiation position of the light beam on the optical information recording medium 1 follows the track on the optical information recording medium 1, and the main part of the present embodiment And a controller for controlling the entire optical information reproducing apparatus 10. And over La 28 are more configuration and operation unit 29 to give various instructions to the controller 28.

  Although not shown, a slide servo circuit that controls the drive device 24 based on the tracking error signal TE and a command from the controller 28 to perform the slide servo that moves the pickup device 23 in the radial direction of the optical information recording medium 1. In addition, a spindle servo circuit for controlling the rotation of the spindle motor 22 based on a command from the controller 28 is also provided.

  The controller 28 receives the basic clock and address information output from the signal processing circuit 27 as inputs, and controls operations of the pickup device 23 and various servo circuits. The controller 28 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and the CPU executes a program stored in the ROM using the RAM as a work area. Thus, the function of the controller 28 is realized.

  The signal processing circuit 27 is a circuit that forms a main part of the present embodiment. The signal processing circuit 27 decodes output data of a CMOS sensor or a CCD array (to be described later) in the pickup device 23 and records it in the data area of the optical information recording medium 1. The reproduced data is reproduced according to a flowchart to be described later, the basic clock is reproduced or the address is discriminated from the reproduced RF signal from the detection circuit 25.

  Next, the configuration of the optical information recording medium 1 and the configuration of the pickup device 23 will be described in more detail with reference to FIG. In FIG. 2, an optical information recording medium 1 includes a hologram recording layer 3 as an information recording layer on which information is recorded using a volume holography on one surface of a disc-shaped transparent substrate 2, and a transparent layer having a function of a protective layer. The substrate 4 and the reflective film 5 made of aluminum are configured as an optical disc in which the substrates 4 are laminated in this order. The transparent substrate 4 is an addressed substrate created by injection, for example, and address / servo areas are provided at predetermined angular intervals, and a section between adjacent address / servo areas is a data area. The hologram recording layer 3 is formed of a known hologram material whose optical characteristics such as refractive index, dielectric constant, and reflectance change according to the intensity of light when irradiated with light.

  On the other hand, the pickup device 23 includes an objective lens 12 facing the transparent substrate 2 side of the optical information recording medium 1, a quarter wavelength plate 13 disposed on the opposite side of the optical information recording medium 1 of the objective lens 12, and a mirror. 14, and a light source 15 such as a laser diode, a collimator lens 16, a defocusing convex lens 17, a polarization beam splitter (PBS) 18, and a photodetector 20.

  The light emitted from the light source 15 is converted into parallel light by the collimator lens 16, and is generated by the defocusing convex lens 17 as the reproduction reference light that diverges and enters the objective lens 12, enters the PBS 18, and is polarized. The light passes through the separation surface 18 a and enters the mirror 14. Further, P-polarized light is made circularly polarized by the quarter-wave plate 13, and is irradiated to the optical information recording medium 1 by the objective lens 12 as reproduction reference light. This reproduction reference light is the same as the recording reference light used when recording information to be reproduced this time on the optical information recording medium 1. The objective lens 12 can be moved in the thickness direction and the radial direction of the optical information recording medium 1 by an actuator (not shown).

  Return light (reproduced light) from the optical information recording medium 1 is transmitted through the objective lens 12, converted from circularly polarized light to S polarized light by the quarter-wave plate 13, reflected by the mirror 14, and incident on the PBS 18. Then, the light is reflected by the polarization splitting surface 18a of the PBS 18 and received by the photodetector 20 comprising a CCD or CMOS sensor as reproduction light detecting means.

  Next, features of the present embodiment will be described. In the present embodiment, a known pattern is recorded and reproduced in order to surely obtain a correct two-dimensional equalizer (EQ) characteristic. Conventionally, recording of a known pattern has been avoided because it reduces the recording capacity of the optical disk medium. However, in this embodiment, the holographic medium is applied to the optical disk, so that the page is divided according to the reference light and the angle. This is because it is possible to use overwriting and realize a dramatic increase in capacity, so that it is not a big problem to provide an area for recording a known pattern.

  Similar to the data pattern recording method, the known pattern recording method superimposes the light modulated with the known pattern information, which is image information, and the reference light inside the optical information recording medium, and forms interference fringes that can be generated at that time. This is done by writing to the information recording layer.

  The following can be considered as recording locations of the known pattern.

(1) Separated from data pattern on page (location is the same)
(2) Separation from data pattern on page (position slightly shifted)
(3) The page is divided into blocks and a known data pattern area and a data pattern area are recorded.

  The above (1) and (2) make use of the fact that the optical disk (optical information recording medium 1 in FIG. 1), which is a holographic medium, can be page-separated by reference light. That is, in the holographic medium, the data pattern and the known pattern can be separated by changing the phase of the reference light. In the above (1), since the data pattern and the known pattern are recorded on the optical disk as the holographic medium (the optical information recording medium 1 in FIG. 1) so as to overlap at the same position, the optical disk is stopped or the same track is recorded. Read again. As a result, the influences of the tilt and surface blur of the optical disk appear in the same way on each page, so that accurate detection and compensation can be expected.

  However, since the optical disk is actually rotating, it is difficult to read the data pattern and the known pattern from exactly the same position as in (1) unless it is controlled by a servo rotation pulse or the like. You have to wait for rotation playback. Therefore, as described in (2) above, when the data pattern and the known pattern are slightly shifted and recorded, and another page is recorded immediately, the optical disk rotates because the frequency of tilt and surface blur of the optical disk is low. However, the same effect as (1) can be expected.

  However, in order to reduce the influence of the location, as shown in FIG. 3, the block I of the known pattern and the block II of the data pattern are physically overlapped by 50% or more as indicated by III on the same page. Of course, it is better. In addition, the above block is a recording unit existing in each page, as in the block (3). The above (3) is that the recording pattern of a specific block in the same page is a known pattern, and the other blocks are data patterns.

  As described above, in the present embodiment, the information recording layer 3 irradiated with the reproduction reference light of the optical information recording medium 1 has a recording pattern of a specific page or block with respect to the first reference light. A known pattern is recorded, and a desired data pattern to be reproduced is recorded for the second reference light.

  Next, examples of known patterns and data patterns will be described. FIG. 4A-1 shows an example of a recording pattern. In FIG. 4A-1, a known pattern is a pattern that is inverted only at the center, as indicated by a black square. That is, it is a pattern composed of bits having a polarity opposite to that of other bits in a page or block. This is an isolated waveform that can be considered two-dimensionally. If this pattern is recorded and reproduced as shown in FIG. 4A-2, this indicates the transfer characteristic itself.

  That is, FIG. 4A-2 shows a pattern having intersymbol interference due to recording / reproduction, and the reproduction level increases from the center inversion pattern toward the periphery (when the reproduction level is the lowest at the center). The pattern corresponds to the amount of light entering the cell when read by the photodetector (20 in FIG. 2). The amount of light corresponds to the shading in the figure.

  Based on the relationship between FIG. 4 (A-1) and FIG. 4 (A-2), the reverse characteristic of the transmission characteristic is derived by calculation and the data pattern is shaped by the reproduction method and reproduction apparatus of the present invention described later. As a result, when a data pattern as shown in FIG. 4B-1 is recorded on the optical information recording medium 1, the reproduced data pattern is intersymbol interference as shown in FIG. 4B-2. The data pattern at the time of recording, in which the intersymbol interference is removed from the recording / reproducing pattern by performing an adaptive equalization process for applying the inverse characteristic of the transmission characteristic derived by the above calculation to the data pattern ( A reproduction pattern as shown in FIG. 4 (B-3) close to B-1) is obtained.

  Next, the operation of the embodiment of the optical information reproducing method and optical information reproducing apparatus according to the present invention will be described with reference to the flowchart of FIG. First, the signal processing circuit 27 in FIG. 1 outputs 2 to the known pattern reproduction signal as shown in FIG. 4A-2 reproduced from the known pattern recording area of the optical information recording medium 1 by the pickup device 23. Dimensional discrete Fourier transform is performed to obtain a first calculation result (step S1 in FIG. 5). Here, the equation of the two-dimensional discrete Fourier transform is defined by the following equation.

ここで、上式中、ｆ（ｘ，ｙ）は実領域の２次元関数で、Ｆ（ｕ，ｖ）はそれに対応する離散フーリエ領域の２次元関数である。また、通常用いられる２次元離散離散フーリエ変換の式は次式で定義される。

Here, in the above formula, f (x, y) is a two-dimensional function in the real domain, and F (u, v) is a corresponding two-dimensional function in the discrete Fourier domain. Moreover, the formula of the two-dimensional discrete discrete Fourier transform used normally is defined by the following formula.

本実施の形態の２次元離散フーリエ変換は、この２次元離散離散フーリエ変換を想定している。光検出器２０から信号処理回路２７に供給される再生信号は、光検出器２０がＣＣＤ又はＣＭＯＳで構成されており、既に離散的な信号であるからである。なお、数２に示す式中、Ｎはサンプル数である。

The two-dimensional discrete Fourier transform of this embodiment assumes this two-dimensional discrete discrete Fourier transform. This is because the reproduction signal supplied from the light detector 20 to the signal processing circuit 27 is already a discrete signal because the light detector 20 is composed of a CCD or a CMOS. In the equation shown in Equation 2, N is the number of samples.

  Subsequently, the signal processing circuit 27 reads out the second calculation result obtained by performing the two-dimensional discrete Fourier transform of the known pattern shown in FIG. (Step S2 in FIG. 5) is subtracted from the first calculation result obtained in Step S1 (Step S3 in FIG. 5). The subtraction value obtained in step S3 is a difference value between the second calculation result of the original known recording pattern and the first calculation result of the reproduced known pattern, and indicates transmission characteristics.

  Subsequently, the signal processing circuit 27 responds to the data pattern reproduction signal as shown in FIG. 4B-2 reproduced from the data pattern recording area of the optical information recording medium 1 by the pickup device 23 of FIG. Then, a two-dimensional discrete Fourier transform is performed by the arithmetic expression shown in Equation 2 to obtain a third calculation result (step S4 in FIG. 5).

  Subsequently, the signal processing circuit 27 subtracts the subtraction value calculated in step S3 from the third calculation result calculated in step S4, thereby removing the influence of the transmission characteristics included in the third calculation result (FIG. 5). In step S5), the two-dimensional inverse discrete Fourier transform (inverse two-dimensional discrete Fourier transform) is performed on the subtraction value calculated in step S5 (step S6 in FIG. 5).

  Here, the two-dimensional inverse discrete Fourier transform (two-dimensional discrete Fourier inverse transform) is generally performed based on the following equation.

また、２次元離散離散フーリエ逆変換は、次式で定義される。

The two-dimensional discrete discrete Fourier inverse transform is defined by the following equation.

本実施の形態のステップＳ６の２次元逆離散フーリエ変換（２次元離散フーリエ逆変換）は、数４で定義される２次元離散離散フーリエ逆変換を想定している。

The two-dimensional inverse discrete Fourier transform (two-dimensional discrete Fourier inverse transform) in step S6 of the present embodiment assumes a two-dimensional discrete discrete Fourier inverse transform defined by Equation 4.

  The signal processing circuit 27 detects the data of the reproduction data pattern based on the calculation result obtained in step S6 (step S7 in FIG. 5). Since the detected data is obtained by performing a two-dimensional inverse discrete Fourier transform (two-dimensional discrete Fourier inverse transform) on the reproduction data pattern from which the influence of the transmission characteristics calculated using the known pattern is removed, Even in the case where data rotation, curvature, distortion, and intersymbol interference caused by aberrations caused by unevenness in thickness, surface blurring, and eccentricity of the optical information recording medium 1 occurred in the reproduced data pattern, the equalization processing was performed accurately. Data can be detected.

  When the known pattern is an isolated waveform as shown in FIG. 4A-1, the data pattern can be reproduced by the flowchart shown in FIG. In the flowchart for explaining the operation of another embodiment of the optical information reproducing method and optical information reproducing apparatus according to the present invention shown in FIG. 6, first, the signal processing circuit 27 of FIG. A two-dimensional discrete Fourier transform is performed on the known pattern reproduction signal reproduced from the known pattern recording area as shown in FIG. Obtain (step S11).

  Subsequently, the signal processing circuit 27 responds to the data pattern reproduction signal as shown in FIG. 4B-2 reproduced from the data pattern recording area of the optical information recording medium 1 by the pickup device 23 of FIG. Then, a two-dimensional discrete Fourier transform is performed using the arithmetic expression shown in Equation 2 to obtain a second calculation result (step S12 in FIG. 6).

  Subsequently, the signal processing circuit 27 subtracts the first calculation result obtained in step S11 from the second calculation result obtained in step S12, thereby removing the influence of the transmission characteristics. The two-dimensional discrete Fourier transform calculation result is obtained (step S13 in FIG. 6). On the other hand, similarly to step S6 in FIG. By performing conversion (step S14 in FIG. 6), data detection is performed (step S15 in FIG. 6).

  In the present embodiment, the processing corresponding to steps S2 and S3 of the embodiment shown in FIG. 5 can be omitted, so that more rapid data detection can be performed.

5 and 6, the two-dimensional discrete discrete Fourier transform has been described. However, a discrete cosine transform can be used instead. The definition of discrete cosine transform and inverse discrete cosine transform is as follows: input signal x _i (i = 0,1,2,3,..., N−1), and transformed coefficient c _i (i = 0,1,1). 2,..., N-1) and these are expressed in the vector notation of x ^ and c ^, and are defined by the following equations.

ここで、上式中、Ｔはｎ行ｎ列の変換行列で、そのｉ行ｊ列の項は以下の式で与えられる。

Here, in the above equation, T is a conversion matrix of n rows and n columns, and the term of i rows and j columns is given by the following equation.

ここで、変換行列Ｔは正則で、逆行列Ｔ^-１が存在し、これらには次式の関係がある。

Here, the transformation matrix T is regular and there is an inverse matrix T ⁻¹ , which has the following relationship.

なお、上式中、ｔは転置行列を表し、バーは複素共役を表している。このような行列をユニタリ行列と呼び、このような行列で表される変換をユニタリ変換という。

In the above equation, t represents a transposed matrix and bar represents a complex conjugate. Such a matrix is called a unitary matrix, and a transformation represented by such a matrix is called a unitary transformation.

  Furthermore, the conversion in two dimensions is expressed as follows using the conversion matrix T used in one dimension.

C = T ・ G ・^t T
The inverse transformation is as follows.

G = T ⁻¹ · C · ( ^t T) ⁻¹
= ^{T T} · C · ^T
Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention. For example, the known pattern is not limited to the isolated waveform described with reference to FIG. 4A-1 and the like, and within the block, only the bit length that is the minimum inversion interval of the information bits is inverted. It may be a pattern composed of bits having polarity.

  The known pattern and data pattern may be baseband signals, LDPC (Low Density Parity Check Code) modulated (or turbo encoded) signals, or rearranged signals thereof, May be a signal obtained by run-length modulation of the rearranged signal. Since LDPC modulation has a correction capability close to the Shannon limit, it is efficient and can achieve a low error rate even with low S / N.

  Further, the known pattern and the data pattern may be a run-length limited signal used in a CD (Compact Disc), a DVD (Digital Versatile Disc) or the like. In such a case, it is desirable that the known data has a pattern of the minimum run length or more from the relationship between the transmission band and S / N.

  Further, the series of processes in the above embodiments can be executed by hardware, but can also be executed by software, and the present invention includes a computer program that executes a series of processes by software. . The computer program may be incorporated in hardware dedicated to the computer, or can execute various functions by installing various programs. For example, a general-purpose personal computer or the like can be loaded from the program storage medium. It may be installed or distributed and installed via a communication network.

  Further, in the present specification, the step of describing the program recorded in the recording medium is not limited to the processing performed in time series in the order described, but of course, it is not necessarily performed in time series. Or the process performed separately is included.

It is a block diagram of one Embodiment of this invention reproducing | regenerating apparatus. It is a block diagram of an example of the pick-up apparatus in FIG. It is a figure which shows the state in which the block of a known pattern and the block of a data pattern have overlapped physically 50% or more on the same page. FIG. 4 is a diagram showing a known pattern of an isolated waveform, a reproduced known pattern signal having intersymbol interference, a data pattern recording signal, a reproduced signal, and a reproduced signal from which intersymbol interference has been removed. It is a flowchart for operation | movement description of one Embodiment of this invention apparatus and this invention method. It is a flowchart for operation | movement description of other embodiment of this invention apparatus and this invention method. It is a figure which shows the Sync code | cord | chord on an optical information recording medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical information recording medium 3 Hologram recording layer 10 Optical information reproducing | regenerating apparatus 12 Objective lens 15 Light source 20 Photodetector 23 Pickup apparatus 25 Detection circuit 27 Signal processing circuit

Claims (7)

An optical information recording medium having an information recording layer on which information is recorded using holography is irradiated with reproduction reference light, and reproduction light generated by irradiating the reproduction reference light is detected. In an optical information reproducing method for reproducing information,
The information recording layer irradiated with the reproduction reference light of the optical information recording medium records a known pattern for the first reference light as a recording pattern of a specific page or block, and the second A data pattern is recorded for the reference beam,
A first calculation is performed by performing a two-dimensional discrete Fourier transform on the reproduction signal of the known pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the first reference light. A first step of obtaining a result;
A second step of obtaining a second calculation result obtained by performing a two-dimensional discrete Fourier transform on the known pattern recorded on the optical information recording medium;
A third step of subtracting the first calculation result and the second calculation result to obtain a first subtraction value;
A third calculation is performed by performing a two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the second reference light. A fourth step of obtaining results;
A fifth step of obtaining a second subtraction value which is a reproduction signal of the data pattern from which the influence of the transmission system is removed by subtracting the first subtraction value from the third calculation result;
A sixth step of performing a two-dimensional inverse discrete Fourier transform on the second subtracted value and detecting data from the calculation result. An optical information recording medium having an information recording layer on which information is recorded using holography is irradiated with reproduction reference light, and reproduction light generated by irradiating the reproduction reference light is detected. In an optical information reproducing method for reproducing information,
On the information recording layer irradiated with the reproduction reference light of the optical information recording medium, a known pattern having an isolated waveform is recorded as a recording pattern of a specific page or block with respect to the first reference light. A data pattern is recorded for the second reference light,
A reproduction signal having a known pattern of the isolated waveform obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the first reference light is subjected to a two-dimensional discrete Fourier transform to perform a second-dimensional discrete Fourier transform. A first step of obtaining an operation result of 1,
A second calculation is performed by performing a two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the second reference light. A second step of obtaining results;
A third step of subtracting the first calculation result from the second calculation result to obtain a subtraction value that is a reproduction signal of the data pattern from which the influence of the transmission system is removed;
A fourth step of performing a two-dimensional inverse discrete Fourier transform on the subtracted value and detecting data from the calculation result.   3. The optical information reproducing method according to claim 1, wherein discrete cosine transform is performed instead of the two-dimensional discrete Fourier transform, and discrete cosine inverse transform is performed instead of the two-dimensional inverse discrete Fourier transform. An optical information recording medium having an information recording layer on which information is recorded using holography is irradiated with reproduction reference light, and reproduction light generated by irradiating the reproduction reference light is detected. In an optical information reproducing apparatus for reproducing information,
The information recording layer irradiated with the reproduction reference light of the optical information recording medium records a known pattern for the first reference light as a recording pattern of a specific page or block, and the second A data pattern is recorded for the reference beam,
A first calculation is performed by performing a two-dimensional discrete Fourier transform on the reproduction signal of the known pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the first reference light. First computing means for obtaining a result;
Second computing means for obtaining a second computation result obtained by performing a two-dimensional discrete Fourier transform on the known pattern recorded on the optical information recording medium;
Third computing means for obtaining a first subtraction value by subtracting the first computation result and the second computation result;
A third calculation is performed by performing a two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the second reference light. A fourth computing means for obtaining a result;
Fifth arithmetic means for obtaining a second subtraction value which is a reproduction signal of the data pattern from which the influence of the transmission system is removed by subtracting the first subtraction value from the third calculation result;
An optical information reproducing apparatus comprising: detecting means for detecting data based on a calculation result obtained by performing two-dimensional inverse discrete Fourier transform on the second subtraction value. An optical information recording medium having an information recording layer on which information is recorded using holography is irradiated with reproduction reference light, and reproduction light generated by irradiating the reproduction reference light is detected. In an optical information reproducing apparatus for reproducing information,
On the information recording layer irradiated with the reproduction reference light of the optical information recording medium, a known pattern having an isolated waveform is recorded as a recording pattern of a specific page or block with respect to the first reference light. A data pattern is recorded for the second reference light,
A two-dimensional discrete Fourier transform is performed on a reproduction signal of a known pattern that is the isolated waveform obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the first reference light. First computing means for obtaining a first computation result;
A second calculation is performed by performing a two-dimensional discrete Fourier transform on the reproduction signal of the data pattern obtained by collecting the reproduction light generated in the information recording layer by being irradiated with the second reference light. A second computing means for obtaining a result;
Third computing means for obtaining a subtraction value which is a reproduction signal of the data pattern from which the influence of the transmission system is removed by subtracting the first computation result from the second computation result;
An optical information reproducing apparatus comprising: detecting means for detecting data based on a calculation result obtained by performing two-dimensional inverse discrete Fourier transform on the subtracted value.   6. The optical information reproducing apparatus according to claim 4, wherein discrete cosine transform is performed instead of the two-dimensional discrete Fourier transform, and discrete cosine inverse transform is performed instead of the two-dimensional inverse discrete Fourier transform. An optical information recording medium having an information recording layer on which information is recorded using holography is irradiated with reproduction reference light, and reproduction light generated by irradiating the reproduction reference light is detected. An optical information reproduction program that causes a computer to execute each step of the optical information reproduction method according to any one of claims 1 to 3 for reproducing information.

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