WO2010067428A1

WO2010067428A1 - Hologram recording method and hologram device

Info

Publication number: WO2010067428A1
Application number: PCT/JP2008/072427
Authority: WO
Inventors: 道一橋本; 潔立石; 充佐藤
Original assignee: パイオニア株式会社
Priority date: 2008-12-10
Filing date: 2008-12-10
Publication date: 2010-06-17

Abstract

A hologram recording method in a hologram device for recording a data page including a marker and a data area displayed on a spatial light modulator on a recording medium, obtaining a reproduced image of the data page by focusing light reproduced from the recording medium onto an image sensor, and reproducing the data page, comprises the step of detecting the presence or absence or the level of a defect in the recording medium, and the step of recording a normal marker as the marker when there is no defect or the level is low and recording a defect-resistant marker as the marker when there is a defect or the level is high.

Description

Hologram recording method and hologram apparatus

The present invention relates to a hologram apparatus system that records data as a hologram or reproduces data from a hologram, and more particularly to a defect detection method and a hologram recording method in a hologram recording medium (hereinafter also simply referred to as a recording medium).

As a recording medium, there is known a hologram memory system in which information is recorded or reproduced optically with respect to a photosensitive material such as a photopolymer or a lithium niobate single crystal.

When recording data on a recording medium, the data is displayed in a spatial light modulator in units of images called data pages, which are two-dimensional data, and the light is spatially modulated to generate signal light. To do. At the time of reproduction, only the reference light under the same condition as that at the time of recording is irradiated to the recording portion of the recording medium, so that the light receiving elements corresponding to the pixels of the spatial light modulator at the time of recording one-to-one or an integer multiple are two-dimensionally arranged. The image sensor is used to receive the reproduction light, sample it, and reproduce the information of the original data page from the reproduction signal.

Recording and reproduction are performed using Fourier transform in the hologram device system.

FIG. 1 is a diagram showing an outline of an example of a conventional hologram recording / reproducing method as shown in FIG. A coherent laser light emitted from a laser light source is divided into two, and one of the lights is converted into parallel light, and a spatial light modulator SLM (transmission / non-transmission 2) such as a transmissive TFT liquid crystal device (LCD) panel. The data page of the two-dimensional pattern is displayed), and the signal light 12a includes a two-dimensional pattern data signal component. The signal light 12 a passes through the Fourier transform lens 16 separated by the focal length f, and the two-dimensional pattern data signal component is Fourier transformed and collected in the recording medium 10.

On the other hand, the other divided light is guided into the recording medium 10 as the recording reference light 12, and forms an optical interference pattern by intersecting the optical path of the signal light 12a with the inside of the recording medium 10, thereby producing optical interference. The entire pattern is recorded as a change in refractive index.

In this way, the signal light 12a, which is the diffracted light from the data page image, is imaged by the Fourier transform lens, and the distribution on the focal plane, that is, the Fourier plane is converted to the distribution of the result of the Fourier transform with the coherent reference light 12. The interference fringes are recorded on a recording medium near the focal point. Angle multiplex recording is possible by changing the crossing angle of the reference light 12 with respect to the signal light 12a for each data page and performing sequential recording.

Next, the data page image is reproduced by performing an inverse Fourier transform at the time of reproduction. In data reproduction, the optical path of the signal light 12a is blocked, and only the reference light 12 is irradiated onto the recording medium 10 at the recording crossing angle. On the opposite side of the recording medium 10 irradiated with the reference light 12, reproduction light ReSB that reproduces the recorded light interference pattern appears. When this reproduction light is guided to the inverse Fourier transform lens 21 and subjected to inverse Fourier transform, a dot pattern signal (data page image) can be reproduced.

Here, in the signal light Fourier-transformed by the spatial light modulator SLM of the Fourier transform hologram recording, the first-order diffracted light due to repetition of pixels of the data page of the spatial light modulator SLM becomes a high frequency component.

FIG. 2 is a schematic perspective view showing a relationship between an example of a display pattern of the spatial light modulator SLM and the Fourier plane FP. For example, the pixel pitch of the spatial light modulator SLM in which square pixels each having a length of a (μm) are arranged in a matrix is a (μm).

As shown in FIG. 2, when the optical axis of the signal light is the z direction and the row direction and the column direction of the pixels in the plane perpendicular to the signal light are the x direction and the y direction, respectively, the signal light and the reference light are caused to interfere with each other. When holographic recording is performed in a recording medium (not shown), the spatial frequency spectrum distribution light intensity (0th-order diffracted light 0th at the center, 1 around it) at a position symmetrical to the optical axis center of the signal light on the Fourier plane of the xy plane. Next diffraction light 1st, etc) is generated.

In hologram recording using a Fourier transform hologram, such a light intensity distribution makes it possible to fit the hologram in a spatially limited space, to record data pages in a distributed manner, and to increase the redundancy of recorded data. There is an advantage that you can. Using the spatial frequency (fsp [lines / mm]) of the recording surface, the wavelength of light (λ), and the focal length (F ₁ ) of the Fourier transform lens, the interval (d ₁ ) can be correlated as follows: d ₁ = fsp * λ * F ₁

For example, when the pixel pitch of the spatial light modulator SLM is 42 μm, the wavelength is 532 nm, and the focal length is 165 mm, the corresponding Fourier spectral interval (d ₁ ) is 2.09 mm according to the above equation. Therefore, information to be recorded exists in a radius range of about 2.1 mm on the optical axis. That is, as shown in FIG. 2, two-dimensional data appearing in the spatial light modulator SLM in a square xy space (x, y ≦ 2d ₁ ) composed of the first-order diffracted light and zero-order light. Can be recorded in a narrow range.

Therefore, an intensity peak (0th order diffracted light 0th, 1st order diffracted light 1st, etc.) corresponding to the Fourier component of the two-dimensional pattern is generated in the Fourier transform image. When a peak occurs in such a Fourier transform image, there is a concern that a defect in the recording medium tends to occur when the number of rewrites increases at the peak position. Even if this is not the case, the presence of defects in the recording medium, such as defects in the recording film, recording sensitivity and diffraction efficiency, is a problem.

FIG. 3 is a schematic plan view showing the state of the recording medium defect DFT on the Fourier plane. The recording medium defect is dust or scratches on the recording medium. Due to the recording medium defect DFT, a specific frequency component of the reproduction signal is not reproduced, or a specific frequency component of the recording signal is not recorded. FIG. 3 shows a case where the recording medium defect DFT is present on the recording medium on the optical axis in the signal light z direction and blocks the 0th-order light (direct current) component 0th of the Fourier image. Here, the recording medium defect DFT is represented by a rectangle for the sake of explanation, but there are actually various shapes. Further, the size of the defect DFT is defined as Ld, where Ld is the defect passing that blocks the 0th-order light (DC) component 0th, and Ls is the distance between the pair of first-order diffracted light components 1st that cross the 0th-order light (DC) component 0th. Expressed as a percentage of / Ls. For example, in the case of a recording medium defect having a defect size of 100% or more and blocking all components of the 0th order light and the 1st order diffracted light, it is difficult to reproduce the data page even by the error correction code technique.

Therefore, even if there is a defective recording block that cannot be repaired even with an error correction code on the optical recording medium, there was an access to a normal recording block without a defect for the purpose of promptly replacing it in another area and repairing the defect. In this case, information is recorded or reproduced in the recording block as it is, and when the defective recording block is accessed, information is not recorded or reproduced in the defective recording block, and the positional relationship between the defective recording block and the replacement recording block is determined. It has been proposed to record or reproduce information in a replacement recording block, which is the next recording block indicated by the moving direction to the replacement recording block, according to information written in the defect management unit that stores and manages (patent) Reference 1).

In addition, when an error occurs during hologram recording, an optical information recording apparatus is provided with a two-dimensional pixel at a predetermined position of an optical information recording medium using holography in order to perform efficient and appropriate recording / reproduction data processing. When recording page data consisting of data as an interference pattern between the information beam carrying the data and the recording reference beam, it is determined whether the page data has been recorded normally, and the page data is determined according to the determination result. There has also been proposed a technique for controlling an optical recording operation so that data is recorded again at a position different from a predetermined position when it is determined that data recording has not been performed normally (see Patent Document 2). ).

Further, in the hologram recording / reproducing apparatus, a reference light irradiating unit for irradiating the hologram recording medium with reference light and a medium so as not to cause trouble in recording / reproducing even when a defect occurs in an optical component related to recording / reproducing. A spatial modulation unit that generates information light modulated using spatial information corresponding to page data to be written to the information, an information light irradiation unit that irradiates information light to the same region as the reference light irradiation region, and a reference light A light detection unit that receives reproduction light generated by irradiating the medium, a known data storage unit that stores the known page data in advance, and the known page data is written on the medium using spatial information corresponding to the known page data. After reading the known page data written on the medium, using the information of the detected defect position, the defect investigation unit that investigates the defect position, such as the light detection unit, Also apparatus and a reproduction control section for restoring reproducing data of defect position contained in the raw light, has been proposed (Patent Document 3, reference).

Further, in a recording / reproducing apparatus that performs recording / reproducing with respect to the hologram recording medium, in order to make it possible to determine the presence / absence of a defect occurring in the optical path, each of the pixels of the spatial light modulator is bit1 / It has also been proposed to determine whether or not each detection value obtained on the image sensor is bit1 / bit0 when bit 0 modulation is applied, and to determine the presence or absence of a defect based on the result. (See Patent Document 4).
JP2003-178538 JP2004-134048 JP2006-236536 JP2007-200385

When recovering the recorded data from the recording part of the recording medium, the quality of the detected data page image is important. For this purpose, the data page includes symbols of a predetermined pattern called positioning markers, and the positions of the markers are displayed at fixed positions. For example, as disclosed in Patent Document 2, codes for alignment are included at one or more places in four corners of rectangular two-dimensional data.

FIG. 4 shows a front view of the spatial light modulator SLM displaying a certain data page. The data page to be recorded on the recording medium is, for example, a two-dimensionally arranged black and white pattern image (light transmission and non-transmission pattern image). Markers MK are placed at the four corners of the data page. This marker MK specifies the position of the central data area DR by detecting the position of this marker during reproduction.

Generally, when a detected image is scanned, a specific frequency component (marker reproduction signal) corresponding to the marker is obtained. Therefore, first, the center coordinates of each marker MK are determined from the marker reproduction signal, and each marker is further determined. Since the overall shape of is determined in advance, the center position of each pixel constituting each marker MK is also obtained by calculation. Then, the pixels other than the markers, that is, the pixel positions in the so-called data region DR, are obtained by calculating each pixel constituting the determined marker as a reference pixel based on the width and height of the pixel from the coordinate value of the reference pixel. be able to. As described above, since the positions of all the data area pixels can be determined, the data page of the two-dimensional data can be detected by reading the data area pixels from the positions. For example, in the hologram apparatus, the position deviation amount between the center of the aperture region of the light receiving objective lens and the data page is obtained based on the marker position in the data page (detected image) read from the hologram recording medium. The position of the data page is corrected so that the center of the data page coincides with the center of the aperture area of the objective lens.

The data page of the data area DR is a set of two-dimensional modulation data pattern symbols such as 2: 4 modulation, for example, and is generally displayed at a high resolution so that white pixels and black pixels are not continuous, For positioning, a marker having a resolution lower than that of the data area DR is selected and displayed.

Thus, markers are important in data page image quality and positioning.

The inventor found that when the recording medium defect DFT (FIG. 3) on the Fourier plane blocks even the 0th-order light (DC) component 0th of the Fourier image at the time of reproduction, the reproduction marker image is greatly deteriorated. It was found through experiments that there was a great influence.

The reproduction marker images of the experimental results are shown in FIGS. When there is no recording medium defect in FIG. 5A, a clear marker image (similar to the normal marker image for recording) is obtained, but the recording medium defect DFT in FIG. 5B is 20% in size. When the low frequency component including the direct current component disappears, the cross-shaped marker image portion surrounded by continuous white is particularly greatly deteriorated. As a result, the detection of the marker coordinates (for example, the intersection of the crosses) may be wrong and data cannot be reproduced. In addition, even a single recording medium defect on the recording medium affects all data pages (also referred to as books) that are angle-multiplexed and recorded at the position where the recording medium is defective. Will also interfere.

However, the above patent document only teaches proposals for dealing with errors due to the entire system, apparatus, and optical components, and does not take into account the recording medium defects related to the marker, and includes the marker. There is no suggestion about countermeasures against small defects in the recording medium itself that is the target of data page recording and reproduction.

That is, in the techniques of Patent Documents 1 and 2, when there is a recording medium defect (verify error), the data is only recorded in another location on the recording medium. In the spatial light modulator, the defect position of the two-dimensional sensor (image sensor) is detected and specified, and the data of the defective part is erased and corrected by the error correction unit, and dummy data is put there, and the defect part The page data is only generated by moving the data to a portion having no defect in the page data (a space area reserved in advance or an area immediately after), and the technique of Patent Document 4 discloses a spatial light modulator. In the prior arts of Patent Documents 3 and 4, the spatial light modulator and the image sensor and the light receiving pattern of the image sensor are merely detected to detect defects in the spatial light modulator, the image sensor, and the optical path. Sen And detecting a defective pixel due to optical components such as, it is only detected in the comparison of the received image of the modulation pattern and the image sensor of the spatial light modulator.

Actually, since the hologram of the Fourier image of the data page (recording signal) is recorded on the recording medium with a distributed intensity distribution, the inventor ignores depending on the position and size of a relatively small recording medium defect. I focused on what I couldn't do.

Therefore, the problem to be solved by the present invention is, for example, to provide a hologram recording method and a hologram apparatus that reduce a marker reproduction error of a data page.

In the hologram recording method of the present invention, a data page including a marker and a data area displayed on the spatial light modulator is recorded on a recording medium, and light reproduced from the recording medium is imaged on an image sensor to form a data page. A hologram recording method in a hologram apparatus for reproducing a data page by obtaining a reproduction image,
Detecting the presence or absence or extent of defects in the recording medium;
Recording a normal marker as the marker when there is no defect or when the degree is low, and recording a defect-resistant marker as the marker when there is a defect or when the degree is high.

The hologram apparatus of the present invention records a data page including a marker and a data area displayed on a spatial light modulator on a recording medium, and images the light reproduced from the recording medium on an image sensor to reproduce the data page. A hologram device for obtaining an image and reproducing a data page,
A defect detection unit that detects the presence or absence or degree of defects in the recording medium;
And a recording unit that records a normal marker as the marker when there is no defect or a low degree, and records a defect-resistant marker as the marker when there is a defect or when the degree is high.

It is a figure which shows the outline of an example of the conventional hologram recording / reproducing method. It is a schematic perspective view which shows an example of the display pattern of the spatial light modulator of a hologram recording / reproducing method, and the relationship of a Fourier surface. It is a schematic plan view which shows the mode of the recording medium defect on the Fourier surface of a hologram recording / reproducing method. It is a front view of the spatial light modulator which displays the data page of a hologram recording / reproducing method. It is a partial top view explaining the reproduction | regeneration marker image in the data page in a hologram recording / reproducing method. It is a schematic block diagram which shows the hologram apparatus of embodiment by this invention. It is a block diagram explaining the decoder of the hologram apparatus of the Example by this invention. It is a flowchart which shows the outline | summary of the flow of the signal processing until the data decoding after receiving the reproduction | regeneration image in the reproduction | regeneration operation | movement of the hologram apparatus of embodiment by this invention. It is a top view of the disk-shaped recording medium in the hologram apparatus of embodiment by this invention. It is a flowchart explaining the shift movement and angle multiplexing in the hologram apparatus of embodiment by this invention. It is a top view which shows the defect detection pattern of the data page of the Example by this invention. It is a top view which shows the defect detection pattern and defect-proof marker of the data page of the other Example by this invention. It is a top view which shows the defect detection pattern image reproduced | regenerated from the recording medium by the recording medium defect detection of the Example by this invention. FIG. 6 shows a change in light amount when a defect amount (recording medium defect) of a defect detection pattern image reproduced from a recording medium by recording medium defect detection according to the present invention is plotted on the horizontal axis and the light amount is plotted on the vertical and peripheral portions. It is a graph. It is a top view which shows the defect detection pattern image reproduced | regenerated from the recording medium by the recording medium defect detection of the other Example by this invention. It is a graph which shows the change of a frequency characteristic by setting the frequency of the defect detection pattern image reproduced | regenerated from the recording medium by the recording medium defect detection by this invention on the horizontal axis, and making an amplitude the vertical axis | shaft. It is a flowchart explaining the angle multiplex recording in the hologram apparatus of embodiment by this invention. It is a flowchart explaining angle multiplexing reproduction in the hologram apparatus of the embodiment according to the present invention. It is a top view which shows the template image in the hologram apparatus of embodiment by this invention. It is a block diagram explaining performing synthetic | combination conversion by the weighted average of the synthetic | combination template image in the hologram apparatus of embodiment by this invention. It is a flowchart which shows the procedure which angle-multiplex-records the data of the 2nd example in the hologram apparatus of embodiment by this invention. It is a flowchart which shows the procedure which carries out angle multiplexing reproduction | regeneration of the data of the 2nd example in the hologram apparatus of embodiment by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Recording medium 20 Image sensor 21 2nd lens 25 Encoder 26 Decoder 32 Controller 16 Objective lens HM Half mirror LD Light source SH1, SH2 Shutter BX Beam expander SLM Spatial light modulator RM1, RM2 Reflection mirror

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the drawings.

<Hologram device>
FIG. 6 shows an example of a hologram apparatus for recording and / or reproducing data pages.

On the optical path of the coherent laser beam 12 emitted from the laser light source LD, a half mirror HM, a second shutter SH2, a beam expander BX, a transmissive spatial light modulator SLM, an objective lens 16, a recording medium 10, A second lens 21 and an image sensor 20 are disposed.

Half mirror HM divides laser beam 12 to generate reference light, and functions as a reference light optical system together with reflection mirrors RM1 and RM2. The movable reflection mirror RM2 is controlled by the controller 32 and controls the incident angle of the reference light beam to the recording medium 10.

The controller 32 includes a CPU (central processing unit), a ROM (read only memory), a RAM (random access memory), an external memory, and the like for executing a predetermined program for controlling the controlled device.

The hologram apparatus includes an encoder 25 and a decoder 26 controlled by a controller 32, and a spatial light modulator SLM and an image sensor 20 are connected to the encoder 25 and the decoder 26, respectively. The controller 32 generates a data page including a data area having predetermined markers at the four corners according to the input information, and supplies the data page to the encoder 25. The controller 32 outputs the information decoded by the decoder 26. The controller 32 generates template images for predetermined markers at the four corners of the data page in advance and supplies them to the decoder 26.

The first shutter SH1 is controlled by the controller 32, and controls the irradiation time of the reference light beam to the recording medium 10.

The second shutter SH2 is controlled by the controller 32 to control the irradiation time of the signal light beam to the recording medium 10.

The controller 32 opens both the first and second shutters SH1 and SH2 during data recording to irradiate the recording medium with signal light and reference light, and closes only the second shutter SH2 during reproduction and irradiates only the reference light to the recording medium. To control.

The beam expander BX expands the diameter of the light that has passed through the second shutter SH2 to be a parallel light beam and irradiates the spatial light modulator SLM.

The spatial light modulator SLM is a liquid crystal display (LCD) panel having a matrix arrangement in which a plurality of modulation pixels are two-dimensionally arranged. The spatial light modulator SLM has, for example, vertical 480 * horizontal 640 pixels, and displays a data page to be recorded supplied from the encoder 25. The parallel light applied to the spatial light modulator SLM is optically modulated into a spatial ON signal and an OFF signal and guided to the objective lens 16 as signal light 12a.

When the second shutter SH2 is opened (during recording), the objective lens 16 performs Fourier transform on the signal light 12a and condenses it so as to focus on the rear side of the mounting position of the recording medium 10.

The recording medium 10 is mounted on a movable support unit 60. For the support unit 60, for example, a spindle motor that is rotated by a turntable (mountable support unit) that detachably holds the disc-shaped recording medium 10 is used. The recording medium 10 is made of a translucent photosensitive material that can store an optical interference pattern, such as a photopolymer, a light anisotropic material, a photorefractive material, a hole burning material, or a photochromic material.

The movable reflection mirror RM2 of the reference light optical system is controlled by the controller 32 to irradiate the recording medium 10 with the reference light 12 at a predetermined incident angle. The reference light 12 crosses the signal light 12a at a predetermined angle inside the recording medium 10 by the action of the reflection mirror RM2. That is, at the time of data recording, both the first shutter SH1 and the second shutter SH2 are opened so that the reference light and the signal light interfere with each other in the recording medium.

Interference fringes between intersecting signal light and reference light are stored in the recording medium 10 as a refractive index grating, whereby data pages are recorded. In addition, angle multiplex recording of a plurality of data pages is possible by changing the crossing angle between the signal light and the reference light.

The image sensor 20 includes an array such as a charge coupled device (CCD) in which a plurality of light receiving elements are two-dimensionally arranged and a complementary metal oxide semiconductor device (MOS). The light receiving elements of the image sensor 20 and the pixels of the spatial light modulator do not have to correspond one-to-one. The image of the data page displayed on the spatial light modulator, particularly the number and arrangement of the light receiving elements that can be distinguished from each pixel. As long as it has. If the image sensor 20 has a high resolution, an image corresponding to the pixel included in the data page imaged on the image sensor 20 is detected by a plurality of pixels of the image sensor 20 by oversampling processing, and the detected values are detected. Based on the averaged result, data corresponding to one pixel included in the data page can be reproduced with high accuracy.

When reproducing the recorded data page from the recording medium 10, the signal light is blocked by the second shutter SH2, the first shutter SH1 is opened, and only the reference light is incident at the same crossing angle as at the time of recording. Reproduction light (diffracted light) corresponding to the recorded signal light appears on the side opposite to the incident side of the recording medium 10 irradiated with the reference light. As a result, the reproduction light ReSB is guided to the image sensor 20 through the second lens 21. The image sensor 20 receives a reconstructed image by the reconstructed light and reconverts it into an electrical reconstructed signal (detected image), then decodes it by the decoder 26 and sends the data DATA to the controller 32, which was originally recorded by the controller 32. Information is output.

As shown in FIG. 7, the decoder 26 includes a detected image memory 41 that stores data from the image sensor 20, a resampling unit 42, a decoding unit 43, and a position detection unit 44 that performs template matching processing. That is, the decoder 26 performs template matching processing using the detected image of the data page acquired by the image sensor and the template image stored in advance to detect the position of the marker at the time of recording, performs re-sampling, and performs decoding. Do. The position detection unit 44 includes a template image memory that stores a template image for template matching processing, and includes a defect detection unit described later.

For example, at the time of reproduction (or rewriting), the images of the markers MK at the four corners of the data page of the two-dimensionally arranged black and white pattern image (light transmission and non-transmission pattern image) displayed as shown in FIG. By re-sampling the data page based on the marker position, the position of the central data region DR is specified, the distortion of the detected image is corrected, and the like can be accurately decoded.

The black and white dot pattern on the data page is displayed when each cell is turned on or off, and becomes a transparent or non-transparent pattern. The spatial light modulator SLM displays a set of two-dimensional modulation data pattern symbols such as 2: 4 modulation in the central data region DR, and displays markers MK at, for example, the four corners thereof. 2: 4 modulation is a method in which input data to be recorded is divided in units of 2 bits, and every 2 bits are modulated into 4 bits (2 * 2 = 4 pixels) two-dimensional modulation pattern symbol. The 2: 4 modulation is an example, and the present invention is not limited to this. The data area DR may be displayed and recorded by another modulation method.

<Decoder signal processing>
In the decoder signal processing for each data page, as shown in FIG. 8, in the detected image detected by the image sensor, first, the coordinates of the markers at the four corners of the data page are detected (marker coordinate detection: step S1), and the next. Next, the re-sampling process of the reproduced image is performed (resampling: step S2), and then the data is decoded (decoding: step S3).

<Marker coordinate detection: Step S1>
The generated template image is stored in advance in a template image memory in the decoder.

After sampling the reproduced image of the data page by the image sensor and obtaining the detected image, template matching processing is performed using the detected image (reproduced signal) and the template image to detect the coordinate positions of the four markers at the time of recording.

The marker coordinate detection method is a template matching process that searches for a position where the correlation value between the template image and the detected image is maximum. The template matching process is generally one of pattern matching methods, and the target pattern is obtained by obtaining the degree of similarity or difference between the inspection target pattern and a standard pattern prepared in advance (for example, a template image similar to a marker). It is known as a method of identification. The template matching process often uses a correlation coefficient, a difference in shading level, or the like as the degree of similarity or difference, but there is a corresponding point search method between two images by the area correlation method.

Here, the correlation value Cxy between the reproduced marker image s (x, y) and the template image t (x, y) is expressed by the following equation (1). Here, (x, y) represents a coordinate position.

Since the detected coordinates are pixel-by-pixel coordinates (integer coordinates by sampling), a more detailed position can be obtained by a method taught in, for example, Japanese Patent Laid-Open No. 10-124666.

<Resampling: Step S2>
Next, the coordinate intervals of the four markers in the detected image are re-equalized so that the coordinate intervals of the four markers included in the data page are equal to the coordinate intervals of the markers in the detected image after resampling. Perform sampling processing.

For example, when the coordinate interval of the marker on the data page is 400 pixels and the coordinate interval of the marker on the detected image is 405 pixels, the marker on the detected image is resampled at an interval of 405/400.

The distortion is corrected by resampling. By the resampling process, the detected image becomes almost the same as the data page. That is, the reproduction signal is almost in the same state as the recording signal.

<Decoding: Step S3>
Next, the monochrome pattern of each pixel in the data area DR is detected, and the data is decoded.

For example, the data region DR of the detected image is image-processed by dividing it into a predetermined two-dimensional modulation pattern size such as 2: 4 modulation, and the cross correlation between the obtained signal and the two-dimensional modulation pattern is calculated. The decoding is performed by detecting the most similar modulation pattern.

<Disc recording medium>
For example, as shown in FIG. 9, the disk-shaped recording medium 10 is provided with a code track DM for detecting a rotation angle on the surface around the rotation center hole. The support unit 60 is controlled by the controller 32 to control the position of the recording medium 10 with respect to the optical axis of the objective lens 16. The hologram apparatus includes a medium rotation angle detection sensor (not shown), thereby detecting the code track DM for detecting the rotation angle of the recording medium 10. The controller 32 includes a rotation position detection unit that is connected to the medium rotation angle detection sensor and generates a rotation position signal of the recording medium, and a spindle servo unit that is connected to a spindle motor and supplies a predetermined signal thereto.

<Shift movement & angle multiplexing>
The hologram apparatus controls the rotation of the recording medium so that a plurality of unit recording areas to be recorded can be sequentially recorded and reproduced at predetermined intervals in each recording and reproducing step, and at a predetermined angle in units of pages in each unit recording area. It is controlled so that angle multiplex recording can be performed at intervals.

In the hologram apparatus of the embodiment, a shift movement (track direction T or radial direction R) operation is performed before and after angle multiplex recording for each unit recording area. This will be described with reference to FIG. 10 (flow chart) and FIG. .

First, as shown in FIG. 6, the recording medium 10 is mounted and fixed on the support portion 60 of the hologram apparatus. Thereafter, the target incident angle of the reference light is fixed by the movable reflecting mirror RM2 in accordance with the target address instruction by the data recording (or reproduction) command from the controller 32 (FIG. 10: Step S11), and the medium rotation angle detection The sensor is activated (FIG. 10: Step S12), and the recording medium 10 is rotated to the target angle position (according to the code track DM for detecting the rotation angle) of the target address information on the recording medium 10, and stopped there (FIG. 10). : Step S13). Next, the recording medium 10 is moved in the radial direction R to the target radial position (FIG. 10: Step S14) and stopped there (shift movement).

After the shift movement, a so-called book is formed by executing an angle-multiplexed recording or reproducing step in the unit recording area at the target position (FIG. 10: step S15). Then, the continuation or end of the angle multiplexing recording or reproduction step is determined (FIG. 10: step S16). If it is continued, the process returns to step S12, and another target address instruction is given.

These shift movement and angle multiplexing steps are sequentially performed to form a plurality of books in the track direction.

For example, as shown in FIG. 9, a plurality of unit recording areas so-called books (portions indicated by ◯) are recorded in alignment on a track (broken line) of the recording medium 10 at a predetermined interval. That is, angle-multiplexed recording or reproduction is performed for each book.

<First Example of Recording Medium Defect Detection>
The inventor proposes a recording medium defect detection method for reducing a marker reproduction error of a data page in a hologram apparatus.

First, a defect detection pattern having a low frequency pattern lower than the resolution of the data area image of the data page is created, and in the hologram apparatus shown in FIG. 6, a data page including a data area in which the defect detection pattern is arranged on the data page, The data is displayed on the spatial light modulator SLM, and the data page is recorded on the recording medium 10 and then reproduced. The defect detecting unit in the position detecting unit 44 of the decoder 26 detects the presence or absence of the recording medium defect. A recording medium defect is detected by detecting the light quantity or frequency distribution of the reproduced image of the pattern.

FIG. 11 and FIG. 12 (A) show examples of defect detection patterns of data pages.

The defect detection pattern shown in FIG. 11 is a direct current pattern with a high frequency pattern at the periphery and white only at the center. In the case of this defect detection pattern, if there is a recording medium defect during data playback, the light amount at the center will be lower than that at the periphery of the playback pattern. By doing so, a recording medium defect can be detected.

Here, as shown in FIG. 3, when the recording medium defect DFT exists on the recording medium on the optical axis in the signal light z direction and blocks the zero-order light (direct current) component 0th of the Fourier image, the size of the defect DFT is large. Ld / Ls is defined as Ld / Ls, where Ld is the defect passing that blocks the 0th-order light (DC) component 0th, and Ls is the distance between the pair of first-order diffracted light components 1st that crosses the 0th-order light (DC) component 0th. We will define it as a percentage.

As a result of the experiment, it is apparent from the defect detection pattern image reproduced when the size of the defect DFT is 0%, 10%, 20%, 40%, 50% on the recording medium shown in FIGS. As can be seen, except in the case of 0% defect, the light amount in the central portion is lower than that in the peripheral portion of the reproduction pattern. FIG. 14 shows the change in light quantity when the defect amount (recording medium defect) of 0%, 10%, 20%, 40%, and 50% of the defect is plotted on the horizontal axis and the light quantity is plotted on the vertical axis. Show.

Therefore, the presence or degree of the recording medium defect can be detected by providing the defect detection unit in the position detection unit 44 of the decoder 26 with a comparator that compares the light quantity in the peripheral part and the central part of the reproduced defect detection pattern. Can do.

The defect detection pattern shown in FIG. 12A is a black and white low frequency periodic pattern (low frequency pattern) as a whole. In the case of this defect detection pattern, when there is a recording medium defect at the time of data reproduction, only the white part edge remains, so that the second order (even order) harmonic component of the periodic pattern appears. A recording medium defect can be detected by detecting this harmonic component during data reproduction.

As a result of the experiment, as apparent from the defect detection pattern images (the defect detection pattern shown in FIG. 12A) when the recording medium shown in FIGS. Only the edge of the part remains bright. FIG. 16 shows changes in frequency characteristics of defect detection pattern images when there is a defect amount (recording medium defect) of 0%, 10%, 20%, and 40% with the horizontal axis representing the frequency and the vertical axis representing the amplitude. Show. For example, it can be seen that the frequency at which the amplitude peak appears differs when the defect amount of the recording medium defect is 0% and the defect amount is 20%.

Therefore, in the defect detection unit in the position detection unit 44 of the decoder 26, a memory that stores in advance the peak value of the frequency distribution of various detection patterns and a comparison that compares the stored peak value with the peak value of the actually detected detection pattern. By providing the device, it is possible to detect the presence or absence of the recording medium defect.

Therefore, in the step of storing the template image, a plurality of template images corresponding to the presence / absence or degree of defects in the recording medium are prepared and stored, so that the result of the defect detection, that is, the defect in the recording medium is reproduced. A suitable one is selected from the plurality of template images in accordance with the presence or absence or the degree.

<Angle multiplex recording operation of hologram device>
FIG. 17 shows a flowchart when the angle multiplex recording is performed.

First, similarly to the shift movement & angle multiplexing operation of FIG. 10, the recording medium is rotationally controlled so that the light beam hits the target position to be recorded, and when the target position is reached, the first ( It is determined whether the page is a specific place. If the angle should be the first page, a defect detection pattern (for example, the defect detection pattern shown in FIG. 11 or 12A) for the controller to detect a recording medium defect in step S112 is a data page (in this case, a dummy). In step S113, pages are recorded on the recording medium via the encoder and the spatial light modulator. Next, in step S114, it is determined whether or not page recording is complete. If it is finished, the recording is finished. If not finished, it is determined in step S115 whether or not it is the last page of the book. If it is not the final page, the reference light incident angle is changed in step S116 and recording is continued. In step S117, the controller generates a normal data page and records the page on the recording medium in step S113. On the other hand, if it is the last page of the book in step S115, it shifts in step S118, returns to step S111, and repeats. Even if it is not the first page of the book in step S111, the process proceeds to step S117, a normal data page is generated, and page recording is performed on the recording medium in step S113 to continue multiple recording.

<Angle multiplex reproduction operation of hologram device>
FIG. 18 shows a flowchart when the angle multiplex reproduction of data is performed.

First, as in the shift movement & angle multiplexing operation of FIG. 10, the recording medium is rotationally controlled so that the light beam strikes the target position to be reproduced, and when the target position is reached, the first of the book is read in step S121. It is determined whether it is a page. If it is not the first page, the reference light incident angle is changed in step S122, and the search for the first page (step S121) is repeated. On the other hand, if the angle is to be the first page, in step S123, the defect detection unit in the position detection unit of the decoder detects the presence or absence of the recording medium defect and the distribution of the light quantity or frequency of the reproduced image of the detection pattern. Thus, it is determined whether or not there is a recording medium defect. If there is no defect, a normal template image (similar to a normal marker) is set for decoder signal processing in step S124. On the other hand, if a recording medium defect is detected, a defect template image is set for decoder signal processing in step S125. The defect template image will be described later.

As described above, a plurality of template images corresponding to the presence or absence or degree of defects in the recording medium are prepared and stored in advance, so that the result of defect detection at the time of reproduction, that is, the presence or absence of defects in the recording medium or A suitable one is selected from the plurality of template images depending on the degree.

After step S124 and step S125, page reproduction is performed in step S126. Next, in step S127, it is determined whether or not page reproduction is complete. If it is finished, the playback is finished. If not finished, it is determined in step S128 whether or not it is the last page of the book. If it is not the last page, the reference light incident angle is changed in step S129, and page reproduction is continued in step S126. On the other hand, if it is the last page of the book, it shifts in step S130, returns to step S121, and repeats.

As described above, by detecting the recording medium defect and changing the marker position detection template image accordingly, the marker position can be correctly detected even when there is a recording medium defect.

<Generation of defect template image>
19A to 19C show a normal template image (similar to a normal marker), a defect template image, and a composite template image, respectively.

The defect template image in FIG. 19B calculates data obtained by processing the normal template image in FIG. 19A with a high-pass filter, and sets the average value as a threshold value. By binarizing the data obtained as a result of the above processing, an image having a resolution higher than that of the normal template image is obtained. Specifically, when the sampling frequency of the light reception pattern in the image sensor is fs, a normal template is passed through a high-pass filter having a cutoff frequency fc (where 0 <fc <fs / 2), and the filter Is binarized using the average value of the image data that has passed through The cut-off frequency fc is determined by the amount of detected defects. That is, the defect template image in FIG. 19B is obtained by performing conversion to remove the low frequency component of the normal template image in FIG. Such conversion can be performed by, for example, using a computer, subjecting a target template image to high-pass filtering, calculating an average value, and binarizing. Specifically, since the image matrix is a real two-dimensional array, linear algebra calculation can be executed while defining a matrix operation using, for example, MATLAB (registered trademark).

The composite template image in FIG. 19C is a second defect template image, and the normal template image in FIG. 19A and the defect template image in FIG. 19B are selected according to the detection level of the recording medium defect. It is possible to create a composite conversion with a weighted average at a certain ratio. As shown in the block diagram of FIG. 20, a normal template is multiplied by a weight K (0 <K <1), a defect template image is multiplied by a weight 1-K, and the result obtained by adding the two is a composite template. It can be an image. K is a coefficient determined by the amount of detected defects. Such a synthesized template image is also obtained as an image having a higher resolution than the normal template image, and further becomes a multi-valued image, for example, a ternary image.

<Second Example of Recording Medium Defect Detection Method>
FIG. 21 shows a flowchart when the data of the second example is angle-multiplexed recorded.

First, similarly to the shift movement and angle multiplexing operation of FIG. 10, the rotation of the recording medium is controlled so that the light beam strikes the target position to be recorded, and when the target position is reached, the first ( It is determined whether the page is a specific place. If the angle should be the first page, a defect detection process for the recording medium is performed before data recording in step S132. In this defect detection process, as shown in FIG. 6, the first shutter SH1 is closed, the second shutter SH2 is opened, only the signal light is passed through the recording medium 10, and a defect detection pattern (for example, FIG. Alternatively, the data page including the defect detection pattern shown in FIG. 12A is received by the image sensor 20, and the recording medium defect is detected by the reproduced defect detection pattern. In step S133, the defect detection result (the presence / absence of defect, degree, etc.) can be stored in the template image memory in the position detection unit 44 of the decoder 26. Further, the defect detection result can be stored in a nonvolatile memory or the like that manages recording medium defects in the controller. Further, in the controller, a database of defect detection results can be constructed by a program so that it can be referred to in defect detection at the next recording and reproduction.

Next, in step S134, the presence / absence of a defect is determined from the defect detection result. If there is a recording medium defect (step S135), the position detection marker shape of the data page to be recorded thereafter is set to a shape that is strong against the recording medium defect (for example, as shown in FIG. (High frequency pattern with many components). If there is no defect in the recording medium (step S136), a normal marker with high position detection performance against noise is set. Then, after completion of any marker setting, in step S137, the controller records the data page on the recording medium via the encoder and the spatial light modulator.

Next, in step S138, it is determined whether or not page recording is complete. If it is finished, the recording is finished. If not finished, it is determined whether or not it is the last page of the book in step S139. If it is not the last page, the reference light incident angle is changed in step S140, and the recording is continued. In step S137, the controller generates a data page and records the page on the recording medium. On the other hand, if it is the last page of the book in step S139, it shifts in step S141, returns to step S132, and repeats. Even if it is not the first page of the book in step S131, the process proceeds to step S137, where page recording is performed on the recording medium and multiplex recording is continued.

On the other hand, the angle multiplex reproduction operation of the hologram apparatus of the second example is performed as follows.

FIG. 22 shows a flowchart when the angle multiplex reproduction of data is performed.

First, similarly to the shift movement & angle multiplexing operation of FIG. 10, the rotation of the recording medium is controlled so that the light beam strikes the target position to be reproduced, and when the target position is reached, the defect management memory in step S151. Then, in step S152, it is determined whether or not there is a recording medium defect. If there is no defect, a normal template image (similar to a normal marker) is set for decoder signal processing in step S153. On the other hand, if there is a recording medium defect, a defect template image (a template image having the same shape as the marker of the recorded data page) is set for decoder signal processing in step S154. After setting the template image, the page is reproduced in step S155. Next, in step S156, it is determined whether or not page reproduction is complete. If it is finished, the playback is finished. If not finished, it is determined in step S157 whether or not it is the last page of the book. If it is not the last page, the reference light incident angle is changed in step S158, and page reproduction is continued in step S155. On the other hand, if it is the last page of the book, it shifts and returns to step S151 to repeat.

Claims

A data page including a marker and a data area displayed on the spatial light modulator is recorded on a recording medium, and light reproduced from the recording medium is imaged on an image sensor to obtain a reproduced image of the data page. A hologram recording method in a hologram apparatus for reproducing,
Detecting the presence or absence or extent of defects in the recording medium;
Recording a normal marker as the marker when there is no defect or when the degree is low, and recording a defect-resistant marker as the marker when there is a defect or when the degree is high. Method.
2. A step of irradiating a recording position of the recording medium with a defect detection pattern and detecting the presence or absence or degree of a defect of the recording medium from a reproduction image of the obtained defect detection pattern. The hologram recording method as described.
3. The hologram recording method according to claim 1, wherein a step of detecting the presence / absence or degree of defects of the recording medium is performed on a plurality of first pages of the data page.
The hologram recording method according to any one of claims 1 to 3, wherein the defect-resistant marker comprises a high-frequency pattern.
5. The light amount ratio between a peripheral portion and a central portion of a reproduced image of the defect detection pattern is detected in the step of detecting the presence or absence or the extent of the defect in the recording medium. Hologram recording method.
6. The hologram recording method according to claim 1, wherein the defect detection pattern comprises a periodic low frequency pattern lower than the data area as a whole.
7. The hologram recording method according to claim 6, wherein, in the step of detecting the presence or absence or degree of defect of the recording medium, a difference in harmonic components of a reproduced image of the defect detection pattern is detected.
8. The presence / absence or degree of a defect in the recording medium is detected by recording the defect detection pattern on the recording medium and reproducing the defect detection pattern. Hologram recording method.
A data page including a marker and a data area displayed on the spatial light modulator is recorded on a recording medium, and light reproduced from the recording medium is imaged on an image sensor to obtain a reproduced image of the data page. A hologram device for reproduction,
A defect detection unit that detects the presence or absence or degree of defects in the recording medium;
And a recording unit for recording a normal marker as the marker when there is no defect or when the degree is low, and a defect-proof marker as the marker when there is a defect or when the degree is high. apparatus.
The defect detection unit irradiates a defect detection pattern to a recording position of the recording medium, and detects the presence or absence or degree of a defect of the recording medium from a reproduced image of the obtained defect detection pattern. 9. The hologram device according to 9.
An apparatus for storing in advance a template image obtained by converting the marker;
A sampling unit that acquires a detection image by sampling a reproduction image of a data page by the image sensor;
The hologram apparatus according to claim 9, further comprising: a position detection unit that performs a template matching process using the detection image and the template image to detect a marker position during recording.