JP2001118252A - Optical recording method, optical recording medium, optical reading method and optical reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the retrieval of recorded data information to be performed with high accuracy at a high speed and the reproduction to be performed with a high BER. SOLUTION: Signal light 5 of P polarized light holding the first data information is recorded as a first hologram on the optical recording medium 10 by reference light 6 of the P polarized light. Next, signal light 5 of P polarized light holding the second data information in the state of subjecting the first data information to an encoding processing is recorded as a second hologram by the reference light 6 of S polarized light in the region of the optical recording medium 10 where the first hologram is recorded. This region is irradiated with the signal light 5 of the P polarized light holding the retrieval data information at the retrieval. At this time, the P polarized light component indicating the correlation between the first data information and the retrieval data information and the S polarized light component indicating the correlation between the second data information and the retrieval data information are simultaneously obtained as diffracted light 7 on the optical path of the reference light 6. The P polarized light component 7P in this diffracted light 7 is detected by a photodetector 43. The region described above is irradiated with the reference light 6 of the P polarized light at the reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording data information as a hologram, and a method and apparatus for retrieving or reproducing data information recorded as a hologram.

[0002]

2. Description of the Related Art Rewritable optical disks such as a phase change type and a magneto-optical type have already become widespread. In order to further increase the density of these optical disks, the beam spot diameter must be reduced. It is necessary to shorten the distance between adjacent tracks or adjacent bits.

A DVD that has been put into practical use by the development of such a technique is DVD. Read-only DVD-RO
M is 4.7 GByte on one side on a 12 cm diameter disk
e can be recorded. In addition,
An erasable DVD-RAM uses a phase change method.
High-density recording of 5.2 GByte is possible on both sides of a disk having a diameter of 12 cm.

As described above, the density of optical disks has been increasing year by year. On the other hand, since the above-mentioned optical disks record data in a plane, the recording density is limited to the diffraction limit of light. 5Gbit / i called physical limit
Approaching nch ² . Therefore, in order to further increase the capacity, three-dimensional (volume type) recording including the depth direction is required.

Therefore, as a next-generation computer file memory, large capacity derived from a three-dimensional recording area and 2
A hologram memory that has high speed derived from the one-dimensional batch recording / reproducing method has attracted attention.

In a hologram memory, a plurality of data pages can be recorded in a multiplexed manner in the same volume, and data can be read out collectively for each page. Instead of analog images, binary digital data “0, 1” is converted into a digital image as “bright, dark” and recorded and reproduced as a hologram, so that digital data can be recorded and reproduced. Recently, specific optical systems of this digital hologram memory system, evaluation of SN ratio and bit error rate based on volume multiplex recording, or proposal of two-dimensional encoding have been proposed, and the influence of aberration of the optical system has been proposed. Research from a more optical point of view is also progressing.

Further, the hologram memory can record and reproduce data two-dimensionally, so that high-speed data search and data correlation detection are possible. More specifically,
In -149660, the following data search method is proposed.

FIG. 6 shows the search method. In this method, the laser light from the laser 101
From 0, the two-dimensional data to be searched which is recorded as a hologram is reproduced, the reproduced image is written to the spatial light modulator 102 of the optical address type, and the spatial address modulator of the LCD (liquid crystal display) configuration is used. Optical modulator 1
03 is written with two-dimensional search data.

Then, a laser beam from another laser 104 is used as a readout beam 105 through an analyzer
Irradiate the D-addressed electrical address type spatial light modulator 103, change its polarization state according to the search data, and reflect the transmitted light by the half mirror prism 107 to form the optical address type spatial light modulator. An image is formed on a reproduction surface 102.

Therefore, in the spatial light modulator 102, the polarization state of the reproduction light is changed for each pixel in accordance with the data to be searched, and the reproduction light is incident on the photodetector array 109 through the analyzer 108, and By detecting the presence / absence of reproduction light from a plurality of pixels in the array 109 collectively, it is possible to detect coincidence / mismatch of a plurality of bits between the data to be searched and the data for search.

Further, "A. Kutanov and
Y. Ichioka: Conjugate Image
Plane Correlator with Ho
logistic Disk Memory, OPT
ICAL REVIEW Vol. 3, No. 4 (19
96) 258-263 "describes the following data recording method and data correlation detection method.

FIG. 7 shows a recording method and a correlation detection method. According to this method, at the time of recording, two-dimensional data to be recorded is displayed on the spatial light modulator 111 of an LCD configuration of the electric address type, and the two-dimensional data that has passed through the spatial light modulator 111 is displayed.
The signal light 112 having the two-dimensional amplitude distribution is Fourier-transformed by the Fourier transform lens 113 to the Fourier transform plane P1 and radiated to the optical memory 110. At the same time, the reference light 114 is radiated to the optical memory 110 and the two-dimensional data is transmitted to the optical memory 110. Record as a Fourier transform hologram.

When a correlation is detected, two-dimensional search data is displayed on an electric address type spatial light modulator 111 having an LCD configuration, and a reading light 115 conjugated with a reference light 114 at the time of recording. Is irradiated to the optical memory 110 to reproduce a hologram of the two-dimensional data to be searched from the optical memory 110, and the reproduced hologram is inversely Fourier-transformed to the inverse Fourier transform plane P2 by the Fourier transform lens 113, and the spatial light modulator 111.

Therefore, the transmitted light of the spatial light modulator 111 is the optical product of the search data and the data to be searched,
When the search data matches the data to be searched, a strong correlation peak appears on the Fourier transform plane P3 of the Fourier transform lens 116, and by detecting this, a correlation of a two-dimensional image or the like can be known.

[0015]

As described above, a hologram memory has attracted attention because it has both large capacity and high speed, and a search method as shown in FIG. 6 and a correlation detection method as shown in FIG. Has also been proposed.

However, in the conventional hologram memory,
1) Noise of photodetector such as CCD, 2) Crosstalk between hologram pages, 3) Crosstalk between pixels within the same hologram page, 4) Diffraction efficiency due to imperfect recording medium and optical system BER (bit error rate) at the time of recording / reproduction decreases due to factors such as fluctuation between pages and within a page.

To solve such a problem, the following encoding method has been proposed. One is [bright, dark]
When the two-dimensional data corresponding to [0, 1] is holographically multiplex-recorded, crosstalk caused by fluctuations in diffraction efficiency is not generated because the total light intensity of signal light at the time of recording is not kept constant by the data. Occurs. In order to avoid this problem, a differential coding method is used in which [dark, light] corresponds to [0] and [light, dark] corresponds to [1]. However, this method alone is not enough to prevent a decrease in BER, and requires advanced coding such as addition of an error correction code used in optical recording or magnetic recording.

Further, when the information to be recorded is image information, further encoding is involved. That is,
Even for the same image (pattern), the binary data image file has a different binary data array depending on the image format (for example, TIFF format, BMP format, GIF format, etc.). Furthermore, at present, there are format formats including various compression formats, which are often combined with compression coding.

As described above, 2 actually recorded on the recording medium
The dimensional data is not a simple code but a combination of various codes. If the search method as shown in FIG. 6 or the correlation detection method as shown in FIG. 7 is applied to such data information, the information of the search data itself and the data to be searched are recorded. Even if the information contained in is the same, the search data and the searched data
Different binary data array due to the effect of encoding,
There is a problem that search accuracy is reduced. In order to avoid this, it is necessary to decrypt the recorded data to be searched once and then perform a search using the search data.
In this method, decoding takes a long time, so that the feature of high speed of the hologram memory is lost.

Therefore, the present invention enables recorded data information to be reproduced at a high BER and allows the recorded data information to be searched with high accuracy and high speed.

[0021]

According to an optical recording method of the present invention, a first signal light for holding first data information by a spatial intensity distribution, and a state in which the first data information is subjected to an encoding process. And the second signal light holding the second data information by the spatial intensity distribution are recorded in the same area of the optical recording medium as holograms by changing the polarization angle of the reference light or the signal light.

According to the optical reading method of the present invention for data retrieval, a first signal light holding first data information by a spatial intensity distribution and a signal light having the first data information encoded are processed. The second signal light holding the second data information by the spatial intensity distribution and the second signal light have different spatial light polarization angles of the reference light and the signal light, and are respectively recorded on the optical recording medium recorded in the same area as the hologram. A third signal light holding the search data information is radiated as readout light according to the intensity distribution, and a correlation between the first data information and the search data information is obtained from a hologram in which the first signal light is recorded. The indicated diffracted light is read out, and the diffracted light is detected by the photodetector.

According to the optical reading method of the present invention for data reproduction, a first signal light holding first data information by a spatial intensity distribution and a signal light having the first data information encoded are processed. The second signal light holding the second data information by the spatial intensity distribution is referred to an optical recording medium recorded in the same area as a hologram by changing the polarization angle of the reference light or the signal light with respect to each other. The light is irradiated as readout light to read out diffracted light from the hologram in which the second signal light is recorded, and the diffracted light is detected by a photodetector.

[0024]

A material exhibiting light-induced birefringence (light-induced anisotropy, light-induced dichroism) is sensitive to the polarization state of light incident thereon and records the polarization angle (polarization direction) of the incident light. be able to. For example, a polymer having a group that photoisomerizes in a side chain or a polymer liquid crystal, or a polymer in which a molecule that photoisomerizes is dispersed, is irradiated with linearly polarized light, photoisomerization is induced, and linearly polarized light is irradiated. Anisotropy of the refractive index occurs depending on the direction, and the polarization direction can be recorded and stored. At this time, by simultaneously irradiating the reference light, the polarization angle of the signal light can be recorded as a hologram.

An ordinary hologram is recorded with the signal light (object light) and the reference light having the same (parallel) polarization direction. Holograms recorded or recorded in this way are referred to herein as parallel holograms.

On the other hand, the above-mentioned material exhibiting light-induced birefringence can record the signal light as a hologram by making the polarization directions of the signal light and the reference light orthogonal. Holograms recorded or recorded in this way are referred to herein as orthogonal holograms. However, similarly to the parallel hologram, the orthogonal hologram can be spatially intensity-modulated according to the two-dimensional data information.

For example, P-polarized signal light can be recorded as a parallel hologram by P-polarized reference light, and can be recorded as orthogonal holograms by S-polarized reference light. The P-polarized signal light recorded as a parallel hologram can be reproduced as P-polarized diffracted light by P-polarized reading light, and can be reproduced as S-polarized diffracted light by S-polarized reading light. it can. The P-polarized signal light recorded as the orthogonal hologram is read by the S-polarized read light,
While it can be reproduced as P-polarized diffraction light,
The P-polarized reading light can be reproduced as S-polarized diffraction light. At the time of recording, instead of changing the polarization angle of the reference light, the polarization angle of the signal light may be changed.

Utilizing this, in the optical recording method of the present invention, as described above, the first signal light holding the first data information by the spatial intensity distribution and the encoding to the first data information are performed. The second signal light that holds the processed second data information in a spatial intensity distribution is recorded as a hologram in the same area of the optical recording medium by changing the polarization angle of the reference light or the signal light. I do.

The first data information is used for data search (data to be searched). A plurality of data, such as not performing encoding for adding an error correction code, so that high-precision and high-speed search can be performed by the search data information. Is not encoded. It is assumed that the second data information is for data reproduction, and is not subjected to any particular restriction on encoding, and has been encoded such as by adding an error correction code so that the data information can be reproduced at a high BER.

The recording order of the signal light may be any order. The polarization angles of the signal light and the reference light are also determined according to the relationship between the polarization angles of the signal light and the reference light at the time of recording the first signal light and the second. For example, first, the first signal light for search is recorded as a parallel hologram on the optical recording medium, and then the second signal light for reproduction is changed. Is recorded as an orthogonal hologram in a region of the optical recording medium where the first signal light is recorded as a parallel hologram.

As described above, the third signal light holding the search data information is read out by the spatial intensity distribution in the area where the first and second signal lights of the optical recording medium are multiplex-recorded as the parallel hologram and the orthogonal hologram. By irradiating as light, the parallel hologram and the orthogonal hologram recorded on the optical recording medium function as a matched filter, and the first hologram recorded on the parallel hologram from the parallel hologram on the optical path of the reference light. Diffracted light indicating the correlation between the first data information of the signal light and the search data information of the read light, the second data information of the second signal light recorded on the orthogonal hologram from the orthogonal hologram, and the read light And the diffracted light indicating the correlation with the search data information are simultaneously obtained as the diffracted lights whose polarization directions are orthogonal to each other.

For example, when the parallel hologram is the first P-polarized light,
Is recorded by the P-polarized reference light, and when the orthogonal hologram is the P-polarized second signal light recorded by the S-polarized reference light, By irradiating P-polarized light as signal light, P-polarized diffracted light is obtained from the parallel hologram, and S-polarized diffracted light is obtained from the orthogonal hologram.

At this time, the diffracted light from the parallel hologram on which the first signal light for search is recorded, that is, the diffracted light of P polarization indicating the correlation between the first data information and the search data information is converted to a polarizer or the like. And the detected data is detected by a search photodetector to determine whether the first data information matches the search data information.

In this case, since the first data information has not been subjected to a plurality of encodings, the recorded data information can be searched with high accuracy and high speed. Also, regardless of the image format of the second data information, including the format of the compression format, the search of the first data information is not affected.

After the search, the area of the optical recording medium where the parallel hologram and the orthogonal hologram are multiplex-recorded is irradiated with the reference light as the readout light instead of the third signal light, whereby the light of the signal light is irradiated. On the road, the diffracted light from the parallel hologram and the diffracted light from the orthogonal hologram are simultaneously obtained as diffracted lights whose polarization directions are orthogonal to each other.

For example, as described above, the parallel hologram is the one in which the first signal light of P polarization is recorded by the reference light of P polarization, and the orthogonal hologram is the second signal light of P polarization.
When the signal light is recorded by the S-polarized reference light, the P-polarized light is emitted from the parallel hologram, and the S-polarized Diffracted light is obtained respectively.

At this time, the diffracted light from the orthogonal hologram in which the second signal light for reproduction is recorded, that is, the S-polarized light is extracted by a polarizer or the like, and detected by a photodetector for reproduction. , Read the second data information.

In this case, since the second data information has been encoded such as by adding an error correction code, the recorded data information can be reproduced at a high BER.

As described above, according to the present invention, recorded data information can be searched with high accuracy and high speed, and can be reproduced with a high BER.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Example of Optical Recording Medium] FIG. 1 shows an example of an optical recording medium used in the method of the present invention, in which a polarization sensitive layer 12 is formed on one surface of a transparent substrate 11 such as a glass substrate. Things.

The polarization-sensitive layer 12 may be any material as long as it exhibits photoinduced birefringence and can record polarization information as a hologram. Having a polymer or polymer liquid crystal,
Alternatively, a polymer in which photoisomerizable molecules are dispersed can be used. Further, as the photoisomerizable group or molecule, for example, those containing an azobenzene skeleton are preferable.

As a preferable example of the polarization sensitive layer 12, a polyester having cyanoazobenzene in a side chain represented by a chemical formula shown in FIG. 2 can be used. As described in detail in JP-A-10-340479, this material can record, reproduce, and erase a hologram having polarization information by photoinduced anisotropy due to photoisomerization of side chain cyanoazobenzene. It is.

In order to record the hologram volumetrically (three-dimensionally), the thickness of the polarization sensitive layer 12 needs to be at least about 10 μm. The larger the thickness, the larger the storage capacity. Note that the entire optical recording medium 10 may be formed as a polarization-sensitive layer exhibiting photoinduced birefringence.

[Example of Apparatus and Method of Recording, Searching, and Reproducing] FIG. 3 shows an example of an optical reading apparatus according to the present invention, which also serves as an optical recording apparatus.

As the light source 21 of the optical head 20, one that emits coherent light sensitive to the polarization sensitive layer 12 of the optical recording medium 10 is used. For example, when a polyester having cyanoazobenzene in the side chain shown in FIG. 2 is used as the polarization sensitive layer 12, a wavelength 5
A 15 nm argon ion laser is used.

The polarization of the light 1 from the light source 21 is, for example, P-polarization perpendicular to the paper surface. The P-polarization light 1 is passed through a spatial filter 22 to remove the disturbance of the wavefront.
To form parallel light, and further split by the beam splitter 24 into two light beams.

(Recording) At the time of recording, the shutter 25 is opened, and the P-polarized light 2 transmitted through the beam splitter 24 is
The light enters the spatial light modulator 26 for forming signal light. A binary two-dimensional data image is displayed on the spatial light modulator 26 by a control circuit not shown in the figure. Thereby, the light 4 transmitted through the spatial light modulator 26 is spatially intensity-modulated in accordance with the value of each pixel of the two-dimensional data image, and a P-polarized signal holding two-dimensional data information by a spatial intensity distribution. It becomes light. As such a spatial light modulator 26, a liquid crystal panel or the like can be used.

The P-polarized signal light 4 from the spatial light modulator 26 is Fourier-transformed by the lens 27, and the converted P-polarized signal light 5 is applied to the optical recording medium 10.

At the time of recording, the shutter 28 is opened, and the P-polarized light 3 reflected by the beam splitter 24 is made incident on the polarization rotation element 29. The polarization rotation is performed in accordance with a control signal from a control circuit not shown in FIG. The polarization angle of light transmitted through the element 29 is rotated. A liquid crystal valve, a Pockels element, a Faraday element, a half-wave plate, or the like can be used as the polarization rotation element 29 that can rotate the polarization angle of transmitted light.

At the time of recording, a P-polarized light or an S-polarized reference light is obtained as the light 6 transmitted through the polarization rotating element 29.
At the time of recording, the P-polarized or S-polarized reference light 6 is reflected by a mirror 31, converted into parallel light having a reduced beam diameter by lenses 32 and 33, and further reflected by mirrors,, and. The region of the recording medium 10 where the signal light 5 is irradiated is irradiated simultaneously with the signal light 5.

Thus, the spatial intensity distribution of the P-polarized signal light 5 in the optical recording medium 10 is determined as a parallel hologram when the reference light 6 is P-polarized light, and as an orthogonal hologram when the reference light 6 is S-polarized light. Be recorded.

As a recording method, first, an image of two-dimensional data for search is displayed on the spatial light modulator 26, and the reference light 6
Is recorded as a P-polarized light on the optical recording medium 10 as a parallel hologram, the signal light of the P-polarized light holding the two-dimensional data information for search by the spatial intensity distribution.
6, an image of the two-dimensional data for reproduction is displayed, the reference light 6 is used as the S-polarized light, and the signal light of the P polarization holding the two-dimensional data information for the reproduction by the spatial intensity distribution is used as the orthogonal hologram. Are multiplexed and recorded in the area where the parallel hologram is recorded.

In order to search the two-dimensional data for retrieval with high accuracy and high speed using the retrieval data, it is assumed that a plurality of encodings are not performed, for example, an encoding for adding an error correction code is not performed. Further, in order to eliminate the difference as binary data depending on the image format, the image data is recorded as an image pattern, and encoding according to the image format is removed. On the other hand, two-dimensional data for reproduction is such that data information can be reproduced at a high BER.
It is assumed that encoding such as adding an error correction code has been performed.

However, conversely, the P-polarized signal light holding the two-dimensional data information for search is recorded as an orthogonal hologram by the S-polarized reference light, and the P-polarized signal light holding the two-dimensional data information for reproduction is recorded. The signal light may be recorded as a parallel hologram using the P-polarized reference light.

The optical recording medium 10 is moved by the motor 60 in FIG.
By rotating the optical recording medium 10 in the circumferential direction as shown by the arrow 19, a plurality of sets of holograms each composed of a parallel hologram and an orthogonal hologram can be recorded. Further, the head moving mechanism 7
0, the optical head 20 is moved in the radial direction of the optical recording medium 10 as shown by an arrow 71 in FIG.
Parallel holograms and orthogonal holograms can be recorded so as to form concentric recording tracks in the optical recording medium 10.

(Search) At the time of search, the shutter 28 is closed, the reference light 6 is blocked, the shutter 25 is opened, and the P-polarized light 2 transmitted through the beam splitter 24 is made incident on the spatial light modulator 26, The search data image is displayed on the optical modulator 26 as a two-dimensional data image. As a result, the light 4 transmitted through the spatial light modulator 26 is spatially intensity-modulated in accordance with the value of each pixel of the search data image, and becomes a P-polarized signal light holding search data information by a spatial intensity distribution. Become. The encoding of the search data information is the same as the encoding of the search data information described above.

The P-polarized signal light 4 from the spatial light modulator 26 is Fourier-transformed by the lens 27, and the converted P-polarized signal light 5 is used as read light as a parallel hologram of the optical recording medium 10 and Irradiate the area where the orthogonal hologram is multiplex-recorded.

At this time, the parallel hologram and the orthogonal hologram recorded on the optical recording medium 10 function as a matched filter, and are recorded on the optical path of the reference light 6 as diffracted light 7 on the parallel hologram from the parallel hologram. P indicating the correlation between the retrieved search data information and the search data information
A polarized diffracted light component and an S-polarized diffracted light component from the orthogonal hologram, which indicate the correlation between the reproduction data information recorded on the orthogonal hologram and the search data information, are obtained at the same time.

The diffracted light 7 is reflected by the mirror 41,
Further, the P-polarized light component 7 in the diffracted light 7 is
P is extracted, and the P-polarized component 7P is imaged on the photodetector 43 in a two-dimensional array.

Therefore, the photodetector 43 can detect a match / mismatch between the search data information recorded on the parallel hologram and the search data information. In this case, since the search data information is not encoded in a plurality, the recorded data information can be searched with high accuracy and high speed. The diffracted light component of the S-polarized light from the orthogonal hologram on which the data information for reproduction is recorded is blocked by the polarizer 42 and does not affect the search.

By rotating the optical recording medium 10 by the motor 60, the search data information can be retrieved from the parallel holograms recorded at different locations in the circumferential direction of the optical recording medium 10. Further, the head moving mechanism 7
By moving the optical head 20 in the radial direction of the optical recording medium 10 according to 0, the search data information can be retrieved from the parallel holograms recorded on the concentric recording tracks of the optical recording medium 10.

(Reproduction) At the time of reproduction, the shutter 25 is closed, the signal light 5 is blocked, and the shutter 28 is opened to obtain a P-polarized read light (reference light) as the light 6 transmitted through the polarization rotation element 29. Then, this is irradiated onto an area of the optical recording medium 10 where the parallel hologram and the orthogonal hologram are multiplex-recorded.

The irradiated readout light 6 is diffracted by the parallel hologram and the orthogonal hologram, and becomes a diffracted light 8 on the optical path of the signal light 5 as a diffracted light component of P-polarized light from the parallel hologram and S-polarized light from the orthogonal hologram. Are obtained at the same time.

The diffracted light 8 is inverse Fourier-transformed by the lens 51, and the S-polarized component 8 S in the diffracted light after the inverse Fourier transform is extracted by the polarizer 52,
The polarization component 8S is imaged on the two-dimensional array of photodetectors 53.

Therefore, the photodetector 53 can read the reproduction data information recorded on the orthogonal hologram. In this case, since the reproduction data information has been encoded such as by adding an error correction code, the recorded data information can be reproduced with a high BER. The diffracted light component of the P-polarized light from the parallel hologram on which the search data information is recorded is blocked by the polarizer 52 and does not affect the data reproduction.

At the time of reproduction, S-polarized light may be irradiated as the reading light 6. In this case, the S-polarized light component from the parallel hologram and the P-polarized light component from the orthogonal hologram are obtained as the diffracted light 8. The S-polarized component from the parallel hologram may be extracted by the polarizer 52 and detected by the photodetector 53.

By rotating the optical recording medium 10 by the motor 60, the reproduction data information can be reproduced from the orthogonal holograms recorded at different places in the circumferential direction of the optical recording medium 10. Further, the head moving mechanism 7
By moving the optical head 20 in the radial direction of the optical recording medium 10 by 0, reproduction data information can be reproduced from orthogonal holograms recorded on concentric recording tracks of the optical recording medium 10.

[Verification by Experiment] With the above-described method and apparatus, recording, retrieval, and reproduction of two-dimensional data information were actually attempted. As the optical recording medium 10, a polarization-sensitive layer 12 formed of polyester having cyanoazobenzene in a side chain was used, and as the light source 21, the above-described argon ion laser having a wavelength of 515 nm was used. The signal light and the reference light at the time of recording are about 0.5 W / cm ² , and the signal light (reading light) at the time of retrieval and the reading light at the time of reproduction are:
0.15 W / cm ² . As the spatial light modulator 26, the size of one pixel is 42 μm × 42 μm and 640 ×
A 480 pixel liquid crystal panel for a projector was used.

First, a P-polarized signal light holding binary image data information including characters, figures, and patterns as shown in FIG. 5A as search data information is converted by a P-polarized reference light. It was recorded on the optical recording medium 10 as a parallel hologram.

However, in the case of such an image, if the content of the image changes, the light amount of the entire page changes, so that the ratio of the light portion to the dark portion in the page becomes constant. The amount of the pattern was adjusted. In addition, the size of the dots, and the width and length of the lines, which constitute the characters, figures and patterns, are represented by at least several pixels of the spatial light modulator 26. As a result, even if the BER is reduced by not adding an error correction code, the reduction in search accuracy can be ignored.

Next, the data information obtained by adding an error correction code for improving the BER to the checkerboard pattern as shown in FIG. 5B and further combining the above-described coding by the differential coding method is reproduced. The P-polarized signal light held as the data data for use was recorded as an orthogonal hologram in the area of the optical recording medium 10 where the above-mentioned parallel hologram was recorded, with the S-polarized reference light.

For the search, the character “A” in the binary image shown in FIG. 5A is placed in the area of the optical recording medium 10 where the parallel hologram and the orthogonal hologram are multiplex-recorded as described above.
The P-polarized signal light holding the binary image data information as search data information is irradiated as readout light.
As a result, the photodetector 43 detected a bright spot at a position corresponding to the character “A” in the binary image shown in FIG.

Next, the same region of the optical recording medium 10 was irradiated with P-polarized reference light as read light, and the data read by the photodetector 53 was decoded. As a result, the BER becomes about 10 ^{-3 with} respect to the case where the above coding is not performed, and 2
It was confirmed that it was improved by more than an order of magnitude.

[0074]

As described above, according to the present invention, recorded data information can be searched with high accuracy and high speed, and can be reproduced with a high BER.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical recording medium used in the method of the present invention.

FIG. 2 is a diagram showing a chemical formula of an example of a material of a polarization sensitive layer of an optical recording medium.

FIG. 3 is a diagram showing an example of the optical reading device of the present invention.

FIG. 4 is a diagram showing rotation of an optical recording medium and movement of an optical head.

FIG. 5 is a diagram showing two-dimensional data used in an experiment.

FIG. 6 is a diagram showing a conventional search method.

FIG. 7 is a diagram showing a conventional correlation detection method.

[Explanation of symbols]

 4,5 ... signal light 6 ... reference light 7,8 ... diffraction light 10 ... optical recording medium 12 ... polarization sensitive layer 20 ... optical head 21 ... light source 24 ... beam splitter 25,28 ... shutter 26 ... spatial light modulator 29 ... Polarization rotating elements 42, 52 ... Polarizers 43, 53 ... Photodetector 60 ... Motor 70 ... Head moving mechanism

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2K008 AA04 BB04 CC01 DD12 EE07 FF07 FF17 FF21 HH01 HH12 HH13 HH18 HH26 HH28 5D090 AA01 BB17 BB18 CC01 CC04 DD03 EE12 FF11 FF21 KK12 KK14 KK15

Claims (8)

[Claims] 1. A first signal light holding first data information according to a spatial intensity distribution, and a second data information obtained by performing an encoding process on the first data information is stored according to a spatial intensity distribution. And a second signal light to be recorded in the same area of the optical recording medium as a hologram by changing the polarization angles of the reference light and the signal light. 2. The optical recording method according to claim 1, wherein the first data information is not subjected to a plurality of encoding processes. 3. A first signal light for holding first data information according to a spatial intensity distribution and a second data information obtained by encoding the first data information according to a spatial intensity distribution. An optical recording medium in which the reference signal or the signal light is changed in polarization angle with respect to the second signal light and the hologram is recorded in the same area. 4. A first signal light for holding first data information according to a spatial intensity distribution, and a second data information in a state where the first data information is subjected to an encoding process is stored as a spatial intensity distribution. The second signal light and the third signal light have the polarization angles of the reference light and the signal light changed from each other, and hold the search data information by spatial intensity distribution on the optical recording medium recorded in the same area as the hologram. Is irradiated as read light, and a diffracted light indicating a correlation between the first data information and the search data information is read from a hologram in which the first signal light is recorded. An optical reading method that is detected by a detector. 5. A first signal light holding first data information according to a spatial intensity distribution, and a second data information obtained by encoding the first data information according to a spatial intensity distribution. The second signal light and the polarization angle of the reference light or the signal light are changed with respect to each other, and the optical recording medium recorded in the same area as the hologram is irradiated with the reference light as the readout light. 2. An optical reading method in which diffracted light is read from a hologram in which the signal light of No. 2 is recorded, and the diffracted light is detected by a photodetector. 6. A first signal light for holding first data information according to a spatial intensity distribution, and a second data information in a state where the first data information is subjected to an encoding process is stored as a spatial intensity distribution. The second signal light and the third signal light have the polarization angles of the reference light and the signal light changed from each other, and hold the search data information by spatial intensity distribution on the optical recording medium recorded in the same area as the hologram. A readout light optical system for irradiating the signal light as readout light, and a diffracted light extracting a polarization component indicating a correlation between the first data information and the search data information from the diffracted light read out by the readout light. An optical reading device comprising: an optical system; and a photodetector that detects the extracted polarization component. 7. A first signal light for holding first data information according to a spatial intensity distribution, and a second data information in a state where the first data information is subjected to an encoding process is stored as a spatial intensity distribution. A reading light optical system for irradiating an optical recording medium recorded in the same area as a hologram with the reference light or the reading light as the reference light or the signal light in which the polarization angle of the reference light or the signal light is changed. A diffracted light optical system that extracts a polarized light component indicating the second data information from the diffracted light read by the read light, and a photodetector that detects the extracted polarized light component. Reader. 8. The optical reading device according to claim 6, wherein the optical recording medium has a disk shape, and the optical reading device includes a medium driving mechanism for rotating the optical recording medium; A head moving mechanism for moving an optical head including a diffracted light optical system and a photodetector in a radial direction of the optical recording medium.