JP3707285B2 - Optical recording method, optical recording apparatus, optical reproducing method, and optical reproducing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for recording two-dimensional data information as a hologram on an optical recording medium and reproducing it from the optical recording medium.
[0002]
[Prior art]
Rewritable optical disks such as phase change type and magneto-optical type are already widely used. These optical disks have a higher recording density than ordinary magnetic disks, but in order to further increase the recording density, it is necessary to reduce the beam spot diameter and shorten the distance between adjacent tracks or adjacent bits. There is.
[0003]
A DVD that has been put to practical use by the development of such a technology is a DVD. A read-only DVD-ROM can record 4.7 GB data on one side of a 12 cm diameter disk. Further, the writable / erasable DVD-RAM is capable of high-density recording of 5.2 GB on both sides of a 12 cm diameter disk by a phase change method.
[0004]
As described above, the density of optical discs has been increasing year by year. However, since the above optical discs record data in the plane, the recording density is limited to the diffraction limit of light, and the physical limits of high-density recording. It is approaching 5Gbit / inch ² said. Therefore, in order to further increase the capacity, three-dimensional (volume type) recording including the depth direction is required.
[0005]
Therefore, a hologram memory having both a large capacity derived from a three-dimensional recording area and a high speed derived from a two-dimensional batch recording / reproducing method has attracted attention as a next-generation computer file memory.
[0006]
In the hologram memory, a plurality of data pages can be recorded by being multiplexed in the same volume, and the data can be read collectively for each page. Digital data can be recorded and reproduced by converting binary digital data “0, 1” into “bright, dark” as a digital image and recording and reproducing it as a hologram instead of an analog image. Recently, specific optical systems of this digital hologram memory system, SN ratio and bit error rate evaluation based on the volume multiplex recording system, or proposal for two-dimensional encoding have been made, such as the influence of aberrations of the optical system, etc. Research from a more optical viewpoint is also progressing.
[0007]
FIG. 6 shows a shift that is an example of a volume multiplex recording system described in the document “D. Psaltis, M. Leavene, A. Pu, G. Barbastasis and K. Curtis; Opt. Lett. 20 (1995) 782”. Multiple recording method is shown.
[0008]
In the shift multiplex recording system disclosed in this document, the hologram recording medium 91 is formed into a disk shape, and the object light 93 obtained through the spatial light modulator 92 is Fourier-transformed by the lens 94 to form the hologram recording medium 91. Simultaneously with the irradiation, the hologram recording medium 91 is irradiated with the spherical wave reference light 96 obtained through the objective lens 95, and a plurality of holograms are overwritten in the same region by the rotation of the hologram recording medium 91. For example, when the beam diameter is 1.5 mmφ, another hologram can be recorded in almost the same region without causing crosstalk by simply moving the hologram recording medium 91 by several tens of μm. This utilizes the fact that the reference beam 96 is a spherical wave, and is equivalent to the change in the angle of the reference beam 96 due to the movement of the hologram recording medium 91.
[0009]
Thus, by rotating the optical recording medium as a disk shape, a hologram can be recorded and reproduced in the two-dimensional direction of the medium surface, and the storage capacity can be increased and the data transfer speed can be improved.
[0010]
However, when recording and reproducing holograms in the two-dimensional direction of the medium surface in this way, the optical system and optical recording for recording and reproduction are performed in both the tracking direction horizontal to the medium surface and the focusing direction perpendicular to the medium surface. If the relative position of the medium is not accurately matched, the S / N ratio of recording / reproduction is lowered. In particular, the signal to be recorded / reproduced is two-dimensional data information as shown in FIG. 5A, and each pixel has a size of about several tens of μm at most, so high-precision alignment is required. .
[0011]
Therefore, as shown in FIG. 5B, in the M × N pixel signal light of each page, alignment patterns Pa are added to the respective m × n pixel portions at the four corners, and a hologram is recorded. A method of controlling the relative position between the optical system and the optical recording medium using a detection signal of the position of the alignment pattern Pa in the hologram diffracted light at the time of reading is considered.
[0012]
[Problems to be solved by the invention]
However, in this method, 4 × m × n pixels out of the available M × N pixels in each page cannot be used for recording / reproducing data information, resulting in a decrease in storage capacity and a decrease in data transfer speed. . Also, data information for (M × N−4 × m × n) pixels is used as a two-dimensional spatial light modulator for forming signal light during recording and a two-dimensional light detector for detecting diffracted light during reproduction. In order to perform recording and reproduction, M × N pixels are required, resulting in an increase in the cost of the spatial light modulator and the photodetector, and an increase in the cost of the recording / reproducing apparatus.
[0013]
Therefore, the present invention can align the optical system and the optical recording medium without adding the alignment pattern to all pages of the signal light, thereby increasing the recording capacity and the data transfer speed. The cost of the recording / reproducing apparatus can be reduced.
[0014]
[Means for Solving the Problems]
In the optical recording method of the present invention,
The first signal light that retains the two-dimensional data information by the spatial intensity distribution and includes the alignment pattern is recorded on the optical recording medium as the first hologram,
Next, the diffracted light is reproduced from the recorded first hologram, the alignment pattern is detected, and the relative position between the signal light and the optical recording medium is controlled by the detection signal. The second signal light that retains the two-dimensional data information by the intensity distribution and does not include the alignment pattern is changed by changing the polarization angle of the reference light or the signal light from the time of recording the first hologram. The hologram is recorded in an area where the first hologram of the optical recording medium is recorded.
[0015]
In the optical regeneration method of the present invention,
The signal light for two pages, each of which holds two-dimensional data information by a spatial intensity distribution and has an alignment pattern added to only one of the pages, changes the polarization angle of the reference light or signal light for each page. Irradiating the optical recording medium recorded in the same area as a hologram with readout light, simultaneously reproducing the diffracted light from the holograms for the two pages, detecting the alignment pattern from the diffracted light, In a state where the relative position between the readout light and the optical recording medium is controlled by the detection signal, the two-dimensional data information of each page is separated and read from the diffracted light.
[0016]
[Action]
A material exhibiting light-induced birefringence (light-induced anisotropy, light-induced dichroism) is sensitive to the polarization state of light incident thereon and can record the polarization angle (polarization direction) of incident light. . For example, a polymer or liquid crystal having a photoisomerizable group in the side chain, or a polymer in which a photoisomerizable molecule is dispersed is irradiated with linearly polarized light, so that photoisomerization is induced and linearly polarized light Depending on the direction, anisotropy of the refractive index occurs, and the polarization direction can be recorded and stored. At this time, if the reference light is irradiated simultaneously, the polarization angle of the signal light can be recorded as a hologram.
[0017]
A normal hologram is recorded with the polarization directions of signal light (object light) and reference light being the same (parallel). A hologram recorded or recorded in this way is referred to as an intensity modulation hologram in this specification.
[0018]
On the other hand, the material exhibiting the above-described 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 to each other. The hologram recorded or recorded in this way is referred to as a polarization modulation hologram in this specification. However, similarly to the intensity modulation hologram, the polarization modulation hologram can be spatially intensity-modulated in accordance with the two-dimensional data information.
[0019]
For example, P-polarized signal light can be recorded as an intensity-modulated hologram by P-polarized reference light, and can be recorded as a polarization-modulated hologram by S-polarized reference light. P-polarized signal light recorded as an intensity-modulated hologram can be reproduced as S-polarized diffracted light by S-polarized readout light, and P-polarized signal light recorded as a polarization-modulated hologram can be reproduced as S-polarized light. It can be reproduced as P-polarized diffracted light by polarized read-out 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.
[0020]
By utilizing this, in the optical recording method of the present invention, first, the first signal light that holds the two-dimensional data information by the spatial intensity distribution and includes the alignment pattern is used as the first hologram, for example, the intensity. A modulation hologram is recorded on an optical recording medium.
[0021]
Next, diffracted light is reproduced from the recorded first hologram, for example, an intensity-modulated hologram, and an alignment pattern is detected, and the relative position between the signal light and the optical recording medium is controlled by the detection signal. . For example, if the intensity-modulated hologram as the first hologram is one in which P-polarized signal light is recorded by P-polarized reference light, S-polarized readout light can be obtained by S-polarized readout light. The alignment pattern can be detected.
[0022]
In a state where the signal light and the optical recording medium are aligned as described above, the second signal light that retains the two-dimensional data information by the spatial intensity distribution and does not include the alignment pattern is used as the first signal light. When the hologram is recorded, the polarization angle of the reference light or signal light is changed, and the first hologram of the optical recording medium, for example, the intensity-modulated hologram, is recorded as the second hologram, for example, as the polarization-modulated hologram. Record in the area.
[0023]
Therefore, the signal light for two pages can be recorded as holograms in the same area of the optical recording medium only by adding the alignment pattern only to the signal light page to be recorded first.
[0024]
After multiplex recording in this way, the intensity modulation hologram and the polarization modulation hologram are mutually polarized in the polarization direction by irradiating the readout light to the area where the intensity modulation hologram and polarization modulation hologram of the optical recording medium are multiplexed and recorded. Can be reproduced at the same time as diffracted beams orthogonal to each other. For example, an intensity-modulated hologram is one in which P-polarized signal light is recorded with P-polarized reference light, and a polarization-modulated hologram is one in which P-polarized signal light is recorded with S-polarized reference light. In some cases, S-polarized diffracted light is obtained from the intensity-modulated hologram and P-polarized diffracted light is obtained from the polarization-modulated hologram by irradiating the S-polarized readout light.
[0025]
Therefore, by separating the hologram diffracted light into an S-polarized component and a P-polarized component by a polarization beam splitter or the like, and detecting each polarized component by a separate photodetector, data information recorded as an intensity-modulated hologram Data information recorded as a polarization modulation hologram can be separated at a high S / N ratio and read simultaneously.
[0026]
In addition, in this case, two pages of the hologram of the intensity modulation type hologram and the polarization modulation type hologram are simultaneously obtained by the alignment pattern added only to one hologram, for example, the intensity modulation type hologram. Can be aligned.
[0027]
As described above, according to the present invention, the alignment of the optical system and the optical recording medium can be performed without adding the alignment pattern to all the pages of the signal light. It is possible to increase the data transfer rate and to reduce the cost of the recording / reproducing apparatus.
[0028]
For example, when an alignment pattern is added to each of the m × n pixels at the four corners in the M × N pixels of the first page, the conventional recording area in the same area of the optical recording medium is used for two pages. Data information can be recorded by 4 × m × n pixels more than the above method. Conversely, when recording the same amount of data information for two pages as in the conventional method, the area of the recording area can be made smaller than that in the conventional method, and the space for forming signal light can be reduced. The number of pixels of the optical modulator and the photodetector for detecting diffracted light can be reduced.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
(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 side of a transparent substrate 11 such as a glass substrate.
[0030]
The polarization sensitive layer 12 may be any material as long as it exhibits light-induced birefringence and can record polarization information as a hologram, but as a preferred example, a polymer having a photoisomerizable group in the side chain. Alternatively, a polymer liquid crystal or a polymer in which molecules to be photoisomerized are dispersed can be used. As the photoisomerizable group or molecule, for example, those containing an azobenzene skeleton are suitable.
[0031]
As one preferred example of the polarization sensitive layer 12, a polyester having cyanoazobenzene in the side chain represented by the chemical formula shown in FIG. 2 can be used. As described in detail in Japanese Patent Application No. 10-32834, this material is capable of recording, reproducing, and erasing holograms having polarization information by photoinduced anisotropy by photoisomerization of cyanoazobenzene in the side chain. Is possible.
[0032]
In order to record the hologram in a volumetric (three-dimensional) manner, the thickness of the polarization sensitive layer 12 needs to be at least about 10 μm, and the storage capacity can be increased as the thickness is increased. The entire optical recording medium 10 can also be formed as a polarization sensitive layer exhibiting light induced birefringence.
[0033]
(Examples of optical recording apparatus and optical reproducing apparatus)
FIG. 3 shows an example of the optical recording apparatus and the optical reproducing apparatus of the present invention.
[0034]
As the light source 21 of the recording / reproducing head 20, a light source that emits sensitive coherent light to the polarization sensitive layer of the optical recording medium 10 is used. For example, when the polyester having cyanoazobenzene in the side chain shown in FIG. 2 is used as the polarization sensitive layer, an argon laser having a wavelength of 515 nm that is sensitive to this is used.
[0035]
The polarized light of the light 1 from the light source 21 is, for example, S-polarized light perpendicular to the paper surface. After the S-polarized light 1 passes through the spatial filter 22 to remove the wavefront disturbance, it is converted into parallel light by the lens 23. The beam is split into two light beams by the beam splitter 24.
[0036]
At the time of recording, the shutter 25 is opened, and the P-polarized light 2 transmitted through the beam splitter 24 is incident on the spatial light modulator 26 for forming signal light. The spatial light modulator 26 includes an alignment pattern as shown in FIG. 5B or includes an alignment pattern as shown in FIG. No binary two-dimensional data image is displayed. As a result, the light 4 transmitted through the spatial light modulator 26 is spatially intensity-modulated according to the value of each pixel of the two-dimensional data image, and a P-polarized signal that retains the two-dimensional data information by the spatial intensity distribution. It becomes light. As such a spatial light modulator 26, a liquid crystal panel or the like can be used.
[0037]
The P-polarized signal light 4 from the spatial light modulator 26 is Fourier-transformed by the lens 27, and the P-polarized signal light 5 after the conversion is applied to the optical recording medium 10.
[0038]
At the same time, the S-polarized light 3 reflected by the beam splitter 24 is incident on the polarization rotation element 28, and the polarization angle of the light transmitted through the polarization rotation element 28 is rotated according to a control signal from the control circuit (not shown in the figure). Let As the polarization rotation element 28 capable of rotating the polarization angle of transmitted light in this way, a liquid crystal bulb, a Pockels element, a Faraday element, a half-wave plate, or the like can be used.
[0039]
At the time of recording, P-polarized light or S-polarized reference light is obtained as the light 6 transmitted through the polarization rotating element 28. In recording, the P-polarized light or S-polarized reference light 6 is reflected by the mirror 29a, condensed by the lens 29b, reflected by the mirror 29c, and irradiated with the signal light 5 of the optical recording medium 10. Irradiate.
[0040]
Thus, the spatial intensity distribution of the P-polarized signal light 5 in the optical recording medium 10 is an intensity-modulated hologram when the reference light 6 is P-polarized, and a polarization-modulated hologram when the reference light 6 is S-polarized. Each is recorded.
[0041]
During reproduction (reading), the shutter 25 is closed to block the signal light 5, and S-polarized read light is obtained as the light 6 transmitted through the polarization rotation element 28, and this is recorded on the hologram of the optical recording medium 10. Irradiate the area. The irradiated read light 6 is diffracted by the hologram, and diffracted light 7 is obtained on the optical path of the signal light 5.
[0042]
In the case of hologram multiplex recording to be described later, when the P-polarized signal light 5 is first recorded as an intensity-modulated hologram by the P-polarized reference light 6 and irradiated with the S-polarized readout light 6, As the diffracted light 7, S-polarized diffracted light from an intensity-modulated hologram is obtained. When the intensity-modulated hologram and the polarization-modulated hologram are multiplexed and recorded in the same area of the optical recording medium 10 and then irradiated with the S-polarized readout light 6, the S-polarized light from the intensity-modulated hologram is used as the diffracted light 7. And a P-polarized component from the polarization modulation hologram are obtained.
[0043]
The diffracted light 7 is converted into parallel light by the lens 51, is incident on the polarizing beam splitter 52, and is separated into the S-polarized component 8 reflected by the polarizing beam splitter 52 and the P-polarized component 9 transmitted through the polarizing beam splitter 52. The S-polarized component 8 is imaged on the photodetector 53s and its spatial intensity distribution is read, and the P-polarized component 9 is imaged on the photodetector 53p and its spatial intensity distribution is read. Therefore, the data information recorded as an intensity modulation hologram and the data information recorded as a polarization modulation hologram can be separated at a high S / N ratio and read simultaneously.
[0044]
(Example of hologram multiplex recording)
When the intensity modulation type hologram and the polarization modulation type hologram are multiplexed and recorded in the same area of the optical recording medium 10 with the apparatus described above, first, in step 101, as shown in the multiple recording processing routine 100 of FIG. As the polarized signal light 5 (4), a signal including the alignment pattern as shown in FIG. 5B is obtained, and as the light 6 transmitted through the polarization rotation element 28, a P-polarized reference light is obtained. Both are simultaneously irradiated onto the optical recording medium 10 to record the intensity-modulated hologram in the optical recording medium 10.
[0045]
Next, in step 102, the signal light 5 is cut off, and S-polarized read light is obtained as the light 6 transmitted through the polarization rotation element 28, which is irradiated to the optical recording medium 10. In step 101, the optical recording medium is obtained. 10 is reproduced as S-polarized diffracted light 8 and the intensity thereof is detected by the photodetector 53s, and the detection signal of the alignment pattern contained in the intensity-modulated hologram is obtained. Based on this, the control circuit 70 controls the head moving mechanism 60 and the motor 40 to align the recording / reproducing head 20 and the optical recording medium 10.
[0046]
If the recording / reproducing head 20 and the optical recording medium 10 are aligned as described above, then in step 103, as the P-polarized signal light 5 (4), an alignment as shown in FIG. The light 6 transmitted through the polarization rotation element 28 is obtained as S-polarized light as reference light while irradiating both onto the area where the intensity-modulated hologram of the optical recording medium 10 is recorded. Then, the polarization modulation hologram is recorded by being multiplexed with the intensity modulation hologram in the region.
[0047]
In step 103, the signal light 5 passes through the optical recording medium 10 and enters the polarization beam splitter 52 via the lens 51. However, since the signal light 5 is P-polarized light, the S-polarized light component 8 of the photodetector 53s The position control by the control circuit 70 based on the detection is not affected.
[0048]
(Example of hologram multiplex reproduction)
When simultaneously reproducing the intensity-modulated hologram and the polarization-modulated hologram that are multiplexed and recorded by the above method, the signal light 5 is blocked and the S-polarized readout light is obtained as the light 6 transmitted through the polarization rotation element 28. Then, this is irradiated to the area where the intensity modulation type hologram and the polarization modulation type hologram of the optical recording medium 10 are recorded in a multiplexed manner.
[0049]
As a result, S-polarized diffracted light 8 is obtained as diffracted light from the intensity-modulated hologram including the alignment pattern, and P-polarized light is diffracted from the polarization-modulated hologram not including the alignment pattern. Light 9 is obtained. Accordingly, the head moving mechanism 60 and the motor 40 are controlled by the control circuit 70 based on the detection signal of the alignment pattern by the photodetector 53s, and the recording / reproducing head 20 and the optical recording medium 10 are aligned.
[0050]
In this state of alignment, in the photodetector 53s, data information recorded as an intensity-modulated hologram from a portion other than the alignment pattern of the S-polarized diffracted light 8 from the intensity-modulated hologram. In the photodetector 53p, the data information recorded as the polarization modulation hologram is read from the P-polarized diffracted light 9 from the polarization modulation hologram, and the data information recorded as the intensity modulation hologram is read. Data information recorded as a polarization modulation hologram can be separated at a high S / N ratio and reproduced simultaneously.
[0051]
(Verification by experiment)
With the method and apparatus described above, an attempt was made to actually record and reproduce two-dimensional data information. As the optical recording medium 10, a polarization sensitive layer formed of polyester having cyanoazobenzene in the side chain was used, and as the light source 21, the above-described argon ion laser having a wavelength of 515 nm was used. Signal light and reference light for recording is about 0.5 W / cm ^2, the reading light at the time of reproduction, was 0.15 W / cm ^2. As the spatial light modulator 26, a liquid crystal panel for a projector having a size of one pixel of 42 μm × 42 μm and 640 × 480 pixels was used.
[0052]
As a result, an intensity modulation hologram and a polarization modulation hologram can be recorded in the same area of the optical recording medium, and crosstalk can be performed by using each as a two-dimensional binary image of the S polarization component 8 and the P polarization component 9. It was possible to reproduce well without generating. Further, high-precision alignment in pixel units can be realized only by the alignment pattern added to the intensity modulation hologram.
[0053]
(Recording-only or playback-only device)
The example of FIG. 3 is a case where recording and reproduction can be performed with one apparatus, but it can also be a recording-only apparatus (however, including hologram reproduction for alignment) or a reproduction-only apparatus. In the recording-dedicated apparatus, the polarizing beam splitter 52 and the photodetector 53p in the above example are unnecessary, and by omitting them, the recording head can be reduced in size and weight and the cost of the recording apparatus can be reduced. it can. In the reproduction-only apparatus, the shutter 25, the spatial light modulator 26 and the lens 27, and the beam splitter 24 and the polarization rotation element 28 are not necessary depending on the configuration. By eliminating these, the reproduction head can be reduced in size and weight and reproduced. Cost reduction of the apparatus can be realized.
[0054]
【The invention's effect】
As described above, according to the present invention, the alignment of the optical system and the optical recording medium can be performed without adding the alignment pattern to all the pages of the signal light. It is possible to increase the data transfer rate and to reduce the cost of the recording / reproducing apparatus.
[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 illustrating a chemical formula of an example of a material of a polarization sensitive layer of an optical recording medium.
FIG. 3 is a diagram illustrating an example of an optical recording apparatus and an optical reproducing apparatus according to the present invention.
FIG. 4 is a diagram illustrating an example of a multiple recording processing routine.
FIG. 5 is a diagram illustrating an example of signal light that does not include an alignment pattern and signal light that includes the signal;
FIG. 6 is a diagram for explaining a shift multiplex recording method.
[Explanation of symbols]
4, 5 ... Signal light 6 ... Reference light, Read light 7 ... Diffracted light 10 ... Optical recording medium 12 ... Polarization sensitive layer 20 ... Recording / reproducing head 21 ... Light source 24 ... Beam splitter 25 ... Shutter 26 ... Spatial light modulator 28 ... Polarization rotating element 40 ... motor 52 ... polarizing beam splitters 53s, 53p ... detector 60 ... head moving mechanism 70 ... control circuit

Claims (7)

The first signal light that retains the two-dimensional data information by the spatial intensity distribution and includes the alignment pattern is recorded on the optical recording medium as the first hologram,
Next, the diffracted light is reproduced from the recorded first hologram, the alignment pattern is detected, and the relative position between the signal light and the optical recording medium is controlled by the detection signal. The second signal light that retains the two-dimensional data information by the intensity distribution and does not include the alignment pattern is changed by changing the polarization angle of the reference light or the signal light from the time of recording the first hologram. An optical recording method for recording the first hologram of the optical recording medium in the region where the first hologram is recorded. A light source that emits coherent light;
A spatial light modulator that intensity-modulates light from the light source according to two-dimensional data information to obtain signal light that retains the two-dimensional data information by a spatial intensity distribution;
A reference light optical system for obtaining reference light from light from the light source;
The reference light from the reference light optical system retains the two-dimensional data information by the spatial intensity distribution as the readout light, and the first signal light including the alignment pattern is the first reference light by the first reference light. A photodetector that detects the intensity of a polarization component having a predetermined polarization angle in the diffracted light obtained from the first hologram by irradiating the optical recording medium recorded as a hologram of
Control means for controlling the relative position of the recording head including the light source, the spatial light modulator, the reference light optical system, and the light detector and the optical recording medium according to the detection signal of the light detector;
With the relative position controlled by the control means, the second signal light that holds the two-dimensional data information by the spatial intensity distribution and does not include the alignment pattern is obtained from the spatial light modulator. At the same time as irradiating the optical recording medium, a second reference light is obtained from the reference light optical system, and the optical recording medium is irradiated with the second signal light as a second hologram. An optical system constituting a part of the recording head for recording in an area where the first hologram of the recording medium is recorded;
The recording head that changes a polarization angle relationship between the second signal light and the second reference light to a polarization angle relationship between the first signal light and the first reference light. A polarization rotation element constituting a part of
An optical recording apparatus comprising: The optical recording apparatus according to claim 2.
The optical recording medium has a disk shape, and the optical recording apparatus includes a medium driving mechanism for rotating the optical recording medium and a head moving mechanism for moving the recording head in a radial direction of the optical recording medium. An optical recording apparatus. The signal light for two pages, each of which holds two-dimensional data information by the spatial intensity distribution and the alignment pattern is added to only one page, changes the polarization angle of the reference light or signal light for each page. Irradiating the optical recording medium recorded in the same area as the hologram with the readout light, simultaneously reproducing the diffracted light from the hologram for the two pages, detecting the alignment pattern from the diffracted light, An optical reproducing method for separating and reading two-dimensional data information of each page from the diffracted light in a state where the relative position of the readout light and the optical recording medium is controlled by the detection signal. The signal light for two pages, each of which holds two-dimensional data information by a spatial intensity distribution and has an alignment pattern added to only one of the pages, changes the polarization angle of the reference light or signal light for each page. A reading light optical system for simultaneously reading out the holograms for the two pages by irradiating the optical recording medium recorded in the same area as the hologram with reading light,
A diffracted light optical system that separates the diffracted light from the two-page hologram into two polarization components orthogonal to each other;
Two photodetectors for detecting the intensity of the two polarization components;
Control means for controlling the relative position of the reproducing head including the readout optical optical system, the diffracted optical system, and two optical detectors, and the optical recording medium, based on the detection signal of the one optical detector;
An optical reproduction apparatus comprising: The optical regenerator according to claim 5.
The optical recording medium has a disk shape, and the optical reproducing apparatus includes a medium driving mechanism for rotating the optical recording medium and a head moving mechanism for moving the reproducing head in the radial direction of the optical recording medium. An optical regenerator. The signal light for two pages, each of which holds two-dimensional data information by the spatial intensity distribution and the alignment pattern is added to only one page, changes the polarization angle of the reference light or signal light for each page. , Optical recording media recorded in the same area as holograms.

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