JP3666553B2 - Optical regeneration method and optical regeneration apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for reading data information from an optical recording medium on which data information is recorded as a hologram.
[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. 5Gbit / inch ² Is approaching. Therefore, in order to further increase the capacity, three-dimensional (volume type) recording including the depth direction is required.
[0005]
Therefore, a hologram memory capable of three-dimensional recording has attracted attention. 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. In this hologram memory, generally, a spatial light intensity distribution corresponding to data is recorded and reproduced as a hologram.
[0006]
[Problems to be solved by the invention]
On the other hand, the applicant previously proposed a method of recording and reproducing a spatial polarization distribution according to data as a hologram according to Japanese Patent Application No. 10-32834 (reference number FN97-00693).
[0007]
According to this method, the degradation of the SN ratio due to the influence of noise as in the case of recording / reproducing the light intensity distribution as a hologram is reduced, and data can be recorded / reproduced at a high density and at a high speed, and the erasing process can be performed. Data can be rewritten at high speed without need.
[0008]
A material exhibiting light-induced birefringence (light-induced anisotropy and light-induced dichroism) is sensitive to the polarization state of light incident thereon, and can record the polarization direction of incident light. For example, when 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, photoisomerization is induced and linear Depending on the direction of polarization, anisotropy of the refractive index is generated, and the polarization direction can be recorded. At this time, if the reference light is irradiated at the same time, the polarization direction of the signal light can be recorded as a hologram.
[0009]
Focusing on this point, the method of the prior application uses an optical recording medium in which a polarization sensitive layer 12 is formed on one surface side of a transparent substrate 11 such as a glass substrate as shown in FIG. 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. As a preferable example, the polarization-sensitive layer 12 has a photoisomerizable group on the side chain described above. A polymer, 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.
[0010]
However, 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, and the storage capacity can be increased as the thickness is increased. Further, the entire optical recording medium 10 may be formed as a polarization sensitive layer. The optical recording medium 10 has a disk shape, for example.
[0011]
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 the prior application, this material is capable of recording, reproducing, and erasing a hologram having polarization information by photo-induced isomerization by photoisomerization of side chain cyanoazobenzene. In addition, the recorded hologram is retained without relaxation under room temperature natural light for several years or more.
[0012]
In the optical recording method of the prior application, the coherent light sensitive to the polarization sensitive layer 12 of the optical recording medium 10 from the light source is divided into two light waves, and one light is converted into parallel light and incident as shown in FIG. The light 6 enters the spatial light modulator 30.
[0013]
The spatial light modulator 30 has a plurality of pixels two-dimensionally, causes each pixel 37 to function as a half-wave plate, and applies a voltage to the corresponding bit data of the two-dimensional data to each pixel 37. It is assumed that the polarization of the light incident on each pixel 37 is modulated by giving the presence or absence of.
[0014]
As shown in FIG. 3, the incident light 6 made into parallel light is incident on the spatial light modulator 30 as s-polarized light. In the pixel 37a to which the voltage of the spatial light modulator 30 is not applied, the axis of the half-wave plate is parallel to the polarization direction of the incident light 6, so that the signal light 1a transmitted through the pixel 37a is s-polarized light. In contrast, in the pixel 37b to which the voltage of the spatial light modulator 30 is applied, the axis of the half-wave plate is rotated by 45 degrees, and the polarization direction of the incident light 6 is rotated by 90 degrees. The transmitted signal light 1b becomes p-polarized light. Therefore, the signal light 1 that has passed through the spatial light modulator 30 has a spatial polarization distribution corresponding to the two-dimensional data given to the spatial light modulator 30.
[0015]
The signal light 1 that has passed through the spatial light modulator 30 is condensed by a lens and irradiated onto the optical recording medium 10. At the same time, the other light of the two light waves described above is irradiated as an s-polarized reference light onto the region of the optical recording medium 10 to which the signal light 1 is irradiated. As a result, the spatial polarization distribution of the signal light 1 corresponding to the two-dimensional data is recorded on the optical recording medium 10 as a hologram.
[0016]
In this case, a plurality of holograms can be recorded at different locations in the circumferential direction of the optical recording medium 10 by rotating the disk-shaped optical recording medium 10. At this time, shift multiplex recording can be performed by using a spherical wave as the reference light. Further, a hologram can be recorded so as to form concentric recording tracks in the optical recording medium 10 by moving a recording head including a light source and a spatial light modulator 30 in the radial direction of the optical recording medium 10. it can.
[0017]
FIG. 4 shows an example of the optical reproduction method of the prior application. On the optical recording medium 10, the signal light 1 holding two-dimensional data is recorded as a hologram by the spatial polarization distribution as shown in FIG. 3 by the method described above.
[0018]
The phase conjugate light of the reference light at the time of recording from the reading light optical system 41 of the reproducing head 40 is irradiated as the reading light 3 to the area where the hologram of the optical recording medium 10 is recorded. Thereby, as diffracted light 4 from the hologram, as shown in FIG. 5, phase conjugate light in which the polarization direction of the signal light during recording is preserved is obtained.
[0019]
The diffracted light 4 is converted into parallel light by a lens 42 and is incident on a polarization beam splitter 43 to be separated into an s-polarized component 7S and a p-polarized component 7P, and the s-polarized component 7S is detected by a photodetector array 44S. The p-polarized component 7P is detected by the photodetector array 44P.
[0020]
As shown in FIG. 5, the s-polarized component 7S and the p-polarized component 7P are in a relationship between a negative image and a positive image, and one of them is detected by one photodetector array, and is held by the spatial polarization distribution of the diffracted light 4 The two-dimensional data recorded, that is, the two-dimensional data recorded on the optical recording medium 10 can be read.
[0021]
By rotating the optical recording medium 10 by the motor 49, it is possible to read out a plurality of holograms recorded at different locations in the circumferential direction of the optical recording medium 10. Further, by moving the reproducing head 40 in the radial direction of the optical recording medium 10, it is possible to read a hologram from a recording track formed concentrically in the optical recording medium 10.
[0022]
Further, in the example of the optical reproduction method of the prior application, the light intensity of the s-polarized component 7S and the p-polarized component 7P separated by the polarizing beam splitter 43 and detected by the photodetector arrays 44S and 44P is compared and calculated. Accordingly, it is possible to cancel the noise caused by the fluctuation of the diffracted light 4, the influence of external light, the imperfection of the optical recording medium 10 and the optical system, etc., and obtain a read output with a higher SN ratio.
[0023]
FIG. 6 shows the comparison calculation method. In the subtraction circuit 45, the detection output of the photodetector array 44S is subtracted from the detection output of the photodetector array 44P for each corresponding pixel (bit).
[0024]
Assuming that the diffracted light of the i-th pixel is p-polarized light, its signal component is Ipi, and the noise component is Ni, for the i-th pixel, the output of the photodetector array 44P is the sum of the signal component Ipi and the noise component Ni. (Ipi + Ni), the output of the photodetector array 44S is only the noise component Ni, and the output of the subtraction circuit 45 is the signal component Ipi with the noise component Ni canceled.
[0025]
If the diffracted light of the jth pixel is s-polarized light, its signal component is Isj, and the noise component is Nj, the output of the photodetector array 44P is only the noise component Nj for the jth pixel, and the photodetector The output of the array 44S is the sum (Isj + Nj) of the signal component Isj and the noise component Nj, and the output of the subtraction circuit 45 is only the signal component -Isj with the noise component Nj canceled.
[0026]
When reading binary digital data, for example, it may be determined as “1” when the output value of the subtraction circuit 45 is positive, and “0” when the output value is negative.
[0027]
Thus, according to an example of the optical reproduction method of the prior application, noise can be canceled for each pixel, and the output value is always set with the output value of zero as a threshold regardless of the light intensity of the diffracted light 4. The data value can be determined based on whether the value is positive or negative.
[0028]
However, in this method, two photodetector arrays 44S and 44P are used to detect the s-polarized component 7S and the p-polarized component 7P of the diffracted light 4. However, in order to record / reproduce data at high speed, it is necessary to increase the number of bits of the two-dimensional data, and it is necessary to increase the number of pixels of the spatial light modulator 30 and the photodetector arrays 44S and 44P. For this reason, the photodetector arrays 44S and 44P are expensive, and the use of the two photodetector arrays 44S and 44P increases the cost of the optical regenerator. On the other hand, when only one of the s-polarized light component 7S and the ice block 7P is detected by one photodetector array, it becomes impossible to cancel the noise and obtain a read output with a higher S / N ratio.
[0029]
Therefore, the present invention cancels noise by a low-cost device in an optical reproduction method for reading a spatial polarization distribution according to data from an optical recording medium in which the spatial polarization distribution according to data is recorded as a hologram. Thus, a higher S / N ratio read output can be obtained.
[0030]
[Means for Solving the Problems]
In the optical regeneration method of the present invention,
As the first stage and the second stage, the optical recording medium in which the signal light holding the data by the spatial polarization distribution composed of the first polarization component and the second polarization component whose polarization directions are different from each other by a predetermined angle is recorded on the hologram, respectively Irradiating the readout light, the first polarization component and the second polarization component of the diffracted light from the hologram are sequentially detected by the same photodetector,
The two detection outputs are compared to detect the presence or absence of a data error. When a data error is detected, reading of the same hologram is repeated until no data error is detected, and detection of the presence or absence of the data error is repeated.
[0031]
[Action]
In the optical reproducing method of the present invention according to the above method, in the first stage, the optical recording medium is irradiated with the readout light to read out the hologram, and the first polarization component of the hologram diffracted light, for example, the s-polarization component, While being detected by the photodetector, in the second stage thereafter, the same region of the optical recording medium is irradiated with the readout light to read out the same hologram, and the second polarization component of the hologram diffracted light, for example, the p-polarization component Are detected by the same photodetector.
[0032]
Further, thereafter, the detection outputs of both are compared to detect the presence or absence of a data error. In the method of the prior application shown in FIG. 4, since the s-polarized component 7S and the p-polarized component 7P of the diffracted light 4 are detected simultaneously by the separate photodetector arrays 44S and 44P, as described above with reference to FIG. Furthermore, the noise components included in both detection outputs are the same, and the noise components are canceled by calculating the difference between the detection outputs of both.
[0033]
However, in the light reproduction method of the present invention, the s-polarized component and the p-polarized component of the diffracted light from the same hologram are detected at the timing shifted by the same photodetector, so that fluctuations in diffracted light and external light are detected. Depending on the detection timing of both, the noise components included in both detection outputs may not be the same, and the noise components are canceled in the difference between the detection outputs of both. Data error may occur.
[0034]
Therefore, in the optical reproduction method of the present invention, when both detection outputs are compared to detect the presence or absence of a data error, and when a data error due to noise that changes with time is detected, the detection timing of both is The same hologram is repeatedly read and the detection of the presence or absence of the data error is repeated until the data error is no longer detected at the appropriate timing when the noise that can be changed is the same or substantially the same. When no data error is detected, the difference between the detection outputs at that time is output as data held by the hologram.
[0035]
As described above, according to the optical regeneration method of the present invention, it is possible to cancel the noise and obtain a higher S / N ratio read output by a single photodetector, thereby reducing the cost of the optical regeneration apparatus. it can.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
[Example of optical recording method]
Although it is the same as the optical recording method of the prior application mentioned above, FIG. 7 shows an example of an optical recording method which is a premise of the optical reproducing method of the present invention.
[0037]
The optical recording medium 10 is of a polarization sensitive type as shown in FIG. 1, and in this example, a polyester having cyanoazobenzene in the side chain shown in FIG. 2 is used as the polarization sensitive layer. In this example, the optical recording medium 10 has a disk shape.
[0038]
As the light source 21, a light source 21 that emits sensitive coherent light is used for the polarization-sensitive optical recording medium 10, and in this example, an argon ion laser that emits laser light of 515 nm belonging to a wavelength at which cyanoazobenzene is photoisomerized is used. . In this example, the polarization of the laser beam 5 is s-polarized light.
[0039]
The laser light 5 from the light source 21 is split into two light waves by the beam splitter 25, and at the time of recording, the shutter 28 is opened, and the laser light transmitted through the beam splitter 25 is converted into parallel light by the lenses 22 and 23 to be spatial light. The light is incident on the modulator 30.
[0040]
The spatial light modulator 30 is assumed to be capable of polarization modulation. As such a spatial light modulator 30, a voltage addressed liquid crystal panel or an electro-optic crystal provided with a matrix electrode can be used, but a polarizer is not provided.
[0041]
As shown in FIG. 3, the spatial light modulator 30 has a plurality of pixels two-dimensionally, and each pixel 37 functions as a half-wave plate so that each pixel 37 has two-dimensional data. It is assumed that the polarization of light incident on each pixel 37 is modulated by giving corresponding bit data as the presence or absence of voltage application.
[0042]
Since the laser light 5 from the light source 21 is s-polarized light, the incident light 6 that is parallel light enters the spatial light modulator 30 as s-polarized light. As shown in FIG. 3, in the pixel 37a to which the voltage of the spatial light modulator 30 is not applied, the axis of the half-wave plate is parallel to the polarization direction of the incident light 6, and therefore the signal light transmitted through the pixel 37a. 1a becomes s-polarized light. In contrast, in the pixel 37b to which the voltage of the spatial light modulator 30 is applied, the axis of the half-wave plate is rotated by 45 degrees, and the polarization direction of the incident light 6 is rotated by 90 degrees. The transmitted signal light 1b becomes p-polarized light. Therefore, the signal light 1 that has passed through the spatial light modulator 30 has a spatial polarization distribution corresponding to the two-dimensional data given to the spatial light modulator 30.
[0043]
As shown in FIG. 7, the signal light 1 that has passed through the spatial light modulator 30 is Fourier-transformed to the Fourier transform plane P <b> 1 by the Fourier transform lens 24, and is irradiated onto the optical recording medium 10. At the same time, the laser beam reflected by the beam splitter 25 is reflected by the mirrors 26 and 27 to irradiate the region of the optical recording medium 10 to which the signal light 1 is irradiated as s-polarized reference light 2. As a result, the spatial polarization distribution of the signal light 1 corresponding to the two-dimensional data is recorded on the optical recording medium 10 as a hologram.
[0044]
In this case, by rotating the optical recording medium 10, it is possible to record a plurality of holograms at different locations in the circumferential direction of the optical recording medium 10. At this time, shift multiplex recording can be performed by using a spherical wave as the reference beam 2. Further, by moving the illustrated recording head in the radial direction of the optical recording medium 10, a hologram can be recorded so as to form concentric recording tracks in the optical recording medium 10.
[0045]
[Embodiments of optical regeneration method and optical regeneration apparatus]
FIG. 8 shows an optical configuration of an embodiment of the optical reproducing apparatus according to the present invention. In the optical recording apparatus of FIG. 7, a polarization rotation element 46, a polarizing plate 47, a lens 42, and a photodetector array 44 are added. is there. On the optical recording medium 10, the signal light 1 holding two-dimensional data is recorded as a hologram by the spatial polarization distribution as shown in FIG. 3 by the method described above.
[0046]
At the time of reproduction, the shutter 28 is closed to block the signal light 1, and the same light as the reference light at the time of recording is irradiated as the readout light 3 to the area where the hologram of the optical recording medium 10 is recorded. As a result, as shown in FIG. 5, hologram diffracted light 4 in which the polarization direction of the signal light during recording is preserved is obtained.
[0047]
The diffracted light 4 passes through the polarization rotation element 46 and the polarizing plate 47, and enters the photodetector array 44 as parallel light through the lens 42. The polarization direction of the diffracted light 4 detected by the photodetector array 44 changes depending on the states of the polarization rotation element 46 and the polarizing plate 47.
[0048]
In this example, the polarizing plate 47 transmits only s-polarized light. Polarization rotation element 46, when the detection of the s-polarized component of the diffracted light 4, the diffracted light 4 is transmitted without changing the polarization direction, at the time of detection of the p-polarized component of the diffracted light 4, 90 ° the polarization direction of the diffracted light 4 Rotate to make it transparent. As such a polarization rotation element 46, a half-wave plate, a liquid crystal bulb, or the like can be used.
[0049]
Therefore, if there is no noise, the photodetector array 44 detects the s-polarized component of the diffracted light 4 as white (bright) and the p-polarized component as black (dark) when detecting the s-polarized component. At the time of component detection, the s-polarized component of the diffracted light 4 is detected as black (dark) and the p-polarized component is detected as white (bright).
[0050]
However, as described above, actually, there is noise caused by fluctuation of the diffracted light 4, the influence of external light, imperfection of the optical recording medium 10 and the optical system, and in the present invention, the diffracted light 4 s-polarized components and p-polarized components are detected by the same photodetector array 44 at timings that are shifted in time. Therefore, the s-polarized components and p-polarized components change with time due to fluctuations in the diffracted light 4 and the influence of external light. The obtained noise component is not canceled in the difference between the detection output of the s-polarized component and the detection output of the p-polarized component, and a data error may occur. Therefore, in the present invention, as described above, until the data error is not detected, reading of the same hologram is repeated, and the detection of the presence or absence of the data error is repeated.
[0051]
FIG. 9 shows an example of a control configuration for that purpose, and a switch circuit 51, a buffer memory 52, a data processing circuit 53, and a control unit 54 are added to the optical configuration of FIG. The switch circuit 51, the buffer memory 52, and the data processing circuit 53 each function as described later.
[0052]
The control unit 54 includes a CPU, a ROM in which a program to be executed by the CPU is described, and a RAM that operates as a work area of the CPU, and executes a reproduction processing routine 60 shown in FIG.
[0053]
The reproduction processing routine 60 of FIG. 10 is for reading two-dimensional data for one page. In this reproduction processing routine 60, the control unit 54 first reproduces the s-polarized component in step 61 so that the s-polarized component can be reproduced. That is, the polarization rotation element 46 is controlled so that the diffracted light 4 is transmitted without changing the polarization direction, and then the switch circuit 51 is switched to the buffer memory 52 side in step 62.
[0054]
In this state, the control unit 54 next turns on the light source 21 in step 63, irradiates the optical recording medium 10 with the readout light 3, reads out the hologram, and then in step 64 by the photodetector array 44. The s-polarized component of the diffracted light 4 is detected, and the detected output 8S is written in the buffer memory 52 in step 65. If no noise exists, at this time, the s-polarized component is detected as white and the p-polarized component is detected as black.
[0055]
Next, the control unit 54 controls the polarization rotation element 46 in step 66 so that the p-polarized light component can be reproduced, that is, to transmit the diffracted light 4 by rotating the polarization direction by 90 degrees, and then in step At 67, the switch circuit 51 is switched to the data processing circuit 53 side.
[0056]
In this state, the control unit 54 next turns on the light source 21 in step 68, irradiates the read light 3 to the optical recording medium 10, reads out the same hologram again, and then in step 69, detects the photodetector array. 44 detects the p-polarized component of the diffracted light 4. If no noise exists, at this time, the s-polarized component is detected as black and the p-polarized component is detected as white.
[0057]
Next, in step 70, the control unit 54 transfers the p-polarized component detection output 8P and the s-polarized component detection output 8S stored in the buffer memory 52 in step 65 to the data processing circuit 53. The data processing circuit 53 calculates the difference between the detection output 8P and the detection output 8S, and further proceeds to step 71 to determine whether or not there is a data error due to noise.
[0058]
A noise component that does not change with time due to incompleteness of the optical recording medium 10 or the optical system is canceled in the difference between the detection output 8P and the detection output 8S. However, a noise component that may change over time due to fluctuations in the diffracted light 4 or the influence of external light is not canceled in the difference between the detection output 8P and the detection output 8S, and a data error may occur.
[0059]
If there is no noise, the detection output 8S detects the s-polarized component as white and the p-polarized component as black. Conversely, the detection output 8P detects the s-polarized component as black and the p-polarized component as white. Thus, the detection output 8S and the detection output 8P are inverted from each other in any pixel (bit) of the two-dimensional data.
[0060]
Therefore, in any pixel of the two-dimensional data, the detection output 8S and the detection output 8P are not the result of inversion of each other, and if they are detected as white or black, a data error occurs due to noise. become.
[0061]
Therefore, in step 70, the control unit 54 takes in the detection outputs 8S and 8P for each pixel of the two-dimensional data from the data processing circuit 53, and detects whether or not both are white or black. Then, in step 71, it is determined from the detection results for all the pixels whether there is a data error.
[0062]
When it is determined that there is no data error, the control unit 54 proceeds from step 71 to step 72, and the difference between the detection output 8P and the detection output 8S at that time calculated from the data processing circuit 53 in step 70. Are output as reproduction data. At this time, the data processing circuit 53 outputs zero as a threshold value, for example, “1” when the difference is positive and “0” when the difference is negative.
[0063]
When it is determined in step 71 that there is a data error, the control unit 54 returns from step 71 to step 61 and repeats the processing in steps 61 to 71 until it is determined in step 71 that there is no data error.
[0064]
Since a data error is caused by the fact that noise that may change over time changes instantaneously at the detection timing of the detection output 8S or the detection timing of the detection output 8P, the same hologram is generated several times by changing the reproduction timing in this way. By reproducing, at an appropriate reproduction timing, the noise that can change with time is the same or almost the same at the detection timing of the detection output 8S and the detection timing of the detection output 8P, so that no data error occurs.
[0065]
As described above, according to the present invention, noise can be canceled and a read output with a higher S / N ratio can be obtained by a single photodetector, and the cost of the optical regenerator can be reduced. Further, in the case where two photodetector arrays are used as in the example of the optical regeneration method of the prior application, it is necessary to match the characteristics of the two photodetector arrays. There is no need.
[0066]
【The invention's effect】
As described above, according to the present invention, in an optical reproduction method for reading a spatial polarization distribution according to data from an optical recording medium in which the spatial polarization distribution according to data is recorded as a hologram, Noise can be canceled and a higher S / N ratio read output can be obtained. Further, there is no complication of matching the characteristics of the two photodetectors.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a polarization-sensitive optical recording medium.
FIG. 2 is a diagram illustrating a chemical formula of an example of a material of a polarization sensitive layer.
FIG. 3 is a diagram showing a spatial polarization distribution of signal light as an example of an optical recording method as a premise of the optical reproducing method of the present invention.
FIG. 4 is a diagram showing an example of an optical reproduction method of a prior application.
FIG. 5 is a diagram showing a spatial polarization distribution of diffracted light according to an example of the optical reproduction method of the prior application.
FIG. 6 is a diagram showing a comparative calculation method as an example of the optical reproduction method of the prior application.
FIG. 7 is a diagram showing an example of an optical recording method which is a premise of the optical reproducing method of the present invention.
FIG. 8 is a diagram showing an optical configuration of an embodiment of an optical reproducing apparatus according to the present invention.
FIG. 9 is a diagram showing a control configuration of an embodiment of an optical regenerator according to the present invention.
FIG. 10 is a diagram showing a regeneration processing routine of an embodiment of the optical regeneration method of the present invention.
[Explanation of symbols]
1 ... Signal light
2 ... Reference light
3 ... Reading light
4 ... Diffraction light
5 ... Laser light
6 ... Incident light
10: Optical recording medium
12 ... Polarization sensitive layer
21 ... Light source
25. Beam splitter
28 ... Shutter
30. Spatial light modulator
44. Photodetector array
46: Polarization rotating element
47 ... Polarizing plate
51 ... Switch circuit
52 ... Buffer memory
53. Data processing circuit
54. Control unit
60: Reproduction processing routine

Claims (4)

As the first stage and the second stage, the optical recording medium in which the signal light holding the data by the spatial polarization distribution composed of the first polarization component and the second polarization component whose polarization directions are different from each other by a predetermined angle is recorded on the hologram, respectively Irradiating the readout light, the first polarization component and the second polarization component of the diffracted light from the hologram are sequentially detected by the same photodetector,
Comparing both detection outputs to detect the presence or absence of a data error. When a data error is detected, the same hologram is read repeatedly until no data error is detected. Method. The optical regeneration method according to claim 1, wherein
A method for reproducing light, comprising: arranging a polarization rotation element and a polarizing plate in an optical path of the diffracted light. A readout light optical system for irradiating readout light onto an optical recording medium in which signal light holding data is recorded as a hologram by a spatial polarization distribution composed of a first polarization component and a second polarization component whose polarization directions are different from each other by a predetermined angle; ,
A diffracted light optical system including a photodetector for sequentially detecting the first polarization component and the second polarization component of the diffracted light from the hologram;
An error detection means for comparing the detection outputs of both to detect the presence or absence of a data error;
When a data error is detected by the error detection means, the diffracted light optical system and the error detection are repeated so that reading of the same hologram is repeated until the data error is no longer detected, and detection of the presence or absence of the data error is repeated. Control means for controlling the means;
An optical reproduction apparatus comprising: The optical regenerator according to claim 3.
An optical reproducing apparatus, wherein the diffracted light optical system includes a polarization rotating element and a polarizing plate.

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