JP3975317B2 - Optical recording method, optical recording apparatus, optical reading method, optical reading apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for optically recording and optically reading multilevel data.
[0002]
[Prior art]
As a method for optically recording multilevel data, JP-A-11-238251 and JP-A-10-340479 employ an optical recording medium provided with an optical recording layer exhibiting light-induced birefringence. There has been proposed a method of recording signal light on an optical recording medium by changing the polarization angle (polarization direction) of the signal light in accordance with the value.
[0003]
In the method of Japanese Patent Laid-Open No. 11-238251, the thickness d of the optical recording layer is set so that the optical recording layer exhibiting the light-induced birefringence of the optical recording medium forms a half-wave plate or a quarter-wave plate, and The refractive index change Δn due to light-induced birefringence is adjusted.
[0004]
That is, assuming that the wavelength of the signal light is λ and m is an integer, when the light transmitted through the optical recording medium is used as reproduction light at the time of reading, the optical recording layer forms a half-wave plate,
Δn × d = (m + 1/2) λ (21)
And
[0005]
In addition, when using the light reflected by the optical recording medium at the time of reading as reproducing light, the optical recording layer forms a quarter-wave plate,
Δn × d = (m + 1/4) λ (22)
In addition, a light reflection layer is formed on the back surface of the optical recording layer.
[0006]
When linearly polarized signal light is irradiated to the optical recording layer of such an optical recording medium, birefringence is induced in the optical recording layer, and a half-wave plate or a quarter-wave plate in the polarization plane direction of the signal light is generated. By forming and rotating the polarization plane direction (polarization angle) of the signal light, the direction of the half-wave plate or the quarter-wave plate is rotated. Therefore, the multi-value data can be recorded by changing the polarization angle of the signal light according to the value of the multi-value data.
[0007]
At the time of reading, the portion of the optical recording layer on which the half-wave plate or quarter-wave plate having a specific orientation was formed was irradiated with readout light having an arbitrary polarization angle and transmitted through the optical recording medium. A change in the polarization angle of the reading light or the reading light reflected by the light reflecting layer on the back surface of the optical recording layer is detected.
[0008]
This change in the polarization angle of the reading light corresponds to twice the difference between the polarization angle of the reading light for reading and the polarization angle of the recorded signal light. Therefore, the value of the recorded multi-value data can be read by detecting the change in the polarization angle of the reading light.
[0009]
On the other hand, the method disclosed in Japanese Patent Laid-Open No. 10-340479 records signal light having a two-dimensional spatial polarization distribution as a hologram. In this method, for example, as shown as vectors D1 to D6 in FIG. Six polarization angles are set as the polarization angles of the signal light within the range from polarization to 90 ° polarization. The six polarization angles can be encoded to represent six bits and can be a number to the base 6 or a binary encoded number to the sixth power.
[0010]
As shown in FIG. 16, assuming that the signal light 1 has pixels 4 distributed two-dimensionally, the polarization angle of the signal light portion of each pixel 4 is changed according to the value of the multi-value data of the corresponding pixel.
[0011]
In the method disclosed in Japanese Patent Laid-Open No. 10-340479, the signal light 1 is irradiated onto the optical recording layer of the optical recording medium, and at the same time, the reference light having an arbitrary polarization angle is irradiated onto the area of the optical recording layer irradiated with the signal light 1. Thus, the spatial polarization distribution of the signal light 1 is recorded as a hologram.
[0012]
At the time of reading, a reference light beam having an arbitrary polarization angle is irradiated to the area where the hologram of the optical recording medium is recorded, and diffracted light having the same polarization distribution as that of the signal light 1 is obtained from the hologram, as shown in FIG. Then, the diffracted light 6 is separated into a 0 ° polarization component 7 and a 90 ° polarization component 8 by a polarization element such as a polarization beam splitter 26, and the 0 ° polarization component 7 is detected by a photodetector array 27, and 90 ° The polarization component 8 is detected by the photodetector array 28.
[0013]
Further, as shown in the figure, for each pixel, the output I0 of the photodetector array 27 and the output I90 of the photodetector array 28 are converted into polarized light comprising a division circuit 41, a square root calculation circuit 42, and an arctangent calculation circuit 43. The angle calculation circuit 40 is supplied to calculate the polarization angle of the diffracted light of the pixel.
[0014]
If the light intensity of the diffracted light of a pixel is I and the polarization angle is θ, the detection light intensity I0 of the 0 ° polarization component 7 and the detection light intensity I90 of the 90 ° polarization component 8 are respectively
I0 = Icos ² θ (23)
I90 = Isin ² θ (24)
It becomes.
[0015]
Therefore, by dividing the output I90 by the output I0 by the division circuit 41, tan ² θ is obtained from the division circuit 41, tan θ is obtained from the square root calculation circuit 42, and the polarization angle θ is obtained from the arctangent calculation circuit 43. .
[0016]
As described above, according to the method disclosed in Japanese Patent Laid-Open No. 10-340479, the value of multi-value data can be read from the polarization angle θ. In the method disclosed in Japanese Patent Application Laid-Open No. 11-238251, the value of multi-value data can be read by calculating the polarization angle using a similar polarization angle calculation circuit.
[0017]
[Problems to be solved by the invention]
However, the conventional method described above requires the polarization angle calculation circuit 40 including the division circuit 41, the square root calculation circuit 42, and the arctangent calculation circuit 43 in order to read the value of the multilevel data. Becomes complicated and expensive, and the reading speed becomes slow.
[0018]
Furthermore, these methods have a problem that an error occurs in the read polarization angle due to noise caused by external light or noise caused by the optical recording medium.
[0019]
FIG. 18 shows the detected light intensity I0 of the 0 ° polarization component 7 of the diffracted light 6 when a certain level of noise of 20% of the intensity of the signal light is added in the range of the polarization angle θin from 0 ° to 90 °. 19 shows the detected light intensity I90 of the 90 ° polarization component 8, and FIG. 19 shows the recorded signal of the polarization angle θout calculated from the detected light intensities I0 and I90 by the polarization angle calculation circuit 40 shown in FIG. The relationship with respect to the polarization angle θin of light is shown. The straight line 51 is when there is noise as shown in FIG. 18, and the straight line 52 is when there is no noise.
[0020]
As is clear from FIG. 19, in the presence of noise, the error becomes zero at θin = 45 °, but an error occurs as the polarization angle θin goes away from 45 °, and the error occurs at θin = 0 ° and θin = 90 °. It reaches nearly 10%.
[0021]
Therefore, in the conventional method, the multi-value that can be recorded by the difference in the polarization angle of the signal light without causing a reading error regardless of noise is at most about 8 values, and it is not possible to record a multi-value higher than that. Difficult, therefore high density recording is difficult. In particular, as shown in FIG. 16, when recording the signal light 1 with various polarization angles distributed in each pixel 4, the influence of noise is different for each pixel 4, which may cause a larger reading error. is there.
[0022]
For example, in order to record 8-bit data in one pixel, the polarization angle needs to be multi-valued over 256 gradations, and a method that can reduce the influence of noise caused by external light and noise caused by the optical recording medium is desired. It is.
[0023]
Therefore, the present invention can read the value of multi-value data at high speed with a simple and low-cost reading device, and can reduce the influence of noise caused by external light and noise caused by the optical recording medium. A multi-valued, higher-density recording can be realized.
[0024]
[Means for Solving the Problems]
In the optical recording method of the present invention,
Signal light having polarization of a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity The canceling light wave is combined, and the combined light wave is recorded on the optical recording medium as recording light.
[0025]
In the optical reading method of the present invention,
Signal light having polarization of a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity Read the reproduction light having the same wavefront as the recording light from the optical recording medium on which the recording light generated by combining the canceling light wave is recorded,
Separate the polarization components of the read reproduction light that are orthogonal to each other, detect the light intensity of the two separated polarization components, calculate the difference between the two detected light intensities, and calculate the value of the multi-value data. read. Alternatively, the read reproduction light is transmitted through the polarization element, the polarization components orthogonal to each other in the reproduction light are interfered with a phase difference π, and the value of the multi-value data is read from the intensity of the light transmitted through the polarization element. .
[0026]
[Action]
In the above method, at the time of reading, the value of multi-value data can be read simply by calculating the difference between the two detected light intensities, or by only allowing the read reproduction light to pass through the polarizing element and enter the photodetector. The value of multi-value data can be read at high speed with a simple and low-cost reading device.
[0027]
In addition, by calculating the difference between the two detected light intensities, it is possible to cancel noise caused by external light and noise caused by the optical recording medium, and reduce the influence of noise. In addition, when coherent noise such as noise caused by the optical recording medium is dominant, the readout reproduction light is transmitted through the polarizing element and incident on the photodetector to cancel the noise similarly. And the influence of noise can be reduced.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiments of Optical Recording Method and Optical Reading Method ... FIGS. 1 to 12]
As an embodiment of the optical recording method and the optical reading method of the present invention, a case where recording light is recorded as a hologram and reproduction light is read as hologram diffraction light is shown. However, the present invention can also be applied to a case where a hologram is not used as will be described later.
[0029]
(Embodiment of optical recording method: FIGS. 1 and 2)
In the optical recording method of the present invention, as shown in FIG. 1, the signal light 1 and the noise canceling light wave 2 are combined, and the combined light wave 3 is used as recording light. It is assumed that the noise canceling light wave 2 has polarized light with a certain polarization angle (this is 0 ° polarized light) and has a constant light intensity | Enc | ² . The signal light 1 has polarized light orthogonal to the noise canceling light wave 2 (which is 90 ° -polarized light), and the light intensity that has been multi-valued according to the value s (s is an integer) of the multi-value data | It shall have a ^{2 |} Es. In other words, the light intensity | Es | ² of the signal light 1 is set to a value at an equal interval according to the value s of the multi-value data.
[0030]
When transferring multi-value data at a high speed, as shown in FIG. 2, it is assumed that the recording light 3 is two-dimensionally distributed in the pixels 4, and the signal light components (90 ° polarization) of the recording light portions of the respective pixels 4 are used. The light intensity of the component is changed in accordance with the value s of the multi-value data of the corresponding pixel.
[0031]
When recording the recording light 3 as a hologram, the recording light 3 is irradiated onto the optical recording medium, and at the same time, the reference light having an arbitrary polarization angle is irradiated onto the area of the optical recording medium irradiated with the recording light 3. As the optical recording medium, one having an optical recording layer exhibiting light-induced birefringence is used.
[0032]
(First Embodiment of Optical Reading Method ... FIGS. 3 to 8)
At the time of reading, a reference light beam having an arbitrary polarization angle is irradiated onto the area where the hologram of the optical recording medium is recorded, and diffracted light having the same wavefront as that of the recording light 3 is obtained from the hologram, as shown in FIG. The diffracted light 6 is separated into a 0 ° polarization component 7 and a 90 ° polarization component 8 by a polarization element such as a polarization beam splitter 26, and the 0 ° polarization component 7 is detected by a photodetector array 27, and 90 ° polarization is performed. The component 8 is detected by the photodetector array 28, and the subtraction circuit 29 calculates the difference (I0-I90) between the output I0 of the photodetector array 27 and the output I90 of the photodetector array 28 for each pixel. To do.
[0033]
If the thickness of the optical recording medium is not uniform or scattered due to this, the diffraction efficiency of the optical recording medium changes depending on the location, and noise is generated. Noise caused by this optical recording medium can be considered as coherent noise. On the other hand, noise due to outside light is considered as incoherent noise. However, for the same pixel, the noise generated in the 0 ° polarization component 7 and the noise generated in the 90 ° polarization component 8 are considered to have substantially the same light intensity.
[0034]
Therefore, if the light intensity of the incoherent noise generated in the 0 ° polarization component 7 and the 90 ° polarization component 8 is Iin, and the light intensity of the coherent noise is Ic, the detection light intensity I0 and 90 ° polarization of the 0 ° polarization component 7 The detected light intensity I90 of the component 8 is represented by the equations (1) and (2) in FIG. 4, respectively, and the output (I0-I90) of the subtracting circuit 29 is represented by the equation (3) in FIG. As described above, both the incoherent noise component Iin and the coherent noise component Ic are canceled and proportional to the difference between the light intensity | Enc | ^{2 of} the noise canceling light wave ² and the light intensity | Es | ² of the signal light 1. Will be.
[0035]
Moreover, the light intensity | Enc | ² of the noise canceling light wave 2 in the output (I 0 -I 90) of the subtracting circuit 29 is constant regardless of the value s of the recorded multi-value data, and the light of the signal light 1 Intensity | Es | ² is a value of skipping at equal intervals according to the value s of the recorded multilevel data, and the output (I0-I90) of the subtraction circuit 29 is the value s of the recorded multilevel data. Changes linearly.
[0036]
Therefore, the value s of the recorded multi-value data can be accurately read from the output (I0-I90) of the subtraction circuit 29 without causing a read error.
[0037]
That is, in the method disclosed in Japanese Patent Laid-Open No. 10-340479, the detection light intensity I0 of the 0 ° polarization component 7 and the 90 ° polarization component 8 of the diffracted light 6 are detected as shown in the equations (23) and (24) and FIG. The light intensity I90 changes relatively linearly with respect to the polarization angle θin when the polarization angle θin is around 45 °, but it changes with respect to the polarization angle θin when the polarization angle θin is near 0 ° or near 90 °. Since it changes slowly and nonlinearly, when the polarization angle θin is near 0 ° and 90 °, an error occurs in the read polarization angle θout due to noise caused by external light and noise caused by the optical recording medium.
[0038]
On the other hand, according to the above-described method of the present invention, noise caused by external light and noise caused by the optical recording medium are canceled, and the output (I0-I90) of the subtracting circuit 29 is the recorded multi-value data. Since it changes linearly with respect to the value s, the value s of the recorded multi-value data can be read accurately without causing a reading error.
[0039]
Moreover, since only the difference (I0−I90) between the two detected light intensities I0 and I90 is calculated, the value s of the multivalued data can be read at high speed with a simple and low-cost reading device.
[0040]
In this case, as a specific example, as shown in Expression (4) of FIG. 5A and the table of FIG. 5B, the amplitude Es of the signal light 1 is changed to the square root and the amplitude E of the value s of the multivalued data. The product of The amplitude E is set as the amplitude of the signal light 1 when s = 1.
[0041]
In this case, the intensity | Es | ² of the signal light 1 becomes s | E | ² , and the output (I0−I90) of the subtraction circuit 29 is proportional to (| Enc | ² −s | E | ² ). As shown in FIG. 6, the larger the value s of the multi-value data, the smaller the value interval becomes in proportion to | E | ² .
[0042]
As another specific example, the amplitude Es of the signal light 1 is set to the square root of the above (| Enc | ² −s | E | ² ) as shown in the equation (5) of FIG.
[0043]
In this case, the intensity | Es | ² of the signal light 1 becomes (| Enc | ² −s | E | ² ), and the output (I 0 −I 90) of the subtraction circuit 29 is expressed by Equation (6) in FIG. as shown, s | E | ² and is obtained by proportional, in 0 when s = 0, and | E | ² at intervals proportional to the value, as shown in FIG. 8, the multi-level data value Since s increases as s increases, the value s of the recorded multi-value data can be read more directly from the output (I0-I90) of the subtraction circuit 29.
[0044]
(Second Embodiment of Optical Reading Method ... FIGS. 9 to 12)
When coherent noise such as noise caused by an optical recording medium is dominant, optical subtraction before light detection is used instead of circuit subtraction after light detection as shown in FIG. Can cancel the noise.
[0045]
In this case, as shown in FIG. 9, the diffracted light 6 from the hologram is made incident on the polarizer 31, and the transmission axis direction of the polarizer 31 is changed to 0 ° polarization component and 90 ° polarization component in the diffracted light 6. The light passing through the polarizer 31 is detected by the photodetector array 32 in the direction of 135 ° that causes interference with a phase difference π.
[0046]
FIG. 10 shows the relationship between the 0 ° polarization component and the 90 ° polarization component and the transmission axis direction of the polarizer 31 where E0 is the amplitude of the 0 ° polarization component in the diffracted light 6 and E90 is the amplitude of the 90 ° polarization component. It is a thing.
[0047]
For the same pixel, the coherent noise generated in the 0 ° polarization component and the coherent noise generated in the 90 ° polarization component have substantially the same amplitude, so the amplitude of the coherent noise generated in the 0 ° polarization component and the 90 ° polarization component is represented by Ec. Then, the amplitude E0 of the 0 ° polarization component and the amplitude E90 of the 90 ° polarization component are expressed by the equations (7) and (8) in FIG. 11, respectively.
[0048]
The transmitted light of the polarizer 31 is output as a result of interference between the 0 ° polarization component represented by the equation (7) and the 90 ° polarization component represented by the equation (8) with a phase difference π. The detected light intensity of the output of the photodetector array 32 is represented by | E0−E90 | ² , and the noise component Ec is canceled as shown in the equation (9) of FIG. This is proportional to the square of the difference between the amplitude Enc of the light wave 2 and the amplitude Es of the signal light 1.
[0049]
Therefore, the value s of the multi-value data can be read at a high speed by a simpler and lower cost reading device than in the case of subtraction after circuit detection as shown in FIG.
[0050]
In this case, as a specific example, as shown in the equation (10) of FIG. 12, the amplitude Es of the signal light 1 is calculated from the amplitude Enc of the noise canceling light wave 2 by the square root of the value s of the multivalued data and the amplitude E. The product is subtracted. The amplitude E is set as the amplitude of the signal light 1 when s = 1.
[0051]
In this case, the output | E0-E90 | ² of the photodetector array 32 is proportional to s | E | ² as shown in the equation (11) of FIG. As the value s of the multi-valued data increases as the value s of the multi-value data increases at an interval of 0 and proportional to | E | ² , from the output | E 0 -E 90 | ^{2 of the} photodetector array 32, The value s of the recorded multi-value data can be read more directly.
[0052]
[Embodiments of Optical Recording Device and Optical Reading Device ... FIGS. 13 and 14]
FIG. 13 shows an embodiment of the optical recording apparatus and the optical reading apparatus of the present invention, in which the recording light is recorded as a hologram and the reproduction light is read out as a hologram diffracted light, and after light detection as shown in FIG. This is a case where incoherent noise and coherent noise are canceled by this circuit subtraction, and an optical recording device and an optical reading device are integrated.
[0053]
Any optical recording medium 9 may be used as long as it has an optical recording layer exhibiting light-induced birefringence. As the light source 11, a light source that emits sensitive laser light to the optical recording layer of the optical recording medium 9 is used.
[0054]
Laser light from the light source 11 is incident on the beam splitter 12, splits into light transmitted through the beam splitter 12 and light reflected by the beam splitter 12, and the light transmitted through the beam splitter 12 is converted into lenses 13 and 14. After that, collimated light having a wide aperture is made incident on the polarization beam splitter 15 and transmitted through the polarization beam splitter 15. The light is polarized perpendicular to the paper surface (this is 90 ° polarization), and the polarization beam splitter 15 The light is branched into reflected polarized light parallel to the paper surface (this is 0 ° polarized light).
[0055]
The 90 ° -polarized light that has passed through the polarization beam splitter 15 is incident on the spatial light modulator 16 for amplitude (intensity) modulation, and the value of the multi-value data of each pixel is set to each pixel of the spatial light modulator 16. As the light transmitted through the spatial light modulator 16 by applying a corresponding voltage, the amplitude Es of each pixel portion is expressed by the equation (4) in FIG. 5A or the equation (5) in FIG. Signal light 1 is obtained. However, the amplitude Enc in the equation (5) is the amplitude of the 0 ° polarized light reflected by the polarization beam splitter 15 and the noise canceling light wave 2 described later.
[0056]
FIG. 14 (A) shows an example of the signal light 1, and the difference in the vector size of each pixel portion represents the difference in amplitude of each pixel portion, and the filled pixel portion has zero amplitude. Show.
[0057]
The signal light 1 transmitted through the spatial light modulator 16 is incident on another polarization beam splitter 17. Further, the 0 ° -polarized light reflected by the polarization beam splitter 15 is reflected by the mirrors 18 and 19 as the noise canceling light wave 2 and is incident on the polarization beam splitter 17. FIG. 14B shows an example of the light wave 2 for noise cancellation, and the fact that the vector sizes of the pixel portions are equal indicates that the amplitudes of the pixel portions are equal.
[0058]
Then, the polarization beam splitter 17 combines the signal light 1 and the noise canceling light wave 2 to generate the recording light 3 as shown in FIG. 14C, and the recording light 3 is collected by the lens 21. Light is applied to the optical recording medium 9.
[0059]
At the same time, the light reflected by the beam splitter 12 is further reflected by the mirrors 23 and 24, and is irradiated as the reference light 5 onto the region where the recording light 3 of the optical recording medium 9 is irradiated. As a result, the recording light 3 is recorded as a hologram on the optical recording layer of the optical recording medium 9.
[0060]
At the time of reading, the recording light 3 is blocked by the shutter 22, and only the reference light 5 is irradiated to the area where the hologram of the optical recording medium 9 is recorded. Thereby, diffracted light 6 having the same wavefront as that of the recording light 3 is obtained from the hologram.
[0061]
The diffracted light 6 is converted into collimated light by the lens 25, then incident on the polarization beam splitter 26, reflected by the polarization beam splitter 26, and 90 ° polarization component 8 transmitted through the polarization beam splitter 26. And the 0 ° polarization component 7 is detected by the photodetector array 27, the 90 ° polarization component 8 is detected by the photodetector array 28, and the photodetector array for each pixel in the subtraction circuit 29. The difference between the output of 27 and the output of the photodetector array 28 is calculated.
[0062]
The above is a case where incoherent noise and coherent noise are canceled by circuit subtraction after light detection. However, when coherent noise such as noise caused by the optical recording medium 9 is dominant, At the time of recording, as the light transmitted through the spatial light modulator 16, the signal light 1 in which the amplitude Es of each pixel portion is represented by the equation (10) in FIG. 12 is obtained, and the recording light 3 is recorded as a hologram. At the time of reading, as shown in FIG. 9, the diffracted light 6 is incident on the polarizer 31, the transmission axis direction of the polarizer 31 is changed, and the phase difference between the 0 ° polarization component and the 90 ° polarization component in the diffracted light 6 is π. The light transmitted through the polarizer 31 in the azimuth direction of 135 ° caused to interfere with each other can be detected by the photodetector array 32.
[0063]
Further, the optical recording device and the optical reading device may be configured separately.
[0064]
[Other Embodiments]
The embodiment described above is a case where recording light is recorded as a hologram and reproduction light is read out as hologram diffracted light. However, the present invention can also be applied to a case where no hologram is used.
[0065]
In this case, when the light transmitted through the optical recording medium is used as reproduction light at the time of reading, the recording light 3 after the signal light 1 and the noise canceling light wave 2 are combined on the optical recording layer of the optical recording medium. When the light reflected by the optical recording medium is used as reproduction light at the time of reading, the optical recording layer of the optical recording medium is formed with the same recording light 3. Is formed so that a quarter-wave plate is formed, and a light reflecting layer is formed on the back surface of the optical recording layer.
[0066]
【The invention's effect】
As described above, according to the present invention, the value of multi-value data can be read at high speed by a simple and low-cost reading device, and the influence of noise caused by external light and noise caused by an optical recording medium is reduced. Therefore, it is possible to realize a multi-value and higher-density recording.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an optical recording method of the present invention.
FIG. 2 is a diagram illustrating an example of recording light.
FIG. 3 is a diagram showing a first embodiment of an optical reading method according to the present invention.
FIG. 4 is a diagram illustrating that noise is canceled in the case of FIG. 3;
5 is a diagram illustrating an example of the amplitude of signal light in the case of FIG. 3; FIG.
6 is a diagram illustrating a relationship between multi-value data values and a subtraction result in the case of FIG. 5;
7 is a diagram showing another example of the amplitude of the signal light in the case of FIG.
8 is a diagram showing the relationship between the multi-value data value and the subtraction result in the case of FIG.
FIG. 9 is a diagram showing a second embodiment of the optical reading method of the present invention.
10 is a diagram showing a transmission axis direction of a polarizer in the case of FIG.
FIG. 11 is a diagram illustrating that noise is canceled in the case of FIG. 9;
12 is a diagram illustrating an example of the amplitude of signal light in the case of FIG. 9;
FIG. 13 is a diagram showing an embodiment of an optical recording apparatus and an optical reading apparatus according to the present invention.
14 is a diagram showing an example of each light wave in the embodiment of FIG.
FIG. 15 is a diagram illustrating an example of a conventional optical recording method.
16 is a diagram illustrating an example of a polarization distribution of signal light in the method of FIG.
17 is a diagram showing a conventional optical reading method corresponding to the optical recording method of FIG.
FIG. 18 is a diagram for explaining the influence of noise in the method of FIG. 17;
FIG. 19 is a diagram for explaining the influence of noise in the method of FIG. 17;
[Explanation of symbols]
1 ... Signal light,
2. Light wave for noise cancellation,
3. Recording light,
4 ... Pixel,
5 ... Reference light,
6 ... Diffracted light,
7: 0 ° polarization component,
8 ... 90 ° polarization component,
9: Optical recording medium,
11 ... Light source,
12 ... Beam splitter,
13, 14 ... lens,
15 ... Polarizing beam splitter,
16 ... Spatial light modulator,
17 ... Polarizing beam splitter,
18, 19 ... Mirror,
21 ... Lens,
22 ... Shutter,
23, 24 ... Mirror,
25 ... Lens,
26: Polarizing beam splitter,
27, 28 ... photodetector array,
29: Subtraction circuit,
31 ... Polarizer,
32. Photodetector array.

Claims (8)

  Signal light having polarization with a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity An optical recording method of combining a canceling light wave and recording the combined light wave on an optical recording medium as recording light. The optical recording method according to claim 1, wherein
An optical recording method for recording the recording light as a hologram by interfering with a reference light. A light source;
A modulation element that generates signal light having light of a certain polarization angle from light from the light source and having multi-valued light intensity according to the value of multi-value data;
An optical element that generates a light wave for noise cancellation having a constant light intensity and having a polarization orthogonal to the signal light from the light from the light source;
An optical element for combining the signal light and the noise canceling light wave;
An imaging optical system that irradiates the optical recording medium with the combined light wave as recording light,
An optical recording apparatus comprising: In the optical recording device of claim light 3,
An optical recording apparatus comprising an optical element that generates reference light for recording the recording light as a hologram on the optical recording medium. Signal light having polarization of a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity Read the reproduction light having the same wavefront as the recording light from the optical recording medium on which the recording light generated by combining the canceling light wave is recorded,
The read-out reproduction light is separated from the orthogonal polarization components, the light intensities of the two separated polarization components are detected, the difference between the two detected light intensities is calculated, and the value of the multi-value data is calculated. Optical reading method to read. Signal light having polarization of a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity Read the reproduction light having the same wavefront as the recording light from the optical recording medium on which the recording light generated by combining the canceling light wave is recorded,
Light that reads the read multi-value data from the intensity of the light transmitted through the polarization element by causing the read-out reproduction light to pass through the polarization element, causing the orthogonal polarization components in the reproduction light to interfere with each other with a phase difference of π. Reading method. Signal light having polarization of a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity A reproduction optical system that reads out reproduction light having the same wavefront as the recording light from an optical recording medium in which recording light generated by combining the canceling light wave is recorded;
A polarizing element that separates polarization components of the read reproduction light that are orthogonal to each other;
A photodetector for detecting the light intensity of the two separated polarization components;
A computing means for calculating the difference between the two detected light intensities;
An optical reader comprising: Signal light having polarization of a certain polarization angle and having light intensity converted into multi-value according to the value of multi-value data, and noise having polarization orthogonal to the signal light and having constant light intensity A reproduction optical system that reads out reproduction light having the same wavefront as the recording light from an optical recording medium in which recording light generated by combining the canceling light wave is recorded;
A polarizing element that is arranged on the optical path of the read reproduction light and that interferes with mutually orthogonal polarization components in the reproduction light with a phase difference of π;
A photodetector for detecting the intensity of light transmitted through the polarizing element;
An optical reader comprising:

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