JP2001291242A - Optical recording method, optical recorder, optical reading method and optical reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of the noise due to the external light or the noise caused by an optical recording medium and to realize the multi-valued and high density recording. SOLUTION: A light wave 2 for noise cancellation has a constant light intensity with a polarization of 0 deg.. A signal light 1 has a light intensity with polarization of 90 deg. multi-valued in accordance with a value s of multi-valued data. The signal light 1 and the light wave 2 for noise cancellation are combined, and a light wave 3 prepared by the combination is recorded on the optical recording medium as a recording light. Reproducing light having the same wave front as that of the recording light 3 is read out from the optical recording medium at the reading time, and the polarization components of the reproducing light orthogonally crossed each other are separated to figure out the difference of light intensity between two polarization components. By this procedure, the noise is cancelled, and a value s of the recorded multi-valued data is read out without error. In the case the coherent noise caused by the optical recording medium is dominative, the reproducing light is made to pass through a polarization element, and the polarization components in the reproducing light orthogonally crossed each other are brought to interference with the phase difference π, then the value s of the multi-valued data is read out from the intensity of the light transmitted through the polarization element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for optically recording and optically reading multi-value data.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open Nos. 11-238251 and 10-3404 disclose optical recording of multi-value data.
No. 79 uses an optical recording medium having an optical recording layer exhibiting photoinduced birefringence, and changes the polarization angle (polarization direction) of the signal light according to the value of the multi-level data to convert the signal light into light. A method of recording on a recording medium has been proposed.

In the method disclosed in Japanese Patent Application Laid-Open No. H11-238251,
The thickness d of the optical recording layer and the refractive index change Δn due to photoinduced birefringence are set so that the optical recording layer of the optical recording medium exhibiting photoinduced birefringence forms a half-wave plate or a quarter-wave plate. adjust.

That is, assuming that the wavelengths of signal light are λ and m are integers, when light transmitted through an 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 + ／) λ (21)

[0005] When light reflected by the optical recording medium is used as reproduction light at the time of reading, Δn × d = (m + ／) λ so that the optical recording layer forms a を wavelength plate. (22) A light reflection layer is formed on the back surface of the optical recording layer.

When the optical recording layer of such an optical recording medium is irradiated with linearly polarized signal light, 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 induced. A wave plate is formed, and by rotating the polarization plane direction (polarization angle) of the signal light, a half wave plate or 1
The orientation of the quarter wave plate rotates. Therefore, by changing the polarization angle of the signal light according to the value of the multi-value data, the multi-value data can be recorded.

At the time of reading, a portion where a half-wave plate or a quarter-wave plate in a specific direction is formed by signal light of the optical recording layer is irradiated with read light having an arbitrary polarization angle.
A change in the polarization angle of the reading light transmitted through the optical recording medium or the reading light reflected by the light reflecting layer on the back surface of the optical recording layer is detected.

[0008] The 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.

On the other hand, the method disclosed in Japanese Patent Laid-Open No. Hei 10-340479 is to record a signal light having a two-dimensional spatial polarization distribution as a hologram.
As shown as vectors D1 to D6, six polarization angles are set as the polarization angles of the signal light within the range from 0 ° 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 coded number to the sixth power.

As shown in FIG. 16, the signal light 1 assumes that the pixels 4 are two-dimensionally distributed, and 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. Change.

In the method disclosed in Japanese Patent Application Laid-Open No. H10-340479,
At the same time that the signal light 1 is applied to the optical recording layer of the optical recording medium, the region of the optical recording layer where the signal light 1 is applied is irradiated with reference light having an arbitrary polarization angle to change the spatial polarization distribution of the signal light 1. Record as a hologram.

At the time of reading, a region where the hologram is recorded on the optical recording medium is irradiated with reference light having an arbitrary polarization angle, and a diffracted light having the same polarization distribution as the signal light 1 is obtained from the hologram. As shown in FIG.
By a polarizing element such as the polarizing beam splitter 26, 0
The polarization component 7 is separated into the polarization component 7 and the polarization component 90. The polarization component 7 is detected by the photodetector array 27, and the polarization component 8 is detected by the photodetector array 28.

Further, as shown in FIG. 1, for each pixel, the output I0 of the photodetector array 27 and the output I90 of the photodetector array 28 are divided by a division circuit 41, a square root calculation circuit 42, and an arc tangent calculation circuit 43. And calculates the polarization angle of the diffracted light of the pixel.

Assuming that the light intensity of the diffracted light of a pixel is I and the polarization angle is θ, the detected light intensities I 0 and 9 of the 0 ° polarization component 7 are
Detection light intensity I90 of 0 ° polarization component 8, respectively, the ^{I0 = Icos 2 θ ... (23} ) I90 = Isin 2 θ ... (24).

Therefore, by dividing the output I90 by the output I0 in the division circuit 41, the division circuit 41
n ² θ is obtained, tan θ is obtained from the square root calculation circuit 42, and the polarization angle θ is obtained from the arc tangent calculation circuit 43.

As described above, according to the method disclosed in Japanese Patent Application Laid-Open No. Hei 10-340479, the value of multi-value data can be read from the polarization angle θ. In the method of JP-A-11-238251,
By calculating the polarization angle by the same polarization angle calculation circuit, the value of the multi-value data can be read.

[0017]

However, in the conventional method described above, the polarization angle calculation circuit 40 including the division circuit 41, the square root calculation circuit 42 and the arc tangent calculation circuit 43 is used to read the value of the multi-value data. Because of the necessity, the configuration of the reading device becomes complicated and expensive, and the reading speed is reduced.

Further, these methods have a problem that an error occurs in the polarization angle to be read due to noise due to external light or noise due to the optical recording medium.

FIG. 18 shows that the polarization angle θin is from 0 ° to 90 °.
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 up to
FIG. 19 shows the detected light intensity I0 of the 90 ° polarization component 8 and the detected light intensity I90 of the 90 ° polarization component 8.
17 shows the relationship between the polarization angle θout calculated by the polarization angle calculation circuit 40 shown in FIG. 17 and the polarization angle θin of the recorded signal light. A straight line 51 is a case where there is noise as shown in FIG. 18, and a straight line 52 is a case where there is no noise.

As apparent from FIG. 19, when there is noise, the error becomes zero at θin = 45 °, but an error occurs as the polarization angle θin departs from 45 °, and θin
At 0 ° and θin = 90 °, the error approaches 10%.

Therefore, in the conventional method, irrespective of noise, multi-values that can be recorded by a difference in the polarization angle of the signal light without causing a reading error are at most about eight values, and more multi-values are recorded. It is difficult to perform high-density recording. In particular, as shown in FIG. 16, the signal light 1 in which the polarization angle is variously distributed in each pixel 4.
Is recorded, since the influence of noise differs for each pixel 4, there is a possibility that a larger reading error may occur.

For example, in order to record 8-bit data in one pixel, it is necessary to make the polarization angle multi-valued over 256 gradations, and it is possible to reduce the influence of noise due to external light and noise due to the optical recording medium. A method is desired.

Therefore, the present invention can read multi-value data at high speed with a simple and low-cost reading device, and reduce the influence of noise due to external light and noise caused by an optical recording medium. Thus, it is possible to realize multi-valued and higher-density recording.

[0024]

According to the optical recording method of the present invention, there is provided a signal light having a polarization of a certain polarization angle and having a light intensity multi-valued according to the value of multi-value data; Light having a polarization perpendicular to the light, and a light wave for noise cancellation having a constant light intensity are combined, and the combined light wave is
Recording is performed on an optical recording medium as recording light.

According to the optical reading method of the present invention, a signal light having a polarization of a certain polarization angle and having a light intensity multi-valued in accordance with the value of multi-value data, and a polarization orthogonal to the signal light are used. A readout light beam having the same wavefront as the recording light is read from an optical recording medium on which a recording light generated by multiplexing a noise canceling lightwave having a constant light intensity is generated. The polarization components orthogonal to each other of the reproduced light are separated, the light intensity of the two separated polarization components is detected, the difference between the two detected light intensities is calculated, and the value of the multi-value data is read. Alternatively, the read reproduction light is transmitted through a polarization element, and mutually orthogonal polarization components in the reproduction light interfere with each other with a phase difference of π, and the value of the multi-value data is read from the intensity of light transmitted through the polarization element. .

[0026]

In the above method, when reading, the difference between the two detected light intensities is simply calculated, or the read reproduction light is transmitted through the polarizing element and incident on the photodetector, and the value of the multi-valued data is obtained. , And the value of the multi-value data can be read at high speed by a simple and low-cost reading device.

Furthermore, by calculating the difference between the two detected light intensities, noise due to external light and noise due to the optical recording medium can be canceled, and the influence of noise can be reduced. When coherent noise such as noise due to an optical recording medium is dominant, the read reproduction light is transmitted through a polarizing element and is incident on a photodetector, thereby similarly canceling the noise. And the effect of noise can be reduced.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment of Optical Recording Method and Optical Reading Method ... FIGS. 1 to 12] As an embodiment of the optical recording method and optical reading method of the present invention, recording light is recorded as a hologram and reproduced. A case where light is read out as hologram diffracted light will be described. However, the present invention can be applied even when a hologram is not used as described later.

(Embodiment of Optical Recording Method: FIGS. 1 and 2) In the optical recording method of the present invention, as shown in FIG. 1, a signal light 1 and a noise canceling light wave 2 are multiplexed, and the multiplexing is performed. The subsequent light wave 3 is used as recording light. It is assumed that the noise canceling lightwave 2 has a polarization of a certain polarization angle (this is defined as 0 ° polarization) and has a constant light intensity | Enc | ² . The signal light 1 has a polarization orthogonal to the noise canceling light wave 2 (this is 90 ° polarization), and has a light intensity | multivalued according to the value s (s is an integer) of the multivalued data. E
s | ² . That is, the light intensity | Es | ² of the signal light 1 is set to discrete values at equal intervals according to the value s of the multi-value data.

In the case of transferring multi-valued data at high speed, as shown in FIG. 2, the recording light 3 is assumed to have a two-dimensional distribution of the pixels 4, and the signal light component of the recording light portion of each pixel 4 ( The light intensity of the 90 ° polarization component is changed according to the value s of the multi-value data of the corresponding pixel.

When the recording light 3 is recorded as a hologram, the recording light 3 is applied to the optical recording medium, and at the same time, the area of the optical recording medium to which the recording light 3 is applied is irradiated with the reference light having an arbitrary polarization angle. . As the optical recording medium, one having an optical recording layer exhibiting photoinduced birefringence is used.

(First Embodiment of Optical Reading Method: FIG. 3)
8) At the time of reading, the area where the hologram is recorded on the optical recording medium is irradiated with reference light having an arbitrary polarization angle, and a diffracted light having the same wavefront as the recording light 3 is obtained from the hologram. As shown in FIG. 7, 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. , 90 ° polarized light component 8 is detected by the photodetector array 28, and the subtraction circuit 2
9, for each pixel, the difference between the output I0 of the photodetector array 27 and the output I90 of the photodetector array 28 (I0−
I90) is calculated.

If the thickness of the optical recording medium is non-uniform or scattered due to this, the diffraction efficiency of the optical recording medium changes depending on the location and noise occurs. The noise caused by the optical recording medium can be considered as coherent noise. On the other hand, noise due to external light is considered to be 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.

Therefore, the 0 ° polarization component 7 and 90 °
Assuming that the light intensity of the incoherent noise generated in the polarization component 8 is Iin and the light intensity of the coherent noise is Ic, 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 Equation (1) in FIG.
And the expression (2), the output (I0-I90) of the subtraction circuit 29 has the incoherent noise component Iin and the coherent noise component Ic as shown in the expression (3) of FIG. Is also canceled, and becomes 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.

Moreover, the output (I0-I9) of the subtraction circuit 29
0), the light intensity of the noise canceling light wave 2 | Enc
| ² is constant irrespective of the value s of the recorded multilevel data, and the light intensity | Es | ² of the signal light 1 is a discrete value at regular intervals according to the value s of the recorded multilevel data. The output (I0-I90) of the subtraction circuit 29 changes linearly with respect to the value s of the recorded multivalued data.

Therefore, the output (I0-
From I90), the value s of the recorded multi-valued data can be accurately read without causing a reading error.

That is, according to the method disclosed in Japanese Patent Application Laid-Open No. H10-340479, as shown in equations (23) and (24) and FIG. 18, the detected light intensity I0 of the 0 ° polarization component 7 of the diffracted light 6 and the 90 ° polarization component 8 is the polarization angle θi
When n is around 45 °, it changes relatively linearly and relatively largely with respect to the polarization angle θin, but when the polarization angle θin is around 0 ° or 90 °, it gradually changes nonlinearly with respect to the polarization angle θin. Therefore, when the polarization angle θin is around 0 ° or 90 °, an error occurs in the read polarization angle θout due to noise due to external light or noise due to the optical recording medium.

On the other hand, in the above-described method of the present invention, noise due to external light and noise due to the optical recording medium are cancelled, and the output (I0
−I90) changes linearly with respect to the value s of the recorded multivalued data, so that the value s of the recorded multivalued data is
Reading can be performed accurately without causing a reading error.

Furthermore, since only the difference (I0-I90) between the two detected light intensities I0 and I90 is calculated, the value s of the multi-value data can be read at high speed by a simple and low-cost reading device.

In this case, as a specific example, as shown in the equation (4) of FIG. 5A and the table of FIG. 5B, the amplitude Es of the signal light 1 is determined by the square root of the value s of the multilevel data. The product with the amplitude E. The amplitude E is set as the amplitude of the signal light 1 when s = 1.

In this case, the intensity | Es | ² of the signal light 1
Becomes s | E | ² , and the output of the subtraction circuit 29 (I0-I
90) is proportional to (| Enc | ² −s | E | ² ), and at intervals of a value proportional to | E | ² , as shown in FIG. The larger, the smaller.

As another specific example, as shown in the equation (5) in FIG. 7, the amplitude Es of the signal light 1 is changed to the above (| Enc | ²
−s | E | ² ).

In this case, the intensity | Es | ² of the signal light 1
Becomes (| Enc | ² −s | E | ² ), and the subtraction circuit 2
9, the output (I0-I90) is proportional to s | E | ² , as shown in equation (6) of FIG. 7, is 0 when s = 0, and is proportional to | E | ² . At intervals of the calculated values, FIG.
As shown in (1), the value becomes larger as the value s of the multi-valued data increases, so that the value s of the recorded multi-valued data can be read more directly from the output (I0-I90) of the subtraction circuit 29.

(Second Embodiment of Optical Reading Method--FIG. 9)
To FIG. 12) When coherent noise such as noise due to an optical recording medium is dominant, optics before light detection are not performed without circuit subtraction after light detection as shown in FIG. The noise can be canceled by the effective subtraction.

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 set to 90 ° with the 0 ° polarization component in the diffracted light 6.
The light transmitted through the polarizer 31 is detected by the photodetector array 32 with the azimuth of 135 ° causing the polarization component to interfere with the phase difference π.

FIG. 10 shows that the amplitude of the 0 ° polarized light component in the diffracted light 6 is E0, and the amplitude of the 90 ° polarized light component is E90.
The relationship between the polarization component and the 90 ° polarization component and the transmission axis direction of the polarizer 31 is shown.

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. Therefore, the amplitude of the coherent noise generated in the 0 ° polarization component and the 90 ° polarization component is obtained. Is Ec, the amplitude E0 of the 0 ° polarization component and the amplitude E90 of the 90 ° polarization component are expressed by Expressions (7) and (8) in FIG. 11, respectively.

The light transmitted through the polarizer 31 includes a 0 ° polarization component represented by the equation (7) and a 9 ° polarization component represented by the equation (8).
Since the result of interference between the 0 ° polarization component and the phase difference π is output, the detected light intensity of the output of the photodetector array 32 is | E
0-E90 ^| those represented by the result by ^two, as shown in equation (9) in FIG. 11, the noise component Ec is canceled, the amplitude Enc noise cancellation for lightwave 2 and the signal light 1
Is proportional to the square of the difference from the amplitude Es.

Therefore, the value s of the multi-valued data can be read at a higher speed by a simpler and lower-cost reading device than by the circuit-based subtraction after the light detection as shown in FIG.

In this case, as a specific example, the equation (1) shown in FIG.
As shown in (0), the amplitude Es of the signal light 1 is obtained by subtracting the product of the square root of the value s of the multi-level data and the amplitude E from the amplitude Enc of the light wave 2 for noise cancellation. The amplitude E is
It is set as the amplitude of the signal light 1 when s = 1.

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) in FIG. When the value is 0, it is 0 and at intervals of a value proportional to | E | ² , as in FIG. 8, the value increases as the value s of the multi-valued data increases. ^{From 2} , the value s of the recorded multilevel data can be read more directly.

[Embodiment of Optical Recording Apparatus and Optical Reading Apparatus: FIGS. 13 and 14] FIG. 13 shows an embodiment of an optical recording apparatus and an optical reading apparatus according to the present invention, in which recording light is recorded as a hologram. In this case, the reproduction light is read as hologram diffraction light, and the incoherent noise and the coherent noise are canceled by circuit subtraction after light detection as shown in FIG. Are integrated.

The optical recording medium 9 may be of any type as long as it has an optical recording layer exhibiting photoinduced birefringence. As the light source 11, a light source that emits a laser beam having a sensitivity to the optical recording layer of the optical recording medium 9 is used.

The laser light from the light source 11 is made incident on the beam splitter 12, and split 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 a lens. 13
After making the collimated light with a large aperture by (14) and (14),
The polarized light that is incident on the polarizing beam splitter 15 and transmitted through the polarizing beam splitter 15 and is perpendicular to the paper surface (this is
0 ° polarized light) and polarized light parallel to the paper surface reflected by the polarizing beam splitter 15 (this is referred to as 0 ° polarized light).
Branches into the light.

90 transmitted through the polarizing beam splitter 15
The polarized light is converted to a spatial light modulator 16 for amplitude (intensity) modulation.
Is applied to each pixel of the spatial light modulator 16, and a voltage corresponding to the value s of the multi-valued data of each pixel is applied. As light transmitted through the spatial light modulator 16, the amplitude Es of each pixel portion is FIG.
The signal light 1 represented by the equation (4) of (A) or the equation (5) of FIG. 7 is obtained. However, the amplitude Enc in the equation (5)
Is the 0 ° polarization reflected by the polarization beam splitter 15,
This is the amplitude of the light wave 2 for noise cancellation described later.

FIG. 14A shows an example of the signal light 1.
The difference in the magnitude of the vector of each pixel portion indicates the difference in the amplitude of each pixel portion, and the solid pixel portion indicates that the amplitude is zero.

The signal light 1 transmitted through the spatial light modulator 16
Is incident on another polarization beam splitter 17. 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 noise canceling light wave 2, and the fact that the magnitude of the vector of each pixel portion is equal indicates that the amplitude of each pixel portion is equal.

Then, the signal light 1 and the noise canceling light wave 2 are multiplexed by the polarization beam splitter 17, and
4C, the recording light 3 as shown in FIG.
Is condensed by the lens 21 and irradiated on the optical recording medium 9.

At the same time, the light reflected by the beam splitter 12 is further reflected by mirrors 23 and 24 to irradiate the reference light 5 on the area of the optical recording medium 9 where the recording light 3 is irradiated. Thus, the recording light 3 is recorded as a hologram on the optical recording layer of the optical recording medium 9.

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 of the optical recording medium 9 where the hologram is recorded. Thus, a diffracted light 6 having the same wavefront as the recording light 3 is obtained from the hologram.

The diffracted light 6 is converted into a collimated light by a lens 25, and then is incident on a polarization beam splitter 26. The 0 ° polarization component 7 reflected by the polarization beam splitter 26 and the 90 ° transmitted through the polarization beam splitter 26. The light is separated into a polarization component 8, the 0 ° polarization component 7 is detected by the photodetector array 27, and the 90 ° polarization component 8 is detected by the photodetector array 28.
The difference between the output of the photodetector array 27 and the output of the photodetector array 28 is calculated for each pixel.

The above is the case where the incoherent noise and the coherent noise are canceled by the circuit-like subtraction after the light detection, and the case where the coherent noise such as the noise due to the optical recording medium 9 is dominant. In recording, as light transmitted through the spatial light modulator 16 during recording,
The signal light 1 whose amplitude Es of each pixel portion is expressed by the equation (10) in FIG. 12 is obtained, the recording light 3 is recorded as a hologram, and at the time of reading, the diffracted light 6 is read as shown in FIG.
Is incident on the polarizer 31 and the transmission axis direction of the polarizer 31 is set to the 135 ° direction in which the 0 ° polarization component and the 90 ° polarization component in the diffracted light 6 interfere with each other with a phase difference of π. The transmitted light may be detected by the photodetector array 32.

The optical recording device and the optical reading device may be configured separately.

[Other Embodiments] In the above-described embodiment, the recording light is recorded as a hologram, and the reproduction light is read out as a hologram diffracted light. However, the present invention can be applied to a case where no hologram is used. Can be.

In this case, at the time of reading, when light transmitted through the optical recording medium is used as reproduction light, the optical recording layer of the optical recording medium is combined with the signal light 1 and the noise canceling light wave 2 described above. When a half-wave plate is formed by irradiating the recording light 3, and when the light reflected by the optical recording medium is used as the reproduction light at the time of reading, the optical recording layer of the optical recording medium is formed in the same manner. A 波長 wavelength plate is formed by irradiation of the recording light 3 and a light reflection layer is formed on the back surface of the optical recording layer.

[0066]

As described above, according to the present invention, the value of multi-value data can be read at a high speed by a simple and low-cost reading device, and noise due to external light and noise due to an optical recording medium can be obtained. Can be reduced, and higher-valued, higher-density recording can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical recording method according to the present invention.

FIG. 2 is a diagram illustrating an example of a recording light.

FIG. 3 is a diagram showing a first embodiment of the optical reading method of the present invention.

FIG. 4 is a diagram showing that noise is canceled in the case of FIG. 3;

FIG. 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 a multivalued data value and a subtraction result in the case of FIG. 5;

FIG. 7 is a diagram illustrating another example of the amplitude of the signal light in the case of FIG. 3;

FIG. 8 is a diagram illustrating a relationship between a multivalued data value and a subtraction result in the case of FIG. 7;

FIG. 9 is a diagram showing a second embodiment of the optical reading method of the present invention.

FIG. 10 is a diagram illustrating a transmission axis direction of a polarizer in the case of FIG. 9;

11 is a diagram showing that noise is canceled in the case of FIG. 9;

12 is a diagram illustrating an example of the amplitude of the signal light in the case of FIG. 9;

FIG. 13 is a diagram showing one embodiment of an optical recording device and an optical reading device of the present invention.

FIG. 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.

FIG. 17 is a diagram showing a conventional optical reading method corresponding to the optical recording method of FIG.

FIG. 18 is a diagram provided for describing an influence of noise in the method of FIG. 17;

FIG. 19 is a diagram provided for describing an influence of noise in the method of FIG. 17;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Signal light, 2 ... Noise canceling light wave, 3 ... Recording light, 4 ... Pixel, 5 ... Reference light, 6 ... Diffraction light, 7 ... 0 degree polarization component, 8 ... 90 degree polarization component, 9 ... Optical recording medium Reference numeral 11: light source, 12: beam splitter, 13, 14: lens, 15: polarization beam splitter, 16: spatial light modulator, 17: polarization beam splitter, 18, 19: mirror, 21: lens, 22: shutter, 23 , 24 ... mirror, 25 ... lens, 26 ... polarization beam splitter, 27, 28 ... photodetector array, 29 ... subtraction circuit, 31 ... polarizer, 32 ... photodetector array.

Claims (9)

[Claims] 1. A signal light having a polarization of a certain polarization angle and having a light intensity multi-valued according to the value of multi-value data, and a signal light having a polarization orthogonal to the signal light and having a constant value. An optical recording method in which a light wave for noise cancellation having light intensity is multiplexed, and the multiplexed light wave is recorded as recording light on an optical recording medium. 2. The optical recording method according to claim 1, wherein the recording light is recorded as a hologram by interfering with the reference light. 3. A light source, and a modulation element for generating, from light from the light source, signal light having a polarization of a certain polarization angle and having a multi-level light intensity according to a value of multi-level data. An optical element having a polarization orthogonal to the signal light and generating a noise canceling lightwave having a constant light intensity from light from the light source; and combining the signal light and the noise canceling lightwave. An optical recording device, comprising: an optical element that performs the above-described operation; and an imaging optical system that irradiates the combined optical wave onto an optical recording medium as recording light. 4. An optical recording apparatus according to claim 3, further comprising an optical element for generating reference light for recording the recording light as a hologram on the optical recording medium. 5. A signal light having a polarization of a certain polarization angle and having a light intensity multi-valued in accordance with the value of multi-value data, and a signal light having a polarization orthogonal to the signal light and having a constant value. A reproduction light having the same wavefront as the recording light is read from an optical recording medium on which a recording light generated by multiplexing a noise canceling light wave having a light intensity is recorded, and the read reproduction lights are orthogonal to each other. An optical reading method for separating a polarized light component to be detected, detecting light intensity of the separated two polarized light components, calculating a difference between the detected two light intensity, and reading a value of the multi-valued data. 6. A signal light having a polarization of a certain polarization angle and having a light intensity multi-valued according to the value of multi-value data, and a signal light having a polarization orthogonal to the signal light and having a constant polarization. A reproduction light having the same wavefront as the recording light is read from an optical recording medium on which a recording light generated by multiplexing a noise canceling light wave having a light intensity is recorded, and the read reproduction light is polarized by a polarizing element. And a light reading method for reading the value of the multi-level data from the intensity of light transmitted through the polarizing element by causing orthogonally polarized light components in the reproduction light to interfere with each other with a phase difference of π. 7. A signal light having a polarization of a certain polarization angle and having a light intensity multi-valued in accordance with the value of multi-value data, and a signal light having a polarization orthogonal to the signal light and having a constant polarization. A reproduction optical system for reading reproduction light having the same wavefront as the recording light from an optical recording medium on which recording light generated by multiplexing a noise canceling light wave having light intensity is recorded; A polarizing element for separating polarized light components orthogonal to each other of the reproduced light, a photodetector for detecting the light intensity of the separated two polarized light components, and a calculating means for calculating a difference between the detected two light intensity An optical reader comprising: 8. A signal light having a polarization of a certain polarization angle and having a light intensity multi-valued in accordance with the value of multi-value data, and a signal light having a polarization orthogonal to the signal light and having a constant polarization. A reproduction optical system for reading reproduction light having the same wavefront as the recording light from an optical recording medium on which recording light generated by multiplexing a noise canceling light wave having light intensity is recorded; A polarizing element arranged on the optical path of the reproduced light, and interfering with each other the polarized components orthogonal to each other in the reproduced light with a phase difference of π; and a photodetector detecting the intensity of the light transmitted through the polarizing element. Reader. 9. A signal light having a polarization of a certain polarization angle and having a light intensity multi-valued in accordance with the value of the multi-valued data, a signal light having a polarization orthogonal to the signal light and having a constant value. An optical recording medium on which recording light generated by combining a noise canceling light wave having light intensity and generated is recorded.