WO2007138867A1

WO2007138867A1 - Optical information recording method and recording medium

Info

Publication number: WO2007138867A1
Application number: PCT/JP2007/060111
Authority: WO
Inventors: Xiaodi Tan
Original assignee: Optware Corporation
Priority date: 2006-05-26
Filing date: 2007-05-17
Publication date: 2007-12-06
Also published as: JP2007316422A; JP4930980B2

Abstract

[PROBLEMS] To provide an optical information recording method by which hologram size is reduced and recording density is improved, and to provide a recording medium. [MEANS FOR SOLVING PROBLEMS] An optical information recording apparatus records interference fringes of a recording reference beam and an information beam by applying the recording reference beam and the information beam spatially modulated by a spatial light modulator (11) having a plurality of pixels (12) to an recording medium by converging the beams to the recording medium by an objective lens (13). The optical axis (22) of the information beam traveling to the objective lens (13) from the spatial light modulator (11) does not accord with the mth diffracted beam (23) (m=0, ±1, ±2 and so on) diffracted by the spatial light modulator, a spatial modulation pattern (1303) for information beams includes a plurality of reference marks (1306), and a spatial frequency in a region of the reference mark (1306) includes a spatial frequency smaller than the basic spatial frequency of the spatial light modulator.

Description

Specification

Optical information recording method and recording medium

Technical field

The present invention relates to an optical information recording method for recording interference fringes due to interference between information light and reference light as a hologram on a recording medium, and a recording medium on which interference fringes are recorded.

Background art

[0002] Holographic recording in which information is recorded on a recording medium using holography is generally performed by using information light carrying image information constituting recording light and reference light for recording inside the recording medium. This is done by superimposing and writing the interference pattern created at that time on the recording medium. When the recorded information is reproduced, the image information is reproduced by diffracting by the interference pattern by irradiating the recording medium with reproduction reference light (see Patent Document 1).

In recent years, volume holography, particularly digital volume holography, has been developed and attracted attention for practical use for ultra-high density optical recording. Volume holography is a method of writing an interference pattern in three dimensions by actively utilizing the thickness direction of the recording medium. Increasing the thickness increases the diffraction efficiency and increases the recording capacity by using multiple recording. There is a feature that can be planned. Digital volume holography uses the same recording medium and recording method as volume holography, but the image information to be recorded is

This is a computer-oriented holographic recording method that is limited to a binary digital pattern. In this digital volume holography, image information such as an analog picture is also digitized and developed into two-dimensional digital pattern information, which is recorded as image information. During playback, the two-dimensional digital pattern information is read and decoded to restore the original image information and display it. As a result, even if the SN ratio (signal-to-noise ratio) is somewhat poor during playback, differential detection is performed, or binary data is coded and error correction is performed, so that the original information is faithfully reproduced. Can be reproduced.

[0004] As an optical recording / reproducing apparatus for performing such holographic recording, the optical axis of the information light and the optical axis of the reference light are coaxial from the same surface side of the recording medium with the information light and the reference light by an object lens. An apparatus for irradiating a recording medium is proposed (Patent Document 1).

In this optical recording / reproducing apparatus, a spatial modulation pattern for information light and a spatial modulation pattern for reference light are provided to a spatial light modulator (also abbreviated as SLM) having a large number of pixels arranged in a lattice pattern. Information light and reference light carrying two-dimensional digital pattern information were generated by changing the state of light phase, intensity, wavelength, etc. for each pixel by a spatial light modulator. A liquid crystal display device may be used as the spatial light modulator, but a DMD (digital 'micromirror' device) may be used. The DMD has a plurality of reflective pixels, and can reflect light by changing the reflection direction for each pixel.

[0006] Since the spatially modulated information light and reference light are irradiated so as to converge on the recording medium by the objective lens, the Fourier transform of the spatial modulation pattern for information light and the spatial modulation pattern for reference light is performed. The converted frequency components form interference fringes.

[0007] FIG. 19 shows a configuration of a pickup of an optical information recording / reproducing apparatus using a DMD. The pick-up 101 is for irradiating the optical information recording medium 151 with reference light and information light and receiving the reproduction light from the optical information recording medium 151. Pickup 101 includes laser light source 103, collimator lens 105, mirror 107, DMD 109, polarization beam splitter 111, relay lens 113, 115, aperture 127, mirror 117, quarter wave plate 119, objective lens 121, ring mask 123, A photodetector 125 is provided.

When information is recorded by the optical information recording / reproducing apparatus in FIG. 19, laser light is emitted from the laser light source 103, converted into parallel rays by the collimator lens 105, and reflected toward the DM D 109 by the mirror 107. The DMD 109 has a plurality of minute mirrors as pixels, and the mirror tilt angle can be changed for each pixel. If the information light spatial modulation pattern and the reference light spatial modulation pattern are displayed on a plurality of pixels of the DMD 109, the reflected light 133 is spatially modulated by the information light spatial modulation pattern and the reference light spatial modulation pattern. Information light and reference light.

The information light and the reference light pass through the polarization beam splitter 111 and propagate so as to form an image on the entrance pupil plane of the objective lens 121 by the pair of relay lenses 113 and 115. On the way, the diffracted light is radiated by the aperture 127 disposed in the focal plane between the pair of relay lenses 113 and 115. Is removed by the mirror 117 and reflected by the mirror 117 toward the objective lens 121, and passes through the quarter-wave plate 119. The objective lens 121 causes information light and recording reference light to interfere with the hologram recording layer 153 of the optical information recording medium 151 to form holography.

In addition, when information is reproduced by the optical information recording / reproducing apparatus in FIG. 19, only the reference modulation spatial modulation pattern for reproduction is displayed on the DMD 109 to generate reproduction reference light, and reproduction reference Light is irradiated onto the interference fringes formed on the hologram recording layer 153 of the optical information recording medium 151 by the objective lens 121. The reproduction light and reproduction reference light reproduced from the interference fringes are reflected by the reflection layer 155 of the optical information recording medium 151, and in the reverse direction, the objective lens 121, the quarter-wave plate 119, the mirror 117, and a pair of relay lenses Propagated via 113 and 115. Here, since the reproduction light and the reproduction reference light change the polarization force S90 ° by passing through the quarter-wave plate 119 twice, the reproduction beam and the reproduction reference light are directed toward the photodetector 125 by the polarization beam splitter 111. The reflected reference light is removed by the ring mask 123, and the reproduced light is incident on the photodetector 125.

Note that the optical information recording medium 151 for recording interference fringes is provided with a hologram recording layer 153 and a reflection layer 155 between two substrates 151a and 151b. The hologram recording layer 153 is mixed with a monomer that is sensitive to information light and reference light, and a part of the monomer reacts with the polymer by interference fringes formed by interference of the information light and reference light. As a result, the optical characteristics such as the refractive index are changed, and interference fringes (holograms) are recorded. That is, by recording the interference fringes, a part of the monomer in the hologram recording layer is consumed. In addition, when the monomer concentration in the recorded portion decreases, the monomer diffuses from the surroundings.

Patent Document 1: Japanese Patent Application Laid-Open No. 2005-32307

Disclosure of the invention

Problems to be solved by the invention

FIG. 20 shows a configuration of a conventional spatial modulation pattern 141 for information light. The spatial modulation pattern 141 for information light is formed by arranging a plurality of block units 143, and each block unit 143 is composed of a reference mark 147 and a symbol unit 145 of a certain amount of two-dimensional pattern information. . [0014] The symbol unit 145 of the two-dimensional pattern information is generated by encoding information to be recorded for each unit of a certain amount of information. In FIG. 20, symbol unit 145 is information to be recorded every 8 bits, and 3 pixels out of 4 × 4 pixels are turned on pixel 145a (indicated by shading in FIG. 20!). , Encoded according to the arrangement of the ON pixels 145a.

[0015] The reference mark 147 is a two-dimensional pattern having a predetermined shape. The position of the entire spatial modulation pattern, the orientation of the entire spatial modulation pattern, and each symbol unit 145 of the two-dimensional pattern information in the spatial modulation pattern. This is a standard for the position or orientation of each symbol unit. Conventionally, the reference mark 147 is represented by turning on all the 4 × 4 square pixels. The symbol unit 145 in FIG. 20 can be recognized as distinguished from the symbol unit 145 if only 4 × 4 pixels are on because only three of the 4 × 4 pixels are on. Can be the standard.

In FIG. 20, a block unit 143 has a 4 × 4 on-pixel 145a at the center as a reference mark 147, and is surrounded by two pixels to obtain a region of 6 × 6 symbol units (24 Arrange 32 symbol units 145 to fill (24 pixels)! In Fig. 20! /, In the spatial modulation pattern for information light 141, there are 4 block units 143 at the top, 6 at the 2nd level, 8 at the 3rd to 6th levels, and 7th level. 6 on the 4th and 4 on the 8th stage. Only the leftmost block unit 143a (indicated by the dotted line) at the top is a configuration in which only the reference mark 147 is arranged at the center, and symbol units of 2D pattern information are arranged around the reference mark 147. Absent. Therefore, the leftmost block unit 143a in the uppermost stage can be distinguished from other block units, and can be used as a reference for the position and orientation of the spatial modulation pattern for information light 141 itself. For example, when the spatial modulation pattern 141 for information light is detected during reproduction, alignment is performed so that the block unit 143a is at the upper left, and then the block unit force on the right of the block unit 143a is also decoded and reproduced in order. can do.

[0017] Furthermore, for each block unit 143, the symbol units are arranged so as to form a square shape with the reference mark 147 as the center. Therefore, the relative position with respect to the reference mark 147 must be specified. Thus, the arrangement of each symbol unit 145 can be specified.

Since the spatial light modulator is an aggregate of minute pixels having a periodic structure, it forms a kind of diffraction grating. The diffraction grating has a diffraction grating period of a, a diffraction light angle of Θ, If the angle is 0, the diffraction order is m (m = 0, ± 1, ± 2), and the light wavelength is

0

Formula 丄: a isin 0 — sm Θ) = m

d 0

Satisfy the relationship.

In the optical information recording / reproducing apparatus of FIG. 19, light 131 from the force of the mirror 107 is incident on the DMD 109 with an incident angle of 0 and is emitted perpendicularly (0 = 0 °) from the DMD 109.

0 1

Is arranged. Figure 21 shows this relationship. The interval between the pixels 13 5 of the DMD 109 is the period a of the diffraction grating, and the angle Θ of the diffracted light 132 is the interval a between the pixels 135 and d

The wavelength of incident light 131 and the angle of incidence Θ force

0

It does not depend on the tilt angle Ψ. On the other hand, the output angle 0 of the reflected light 133 (in FIG. 21—overlapping the third-order diffracted light) is 0 for the incident light 131 and 13 for the DMD 109.

Ten

From an inclination angle Ψ of 5

Equation 2: θ = θ-2Ψ

It depends on. In FIG. 21, since the exit angle 0 of the reflected light 133 is 0 °, the exit angle is

1

Θ is not shown.

1

FIG. 21 shows a case where all the pixels 135 of the spatial light modulator 109 are turned on, and the interval “a” of the pixels 135 is the period of the diffraction grating. However, in the case of a spatial light modulator displaying a spatial modulation pattern for information light or a spatial modulation pattern for reference light, the spatial modulation pattern for information light or the spatial modulation pattern for reference light has an on pixel and an off pixel. Since they are formed in combination, they have various periodic components, and the period of the diffraction grating is not limited to the interval a between adjacent pixels. However, since the pattern displayed in the spatial light modulator 109 is configured with the pixel 135 as a reference unit element, the pixel interval “a” is minimized as the period of the diffraction grating. Therefore, the spatial frequency with all the pixels 135 turned on is called the fundamental spatial frequency in the spatial light modulator.

Conventionally, the optical axes (Θ) of the information light, the recording reference light, and the reproduction reference light reflected and generated by the DMD 109 coincide with the traveling direction (0) of a part of the diffracted light 132. Do

1 d

(Patent Document 1, paragraph 0029). That is, a (sin 0-sin 0) = m

It was constructed so that 1 0 was satisfied and the incident angle Θ was −a ′ sin 0 = πι λ.

0 0

[0022] When a transmissive liquid crystal display device or the like is used as the SLM, light is emitted to the SLM. Because we used light that was incident vertically (0 = 0 °) and emitted vertically (0 = 0 °),

0 1

The incident angle is equal to the outgoing angle, and the 0th-order diffracted light coincides with the optical axis! /.

[0023] In the Japanese Patent Application No. 2005-312513, the present inventor compared the optical information recording / reproducing apparatus with the optical axis of information light from the spatial light modulator toward the objective lens by the spatial light modulator. We proposed an optical information recording device that was constructed so as not to match the diffracted light of the mth order (m = 0, ± 1, ± 2 ···). When the optical axis of the information light is configured so as not to coincide with the diffracted light, the bright spot generated by the fundamental spatial frequency of the spatial light modulator Fourier-transformed by the objective lens is placed in the region with the highest light intensity. The interference fringes can be strengthened and the hologram size can be reduced.

The present invention makes it possible to further reduce the hologram size and increase the recording density when the optical axis of the information light does not coincide with the diffracted light! It is an object of the present invention to provide a possible optical information recording method and recording medium. It is another object of the present invention to provide an optical information recording method and a recording medium that can improve the reliability of recording and reproduction more than ever.

Means for solving the problem

In order to solve the above-described problems, the optical information recording method of the present invention uses a recording reference light and a spatial modulation pattern for information light displayed on a spatial light modulator having a plurality of pixels. Light for recording interference fringes between the recording reference light and the information light in the hologram recording layer of the recording medium by irradiating the spatially modulated information light with the objective lens so as to converge on the recording medium In the information recording method, the optical axial force of the information light directed from the spatial light modulator to the objective lens is m-order (m = 0, ± 1, ± diffracted by the spatial light modulator. 2)), the information light spatial modulation pattern includes a plurality of reference marks, and the spatial frequency in the area of the reference marks is higher than the basic spatial frequency of the spatial light modulator. It includes a small spatial frequency.

[0026] Further, in the optical information recording method, the direction of the optical axis of the information light is within the range of the traveling direction of the (m + O. 2) order to (m + O. 8) order diffracted light. It is preferable. Further, in the spatial light modulator, the plurality of pixels are arranged in a lattice shape, and the optical axis direction of the information light is approximately (m + O) with respect to the diagonal direction of the lattice of the plurality of pixels. 5) Next It is preferable to coincide with the traveling direction of the diffracted light.

Furthermore, in the optical information recording method, it is preferable that the spatial frequency in the area of the reference mark includes a spatial frequency that is half of the fundamental spatial frequency of the spatial light modulator. The reference mark preferably includes a pattern in which pixels having different attributes are alternately arranged.

Furthermore, in the optical information recording method, it is preferable that the direction of the optical axis of the information light is perpendicular to the spatial light modulator.

[0029] Further, the recording medium of the present invention is characterized in that interference fringes are recorded on the hologram recording layer by the optical information recording method.

The invention's effect

[0030] In the optical information recording method of the present invention, bright spots with a plurality of fundamental spatial frequencies are arranged in the strongest region by shifting the optical axis of the outgoing light toward the objective lens from the m-th order diffracted light. And the intensity of the interference fringes can be increased. In addition, the output angle Θ from the spatial light modulator is caused by errors in the tilt angle of the reflective surface of the pixel.

Even if variations occur in 1 and the position of the shape component pattern in the Fourier plane deviates, there are bright spots with multiple fundamental spatial frequencies, so strong intensity can be maintained within the hologram recording area, and reliability can be maintained. Improves.

[0031] Further, conventionally, since a region of very strong light intensity is localized at the center, the monomer concentration in the hologram recording layer of the optical information recording medium is partially depleted. In some cases, the optical information recording method of the present invention has a plurality of bright spots arranged in a region where the light intensity is high. Therefore, if the light intensity distribution in the hologram recording region is compared with the conventional method. Can be averaged. As a result, the monomer concentration also decreases on average, and the multiple recording characteristics can be improved, so that the recording capacity can be increased.

[0032] In addition, in the optical information recording method of the present invention, all the spatial frequency characteristics are indicated by four bright spots located in the vicinity of the optical axis. In this way, the recording area of the hologram can be reduced. Accordingly, the size of each hologram can be reduced, so that more holograms can be recorded and the recording capacity can be increased. [0033] Power! In the optical information recording method of the present invention, the spatial modulation pattern for information light includes a plurality of reference marks, and the spatial frequency in the area of the reference mark is smaller than the basic spatial frequency of the spatial light modulator. Since the frequency is included, the bright spot generated by Fourier transform of the reference mark exists inside the bright spot with the four basic spatial frequencies, and even if the hologram size is reduced, the reference mark does not disappear and reliability is improved. Can be improved. Further, the size of the hologram can be further reduced, and it is possible to improve the recording capacity.

Brief Description of Drawings

[0034] FIG. 1 is a diagram for explaining the relationship of light in the spatial light modulator of the present invention.

[Figure 2] Fourier transform image in a conventional optical information recording / reproducing apparatus

FIG. 3 is a Fourier transform image in the optical information recording / reproducing apparatus of the present invention.

[Fig.4] Diagram explaining synthesis of Fourier transform by one-dimensional Fourier transform waveform

FIG. 5 is a table showing one condition of DMD that can implement the present invention.

[Figure 6] Fourier transform image in comparative example

FIG. 7: Fourier transform image in the present invention

[Fig. 8] Fourier transform image in the present invention

[Fig. 9] Fourier transform image in the present invention.

FIG. 10 is a diagram for explaining the relationship of light in the transmissive spatial light modulator of the present invention.

[FIG. 11] (A) to (C) are diagrams for explaining the relationship between the spatial modulation pattern and the periodicity t.

[FIG. 12] (A) and (B) are diagrams showing Fourier transform images in each spatial modulation pattern.

FIG. 13 (A) is a diagram showing a conventional spatial light modulation pattern according to an embodiment of the present invention (B).

[Fig.14] Image reproduced from hologram recorded by conventional method

FIG. 15 is an image obtained by reproducing a hologram recorded by the optical information recording method of the present invention.

[Fig.16] Diagram showing the relationship between the aperture size and the bit error rate of the reproduced reference mark

[FIG. 17] (A) to (H) are diagrams showing another embodiment of the fiducial mark of the present invention.

FIG. 18 is a schematic configuration diagram showing a configuration of a pickup of the optical information recording / reproducing apparatus of the present invention.

FIG. 19 is a schematic configuration diagram showing a configuration of a pickup of a conventional optical information recording / reproducing apparatus.

FIG. 20 is a diagram for explaining the relationship of light in a conventional spatial light modulator. FIG. 21 is a diagram for explaining the relationship of light in a conventional spatial light modulator.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035] First, the relationship among incident light 21, emitted light 22, and diffracted light 23 in the spatial light modulator 11 of the present invention will be described with reference to FIG. The optical information recording / reproducing apparatus of the present invention displays the spatial modulation pattern for information light and the spatial modulation pattern for reference light for recording on the spatial light modulator 11 during recording to spatially modulate the light. Information light and recording reference light are generated. If the recording reference light does not have to be spatially modulated, only the information light spatial modulation pattern may be displayed on the spatial light modulator 11. Then, the information light and the recording reference light are irradiated so as to converge on the recording medium (not shown) by the objective lens 13, and interfere with the hologram recording layer of the recording medium. Interference fringes of the recording reference beam are recorded on the hologram recording layer. Next, when reproducing the interference fringes recorded using the spatially modulated reference light for recording, the spatial light modulator 11 generates the reference light for recording after recording in the spatial light modulator 11. The reproduction reference light spatial modulation pattern that is the same as the modulation pattern is displayed, and the light is spatially modulated to generate reproduction reference light. The reproduction reference light is irradiated by the objective lens 13 so as to converge on the recording medium, and interferes with interference fringes recorded on the hologram recording layer of the recording medium to generate reproduction light. The generated reproduction light is propagated by the optical system including the objective lens 13, and the spatial modulation pattern is detected by the photodetector.

In the present invention, the optical axis of the outgoing light 22 (information light, recording reference light or reproduction reference light) directed from the spatial light modulator 11 toward the objective lens 13 is diffracted by the spatial light modulator 11. It is configured not to match the diffracted light 23 of the mth order (m = 0, ± 1, ± 2 ···). This means that the emitted light 22 is located between the m-th order and the (m + 1) -th order diffracted light 23. In FIG. 1, the outgoing light 22 is located between the first-order diffracted light and the zeroth-order diffracted light. Further, the incident angle of the light 21 incident on the spatial light modulator 11 is 0, and is emitted from the spatial light modulator 11.

0

The emission angle of the light 22 is Θ, the wavelength of the light is obtained, and the circumference of the plurality of pixels 12 in the spatial light modulator 11 is obtained.

1

If the period is a and the diffraction order of the diffracted light 23 is m (m = 0, ± 1, ± 2 ···),

Equation 3: m 7 = a (sm Θ — sm θ)

Ten

The apparatus is configured to satisfy the following relational expression. In FIG. 1, the reflection-type spatial light modulation Although it is exemplified by the tuner, the same applies to a transmissive spatial light modulator.

Here, the direction of the optical axis of the emitted light 22 is preferably within the range of the traveling direction of the (m + O. 2) th to (m + O.8) th diffracted light 23. In particular, the traveling direction of the diffracted light 23 of about (m + O.5) order is preferable. That is, (m + O. 2) λ≤a (sin 0 -sin 0) ≤ (m + 0. 8)

Ten

It is particularly preferable to satisfy the relation of (m + O. 5) l = a (sin 0 sin 0)

It is more preferable to satisfy 1 0 expression.

[0038] Also, in FIG. 1, the angle Θ of the emitted light 22 is emitted obliquely so that it can be easily divided.

1

However, when the two-dimensional pattern information is Fourier transformed by the objective lens 13, the display surface of the spatial light modulator 11 that displays the two-dimensional pattern information is the entrance pupil plane of the objective lens 13 (perpendicular to the optical axis). ), The exit angle 0 is 0 °,

1

That is, it is preferable to configure the optical axis of the emitted light 22 to be perpendicular to the spatial light modulator 11. In this case, since sin Θ = 0, Equation 3 becomes m ≠ — a 'sin Θ and the incident angle

Ten

As Θ, it is preferable to satisfy the relation (m + 0.2) λ≤-a-sin 0 ≤ (m + 0.8)

0 0

In particular, it is more preferable to satisfy the relational expression of about (m + 0.5) λ = —a 'sin Θ.

0

[0039] Further, in the case of a DMD having a reflection type pixel, if the angle of the reflection surface of the pixel is Ψ, the emission angle is 0 = 0−2Ψ. Tilt angle Ψ

Ten

Satisfies the relational expression m ≠ — a ′ sin2 ¥, the optical axis of the outgoing light 22 is perpendicular to the spatial light modulator 11 and does not coincide with the diffracted light. It is preferable that the period a and the inclination angle Ψ of the pixel of the spatial light modulator 11 satisfy the relational expression (m + 0.2) l≤-a-sin2 ¥ ≤ (m + 0.8) In particular, it is more preferable to satisfy the relational expression of about (m + 0.5) λ = — a 'sin2 ¥.

FIG. 2 shows a conventional optical information recording / reproducing apparatus in which the angle 0 of the emitted light coincides with the mth-order diffracted light.

1

Fig. 3 shows that the angle 0 of the emitted light coincides with the mth-order diffracted light.

1

4 shows a Fourier transform image in the optical information recording / reproducing apparatus according to the present invention.

[0041] As shown in the upper left of FIG. 2, when all the pixels 135 of the spatial light modulator 109 having a plurality of pixels 135 arranged in a lattice shape are turned on, the Fourier transform is performed by the objective lens. It is converted to pattern 137 as shown in the upper right of the figure. In FIG. 2, since all the pixels 135 of the spatial light modulator 109 are on, they are displayed on the spatial light modulator 109. A no-turn is a pattern composed of a basic spatial frequency, and its Fourier-transformed pattern 137 indicates a frequency component of the basic spatial frequency. The bright spot 138 in the pattern 137 is called “the bright spot by the fundamental spatial frequency”.

[0042] The bright spot 138 by each fundamental spatial frequency is m-th order diffracted light in each direction, and the position of each bright spot 138 is in the above-described formula 1: a (sin 0-sin 0) = m Diffraction angle 0 d 0

Sought by. In Fig. 2, the optical axis of the outgoing light directed toward the objective lens

Since it coincides with the folded light, the bright spot 138 based on the fundamental spatial frequency is located on the optical axis (center).

[0043] In analyzing the Fourier transform of the light spatially modulated by the spatial light modulator 109, the components of the spatial light modulator 109 are the arrangement component 135a resulting from the arrangement of the pixel 135 and the shape of the pixel 135. It can be decomposed into the shape component 135b caused by In FIGS. 2 and 3, the “*” between the arrangement component and the shape component is a convolution calculation symbol.

The arrangement component 135a is subjected to Fourier transform to obtain an arrangement component pattern 137a having a bright spot 138a arranged in a similar shape to the arrangement component 135a, and the shape component 135b is converted to a pixel shape after Fourier transformation. The resulting shape component pattern 137b has an intensity distribution. In FIG. 2, a shape component pattern 137b for a square pixel 135 is shown. In the intensity distribution of the shape component pattern 137b, the region with the strongest intensity is located in the center, and the force is also periodically arranged in the direction facing each side of the square of the pixel 135 (up, down, left and right in Fig. 2). Then, the strength gradually weakens as the central force increases. In addition, in the diagonal direction of pixel 135 (oblique direction in FIG. 2), there is a region only in the vicinity of the central portion, and the light intensity in that region gradually decreases as the central partial force increases. The position of the shape component pattern 137b is determined by the exit angle Θ in Equation 2 above: θ = θ −2Ψ.

1 0 1

It is done.

The pattern 137 is a pattern in which the arrangement component pattern 137a and the shape component pattern 137b are overlapped and multiplied by the intensity. This point will first be explained using a one-dimensional Fourier transform waveform. As shown in FIG. 4, a periodic peak corresponding to the arrangement component is shown in the shape component pattern 41 obtained by Fourier transforming the rectangular wave corresponding to the shape component. The composite pattern 44 is obtained by superposing the arrangement component patterns 42 and multiplying them by the intensity. Tsuma Thus, the intensity of the shape component pattern 41 at the peak position of the arrangement component pattern 42 becomes the composite pattern 44. In the composite pattern 44, the shape component pattern 41 is indicated by a dotted line. The synthesized pattern 44 corresponds to the Fourier transform pattern 137 in the conventional optical information recording / reproducing apparatus in that the center of the shape component pattern 41 and the center of the arrangement component pattern 42 are aligned.

In FIG. 2, the angle 0 of the emitted light matches the angle 0 of the mth-order diffracted light.

1 d

The center of the arrangement component pattern 137a and the center of the shape component pattern 137b coincide. The Fourier transform pattern 137 has the strongest light intensity in the m-th order diffracted light located at the center. From there, the next bright spot 138 (m ± l, 2...) Is moved away from the center. The strength decreases as the difference from m increases. In addition, in the diagonal direction (diagonal direction in Fig. 2), the shape component pattern 137b exists only in the vicinity of the center portion, so each bright spot of the Fourier transform pattern 137 (m ± l, 2 ...) is It exists only in the vicinity of the central part, and the intensity decreases as the luminescent spot and central force move away (the difference from m increases).

Next, as shown in the upper left of FIG. 3, in the recording / reproducing method of the present invention, all the pixels 12 of the spatial light modulator 11 having a plurality of pixels 12 arranged in a grid are turned on. In this case, when the Fourier transform is performed by the objective lens, the pattern 31 is transformed as shown in the upper right of the figure. In FIG. 3, the spatial light modulator 11 is rotated by 45 ° about the optical axis. This is a configuration in which each pixel 12 of the DMD rotates about the vertical diagonal line in FIG. This is because the rotating shaft is arranged vertically in the apparatus. When the spatial light modulator 11 is rotated, the Fourier transformed pattern 31 also rotates. The shape of the pattern 31 itself does not change. Pattern 31 in Fig. 3 also shows the frequency components of the fundamental spatial frequency. The bright spot 33 at 31 is also a bright spot by the fundamental spatial frequency.

The spatial light modulator 11 in FIG. 3 can also be decomposed into an arrangement component 12 a resulting from the arrangement of the pixel 12 and a shape component 12 b resulting from the shape of the pixel 12 as in the case of FIG. The arrangement component 12a is subjected to Fourier transform to obtain an arrangement component pattern 3la having a bright spot 33a arranged in a similar shape to the arrangement component 12a, and the shape component 12b is converted to a pixel shape by Fourier transformation. The resulting shape component pattern 31b has an intensity distribution. The arrangement component pattern 31a and the shape component pattern 31b in FIG. 3 are the same as those obtained by rotating the arrangement component pattern 137a and the shape component pattern 137b in FIG. 2 by 45 °.

As shown in FIG. 3, when the optical axis of the outgoing light directed toward the objective lens is configured not to match the m-th order diffracted light, the bright spot 33a of the arrangement component pattern 31a is shifted from the optical axis. This corresponds to the relationship of the composite pattern 45 when the arrangement component pattern 43 is overlapped and multiplied with the shape component pattern 41 of FIG. In the composite pattern 45, the shape component pattern 41 is indicated by a dotted line, and it can be seen that the two peaks near the center are both strong and strong.

[0050] In FIG. 3, the position of the m + O. 5th-order diffracted light coincides with the optical axis in the diagonal direction of pixel 12 (lateral direction 15 in FIG. 3, oblique 45 ° direction in FIG. 2). The optical axis is the center of the four bright spots 33a. Here, the period a in Equation 3: m ≠ a (sin 0 -sin 0) for obtaining the diffraction order in the diagonal direction is the rotation axis 1 as shown in Fig. 3.

Ten

The interval between 4 (half the diagonal of the pixel). In other words, if the length of one side of the pixel is L, then 2 ^1/2 · L / 2.

[0051] On the other hand, the position of the shape component pattern 3 lb is expressed in the above-described formula 2: 0 = Θ — 2Ψ.

Ten

The center of the shape component pattern 31b is the output angle Θ.

1 1 Matches the optical axis of the incident light. For this reason, the pattern 31 obtained by superimposing the arrangement component pattern 3 la and the shape component pattern 3 lb overlaps with each other as the strength increases at the bright spot 33 at the four basic spatial frequencies near the optical axis. The intensity of the bright spot 33 due to each fundamental spatial frequency decreases.

[0052] As described above, when the optical axis of the outgoing light directed toward the objective lens is configured not to match the m-th order diffracted light, the bright spot due to the fundamental spatial frequency of the spatial light modulator is shown in the strongest region. A plurality of 33 can be arranged, and the intensity of interference fringes can be increased.

[0053] Further, the output angle Θ varies due to an error in the tilt angle of the reflective surface of the pixel.

1

Even if the position of the shape component pattern 31b in the Fourier plane is shifted, there are bright spots 33 with a plurality of fundamental spatial frequencies, so that strong intensity can be maintained in the hologram recording area, and reliability is improved. . [0054] Further, conventionally, since a region of very strong light intensity is localized at the center, the monomer concentration in the hologram recording layer of the optical information recording medium is partially depleted. In the present invention, since the bright spots 33 having a plurality of fundamental spatial frequencies are arranged in the region where the light intensity is strong, the light intensity distribution in the hologram recording region is compared with the conventional one. Can be averaged. As a result, the monomer concentration also decreases on average, and the multiple recording characteristics can be improved, so that the recording capacity can be increased.

[0055] As another advantage, if the optical axis of the outgoing light directed toward the objective lens is configured not to match the m-th order diffracted light, the hologram size can be reduced. In the pattern 137 in FIG. 2, the hologram recording area 139 is indicated by a white circle. In FIG. 2, in order to obtain all the spatial frequency characteristics, it is necessary to include at least the central bright spot 138 and the bright spots 138 located in the four directions in the hologram recording area 139. In contrast, as shown in the pattern 31 of FIG. 3, in the present invention, all four bright spots 33 located in the vicinity of the optical axis indicate all the spatial frequency characteristics. The hologram recording area 34 (indicated by white circles) can be reduced to a size that includes it. Accordingly, since the size of each hologram can be reduced, a larger number of holograms can be recorded accordingly, and the recording capacity can be increased.

[0056] Specifically, in the DMD, the DMD emits perpendicularly to the objective lens (0 =

1

0) When the optical axis of the emitted light is the (m + O.5) -order diffracted light traveling direction, the relational expression (m + O.5) λ = —a ′ sin2 ¥ is satisfied. For example, in the case of a 0.7 inch XGA (1024 X 768 pixels) DMD manufactured by Texas Instruments Inc., the square pixel pitch is 1 3.68 / zm, so (m + O.5 in the diagonal direction) ) When the traveling direction of the next diffracted light is selected, the pixel period a is 2 ^{1 2} · 13. 68 ^ πι / 2 = 9.65 / zm. Fig. 5 shows the tilt angle of the pixel, which is the traveling direction of the diffracted light in the diagonal direction (m + O.5) when using light with a wavelength of 532 nm and light with a wavelength of 410 nm. Incident angle. The DMD tilt angle is designed to be 11 to 13 °. Therefore, within the angle range, when using light with a wavelength of 532 nm, the tilt of the pixel is set to be the direction of travel of the fifth-order light. If the angle is 12.18 °, the angle of incidence on the DMD is 24.36 °, and light with a wavelength of 410 nm is used, the pixel tilt angle is 11.87 so that the 9.5th-order light travels. ° To DMD The incident angle is 23.74 °.

[0057] FIGS. 6 to 9 show that for a DMD using light with a wavelength of 532 nm and pixel tilt angles of 11.4 °, 12.0 °, 12.2 °, and 12.4 °, 24.4 A Fourier transform image is shown when light is incident at an incident angle of °. The upper row shows the case where all the pixels are in the on state, and the lower row shows the case where the pixels in the on state and the off state (hatched with hatching) are randomly arranged.

[0058] In FIG. 6, since the tilt angle of the pixel 62 of the DMD 61 is 11.4 °, the output angle is 24.4 ° —2

X I I. 4 ° = 1.6 °. The diffraction order at an output angle of 1.6 ° is 9.65 / z m X (sin (l.6 °) -sin (24.4 °)) Z532nm = —7.00th order light. Therefore, in FIG. 6, as in the conventional optical information recording / reproducing apparatus, the optical axis of the emitted light coincides with the diffracted light. In FIG. 6, in the upper Fourier transform pattern 63, the optical axis is located at the bright spot with the fundamental spatial frequency on the left side of the center, and the light intensity is strong at that position. However, in the essential hologram recording area (white circle) 64, the light intensity is weak and the interference fringes are weak. Further, in the lower Fourier transform pattern 65 in which the on-pixel 62a and the off-pixel 62b are randomly arranged, each bright spot is blurred and the light intensity distribution is widened. However, the light intensity is still weak in a part of the hologram recording area (white circle) 64, and it is difficult to record and reproduce reliable information.

[0059] In FIG. 7, since the tilt angle of the pixel 72 of the DMD 71 is 12.0 °, the output angle is 24.4 ° —2

X 12. 0 ° = 0.4 °. The diffraction order at an output angle of 0.4 ° is 9.65 m X (sin (0.4 °) -sin (24.4 °)) Z532nm = — 7.37th order light. Therefore, in FIG. 7, the optical axis of the emitted light does not coincide with the diffracted light. In Fig. 7, the upper Fourier transform pattern 73 shows that the light intensity of the left bright spot is slightly strong among the four basic spatial frequency bright spots near the center, but the other three bright spots have sufficient light intensity. It is possible to record interference fringes in the entire hologram recording area (white circle) 74. The lower Fourier transform pattern 75 in which the on-pixel 72a and the off-pixel 72b are randomly arranged is also slightly deviated to the left of the center, but the light intensity distribution spreads over the entire hologram recording area (white circle) 74. Therefore, interference fringes can be recorded and information can be recorded and reproduced with high reliability.

[0060] In FIG. 8, since the tilt angle of the pixel 82 of the DMD81 is 12.2 °, the output angle is 24.4 ° -2 X 12. 2 ° = 0 °. The diffraction order at an output angle of 0 ° is 9.65 m X (sin (0 °) —sin (24.4 °)) Z532nm = — 7. 49th order light. Therefore, in FIG. 8, the optical axis of the emitted light does not coincide with the diffracted light. In Fig. 8, the Fourier transform pattern 83 in the upper part shows that the bright spots of the four basic spatial frequencies in the vicinity of the center are equally strong in light intensity, and records uniform interference fringes throughout the hologram recording area (white circle) 84. Is possible. Even in the lower Fourier transform pattern 85 in which the ON pixels 82a and OFF pixels 82b are randomly arranged, the light intensity distribution spreads out over the entire hologram recording area (white circle) 84, so that interference fringes are recorded evenly. It is possible to record and reproduce reliable information

[0061] In Fig. 9, since the tilt angle of the pixel 92 of the DMD 91 is 12.4 °, the exit angle is 24.4 ° -2

X 12. 4 ° = -0. 4 °. The diffraction angle at the exit angle—0.4 ° is 9.65 m X (sin (−0.4 °) —sin (24.4 °)) Z532nm = —7.62nd order light. Therefore, in FIG. 9, the optical axis of the emitted light does not coincide with the diffracted light. In Fig. 9, the upper Fourier transform pattern 93 has a slightly strong light intensity at the right bright spot among the four bright spots with four fundamental spatial frequencies near the center, but the other three bright spots are sufficiently strong. The hologram recording area (white circle) 94 can record interference fringes throughout. In the lower Fourier transform pattern 95 in which the on-pixel 92a and the off-pixel 92b are randomly arranged, it is slightly shifted to the left of the center! However, the entire hologram recording area (white circle) 94 Since the light intensity distribution is widened, interference fringes can be recorded and information can be recorded and reproduced with high reliability.

[0062] The range of the tilt angle is a design value for one product, and is not limited to the above numerical value. For example, if the tilt angle is 10.5 °, the direction of travel of the quintic light can be used when using light with a wavelength of 532 nm, and when using light with a wavelength of 410 nm, 8. Since the direction of travel of the fifth-order light can be set, a highly versatile DMD can be manufactured. Also, if the pixel spacing is changed, the angle must be redesigned.

In addition, the present invention can also be applied to a force-transmitting spatial light modulator that mainly describes a spatial light modulator having a reflective pixel, such as a DMD. FIG. 10 shows the relationship between the incident light 21, the emitted light 22, and the diffracted light 23 in the transmissive spatial light modulator 11. First, in the transmissive spatial light modulator 11, the incident angle of the incident light 21 is Θ

0 The angle of light 22 emitted from the optical modulator 11 is Θ, the wavelength of the light is obtained, and the spatial light modulator 11

1

If the period of multiple pixels 12 in a is a and the diffraction order of the diffracted light 23 is m (m = 0, ± 1, ± 2 ...), the relational expression of Equation 3: 111 ≠ ≠ & 110 -sin0) is obtained. Configure the device to meet.

Ten

However, in FIG. 10, the exit angle Θ is not shown because it is 0 °. Because of this, transmission

1

The spatial light modulator 11 of the type has a refracting means 16. In FIG. 10, incident light 21 is incident on the spatial light modulator 11 at an incident angle Θ. Multiple pixels of spatial light modulator 11 12

0

The outgoing light 22 modulated by is emitted through the refracting means 16 at an outgoing angle Θ. Transparent

1

In the spatial light modulator 11 of the type, since the incident light 21 is refracted by the refracting means 16, if the angle of the emitted light 22 with respect to the incident light 21 is 0, 0 = 0−0. On the other hand, r 1 0 r

Since the plurality of pixels 12 of the spatial light modulator 11 function as a diffraction grating, the diffraction angle 0 is determined according to the equation l _: a (sin0-d sin0) = m (m = 0, ± 1, ± 2 ...) Diffracted light 23 is generated

0 d

As shown in FIG. 10, the angle 0 of the outgoing light 22 is 0 °, that is, the optical axis of the outgoing light 22

1

Is preferably perpendicular to the spatial light modulator 11. In this case, sin Θ = 0, so Equation 3 becomes m ≠ — a'sin0, and the incident angle 0 is (m + O.2)

1 0 0

It is particularly preferable to satisfy the relation of λ≤-α · 3ίηθ ≤ (m + 0.8) (m + O.5)

0

It is more preferable to satisfy the relational expression of l = -a-sin0. Where θ = θ — Θ

0 1 0 r et al., When Θ = 0, θ = θ, and the above equation 3 becomes m ≠ — a'sin0, and the output light 22

1 0 r r

The angle Θ with respect to incident light 21 is r 0 of (m + O.2) l≤-a-sin0 ≤ (m + O.8)

It is preferable to satisfy the relational expression. From another viewpoint, the angle of the output light 22 with respect to the incident light 21 satisfies the relation of 0 force m ≠ —a'sin0, and the optical axis of the output light 22 is perpendicular to the spatial light modulator 11. And the configuration does not match the diffracted light.

As the refracting means 16, an angled phase plate can be used.

If the edge of a transparent member having a refractive index different from that of the surrounding material is angled, a phase difference is generated because the thickness is partially different. Further, the phase plate is a transparent member in which a portion having a different refractive index is provided, and a phase difference is generated depending on the thickness of the portion having a different refractive index. In FIG. 10, the refracting means 16 is provided on the exit surface side of the spatial light modulator 11. However, the refracting means 16 may be arranged on the incident surface side, or the refracting means 16 may be realized as a function inside the spatial light modulator 11.

Furthermore, in the optical information recording method of the present invention, the spatial modulation pattern for information light includes a plurality of reference marks, and the spatial frequency in the reference mark region is smaller than the basic spatial frequency of the spatial light modulator. To include the frequency. From another viewpoint, it is sufficient that the periodicity of the pixels in the reference mark region is larger than the periodicity of the pixels of the spatial light modulator. For example, the spatial frequency of a pattern in which ON pixels and OFF pixels are alternately arranged is half the basic spatial frequency.

[0068] FIGS. 11 (A) to 11 (C) each show an 8-pixel spatial modulation pattern arranged linearly in the upper stage, and the light intensity and periodicity t in the lower stage. It is a figure for demonstrating the relationship between and periodicity t. In FIGS. 11A to 11C, the spatial modulation pattern is composed of a binary force of an on state and an off state.

[0069] FIG. 11 (A) shows a spatial modulation pattern 1101 in which all eight pixels are in the ON state, and has a period t of the distance a between adjacent pixels, so that the spatial frequency is the fundamental spatial frequency.

1

Become. In FIG. 11 (A), the light intensity between the pixels is 0 because of the gap between the pixels of the spatial light modulator. FIG. 11B shows a spatial modulation pattern 1102 in which ON pixels and OFF pixels are alternately arranged, and has a period t of an interval of 2 pixels (2 Xa). The period t of the spatial modulation pattern 1102 in Fig. 11 (B) is the spatial modulation in Fig. 11 (A).

twenty two

Since it is twice the period t of pattern 1101, the spatial frequency of spatial modulation pattern 1102 is

1

Half of the fundamental spatial frequency. Fig. 11 (C) shows a spatial modulation pattern 1103 in which ON and OFF pixels are arranged alternately in two pixels, with a period t of 4 pixels (4 X a) and one image.

3 has a period t with an interval a. Of these, the period t is four times the period t.

1 3 1

The intermodulation pattern 1103 includes a spatial frequency that is a quarter of the fundamental spatial frequency.

[0070] When the period of the spatial modulation pattern increases, the spatial frequency decreases, and when a spatial modulation pattern having a large period is Fourier transformed, a bright spot is generated between the bright spot and the bright spot by the basic spatial frequency. That is, in the present invention, a bright spot generated by Fourier transform of the reference mark (hereinafter referred to as “bright spot by the reference mark”) is generated between the bright spot by the basic spatial frequency. [0071] FIGS. 12A and 12B are similar to FIG. 3, in which the position of the m + O. Fifth-order diffracted light in the diagonal direction of the pixel coincides with the optical axis, that is, there are four optical axes. A spatially transformed pattern 1201 in which all the pixels are in an on state and a spatial modulation pattern 1202 in which the pixels are in an on state in a lattice form in the state of being the center of the bright spot 33 by the basic spatial frequency is shown.

[0072] In the case of the spatial modulation pattern 1201 in which all the pixels in FIG. 12A are in the on state, the fundamental spatial frequency force is also obtained, and as shown in the pattern 1203, the bright spots 1205 by the four basic spatial frequencies 1205 The center of is the optical axis. As shown in Fig. 20, in the conventional spatial light modulation pattern for information light, the reference mark 147 has all the 4 x 4 square pixels turned on (Fig.

In Fig. 20, the pattern is indicated by shading). For this reason, the spatial frequency in the region of the reference mark 147 becomes the fundamental spatial frequency, and the bright spot by the reference mark obtained by Fourier transform becomes the pattern 1203 in FIG. For this reason, in pattern 1203 in FIG. 12 (A), when the size of hologram 1207 is reduced, the bright spot due to the reference mark first deviates from the range of hologram 1207. Becomes worse. If the hologram 1207 is further reduced in size, the reference mark disappears from the reproduced spatial modulation pattern, and information cannot be reproduced.

On the other hand, as shown in FIG. 12 (B), in the case of the spatial modulation pattern 1202 in which the pixels are turned on in a lattice shape, the spatial frequency is half of the basic spatial frequency. As shown in Fig. 5, a bright spot is also generated at the center position of a square (see dotted line 1206 in Figs. 12A and 12B) formed by bright spots 1205 having four adjacent fundamental spatial frequencies. For this reason, when a lattice-like spatial modulation pattern as shown in Fig. 12 (B) is used as a reference mark, the spatial frequency in that region becomes half of the basic spatial frequency, and the bright spot by the reference mark is shown in Fig. 12. It becomes like pattern 1204 of (B). As a result, the bright spot due to the reference mark exists inside the bright spot with the four fundamental spatial frequencies, and even if the size of the hologram 1207 is reduced, the reference mark does not disappear and the reliability can be improved. Further, the size of the hologram can be further reduced, and the recording capacity can be improved.

[0074] In particular, it is preferable that the bright spot by the reference mark is located on the optical axis because the reference mark can be reproduced more reliably. For example, as shown in FIG. m + 0. If the position of the fifth-order diffracted light coincides with the optical axis, that is, the center of the bright spot 33 by the basic spatial frequency of the optical axis force, the reference mark has a spatial frequency that is half the basic spatial frequency. If you include it.

FIG. 13 (A) shows a conventional spatial light modulation pattern for information light 1301 and a spatial light modulation pattern for reference light 1302, and FIG. 13 (B) is a space for information light in one embodiment of the present invention. An optical modulation pattern 1303 and a spatial light modulation pattern 1302 for reference light are shown. In FIGS. 13A and 13B, information light spatial light modulation patterns 1301 and 1303 are arranged at the center, and an annular reference light spatial light modulation pattern 1302 is arranged therearound. In the center, the overall configuration of the spatial light modulation patterns 1301 and 1303 for information light encodes the information to be recorded for each unit of a certain amount of information to generate a symbol unit of two-dimensional pattern information, The symbol unit and the reference mark are formed as one block unit, and are formed by arranging a plurality of block units.

Then, in the conventional spatial light modulation pattern for information light 1301 shown in FIG. 13 (A), as is clear from the partially enlarged view shown on the left side of FIG. In the spatial light modulation pattern for information light 1303 in FIG. 13B, the reference mark 1306 is a pixel, as is clear from the partially enlarged view shown on the left side of the figure. Is a pattern in which is turned on in a lattice shape. Note that the enlarged portions of FIGS. 13A and 13B are portions of block units in which only the reference marks 1305 and 1306 are arranged and symbol units are not arranged, and the spatial light modulation pattern for information light 1301 , 1303 itself is the location and orientation standard.

FIG. 14 and FIG. 15 show the spatial light modulation when reproducing the recorded interference fringes by actually changing the size of the aperture (indicated by reference numeral 227 in FIG. 18) (also called aperture size). It is a pattern. The size of the aperture affects the size of the interference fringes to be recorded (= hologram size). The larger the aperture, the larger the interference fringe recorded, and the smaller the aperture, the smaller the interference fringe recorded. 14 uses the spatial modulation pattern for information light 1301 and the spatial modulation pattern for reference light 1302 in FIG. 13 (A), and FIG. 15 uses the spatial modulation pattern for information light 1303 and the reference light in FIG. 13 (B). Holograms were recorded using the spatial modulation pattern 1302. In Fig. 14 and Fig. 15, the upper five reproduced images have 8.4m in opening size in order of left force. m, 8. Omm, 7.6 mm, 7.2 mm, and 6.8 mm were recorded and played back. The four playback images in the lower row had an aperture size of 6.4 mm, 6. Omm in order from the left. , 5.6mm and 5.2mm recorded and reproduced.

[0078] When the conventional optical information recording method of FIG. 14 is used, the reference mark can be confirmed in the upper stage. The reference mark disappears in the lower stage where the aperture size is 6.4 mm or less. The mark cannot be played. When the optical information recording method of the present invention shown in FIG. 15 was used, the fiducial mark could be confirmed both in the upper and lower stages, and the fiducial mark could be reproduced even if the aperture was reduced.

FIG. 16 is a diagram showing the relationship between the aperture size (aperture size) and the bit error rate of the reproduced reference mark. If the aperture is reduced, the size of the recorded hologram is also reduced. In Fig. 16, in the case of the conventional reference mark with all the 4 x 4 square pixels in the ON state (folded line), the bit error rate increases rapidly when the aperture size is 6.4 mm or less. However, it cannot be played at all. On the other hand, in the case of a fiducial mark in which the pixels are turned on in a grid pattern (garden line), the bit error rate does not increase so much even if the aperture size is 6.4 mm or less, and it becomes 4 mm. However, the bit error rate could be reduced to about 0.2.

FIGS. 17A to 17H show another embodiment of the reference mark of the present invention. In FIGS. 17A to 17H, the white pixels are in the on state and the shaded pixels are in the off state. In FIGS. 17A to 17D, the force is not limited to 4 × 4 pixels with 4 × 4 pixels as the reference mark region. In FIG. 17 (F), the reference mark region is a 3 × 4 pixel, and in FIGS. 17 (G) and (H), the reference mark region is a 5 × 5 pixel.

FIG. 18 shows the configuration of the pickup 201 of the optical information recording / reproducing apparatus of the present invention using a reflective spatial light modulator. The pickup 201 of the present invention is the same as the pickup 201 of the optical information recording / reproducing apparatus of the present invention, the recording / reproducing light source 203, collimator lens 205, mirror 207, spatial light modulator 209, polarization beam splitter 211, relay lenses 213, 215, An aperture 227, a mirror 217, a quarter-wave plate 219, an objective lens 221, a ring mask 223, and a light detection means 225 are provided. In the pickup 201 of FIG. 18, when information is recorded or reproduced, the light emitted from the recording / reproducing light source 203 is converted into parallel rays by the collimator lens 205 and directed to the spatial light modulator 209 by the mirror 207. Reflected with force. In the present invention, the wavelength of the light emitted from the recording / reproducing light source 203, the mirror 207 so that the outgoing light 232 of the spatial light modulator 209 does not coincide with the diffracted light 233 (shown by a dotted line) by the spatial light modulator 209. The incident angle of the incident light 231 to the spatial light modulator and the period of the pixels of the spatial light modulator are configured. When a spatial light modulator having a reflective pixel as shown in FIG. 18 is used, the angle of inclination of the reflective surface of the pixel is also set so that the outgoing light 232 of the spatial light modulator does not match the diffracted light 233. Composed. Hereinafter, each component of the optical information recording / reproducing apparatus will be described in order.

The recording / reproducing light source 203 emits light for forming information light for recording information and light for forming reference light for recording and light for forming reference light for reproduction for reproducing information. . As the light source 203, for example, a semiconductor laser that generates a coherent linearly polarized light beam can be used. As the recording / reproducing light source 203, a shorter wavelength is advantageous in order to perform high-density recording, and it is preferable to employ a blue laser (for example, wavelength 532 nm) or a green laser (for example, wavelength 410 nm). Further, a solid laser can be used as the light source 203.

The collimator lens 205 converts the divergent light beam from the recording / reproducing light source 61 into a substantially parallel light beam.

The mirror 207 reflects the light from the recording / reproducing light source 203 toward the spatial light modulator 209. With the mirror 207, the incident angle of the light 231 incident on the spatial light modulator 209 can be adjusted. For example, the position or angle of the mirror may be changed with respect to light having different wavelengths so that the outgoing light 232 of the spatial light modulator does not coincide with the diffracted light 233.

Spatial light modulator 209 has a plurality of pixels, and uses a transmissive or reflective spatial light modulator that can modulate the phase or Z and intensity of emitted light for each pixel. be able to. As the spatial light modulator 209, a DMD (digital 'micromirror' device) or a matrix type liquid crystal element can be used. DMD spatially modulates the intensity of incident light by changing the reflection direction for each pixel, and reflects the incident light for each pixel. The phase can be spatially modulated by changing the position. The liquid crystal element can spatially modulate the intensity and phase of incident light by controlling the alignment state of the liquid crystal for each pixel. For example, the phase of light can be spatially modulated by setting the phase of outgoing light for each pixel to one of two values that differ from each other by π radians. In FIG. 18, the spatial light modulator 209 is of a reflective type, and is disposed so as to reflect incident light and emit it perpendicularly to the spatial light modulator.

[0087] Then, the information light spatial modulation pattern is displayed on the display surface of the spatial light modulator 209, and information light is generated by spatially modulating the light with the displayed information light spatial modulation pattern. be able to. The spatial modulation pattern for information light includes two-dimensional pattern information obtained by encoding information to be recorded, and is represented by two-dimensionally arranging pixels whose attributes are changed in multiple stages. For each pixel of the spatial modulation pattern for information light, for example, the state of light such as phase and intensity is changed in multiple stages. In the following explanation, the power explained in the method of changing the light intensity for each pixel in two steps of on (white pixel) and off (black or shaded pixel) is not limited to this method. Absent. For example, the phase of light may be changed, or it may be changed to three or more steps instead of two steps.

[0088] The recording reference light may be spatially modulated or may not be spatially modulated. When the recording reference light is spatially modulated, multiple recording can be performed by changing the spatial modulation pattern of the recording reference light, and information recording can be performed by keeping the spatial modulation pattern of the recording reference light as a key. Security against unauthorized access can be improved. When the reference light is spatially modulated, for example, the spatial light modulator displaying the reference light spatial modulation pattern is irradiated with light to generate the reference light spatially modulated by the reference light spatial modulation pattern. it can. When the information light and the recording reference light are generated by one spatial light modulator 209, an information light region and a reference light region are provided on the display surface of the spatial light modulator 209, respectively. The pattern and the spatial modulation pattern for recording reference light may be displayed. The information light region is preferably arranged near the center of the spatial light modulator 209, and the reference light region is preferably arranged in an annular shape so as to surround the information light region. A spatial light modulator that generates information light and recording reference light may be provided separately. For example, the light from the light source 203 is split by a beam splitter or the like, and one light is Information light may be spatially modulated by one spatial light modulator, and reference light may be generated by spatially modulating the other light by a second spatial light modulator. In this case, since the information light spatial modulation pattern and the reference light spatial modulation pattern need to be imaged on the entrance pupil plane of the objective lens 221, the spatial light modulator that generates the information light and the reference light are generated. The spatial light modulator has a conjugate relationship, and is propagated to the entrance pupil plane of the object lens 221 by the pair of relay lenses 213 and 215.

[0089] In the case where a plurality of pixels of the spatial light modulator 209 are arranged in a lattice pattern, the optical axis of the outgoing light 23 emitted from the spatial light modulator 209 is about the diagonal direction of the lattice of the plurality of pixels. When the diffraction order is shifted, the optical axis moves in the diagonal direction of the bright spot on the Fourier plane as shown in the arrangement component pattern 31a in FIG. 3, so the distance to each bright spot close to the optical axis force This is preferable because it is easy to equalize. In particular, if the exit angle of the optical axis of the emitted light 23 is equal to the (m ± 0.5) order diffraction angle in the diagonal direction of the grating by the pixel, the distances to four adjacent bright spots will be equal. The intensity of the Fourier transform image can be flattened. Even when the plurality of pixels of the spatial light modulator 209 are arranged in a non-lattice arrangement, for example, a honeycomb and shifted in a stepwise manner, the optical axis does not coincide with the m-th order diffracted light. As a result, a plurality of bright spots can be arranged in a strong region in the Fourier transform image. When the arrangement is changed, the arrangement component pattern 31a in FIG. 3 is changed.

[0090] The plurality of pixels of the spatial light modulator 209 may have a shape other than a square shape. For example, it may be a rectangle, rhombus, hexagon, triangle, or circle. In this case, the shape component pattern 31b in FIG. 3 changes according to the shape.

The polarization beam splitter 211 has a semi-reflective surface that reflects or transmits linearly polarized light (for example, P-polarized light) and transmits or reflects linearly polarized light (for example, S-polarized light) perpendicular to the polarized light. In FIG. 18, a polarization beam splitter 211 transmits information light, recording reference light, or reproduction reference light emitted from the spatial light modulator 209, and reproduces and records the reproduction light generated from the hologram recording layer of the recording medium. The reproduction reference light reflected by the medium is reflected toward the light detection means 225.

[0092] The pair of relay lenses 213 and 215 are arranged between the spatial light modulator 209 and the objective lens 221. The image displayed on the spatial light modulator 209 is formed on the entrance pupil plane of the objective lens 221. That is, the distance from the spatial light modulator 209 to the first relay lens 213 is the focal length fl of the first relay lens 213, and the distance from the second relay lens 215 to the entrance pupil plane of the objective lens 221 is the second distance The distance between the first and second relay lenses 213 and 215 is the sum of the focal length fl of the first relay lens 213 and the focal length f2 of the second relay lens 215. It is arranged to become.

In FIG. 18, a pair of relay lenses 213 and 215 are arranged between the objective lens 221 and the light detection means 225, and the hologram recording layer 253 of the recording medium 251 is read by reference light for reproduction. The light detection means 225 is arranged again to form an image on the exit pupil plane of the objective lens 221 of the reproduction light generated from the light. That is, the exit pupil surface force of the objective lens 221 is also the distance to the second relay lens 215 is the focal length f2, the distance from the first relay lens 213 to the light detecting means 225 is the focal length fl, and the first and first The second relay lenses 213 and 215 are arranged such that the distance between them is the sum of the focal length fl and the focal length f2.

[0094] Note that the arrangement of the pair of relay lenses 213 and 215 changes by appropriately arranging other optical elements. For example, if a magnifying lens is placed between the first relay lens 213 and the light detection means 225, the distance from the first relay lens 213 to the entrance pupil plane of the magnifying lens is the focal distance fl. Be placed.

The aperture 227 is disposed at the focal position between the first and second relay lenses 213 and 215, and removes higher-order diffracted light. Depending on the size of the opening 227, the size of the recording area of the hologram can be adjusted. In the present invention, since it is configured not to coincide with the diffracted light 233 of the optical axis force m order (m = 0, ± 1, ± 2...) Of the outgoing light 232 of the spatial light modulator 209 force, The recording area of the hologram can be reduced. Furthermore, since the spatial frequency in the area of the reference mark includes a spatial frequency smaller than the basic spatial frequency of the spatial light modulator, it can be reproduced even if the hologram recording area is reduced. Therefore, the opening 227 may be reduced to reduce the hologram recording area. In Fig. 18, when the optical axis of outgoing light 232 matches the traveling direction of m + O. 5th order diffracted light, The m-order and m + 1 first-order diffracted light 233 in the vicinity thereof may be passed, and diffracted light having a higher order may be blocked. The means for adjusting the recording area of the hologram is not limited to the opening 227.

The mirror 217 reflects the traveling direction of light toward the objective lens 221 and is not necessary depending on the configuration of the optical system.

The quarter-wave plate 219 is a phase plate that changes the optical path difference of polarized light that vibrates in directions perpendicular to each other by a quarter wavelength. P-polarized light is converted to circularly polarized light by the quarter-wave plate 219, and further, when this circularly polarized light passes through the quarter-wave plate 219, it is changed to S-polarized light. By this quarter-wave plate 219, the reference beam for reproduction and the reproduction beam at the time of reproduction can be separated by the polarization beam splitter 211.

[0098] At the time of recording, the objective lens 221 irradiates the recording medium 251 with information light and recording reference light imaged on the entrance pupil plane, and causes the hologram recording layer 253 to interfere and record. At the time of reproduction, the reproduction reference light imaged on the entrance pupil plane is irradiated onto the recording medium 251 and the reproduction light generated from the hologram recording layer 253 of the recording medium 251 is incident on the exit pupil plane. The image is formed. In FIG. 18, the objective lens 221 is shown as a single lens, but a compound lens may be used.

The ring mask 223 is for removing reproduction reference light reflected by the reflective layer 255 of the recording medium 251 together with reproduction light during reproduction.

[0100] The light detection means 225 has a plurality of light receiving pixels, and can detect the intensity of light received for each light receiving pixel. As the light detection means 225, a CCD solid-state image sensor or a MOS type solid-state image sensor can be used. In addition, as the light detection means 225, a smart optical sensor in which a MOS type solid-state imaging device and a signal processing circuit are integrated on one chip (for example, WO plus E, September 1996, No. 202, pages 93 to 99) : Shine ,.) use! /, Techi,. This smart optical sensor has a high transfer function with a large transfer rate, so it can be played back at high speed by using this smart optical sensor, for example, with a transfer rate on the order of G (giga) bits Z seconds. Playback can be performed.

[0101] The recording medium 251 has a hologram recording layer 253 on which interference fringes are recorded. In FIG. 18, the recording medium 251 further includes a first substrate 251a, a reflective layer 255, and a second transparent substrate 251b. Have . As the recording medium 251, a disk-shaped or card-shaped one can be used, and recording and reproduction may be performed while the recording medium 251 is rotated, or may be fixed at the time of recording and reproduction. In the case of using a disk-shaped recording medium as the recording medium 251 and performing recording and reproduction while rotating, the disk drive mechanism used in CD drives and DVD drives can be used. Is preferred because it makes it easier to have compatibility with CD and DVD drives.

[0102] It is preferable that information for positioning is recorded in advance on the recording medium 251 and a feedback mechanism is used for positioning of the irradiation position because more accurate positioning can be performed. For example, a pit may be formed as positioning information on the surface of the reflective layer 255 of the recording medium 251 and the positioning information may be recorded in advance. When light with a wavelength different from that for recording or reproduction is used as the light for reading positioning information, the light for recording or reproduction is separated from the reflection layer for the light for reading the positioning information forming the pits. A wavelength selective reflection layer that reflects light may be provided. For example, if a wavelength selective reflection layer that reflects light for recording or reproduction and transmits light for reading positioning information is formed between the reflective layer and the hologram recording layer, the positioning information is superimposed on the recording / reproducing area. Recording can be performed, and the pickup device can be arranged on the same side of the recording medium, so that the recording / reproducing apparatus can be downsized.

The operation of the optical information recording apparatus will be described. Light emitted from the light source 203 is converted into parallel light by the collimator lens 205 and reflected by the mirror 207 toward the spatial light modulator 209. Information light and recording reference light are generated by the information light spatial modulation pattern and the reference light spatial modulation pattern displayed on the spatial light modulator 209. In the optical information recording method of the present invention, the spatial modulation pattern for information light has a plurality of reference marks, and the spatial frequency in the region of the reference mark is smaller than the basic spatial frequency of the spatial light modulator 209. To include. Further, the optical axis of light directed toward the spatial light modulator 209 force objective lens (the central ray in the figure) is arranged so as not to coincide with the traveling direction of the m-th order diffracted light 233. In FIG. 18, since the information light is arranged at the center and the annular recording reference light is arranged around it, the optical axis of the information light and the optical axis of the recording reference light are located on the same line. Coincides with the traveling direction of m-order diffracted light 233 Not done.

[0104] The information light and the recording reference light pass through the polarization beam splitter 211, and are displayed on the spatial light modulator 209 on the entrance pupil plane of the objective lens 221 by the pair of relay lenses 213 and 215. The modulation pattern is propagated to form an image. On the way, high-order diffracted light is removed by the aperture 227, reflected by the mirror 217 toward the objective lens 221, and passes through the quarter-wave plate 219. Interference fringes of information light and recording reference light are recorded on the hologram recording layer 253 of the recording medium 251.

[0105] Thus, the recording medium on which the interference fringes are recorded by the recording method of the present invention can reproduce information by reproducing the reference mark even when the hologram size is small! Therefore, the reliability as an information recording medium is improved, and the recording capacity is also improved.

Further, the operation as the optical information reproducing apparatus will be described. The light emitted from the light source 203 is converted into parallel light by the collimator lens 205 and reflected by the mirror 207 toward the spatial light modulator 209. Then, the reference light for reproduction is generated by the spatial modulation pattern for reference light displayed on the spatial light modulator 209. Note that the reference light spatial modulation pattern of the reproduction reference light at the time of reproduction is a reference light spatial modulation pattern of the recording reference light irradiated when information recorded on the recording medium is recorded. Here, the optical axis of light directed from the spatial light modulator 209 to the objective lens (the central ray in the figure) does not coincide with the traveling direction of the m-th order diffracted light 233. In FIG. 18, an annular reproduction reference beam is arranged, and its optical axis does not coincide with the traveling direction of the mth-order diffracted beam 233.

The reproduction reference light emitted from the spatial light modulator 209 passes through the polarization beam splitter 211 and is displayed on the spatial light modulator 209 on the entrance pupil plane of the objective lens 221 by the pair of relay lenses 213 and 215. The transmitted spatial modulation pattern for reference light is propagated so as to form an image. On the way, high-order diffracted light is removed by the aperture 227, reflected by the mirror 217 toward the objective lens 221, and passes through the quarter-wave plate 219. Then, the recording medium 251 is irradiated by the objective lens 221 and is diffracted by the interference fringes recorded on the hologram recording layer 253 of the recording medium 251 to generate reproduction light having the same information as the information light at the time of recording.

[0108] The reproduction light is reflected by the reflection layer 255 of the recording medium 251 and is reflected from the recording medium 251 to the objective lens 2. A pair of relay lenses 215 are emitted so as to form a spatial modulation pattern for information light on the exit pupil plane by the objective lens 221 so that a powerful image is formed again on the light detection means 255. , 213. In the meantime, the reproduction light passes through the quarter-wave plate 219 and is reflected by the mirror 217 toward the polarization beam splitter 211. Since the reproduction light passes through the quarter-wave plate 219 twice compared to the reproduction reference light at the time of irradiation, the polarization direction is shifted by 90 °. Reflected toward 255. Then, the reproduction reference light is removed by the ring mask 223, and the spatial modulation pattern of the reproduction light is detected by the light detection means 225. The detected information is sent to a control means (not shown), and the control means decodes and reproduces the information. Note that the present invention is not limited to the above-described embodiment, and various kinds are necessary as necessary. Can be changed. For example, in FIG. 18, a hologram is formed by irradiating the recording medium with the same surface side force information light and the reference light of the recording medium so that the optical axis of the information light and the optical axis of the reference light are coaxial. However, a two-beam interference type hologram may be formed by irradiating the recording medium with the information light and the reference light so that the optical axis of the information light and the optical axis of the reference light intersect at a certain angle. In this case, it is preferable that at least one of the light spatially modulated by the spatial light modulator is configured such that the light emitted from the spatial light modulator does not coincide with the mth-order diffracted light as described above. ,.

Claims

The scope of the claims

[1] The reference light for recording and the information light spatially modulated by the spatial modulation pattern for information light displayed on the spatial light modulator having a plurality of pixels are converged on the recording medium by the objective lens. In the optical information recording method for recording interference fringes between the recording reference light and the information light in the hologram recording layer of the recording medium, the information light directed from the spatial light modulator toward the objective lens The optical axis does not coincide with the mth order (m = 0, ± 1, ± 2 ...) diffracted light diffracted by the spatial light modulator, and the spatial modulation pattern for information light has a plurality of reference marks. An optical information recording method comprising: a spatial frequency in a region of the reference mark including a spatial frequency smaller than a basic spatial frequency of the spatial light modulator.

[2] The direction of the optical axis of the information light is in the range of the traveling direction of the (m + O. 2) th to (m + O. 8) th diffracted light. The optical information recording method according to 1.

[3] In the spatial light modulator, the plurality of pixels are arranged in a grid pattern, and an optical axis direction of the information light is approximately (m + O) with respect to a diagonal direction of the grid formed by the plurality of pixels. 5. The optical information recording method according to claim 1, wherein the optical information recording method coincides with the traveling direction of the next diffracted light.

[4] The optical information according to any one of [1] to [3], wherein a spatial frequency in a region of the reference mark includes a spatial frequency that is half of a basic spatial frequency of the spatial light modulator. Recording method.

5. The optical information recording method according to any one of claims 1 to 3, wherein the reference mark includes a pattern in which pixels having different attributes are alternately arranged.

6. The optical information recording method according to any one of claims 1 to 5, wherein an optical axis direction of the information light is perpendicular to the spatial light modulator.

[7] A recording medium, wherein interference fringes are recorded on the hologram recording layer by the optical information recording method according to any one of [1] to [6].