JP2002368329A - Coherent light generation apparatus and method, and optical information recording apparatus and method - Google Patents

Abstract

(57) [Problem] To generate coherent light having uniform coherence over a predetermined period while using a laser which generates relaxation oscillation after rising of a light emission output. SOLUTION: A coherent light generation device 101 includes a semiconductor laser 102 as a laser that generates relaxation oscillation after a rising of a light emission output, a driving circuit 103 for driving the semiconductor laser 102, and a control circuit 104 for controlling the driving circuit 103. And The control circuit 104 repeatedly outputs a light pulse including only the first peak in the relaxation oscillation from the semiconductor laser 102 over a predetermined period, and the coherent light having uniform coherence over a predetermined period by a plurality of light pulses within the predetermined period. The driving circuit 103 is controlled so that is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coherent light generating apparatus and method for generating coherent light having uniform coherence over a predetermined period, and optical information for recording information on a recording medium using holography. The present invention relates to a recording apparatus and a recording method.

[0002]

2. Description of the Related Art In general, holographic recording in which information is recorded on a recording medium using holography is performed by superimposing light having image information and reference light inside a recording medium, and generating interference at that time. This is performed by writing a pattern on a recording medium. When the recorded information is reproduced, the image information is reproduced by irradiating the recording medium with the reference light and diffracting by the interference pattern.

In recent years, volume holography, especially digital volume holography, has been developed in the practical range for ultra-high-density optical recording and has attracted attention. Volume holography is a system in which an interference pattern is written three-dimensionally by actively utilizing the thickness direction of a recording medium.
The feature is that the diffraction efficiency can be increased by increasing the thickness, and the recording capacity can be increased by using multiplex recording. Digital volume holography is a computer-oriented holographic recording method that uses the same recording medium and recording method as volume holography, but limits image information to be recorded to binary digital patterns. In this digital volume holography, for example, image information such as an analog picture is once digitized and developed into two-dimensional digital pattern information.
This is recorded as image information. During playback, by reading and decoding this digital pattern information,
Return to the original image information and display. Thereby, even if the signal-to-noise ratio (S / N ratio) is somewhat poor at the time of reproduction, the original information can be reproduced very faithfully by performing differential detection or encoding the binary data and performing error correction. It becomes possible.

[0004]

By the way, a general optical information recording apparatus for recording information on a disc-shaped recording medium by using light is a method of irradiating a recording medium with light for recording information. It has a head. In this optical information recording apparatus, information is recorded on the recording medium by irradiating the recording medium with light from the optical head while rotating the recording medium.

In an optical information recording apparatus using holographic recording, similarly to the above-mentioned general optical information recording apparatus, the recording medium is irradiated with information light and reference light while rotating the recording medium. It is conceivable to sequentially record information in a plurality of information recording areas on a recording medium. In this case, in order to separate each information recorded in each information recording area from each other, the intensity of the information light and the reference light applied to the recording medium is increased in each information recording area, and is increased in other areas. Need to be smaller. One way to achieve this is to generate information light and reference light based on light pulses.

[0006] The conditions required for the light pulse used in the holographic recording as described above include coherence, that is, coherence, and energy sufficient to change the optical characteristics of the recording medium. Is to have.

Conventionally, a pulse laser has been known as a light source for generating a coherent and high-energy light pulse. However, pulse lasers are large and impractical to incorporate into optical information recording devices.

[0008] In a general optical information recording apparatus, a semiconductor laser is used as a light source. In an optical information recording apparatus using holographic recording, it is desirable to use a practical semiconductor laser as a light source.

However, as is well known,
When an optical pulse is generated by directly modulating a semiconductor laser, relaxation oscillation occurs after the rise of the optical pulse, and the coherence of light decreases during the period in which the relaxation oscillation occurs. Therefore, an optical pulse generated by directly modulating a semiconductor laser has a problem that coherence is low even in the entire optical pulse.

[0010] On the other hand, various pulsed light sources have been proposed which generate an optical pulse having a very short pulse width using a semiconductor laser. Such a pulsed light source has, for example, a half width of tens of ps (picoseconds) and a peak power of tens to hundreds of tens of mW.
Is output at a repetition frequency of up to about several MHz. However, there is a problem in that the light pulse generated by the pulse light source cannot obtain sufficient energy to change the optical characteristics of the recording medium.

Incidentally, in a general optical disk device, as a light for reproducing information, a light of a semiconductor laser which has been made into a multi-mode by superimposing at a high frequency is used. This light for information reproduction cannot be used for holographic recording because its coherence is reduced.

The present invention has been made in view of such a problem, and a first object of the present invention is to provide a coherent light having uniform coherence over a predetermined period while using a laser which generates relaxation oscillation after the rise of the emission output. It is an object of the present invention to provide a coherent light generation device and method capable of generating a coherent light.

A second object of the present invention is to provide an optical information recording apparatus and method for recording information on a recording medium by using holography, wherein a laser which generates relaxation oscillation after rising of a light emission output is used. An object of the present invention is to provide an optical information recording apparatus and method capable of generating coherent light having uniform coherence over a predetermined period, and recording information using the coherent light.

[0014]

According to the present invention, there is provided a coherent light generating apparatus for generating coherent light having uniform coherence over a predetermined period of time, comprising: a laser which generates relaxation oscillation after a rising of a light emission output; A driving circuit for driving the laser, and an optical pulse including only the first peak in the relaxation oscillation from the laser is repeatedly output over a predetermined period, and a plurality of light pulses within the predetermined period provide a coherent with uniform coherence over a predetermined period. Control means for controlling the drive circuit so that light is generated.

The method of generating coherent light of the present invention is a method of generating coherent light having uniform coherence over a predetermined period. The method drives a laser that generates relaxation oscillation after the rising of the light emission output. A procedure for outputting an optical pulse including only the first peak in the relaxation oscillation, and a procedure for outputting the optical pulse over a predetermined period are repeatedly executed, and a plurality of light pulses generated within the predetermined period provide uniform light over a predetermined period. Generating coherent light having coherence.

In the coherent light generating apparatus or method according to the present invention, an optical pulse including only the first peak in the relaxation oscillation is repeatedly output from the laser over a predetermined period, and a plurality of light pulses within the predetermined period uniformly output the laser light over a predetermined period. Coherent light having high coherence is generated. In the coherent light generation device or method of the present invention, the laser may be a semiconductor laser.

The optical information recording apparatus of the present invention is an apparatus for recording information using holography in each information recording area of a recording medium having a plurality of information recording areas, and is capable of recording information uniformly over a predetermined period. A coherent light generating device for generating coherent light having coherence, and, based on the coherent light generated by the coherent light generating device, generating information light and reference light carrying information to be recorded, and generating information in an information recording area. An optical system for irradiating the recording medium with the information light and the reference light so that the information is recorded by an interference pattern due to the interference between the light and the reference light.

In the optical information recording apparatus according to the present invention, the coherent light generating apparatus includes a laser that generates a relaxation oscillation after the rising of the emission output, a driving circuit for driving the laser, and a light including only the first peak in the relaxation oscillation from the laser. Control means for controlling the drive circuit such that the pulses are repeatedly output over a predetermined period, and a plurality of light pulses within the predetermined period generate coherent light having uniform coherence over a predetermined period. I have.

An optical information recording method according to the present invention is a method for recording information using holography in each information recording area of a recording medium having a plurality of information recording areas, wherein a uniform coherent A procedure for generating coherent light having the following, and, based on the coherent light generated by the procedure for generating coherent light, generate information light and reference light carrying information to be recorded, and generate the information light and the reference in the information recording area. Irradiating the recording medium with information light and reference light so that the information is recorded by an interference pattern due to interference with light.

In the optical information recording method of the present invention, the step of generating coherent light includes driving a laser that generates relaxation oscillation after the rise of the light emission output, and generating an optical pulse containing only the first peak in the relaxation oscillation from the laser. A step of outputting, and a step of repeatedly outputting a light pulse over a predetermined period, and a step of generating coherent light having uniform coherence over a predetermined period by a plurality of light pulses generated within the predetermined period. Contains.

In the optical information recording apparatus or method according to the present invention,
An optical pulse including only the first peak in the relaxation oscillation is repeatedly output from the laser over a predetermined period, and a plurality of light pulses within the predetermined period generate coherent light having uniform coherence over a predetermined period. Then, the information light and the reference light are generated based on the coherent light, and the information light and the reference light are generated on the recording medium such that the information is recorded in the information recording area by the interference pattern due to the interference between the information light and the reference light. Irradiation with reference light is performed.
In the optical information recording device or method according to the present invention, the laser may be a semiconductor laser.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, a configuration of a coherent light generation device according to an embodiment of the present invention will be described with reference to FIG. The coherent light generation device 101 according to the present embodiment is a device that generates coherent light having uniform coherence over a predetermined period. The coherent light generation device 101 includes a semiconductor laser 102 as a laser that generates relaxation oscillation after the emission output rises, a drive circuit 103 for driving the semiconductor laser 102, and a control circuit 104 for controlling the drive circuit 103. ing. The control circuit 104 corresponds to the control means in the present invention.

The drive circuit 103 switches the value of the drive current supplied to the semiconductor laser 102 between zero and a predetermined value equal to or higher than the light emission threshold based on a control signal from the control circuit 104. ing.

The control circuit 104 repeatedly outputs a light pulse including only the first peak in the relaxation oscillation from the semiconductor laser 102 over a predetermined period. The plurality of light pulses within the predetermined period provide uniform coherence over a predetermined period. The driving circuit 103 is controlled so as to generate the coherent light. Specifically, the control circuit 104 gives the drive circuit 103 a control signal indicating a timing for switching the value of the drive current supplied from the drive circuit 103 to the semiconductor laser 102 between zero and a predetermined value. It has become. Control circuit 10
4 can be constituted by a microcomputer, for example. In this case, the microcomputer uses the CP
U (central processing unit), ROM (read only memory) and RAM (random access memory), and the CPU executes the program stored in the ROM by using the RAM as a work area. Circuit 1
04 functions are realized.

Next, the operation of the coherent light generation device 101 according to the present embodiment and the coherent light generation method according to the present embodiment will be described with reference to FIGS.

FIGS. 2 and 3 show an example of the operation of the coherent light generation apparatus 101. FIG. In FIG.
(A) shows the relationship between the drive current supplied to the semiconductor laser 102 and the emission output of the semiconductor laser 102, (b) shows the waveform of the drive current, and (c) shows the waveform of the emission output. 3A shows the waveform of the drive current, and FIG. 3B shows the waveform of the light emission output.

In this embodiment, the value of the drive current supplied from the drive circuit 103 to the semiconductor laser 102 is switched between zero and a predetermined value. In the present embodiment, the time during which the value of the drive current becomes the predetermined value is set shorter than the period of the relaxation oscillation that occurs after the rising of the emission output of the semiconductor laser 102. Thus, in this embodiment, the semiconductor laser 102 outputs an optical pulse including only the first peak in the relaxation oscillation. Further, in the present embodiment, the switching cycle of the drive current value is set to be equal to or longer than the time from when the emission output of the semiconductor laser 102 rises to when it returns to zero. In this manner, in the present embodiment, a plurality of light pulses including only the first peak in the relaxation oscillation are repeatedly output from the semiconductor laser 102 while the light emission output temporarily returns to zero between each light pulse. In the examples shown in FIGS. 2 and 3, the time when the value of the drive current becomes a predetermined value is set to 40 ps, and the cycle of switching the value of the drive current is set to 100 ps.

Further, in the present embodiment, the procedure for outputting the optical pulse as described above is repeatedly executed over a predetermined period, and a plurality of light pulses generated within the predetermined period allow uniform coherent interference over a predetermined period. To generate coherent light having a characteristic. The predetermined period depends on the use of the coherent light. For example, when using coherent light for holographic recording, the predetermined period
This is a period during which the coherent light has sufficient energy to change the optical characteristics of the recording medium. FIG.
In the example shown in FIG. 3, the predetermined period is set to 50 ns (nanosecond).

Here, for comparison with the present embodiment,
For a predetermined period, for example, 50 ns, the semiconductor laser 1
FIG. 4 shows an example of the relationship between the drive current and the light emission output of the semiconductor laser 102 when a drive current having a constant value equal to or larger than the light emission threshold is supplied to the laser diode 02. In FIG.
(A) shows the waveform of the drive current, and (b) shows the waveform of the light emission output. In this case, the optical pulse shown in FIG. 4B is obtained according to the pulsed drive current as shown in FIG. However, with this light pulse, relaxation oscillation occurs after the rising of the light emission output. During the period in which the relaxation oscillation occurs, the coherence of light decreases. Therefore, the coherence is low even in the entire light pulse.

On the other hand, in the present embodiment, as shown in FIG. 3, the semiconductor laser 102 repeatedly outputs an optical pulse including only the first peak in the relaxation oscillation for a predetermined period, and Coherent light is generated by a plurality of light pulses. During the period in which the relaxation oscillation occurs, the coherence of light decreases because the oscillation mode of the semiconductor laser 102 changes. However, looking only at a period including only the first peak in the relaxation oscillation, the oscillation mode of the semiconductor laser 102 is almost constant. Therefore, as in the present embodiment, the semiconductor laser 102
By repeatedly outputting an optical pulse including only the first peak in the relaxation oscillation over a predetermined period, coherent light having uniform coherence can be generated over a predetermined period by a plurality of light pulses within the predetermined period.

As described above, according to the coherent light generation apparatus and method according to the present embodiment, the semiconductor laser 102 that generates relaxation oscillation after the rise of the light emission output
, It is possible to generate coherent light having uniform coherence over a predetermined period.

An optical information recording apparatus and method using the coherent light generating apparatus and method according to the present embodiment will be described below. FIG.
FIG. 2 is a block diagram illustrating a configuration of an optical information recording / reproducing device including the optical information recording device according to the present embodiment. FIG. 6 is a sectional view of an optical head in the optical information recording / reproducing apparatus shown in FIG.

First, the recording medium 1 used in the present embodiment will be described with reference to FIGS. The recording medium 1 has a disk shape. The recording medium 1 has a plurality of tracks arranged concentrically. Each track is provided with a plurality of address servo areas 6 at equal intervals. One or more information recording areas 7 are provided between adjacent address / servo areas 6.

The address / servo area 6 includes information for generating a basic clock which is a reference for timings of various operations in the optical information recording / reproducing apparatus, information for performing focus servo by a sampled servo method, and information for sampled servo. Information and address information for performing tracking servo by a servo method are recorded in advance by emboss pits or the like. Note that information for performing focus servo may not be recorded in the address servo area 6, and focus servo may be performed using an interface between an air gap layer and a reflective film, which will be described later. The address information is information for identifying each information recording area 7.

The recording medium 1 has a disc-shaped transparent substrate 2 made of polycarbonate or the like, and an information recording layer arranged in this order on the transparent substrate 2 on the side opposite to the light incident / exit side. 3, air gap layer 4, reflection film 5
It has. The information recording layer 3 is a layer on which information is recorded using holography, and a hologram whose optical characteristics such as a refractive index, a dielectric constant, and a reflectivity change according to the intensity of light when irradiated with light. It is formed of a material. As a hologram material, for example, Dupont
t) Photopolymers manufactured by the company
HRF-600 (product name), Aprilis (April)
s) Photopolymer ULSH-500 (product name) manufactured by the company is used. The reflection film 5 is formed of, for example, aluminum. In the recording medium 1, the information recording layer 3 and the reflection film 5 may be adjacent to each other without providing the air gap layer 4.

Next, the configuration of the optical information recording / reproducing apparatus will be described with reference to FIG. This optical information recording / reproducing device 1
0 is a spindle 81 to which the recording medium 1 is attached,
A spindle motor 82 for rotating the spindle 81
And a spindle servo circuit 83 for controlling the spindle motor 82 so as to keep the rotation speed of the recording medium 1 at a predetermined value. The optical information recording / reproducing apparatus 10 further irradiates the recording medium 1 with an information light carrying information to be recorded and a recording reference light to record the information, and also reproduces the reproduction reference information on the recording medium 1. Irradiate the light, detect the reproduction light,
An optical head 40 for reproducing information recorded on the recording medium 1 and a driving device 84 for moving the optical head 40 in the radial direction of the recording medium 1 are provided.

The optical head 40 generates the information light and the reference light based on the coherent light generator 101 according to the present embodiment and the coherent light generated by the coherent light generator 101, And an optical system for irradiating the recording medium 1 with the information light and the recording reference light so that information is recorded by an interference pattern due to interference between the information light and the recording reference light.

The optical information recording / reproducing apparatus 10 further includes a detection circuit 85 for detecting the focus error signal FE, the tracking error signal TE, and the reproduction signal RF from the output signal of the optical head 40. A focus servo circuit 86 that drives an actuator 50 of the optical head 40, which will be described later, based on the focus error signal FE to perform focus servo, and drives the actuator 50 based on a tracking error signal TE detected by the detection circuit 85. A tracking servo circuit 87 for performing tracking servo, and an optical head 4 by controlling a driving device 84 based on a tracking error signal TE and a command from a controller described later.
And a slide servo circuit 88 for performing a slide servo for moving 0 in the radial direction of the recording medium 1.

The optical information recording / reproducing device 10 further decodes output data of a later-described photodetector 45 in the optical head 40 to reproduce data recorded in the information recording area 7 of the recording medium 1, A signal processing circuit 89 for reproducing a basic clock and determining an address from a reproduction signal RF from a detection circuit 85, a controller 90 for controlling the entire optical information recording / reproducing apparatus 10, and various types of the controller 90 And an operation unit 91 for giving an instruction.

The controller 90 receives the basic clock and address information output from the signal processing circuit 89, and controls the optical head 40, the spindle servo circuit 83, the slide servo circuit 88 and the like. The spindle servo circuit 83 receives the basic clock output from the signal processing circuit 89. The controller 90 includes a CPU (Central Processing Unit), R
It has an OM (read only memory) and a RAM (random access memory), and the CPU implements the function of the controller 90 by executing a program stored in the ROM using the RAM as a work area. It has become.

Next, the principle of information recording in the optical information recording / reproducing apparatus according to the present embodiment will be described. In the present embodiment, the information light and the recording reference light are generated such that information is recorded on the information recording layer 3 by an interference pattern due to the interference between the information light and the recording reference light. The information recording layer 3 of the recording medium 1 is irradiated with light. Information light is generated by spatially modulating the phase of light based on information to be recorded.

Hereinafter, the optical information recording method according to the present embodiment will be described in detail with reference to FIG. FIG.
Shows a part of an example of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment. The recording / reproducing optical system in this example includes a transparent substrate 2 of a recording medium 1.
The objective lens 11 has a beam splitter 12 and a phase spatial light modulator 13 arranged on the opposite side of the objective lens 11 from the objective lens 11 side. The beam splitter 12 has a normal direction of 45 ° with respect to the optical axis direction of the objective lens 11.
It has an inclined semi-reflective surface 12a. The recording / reproducing optical system shown in FIG. 7 further has a photodetector 14 arranged in a direction in which return light from the recording medium 1 is reflected by the semi-reflective surface 12a of the beam splitter 12. The phase spatial light modulator 13 has a large number of pixels arranged in a grid pattern, and can spatially modulate the light phase by selecting the phase of the emitted light for each pixel. ing.
Further, the photodetector 14 has a large number of pixels arranged in a lattice pattern, and can detect the intensity of light received for each pixel.

In the example shown in FIG. 7, the phase spatial light modulator 1
3, the information light and the recording reference light are generated. Coherent parallel light having a constant phase and intensity is incident on the phase spatial light modulator 13. At the time of recording information, the phase spatial light modulator 1
3 is to select the phase of the emitted light for each pixel based on the information to be recorded in one half area 13A,
The information light is generated by spatially modulating the light phase, and in the other half area 13B, the reference light for recording is generated with the same phase of the emitted light for all the pixels.

In the region 13A, the phase spatial light modulator 13 converts the phase of the modulated light into a first phase and a reference phase whose phase difference with respect to a predetermined reference phase is + π / 2 (rad) for each pixel. Is set to one of the second phases at which the phase difference with respect to -π / 2 (rad) is obtained. First
Is a phase difference of π (rad).
In addition, the phase spatial light modulator 13 has a region 13A.
The phase of the modulated light may be set to one of three or more values for each pixel. Further, in the region 13B, the phase spatial light modulator 13 sets the phase of the emitted light of all the pixels to the first phase in which the phase difference with respect to a predetermined reference phase is + π / 2 (rad).
Phase. In addition, the phase spatial light modulator 13 may set the phase of the emitted light of all the pixels in the region 13B as the second phase, or may set the phase of the emitted light as a constant phase different from any of the first phase and the second phase. Good.

FIG. 7 shows the incident light of the phase spatial light modulator 13, the output light of the phase spatial light modulator 13, the incident light of the objective lens 11 before the recording medium 1 is irradiated, and the light of the beam splitter 12. It shows the phase and intensity of the return light from the recording medium 1 reflected by the semi-reflective surface 12a. In FIG. 7, the first phase is represented by a symbol “+”, and the second phase is represented by a symbol “−”. In FIG. 7, the maximum value of the intensity is represented by “1” and the minimum value of the intensity is represented by “0”.

In the example shown in FIG. 7, when recording information,
Coherent parallel light 21 having a constant phase and intensity is incident on the phase spatial light modulator 13. Of the light that has entered the phase spatial light modulator 13, the light that has passed through the region 13A has its phase spatially modulated based on the information to be recorded, and becomes information light 22A. In the information beam 22A, the intensity locally decreases at the boundary between the pixel of the first phase and the pixel of the second phase. On the other hand, of the light that has entered the phase spatial light modulator 13, the light that has passed through the region 13B is not spatially modulated in phase and becomes the recording reference light 22B. The information beam 22A and the recording reference beam 22B are transmitted to the beam splitter 1
2, a part thereof passes through the semi-reflective surface 12 a, further passes through the objective lens 11, and becomes the converging information beam 23 </ b> A and the converging recording reference beam 23 </ b> B. The information light 23 </ b> A and the recording reference light 23 </ b> B pass through the information recording layer 3, converge so as to have the smallest diameter on the boundary between the air gap layer 4 and the reflection film 5, and are reflected by the reflection film 5. The information light 24A and the recording reference light 24B after being reflected by the reflection film 5 become diffused light and pass through the information recording layer 3 again.

In the information recording layer 3, the information light 23 A before being reflected by the reflection film 5 and the recording reference light 24 B after being reflected by the reflection film 5 interfere with each other to form an interference pattern. Information light 24A after reflection by the light 5 and the reflection film 5
And the recording reference light 23B before being reflected by the laser beam interferes to form an interference pattern. Then, these interference patterns are volumetrically recorded in the information recording layer 3.

The information light 24A and the recording reference light 24B after being reflected by the reflection film 5 are emitted from the recording medium 1, and become parallel information light 25A and recording reference light 25B by the objective lens 11. These lights 25A and 25B are incident on the beam splitter 12, partly reflected by the semi-reflective surface 12a, and received by the photodetector 14.

Next, the principle of reproducing information in the optical information recording / reproducing apparatus according to the present embodiment will be described. In the present embodiment, the reproduction reference light is generated, and the reproduction reference light is applied to the information recording layer 3 of the recording medium 1, and the reproduction reference light is applied to the information recording layer 3. The generated reproduction light is collected, the reproduction light and the reproduction reference light are overlapped to generate a combined light, and the combined light is detected.

Hereinafter, the optical information reproducing method according to the present embodiment will be described in detail with reference to FIG. FIG.
7 shows a part of an example of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment, similarly to FIG.

FIG. 8 shows a phase spatial light modulator 13.
Incident light, output light of the phase spatial light modulator 13, recording medium 1
2 shows the phase and intensity of the incident light of the objective lens 11 before being irradiated to the recording medium 1 and the return light from the recording medium 1 reflected by the semi-reflective surface 12a of the beam splitter 12. The representation of the phase and intensity in FIG. 8 is the same as in FIG.

In the example shown in FIG. 8, when reproducing information,
Coherent parallel light 31 having a constant phase and intensity is incident on the phase spatial light modulator 13. At the time of reproducing information, the phase spatial light modulator 13 sets the phase of the outgoing light for all pixels so that the phase difference with respect to a predetermined reference phase is + π /
2 (rad) as the first phase and the reproduction reference light 32
Generate The reproduction reference light 32 is incident on the beam splitter 12, a part of which passes through the semi-reflective surface 12a, and further becomes the reproduction reference light 33 which converges after passing through the objective lens 11, and is irradiated on the recording medium 1. You. The reproduction reference light 33 is
The light passes through the information recording layer 3, converges on the boundary surface between the air gap layer 4 and the reflection film 5 so as to have the smallest diameter, and is reflected by the reflection film 5. The reference light for reproduction after being reflected by the reflection film 5 is
The light becomes diffused light and passes through the information recording layer 3 again.

In the information recording layer 3, the reproduction reference light 33 before being reflected by the reflection film 5 generates reproduction light traveling to the opposite side to the reflection film 5, and after being reflected by the reflection film 5. Due to the reproduction reference light, reproduction light traveling toward the reflection film 5 side is generated. The reproduction light traveling to the opposite side to the reflection film 5 is emitted from the recording medium 1 as it is, and the reproduction light traveling to the reflection film 5 is reflected by the reflection film 5 and emitted from the recording medium 1.

As described above, at the time of reproduction, the return light 34 from the recording medium 1 includes the reproduction light and the reproduction-specific reference light after being reflected by the reflection film 5. The return light 34 is converted into parallel light return light 35 by the objective lens 11, enters the beam splitter 12, is partially reflected by the semi-reflective surface 12 a, and is received by the photodetector 14. The return light 35 incident on the photodetector 14 includes the reproduction light 36 and the reflection film 5.
And the reference light 37 for reproduction after being reflected by the light source. The reproduction light 36 is light whose phase is spatially modulated according to information recorded on the information recording layer 3. In FIG. 8, for convenience, the reproduction light 36 and the reproduction reference light 37 are separated, and the phase and intensity are shown for each. However, in practice, the reproduction light 36 and the reproduction reference light 37 are superimposed to generate a combined light, and the combined light is received by the photodetector 14. The combined light is light whose intensity is spatially modulated according to the recorded information. Therefore, the two-dimensional pattern of the intensity of the combined light is detected by the photodetector 14, whereby information is reproduced.

As shown in FIGS. 7 and 8, in the optical information recording / reproducing apparatus according to the present embodiment, the information light, the recording reference light, the reproduction reference light, and the reproduction light are arranged coaxially. The irradiation of the information light, the recording reference light, and the reproduction reference light and the collection of the reproduction light are performed from the same surface side of the information recording layer 3. The information light, the recording reference light, and the reproduction reference light all converge so as to have the smallest diameter at the same position.
In FIG. 7, the information beam 23A and the recording reference beam 23B applied to the information recording layer 3 are light beams having a semicircular cross section. It is coaxial because it constitutes.

Here, with reference to FIG.
6. The reference light 37 for reproduction and the combined light will be described in detail. 9A shows the intensity of the reproduction light 36,
(B) is the phase of the reproduction light 36, and (c) is the reference light 37 for reproduction.
(D) shows the phase of the reference light for reproduction 37, and (e) shows the intensity of the combined light. FIG. 9 shows the phase of the information light for each pixel, where the phase difference from the reference phase is + π / 2 (rad).
The phase difference between the first phase and the reference phase is -π / 2
An example is shown in the case where the phase is set to one of the second phases (rad). Accordingly, in the example shown in FIG. 9, the phase of each pixel of the reproduction light 36 is, like the information light,
Either the first phase or the second phase. In addition, the phase of each pixel of the reproduction reference light 37 is all the first phase. Here, the intensity of the reproduction light 36 and the reproduction reference light 37
If the intensities are equal, as shown in FIG.
In a pixel in which the phase of the reproduction light 36 is the first phase, the intensity of the combined light is greater than the intensity of the reproduction light 36 and the intensity of the reproduction-specific reference light 37, and the phase of the reproduction light 36 is the second phase. In the pixel, the intensity of the combined light is zero in principle.

Next, the phase of the reproduction light, including the case where the phase of the information light is set to one of two values during recording and the case where the phase of the information light is set to one of three or more values, are included. The relationship between and the intensity of the combined light will be described in detail.

The combined light includes a reproduction light and a reference light for reproduction.
It is a superposition of two light waves. Accordingly, the both a ₀ amplitude and the amplitude of the reference light for reproduction of the reproduction light, when the phase difference between the reproduction-specific reference light and the reproduction light and [delta], the intensity I of the combined light is expressed by the following equation (1) You.

[0059] ^{_{I = 2a 0 2 + 2a 0}} 2 cosδ = 2a 0 2 (1 + cosδ) = 4a 0 2 cos 2 (δ / 2) ... (1)

Since the phase of the reference light for reproduction is constant irrespective of the pixel, it can be seen from the above equation that the intensity I of the combined light changes according to the phase of the reproduction light. Further, the phase of the information light is changed, for example, from + π / 2 (rad) to −π / 2 (rad).
Is set to any one of n values (n is an integer of 2 or more) within the range, the intensity I of the combined light also becomes one of the n values.

As described above, in the optical information recording method according to this embodiment, the information to be recorded is detected by detecting the two-dimensional pattern of the intensity of the combined light generated by superimposing the reproduction light and the reproduction reference light. The information recorded on the information recording layer 3 can be reproduced by an interference pattern caused by interference between the information light whose light phase is spatially modulated based on the information light and the recording reference light.

By the way, in the present embodiment, the multiplexed recording by the phase encoding multiplexing method and the information multiplexed and recorded in this manner are performed by using the recording reference light and the reproduction reference light whose phases are spatially modulated. May be performed. Hereinafter, the principle of information recording and the principle of reproduction in the case of performing multiplex recording by the phase encoding multiplex method will be described with reference to FIGS.

First, with reference to FIG. 10, the principle of information recording in the case of performing multiplex recording by the phase encoding multiplex method will be described. FIG. 10 shows a part of an example of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment. The configuration of the optical system shown in FIG. 10 is the same as that in FIG. In FIG. 10, the phase spatial light modulator 1
3, the output light of the phase spatial light modulator 13, the incident light of the objective lens 11 before being irradiated on the recording medium 1, and the return from the recording medium 1 reflected by the semi-reflective surface 12a of the beam splitter 12. The phase and intensity of light are shown. FIG. 7 shows how to represent the phase and intensity of light in FIG.
Is the same as

At the time of recording information, the phase spatial light modulator 13
And a coherent parallel light 21 having a constant phase and intensity.
Is incident. One half area 13A of the phase spatial light modulator 13 has a spatially spatial phase by selecting the phase of outgoing light from binary or three or more values for each pixel based on information to be recorded. Modulated information light 22A
Generate Here, for simplicity of explanation, the region 13A sets the phase of the outgoing light for each pixel to the position relative to the first phase and the reference phase whose phase difference with respect to a predetermined reference phase is + π / 2 (rad). By setting the phase difference to one of the second phases at which the phase difference becomes -π / 2 (rad), the phase of light is spatially modulated. On the other hand, the other half area 13B of the phase spatial light modulator 13 has its phase spatially modulated by selecting the phase of the outgoing light for each pixel from two values or three or more values. The recording reference light 22B is generated. Here, in order to simplify the description, the region 13B sets the phase of the emitted light for each pixel to one of the reference phase, the first phase, and the second phase, thereby changing the phase of the light. It shall be spatially modulated.

The information light 22A and the recording reference light 22B are incident on the beam splitter 12, and a part thereof is a semi-reflective surface 12a.
Pass through the objective lens 11 and converge as an information beam 23A and a converging recording reference beam 23B.
The recording medium 1 is irradiated. The information light 23 </ b> A and the recording reference light 23 </ b> B pass through the information recording layer 3, converge so as to have the smallest diameter on the boundary between the air gap layer 4 and the reflection film 5, and are reflected by the reflection film 5. The information light 24A and the recording reference light 24B after being reflected by the reflection film 5 become diffused light and pass through the information recording layer 3 again.

In the information recording layer 3, the information light 23 A before being reflected by the reflection film 5 and the recording reference light 24 B after being reflected by the reflection film 5 interfere with each other to form an interference pattern. Information light 24A after reflection by the light 5 and the reflection film 5
And the recording reference light 23B before being reflected by the laser beam interferes to form an interference pattern. Then, these interference patterns are volumetrically recorded in the information recording layer 3.

The information beam 24A and the recording reference beam 24B after being reflected by the reflection film 5 are emitted from the recording medium 1, and become parallel information beam 25A and recording reference beam 25B by the objective lens 11. These lights 25A and 25B are incident on the beam splitter 12, partly reflected by the semi-reflective surface 12a, and received by the photodetector 14.

Next, with reference to FIG. 11, the principle of information reproduction in the case of performing multiplex recording by the phase encoding multiplex method will be described. FIG. 11 shows a part of an example of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment, similarly to FIG. FIG.
The incident light of the phase spatial light modulator 13, the output light of the phase spatial light modulator 13, the incident light of the objective lens 11 before being irradiated on the recording medium 1, and the beam splitter 12
2 shows the phase and intensity of the return light from the recording medium 1 reflected by the semi-reflective surface 12a. The expression of the phase and the intensity in FIG. 11 is the same as that in FIG.

When reproducing information, the phase spatial light modulator 13
And a coherent parallel light 31 having a constant phase and intensity.
Is incident. The half area 13B of the phase spatial light modulator 13 can select the phase of the emitted light from binary or three or more values for each pixel, so that the recording reference light 2
Phase in the same modulation pattern and 2B generates a spatially modulated reference beam 32B ₁ for reproduction. On the other hand, half of the region 13A of the phase spatial light modulator 13, by selecting the phase of the outgoing light for each pixel from the binary or more values, relative to the modulation pattern of the reference light for reproduction 32B ₁ Thus, the reproduction reference light 32B ₂ whose phase is spatially modulated in a point-symmetric pattern with respect to the position of the optical axis of the optical system that irradiates the recording reference light and the reproduction reference light to the information recording layer 3.
Generate

These reproduction reference beams 32B₁, 32B_TwoIs
Part of the light enters the beam splitter 12 and is partially semi-reflective 12a.
Which passes through the lens and further converges through the objective lens 11
Reference beam 33B₁, 33B_TwoIrradiates the recording medium 1
Is done. Reference beam for reproduction 33B ₁, 33B_TwoIs the information recording layer
3 on the interface between the air gap layer 4 and the reflective film 5
The light converges to have the smallest diameter and is reflected by the reflection film 5.
The reproduction reference light reflected by the reflection film 5 is diffused light.
Then, it passes through the information recording layer 3 again.

In the information recording layer 3, the reproduction reference light 33 B ₂ before being reflected by the reflection film 5 generates reproduction light traveling to the opposite side to the reflection film 5 and is reflected by the reflection film 5. the reference beam 33B ₂ for regeneration after, reproduction light is generated that travels to the reflecting film 5 side. The reproduction light traveling to the opposite side to the reflection film 5 is emitted from the recording medium 1 as it is, and the reproduction light traveling to the reflection film 5 is reflected by the reflection film 5,
The light is emitted from the recording medium 1. These reproduction light are both represented by reference numeral 34A _1.

In the information recording layer 3, the reproduction reference light 33 B ₁ before being reflected by the reflection film 5 generates reproduction light traveling to the opposite side to the reflection film 5,
In the reference light 33B ₁ for regeneration after being reflected, the reproduction light is generated which travels to the reflecting film 5 side. The reproduction light traveling to the opposite side to the reflection film 5 is emitted from the recording medium 1 as it is, and the reproduction light traveling to the reflection film 5 is reflected by the reflection film 5 and emitted from the recording medium 1. These reproduction light are both represented by reference numeral 34A _2.

On the other hand, the reproduction reference beam 33B ₁
In is reflected, the reference light 34B ₁ for reproduction proceeds in the same direction as the reproduction light 34A _1. The reference beam for reproduction 33B ₂ is
It is reflected by the reflecting film 5, the reproduction-specific reference light 34B ₂ traveling in the same direction as the reproduction light 34A _2.

The reproduction beams 34A ₁ and 34A ₂ and the reproduction reference beams 34B ₁ and 34B ₂ are converted into parallel reproduction beams 35A ₁ and 35A ₂ and reproduction reference beams 35B ₁ and 35B ₂ by the objective lens 11. Incident on the beam splitter 12 and a part thereof is reflected by the semi-reflective surface 12a.
Is received by the

Each of the reproduction light beams 35A ₁ and 35A ₂ is light whose phase is spatially modulated similarly to the information light at the time of recording. However, the modulation patterns of the phases of the reproduction lights 35A ₁ and 35A ₂ are point-symmetric with each other.

[0076] in one half of the area of the photodetector 14, the combined light generated is superimposed with reproduction light 35A ₁ and the reproduction-specific reference light 35B ₁ is is incident. In the other half area of the photodetector 14, the reproduction light 35A ₂ and the reproduction reference light 35B ₂
And the combined light generated by superimposing. Each of these two types of combined light is light whose intensity is spatially modulated according to the recorded information. However, the intensity modulation patterns of the two types of combined light are point-symmetric with each other. Therefore, information can be reproduced by detecting a two-dimensional pattern of one of the two types of combined light in the photodetector 14. Here, it is assumed that reproduces information by detecting the two-dimensional patterns of the intensity of the combined light generated is superimposed with reproduction light 35A ₁ and the reproduction-specific reference light 35B ₁ is.

Next, the reproduction light, the reproduction reference light and the combined light will be described in detail with reference to FIG. FIG.
2, (a) is the intensity of the reproduction light, (b) is the phase of the reproduction light, (c) is the intensity of the reproduction reference light, (d) is the phase of the reproduction reference light, and (e) is the intensity of the combined light. Represents strength. FIG.
2 sets the phase of each pixel of the information light to one of the first phase and the second phase, and sets the phase of each pixel of the recording reference light and the reproduction reference light to each of the reference phase and the second phase. An example in the case where the phase is set to one of the first phase and the second phase is shown. In this case, the phase of the reproduction light for each pixel is one of the first phase and the second phase, similarly to the information light. Therefore, the phase difference between the reproduction light and the reference light for reproduction is zero, ± π / 2 (rad), or ± π (rad). Here, assuming that the intensity of the reproduction light is equal to the intensity of the reproduction reference light, the phase difference between the reproduction light and the reproduction reference light is zero as shown in FIG. In a pixel where the phase difference between the reproduction light and the reproduction reference light is ± π (rad), it becomes zero in principle, and the phase difference between the reproduction light and the reproduction reference light is ± π / rad. 2 (ra
In the pixel of d), the intensity is １ ／ of the intensity of the pixel in which the phase difference is zero. In FIG. 12E, the phase difference is ± π
(Rad) is represented by “0”, the intensity of a pixel having a phase difference of ± π / 2 (rad) is represented by “1”, and the intensity of a pixel having a phase difference of zero is represented by “2”. It is represented by

In the examples shown in FIGS. 10 to 12, the intensity of the combined light for each pixel is ternary. And, for example, FIG.
As shown in FIG. 2 (e), the intensity “0” corresponds to the 2-bit data “00”, the intensity “1” corresponds to the 2-bit data “01”, and the intensity “2” corresponds to the 2-bit data. It can correspond to data “10”. Thus, FIG.
In the examples shown in FIGS. 0 to 12, the intensity and phase of the reproduction light are made similar to those in the case shown in FIGS. The amount of information carried by the combined light can be increased, and as a result,
The recording density of the recording medium 1 can be improved.

Assuming that the phase difference between the reproduction light and the reference light for reproduction is δ, the intensity I of the combined light is expressed by the above equation (1). Equation (1) shows that the intensity I of the combined light changes according to the phase difference between the reproduction light and the reproduction-specific reference light. Therefore, the absolute value of the phase difference between the reproduction light and the reproduction reference light, that is, the absolute value of the phase difference between the information light and the reproduction reference light is, for example, n (n is n) within a range from zero to π (rad). If it is set to a value (an integer of 2 or more), the intensity I of the combined light also becomes the n value.

As described above, information is recorded on the information recording layer 3 of the recording medium 1 using the information light whose phase is spatially modulated and the recording reference light whose phase is spatially modulated. In this case, the modulation pattern of the phase of the information light is determined based on the information to be recorded and the modulation pattern of the phase of the recording reference light used for recording the information. This will be described in detail with reference to FIG. Since the information recorded in the information recording layer 3 is reproduced based on the pattern of the intensity of the combined light, the information to be recorded is the data of the pattern of the desired intensity of the combined light as shown in FIG. Is converted to The modulation pattern of the phase of the recording reference light is the same as the modulation pattern of the phase of the reproduction reference light as shown in FIG. The modulation pattern of the phase of the information light is
The data of the desired intensity pattern of the combined light as shown in FIG. 12E and the data of the phase modulation pattern of the reproduction reference light and the recording reference light as shown in FIG. The phase calculation used is determined so that the modulation pattern is the same as the modulation pattern of the phase of the desired reproduction light as shown in FIG.

As shown in FIG. 12D, the information recording layer 3 on which information has been recorded using the information light having the phase modulation pattern determined as described above and the recording reference light is used. By irradiating a reproduction reference light having a modulation pattern having the same phase as that of the recording reference light, a combined light having an intensity pattern as shown in FIG. The information recorded on the information recording layer 3 is reproduced based on the pattern.

The phase modulation pattern of the recording reference light and the reproduction reference light may be created based on information unique to the individual who is the user. Information unique to an individual includes a password, a fingerprint, a voiceprint, and an iris pattern. In this case, only a specific individual who has recorded information on the recording medium 1 can reproduce the information.

As described above, by using the recording reference light and the reproduction reference light whose phases are spatially modulated, the multiplex recording by the phase encoding multiplexing method and the information multiplexed recording Playback can be performed.

Next, the configuration of the optical head 40 will be described with reference to FIG. FIG. 6 is a sectional view showing the optical head 40. As shown in FIG. 6, the optical head 40 has a head main body 41 containing a recording / reproducing optical system, a direction perpendicular to the recording medium 1 and a direction crossing tracks on the recording medium 1. And an actuator 50 that can move the optical head main body 41 within the range. The semiconductor laser 1 of the coherent light generation device 101 is provided on the bottom of the head body 41 via a support 42.
02 is fixed, and the reflection-type phase spatial light modulator 44 and the photodetector 45 are fixed. Photodetector 45
A microlens array 46 is attached to the light receiving surface of. In the head body 41, a prism block 48 is provided above the phase spatial light modulator 44 and the photodetector 45. A collimator lens 47 is provided near the end of the prism block 48 on the semiconductor laser 102 side. An opening is formed in the surface of the head main body 41 facing the recording medium 1, and the objective lens 11 is provided in this opening. This objective lens 11
A quarter wave plate 49 between the prism block 48 and the
Is provided.

The phase spatial light modulator 44 has a large number of pixels arranged in a lattice, and sets the phase of emitted light to one of two values different from each other by π (rad) for each pixel. As a result, the phase of light can be spatially modulated. The phase spatial light modulator 44 further sets the polarization direction of the outgoing light to 9 relative to the polarization direction of the incident light.
It is designed to rotate by 0 °. Phase spatial light modulator 4
As 4, for example, a reflective liquid crystal element can be used.

The photodetector 45 has a large number of pixels arranged in a lattice, and can detect the intensity of light received for each pixel. Also, the micro lens array 46
Has a plurality of microlenses arranged at positions facing the light receiving surface of each pixel of the photodetector 45.

As the photodetector 45, a CCD solid-state imaging device or a MOS solid-state imaging device can be used. In addition, as the photodetector 45, a smart photosensor in which a MOS solid-state imaging device and a signal processing circuit are integrated on one chip (for example, the document “O plus E, September 1996,
No. 202, pages 93-99 ". ) May be used. Since this smart optical sensor has a high transfer rate and a high-speed calculation function, high-speed reproduction can be performed by using this smart optical sensor. For example, reproduction at a transfer rate of the order of G bits / second can be performed. Becomes possible.

The prism block 48 has a polarizing beam splitter surface 48a and a reflecting surface 48b. The polarization beam splitter surface 48a of the polarization beam splitter surface 48a and the reflection surface 48b is disposed closer to the collimator lens 47. Polarizing beam splitter surface 48a and reflecting surface 4
8b, the normal direction of each of them is inclined by 45 ° with respect to the optical axis direction of the collimator lens 47, and they are arranged in parallel with each other.

The phase spatial light modulator 44 is arranged below the polarizing beam splitter surface 48a, and the photodetector 45 is arranged below the reflecting surface 48b. Also, 4
The half-wave plate 49 and the objective lens 11 are arranged at a position above the polarizing beam splitter surface 48a. In addition,
The collimator lens 47 and the objective lens 11 may be hologram lenses.

As will be described later in detail, the polarization beam splitter surface 48a of the prism block 48 has an information beam, a recording reference beam, and a reproduction beam before passing through a quarter-wave plate 49 due to a difference in polarization direction. The optical path of the reference light and the optical path of the return light from the recording medium 1 after passing through the quarter-wave plate 49 are separated.

The prism block 48, the phase spatial light modulator 44, and the photodetector 45 in FIG. 6 correspond to the beam splitter 12, the phase spatial light modulator 1 in FIG.
3. Corresponds to the photodetector 14.

Next, the operation of the recording / reproducing optical system when recording information will be described. The semiconductor laser 102 emits coherent S-polarized light. Note that S-polarized light is linearly polarized light whose polarization direction is perpendicular to the plane of incidence (the paper surface in FIG. 6), and P-polarized light described below is linearly polarized light whose polarization direction is parallel to the plane of incidence.

The S-polarized laser light emitted from the semiconductor laser 102 is collimated by the collimator lens 47, enters the polarization beam splitter surface 48a of the prism block 48, and is reflected by the polarization beam splitter surface 48a. The light enters the phase spatial light modulator 44. The light emitted from the phase spatial light modulator 44 becomes information light in which the phase of the light is spatially modulated based on the information to be recorded in one half area, and is emitted from all the pixels in the other half area. The recording reference light having the same phase of the emitted light or the recording reference light whose phase is spatially modulated. The light emitted from the phase spatial light modulator 44 has its polarization direction rotated by 90 °, and
It becomes polarized light.

Since the information light and the recording reference light, which are the light emitted from the phase spatial light modulator 44, are P-polarized light, they pass through the polarization beam splitter surface 48a of the prism block 48 and pass through the quarter-wave plate 49. The light passes through to become circularly polarized light.
The information light and the recording reference light are condensed by the objective lens 11 and irradiated on the recording medium 1. The information light and the recording reference light pass through the information recording layer 3, converge so as to have the smallest diameter on the boundary surface between the air gap layer 4 and the reflection film 5, and are reflected by the reflection film 5. The information light and the recording reference light that have been reflected by the reflection film 5 become diffused light and pass through the information recording layer 3 again. Semiconductor laser 10
2 is set to a high output for recording, an interference pattern due to interference between the information light and the reference light for recording is recorded on the information recording layer 3.

The return light from the recording medium 1 is
The light is collimated by 1 and passes through the quarter-wave plate 49 to become S-polarized light. This return light is reflected by the polarization beam splitter surface 48a of the prism block 48, further reflected by the reflection surface 48b, and enters the photodetector 45 via the micro lens array 46.

In recording information, during the period when the light beam from the objective lens 11 passes through the address servo area 6 of the recording medium 1, the output of the semiconductor laser 102 is set to a low output for reproduction, and Phase spatial light modulator 44
Emits light with the same phase for all pixels without modulating the phase of the light. Based on the output of the photodetector 45 at this time, a basic clock, address information, a focus error signal, and tracking error information can be obtained.

Next, the operation of the recording / reproducing optical system at the time of reproducing information will be described. When reproducing information, the output of the semiconductor laser 102 is set to a low output for reproduction.
The S-polarized laser light emitted from the semiconductor laser 102 is converted into parallel light by the collimator lens 47, enters the polarization beam splitter surface 48a of the prism block 48, is reflected by the polarization beam splitter surface 48a, and becomes a phase spatial light. The light enters the modulator 44. The light emitted from the phase spatial light modulator 44 is the reproduction reference light in which the phase of the emitted light is the same for all pixels or the reproduction reference light in which the phase is spatially modulated. Further, the light emitted from the phase spatial light modulator 44 is turned into a P-polarized light by rotating the polarization direction by 90 °.

Since the reference light for reproduction, which is the light emitted from the phase spatial light modulator 44, is P-polarized light, the prism block 48
The light passes through the polarizing beam splitter surface 48a, passes through the quarter wavelength plate 49, and becomes circularly polarized light. This reference light for reproduction is condensed by the objective lens 11 and is irradiated on the recording medium 1. The reproduction reference light passes through the information recording layer 3, converges on the boundary surface between the air gap layer 4 and the reflection film 5 so as to have the smallest diameter, and is reflected by the reflection film 5. Reflective film 5
The reference light for reproduction after being reflected by the light becomes diffused light and passes through the information recording layer 3 again. Reproduction light is generated from the information recording layer 3 by the reproduction reference light.

The return light from the recording medium 1 includes a reproduction light and a reproduction reference light. This return light is converted into parallel light by the objective lens 11, passes through the quarter wavelength plate 49, and becomes S-polarized light. This return light is reflected by the polarization beam splitter surface 48a of the prism block 48, further reflected by the reflection surface 48b, passes through the micro lens array 46,
The light enters the photodetector 45. The information recorded on the recording medium 1 can be reproduced based on the output of the photodetector 45.

In reproducing information, during the period when the light beam from the objective lens 11 passes through the address servo area 6 of the recording medium 1, the basic clock, the address information, and the focus error are output based on the output of the photodetector 45. Signal and tracking error information can be obtained.

The phase spatial light modulator 44 may not rotate the polarization direction of light. In this case,
The polarization beam splitter surface 48a of the prism block 48 in FIG. 6 is changed to a semi-reflective surface. Alternatively, a quarter-wave plate is provided between the prism block 48 and the phase spatial light modulator 44, and the S-polarized light from the prism block 48 is converted into circularly-polarized light by the quarter-wave plate. Incident on the phase spatial light modulator 44,
May be converted into P-polarized light by a quarter-wave plate and transmitted through the polarizing beam splitter surface 48a. Further, the phase spatial light modulator that can set the phase of the emitted light to any one of three or more values for each pixel is not limited to the one using liquid crystal. May be configured such that the position of the reflection surface is adjusted for each pixel in the traveling direction of.

Next, an example of a method of generating focus error information in the present embodiment will be described with reference to FIG. FIG. 13 is an explanatory diagram showing the contour of the incident light on the light receiving surface of the photodetector 45. In the method of generating focus error information in the present example, focus error information is generated based on the size of the contour of incident light on the light receiving surface of the photodetector 45 as described below. First, when the light beam from the objective lens 11 is in a focused state in which the light beam converges on the boundary surface between the air gap layer 4 and the reflective film 5 on the recording medium 1 so as to have the smallest diameter, the light beam on the light receiving surface of the photodetector 45 It is assumed that the contour of the incident light is the contour indicated by reference numeral 60 in FIG. The position where the light beam from the objective lens 11 has the smallest diameter is the air gap layer 4 and the reflection film 5.
Is shifted to the near side from the boundary surface of the photodetector 45,
The diameter of the contour of the incident light on the light receiving surface becomes smaller as indicated by reference numeral 61 in FIG. Conversely, if the position where the light beam from the objective lens 11 has the smallest diameter is shifted farther than the boundary surface between the air gap layer 4 and the reflection film 5, the incident light on the light receiving surface of the photodetector 45 The contour has a larger diameter as indicated by reference numeral 62 in FIG.
Therefore, a focus error signal can be obtained by detecting a signal corresponding to a change in the diameter of the contour of the incident light on the light receiving surface of the photodetector 45 based on the in-focus state. Specifically, for example, it is possible to generate a focus error signal based on the increase / decrease number of pixels corresponding to a bright portion on the light receiving surface of the photodetector 45 based on the in-focus state.

In this embodiment, the optical head main body 4 in the direction perpendicular to the recording medium 1 is set based on the focus error signal so that the light beam is always in focus.
Adjust the position of 1 to perform focus servo. In addition,
When the light beam passes through the information recording area 7, focus servo is not performed, and the state at the time when the light beam passed through the immediately preceding address servo area 6 is maintained.

Next, an example of a method of generating tracking error information and a method of tracking servo according to the present embodiment will be described with reference to FIGS.
In this example, the address servo area 6 of the recording medium 1 includes positioning information used for tracking servo, as shown in FIG. Two pits 71A, one pit 71B, one pit 71C in order from
Are formed. The two pits 71A are arranged symmetrically with respect to the track 70 at the position indicated by the symbol A in FIG. The pit 71B is shown in FIG.
In the position indicated by the symbol B, the track 70 is disposed at a position shifted to one side with respect to the track 70. Pit 71C
Are arranged at positions indicated by reference numeral C in FIG.

As shown in FIG. 14A, the light beam 7
When the light beam 72 passes through the positions A, B, and C, the light detector 45
Are as shown in FIG. 14B. That is, the amount of light received when passing through the position A is the largest, and the amount of light received when passing through the position B and the amount of light received through the position C are equal to each other and smaller than the amount of light received when passing through the position A.

On the other hand, as shown in FIG. 15 (a), when the light beam 72 is shifted toward the pit 71C with respect to the track 70, the light beam 72
The total amount of light received by the photodetector 45 when passing through C is shown in FIG.
The result is as shown in FIG. That is, the amount of light received when passing through position A is the largest, the amount of light received when passing through position C is the largest, and the amount of light received when passing through position B is the smallest. The absolute value of the difference between the amount of light received when passing through the position B and the amount of light received when passing through the position C increases as the amount of deviation of the light beam 72 from the track 70 increases.

Although not shown, when the light beam 72 is shifted toward the pit 71B with respect to the track 70, the amount of light received when passing through the position A is the largest, and then the amount of light received when passing through the position B is the largest. Is large, and the amount of received light when passing through the position C is the smallest. The absolute value of the difference between the amount of light received when passing through the position B and the amount of light received when passing through the position C is determined by the
It becomes larger as the amount of deviation from becomes larger.

From the above, the direction and magnitude of the displacement of the light beam 72 with respect to the track 70 can be determined from the difference between the amount of light received when passing the position B and the amount of light received when passing the position C. Accordingly, the difference between the amount of light received when passing through position B and the amount of light received when passing through position C can be used as a tracking error signal. The pit 71A serves as a reference for detecting the amount of light received when passing through the position B and the amount of light received when passing through the position C.

The tracking servo in this example is specifically performed as follows. First, the photodetector 4
5, the timing at which the total amount of received light first reaches a peak, that is, the timing when passing through the position A is detected. Next, the timing at the time of passing through the position B and the timing at the time of passing through the position C are predicted based on the timing at the time of passing through the position A. Next, at each predicted timing, the amount of light received when passing through position B and the amount of light received when passing through position C are detected. Finally, the difference between the amount of light received when passing through the position B and the amount of light received when passing through the position C is detected, and this is used as a tracking error signal. Then, tracking servo is performed based on the tracking error signal so that the light beam 72 always follows the track 70. When the light beam 72 passes through the information recording area 7, tracking servo is not performed, and the state at the time when the light beam 72 passes through the immediately preceding address servo area 6 is maintained.

Note that the method of generating tracking error information and the method of tracking servo in this embodiment are as follows.
Instead of the above method, for example, a push-pull method may be used. In this case, a row of pits along the track direction is formed in the address servo area 6 as positioning information used for tracking servo, and the shape of incident light on the light receiving surface of the photodetector 45 is determined. The change is detected to generate tracking error information.

In the present embodiment, coherent light is generated by repeatedly outputting an optical pulse including only the first peak in the relaxation oscillation from the semiconductor laser 102 for a predetermined period. Therefore, according to the present embodiment, it is possible to generate coherent light having uniform coherence over a predetermined period and having sufficient energy to change the optical characteristics of the information recording layer 3 of the recording medium 1. Can be. In the present embodiment, the information light and the recording reference light are generated based on the coherent light, and information is recorded in the information recording area 7 by an interference pattern due to the interference between the information light and the recording reference light. Then, the recording medium 1 is irradiated with the information light and the recording reference light. Therefore, according to the present embodiment, the information recording layer 3 has uniform coherence over a predetermined period while using the semiconductor laser 102 that generates relaxation oscillation after the rise of the light emission output.
, Coherent light having sufficient energy to change the optical characteristics of the hologram is generated, and information can be recorded using holography using the coherent light.

In this embodiment, the recording medium 1 is provided with the address servo area 6. The address servo area 6 includes address information for identifying each information recording area 7 and positioning information for matching the irradiation positions of the information light, the recording reference light, and the reproduction reference light with respect to each information recording area 7. Has been recorded. The optical information recording / reproducing apparatus detects address information recorded in the address servo area 6 and identifies each information recording area 7. Therefore, according to the present embodiment, each information recording area 7 can be easily identified. Further, the optical information recording / reproducing apparatus detects the positioning information recorded in the address servo area 6 and adjusts the irradiation position of the information light, the recording reference light, and the reproduction reference light to each information recording area 7. . Therefore, according to the present embodiment, an information beam,
The irradiation positions of the recording reference light and the reproduction reference light can be easily adjusted.

Further, in the present embodiment, at the time of recording information, the information light whose recording light is spatially modulated based on the information to be recorded and the recording reference light are transmitted to the information recording layer 3 of the recording medium 1. And information is recorded on the information recording layer 3 by an interference pattern due to interference between the information light and the recording reference light.
When reproducing information, the reference light for reproduction is applied to the information recording layer 3.
To generate a combined light by superimposing the reproduction light generated by the information recording layer 3 and the reproduction reference light,
The information is reproduced by detecting the combined light.

Therefore, according to the present embodiment, it is not necessary to separate the reproduction light and the reproduction reference light when reproducing information.
Therefore, at the time of recording information, it is not necessary to make the information light and the recording reference light incident on the recording medium at a predetermined angle to each other. In fact, in the present embodiment, the irradiation of the information light, the recording reference light and the reproduction reference light and the reproduction light are performed so that the information light, the recording reference light, the reproduction reference light and the reproduction light are coaxially arranged. Is performed from the same surface side of the information recording layer 3. Therefore, according to the present embodiment, the optical system for recording and reproduction can be made small.

In the conventional reproducing method, the reproducing light and the reproducing reference light are separated and only the reproducing light is detected. Therefore, the reproducing reference light also enters the photodetector for detecting the reproducing light. Thus, there is a problem that the SN ratio of the reproduction information is deteriorated. On the other hand, in the present embodiment, since information is reproduced using the reproduction light and the reproduction reference light, the SN ratio of the reproduction information does not deteriorate due to the reproduction reference light. Therefore, according to the present embodiment, it is possible to improve the SN ratio of the reproduction information.

Further, according to the present embodiment, all of the information light, the recording reference light and the reproduction reference light are arranged coaxially and converge so as to have the smallest diameter at the same position. Therefore, the configuration of the optical system for recording and reproduction can be simplified.

Note that the present invention is not limited to the above-described embodiment, and various changes can be made. For example, the coherent light generation apparatus and method of the present invention can be applied not only to the case where a semiconductor laser is used, but also to the case where another laser that generates relaxation oscillation after the emission output rises is used.

The optical information recording apparatus and method according to the present invention are not limited to the apparatus and method described in the embodiment, but generate information light and reference light based on coherent light. The present invention can be applied to all apparatuses and methods for recording information by irradiating the recording medium with the information.

[0119]

As described above, in the coherent light generating apparatus or method according to the present invention, the laser repeatedly outputs an optical pulse including only the first peak in the relaxation oscillation over a predetermined period, and outputs a plurality of pulses within this predetermined period. Generates coherent light having uniform coherence over a predetermined period of time. Therefore, according to the present invention, it is possible to generate coherent light having uniform coherence over a predetermined period while using a laser that generates relaxation oscillation after the emission output rises.

Further, in the optical information recording apparatus or method according to the present invention, the laser repeatedly outputs an optical pulse including only the first peak in the relaxation oscillation over a predetermined period. To generate coherent light with uniform coherence over Then, an information light and a reference light are generated based on the coherent light, and the information light and the reference light are generated on the recording medium such that information is recorded in an information recording area by an interference pattern due to interference between the information light and the reference light. Irradiate with reference light.
Therefore, according to the present invention, coherent light having uniform coherence is generated over a predetermined period while using a laser that generates relaxation oscillation after the rising of the light emission output, and information using holography is generated by using the coherent light. This has the effect that the recording can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a coherent light generation device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of an operation of the coherent light generation device according to one embodiment of the present invention.

FIG. 3 is a waveform chart showing an example of the operation of the coherent light generation device according to one embodiment of the present invention.

FIG. 4 is a waveform diagram showing an example of a relationship between a drive current and a light emission output of a semiconductor laser when a drive current having a constant value equal to or more than a light emission threshold is supplied to the semiconductor laser over a predetermined period.

FIG. 5 is a block diagram showing a configuration of an optical information recording / reproducing apparatus according to one embodiment of the present invention.

FIG. 6 is a sectional view of an optical head in the optical information recording / reproducing apparatus shown in FIG.

FIG. 7 is an explanatory diagram showing a principle of information recording in the optical information recording / reproducing apparatus shown in FIG.

FIG. 8 is an explanatory diagram showing the principle of information reproduction in the optical information recording / reproducing apparatus shown in FIG.

9 is a waveform chart for explaining in detail the principle of information reproduction in the optical information recording / reproducing apparatus shown in FIG.

FIG. 10 is an explanatory diagram showing a principle of information recording when performing multiplex recording by a phase encoding multiplex method in the optical information recording / reproducing apparatus shown in FIG.

11 is an explanatory diagram showing the principle of information reproduction in the case of performing multiplex recording by the phase encoding multiplex method in the optical information recording / reproducing apparatus shown in FIG.

12 is a waveform diagram for explaining in detail the principle of information reproduction in the case of performing multiplex recording by the phase encoding multiplex method in the optical information recording / reproducing apparatus shown in FIG.

13 is an explanatory diagram illustrating an example of a method of generating focus error information in the optical information recording / reproducing device illustrated in FIG.

14 is an explanatory diagram for describing an example of a method of generating tracking error information and a method of tracking servo in the optical information recording / reproducing apparatus shown in FIG.

FIG. 15 is an explanatory diagram for explaining an example of a method of generating tracking error information and a method of tracking servo in the optical information recording / reproducing apparatus shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Recording medium, 3 ... Information recording layer, 5 ... Reflection film, 6 ... Address servo area, 7 ... Information recording area, 11 ... Objective lens, 40 ... Optical head, 41 ... Head main body, 44 ... Phase spatial light modulation Detector 45 photodetector 47 collimator lens 48 prism block 48a polarizing beam splitter surface 49 quarter-wave plate 101 coherent light generator 102 semiconductor laser 103 driving circuit , 104 ... Control circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D090 AA01 BB16 CC01 EE01 KK20 LL01 5D119 AA21 BA01 FA02 HA36 5F073 AB27 BA06 EA03 EA13 FA05 FA06 FA30 GA04 GA12

Claims (8)

[Claims] 1. A coherent light generation device that generates coherent light having uniform coherence over a predetermined period, comprising: a laser that generates relaxation oscillation after rising of a light emission output; a driving circuit that drives the laser; An optical pulse including only the first peak in the relaxation oscillation is repeatedly output from the laser over a predetermined period, and a plurality of light pulses within the predetermined period generate coherent light having uniform coherence over a predetermined period. And a control means for controlling the driving circuit. 2. The coherent light generation device according to claim 1, wherein said laser is a semiconductor laser. 3. A coherent light generation method for generating coherent light having uniform coherence over a predetermined period, comprising: driving a laser that generates relaxation oscillation after a rising of a light emission output; And outputting a light pulse including only the first peak in a predetermined period, and repeatedly outputting the light pulse over a predetermined period, by a plurality of light pulses generated within the predetermined period, uniform over a predetermined period Generating a coherent light having coherence. 4. The method according to claim 3, wherein the laser is a semiconductor laser. 5. An optical information recording apparatus for recording information using holography in each information recording area of a recording medium having a plurality of information recording areas, wherein the apparatus has uniform coherence over a predetermined period. A coherent light generation device that generates coherent light, and, based on the coherent light generated by the coherent light generation device, generate information light and reference light that carry information to be recorded, and generate information light in the information recording area. An optical system that irradiates the recording medium with information light and reference light so that information is recorded by an interference pattern due to interference with the reference light, wherein the coherent light generation device includes: A laser that generates relaxation oscillation; a driving circuit that drives the laser; and only a first peak in the relaxation oscillation from the laser. Control means for controlling the drive circuit so that the light pulses including the light pulses are repeatedly output over a predetermined period, and a plurality of light pulses within the predetermined period generate coherent light having uniform coherence over a predetermined period. An optical information recording device, comprising: 6. The optical information recording apparatus according to claim 5, wherein said laser is a semiconductor laser. 7. An optical information recording method for recording information in each information recording area of a recording medium having a plurality of information recording areas by using holography, comprising: coherent light having uniform coherence over a predetermined period. Generating an information light and a reference light carrying information to be recorded, based on the coherent light generated by the step of generating the coherent light, and an information light and a reference light in the information recording area. Irradiating the recording medium with information light and reference light so that information is recorded by an interference pattern caused by the interference of the light. The step of generating the coherent light includes: Driving the laser to generate a light pulse including only the first peak in the relaxation oscillation from the laser; A step of repeatedly executing the procedure of outputting the optical pulse over a period of time, and generating a coherent light having uniform coherence over a predetermined period by a plurality of light pulses generated within the predetermined period. Optical information recording method. 8. The optical information recording method according to claim 7, wherein said laser is a semiconductor laser.