JP2005203095A - Optical information recording device and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To record information in each information recording area by holography while moving a recording medium having two or more information recording areas using a practical light source. <P>SOLUTION: This device has a recording medium moving means 81 to move a recording medium 401, an optical head 440 to radiate information light and recording reference light to the recording medium, and a control means to make the position irradiated with the information light and the recording reference light follow the movement of the recording medium at least for a certain time. The optical head has a recording laser 411 to emit a recording laser used to generate the information light and the recording reference light, and a servo laser 412 to emit a servo laser in a wavelength different from the recording laser used for positioning. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides an optical information recording apparatus for recording information on a recording medium by irradiating information light and a recording reference light on a recording medium on which information is recorded using holography, and information recording. Information recording / reproducing apparatus for reproducing information from the recording medium by irradiating the recording medium with the reproducing light

  Holographic recording, in which information is recorded on a recording medium using holography, is generally performed by superimposing light having image information and reference light inside the recording medium, and forming an interference pattern at that time on the recording medium. Done by writing. At the time of reproducing the recorded information, the image information is reproduced by diffraction by the interference pattern by irradiating the recording medium with the reference light.

  In recent years, volume holography, particularly digital volume holography, has been developed and attracted attention for practical use for ultra-high density optical recording. Volume holography is a method of writing interference patterns in three dimensions by actively utilizing the thickness direction of the recording medium. Increasing the thickness increases the diffraction efficiency and increases the recording capacity using multiple recording. There is a feature that can be planned. Digital volume holography is a computer-oriented holographic recording method that uses a recording medium and a recording method similar to those of volume holography, but restricts image information to be recorded to a binarized digital pattern. In this digital volume holography, for example, image information such as an analog picture is once digitized, developed into two-dimensional digital pattern information, and recorded as image information. At the time of reproduction, the digital pattern information is read and decoded so that the original image information is restored and displayed. As a result, 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 binary data and performing error correction. It becomes possible.

  Incidentally, a general recording apparatus that records information on a disk-shaped recording medium using light includes an optical head that irradiates the recording medium with light for information recording. In this recording apparatus, information is recorded on the recording medium by irradiating the recording medium with light for recording information from the optical head while rotating the recording medium. In this recording apparatus, a semiconductor laser is generally used as a light source for generating information recording light.

  In holographic recording, as in the general recording apparatus described above, while rotating the recording medium, the recording medium is irradiated with the information light and the reference light, and a plurality of information recording areas in the recording medium are sequentially applied. It is conceivable to record information. In this case, it is desirable to use a practical semiconductor laser as a light source for information light and reference light as in a general recording apparatus.

  However, a recording medium for holographic recording is formed using the current holographic photosensitive material, and the recording medium is irradiated with information light and reference light generated using a semiconductor laser while rotating the recording medium. In such a case, there are the following problems. That is, in this case, there is a problem in that it is difficult to give sufficient exposure energy to record information with an interference pattern in one information recording area of the recording medium in a short time. Therefore, it is conceivable to lengthen the exposure time in order to give sufficient exposure energy to one information recording area. However, if this is done, the movement distance of the information recording area during the exposure time for one information recording area increases, and the accuracy of information decreases.

  Here, the above problem will be described in detail with a specific example. When a high-power light source such as a pulse laser is used as the light source instead of a semiconductor laser, it is possible to record information on the recording medium while rotating the recording medium. For example, consider a case where a pulse laser having a maximum output of several kW and capable of generating pulsed light of several tens of ns is used as the light source. In this case, it is assumed that the light intensity on the recording medium is 200 W. The pulse width of the pulsed light is 20 ns, and the linear velocity of the information recording area is 2 m / s. In this case, the moving distance of the information recording area during the exposure time for one information recording area is 0.04 μm, which is one tenth or less of the wavelength of light, and the accuracy of information can be sufficiently maintained. However, it is not practical to use the pulse laser as described above as the light source.

  Next, consider the case where a semiconductor laser is used as the light source. In this case, it is assumed that the light intensity on the recording medium is 20 mW, and the linear velocity of the information recording area is 2 m / s. In this case, in order to give the same exposure energy as in the case of using the pulse laser to one information recording area, the exposure time is required to be 200 μs, which is 10,000 times that in the case of using the pulse laser. . The moving distance of the information recording area during this exposure time reaches 400 μm, and it becomes difficult to record information by the interference pattern.

  The present invention has been made in view of such problems, and its purpose is to use holography in each information recording area while moving a recording medium having a plurality of information recording areas using a practical light source. An object of the present invention is to provide an optical information recording apparatus and method capable of recording information.

  An optical information recording apparatus of the present invention is an optical information recording apparatus for recording information on the recording medium by irradiating the recording medium on which information is recorded using holography with information light and recording reference light, A recording medium moving means for moving the recording medium; an optical head for irradiating the recording medium with the information light and the recording reference light; and the information light irradiated from the optical head for at least a predetermined period; Control means for following the movement of the recording medium with the irradiation position of the recording reference light on the recording medium, and the optical head is used for generating the information light and the recording reference light. The recording laser that emits the recording laser light and the recording laser light used for the servo for positioning the information light and the recording reference light with respect to the recording medium have a wavelength Using servo lasers that emit different servo laser light, information light generating means for generating information light that spatially modulates and carries information using the recording laser light, and using the recording laser light The information light and the recording are recorded so that information is recorded on the recording medium by a recording reference light generating means for generating recording reference light and an interference pattern due to interference between the information light and the recording reference light. An optical system for irradiating the recording medium with the reference light for recording and irradiating the recording medium with the servo laser light; and a photodetector for detecting the servo laser light irradiating the recording medium and carrying positioning information; It is provided with.

  Further, in the optical information recording apparatus of the present invention, the control means irradiates the recording medium with the information light and the recording reference light emitted from the optical head according to positioning information detected by the photodetector. It is preferable that the position follows the movement of the recording medium.

  The optical information recording / reproducing apparatus of the present invention records information on the recording medium by irradiating the recording medium on which information is recorded using holography with the information light and the recording reference light, and the information is recorded. An optical information recording / reproducing apparatus for reproducing information from the recording medium by irradiating the recording medium with reproduction light, and a recording medium moving means for moving the recording medium, and the recording medium The optical head that irradiates the information light, the recording reference light, and the reproduction light, and the irradiation position in the recording medium of the information light and the recording reference light that are irradiated from the optical head for at least a certain period of time. Control means for following movement, and the optical head emits a recording / reproducing laser beam used for generating the information light, the recording reference light, and the reproducing light. A servo laser beam having a wavelength different from that of the recording / reproducing laser beam used for positioning the information beam, the recording reference beam and the reproducing beam with respect to the recording medium. A laser, information light generating means for generating information light for spatially modulating and carrying information using the recording / reproducing laser light, and recording reference light using the recording / reproducing laser light Reference light generation means for recording, reproduction light generation means for generating reproduction light using the recording / reproduction laser light, and an interference pattern due to interference between the information light and the recording reference light on the recording medium Reproduction generated from the recording medium by the reproduction light by irradiating the recording medium with the information light and the recording reference light, irradiating the recording light with the reproduction light so that information is recorded An optical system for irradiating the recording medium with the servo laser light, a photodetector for detecting the reproduction light, and detecting the servo laser light that irradiates the recording medium and carries positioning information. And a photodetector.

  Further, in the optical information recording apparatus of the present invention, the control means irradiates the recording medium with the information light and the recording reference light emitted from the optical head according to positioning information detected by the photodetector. It is preferable that the position follows the movement of the recording medium.

  In the optical information recording apparatus of the present invention, the recording medium is moved by the recording medium moving means, and the information light and the reference light are irradiated to the recording medium by the irradiation means. Further, the irradiation position of the information light and the reference light is moved by the control means so that the irradiation position of the information light and the reference light follows one moving information recording area for a predetermined period. Thereby, information light and reference light are continuously irradiated to one information recording area for a predetermined period. Therefore, the information recording area is irradiated with the information light and the reference light for a time sufficient to record information in the information recording area without causing a deviation between the information recording area and the irradiation position of the information light and the reference light. Is possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment] First, an outline of a recording medium 1 used in the first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a part of one track in the recording medium 1. The recording medium 1 has a disk shape and has a plurality of tracks TR. Each track TR is provided with a plurality of address / servo areas 6 at equal intervals. Between adjacent address / servo areas 6, one or a plurality of information recording areas 7 are provided. FIG. 1 shows an example in which four information recording areas 7 are provided at equal intervals between adjacent address / servo areas 6.

  The address / servo area 6 includes information for generating a basic clock as a reference for various operation timings in the optical information recording / reproducing apparatus, information for performing focus servo by the sampled servo system, and by sampled servo system. Information for performing tracking servo and address information are recorded in advance by embossed pits or the like. In addition, information for performing focus servo is not recorded in the address / servo area 6, and focus servo may be performed using a boundary surface 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 and corresponds to the identification information in the present invention. The information for generating the basic clock, the information for performing the focus servo, and the information for performing the tracking servo are the irradiation positions of the information light, the recording reference light, and the reproduction reference light with respect to each information recording area 7. This is information for matching and corresponds to the positioning information in the present invention.

  Here, an outline of the optical information recording method according to the present embodiment will be described with reference to FIG. In the present embodiment, when information is recorded in the information recording area 7 of the recording medium 1, the recording medium 1 is rotated (moved) in the direction indicated by the symbol R in FIG. As a result, the address / servo area 6 and the information recording area 7 move in the direction indicated by the symbol R. An optical head, which will be described later, irradiates the recording medium 1 with information light and recording reference light so that information is recorded on the information recording area 7 by an interference pattern due to interference between the information light and the recording reference light. . The optical head moves the irradiation position of the information light and the recording reference light so that the irradiation position of the information light and the recording reference light follows the one information recording area 7 that moves for a predetermined period. Thereby, the information light and the recording reference light are continuously irradiated to one information recording area 7 for a predetermined period. Accordingly, the information light and the recording light are recorded in the information recording area 7 for a time sufficient to record the information in the information recording area 7 without causing a deviation between the irradiation position of the information recording area 7 and the information light and the recording reference light. It becomes possible to irradiate the reference light.

  Next, the configuration of the optical information recording / reproducing apparatus including the optical information recording apparatus according to the present embodiment will be described with reference to FIG. The optical information recording / reproducing apparatus 10 controls a spindle 81 to which the recording medium 1 is attached, a spindle motor 82 for rotating the spindle 81, and the spindle motor 82 so as to keep the rotational speed of the recording medium 1 at a predetermined value. And a spindle servo circuit 83. The optical information recording / reproducing apparatus 10 further records the information by irradiating the recording medium 1 with the information light and the recording reference light, and irradiates the recording medium 1 with the reproduction reference light. And an optical head 40 for reproducing the information recorded on the recording medium 1 and a drive device 84 that enables the optical head 40 to move in the radial direction of the recording medium 1.

  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, and the focus error detected by the detection circuit 85. Based on the signal FE, a focus servo circuit 86 for performing focus servo by moving a head body (to be described later) in the optical head 40 in a direction perpendicular to the surface of the recording medium 1, and a tracking error signal TE detected by the detection circuit 85. The optical head 40 is controlled by controlling the driving device 84 based on the tracking error signal TE and a command from a controller to be described later, and a tracking servo circuit 87 that performs tracking servo by moving the head body in the radial direction of the recording medium 1 based on the above. Slide to move the recording medium in the radial direction of the recording medium 1 And a slide servo circuit 88 that performs turbo.

  The optical information recording / reproducing apparatus 10 further decodes output data of a later-described CCD array in the optical head 40 to reproduce the data recorded in the information recording area 7 of the recording medium 1, or from the detection circuit 85. A signal processing circuit 89 that reproduces a basic clock and discriminates an address from the reproduction signal RF, a controller 90 that controls the entire optical information recording / reproducing apparatus 10, and an operation unit that gives various instructions to the controller 90. 91.

  The optical information recording / reproducing apparatus 10 further includes an inclination detection circuit 92 that detects a relative inclination between the recording medium 1 and the head body based on an output signal of the signal processing circuit 89, and an output signal of the inclination detection circuit 92. And a tilt correction circuit 93 that corrects the relative tilt between the recording medium 1 and the head body by changing the position of the head body in a direction in which the tilt of the head body with respect to the surface of the recording medium 1 changes. ing.

  The optical information recording / reproducing apparatus 10 further moves the head main body in a direction substantially along the track during information recording, so that the information light and the recording reference light are moved to one information recording area 7 that moves for a predetermined period. Is provided with a follow-up control circuit 94 that controls the irradiation position of the information light and the recording reference light so that the irradiation position of the recording light follows.

  The controller 90 inputs 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, the tracking control circuit 94, 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), a ROM (Read Only Memory), and a RAM (Random Access Memory), and the CPU executes a program stored in the ROM using the RAM as a work area. Thus, the function of the controller 90 is realized.

  Next, with reference to FIG. 3, the drive mechanism of the head body in the optical head 40 will be described. FIG. 3 is a plan view of the optical head 40. In FIG. 3, a symbol TR represents a track on the recording medium 1. The optical head 40 has a head body 41 that records information on the recording medium 1 and reproduces information from the recording medium 1. The head body 41 has an objective lens 11 that faces the recording medium 1. Elastic arm fixing portions 140a and 140b are provided at both ends of the head main body 41 in the track tangential direction (left and right direction in FIG. 3). One end of an elastic arm 149 formed of an elastic member such as rubber, a leaf spring, a coil spring, or a wire is fixed to the elastic arm fixing portions 140a and 140b. The other end of each elastic arm 149 is fixed to the arm support portion 150. The arm support 150 is attached to a piezoelectric actuator 170 that can move the arm support 150 in the radial direction of the recording medium 1 (vertical direction in FIG. 3) within a predetermined range.

  Focus servo and tilt adjustment coils 151 and 152 and irradiation position tracking coils 155 and 156 are attached to one end of the recording medium 1 in the radial direction of the head main body 41. Similarly, focus servo and tilt adjustment coils 153 and 154 and irradiation position tracking coils 157 and 158 are attached to the other end of the head body 41 in the radial direction of the recording medium 1.

  The optical head 40 further includes magnets 161, 162, 163, and 164 provided so as to penetrate the coils 151, 152, 153, and 154, and a magnet 165 that is disposed at a position facing the coils 155 and 156, respectively. And a magnet 166 disposed at a position facing the coils 157 and 158.

  In the optical head 40, the coils 151 to 154 and the magnets 161 to 164 change the direction perpendicular to the surface of the recording medium 1 (direction perpendicular to the paper surface in FIG. 3) and the inclination of the head body 41 with respect to the surface of the recording medium 1. The position of the head body 41 can be changed in the direction. In the optical head 40, the position of the head main body 41 can be changed in the radial direction of the recording medium 1 by the piezoelectric actuator 170. Further, in the optical head 40, the position of the head main body 41 can be changed substantially in the direction along the track TR by the elastic arm 149, the coils 155 to 158 and the magnets 165 and 166. The elastic arm 149, the coils 155 to 158, and the magnets 165 and 166 correspond to the irradiation position moving means in the present invention.

  The coils 151 to 154 are driven by the focus servo circuit 86 and the inclination correction circuit 93 in FIG. The coils 155 to 158 are driven by the follow-up control circuit 94 in FIG. The piezoelectric actuator 170 is driven by a tracking servo circuit 87 in FIG.

  Next, the configuration of the recording medium used in the present embodiment will be described with reference to FIG. The recording medium 1 in the present embodiment includes a disc-shaped transparent substrate 2 made of polycarbonate or the like, and information arranged in order from the transparent substrate 2 on the side opposite to the light incident / exit side of the transparent substrate 2. A recording layer 3, an air gap layer 4, and a reflective film 5 are provided. The information recording layer 3 is a layer on which information is recorded using holography, and a hologram whose optical characteristics such as refractive index, dielectric constant, and reflectance change according to light intensity when irradiated with light. It is made of material. As the hologram material, for example, a photopolymer HRF-600 (product name) manufactured by DuPont, a photopolymer ULSH-500 (product name) manufactured by Aprilis, or the like is used. The reflective film 5 is made of aluminum, for example. In the recording medium 1, the information recording layer 3 and the reflective film 5 may be adjacent to each other without providing the air gap layer 4.

  Next, the principle of information recording in the optical information recording / reproducing apparatus according to the present embodiment will be described. In this embodiment, the information light and the recording reference light are generated, and the information light and the recording reference light are recorded on the information recording layer 3 by the 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. 4 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 an objective lens 11 facing the transparent substrate 2 side of the recording medium 1, and a beam disposed in order from the objective lens 11 side on the opposite side of the objective lens 11 from the recording medium 1. A splitter 12 and a phase spatial light modulator 13 are included. The beam splitter 12 has a semi-reflective surface 12 a whose normal direction is inclined by 45 ° with respect to the optical axis direction of the objective lens 11. The recording / reproducing optical system shown in FIG. 4 further includes a photodetector 14 arranged in a direction in which the return light from the recording medium 1 is reflected by the semi-reflecting surface 12a of the beam splitter 12. The phase spatial light modulator 13 has a large number of pixels arranged in a lattice pattern, and the phase of the light can be spatially modulated by selecting the phase of the emitted light for each pixel. ing. The photodetector 14 has a large number of pixels arranged in a lattice pattern, and can detect the intensity of the received light for each pixel.

  In the example shown in FIG. 4, information light and recording reference light are generated by the phase spatial light modulator 13. Coherent parallel light having a constant phase and intensity is incident on the phase spatial light modulator 13. At the time of information recording, the phase spatial light modulator 13 spatially modulates the phase of the light in one half region 13A by selecting the phase of the emitted light for each pixel based on the information to be recorded. In the other half region 13B, the recording reference light is generated with the phase of the emitted light being the same for all the pixels.

  In the region 13A, the phase spatial light modulator 13 determines, for each pixel, the phase of the modulated light, the first phase where the phase difference with respect to a predetermined reference phase is + π / 2 (rad), and the phase difference with respect to the reference phase. Is set to one of the second phases where −π / 2 (rad). The phase difference between the first phase and the second phase is π (rad). The phase spatial light modulator 13 may set the phase of the modulated light to any of three or more values for each pixel in the region 13A. 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 where the phase difference with respect to a predetermined reference phase is + π / 2 (rad). Yes. Note that the phase spatial light modulator 13 may set the phase of the emitted light of all pixels to the second phase in the region 13B, or may be a constant phase different from both the first phase and the second phase. Good.

  In FIG. 4, the incident light of the phase spatial light modulator 13, the outgoing light of the phase spatial light modulator 13, the incident light of the objective lens 11 before being irradiated onto the recording medium 1, and the semi-reflective surface of the beam splitter 12 The phase and intensity of the return light from the recording medium 1 reflected by 12a are shown. In FIG. 4, the first phase is represented by a symbol “+”, and the second phase is represented by a symbol “−”. In FIG. 4, the maximum intensity value is represented by “1” and the minimum intensity value “0”.

  In the example shown in FIG. 4, coherent parallel light 21 having a constant phase and intensity is incident on the phase spatial light modulator 13 during information recording. Of the light incident on the phase spatial light modulator 13, the light that has passed through the region 13A is spatially modulated based on the information to be recorded to become the information light 22A. In the information light 22A, the intensity locally decreases at the boundary portion between the first phase pixel and the second phase pixel. On the other hand, the light that has passed through the region 13B out of the light incident on the phase spatial light modulator 13 is not spatially modulated in phase, and becomes recording reference light 22B. The information light 22A and the recording reference light 22B are incident on the beam splitter 12, a part of the information light 23A passes through the semi-reflective surface 12a, and further passes through the objective lens 11 and converges, and the recording reference light 23B converges. Thus, 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 surface between the air gap layer 4 and the reflective film 5, and are reflected by the reflective film 5. The information light 24 </ b> A and the recording reference light 24 </ b> B after being reflected by the reflective film 5 become diffused light and pass through the information recording layer 3 again.

  In the information recording layer 3, the information light 23 </ b> A before being reflected by the reflective film 5 interferes with the recording reference light 24 </ b> B after being reflected by the reflective film 5 to form an interference pattern and reflected by the reflective film 5. The information light 24A after the recording and the recording reference light 23B before being reflected by the reflective film 5 interfere with each other to form an interference pattern. These interference patterns are recorded in volume in the information recording layer 3.

  The information light 24A and the recording reference light 24B after being reflected by the reflective 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 25 </ b> A and 25 </ b> B are incident on the beam splitter 12, and a part thereof is reflected by the semi-reflective surface 12 a and is received by the photodetector 14.

  Next, the principle of information reproduction in the optical information recording / reproducing apparatus according to the present embodiment will be described. In the present embodiment, reproduction reference light is generated, and this reproduction reference light is applied to the information recording layer 3 of the recording medium 1 and the reproduction reference light is emitted from the information recording layer 3. The generated reproduction light is collected, and the reproduction light and the reproduction reference light are overlapped to generate 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. 5 shows a part of an example of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment, as in FIG.

  Further, in FIG. 5, the incident light of the phase spatial light modulator 13, the outgoing light of the phase spatial light modulator 13, the incident light of the objective lens 11 before being irradiated onto the recording medium 1, and the half of the beam splitter 12. The phase and intensity of the return light from the recording medium 1 reflected by the reflecting surface 12a are shown. The way of expressing the phase and intensity in FIG. 5 is the same as in FIG.

  In the example shown in FIG. 5, at the time of 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 information reproduction, the phase spatial light modulator 13 sets the phase of the emitted light for all the pixels to the first phase where the phase difference with respect to a predetermined reference phase is + π / 2 (rad), and the reproduction reference light 32 is generated. The reproduction reference light 32 is incident on the beam splitter 12, and part of the reproduction reference light 32 passes through the semi-reflective surface 12 a, and further passes through the objective lens 11 to be converged. As a result, the reproduction reference light 33 is irradiated onto the recording medium 1. The The reproduction reference beam 33 passes through the information recording layer 3, converges to have the smallest diameter on the boundary surface between the air gap layer 4 and the reflective film 5, and is reflected by the reflective film 5. The reproduction reference light reflected by the reflective film 5 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 that travels to the opposite side of the reflection film 5 and also for reproduction after being reflected by the reflection film 5. The reference light generates reproduction light that travels to the reflective film 5 side. The reproduction light traveling to the side opposite 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 side is reflected by the reflection film 5 and emitted from the recording medium 1.

  Thus, at the time of reproduction, the return light 34 from the recording medium 1 includes the reproduction light and the reproduction reference light after being reflected by the reflective film 5. The return light 34 is converted into parallel return light 35 by the objective lens 11 and enters the beam splitter 12. A part of the return light 34 is reflected by the semi-reflective surface 12 a and received by the photodetector 14. The return light 35 incident on the photodetector 14 includes reproduction light 36 and reproduction reference light 37 after being reflected by the reflective film 5. The reproduction light 36 is light in which the phase of light is spatially modulated corresponding to information recorded in the information recording layer 3. In FIG. 5, 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 combined light, and this combined light is received by the photodetector 14. The combined light is light whose intensity is spatially modulated corresponding to the recorded information. Accordingly, a two-dimensional pattern of the intensity of the combined light is detected by the photodetector 14, and information is reproduced thereby.

  As shown in FIGS. 4 and 5, 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 light, the reference light for recording and the reference light for reproduction and the collection of the reproduction light are performed from the same surface side of the information recording layer 3. Further, 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. 4, the information light 23A and the recording reference light 23B applied to the information recording layer 3 are light beams having a semicircular cross section. These are half of the light beam having a circular cross section. Because it is configured, it is coaxial.

  Here, the reproduction light 36, the reproduction reference light 37, and the combined light will be described in detail with reference to FIG. 6, (a) is the intensity of the reproduction light 36, (b) is the phase of the reproduction light 36, (c) is the intensity of the reproduction reference light 37, (d) is the phase of the reproduction reference light 37, (e ) Represents the intensity of the synthesized light. FIG. 6 illustrates the phase of each pixel of the information light in the second phase in which the phase difference with respect to the reference phase is + π / 2 (rad) and the phase difference with respect to the reference phase is −π / 2 (rad). The example about the case where it sets to one of these phases is shown. Therefore, in the example shown in FIG. 6, the phase of each pixel of the reproduction light 36 is either the first phase or the second phase, like the information light. Further, the phase of each pixel of the reproduction reference beam 37 is the first phase. Here, if it is assumed that the intensity of the reproduction light 36 and the intensity of the reproduction reference light 37 are equal, as shown in FIG. 6E, in the pixel in which the phase of the reproduction light 36 is the first phase, the combined light Is larger than the intensity of the reproduction light 36 and the intensity of the reproduction reference light 37, and in principle, the intensity of the combined light is zero in a pixel in which the phase of the reproduction light 36 is the second phase.

  Next, 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 any one of three or more values, the phase of the reproduction light and the combined light The relationship with the strength of the will be described in detail.

The combined light is a superposition of two light waves, a reproduction light and a reproduction reference light. Accordingly, if the amplitude of the reproduction light and the reproduction reference light are both a0 and the phase difference between the reproduction light and the reproduction reference light is δ, the intensity I of the combined light is expressed by the following equation (1). .
I = 2a ₀ ² + 2a ₀ ² cos δ
= 2a ₀ ² (1 + cos δ)
= 4a ₀ ² cos ² (δ / 2) (1)
Since the phase of the reproduction reference light is constant regardless of the pixel, it can be seen from the above formula that the intensity I of the combined light changes according to the phase of the reproduction light. Further, if the phase of the information light is set to any one of n (n is an integer of 2 or more) within a range of, for example, + π / 2 (rad) to −π / 2 (rad), the intensity of the combined light I is also one of n values.

  Thus, in the optical information recording method according to the present embodiment, based on the information to be recorded by detecting the two-dimensional pattern of the intensity of the combined light generated by superimposing the reproduction light and the reproduction reference light. Information recorded on the information recording layer 3 can be reproduced by an interference pattern due to interference between the information light whose light phase is spatially modulated and the recording reference light.

  By the way, in the present embodiment, by using the recording reference light and the reproduction reference light whose phases are spatially modulated, the multiplex recording by the phase encoding multiplex method and the reproduction of the information thus multiplexed and recorded are performed. It may be possible to perform. 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, the principle of information recording when performing multiplex recording by the phase encoding multiplex method will be described 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. The configuration of the optical system shown in FIG. 7 is the same as that of FIG. In FIG. 7, the incident light of the phase spatial light modulator 13, the outgoing light of the phase spatial light modulator 13, the incident light of the objective lens 11 before irradiating the recording medium 1, and the semi-reflective surface of the beam splitter 12 The phase and intensity of the return light from the recording medium 1 reflected by 12a are shown. The way of expressing the phase and intensity of light in FIG. 7 is the same as in FIG.

  At the time of recording information, coherent parallel light 21 having a constant phase and intensity is incident on the phase spatial light modulator 13. In one half region 13A of the phase spatial light modulator 13, the phase of the phase is spatially selected by selecting the phase of the emitted light from two or more values for each pixel based on the information to be recorded. Modulated information light 22A is generated. Here, for simplification of description, the region 13A has the phase of the emitted light for each pixel, the first phase where the phase difference with respect to a predetermined reference phase is + π / 2 (rad), and the level with respect to the reference phase. It is assumed that the phase of light is spatially modulated by setting to any one of the second phases where the phase difference is −π / 2 (rad). On the other hand, in the other half region 13B of the phase spatial light modulator 13, the phase is spatially modulated by selecting the phase of the emitted light from two values or three or more values for each pixel. The recording reference beam 22B is generated. Here, in order to simplify the description, the region 13B sets the phase of the light by setting the phase of the emitted light to any one of the reference phase, the first phase, and the second phase for each pixel. It shall be spatially modulated.

  The information light 22A and the recording reference light 22B are incident on the beam splitter 12, a part of which passes through the semi-reflective surface 12a, and further passes through the objective lens 11 to converge and the convergent recording reference light 23B. Thus, 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 surface between the air gap layer 4 and the reflective film 5, and are reflected by the reflective film 5. The information light 24 </ b> A and the recording reference light 24 </ b> B after being reflected by the reflective film 5 become diffused light and pass through the information recording layer 3 again.

  In the information recording layer 3, the information light 23 </ b> A before being reflected by the reflective film 5 interferes with the recording reference light 24 </ b> B after being reflected by the reflective film 5 to form an interference pattern and reflected by the reflective film 5. The information light 24A after the recording and the recording reference light 23B before being reflected by the reflective film 5 interfere with each other to form an interference pattern. These interference patterns are recorded in volume in the information recording layer 3.

  The information light 24A and the recording reference light 24B after being reflected by the reflective 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 25 </ b> A and 25 </ b> B are incident on the beam splitter 12, and a part thereof is reflected by the semi-reflective surface 12 a and is received by the photodetector 14.

  Next, with reference to FIG. 8, the principle of information reproduction when performing multiplex recording by the phase encoding multiplex method will be described. FIG. 8 shows a part of an example of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment, as in FIG. Further, in FIG. 8, the incident light of the phase spatial light modulator 13, the outgoing light of the phase spatial light modulator 13, the incident light of the objective lens 11 before being irradiated onto the recording medium 1, and the half of the beam splitter 12. The phase and intensity of the return light from the recording medium 1 reflected by the reflecting surface 12a are shown. The way of expressing the phase and intensity in FIG. 8 is the same as in FIG.

At the time of reproducing information, coherent parallel light 31 having a constant phase and intensity is incident on the phase spatial light modulator 13. The half region 13B in the phase spatial light modulator 13 has a modulation pattern similar to that of the recording reference light 22B by selecting the phase of the emitted light from two values or three or more values for each pixel. generating a spatially modulated reference beam 32B ₁ for reproduction. On the other hand, the half region 13A in the phase spatial light modulator 13 selects the phase of the emitted light from among two values or three or more values for each pixel, thereby making the modulation pattern of the reproduction reference light 32B ₁ with respect to the modulation pattern. Thus, the reproduction reference beam 32B ₂ whose phase is spatially modulated in a point-symmetric pattern around the position of the optical axis of the optical system that irradiates the information recording layer 3 with the recording reference beam and the reproduction reference beam is generated. To do.

These reproduction reference beams 32B ₁ and 32B ₂ are incident on the beam splitter 12, and part of the reproduction reference beams 33B ₁ and 33B ₂ that pass through the semi-reflective surface 12a and further pass through the objective lens 11 and converge. Thus, the recording medium 1 is irradiated. The reproduction reference beams 33B ₁ and 33B ₂ 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 reflective film 5, and are reflected by the reflective film 5. The reproduction reference light reflected by the reflective film 5 becomes diffused light and passes through the information recording layer 3 again.

In the information recording layer 3, the reproduction reference light 33 </ _b > B ₂ before being reflected by the reflection film 5 generates reproduction light that travels to the opposite side of the reflection film 5, and reproduction after being reflected by the reflection film 5. by use reference light 33B _2, reproduction light is generated that travels to the reflecting film 5 side. The reproduction light traveling to the side opposite 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 side is reflected by the reflection film 5 and 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> B ₁ before being reflected by the reflection film 5 generates reproduction light that travels on the opposite side of the reflection film 5 and is reflected by the reflection film 5. by the reproduction-specific reference light 33B _1, the reproduction light is generated that travels to the reflecting film 5 side. The reproduction light traveling to the side opposite 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 side 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 light 33B ₁ is reflected by the reflective film 5 and becomes reproduction reference light 34B ₁ that travels in the same direction as the reproduction light 34A ₁ . The reproduction reference light 33B ₂ is reflected by the reflective film 5 and becomes reproduction reference light 34B ₂ that travels in the same direction as the reproduction light 34A ₂ .

These reproduction lights 34A ₁ , 34A ₂ and reproduction reference lights 34B ₁ , 34B ₂ are converted into parallel reproduction lights 35A ₁ , 35A ₂ and reproduction reference lights 35B ₁ , 35B ₂ by the objective lens 11, and are beam splitters. 12 is partially reflected by the semi-reflective surface 12 a and received by the photodetector 14.

Both the reproduction lights 35A ₁ and 35A ₂ are lights whose phases are spatially modulated in the same manner as 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.

The combined light generated by superimposing the reproduction light 35A ₁ and the reproduction reference light 35B ₁ is incident on one half region of the photodetector 14. The combined light generated by superimposing the reproduction light 35A ₂ and the reproduction reference light 35B ₂ is incident on the other half region of the photodetector 14. Both of these two types of combined light are light whose intensity is spatially modulated corresponding to the recorded information. However, the modulation patterns of the intensity of the two types of combined light are point-symmetric with each other. Therefore, the information can be reproduced by detecting the two-dimensional pattern of the intensity 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 intensity pattern of the composite 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. In FIG. 9, (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 combined light. Represents the strength of 9 sets the phase of each pixel of the information light to either the first phase or the second phase, and sets the phase of each pixel of the recording reference light and the reproduction reference light to the reference phase, The example about the case where it sets to either the 1st phase and the 2nd phase is shown. In this case, the phase of the reproduction light for each pixel is either the first phase or the second phase, similar to the information light. Therefore, the phase difference between the reproduction light and the reproduction reference light is zero, ± π / 2 (rad), or ± π (rad). Here, if the intensity of the reproduction light and the intensity of the reference light for reproduction are equal, as shown in FIG. 9E, the intensity of the combined light is zero in the phase difference between the reproduction light and the reference light for reproduction. Is the largest, and in principle, the pixel where the phase difference between the reproduction light and the reproduction reference light is ± π (rad) is zero, and the phase difference between the reproduction light and the reproduction reference light is ± π / In a pixel having 2 (rad), the intensity is ½ of that in a pixel having a phase difference of zero. In FIG. 9E, the intensity at a pixel with a phase difference of ± π (rad) is represented by “0”, and the intensity at a pixel with a phase difference of ± π / 2 (rad) is represented by “1”. The intensity at the pixel where the phase difference is zero is represented by “2”.

  In the examples shown in FIGS. 7 to 9, the intensity of the synthesized light for each pixel is ternary. For example, as shown in FIG. 9E, the intensity “0” corresponds to the 2-bit data “00”, the intensity “1” corresponds to the 2-bit data “01”, and the intensity “2”. "Can correspond to 2-bit data" 10 ". As described above, in the example shown in FIGS. 7 to 9, compared with the case where the intensity of each pixel of the synthesized light is binary as in the examples shown in FIGS. In the same manner, 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.

  When the phase difference between the reproduction light and the reproduction reference light is δ, the intensity I of the combined light is expressed by the above formula (1). From equation (1), it can be seen that the intensity I of the combined light changes according to the phase difference between the reproduction light and the reproduction 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 within a range from zero to π (rad)). If the value is an integer greater than or equal to 2, the intensity I of the combined light also becomes an n value.

  By the way, as described above, when information is recorded on the information recording layer 3 of the recording medium 1 using information light whose phase is spatially modulated and recording reference light whose phase is spatially modulated. Determines the phase modulation pattern of the information light based on the information to be recorded and the phase modulation pattern of the recording reference light used when 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 synthetic light intensity pattern, the information to be recorded is the desired synthetic light intensity pattern data as shown in FIG. Is converted to The phase modulation pattern of the recording reference light is the same as the phase modulation pattern of the reproduction reference light as shown in FIG. The modulation pattern of the phase of the information light includes the desired combined light intensity pattern data as shown in FIG. 9 (e), the reproduction reference light and the recording reference light as shown in FIG. 9 (d). The phase calculation using the phase modulation pattern data is determined so that the modulation pattern is the same as that of the desired reproduction light phase as shown in FIG. Is done.

  For the information recording layer 3 on which information is recorded using the information light whose phase modulation pattern is determined as described above and the recording reference light, as shown in FIG. When the reproduction reference light having the same phase modulation pattern as that of the reference light is irradiated, a composite light having an intensity pattern as shown in FIG. 9E is obtained. Based on the intensity pattern of the composite light Thus, the information recorded in the information recording layer 3 is reproduced.

  You may make it produce the modulation pattern of the phase of the reference light for recording and the reference light for reproduction | regeneration based on the specific information of the individual who becomes a user. Information unique to an individual includes a personal identification number, a fingerprint, a voiceprint, and an iris pattern. In this case, only a specific individual who 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 multiplex method and the reproduction of the information thus multiplexed recorded can be performed. It becomes possible to do.

  Next, the recording / reproducing optical system provided in the optical head 40 will be described with reference to FIG. FIG. 10 is a cross-sectional view showing the optical head 40. As shown in FIG. 10, the optical head 40 has a head main body 41 that accommodates elements to be described later. A semiconductor laser 43 is fixed to the bottom of the head main body 41 via a support base 42, and a reflective phase spatial light modulator 44 and a photodetector 45 are fixed. A microlens array 46 is attached to the light receiving surface of the photodetector 45. 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 43 side. Further, an opening is formed in the surface of the head body 41 facing the recording medium 1, and the objective lens 11 is provided in this opening. A quarter wave plate 49 is provided between the objective lens 11 and the prism block 48.

  The phase spatial light modulator 44 has a large number of pixels arranged in a lattice pattern, and by setting the phase of the emitted light to one of two values different from each other by π (rad), The phase of light can be spatially modulated. The phase spatial light modulator 44 further rotates the polarization direction of the outgoing light by 90 ° with respect to the polarization direction of the incident light. As the phase spatial light modulator 44, for example, a reflective liquid crystal element can be used.

  The light detector 45 has a large number of pixels arranged in a lattice shape, and can detect the intensity of light received for each pixel. Further, the microlens 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 image sensor or a MOS solid-state image sensor can be used. Further, as the photodetector 45, a smart optical sensor in which a MOS solid-state imaging device and a signal processing circuit are integrated on one chip (for example, a document “O plus E, September 1996, No. 202, Nos. 93 to 93). (See page 99). Since this smart optical sensor has a high transfer rate and a high-speed calculation function, it is possible to perform high-speed reproduction by using this smart optical sensor, for example, reproduction at a transfer rate on the order of G bits / second. Is possible.

  The prism block 48 has a polarization beam splitter surface 48a and a reflection surface 48b. Of the polarization beam splitter surface 48 a and the reflection surface 48 b, the polarization beam splitter surface 48 a is disposed closer to the collimator lens 47. The polarization beam splitter surface 48 a and the reflection surface 48 b are both arranged in parallel to each other with their normal directions inclined 45 ° with respect to the optical axis direction of the collimator lens 47.

  The phase spatial light modulator 44 is disposed at a position below the polarization beam splitter surface 48a, and the photodetector 45 is disposed at a position below the reflecting surface 48b. The quarter-wave plate 49 and the objective lens 11 are disposed at a position above the polarization beam splitter surface 48a. The collimator lens 47 and the objective lens 11 may be hologram lenses.

  As will be described in detail later, the polarization beam splitter surface 48a of the prism block 48 is formed of the information light, the recording reference light, and the reproduction reference light before passing through the quarter-wave plate 49 due to the difference in polarization direction. The optical path 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. 10 correspond to the beam splitter 12, the phase spatial light modulator 13, and the photodetector 14 in FIG.

  Next, the operation of the recording / reproducing optical system during information recording will be described. The semiconductor laser 43 emits coherent S-polarized light. Note that S-polarized light is linearly polarized light whose polarization direction is perpendicular to the incident plane (the paper surface in FIG. 10), and P-polarized light described later is linearly polarized light whose polarization direction is parallel to the incident plane.

  The S-polarized laser light emitted from the semiconductor laser 43 is converted into parallel light by the collimator lens 47, is incident on the polarization beam splitter surface 48a of the prism block 48, is reflected by the polarization beam splitter surface 48a, and is phase phase light. The light enters the modulator 44. The light emitted from the phase spatial light modulator 44 is 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 for all pixels in the other half area. Recording reference light having the same phase of the incident light or recording reference light having a spatially modulated phase is obtained. In addition, the outgoing light of the phase spatial light modulator 44 is rotated in the polarization direction by 90 ° to become P-polarized light.

  Since the information light and the recording reference light that are 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. Circularly polarized light. The information light and the recording reference light are collected by the objective lens 11 and irradiated onto the recording medium 1. The information light and the recording reference light pass through the information recording layer 3, converge to have the smallest diameter on the boundary surface between the air gap layer 4 and the reflective film 5, and are reflected by the reflective film 5. The information light and the recording reference light reflected by the reflective film 5 become diffused light and pass through the information recording layer 3 again. When the output of the semiconductor laser 43 is set to a high output for recording, an interference pattern due to the interference between the information light and the recording reference light is recorded on the information recording layer 3.

  The return light from the recording medium 1 is converted into parallel light by the objective lens 11 and passes through the quarter-wave plate 49 to become S-polarized light. The return light is reflected by the polarization beam splitter surface 48 a of the prism block 48, further reflected by the reflection surface 48 b, and enters the photodetector 45 through the microlens array 46.

  At the time of recording information, during the period in which 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 43 is set to a low output for reproduction and phase space light. The modulator 44 emits light having the same phase for all pixels without modulating the phase of the light. Based on the output of the photodetector 45 at this time, the basic clock, address information, focus error signal, and tracking error information can be obtained.

  Next, the operation of the recording / reproducing optical system during information reproduction will be described. At the time of information reproduction, the output of the semiconductor laser 43 is set to a low output for reproduction. The S-polarized laser light emitted from the semiconductor laser 43 is converted into parallel light by the collimator lens 47, is incident on the polarization beam splitter surface 48a of the prism block 48, is reflected by the polarization beam splitter surface 48a, and is phase phase light. The light enters the modulator 44. The light emitted from the phase spatial light modulator 44 becomes reproduction reference light whose reproduction light has the same phase for all pixels or reproduction reference light whose phase is spatially modulated. In addition, the outgoing light of the phase spatial light modulator 44 is rotated in the polarization direction by 90 ° to become P-polarized light.

  Since the reproduction reference light that is emitted from the phase spatial light modulator 44 is P-polarized light, it passes through the polarization beam splitter surface 48a of the prism block 48, passes through the quarter-wave plate 49, and is circularly polarized. Become light. The reproduction reference light is collected by the objective lens 11 and irradiated onto the recording medium 1. The reproduction reference light passes through the information recording layer 3, converges to have the smallest diameter on the boundary surface between the air gap layer 4 and the reflective film 5, and is reflected by the reflective film 5. The reproduction reference light reflected by the reflective film 5 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 reproduction light and reproduction reference light. The return light is converted into parallel light by the objective lens 11 and passes through the quarter-wave plate 49 to become S-polarized light. The return light is reflected by the polarization beam splitter surface 48 a of the prism block 48, further reflected by the reflection surface 48 b, and enters the photodetector 45 through the microlens array 46. Based on the output of the photodetector 45, the information recorded on the recording medium 1 can be reproduced.

  During reproduction of information, during the period in which the light beam from the objective lens 11 passes through the address / servo area 6 of the recording medium 1, the basic clock, address information, focus error signal, and tracking are based on the output of the photodetector 45. Error information can be obtained.

  The phase spatial light modulator 44 may be one that does not rotate the polarization direction of light. In this case, the polarization beam splitter surface 48a of the prism block 48 in FIG. 10 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 S-polarized light from the prism block 48 is converted into circularly-polarized light by the quarter-wave plate. The circularly polarized light from the phase spatial light modulator 44 is converted into P-polarized light by the quarter-wave plate and transmitted through the polarization beam splitter surface 48a. May be. In addition, the phase spatial light modulator that can set the phase of the emitted light to any of three or more values for each pixel is not limited to the one using liquid crystal, for example, incident light using a micromirror device. With respect to the advancing direction, the position of the reflecting surface may be adjusted for each pixel.

  Next, an example of a method for generating focus error information in the present embodiment will be described with reference to FIG. FIG. 11 is an explanatory diagram showing an outline of incident light on the light receiving surface of the photodetector 45. In the method of generating focus error information in this 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 follows. First, in a focused state where the light beam from the objective lens 11 converges to have the smallest diameter on the boundary surface between the air gap layer 4 and the reflective film 5 in the recording medium 1, the light beam on the light receiving surface of the light detector 45. The contour of the incident light is the contour indicated by reference numeral 60 in FIG. When the position at which the light beam from the objective lens 11 has the smallest diameter is shifted to the near side of the boundary surface between the air gap layer 4 and the reflective film 5, the contour of the incident light on the light receiving surface of the photodetector 45 is As shown by the reference numeral 61 in FIG. On the contrary, when the position where the light beam from the objective lens 11 has the smallest diameter is shifted to the back side from the boundary surface between the air gap layer 4 and the reflective 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. Accordingly, a focus error signal can be obtained by detecting a signal corresponding to a change in the diameter of the contour of incident light on the light receiving surface of the photodetector 45 with reference to the in-focus state. Specifically, for example, the focus error signal can be generated based on the increase / decrease number of pixels corresponding to the bright portion on the light receiving surface of the photodetector 45 with reference to the in-focus state.

  In the present embodiment, the position of the optical head body 41 in the direction perpendicular to the recording medium 1 is adjusted based on the focus error signal so that the light beam is always in focus, and focus servo is performed. Do. When the light beam passes through the information recording area 7, focus servo is not performed, and the state at the time of passing through the previous address / servo area 6 is maintained.

  Next, an example of a tracking error information generation method and a tracking servo method according to the present embodiment will be described with reference to FIGS. In this example, in the address / servo area 6 of the recording medium 1, as positioning information used for tracking servo, as shown in FIG. 12A, the front side of the traveling direction of the light beam 72 along the track 70. In order, two pits 71A, one pit 71B, and one pit 71C are formed. The two pits 71A are arranged at positions symmetrical with respect to the track 70 at the position indicated by symbol A in FIG. The pit 71B is disposed at a position shifted to one side with respect to the track 70 at the position indicated by reference numeral B in FIG. The pit 71C is arranged at a position shifted to the opposite side of the pit 71B with respect to the track 70 at the position indicated by the symbol C in FIG.

  As shown in FIG. 12A, when the light beam 72 accurately travels on the track 70, the entire light reception of the photodetector 45 when the light beam 72 passes through each position A, B, C. The amount is as shown in FIG. That is, the amount of received light when passing through position A is the largest, and the amount of received light when passing through position B and the amount of received light when passing through position C are equal to each other and smaller than the amount of received light when passing through position A.

  On the other hand, as shown in FIG. 13A, when the light beam 72 travels away from the pit 71C with respect to the track 70, the light beam 72 passes through the positions A, B, and C. The total amount of light received by the photodetector 45 is as shown in FIG. That is, the amount of received light when passing through position A is the largest, the amount of received light when passing through position C is the next largest, and the amount of received light when passing through position B is the smallest. The absolute value of the difference between the amount of light received when passing through position B and the amount of light received when passing through position C increases as the amount of deviation of light beam 72 from track 70 increases.

  Although not shown, when the light beam 72 travels away from the pit 71B with respect to the track 70, 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 next is large. The amount of light received when passing through position C is the smallest. The absolute value of the difference between the amount of light received when passing through position B and the amount of light received when passing through position C increases as the amount of deviation of light beam 72 from track 70 increases.

  From the above, the direction and magnitude of the deviation 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 through the position B and the amount of light received when passing through the position C. Therefore, the difference between the amount of received light when passing through position B and the amount of received light when passing through position C can be used as a tracking error signal. The pit 71A serves as a reference for the timing of detecting the amount of light received when passing through position B and the amount of light received when passing through position C.

  Specifically, the tracking servo in this example is performed as follows. First, the timing at which the total amount of light received by the photodetector 45 first reaches a peak, that is, the timing when passing through the position A is detected. Next, based on the timing when the position A passes, the timing when the position B passes and the timing when the position C passes are predicted. 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, a difference between the amount of received light when passing through position B and the amount of received light when passing through 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 of passing through the previous 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 not limited to the above methods, and for example, a push-pull method may be used. In this case, in the address / servo area 6, a single pit row is formed along the track direction as positioning information used for tracking servo, and the shape of the incident light on the light receiving surface of the photodetector 45 is formed. A change is detected and tracking error information is generated.

  Next, the operation of the optical head 40 during information recording will be described with reference to FIG. FIG. 14 shows the movement of the track TR during information recording and the movement of the irradiation position 101 of the information light and the recording reference light. In FIG. 14, the symbol R represents the moving direction of the recording medium 1. In FIG. 14, for the sake of convenience, the irradiation position 101 is shown not to overlap the track TR, but actually, the irradiation position 101 overlaps the track TR.

  In the present embodiment, as shown in FIG. 14 (a), before recording information in the information recording area 7 of the recording medium 1, the irradiation position 101 moves in the moving direction R of the recording medium 1 more than the neutral position. Is moved in the opposite direction (hereinafter also referred to as the advance direction). At this time, the irradiation position 101 passes through the address / servo area 6, and information recorded in the address / servo area 6 is detected by the optical head 40.

  Next, as shown in FIG. 14B, when the irradiation position 101 reaches the end E1 of the moving range in the advance direction, the irradiation position 101 is now moved in the moving direction R (hereinafter referred to as the delay direction). Moved to say.) Immediately after the start of movement of the irradiation position 101 in the delay direction, the movement speed of the irradiation position 101 is lower than the movement speed of the desired information recording area 7 on which information is to be recorded. Accordingly, the irradiation position 101 eventually overlaps the desired information recording area 7.

  As shown in FIG. 14C, when the irradiation position 101 overlaps the desired information recording area 7, the movement speed of the irradiation position 101 is adjusted to be equal to the movement speed of the information recording area 7. Thereby, the irradiation position 101 is moved so that the irradiation position 101 follows the desired information recording area 7.

  Next, as shown in FIG. 14D, when the irradiation position 101 reaches the end E2 of the moving range in the delay direction, the irradiation position 101 is moved again in the advancing direction, as shown in FIG. Operation is performed. In this way, the operations shown in FIGS. 14A to 14D are repeatedly executed.

  As described above, in the present embodiment, the irradiation position 101 is moved so that the irradiation position 101 of the information light and the recording reference light follows the one information recording area 7 that moves for a predetermined period. Thereby, information light and recording reference light are continuously irradiated to one information recording area 7 for a predetermined period, and information is recorded in the information recording area 7 by an interference pattern due to interference between the information light and the recording reference light. Is done. Hereinafter, a period in which the irradiation position 101 follows the information recording area 7 is referred to as a tracking period, and the other period is referred to as a catch-up period.

  FIG. 15 shows the movement of the irradiation position 101 described above in a coordinate system in which the horizontal axis is an absolute position and the vertical axis is time. The symbols R, E1, and E2 in FIG. 15 indicate the movement direction of the recording medium 1, the end of the movement range in the advance direction of the irradiation position 101, and the end of the movement range in the delay direction of the irradiation position 101, as described above. Represents. In FIG. 15, symbol T1 represents a follow-up period, and symbol T2 represents a catch-up period.

  As shown in FIG. 15, in the present embodiment, in the follow-up period T1, the information light and the recording reference light are continuously irradiated to one information recording area 7, whereby the information recording area 7 An interference pattern by interference with the recording reference beam, that is, a hologram carrying information is formed. In FIG. 15, symbols H1 to H6 represent holograms recorded in this order.

  By the way, the irradiation position 101 is moved by moving the head main body 41 including the objective lens 11 which is the emission position of the information light and the recording reference light in a direction substantially along the track. Here, FIG. 16 shows an example of a change in the position of the objective lens 11 and a change in the driving voltage for the coils 155 to 158 for moving the head main body 41 in a direction substantially along the track. 16A shows a change in the position of the objective lens 11, and FIG. 16B shows a change in the drive voltage.

  In the example shown in FIG. 16A, the objective lens 11 moves at a constant speed equal to the moving speed of the information recording area 7 in the follow-up period T1. Further, the objective lens 11 temporarily stops at the end of the movement range in the delay direction during the catch-up period T2, then starts moving in the advance direction, and reaches the end of the movement range in the advance direction. After temporarily stopping at the position, the movement starts in the delay direction at a speed that is lower than the movement speed of the information recording area 7.

  In the example shown in FIG. 16B, when the drive voltage is a positive value, a force is applied to the head body 41 to move in the advance direction. Gives you the power to move to.

  Next, with reference to FIG. 17, a method for matching the irradiation position 101 of the information light and the recording reference light to the position of the desired information recording area 7 will be described. In FIG. 17, (c) shows three tracks TR1, TR2 and TR3. In each track, four information recording areas 7 are provided between two adjacent address / servo areas 6. In FIG. 17C, the positions of these four information recording areas 7 are represented by symbols a, b, c, and d.

  17D and 17E show the trajectories of the irradiation position 101 of the information light and the recording reference light when recording is performed on the tracks TR1 and TR2, respectively. 17D and 17E, the horizontal axis represents the relative position of the irradiation position 101 with respect to the track shown in FIG. 17C, and the vertical axis represents time. In the present embodiment, the irradiation position 101 passes through the address / servo area 6 during the catch-up period T2, and the information recorded in the address / servo area 6 is detected by the optical head 40. Then, based on the detection output of the optical head 40, the controller 90 in FIG. 2 records the information recording area 7 existing between the address / servo area 6 through which the irradiation position 101 has passed and the next address / servo area 6. The address is recognized. Further, when the irradiation position 101 passes through the address / servo area 6, a basic clock is generated based on the detection output of the optical head 40.

  The controller 90 selects an information recording area 7 in which information is to be recorded, from among four information recording areas 7 existing between two adjacent address / servo areas 6. The positions of the four information recording areas 7 existing between two adjacent address / servo areas 6, that is, the positions a to d in FIG. 17C are specified by the time represented by using the basic clock. can do. The controller 90 adjusts the irradiation position 101 to the position of the information recording area 7 by changing the drive voltage profile as shown in FIG. 16 according to the position of the information recording area 7 where information is to be recorded. .

  In this embodiment, as shown in FIGS. 17D and 17E, information recording on a predetermined track is performed as follows. First, during one rotation of the recording medium 1, information is recorded in each information recording area 7 existing at the position a in FIG. During the next one rotation, information is recorded in each information recording area 7 existing at the position b in FIG. 17C in the same track. Similarly, during the next one rotation, information is recorded in each information recording area 7 existing at the position c in FIG. 17C in the same track, and during the next one rotation, In the same track, information is recorded in each information recording area 7 existing at the position d in FIG. In this manner, when information recording on each information recording area 7 existing at all positions a to d in one track is completed, the same recording is performed on the next track. In FIGS. 17D and 17E, the locus of the irradiation position 101 for each rotation of the recording medium 1 is shown packed in the time axis direction.

  Incidentally, in the catch-up period T2, the relative speed of the irradiation position 101 with respect to the recording medium 1 (address / servo area 6) changes in the order of increasing, constant, and decreasing. When detecting information recorded in the address / servo area 6 only during a period when the relative speed of the irradiation position 101 is constant, the length of the pit recorded in the address / servo area 6 and the length between two adjacent pits are used. For example, the length can be an integral multiple of the reference length. However, in this case, the length of the address / servo area 6 cannot be made too large.

  If the information recorded in the address / servo area 6 can be detected not only during a period when the relative speed of the irradiation position 101 is constant but also during a period when the relative speed of the irradiation position 101 increases or decreases, the address / servo area can be detected. The length of 6 can be increased, and more information can be recorded in the address / servo area 6. However, in this case, even if the pit length and the length between two adjacent pits are constant, the pit time and the pit interval in the detection output of the optical head 40 according to the relative speed of the irradiation position 101 The time changes. Therefore, in order to generate an accurate basic clock or to accurately recognize information recorded in the address / servo area 6, some measures are required. Hereinafter, two examples of such measures will be described.

  As shown in FIG. 17A, the first countermeasure is to set the reference length of the length of the pit P recorded in the address / servo area 6 and the length between two adjacent pits P to the irradiation position. It is changed so as to be proportional to the relative speed of 101. In FIG. 17A, the central pit is a special pit represented at the central position of the address / servo area 6.

  As shown in FIG. 17B, the second countermeasure is that the length of the pit P recorded in the address / servo area 6 and the length serving as a reference for the length between two adjacent pits P are not changed. In the signal processing circuit 89 in FIG. 2, the pit time and the pit time in the detection output of the optical head 40 are converted into the actual pit length and the pit length.

  FIG. 18 shows a specific example of the change in the pit length when the above first countermeasure is adopted. In FIG. 18, the vertical axis represents the relative speed of the irradiation position 101 with respect to the recording medium 1 (address / servo area 6), and the horizontal axis represents time. In FIG. 18, reference symbols P <b> 1 to P <b> 8 represent pits at each timing. Note that the pits P1 to P8 should be determined to have the same length in terms of signal processing. In FIG. 18, the symbol LP represents a change in the output of the semiconductor laser 43. In the first countermeasure, the lengths of the pits P1 to P8 are proportional to the relative speed of the irradiation position 101. Thereby, the time of the pits P1 to P8 in the detection output of the optical head 40 becomes constant. Therefore, when the first countermeasure is adopted, the pit length and the pit length are recognized as they are from the pit time and the pit time in the detection output of the optical head 40, and the address servo area 6 Can be recognized.

  FIG. 19 shows a specific example of the change in the pit time and the time between pits when the second countermeasure is adopted. FIG. 19 shows a case where the irradiation position 101 passes through a pit row in which the pit length and the length between the pits are constant during a period in which the relative speed of the irradiation position 101 decreases. 19A shows a reproduction signal RF output from the detection circuit 85 in FIG. 2, and FIG. 19B shows a system clock used in the optical information recording / reproducing apparatus. In (a), a high level period corresponds to a pit period, and a low level period corresponds to a period between two adjacent pits. As shown in FIG. 19A, in the period in which the relative speed of the irradiation position 101 decreases, the pit time and the time between pits in the reproduction signal RF are the same even if the pit length and the pit length are constant. Increase gradually. The signal processing circuit 89 in FIG. 2 obtains information on the relative speed of the irradiation position 101 from the controller 90, multiplies the time of pits in the reproduction signal RF and the time between pits by the relative speed of the irradiation position 101, and Find the length and the length between pits. The lengths of pits and the lengths between pits thus obtained by calculation coincide with the actual pit lengths and the lengths between pits. Therefore, when the second countermeasure is adopted, the information recorded in the address / servo area 6 can be recognized using the pit length obtained by calculation or the length between pits.

  As described above, in the present embodiment, irradiation of information light and recording reference light is performed so that the irradiation position of information light and recording reference light follows one information recording area 7 that moves for a predetermined period. Move position. Thereby, the information light and the recording reference light are continuously irradiated to one information recording area 7 for a predetermined period. Therefore, according to the present embodiment, the information recording area 7 and the irradiation position of the information light and the recording reference light are not shifted and the information is recorded for a time sufficient to record information in the information recording area 7. It is possible to irradiate the recording area 7 with information light and recording reference light. As a result, according to the present embodiment, holography is used for each information recording area 7 while rotating the recording medium 1 having the plurality of information recording areas 7 using the semiconductor laser 43 that is a practical light source. Thus, information can be recorded.

  In the present embodiment, an address / servo area 6 is provided in the recording medium 1. In the address / servo area 6, 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 are provided. It is recorded. The optical information recording / reproducing apparatus identifies each information recording area 7 by detecting the address information recorded in the address / servo area 6. Therefore, according to the present embodiment, each information recording area 7 can be easily identified. The optical information recording / reproducing apparatus detects the positioning information recorded in the address / servo area 6 and matches the irradiation positions 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, it is possible to easily match the irradiation positions of the information light, the recording reference light, and the reproduction reference light to each information recording area 7.

  In the present embodiment, when recording information, the information recording layer 3 of the recording medium 1 is irradiated with information light whose phase of light is spatially modulated based on the information to be recorded and recording reference light. Thus, 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. Further, when reproducing information, the information recording layer 3 is irradiated with reproduction reference light, whereby the reproduction light generated from the information recording layer 3 and the reproduction reference light are superimposed to generate synthesized light. Recover information by detecting 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, it is not necessary to make the information light and the recording reference light incident on the recording medium at a predetermined angle when recording information. Actually, in the present embodiment, the information light, the recording reference light, the reproduction reference light, and the reproduction light are radiated and reproduced so that the information light, the recording reference light, and the reproduction light are coaxially arranged. Is collected 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.

  Further, in the conventional reproduction method, the reproduction light and the reproduction reference light are separated and only the reproduction light is detected. Therefore, if the reproduction reference light is incident on the photodetector for detecting the reproduction light, the reproduction light is reproduced. There was a problem that the SN ratio of information deteriorated. On the other hand, in the present embodiment, information is reproduced using reproduction light and reproduction reference light, so that the SN ratio of reproduction information does not deteriorate due to 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 coaxially arranged and converge so as to have the smallest diameter at the same position. In addition, the configuration of the optical system for reproduction can be simplified.

  [Second Embodiment] Next, an optical information recording / reproducing apparatus according to a second embodiment of the present invention will be described. FIG. 20 is a plan view showing an optical head driving mechanism in the optical information recording / reproducing apparatus according to the present embodiment. In this embodiment, the driving mechanism of the optical head is different from that of the first embodiment.

  The optical head 40 in the present embodiment has a fixed part 201, a first movable part 202, and a second movable part 203. The fixing unit 201 is fixed to the main body of the optical information recording / reproducing apparatus. Two rails 221 extending in the radial direction of the recording medium 1 (vertical direction in FIG. 20) are attached to the main body of the optical information recording / reproducing apparatus. The first movable portion 202 is supported by the two rails 221 so as to be movable in the radial direction of the recording medium 1. The optical head 40 also includes a linear motor 222 that moves the first movable unit 202 in the radial direction of the recording medium 1 with respect to the main body of the optical information recording / reproducing apparatus.

  Two rails 231 extending in the track tangential direction (left-right direction in FIG. 20) are attached to the first movable portion 202. The second movable portion 203 is supported by the two rails 231 so as to be movable in the track tangential direction. The optical head 40 also includes a linear motor 232 that moves the second movable portion 203 in the track tangential direction with respect to the first movable portion 202.

  A support plate 204 that supports the objective lens 11 so as to be movable in a direction perpendicular to the surface of the recording medium 1 (a direction orthogonal to the paper surface in FIG. 20) is attached to the second movable portion 203. The optical head 40 also includes an actuator 241 that moves the objective lens 11 in a direction perpendicular to the surface of the recording medium 1 with respect to the second movable portion 203.

  In the optical head 40 according to the present embodiment, in the recording / reproducing optical system, the objective lens 11 is attached to the support plate 204 and most of the other is provided to the fixed portion 201. The first movable unit 202 and the second movable unit 203 guide light LB from the optical system provided in the fixed unit 201 to the objective lens 11 and light incident on the objective lens 11 from the recording medium 1 side. A relay optical system is provided to guide the optical system provided in the fixing unit 201. FIG. 20 shows a mirror 223 that is fixed to the first movable portion 202 and forms a part of the relay optical system.

  In the optical head 40 according to the present embodiment, the actuator 241 can change the position of the objective lens 11 in the direction perpendicular to the surface of the recording medium 1, thereby performing focus servo. Further, in the optical head 40, the position of the objective lens 11 can be changed in the radial direction of the recording medium 1 by the linear motor 222, whereby access to a desired track and tracking servo can be performed. . In the optical head 40, the position of the objective lens 11 can be changed by the linear motor 232 in the tangential direction of the track, that is, in a direction substantially along the track. Thereby, it is possible to control the information recording area 7 to follow the irradiation position of the information light and the recording reference light. The linear motor 232 corresponds to the irradiation position moving means in the present invention.

  The actuator 241 is driven by the focus servo circuit 86 in FIG. The linear motor 222 is driven by a tracking servo circuit 87 and a slide servo circuit 88 in FIG. The linear motor 232 is driven by the follow-up control circuit 94 in FIG.

  In the present embodiment, since the optical head 40 has the function of the driving device 84 in FIG. 2, this driving device 84 is not provided. In the present embodiment, the function of correcting the relative inclination between the recording medium 1 and the optical head 40 is not provided, and the inclination correction circuit 93 in FIG. 2 is not provided.

  Other configurations, operations, and effects in the present embodiment are the same as those in the first embodiment.

  [Third Embodiment] Next, an optical information recording / reproducing apparatus according to a third embodiment of the present invention will be described. FIG. 21 is an explanatory diagram showing a main part of a recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment.

  First, the configuration of the recording medium according to the present embodiment will be described with reference to FIG. The recording medium 301 according to the present embodiment has a disk shape and has a plurality of tracks, like the recording medium 1 according to the first embodiment. In each track, a plurality of address / servo areas 306 are provided at equal intervals. One or more information recording areas 307 are provided between adjacent address / servo areas 306.

  The recording medium 301 includes two disc-shaped transparent substrates 302 and 304 formed of polycarbonate or the like, an information recording layer 303 provided between the transparent substrates 302 and 304, and information recording on the transparent substrate 302. A protective layer 305 is provided so as to be adjacent to a surface opposite to the layer 303.

  The information recording layer 303 is a layer on which information is recorded using holography, and is formed of the same hologram material as that of the information recording layer 3 of the recording medium 1 in the first embodiment.

  In this recording medium 301, the surface opposite to the transparent substrate 302 of the protective layer 305 (the lower surface in FIG. 21) receives the recording reference light and the reproduction reference light, and the reproduction light is emitted. The first surface 301a and the surface opposite to the information recording layer 303 of the transparent substrate 304 (the upper surface in FIG. 21) become the second surface 301b on which information light carrying information to be recorded is incident. Yes.

  In the address / servo area 306, emboss pits representing address information and the like are formed on the boundary surface between the transparent substrate 302 and the protective layer 305. Note that the focus servo can also be performed using the boundary surface between the transparent substrate 302 and the protective layer 305.

  As shown in FIG. 22, the recording medium 301 has an emboss pit representing address information or the like provided on the boundary surface between the transparent substrate 302 and the information recording layer 303 in the address / servo area 306. Also good. In this case, the protective layer 305 is not necessary.

  Next, the main part of the recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment will be described with reference to FIG. The recording / reproducing optical system includes an objective lens 321 facing the transparent substrate 304 side of the recording medium 301, and a quarter of the objective lens 321 arranged in order from the objective lens 321 side on the side opposite to the recording medium 301. A wave plate 322 and a polarizing beam splitter 323 are provided. The polarization beam splitter 323 has a polarization beam splitter surface 323a that reflects S-polarized light and transmits P-polarized light. The polarization beam splitter surface 323 a forms 45 ° with respect to the surface of the recording medium 301. In the polarization beam splitter 323, the right surface in FIG. 21 is the information light incident surface 323b. The recording / reproducing optical system further includes a spatial light modulator 327 disposed on the optical path of the light incident on the information light incident surface 323b of the polarization beam splitter 323. The spatial light modulator 327 has a large number of pixels arranged in a lattice pattern. For example, the spatial light modulator 327 spatially modulates the intensity of emitted light by selecting a light transmission state and a light blocking state for each pixel. Thus, information light carrying information can be generated. As the spatial light modulator 327, for example, a liquid crystal element can be used.

  The recording / reproducing optical system further includes an objective lens 331 facing the protective layer 305 side of the recording medium 301, and a quadrant arranged in order from the objective lens 331 side on the opposite side of the objective lens 331 from the recording medium 301. 1 wavelength plate 332, polarization beam splitter 333, and photodetector 334. The polarization beam splitter 333 has a polarization beam splitter surface 333a that reflects S-polarized light and transmits P-polarized light. The polarization beam splitter surface 333 a forms 45 ° with respect to the surface of the recording medium 301. In the polarization beam splitter 333, the right side surface in FIG. 21 is a reference light incident surface 333b. The recording / reproducing optical system further includes a phase spatial light modulator 338 disposed on the optical path of the light incident on the reference light incident surface 333b of the polarization beam splitter 333. The phase spatial light modulator 338 has a large number of pixels arranged in a lattice pattern, and the phase of the light is selected by selecting the phase of the emitted light from among two or more values for each pixel. Can be spatially modulated.

  The light detector 334 has a large number of pixels arranged in a lattice pattern, and can detect the intensity of light received for each pixel. As the photodetector 334, a CCD solid-state imaging device, a MOS solid-state imaging device, or a smart light sensor is used.

  Next, the overall configuration of the recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment will be described with reference to FIG.

  First, a portion related to information light in the recording / reproducing optical system will be described. The recording / reproducing optical system includes the objective lens 321, the quarter wavelength plate 322, and the polarization beam splitter 323 that have already been described. The recording / reproducing optical system further includes a convex lens 324, a pinhole 325, a convex lens 326, and spatial light modulation arranged in order from the polarizing beam splitter 323 side on the optical path of the light incident on the information light incident surface 323 b of the polarizing beam splitter 323. A container 327.

  The focal lengths of the convex lens 324 and the convex lens 326 are equal. Let this focal length be fs. The center of the convex lens 324, the pinhole 325, the center of the convex lens 326, and the image forming surface of the spatial light modulator 327 are arranged with an interval of the focal length fs. Accordingly, the parallel light flux that has passed through the spatial light modulator 327 is condensed by the convex lens 326, has the smallest diameter at the position of the pinhole 325, and passes through the pinhole 325. The light that has passed through the pinhole 325 becomes diffused light and is incident on the convex lens 324, and is incident on the information light incident surface 323b of the polarization beam splitter 323 as a parallel light flux. An image plane 351 conjugated with the image forming plane of the spatial light modulator 327 is formed between the convex lens 324 and the polarization beam splitter 323 at a position separated from the center of the convex lens 324 by the focal length fs.

  If the distance between the center of the polarization beam splitter 323 and the image plane 351 is f1, the distance between the center of the polarization beam splitter 323 and the center of the objective lens 321 is f2, and the focal length of the objective lens 321 is f, f = F1 + f2. A boundary surface between the transparent substrate 302 and the protective layer 305 in the recording medium 301 is arranged at a position separated from the center of the objective lens 321 by a focal length f. With such a configuration, the spatial light modulator 327 can be disposed at a position away from the objective lens 321 and the degree of freedom in designing the optical system is increased.

  Next, portions of the recording / reproducing optical system related to the recording reference light, the reproducing reference light, and the reproducing light will be described. The recording / reproducing optical system includes the objective lens 331, the quarter-wave plate 332, the polarization beam splitter 333, and the photodetector 334 that have already been described. The recording / reproducing optical system further includes a polarization beam splitter 335 disposed on the optical path of the light incident on the reference light incident surface 333b of the polarization beam splitter 333. The polarization beam splitter 335 is disposed in parallel with the polarization beam splitter surface 333a of the polarization beam splitter 333, and has a polarization beam splitter surface 335a that reflects S-polarized light and transmits P-polarized light.

  The recording / reproducing optical system further includes a convex lens 336, a concave lens 337, and a phase spatial light modulator 338, which are arranged in this order from the polarizing beam splitter 335 side below the polarizing beam splitter 335 in FIG. The phase spatial light modulator 338 is a reflection type. An image plane 352 conjugate with the image forming plane of the phase spatial light modulator 338 is formed between the polarization beam splitter 335 and the polarization beam splitter 333.

  The distance between the center of the polarization beam splitter 333 and the image plane 352 is equal to the distance between the center of the polarization beam splitter 323 and the image plane 351 and is f1. The distance between the center of the polarizing beam splitter 333 and the center of the objective lens 331 is equal to the distance between the center of the polarizing beam splitter 323 and the center of the objective lens 321 and is f2. The focal length of the objective lens 331 is f equal to the focal length of the objective lens 321. The boundary surface between the transparent substrate 302 and the protective layer 305 in the recording medium 301 is arranged at a position separated from the center of the objective lens 331 by the focal length f. With such a configuration, the phase spatial light modulator 338 can be disposed at a position away from the objective lens 331, and the degree of freedom in designing the optical system is increased.

  The recording / reproducing optical system further includes a mirror 339 disposed so as to form 90 ° with respect to the polarization beam splitter surface 335 a on the upper side of the polarization beam splitter 335 in FIG. 23, and a mirror disposed in parallel with the mirror 339. 340.

  Next, a portion common to the information light, the recording reference light, and the reproduction reference light in the recording / reproducing optical system will be described. The recording / reproducing optical system includes a semiconductor laser 342 that emits a coherent linearly polarized laser beam, and a collimator lens 343, a mirror 344, and a collimator lens 343 that are sequentially arranged on the optical path of the light emitted from the semiconductor laser 342 from the semiconductor laser 342 side. An optical rotatory element 345 and a polarization beam splitter 346 are provided. As the optical rotation optical element 345, for example, a half-wave plate or an optical rotation plate is used. The polarization beam splitter 346 has a polarization beam splitter surface 346a that reflects S-polarized light and transmits P-polarized light.

  In FIG. 21, in order to show the main part of the recording / reproducing optical system shown in FIG. As shown, it is arranged at the position of the image plane 352.

  Next, an outline of the operation of the recording / reproducing optical system shown in FIG. 23 will be described. The semiconductor laser 342 emits S-polarized light or P-polarized linearly polarized light. The collimator lens 343 emits the light emitted from the semiconductor laser 342 as a parallel light beam. The optical rotatory optical element 345 rotates the light emitted from the collimator lens 343 and reflected by the mirror 344, and emits light including an S-polarized component and a P-polarized component.

  Of the light emitted from the optical rotatory optical element 345, the S-polarized light component is reflected by the polarization beam splitter surface 346a of the polarization beam splitter 346 and is incident on the spatial light modulator 327. The spatial light modulator 327 reduces the intensity of the light. Information light is generated by spatial modulation. Information light emitted from the spatial light modulator 327 sequentially passes through the convex lens 326, the pinhole 325, and the convex lens 324, is reflected by the polarizing beam splitter surface 323 a of the polarizing beam splitter 323, and is reflected on the quarter-wave plate 322. Incident. The information light that has passed through the quarter-wave plate 322 becomes circularly polarized light, is condensed by the objective lens 321, and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. However, the recording medium 301 is irradiated. Note that spatial filtering may be performed in an optical system including the convex lens 326, the pinhole 325, and the convex lens 324.

  On the other hand, of the light emitted from the optical rotatory optical element 345, the P-polarized light component is transmitted through the polarization beam splitter surface 346a of the polarization beam splitter 346, reflected by the mirrors 340 and 339, and the polarization beam splitter surface 335a of the polarization beam splitter 335. , Passes through the convex lens 336 and the concave lens 337, and enters the phase spatial light modulator 338 as a parallel light beam. For example, the phase spatial light modulator 338 spatially modulates the phase of the light by setting the phase of the emitted light to one of two values different from each other by π (rad) for each pixel. It has become. The light modulated by the phase spatial light modulator 338 becomes a recording reference light or a reproduction reference light. The phase spatial light modulator 338 further rotates the polarization direction of the outgoing light by 90 ° with respect to the polarization direction of the incident light. Therefore, the light emitted from the phase spatial light modulator 338 becomes S-polarized light. The light emitted from the phase spatial light modulator 338 passes through the concave lens 337 and the convex lens 336, is reflected by the polarizing beam splitter surface 335a of the polarizing beam splitter 335, and further reflected by the polarizing beam splitter surface 333a of the polarizing beam splitter 333. The light enters the half-wave plate 332. The light that has passed through the quarter-wave plate 332 becomes circularly polarized light, is condensed by the objective lens 331, and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. The recording medium 301 is irradiated.

  Depending on the return light generated by reflecting the light applied to the recording medium 301 from the objective lens 331 at the boundary surface between the transparent substrate 302 and the protective layer 305 or the reproduction reference light applied to the recording medium 301 from the objective lens 331. The reproduction light generated from the information recording layer 303 passes through the objective lens 331 and becomes a parallel light beam, passes through the quarter-wave plate 332 and becomes P-polarized light, and the polarization beam splitter surface 333 a of the polarization beam splitter 333. And enters the photodetector 334.

  In the case where the recording medium 301 has the configuration shown in FIG. 22, the light from the objective lens 321 and the light from the objective lens 331 are both on the boundary surface between the transparent substrate 302 and the information recording layer 303. The recording medium 301 is irradiated while converging to the smallest diameter.

  Next, the configuration of the optical information recording / reproducing apparatus according to the present embodiment will be described with reference to FIG. This optical information recording / reproducing apparatus 310 uses an optical head lower part 40A and an optical head upper part 40B instead of the optical head 40 and the drive unit 84 in the optical information recording / reproducing apparatus 10 according to the first embodiment shown in FIG. And a fixing portion 40C. The optical head lower portion 40A is disposed below the recording medium 301, and irradiates the recording medium 301 with the recording reference light or the reproduction reference light and collects the reproduction light. The optical head upper part 40B is arranged on the upper side of the recording medium 301 so as to irradiate the recording medium 301 with information light. The fixing unit 40C is fixed to the main body of the optical information recording / reproducing apparatus 310.

  The optical head lower portion 40A includes an objective lens 331, a quarter-wave plate 332, a polarizing beam splitter 333, a photodetector 334, a polarizing beam splitter 335, and a convex lens among the components of the recording / reproducing optical system shown in FIG. 336, a concave lens 337, a phase spatial light modulator 338, and a mirror 339 are accommodated. The optical head upper portion 40B includes an objective lens 321, a quarter-wave plate 322, a polarizing beam splitter 323, a convex lens 324, a pinhole 325, a convex lens 326, and a spatial light modulator in the recording / reproducing optical system shown in FIG. 327 is stored. The fixing unit 40C houses a semiconductor laser 342, a collimator lens 343, a mirror 344, an optical element for optical rotation 345, a polarization beam splitter 346, and a mirror 340.

  The optical head lower portion 40A and the optical head upper portion 40B are driven while maintaining the positional relationship facing each other with the recording medium 301 interposed therebetween, by the same drive mechanism as that of the optical head 40 shown in FIG. ing. In the present embodiment, the optical head lower portion 40A and the optical head upper portion 40B each have the function of the driving device 84 in FIG. 2, and thus this driving device 84 is not provided. Further, in the present embodiment, the function of correcting the relative inclination between the recording medium 301 and the optical head lower part 40A and the optical head upper part 40B is not provided, and the inclination correction circuit 93 in FIG. 2 is not provided. Other circuit configurations of the optical information recording / reproducing apparatus 310 are the same as those of the optical information recording / reproducing apparatus 10 shown in FIG.

  In the optical head lower portion 40A and the optical head upper portion 40B in the present embodiment, the positions of the objective lenses 321 and 331 can be changed in the direction perpendicular to the surface of the recording medium 301 by the actuator 241 in FIG. Focus servo can be performed. Further, in the optical head lower portion 40A and the optical head upper portion 40B, the positions of the objective lenses 321 and 331 can be changed in the radial direction of the recording medium 301 by the linear motor 222 in FIG. Access and tracking servo. In the optical head lower portion 40A and the optical head upper portion 40B, the positions of the objective lenses 321 and 331 can be changed by the linear motor 232 in the tangential direction of the track, that is, substantially in the direction along the track. Thereby, it is possible to control the information recording area 307 to follow the irradiation position of the information light and the recording reference light.

  The semiconductor laser 342, the spatial light modulator 327, and the phase spatial light modulator 338 are controlled by the controller 90 in FIG. The controller 90 holds information on a plurality of modulation patterns for spatially modulating the phase of light in the phase spatial light modulator 338. The operation unit 91 can select an arbitrary modulation pattern from a plurality of modulation patterns. Then, the controller 90 provides the phase spatial light modulator 338 with the modulation pattern selected by the controller 90 according to a predetermined condition or the information of the modulation pattern selected by the operation unit 91. The phase spatial light modulator 338 provides the information from the controller 90. The phase of light is spatially modulated with a corresponding modulation pattern in accordance with information on the modulation pattern to be obtained.

  Next, the operation of the optical information recording / reproducing apparatus according to the present embodiment will be described in order, divided into servo, information recording, and information reproduction.

  First, with reference to FIGS. 23 and 25, the operation during servo will be described. FIG. 25 is an explanatory view showing a state of a main part of the recording / reproducing optical system at the time of servo. At the time of servo, the spatial light modulator 327 is in a state where all pixels are cut off. The phase spatial light modulator 338 is set so that all light passing through each pixel has the same phase. The output of the emitted light from the semiconductor laser 342 is set to a low output for reproduction. The controller 90 predicts the timing at which the emitted light from the objective lens 331 passes through the address / servo area 306 based on the basic clock reproduced from the reproduction signal RF, and the emitted light from the objective lens 331 is used as the address / servo area. While passing through 306, the above setting is made.

  The light emitted from the semiconductor laser 342 is converted into a parallel beam by the collimator lens 343, passes through the mirror 344 and the optical element 345 for optical rotation, and enters the polarization beam splitter 346. The S-polarized component of the light incident on the polarization beam splitter 346 is reflected by the polarization beam splitter surface 346a and blocked by the spatial light modulator 327.

  The P-polarized component of the light incident on the polarization beam splitter 346 is transmitted through the polarization beam splitter surface 346a, passes through the mirrors 340 and 339, is transmitted through the polarization beam splitter surface 335a of the polarization beam splitter 335, and the convex lens 336, The light passes through the concave lens 337 and enters the phase spatial light modulator 338. Since the phase spatial light modulator 338 rotates the polarization direction of the outgoing light by 90 ° with respect to the polarization direction of the incident light, the outgoing light of the phase spatial light modulator 338 becomes S-polarized light. The light emitted from the phase spatial light modulator 338 passes through the concave lens 337 and the convex lens 336, is reflected by the polarizing beam splitter surface 335a of the polarizing beam splitter 335, and is further reflected by the polarizing beam splitter surface 333a of the polarizing beam splitter 333. The light enters the quarter wave plate 332. The light that has passed through the quarter-wave plate 332 becomes circularly polarized light, is condensed by the objective lens 331, and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. The recording medium 301 is irradiated.

  The return light generated by reflecting the light irradiated to the recording medium 301 from the objective lens 331 at the boundary surface between the transparent substrate 302 and the protective layer 305 passes through the objective lens 331 to become a parallel light flux, and is a quarter-wave plate. The light passes through 332 and becomes P-polarized light, passes through the polarization beam splitter surface 333 a of the polarization beam splitter 333, and enters the photodetector 334. Based on the output of the photodetector 334, the detection circuit 85 generates a focus error signal FE, a tracking error signal TE, and a reproduction signal RF. Based on these signals, focus servo and tracking servo are performed, and the basic clock is reproduced and the address is discriminated.

  In the setting at the time of the servo, the configuration of the optical head lower portion 40A is the same as the configuration of an optical head for recording and reproduction on a normal optical disc. Therefore, the optical information recording / reproducing apparatus in the present embodiment can perform recording and reproduction using a normal optical disk.

  Next, with reference to FIG. 23 and FIG. 26, the operation at the time of recording information will be described. FIG. 26 is an explanatory diagram showing the state of the main part of the recording / reproducing optical system during recording. At the time of recording, the spatial light modulator 327 selects a transmission state (hereinafter also referred to as “on”) and a cutoff state (hereinafter also referred to as “off”) for each pixel according to information to be recorded, and transmits light passing therethrough. Information light is generated by spatially modulating the intensity. The phase spatial light modulator 338 selectively gives a phase difference of 0 (rad) or π (rad) to the passing light according to a predetermined modulation pattern with respect to a predetermined phase for each pixel. Thus, the phase of light is spatially modulated to generate recording reference light whose phase is spatially modulated.

  The controller 90 provides the phase spatial light modulator 338 with the modulation pattern selected by the controller 90 or the information of the modulation pattern selected by the operation unit 91 according to a predetermined condition, and the phase spatial light modulator 338 receives the modulation given by the controller 90. According to the pattern information, the phase of light passing therethrough is spatially modulated.

  The output of the emitted light from the semiconductor laser 342 is pulsed to a high output for recording. Note that focus servo and tracking servo are not performed during a period in which the light emitted from the objective lenses 321 and 331 passes through an area other than the address / servo area 306 under the control of the controller 90.

  The light emitted from the semiconductor laser 342 is converted into a parallel beam by the collimator lens 343, passes through the mirror 344 and the optical element 345 for optical rotation, and enters the polarization beam splitter 346. The S-polarized component of the light incident on the polarization beam splitter 346 is reflected by the polarization beam splitter surface 346a and passes through the spatial light modulator 327. At that time, the intensity of the light is spatially determined according to the information to be recorded. Modulated into information light. The information light passes through the convex lens 326, the pinhole 325, and the convex lens 324 in order, is reflected by the polarization beam splitter surface 323 a of the polarization beam splitter 323, and enters the quarter-wave plate 322. The information light that has passed through the quarter-wave plate 322 becomes circularly polarized light, is condensed by the objective lens 321, and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. However, the recording medium 301 is irradiated. As shown in FIG. 26, the information light passes through the information recording layer 303 while converging in the recording medium 301.

  The P-polarized component of the light incident on the polarization beam splitter 346 is transmitted through the polarization beam splitter surface 346a, passes through the mirrors 340 and 339, is transmitted through the polarization beam splitter surface 335a of the polarization beam splitter 335, and the convex lens 336, The light passes through the concave lens 337, enters the phase spatial light modulator 338, and the phase of the light is spatially modulated to become recording reference light. Since the recording reference light emitted from the phase spatial light modulator 338 is S-polarized light, after passing through the concave lens 337 and the convex lens 336, it is reflected by the polarizing beam splitter surface 335a of the polarizing beam splitter 335, and The light is reflected by the polarization beam splitter surface 333 a of the polarization beam splitter 333 and enters the quarter-wave plate 332. The recording reference light that has passed through the quarter-wave plate 332 becomes circularly polarized light, is condensed by the objective lens 331, and has the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. The recording medium 301 is irradiated while converging. As shown in FIG. 26, the recording reference light passes through the information recording layer 303 while diverging in the recording medium 301.

  As described above, at the time of recording, the information light and the recording reference light are coaxially irradiated to the information recording layer 303 from the opposite surface sides, and the same position (on the boundary surface between the transparent substrate 302 and the protective layer 305). ) To converge to the smallest diameter. In the information recording layer 303, information light and recording reference light interfere to form an interference pattern. When the output of the light emitted from the semiconductor laser 342 becomes a high output for recording, this interference pattern is generated. Volumetric recording is performed in the information recording layer 303 to form a reflection (Lippmann) hologram.

  In the present embodiment, a plurality of pieces of information can be multiplexed and recorded at the same location of the information recording layer 303 by the phase encoding multiplexing method by changing the phase modulation pattern of the recording reference light for each information to be recorded. it can.

  In the present embodiment, it is also possible to multiplex-record a plurality of data using a method called shift multiplexing. Shift multiplexing is a method of multiplexing a plurality of pieces of information by forming a plurality of hologram forming regions corresponding to each piece of information on the information recording layer 303 by slightly shifting each other in the horizontal direction and partially overlapping each other. It is a method of recording.

  Only one of the multiplex recording by the phase encoding multiplex system and the multiplex recording by shift multiplexing can be used, or they can be used in combination.

  Next, with reference to FIG. 23 and FIG. 27, the operation at the time of reproducing information will be described. FIG. 27 is an explanatory diagram showing the state of the main part of the recording / reproducing optical system during reproduction. At the time of reproduction, all the pixels of the spatial light modulator 327 are blocked. The phase spatial light modulator 338 selectively gives a phase difference of 0 (rad) or π (rad) to the passing light according to a predetermined modulation pattern with respect to a predetermined phase for each pixel. Thus, the phase of light is spatially modulated to generate reproduction reference light whose phase is spatially modulated.

  The controller 90 provides the phase spatial light modulator 338 with the modulation pattern selected by the controller 90 according to a predetermined condition or the information of the modulation pattern selected by the operation unit 91, and the phase spatial light modulator 338 receives the modulation given by the controller 90. According to the pattern information, the phase of light passing therethrough is spatially modulated.

  The output of the emitted light from the semiconductor laser 342 is set to a low output for reproduction. Note that focus servo and tracking servo are not performed during a period in which the light emitted from the objective lenses 321 and 331 passes through an area other than the address / servo area 306 under the control of the controller 90.

  The light emitted from the semiconductor laser 342 is converted into a parallel beam by the collimator lens 343, passes through the mirror 344 and the optical element 345 for optical rotation, and enters the polarization beam splitter 346. The S-polarized component of the light incident on the polarization beam splitter 346 is reflected by the polarization beam splitter surface 346a and blocked by the spatial light modulator 327.

  The P-polarized component of the light incident on the polarization beam splitter 346 is transmitted through the polarization beam splitter surface 346a, passes through the mirrors 340 and 339, is transmitted through the polarization beam splitter surface 335a of the polarization beam splitter 335, and the convex lens 336, The light passes through the concave lens 337, enters the phase spatial light modulator 338, and the phase of the light is spatially modulated to become reproduction reference light. Since the reproduction reference light emitted from the phase spatial light modulator 338 is S-polarized light, it passes through the concave lens 337 and the convex lens 336, is reflected by the polarization beam splitter surface 335a of the polarization beam splitter 335, and The light is reflected by the polarization beam splitter surface 333 a of the polarization beam splitter 333 and enters the quarter-wave plate 332. The reproduction reference light that has passed through the quarter-wave plate 332 becomes circularly polarized light, is condensed by the objective lens 331, and has the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. The recording medium 301 is irradiated while converging. As shown in FIG. 27, the reference light for reproduction passes through the information recording layer 303 while diverging in the recording medium 301.

  In the information recording layer 303, reproduction light corresponding to the information light at the time of recording is generated by irradiating the reference light for reproduction. The reproduction light travels toward the transparent substrate 302 while converging, and after reaching the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305, the reproduction light is emitted from the recording medium 301 while diverging, and the objective lens 331. Passes through the quarter-wave plate 332, becomes P-polarized light, passes through the polarization beam splitter surface 333a of the polarization beam splitter 333, and enters the photodetector 334.

  On the photodetector 334, an on / off pattern is formed by the spatial light modulator 327 during recording, and information is reproduced by detecting this pattern. When a plurality of pieces of information are recorded in the information recording layer 303 by changing the modulation pattern of the recording reference light, only information corresponding to the modulation pattern of the reproduction reference light is included in the plurality of pieces of information. Played.

  As described above, during reproduction, the recording medium 301 is irradiated with reproduction reference light that converges to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. The reproduction reference light is irradiated and the reproduction light is collected from the recording reference light incident side of the recording medium 301, and the reproduction reference light and the reproduction light are coaxially arranged.

  In the present embodiment, at the time of recording information, the optical head upper portion 40B and the optical head lower portion 40A are configured so that the irradiation positions of the information light and the recording reference light follow the one information recording area 307 that moves for a predetermined period. Next, the irradiation position of the information light and the recording reference light is moved. Thereby, the information light and the recording reference light are continuously irradiated to one information recording area 307 for a predetermined period.

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

  In the present embodiment, information light can carry information using the entire cross section of the light beam, and similarly, reproduction light can carry information using the entire cross section of the light beam.

  Thus, according to the present embodiment, information can be recorded and reproduced using holography, and the configuration of the optical system for recording and reproduction can be simplified without reducing the amount of information. It becomes possible to do.

  In the present embodiment, the recording medium 301 is provided with a positioning area (address / servo area 306) in which information for aligning information light, recording reference light, and reproduction reference light is recorded, and recording / reproduction is performed. The optical system irradiates the recording medium 301 with the information light, the recording reference light, and the reproduction reference light while converging so as to have the smallest diameter at the position where the positioning region is provided. As a result, similarly to the recording reference light and the reproduction reference light, the positioning area is irradiated with light that converges to have the smallest diameter at the position where the positioning area is provided, and the return light from the positioning area is detected. Thus, the information light, the recording reference light, and the reproduction reference light can be positioned using the information recorded in the positioning area. Therefore, according to the present embodiment, it is possible to accurately position the information light, the recording reference light, and the reproduction reference light with respect to the recording medium 301 without complicating the configuration of the recording / reproducing optical system. .

  Further, according to the present embodiment, since the positioning area is arranged on the incident side of the recording reference light with respect to the information recording layer 303, the return light from the positioning area does not pass through the information recording layer 303. Therefore, it is possible to prevent the light used for positioning from being disturbed by the information recording layer 303 and reducing the reproduction accuracy of information for positioning.

  Other configurations, operations, and effects in the present embodiment are the same as those in the first embodiment or the second embodiment.

  [Fourth Embodiment] Next, an optical information recording / reproducing apparatus according to a fourth embodiment of the present invention will be described. FIG. 28 is an explanatory diagram showing the overall configuration of the recording / reproducing optical system in the optical information recording / reproducing apparatus according to the present embodiment.

  In this embodiment, information light is generated by spatially modulating the phase of light based on information to be recorded. In the recording / reproducing optical system in the present embodiment, a phase spatial light modulator 347 is provided instead of the spatial light modulator 327 in FIG. 23, and further, between the phase spatial light modulator 347 and the polarization beam splitter 346. A shutter 348 for selecting a light transmission state and a light blocking state is provided. The phase spatial light modulator 347 has a large number of pixels arranged in a lattice pattern, and the phase of the light is selected by selecting the phase of the emitted light from among two or more values for each pixel. It can be spatially modulated. As the phase spatial light modulator 347, for example, a liquid crystal element can be used. A liquid crystal element can also be used for the shutter 348.

  Next, the operation of the optical information recording / reproducing apparatus according to the present embodiment will be described in order, divided into servo, information recording, and information reproduction.

  First, the operation during servo will be described. During servo operation, the shutter 348 is in a shut-off state. Other operations during the servo operation are the same as those of the third embodiment.

  Next, with reference to FIG. 29, an explanation will be given on the operation at the time of recording when information is recorded using information light whose phase is spatially modulated and recording reference light whose phase is not spatially modulated. FIG. 29 is an explanatory diagram showing the state of the main part of the recording / reproducing optical system during recording. At the time of recording, the shutter 348 is in a transmissive state, and the phase spatial light modulator 347 selects the phase of the emitted light from two values or three or more values for each pixel according to the information to be recorded. , Spatially modulate the phase of light. Here, for simplicity of explanation, the phase spatial light modulator 347 uses the phase of the emitted light for each pixel as the first phase with a phase difference of + π / 2 (rad) with respect to a predetermined reference phase. It is assumed that the light phase is spatially modulated by setting one of the second phases where the phase difference with respect to the reference phase is −π / 2 (rad). The phase difference between the first phase and the second phase is π (rad). In this way, information light whose phase is spatially modulated is generated. In the information light, the intensity locally decreases at the boundary portion between the first phase pixel and the second phase pixel.

  As in the third embodiment, the information light is condensed by the objective lens 321 and irradiated onto the recording medium 301 while converging so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. Is done. Then, the information light passes through the information recording layer 303 while converging in the recording medium 301.

  Here, the phase spatial light modulator 338 does not spatially modulate the phase of the light, and the phase of the emitted light of all the pixels is the first that has a phase difference of + π / 2 (rad) with respect to a predetermined reference phase. It is assumed that recording reference light is generated as the phase. Note that the phase spatial light modulator 338 may set the phase of the emitted light of all the pixels as the second phase, or may be a constant phase different from both the first phase and the second phase.

  In FIG. 29, the first phase is represented by a symbol “+”, and the second phase is represented by a symbol “−”. In FIG. 29, the maximum intensity value is represented by “1” and the minimum intensity value “0”.

  As in the third embodiment, the recording reference light is condensed by the objective lens 331 and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305 while recording medium 301. Is irradiated. The recording reference light passes through the information recording layer 303 while diverging in the recording medium 301.

  Similar to the third embodiment, in the information recording layer 303, information light and recording reference light interfere with each other to form an interference pattern, and the output of the emitted light from the semiconductor laser 342 is high output for recording. Then, this interference pattern is recorded in volume in the information recording layer 303, and a reflection type (Lippmann type) hologram is formed.

  Next, with reference to FIG. 30, an explanation will be given on the operation at the time of reproducing the information recorded using the information light whose phase is spatially modulated and the recording reference light whose phase is not spatially modulated. FIG. 30 is an explanatory diagram showing the state of the main part of the recording / reproducing optical system during reproduction. At the time of reproduction, the shutter 348 is shut off. In addition, the phase spatial light modulator 338 does not spatially modulate the phase of the light, and the phase of the emitted light of all the pixels is a first difference in which the phase difference with respect to a predetermined reference phase is + π / 2 (rad). As a phase, reproduction reference light is generated. In FIG. 30, the phase and intensity are represented in the same manner as in FIG.

  As in the third embodiment, the reproduction reference light is collected by the objective lens 331 and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305, while being recorded. Is irradiated. Then, the reproduction reference light passes through the information recording layer 303 while diverging in the recording medium 301.

  In the information recording layer 303, reproduction light corresponding to the information light at the time of recording is generated by irradiating the reference light for reproduction. Similar to the information light at the time of recording, the reproduction light is a light whose phase is spatially modulated. The reproduction light travels toward the transparent substrate 302 while converging, and after reaching the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305, the reproduction light is emitted from the recording medium 301 while diverging, and passes through the objective lens 331. The light passes through and becomes a parallel light beam, passes through the quarter-wave plate 332 and the polarizing beam splitter surface 333 a of the polarizing beam splitter 333, and enters the photodetector 334.

  In addition, a part of the reproduction reference light irradiated on the recording medium 301 is reflected on the boundary surface between the transparent substrate 302 and the protective layer 305 and is emitted from the recording medium 301 while diverging and passes through the objective lens 331. Then, the light beam becomes a parallel light beam, passes through the quarter-wave plate 332 and the polarizing beam splitter surface 333 a of the polarizing beam splitter 333, and enters the photodetector 334.

  Actually, the reproduction light and the reproduction reference light reflected on the boundary surface between the transparent substrate 302 and the protective layer 305 are superimposed to generate combined light, and this combined light is received by the photodetector 334. Is done. The combined light is light whose intensity is spatially modulated corresponding to the recorded information. Therefore, a two-dimensional pattern of the intensity of the combined light is detected by the photodetector 334, thereby reproducing information.

  Here, with reference to FIG. 31, the reproduction light, the reproduction reference light, and the combined light at the time of reproduction described above will be described in detail. In FIG. 31, (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 combined light. Represents the strength of In FIG. 31, the phase of each pixel of the information light is a second phase in which the phase difference with respect to the reference phase is + π / 2 (rad) and the phase difference with respect to the reference phase is −π / 2 (rad). The example about the case where it sets to one of these phases is shown. Therefore, in the example shown in FIG. 31, the phase of each pixel of the reproduction light is either the first phase or the second phase, like the information light. Further, the phase of each reference pixel for reproduction is the first phase. Here, if the intensity of the reproduction light and the intensity of the reference light for reproduction are equal, as shown in FIG. 31 (e), the intensity of the combined light in the pixel in which the phase of the reproduction light is the first phase is In principle, the intensity of the combined light is zero in a pixel that is larger than the intensity of the reproduction light and the intensity of the reproduction reference light and the phase of the reproduction light is the second phase.

  Next, with reference to FIG. 32, an explanation will be given on the operation at the time of recording when information is recorded using information light whose phase is spatially modulated and recording reference light whose phase is spatially modulated. . FIG. 32 is an explanatory view showing the state of the main part of the recording / reproducing optical system during recording. At the time of recording, the shutter 348 is in a transmissive state, and the phase spatial light modulator 347 selects the phase of the emitted light from two values or three or more values for each pixel according to the information to be recorded. , Spatially modulate the phase of light. Here, in order to simplify the explanation, the phase spatial light modulator 347 sets the phase of the emitted light to either the first phase or the second phase for each pixel, thereby making the light phase Is spatially modulated. In this way, information light whose phase is spatially modulated is generated.

  As in the third embodiment, the information light is condensed by the objective lens 321 and irradiated onto the recording medium 301 while converging so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305. Is done. Then, the information light passes through the information recording layer 303 while converging in the recording medium 301.

  The phase spatial light modulator 338 spatially modulates the light phase by selecting the phase of the emitted light from two values or three or more values for each pixel. Here, the phase spatial light modulator 338 sets the phase of the emitted light for each pixel to a predetermined reference phase, a first phase whose phase difference with respect to the reference phase is + π / 2 (rad), and a reference phase. It is assumed that the phase of light is spatially modulated by setting to any one of the second phases where the phase difference is −π / 2 (rad). In FIG. 32, the reference phase is represented by the symbol “0”. Other ways of expressing the phase and intensity in FIG. 32 are the same as those in FIG. In the recording reference light, the intensity locally decreases at the portion where the phase changes.

  As in the third embodiment, the recording reference light is condensed by the objective lens 331 and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305 while recording medium 301. Is irradiated. The recording reference light passes through the information recording layer 303 while diverging in the recording medium 301.

  Similar to the third embodiment, in the information recording layer 303, information light and recording reference light interfere with each other to form an interference pattern, and the output of the emitted light from the semiconductor laser 342 is high output for recording. Then, this interference pattern is recorded in volume in the information recording layer 303, and a reflection type (Lippmann type) hologram is formed.

  Next, with reference to FIG. 33, the operation at the time of reproducing the information recorded using the information light whose phase is spatially modulated and the recording reference light whose phase is spatially modulated will be described. FIG. 33 is an explanatory diagram showing the state of the main part of the recording / reproducing optical system during reproduction. At the time of reproduction, the shutter 348 is shut off. Similarly to the recording, the phase spatial light modulator 338 spatially modulates the phase of the emitted light to generate reproduction reference light whose phase is spatially modulated. In FIG. 33, the phase and intensity are represented in the same manner as in FIG.

  As in the third embodiment, the reproduction reference light is collected by the objective lens 331 and converges so as to have the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305, while being recorded. Is irradiated. Then, the reproduction reference light passes through the information recording layer 303 while diverging in the recording medium 301.

  In the information recording layer 303, reproduction light corresponding to the information light at the time of recording is generated by irradiating the reference light for reproduction. Similar to the information light at the time of recording, the reproduction light is a light whose phase is spatially modulated. The reproduction light travels toward the transparent substrate 302 while converging, and after reaching the smallest diameter on the boundary surface between the transparent substrate 302 and the protective layer 305, the reproduction light is emitted from the recording medium 301 while diverging, and passes through the objective lens 331. The light passes through and becomes a parallel light beam, passes through the quarter-wave plate 332 and the polarizing beam splitter surface 333 a of the polarizing beam splitter 333, and enters the photodetector 334.

  In addition, a part of the reproduction reference light irradiated on the recording medium 301 is reflected on the boundary surface between the transparent substrate 302 and the protective layer 305 and is emitted from the recording medium 301 while diverging and passes through the objective lens 331. Then, the light beam becomes a parallel light beam, passes through the quarter-wave plate 332 and the polarizing beam splitter surface 333 a of the polarizing beam splitter 333, and enters the photodetector 334.

  Actually, the reproduction light and the reproduction reference light reflected on the boundary surface between the transparent substrate 302 and the protective layer 305 are superimposed to generate combined light, and this combined light is received by the photodetector 334. Is done. The combined light is light whose intensity is spatially modulated corresponding to the recorded information. Therefore, a two-dimensional pattern of the intensity of the combined light is detected by the photodetector 334, thereby reproducing information.

  Here, with reference to FIG. 34, the reproduction light, the reproduction reference light, and the combined light at the time of reproduction described above will be described in detail. 34, (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 combined light. Represents the strength of FIG. 34 sets the phase of each pixel of information light to either the first phase or the second phase, and sets the phase of each pixel of the recording reference light and reproduction reference light to the reference phase, The example about the case where it sets to either the 1st phase and the 2nd phase is shown. In this case, the phase of the reproduction light for each pixel is either the first phase or the second phase, similar to the information light. Therefore, the phase difference between the reproduction light and the reproduction reference light is zero, ± π / 2 (rad), or ± π (rad). Here, if the intensity of the reproduction light and the intensity of the reference light for reproduction are equal, as shown in FIG. 34E, the intensity of the combined light is zero in the phase difference between the reproduction light and the reference light for reproduction. Is the largest, and in principle, the pixel where the phase difference between the reproduction light and the reproduction reference light is ± π (rad) is zero, and the phase difference between the reproduction light and the reproduction reference light is ± π / In a pixel having 2 (rad), the intensity is ½ of that in a pixel having a phase difference of zero. In FIG. 34 (e), the intensity at a pixel having a phase difference of ± π (rad) is represented by “0”, and the intensity at a pixel having a phase difference of ± π / 2 (rad) is represented by “1”. The intensity at the pixel where the phase difference is zero is represented by “2”.

  In the example shown in FIGS. 32 to 34, the intensity of the synthesized light for each pixel is ternary. For example, as shown in FIG. 34 (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”. "Can correspond to 2-bit data" 10 ". Thus, in the example shown in FIGS. 32 to 34, compared with the case where the intensity of each pixel of the synthesized light is binary as in the example shown in FIGS. In the same manner, the amount of information carried by the combined light can be increased, and as a result, the recording density of the recording medium 301 can be improved.

  As described above, in the present embodiment, when information is recorded, the information light whose phase is spatially modulated based on the information to be recorded and the recording reference light are applied to the information recording layer 303 of the recording medium 301. Irradiation is performed, and information is recorded on the information recording layer 303 by an interference pattern due to interference between the information light and the recording reference light. Further, at the time of information reproduction, the information recording layer 303 is irradiated with reproduction reference light, whereby the reproduction light generated from the information recording layer 303 and the reproduction reference light are overlapped to generate synthesized light. Recover information by detecting 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, it is not necessary to make the information light and the recording reference light incident on the recording medium at a predetermined angle when recording information. Therefore, according to the present embodiment, the optical system for recording and reproduction can be made small.

  Further, in the conventional reproduction method, the reproduction light and the reproduction reference light are separated and only the reproduction light is detected. Therefore, if the reproduction reference light is incident on the photodetector for detecting the reproduction light, the reproduction light is reproduced. There was a problem that the SN ratio of information deteriorated. On the other hand, in the present embodiment, information is reproduced using reproduction light and reproduction reference light, so that the SN ratio of reproduction information does not deteriorate due to reproduction reference light. Therefore, according to the present embodiment, it is possible to improve the SN ratio of the reproduction information.

  Other configurations, operations, and effects in the present embodiment are the same as those in the third embodiment.

  [Fifth Embodiment] Next, an optical information recording / reproducing apparatus according to a fifth embodiment of the present invention will be described. In the present embodiment, as in the fourth embodiment, information light is generated by spatially modulating the phase of light based on information to be recorded. The configuration of the recording / reproducing optical system is different from that of the fourth embodiment.

  35 is a plan view showing the optical head and the recording medium in the present embodiment, FIG. 36 is a cross-sectional view showing the configuration of the optical head in the present embodiment, and FIG. 37 is a cross-sectional view showing the configuration of the recording medium in the present embodiment. FIG.

  As shown in FIGS. 35 and 36, the optical information recording / reproducing apparatus according to the present embodiment includes the optical head 40 and the driving device in the optical information recording / reproducing apparatus 10 according to the first embodiment shown in FIG. Instead of 84, an optical head 440 and a driving device 484 are provided. In this embodiment, the function of correcting the relative inclination between the recording medium 401 and the optical head 440 is not provided, and the inclination correction circuit 93 in FIG. 2 is not provided. The other circuit configuration of the optical information recording / reproducing apparatus according to the present embodiment is the same as that of the optical information recording / reproducing apparatus 10 shown in FIG.

  The optical head 440 has a first movable part 441 and a second movable part 442. The first movable portion 441 is moved in the radial direction of the recording medium 401 in the present embodiment by the driving device 484. The second movable portion 442 includes a lower arm portion 442A disposed on the lower side of the recording medium 401, an upper arm portion 442B disposed on the upper side of the recording medium 401, and a position outside the outer peripheral portion of the recording medium 401. And a connecting portion 442C for connecting the lower arm portion 442A and the upper arm portion 442B. The tip portions of the lower arm portion 442A and the upper arm portion 442B are arranged at positions facing each other with the recording medium 401 interposed therebetween.

  The connecting portion 442C is rotatably connected to the first movable portion 441 via a ball bearing 443. Two coils 444 for tracking the irradiation position are attached to the end of the connecting portion 442C opposite to the lower arm portion 442A and the upper arm portion 442B. Two magnets 445 are attached to the first movable portion 441 at positions facing each other with the coils 444 interposed therebetween. In the optical head 440, the positions of the respective distal end portions of the lower arm portion 442A and the upper arm portion 442B are determined by rotating the second movable portion 442 relative to the first movable portion 441 by the coil 444 and the magnet 445. The recording medium 401 can be changed in a direction substantially along the track.

  Next, the configuration of the recording / reproducing optical system provided in the second movable portion 442 will be described with reference to FIG. The recording / reproducing optical system includes a recording / reproducing semiconductor laser 411 and a servo semiconductor laser 412 fixed to the ends of the connecting portion 442C opposite to the lower arm portion 442A and the upper arm portion 442B. The recording / reproducing optical system further includes a collimator lens 413, a dichroic mirror 414, a transmission-type phase spatial light modulator 415, and a polarization that are sequentially arranged from the semiconductor laser 412 side on the optical path of the light emitted from the servo semiconductor laser 412. A beam splitter 416, a relay lens system 417, a quarter wave plate 418, and a mirror 419 are included. The dichroic mirror 414 has a reflecting surface that reflects light of a predetermined wavelength and transmits light of other wavelengths. The reflecting surface reflects the light emitted from the recording / reproducing semiconductor laser 411 and transmits the light emitted from the servo semiconductor laser 412. The polarization beam splitter 416 has a polarization beam splitter surface that reflects or transmits light according to the polarization direction of the light.

  The recording / reproducing optical system is further disposed at the distal end of the lower arm 442A, facing the lower surface of the recording medium 401, and the objective lens 420 in a direction perpendicular to the surface of the recording medium 401. And an actuator 421 that moves. The mirror 419 reflects the light incident from the quarter-wave plate 418 side and guides it to the objective lens 420. The recording / reproducing optical system further includes a photodetector 422 that receives light incident on the polarization beam splitter 416 from the relay lens system 417 side and reflected by the polarization beam splitter surface.

  The recording / reproducing optical system further includes a collimator lens 423, a half-wave plate 424, a polarization beam splitter 425, and a mirror arranged in order from the semiconductor laser 411 side on the optical path of the light emitted from the recording / reproducing semiconductor laser 411. 426. The polarization beam splitter 425 has a polarization beam splitter surface. The mirror 426 reflects light incident from the polarization beam splitter 425 side and guides it to the reflecting surface of the dichroic mirror 414.

  The recording / reproducing optical system further includes a polarizing beam splitter 427 disposed on the optical path of the light incident on the polarizing beam splitter 425 from the half-wave plate 424 side and reflected by the polarizing beam splitter surface. ing. The recording / reproducing optical system further has a shutter 428 arranged in order from the polarization beam splitter 427 side on the optical path of the light incident on the polarization beam splitter 427 from the polarization beam splitter 425 side and reflected by the polarization beam splitter surface. A half-wave plate 429, a transmissive phase spatial light modulator 430, a polarization beam splitter 431, a relay lens system 432, a quarter-wave plate 433 and a mirror 434 are provided. The polarization beam splitter 431 has a polarization beam splitter surface.

  The recording / reproducing optical system is further arranged at the tip of the upper arm 442B, and an objective lens 435 facing the upper surface of the recording medium 401, and the objective lens 435 is moved in a direction perpendicular to the surface of the recording medium 401. And an actuator 436. The mirror 434 reflects light incident from the quarter-wave plate 433 side and guides it to the objective lens 436. The recording / reproducing optical system further includes a photodetector 437 that receives light incident on the polarization beam splitter 431 from the relay lens system 432 side and reflected by the polarization beam splitter surface.

  Next, the configuration of the recording medium 401 in the present embodiment will be described with reference to FIG. Similar to the recording medium 1 in the first embodiment, the recording medium 401 has a disk shape and has a plurality of tracks. A plurality of address / servo areas are provided at equal intervals in each track. One or a plurality of information recording areas are provided between adjacent address / servo areas.

  The recording medium 401 includes two disc-shaped transparent substrates 402 and 404 formed of polycarbonate or the like, a spacer 406 that separates the transparent substrates 402 and 404 at a predetermined interval, and the transparent substrates 402 and 404. The provided information recording layer 403 and a transparent substrate 405 bonded to the surface of the transparent substrate 404 opposite to the information recording layer 403 through an adhesive layer 407 are provided.

  The information recording layer 403 is a layer on which information is recorded using holography, and is formed of a hologram material having sensitivity to light in a predetermined wavelength region. The recording / reproducing semiconductor laser 411 emits light having a wavelength with which the hologram material constituting the information recording layer 403 has sensitivity. The servo semiconductor laser 412 has a wavelength region with which the hologram material constituting the information recording layer 403 has sensitivity. Light of an outside wavelength is emitted. As a combination of the wavelength of the emitted light of the recording / reproducing semiconductor laser 411 and the wavelength of the emitted light of the servo semiconductor laser 412, there are a combination of 650 nm and 780 nm, a combination of 523 nm and 650 nm, a combination of 405 nm and 650 nm, and the like.

  In the address / servo area, emboss pits representing address information and the like are formed on the surface of the transparent substrate 405 on the transparent substrate 404 side. The focus servo can also be performed using the surface of the transparent substrate 405 on the transparent substrate 404 side.

  In the recording medium 401, the total optical thickness of the transparent substrate 402, the information recording layer 403, the transparent substrate 404, and the adhesive layer 407 is equal to the optical thickness of the transparent substrate 405.

  In the recording medium 401, the surface of the transparent substrate 405 opposite to the transparent substrate 404 (the lower surface in FIG. 37) is a surface on which the recording reference light and the reproduction reference light are incident and the reproduction light is emitted. The surface of the transparent substrate 402 opposite to the information recording layer 403 (the upper surface in FIG. 37) is a surface on which information light carrying information to be recorded is incident.

  Next, the operation of the optical head 440 in the present embodiment will be described in order, divided into servo, information recording, and information reproduction. First, the operation during servo will be described. During servo, the servo semiconductor laser 412 emits light, and the recording / reproducing semiconductor laser 411 does not emit light. The servo semiconductor laser 412 emits P-polarized light. The light emitted from the semiconductor laser 412 is collimated by the collimator lens 413, passes through the reflecting surface of the dichroic mirror 414, passes through the phase spatial light modulator 415, and passes through the polarizing beam splitter surface of the polarizing beam splitter 416. The light passes through the relay lens system 417, passes through the quarter-wave plate 418, and becomes circularly polarized light. This light is reflected by the mirror 419 and incident on the objective lens 420, is collected by the objective lens 420, and converges so as to have the smallest diameter on the surface of the transparent substrate 405 on the transparent substrate 404 side. 401 is irradiated.

  The return light generated by reflecting the light irradiated to the recording medium 401 from the objective lens 420 on the surface of the transparent substrate 405 on the transparent substrate 404 side passes through the objective lens 420 to become a parallel light beam, reflected by the mirror 419, and 4 It passes through the half-wave plate 418 and becomes S-polarized light. This light passes through the relay lens system 417, is reflected by the polarization beam splitter surface of the polarization beam splitter 416, and enters the photodetector 422. Based on the output of the photodetector 422, a focus error signal for the objective lens 420 is obtained by a method similar to the method described with reference to FIG. Based on the focus error signal, the position of the objective lens 420 is adjusted by the actuator 421, and focus servo for the objective lens 420 is performed.

  Further, the light that is irradiated onto the recording medium 401 from the objective lens 420 and passes through the recording medium 401 passes through the objective lens 435 to become a parallel light beam, is reflected by the mirror 434, and passes through the quarter-wave plate 433. S-polarized light. This light passes through the relay lens system 432, is reflected by the polarization beam splitter surface of the polarization beam splitter 431, and enters the photodetector 437. Based on the output of the photodetector 437, a focus error signal for the objective lens 435 is obtained by a method similar to the method described with reference to FIG. The position of the objective lens 435 is adjusted by the actuator 436 based on the focus error signal, and focus servo for the objective lens 435 is performed.

  Further, based on the output of at least one of the photodetectors 422 and 437, a tracking error signal is obtained by a method similar to the method described with reference to FIGS. Further, based on the output of at least one of the photodetectors 422 and 437, a basic clock is generated and an address is recognized.

  Next, the operation at the time of recording information will be described. During recording, the recording / reproducing semiconductor laser 411 emits light, and the servo semiconductor laser 412 does not emit light. At the time of recording, the shutter 428 is in a transmission state, and the phase spatial light modulator 430 selects the phase of the emitted light from two values or three or more values for each pixel according to the information to be recorded. The information light is generated by spatially modulating the phase of the light. The phase spatial light modulator 415 spatially modulates the phase of the light by selecting the phase of the emitted light from two or more values for each pixel according to a predetermined modulation pattern. Recording reference light.

  The controller 90 provides the phase spatial light modulator 415 with the modulation pattern selected by the controller 90 according to a predetermined condition or the information of the modulation pattern selected by the operation unit 91, and the phase spatial light modulator 415 receives the modulation given by the controller 90. According to the pattern information, the phase of light passing therethrough is spatially modulated. The output of the emitted light from the recording / reproducing semiconductor laser 411 is pulsed to a high output for recording. Note that focus servo and tracking servo are not performed during a period in which the light emitted from the objective lenses 420 and 435 passes through an area other than the address / servo area under the control of the controller 90.

  The recording / reproducing semiconductor laser 411 emits P-polarized light or S-polarized light. The light emitted from the semiconductor laser 411 passes through the half-wave plate 424 and becomes light including a P-polarized component and an S-polarized component. The P-polarized component light from the half-wave plate 424 passes through the polarization beam splitter surface of the polarization beam splitter 425, is reflected by the mirror 426, and is reflected by the reflection surface of the dichroic mirror 414. This light passes through the phase spatial light modulator 415 and becomes recording reference light. The recording reference light passes through the polarization beam splitter surface of the polarization beam splitter 416, passes through the relay lens system 417, passes through the quarter-wave plate 418, and becomes circularly polarized light. The recording reference light is reflected by the mirror 419 and incident on the objective lens 420, is collected by the objective lens 420, and converges to have the smallest diameter on the surface of the transparent substrate 405 on the transparent substrate 404 side. The recording medium 401 is irradiated. The recording reference light passes through the information recording layer 403 while diverging in the recording medium 401.

  On the other hand, the S-polarized component light from the half-wave plate 424 is reflected by the polarization beam splitter surface of the polarization beam splitter 425, further reflected by the polarization beam splitter surface of the polarization beam splitter 427, and passes through the shutter 428. The light passes through the half-wave plate 429 and becomes P-polarized light. This light passes through the phase spatial light modulator 430 and becomes information light. This information light passes through the polarization beam splitter surface of the polarization beam splitter 431, passes through the relay lens system 432, passes through the quarter wavelength plate 433, and becomes circularly polarized light. The information light is reflected by the mirror 434, enters the objective lens 435, is collected by the objective lens 435, and is recorded while being converged to have the smallest diameter on the surface of the transparent substrate 405 on the transparent substrate 404 side. The medium 401 is irradiated. Then, the information light passes through the information recording layer 403 while converging in the recording medium 401.

  In the present embodiment, the optical path length from the recording / reproducing semiconductor laser 411 to the objective lens 420 is equal to the optical path length from the recording / reproducing semiconductor laser 411 to the objective lens 435.

  In the information recording layer 403, an interference pattern is formed by interference between the information light and the recording reference light. When the output of the light emitted from the semiconductor laser 411 becomes a high output for recording, this interference pattern is generated. Volume recording is performed in the information recording layer 403 to form a reflection type (Lippmann type) hologram.

  Next, the operation at the time of reproducing information will be described. During reproduction, the recording / reproducing semiconductor laser 411 emits light, and the servo semiconductor laser 412 does not emit light. At the time of reproduction, the shutter 428 is cut off, and the phase spatial light modulator 415 selects the phase of the emitted light from two values or three or more values for each pixel according to a predetermined modulation pattern. A reference light for reproduction is generated by spatially modulating the phase of the light. The reference light for reproduction follows the same path as the reference light for recording, and irradiates the recording medium 401 while converging to have the smallest diameter on the surface of the transparent substrate 405 on the transparent substrate 404 side. Then, the reproduction reference light passes through the information recording layer 403 while diverging in the recording medium 401.

  In the information recording layer 403, reproduction light corresponding to the information light at the time of recording is generated by irradiating the reference light for reproduction. Similar to the information light at the time of recording, the reproduction light is a light whose phase is spatially modulated. The reproduction light travels toward the transparent substrate 405 while converging, becomes the smallest diameter on the surface of the transparent substrate 405 on the transparent substrate 404 side, and then is emitted from the recording medium 401 while diverging and passes through the objective lens 420. Then, it becomes a parallel light beam, is reflected by the mirror 419, passes through the quarter-wave plate 418, and becomes S-polarized light. This reproduced light passes through the relay lens system 417, is reflected by the polarization beam splitter surface of the polarization beam splitter 416, and enters the photodetector 422.

  In addition, a part of the reproduction reference light irradiated to the recording medium 401 is reflected on the surface of the transparent substrate 405 on the transparent substrate 404 side and emitted from the recording medium 401 while passing through the objective lens 420 while diverging. Into a parallel light beam, reflected by the mirror 419, passes through the quarter-wave plate 418, and becomes S-polarized light. This reproduced light passes through the relay lens system 417, is reflected by the polarization beam splitter surface of the polarization beam splitter 416, and enters the photodetector 422.

  Actually, the reproduction light and the reproduction reference light reflected on the surface of the transparent substrate 405 on the transparent substrate 404 side are superimposed to generate combined light, and this combined light is received by the photodetector 422. The The combined light is light whose intensity is spatially modulated corresponding to the recorded information. Therefore, a two-dimensional pattern of the intensity of the combined light is detected by the photodetector 422, thereby reproducing information.

  The principle of information recording and reproduction in the present embodiment is the same as that in the fourth embodiment.

  In the present embodiment, the actuators 421 and 436 can change the positions of the objective lenses 420 and 435 in the direction perpendicular to the surface of the recording medium 401, thereby performing focus servo. In the present embodiment, the positions of the objective lenses 420 and 435 in the radial direction of the recording medium 401 are moved by moving the entire optical head 440 in the radial direction of the recording medium 401 by the driving device 484 shown in FIG. Thus, access to a desired track and tracking servo can be performed. In the present embodiment, the second movable portion 442 is rotated with respect to the first movable portion 441 by the coil 444 and the magnet 445, so that the objective lenses 420 and 435 are substantially aligned with the track. The position can be changed. Thereby, it is possible to perform control for causing the information recording area to follow the irradiation position of the information light and the recording reference light. In this control, as in the first embodiment, a drive voltage as shown in FIG. 16B is supplied to the coil 444, and the objective lenses 420 and 435 are supplied as shown in FIG. The position may be changed, or the positions of the objective lenses 420 and 435 may be changed by a simpler method as described below.

  Here, a method of changing the positions of the objective lenses 420 and 435 by a simpler method will be described with reference to FIG. FIG. 38 shows an example of changes in the positions of the objective lenses 420 and 435 and changes in the driving voltage for the coil 444. 38A shows changes in the positions of the objective lenses 420 and 435, and FIG. 38B shows changes in the drive voltage. In this method, as shown in FIG. 38A, the objective lenses 420 and 435 are simply vibrated around the neutral position. In this method, a period in which the moving speed of the positions of the objective lenses 420 and 435 is substantially equal to the moving speed of the information recording area in the recording medium 401 is set as the follow-up period T1, and the other period is set as the catch-up period T2.

  When the positions of the objective lenses 420 and 435 are changed as shown in FIG. 38A, a driving voltage that changes in a sine wave shape can be used as shown in FIG. Such a drive voltage can be easily generated by configuring an oscillation circuit and a resonance circuit. When a plurality of information recording areas are provided between two adjacent address / servo areas, the information recording area for tracking the positions of the objective lenses 420 and 435 is controlled by controlling the phase of the drive voltage. It is possible to select.

  The simple control method as shown in FIG. 38 can also be used in the first to fourth embodiments.

  Other configurations, operations, and effects in the present embodiment are the same as those in the fourth embodiment.

  In addition, this invention is not limited to said each embodiment, A various change is possible. For example, the present invention can be applied not only to recording information on a rotating disk-shaped recording medium but also to recording information on a linearly moving recording medium such as a card.

  In each of the above embodiments, address information or the like is recorded in advance in the address / servo area of the recording medium by embossed pits. However, address information is not provided in advance as described below. Etc. may be recorded. In this case, address information and the like are recorded by selectively irradiating a portion of the information recording layer close to one surface with a high-power laser beam and selectively changing the refractive index of that portion. Format.

It is explanatory drawing which shows the recording medium used in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the optical information recording / reproducing apparatus which concerns on the 1st Embodiment of this invention. It is a top view of the optical head in the 1st Embodiment of this invention. It is explanatory drawing which shows the principle of the recording of the information in the 1st Embodiment of this invention. It is explanatory drawing which shows the principle of the reproduction | regeneration of the information in the 1st Embodiment of this invention. It is a wave form diagram for explaining in detail the principle of reproduction of information in a 1st embodiment of the present invention. It is explanatory drawing which shows the principle of the recording of information in the case of performing the multiplex recording by a phase encoding multiplex system in the 1st Embodiment of this invention. It is explanatory drawing which shows the principle of the reproduction | regeneration of information in the case of performing the multiplex recording by a phase encoding multiplex system in the 1st Embodiment of this invention. FIG. 5 is a waveform diagram for explaining in detail the principle of information reproduction when performing multiplex recording by the phase encoding multiplex method in the first embodiment of the present invention. It is sectional drawing which shows the optical head in the 1st Embodiment of this invention. It is explanatory drawing for demonstrating an example of the production | generation method of the focus error information in the 1st Embodiment of this invention. It is explanatory drawing for demonstrating an example of the generation method of the tracking error information in the 1st Embodiment of this invention, and the method of tracking servo. It is explanatory drawing for demonstrating an example of the generation method of the tracking error information in the 1st Embodiment of this invention, and the method of tracking servo. It is explanatory drawing which shows operation | movement of the optical head at the time of the recording of the information in the 1st Embodiment of this invention. It is explanatory drawing which shows the motion of the irradiation position of the information beam and the recording reference beam in the first embodiment of the present invention. It is explanatory drawing which shows an example of the change of the drive voltage for moving the position of the objective lens in the 1st Embodiment of this invention, and a head main body to the tangent direction of a track | truck. It is explanatory drawing for demonstrating the method to match | combine the irradiation position of information light and the reference light for recording with the position of a desired information recording area in the 1st Embodiment of this invention. It is explanatory drawing which shows the specific example of the change of the length of the pit in the 1st Embodiment of this invention. It is explanatory drawing which shows the specific example of the change of the time of the pit in the 1st Embodiment of this invention, and the time between pits. It is a top view which shows the drive mechanism of the optical head in the optical information recording / reproducing apparatus which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which shows the principal part of the recording / reproducing optical system in the optical information recording / reproducing apparatus which concerns on the 3rd Embodiment of this invention. It is explanatory drawing which shows the other example of the optical information recording medium in the 3rd Embodiment of this invention. It is explanatory drawing which shows the whole structure of the recording / reproducing optical system in the optical information recording / reproducing apparatus which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the optical information recording / reproducing apparatus which concerns on the 3rd Embodiment of this invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of the servo in the 3rd Embodiment of this invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of recording in the 3rd Embodiment of this invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of reproduction | regeneration in the 3rd Embodiment of this invention. It is explanatory drawing which shows the whole structure of the recording / reproducing optical system in the optical information recording / reproducing apparatus which concerns on the 4th Embodiment of this invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of recording in the case of using the reference light for recording in which the phase of light is not spatially modulated in the 4th Embodiment of this invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of reproduction | regeneration in the case of using the reference light for reproduction | regeneration whose light phase is not spatially modulated in the 4th Embodiment of this invention. FIG. 10 is a waveform diagram for explaining in detail the principle of information reproduction when using reproduction reference light whose phase of light is not spatially modulated in the optical information recording / reproducing apparatus according to the fourth embodiment of the present invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of recording in the case of using the reference light for recording in which the phase of the light was spatially modulated in the 4th Embodiment of this invention. It is explanatory drawing which shows the state of the principal part of the recording / reproducing optical system at the time of reproduction | regeneration in the case of using the reference light for reproduction | regeneration in which the phase of light was spatially modulated in the 4th Embodiment of this invention. FIG. 11 is a waveform diagram for explaining in detail the principle of information reproduction when using a reproduction reference beam in which the phase of light is spatially modulated in an optical information recording / reproducing apparatus according to a fourth embodiment of the present invention. . It is a top view which shows the optical head and recording medium in the 5th Embodiment of this invention. It is sectional drawing which shows the structure of the optical head in the 5th Embodiment of this invention. It is sectional drawing which shows the structure of the recording medium in the 5th Embodiment of this invention. It is explanatory drawing which shows an example of the change of the drive voltage for moving the position of the objective lens in the 5th Embodiment of this invention, and the position of an objective lens to the tangent direction of a track | truck.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Recording medium, 3 ... Information recording layer, 5 ... Reflective film, 6 ... Address / servo area, 7 ... Information recording area, 11 ... Objective lens, 40 ... Optical head, 41 ... Head main body, 43 ... Semiconductor laser, 44 A phase spatial light modulator, 45 a photodetector, 47 a collimator lens, 48 a prism block, 48 a a polarizing beam splitter surface, 49 a quarter-wave plate.

Claims (6)

An optical information recording apparatus for recording information on the recording medium by irradiating the recording medium on which information is recorded using holography with information light and recording reference light,
Recording medium moving means for moving the recording medium;
An optical head for irradiating the recording medium with the information light and the recording reference light;
Control means for following the movement of the recording medium with the irradiation position on the recording medium of the information light and the recording reference light irradiated from the optical head for at least a fixed period;
The optical head is
A recording laser that emits a recording laser beam used to generate the information beam and the recording reference beam;
A servo laser that emits a servo laser beam having a wavelength different from that of the recording laser beam used for the servo for positioning the information beam and the recording reference beam with respect to the recording medium;
Information light generating means for generating information light that spatially modulates and carries information using the recording laser light;
Recording reference light generating means for generating recording reference light using the recording laser light;
The servo laser light is irradiated with the information light and the recording reference light so that information is recorded on the recording medium by an interference pattern due to interference between the information light and the recording reference light. An optical system for irradiating the recording medium;
An optical information recording apparatus comprising: a photodetector for detecting servo laser light that is irradiated onto the recording medium and carries positioning information. The control means causes the irradiation position on the recording medium of the information light and the recording reference light irradiated from the optical head to follow the movement of the recording medium based on the positioning information detected by the photodetector. The optical information recording apparatus according to claim 1. An optical information reproducing apparatus for reproducing information from the recording medium by irradiating the reproducing medium with a recording light on which information is recorded using holography,
Recording medium moving means for moving the recording medium;
An optical head for irradiating the recording medium with the reproduction light;
Control means for following the movement of the recording medium the irradiation position in the recording medium of the reproduction light irradiated from the optical head for at least a fixed period,
The optical head is
A reproduction laser that emits a reproduction laser beam used to generate the reproduction light; and
A servo laser that emits servo laser light having a wavelength different from that of the reproduction laser light used for servo for positioning the reproduction light with respect to the recording medium;
Reproduction light generating means for generating reproduction light using the reproduction laser light;
An optical system for irradiating the recording medium with the reproducing light, collecting the reproducing light generated from the recording medium by the reproducing light, and irradiating the recording medium with the servo laser light;
A photodetector for detecting the reproduction light;
An optical information reproducing apparatus comprising: a photodetector for detecting servo laser light that is irradiated onto the recording medium and carries positioning information. The control means causes the irradiation position on the recording medium of the reproduction light irradiated from the optical head to follow the movement of the recording medium based on positioning information detected by the photodetector. Item 4. The optical information reproducing apparatus according to Item 3. By recording information on the recording medium by irradiating the recording medium on which information is recorded using holography with the reference light for recording, and by irradiating the recording medium on which the information is recorded with reproduction light An optical information recording / reproducing apparatus for reproducing information from the recording medium,
Recording medium moving means for moving the recording medium;
An optical head that irradiates the recording medium with the information light, the recording reference light, and the reproduction light;
Control means for following the movement of the recording medium the irradiation position on the recording medium of the information light and the reference light for recording irradiated from the optical head for at least a fixed period,
The optical head is
A recording / reproducing laser that emits a recording / reproducing laser beam used to generate the information light, the recording reference light, and the reproducing light;
A servo laser that emits a servo laser beam having a wavelength different from that of the recording / reproduction laser beam used for the servo for positioning the information light, the recording reference light, and the reproduction light with respect to the recording medium;
Information light generating means for generating information light that spatially modulates and carries information using the recording / reproducing laser light;
Recording reference light generating means for generating recording reference light using the recording / reproducing laser beam; and
Reproduction light generating means for generating reproduction light using the recording / reproduction laser beam;
The information light and the recording reference light are irradiated onto the recording medium so that information is recorded on the recording medium by an interference pattern due to interference between the information light and the recording reference light, and the reproduction light is applied to the recording medium. An optical system for irradiating the recording medium, collecting reproduction light generated from the recording medium by the reproduction light, and irradiating the recording medium with the servo laser light;
A photodetector for detecting the reproduction light;
An optical information recording / reproducing apparatus comprising: a photodetector for detecting a servo laser beam irradiated on the recording medium and carrying positioning information. The control means causes the irradiation position on the recording medium of the information light and the recording reference light irradiated from the optical head to follow the movement of the recording medium based on the positioning information detected by the photodetector. The optical information recording / reproducing apparatus according to claim 5.

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