Apparatus and method for recording and reproducing optical information

An optical information recording/reproducing apparatus generates information light by modulating light emitted by a light source device with a light modulator depending on the information to be recorded and generates reference light for recording by modulating the light emitted by a light source device with a light modulator. The information light and the reference light for recording are projected upon an optical information recording medium such that they converge in different positions, and information is recorded in a hologram layer in the form of an interference pattern between the information light and the reference light for recording.

TECHNICAL FIELD

The present invention relates to an optical information recording apparatus and a method for the same for recording information in an optical information recording medium utilizing holography, an optical information reproducing apparatus and a method for the same for reproducing information from an optical information recording medium utilizing holography, an optical information recording/reproducing apparatus for recording information in an optical information recording medium and reproducing information from an optical information recording medium utilizing holography and an optical information recording medium in which information is recorded utilizing holography.

BACKGROUND ART

In general, holographic recording for recording information in a recording medium utilizing holography is performed by overlapping light carrying image information and reference light in a recording medium and writing resultant interference fringes in the recording medium. When the recorded information is reproduced, the recording medium is illuminated with reference light to cause diffraction attributable to the interference fringes which reproduces the image information.

Recently, volume holography and, more particularly, digital volume holography has been developed and is attracting attention in practical fields for high density optical recording. Volume holography is a method for writing interference fringes on a three-dimensional basis by actively using a recording medium even in the direction of the thickness thereof, which is characterized in that diffracting efficiency is improved by an increased thickness and in that an increased storage capacity can be achieved utilizing multiplex recording. Digital volume holography is a computer-oriented method for holographic recording in which image information to be recorded is limited to binary digital patterns in spite of the fact that the same recording media and recording method as the volume holography are used. According to the digital volume holography, for example, analog image information such as a picture is once digitized to develop two-dimensional digital pattern information which is in turn recorded as image information. When reproduced, the digital pattern information is read and decoded to restore and display the original image information. Since this makes it possible to perform differential detection and error correction on encoded binary data, the original information can be reproduced with extremely high fidelity even with a somewhat poor SN ratio (signal-to-noise ratio) during reproduction.

FIG. 75is a perspective view of a schematic configuration of a prior-art recording/reproducing system for digital volume holography. The recording/reproducing system has: a spatial light modulator101for generating information light102based on two-dimensional digital pattern information; a lens103for collecting the information light102from the spatial light modulator101to illuminate a hologram recording medium100with the same; reference light illumination means (not shown) for illuminating the hologram recording medium100with reference light104in a direction orthogonal to the information light102; a CCD (charge-coupled device) array107for detecting reproduced two-dimensional digital pattern information; and a lens106for collecting reproduction light105emerging from the hologram recording medium100to illuminate the CCD array107with the same. Crystals of LiNbO3or the like are used for the hologram recording medium100.

In the recording/reproducing system shown inFIG. 75, recording is performed by digitizing information of an original image or the like to be recorded and by arranging the resultant signals having a value of 1 or 0 on a two-dimensional basis to generate two-dimensional digital pattern information. One piece of two-dimensional digital pattern information is referred to as “page data”. Let us assume here that page data #1through #n are recorded in the same hologram recording medium100on a multiplex basis. In this case, the spatial light modulator101first chooses to transmit or block light for each pixel based on the page data #1to generate spatially modulated information light102with which the hologram recording medium100is illuminated through the lens103. Simultaneously, the hologram recording medium100is illuminated with reference light104in a direction θ1substantially orthogonal to the information light102to record interference fringes resulting from overlap between the information light102and the reference light104inside the hologram recording medium100. In order to improve diffracting efficiency, the reference light104is transformed by a cylindrical lens or the like into flat beams to record the interference fringes in the hologram recording medium100even in the direction of the thickness thereof. To record the next page data #2, the reference light104is projected at an angle θ2different from θ1and is overlapped with the information light102to perform multiplex recording of information in the same hologram recording medium100. Similarly, to record the other page data #3through #n, the reference light104is projected at respective different angles θ3through θn to record information on a multiplex basis. Such a hologram having information recorded therein on a multiplex basis is referred to as “stack”. In the example shown inFIG. 75, the hologram recording medium100has a plurality of stacks (stack1, stack2, . . . , stack m, . . . ).

Arbitrary page data can be reproduced from a stack by illuminating the stack with reference light104at the same incident angle as that for the recording of the page data. As a result, the reference light104is selectively diffracted by interference fringes associated with the page data to generate reproduction light105. The reproduction light105impinges upon the CCD array107through the lens106, and the CCD array107detects a two-dimensional pattern of the reproduction light. The detected two-dimensional pattern of the reproduction light is decoded conversely to the process performed during recording so that information such as an original image is reproduced.

While the configuration shown inFIG. 75allows multiplex recording of information in the same hologram recording medium100, in order to record information with a high density, the positioning of the information light102and reference light104in the hologram recording medium100is important. In the configuration shown inFIG. 75, however, since the hologram recording medium100itself carries no information for positioning, there is only a mechanical way to position the information light102and reference light104on the hologram recording medium100, which makes it difficult to perform the positioning with high accuracy. This has resulted in problems in that removability (the ease of performing recording and reproduction of a hologram recording medium on a recording/reproducing apparatus after moving it from another recording/reproducing apparatus with the same results as on the previous apparatus) is poor; random access is difficult; and high density recording is difficult. The configuration shown inFIG. 75has another problem in that it involves a large optical system for recording or reproduction because the optical axes of the information light102, reference light104and reproduction light105are located in different spatial positions.

Various methods for multiplex recording have been proposed in an attempt to increase the recording capacity of holographic recording by improving the recording density. One of such methods is angle multiplexing as shown inFIG. 75. However, such angle multiplexing has a problem particularly in that it involves a large and complex optical system for recording or reproduction because the angle of the reference light must be varied.

In addition to the above-described angle multiplex, proposed prior-art methods for multiplex recording for holographic recording include: phase-encoding multiplexing as disclosed, for example, in an article of J. R. Heanue et al., “Recall of linear combinations of stored data pages based on phase-code multiplexing in volume holography”, Optics Letters, Vol. 19, No. 14, pp. 1079–1081, 1994 and an article of J. F. Heanue et al., “Encrypted holographic data storage based on orthogonal-phase-encoding multiplexing”, Applied Optics, Vol. 34, No. 26, pp. 6012–6015, 1995; and hole burning type wavelength multiplexing as disclosed, for example, in an article by Eiji YEGYU et al., “A study on novel recording and reproduction of 3-D imaging technique by frequency multiplexed PHB holograms”, Technical Report of IEICE, EDI93-87 HC93-54, pp. 1–5, 1993.

In any of the methods for multiplex recording, optical systems for recording or reproduction proposed in prior art have a problem in that their size is increased by the fact that the optical axes of information light, reference light and reproduction light are located in spatially different positions and in that a dramatic improvement in the recording density is not achievable because the hologram recording media themselves have no information for positioning and it is therefore difficult to position light for recording or reproduction on the hologram recording media with high accuracy.

DISCLOSURE OF THE INVENTION

The present invention has been conceived taking such problems into consideration, and it is a first object of the invention to provide an apparatus and a method for recording optical information capable of performing multiplex recording of information in an optical information recording medium in which information is recorded utilizing holography and an apparatus and a method for reproducing optical information to reproduce information from an optical information recording medium carrying information recorded in such a manner, in which an optical system for recording or reproducing can be compactly configured.

In addition to the above-described first object, it is a second object of the invention to provide an apparatus and a method for recording optical information and an apparatus and a method for reproducing optical information, in which light for recording or reproduction can be accurately positioned relative to an optical information recording medium.

It is a third object of the invention to provide an optical information recording apparatus for recording information in an optical information recording medium utilizing holography, an optical information reproducing apparatus for reproducing information from an optical information recording medium utilizing holography and an optical information recording/reproducing apparatus for recording information in and reproducing information from an optical information recording medium utilizing holography, in which an optical system for recording or reproduction can be compactly configured and in which random access to the optical information recording medium is facilitated.

It is a fourth object of the invention to provide an optical information recording medium for recording information utilizing holography with which random access and high density recording can be easily achieved.

A first optical information recording apparatus according to the invention is an optical information recording apparatus for recording information in an optical information recording medium having an information recording layer in which information is recorded utilizing holography, the apparatus comprising: information light generation means for generating information light carrying information; recording reference light generation means including phase modulation means for spatially modulating the phase of light, for generating reference light for recording whose phase has been spatially modulated by the phase modulation means; and a recording optical system for illuminating the information recording layer on the same side thereof with the information light generated by the information light generation means and the reference light for recording generated by the recording reference light generation means such that the information is recorded in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

A first method for recording optical information according to the invention is a method for recording information in an optical information recording medium having an information recording layer in which information is recorded utilizing holography, the method comprising the steps of: generating information light carrying information; spatially modulating the phase of light to generate reference light for recording having a spatially modulated phase; and illuminating the information recording layer on the same side thereof with the information light and the reference light for recording to record the information in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

In the first apparatus or method for recording optical information according to the invention, the information recording layer is illuminated on the same side thereof with the information light carrying information and the reference light for recording having a spatially modulated phase to record the information in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

A first optical information reproducing apparatus according to the invention is an optical information reproducing apparatus for reproducing information utilizing holography from an optical information recording medium having an information recording layer in which the information is recorded in the form of an interference pattern as a result of interference between information light carrying the information and reference light for recording having a spatially modulated phase, the apparatus comprising: reproduction reference light generation means including phase modulation means for spatially modulating the phase of light, for generating reference light for reproduction having a phase spatially modulated by the phase modulation means; a reproducing optical system for illuminating the information recording layer with the reference light for reproduction generated by the reproduction reference light generation means and for collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detection means for detecting the reproduction light collected by the reproducing optical system.

A first method for reproducing optical information according to the invention is a method for reproducing information utilizing holography from an optical information recording medium having an information recording layer in which the information is recorded in the form of an interference pattern as a result of interference between information light carrying the information and reference light for recording having a spatially modulated phase, the method comprising the steps of: spatially modulating the phase of light to generate reference light for reproduction having a spatially modulated phase; illuminating the information recording layer with the reference light for reproduction and collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detecting the collected reproduction light.

In the first apparatus or method for reproducing optical information according to the invention, the information recording layer is illuminated with the reference light for reproduction having a spatially modulated phase; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected.

A second optical information recording apparatus according to the invention is an optical information recording apparatus for recording information in an optical information recording medium having an information recording layer in which a change in absorbance occurs in an absorption spectrum thereof in the position of a wavelength of incident light and in which information is recorded utilizing holography, the apparatus comprising: wavelength selection means for selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; information light generation means for generating information light having the wavelength selected by the wavelength selection means and carrying information; recording reference light generation means for generating reference light for recording having the wavelength selected by the wavelength selection means; and a recording optical system for illuminating the information recording layer on the same side thereof with the information light generated by the information light generation means and the reference light for recording generated by the recording reference light generation means such that the information is recorded in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

A second method for recording optical information according to the invention is a method for recording information in an optical information recording medium having an information recording layer in which a change in absorbance occurs in an absorption spectrum thereof in the position of a wavelength of incident light and in which information is recorded utilizing holography, the method comprising the steps of: selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; generating information light having the selected wavelength and carrying information; generating reference light for recording having the selected wavelength; and illuminating the information recording layer on the same side thereof with the information light and the reference light for recording to record the information in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

In the second apparatus or method for recording optical information according to the invention, the information recording layer is illuminated on the same side thereof with the information light having the selected wavelength and carrying information and the reference light for recording having the selected wavelength to record the information in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

A second optical information reproducing apparatus according to the invention is an optical information reproducing apparatus for reproducing information utilizing holography from an optical information recording medium having an information recording layer in which the information is recorded in the form of an interference pattern as a result of interference between information light having a wavelength selected from among a plurality of wavelengths and carrying the information and reference light for recording having the wavelength selected from among a plurality of wavelengths, the apparatus comprising: wavelength selection means for selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; reproduction reference light generation means for generating reference light for reproduction having the wavelength selected by the wavelength selection means; a reproducing optical system for illuminating the information recording layer with the reference light for reproduction generated by the reproduction reference light generation means and for collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detection means for detecting the reproduction light collected by the reproducing optical system.

A second method for reproducing optical information is an optical information reproducing method for reproducing information utilizing holography from an optical information recording medium having an information recording layer in which the information is recorded in the form of an interference pattern as a result of interference between information light having a wavelength selected from among a plurality of wavelengths and carrying the information and reference light for recording having the wavelength selected from among a plurality of wavelengths, the method comprising the steps of: selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; generating reference light for reproduction having the selected wavelength; illuminating the information recording layer with the reference light for reproduction and collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detecting the collected reproduction light.

In the second apparatus or method for reproducing optical information according to the invention, the information recording layer is illuminated with the reference light for reproduction having the selected wavelength; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected.

A third optical information recording apparatus according to the invention is an optical information recording apparatus for recording information in an optical information recording medium having an information recording layer in which a change in absorbance occurs in an absorption spectrum thereof in the position of a wavelength of incident light and in which information is recorded utilizing holography, the apparatus comprising: wavelength selection means for selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; information light generation means for generating information light having the wavelength selected by the wavelength selection means and carrying information; recording reference light generation means including phase modulation means for spatially modulating the phase of light, for generating reference light for recording having the wavelength selected by the wavelength selection means and having a phase spatially modulated by the phase modulation means; and a recording optical system for illuminating the information recording layer on the same side thereof with the information light generated by the information light generation means and the reference light for recording generated by the recording reference light generation means such that the information is recorded in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

A third method for recording optical information according to the invention is an optical information recording method for recording information in an optical information recording medium having an information recording layer in which a change in absorbance occurs in an absorption spectrum thereof in the position of a wavelength of incident light and in which information is recorded utilizing holography, the method comprising the steps of: selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; generating information light having the selected wavelength and carrying information; spatially modulating the phase of light to generate reference light for recording having the selected wavelength and a spatially modulated phase; and illuminating the information recording layer on the same side thereof with the information light and the reference light for recording to record the information in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

In the third apparatus or method for recording optical information according to the invention, the information recording layer is illuminated on the same side thereof with the information light having the selected wavelength and carrying information and the reference light for recording having the selected wavelength and a spatially modulated phase to record the information in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

A third optical information reproducing apparatus according to the invention is an optical information reproducing apparatus for reproducing information utilizing holography from an optical information recording medium having an information recording layer in which the information is recorded in the form of an interference pattern as a result of interference between information light having a wavelength selected from among a plurality of wavelengths and carrying the information and reference light for recording having the wavelength selected from among a plurality of wavelengths and having a spatially modulated phase, the apparatus comprising: wavelength selection means for selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; reproduction reference light generation means including phase modulation means for spatially modulating the phase of light, for generating reference light for reproduction having the wavelength selected by the wavelength selection means and having a phase spatially modulated by the phase modulation means; a reproducing optical system for illuminating the information recording layer with the reference light for reproduction generated by the reproduction reference light generation means and for collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detection means for detecting the reproduction light collected by the reproducing optical system.

A third method for reproducing optical information according to the invention is an optical information reproducing method for reproducing information utilizing holography from an optical information recording medium having an information recording layer in which the information is recorded in the form of an interference pattern as a result of interference between information light having a wavelength selected from among a plurality of wavelengths and carrying the information and reference light for recording having the wavelength selected from among a plurality of wavelengths and having a spatially modulated phase, the method comprising the steps of: selecting a wavelength of light illuminating the information recording layer from among a plurality of wavelengths; spatially modulating the phase of light to generate reference light for reproduction having the selected wavelength and a spatially modulated phase; illuminating the information recording layer with the reference light for reproduction and collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detecting the collected reproduction light.

In the third apparatus or method for reproducing optical information, the information recording layer is illuminated with the reference light for reproduction having the selected wavelength and spatially modulated phase; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected light is detected.

A fourth optical information recording apparatus according to the invention is an optical information recording apparatus for recording information in an optical information recording medium having an information recording layer in which information is recorded utilizing holography, the apparatus comprising a pick-up device provided in a face-to-face relationship with the optical information recording medium, the pick-up device having: a light source for emitting beams of light; information light generation means for spatially modulating the beams of light emitted by the light source to generate information light carrying information; recording reference light generation means for generating reference light for recording using the beams of light emitted by the light source; and a recording optical system for illuminating the information recording layer on the same side thereof with the information light generated by the information light generation means and the reference light for recording generated by the recording reference light generation means such that the information is recorded in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording.

In the fourth optical information recording apparatus according to the invention, the pick-up device provided in a face-to-face relationship with the optical information recording medium illuminates the information recording layer on the same side thereof with the information light and the reference light for recording to record the information in the information recording layer in the form of an interference pattern as a result of interface between the information light and the reference light for recording.

A fourth optical information reproducing apparatus according to the invention is an optical information reproducing apparatus for reproducing information from an optical information recording medium having an information recording layer with information recorded therein utilizing holography, the apparatus comprising a pick-up device provided in a face-to-face relationship with the optical information recording medium, the pick-up device having: a light source for emitting beams of light; reproduction reference light generation means for generating reference light for reproduction using the beams of light emitted by the light source; a reproducing optical system for illuminating the information recording layer with the reference light for reproduction generated by the reproduction reference light generation means and for collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detection means for detecting the reproduction light collected by the reproducing optical system.

In the fourth optical information reproducing apparatus according to the invention, the pick-up device provided in a face-to-face relationship with the optical information recording medium illuminates the information recording layer with the reference light for reproduction; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reference light is detected.

An optical information recording/reproducing apparatus according to the present invention is an optical information recording/reproducing apparatus for recording information in an optical information recording medium having an information recording layer in which information is recorded utilizing holography and for reproducing the information from the optical information recording medium, the apparatus comprising a pick-up device provided in a face-to-face relationship with the optical information recording medium, the pick-up device having: a light source for emitting beams of light; information light generation means for generating information light carrying information by spatially modulating the beams of light emitted by the light source; recording reference light generation means for generating reference light for recording using the beams of light emitted by the light source; reproduction reference light generation means for generating reference light for reproduction using the beams of light emitted by the light source; a recording/reproducing optical system for illuminating the information recording layer on the same side thereof with the information light generated by the information light generation means and the reference light for recording generated by the recording reference light generation means such that the information is recorded in the information recording layer in the form of an interference pattern as a result of interference between the information light and the reference light for recording, for illuminating the information recording layer with the reference light for reproduction generated by the reproduction reference light generation means and for collecting reproduction light generated at the information recording layer when illuminated with the reference light for reproduction on the same side of the information recording layer that is illuminated with the reference light for reproduction; and detection means for detecting the reproduction light collected by the reproducing/reproducing optical system.

In the optical information recording/reproducing apparatus according to the invention, during recording, the pick-up device provided in a face-to-face relationship with the optical information recording medium projects the information light and the reference light for recording upon the information recording layer on the same side thereof to record information in the information recording layer using an interference pattern as a result of interference between the information light and the reference light for recording. During reproduction, the pick-up device illuminates the information recording layer with the reference light for reproduction; reproduction light generated at the information recording light when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected.

An optical information recording medium according to the invention comprises: a first information layer for recording information in the form of an interference pattern as a result of interference between information light and reference light for recording utilizing holography and for generating reproduction light associated with the recorded information when illuminated with reference light for reproduction; and a second information layer which is provided in a position different from the position of the first information layer in the direction of the thickness and in which information is recorded using means different from that for the recording of information in the first information layer.

In the optical information recording medium according to the invention, information is recorded in the first recording layer in the form of an interference pattern as a result of interference between information light and reference light for recording utilizing holography, and information is recorded in the second recording layer using means other than that for recording of information in the first information layer.

Other objects, features and objectives of the invention will become sufficiently clear from the following description.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detail with reference to the drawings. A first embodiment of the invention is an example in which multiplex recording is realized using phase encoding multiplexing.FIG. 1is an illustration showing a configuration of a pick-up of an optical information recording/reproducing apparatus as an optical information recording apparatus and an optical information reproducing apparatus according to the present embodiment and a configuration of an optical information recording medium according to the present embodiment.FIG. 2is a block diagram of a general configuration of the optical information recording/reproducing apparatus according to the present embodiment.

First, the configuration of the optical information recording medium according to the present embodiment will be described with reference toFIG. 1. The optical information recording medium1is configured by forming: a hologram layer3as an information recording layer for recording information utilizing volume holography; a reflecting film5; and a protective film4in the order listed on one surface of a disk-shaped transparent substrate2formed from polycarbonate or the like. A plurality of address servo areas6as positioning regions extending linearly in the radial direction are provided at predetermined angular intervals at the interface between the hologram layer3and the protective layer4. Sections in the form of sectors between the adjoining address servo areas6are data areas7. Information for performing focus servo and tracking servo using a sampled servo system and address information are recorded in advance in the form of emboss pits in the address servo areas6. Focus servo can be performed using a reflecting surface of the reflecting film5. For example, wobble pits may be used as the information for performing tracking servo. For example, the transparent substrate2has an appropriate thickness of 0.6 mm or less, and the hologram layer3has an appropriate thickness of 10 μm or more. The hologram layer3is formed of a hologram material whose optical characteristics such as a refractive index, permittivity and reflectivity change depending on the intensity of light when illuminated with the light. For example, photopolymer HRF-600 (product name) manufactured by DuPont or the like is used as such a hologram material. For example, the reflecting film5is formed of aluminum.

The configuration of the optical information recording/reproducing apparatus according to the present embodiment will now be described with reference toFIG. 2. An optical information recording/reproducing apparatus10has: a spindle81to which the optical information recording medium1is mounted; a spindle motor82for rotating the spindle81; and a spindle servo circuit83for controlling the spindle motor82to keep the rotating speed of the optical information recording medium1at a predetermined value. The optical information recording/reproducing apparatus10further has: a pick-up11for recording information in the optical information recording medium1by illuminating it with information light and recording reference light and for reproducing the information recorded in the optical information recording medium1by illuminating the optical information recording medium1with reference light for reproduction and by detecting reproduction light; and a driver84for allowing the pick-up11to move in the radial direction of the optical information recording medium1.

The optical information recording/reproducing apparatus10further has: a detection circuit85for detecting a focus error signal FE, a tracking error signal TE and a reproduction signal RF from a signal output by the pick-up11; a focus servo circuit86for performing focus servo by driving an actuator in the pick-up11based on the focus error signal FE detected by the detection circuit85to move an objective lens in the direction of the thickness of the optical information recording medium1; a tracking servo circuit87for performing tracking servo by driving the actuator in the pick-up11based on the tracking error signal TE detected by the detection circuit85to move the objective lens in the radial direction of the optical information recording medium1; and a slide servo circuit88for performing slide servo by controlling the driver84based on the tracking error signal TE and a command from a controller to be described later to move the pick-up11in the radial direction of the optical information recording medium1.

The optical information recording/reproducing apparatus10further has: a signal processing circuit89for reproducing data recorded in the data areas7of the optical information recording medium1by decoding data output by a CCD array to be described later in the pick-up11and for reproducing a basic clock and determining an address from the reproduction signal RF from the detection circuit85; a controller90for controlling the optical information recording/reproducing apparatus10as a whole; and an operating portion91for supplying various instructions to the controller90. The controller90receives input of the basic clock and address information output by the signal processing circuit89and controls the pick-up11, spindle servo circuit83, slide servo circuit88and the like. The basic clock output by the signal processing circuit89is input to the spindle servo circuit83. The controller90has a CPU (central processing unit), a ROM (read only memory) and a RAM (random access memory), and the CPU executes programs stored in the ROM using the RAM as a work area to realize the functions of the controller90.

The detection circuit85, focus servo circuit86, tracking servo circuit87and slide servo circuit88correspond to the position control means according to the invention.

A configuration of the pick-up11of the present embodiment will now be described with reference toFIG. 1. The pick-up11has: an objective lens12which faces the transparent substrate2of the optical information recording medium1when the optical information recording medium1is secured to the spindle81; an actuator13capable of moving the objective lens12in the direction of the thickness of the optical information recording medium1and the radial direction of the same; and a double optically rotating plate14and a prism block15which are disposed on the side of the objective lens12opposite to the optical information recording medium1in the order listed which is the order of their closeness to the objective lens12. The double optically rotating plate14has: an optically rotating plate14L provided on the left side of the optical axis inFIG. 1; and an optically rotating plate14R provided on the right side of the optical axis inFIG. 1. The optically rotating plate14L optically rotates a polarizing direction at +45°, and the optically rotating plate14R optically rotates a polarizing direction at −45°. The prism block15has a half-reflecting surface15aand a reflecting surface15bwhich are arranged in the order listed which is the order of their closeness to the double optically rotating plate14. The normal directions of both of the half-reflecting surface15aand the reflecting surface15bare at 45° to the direction of the optical axis of the objective lens12and are in parallel with each other.

The pick-up11further has a prism block19provided on a side of the prism block15. The prism block19has: a reflecting surface19awhich is provided in a position associated with the half-reflecting surface15aof the prism block15and which is in parallel with the half-reflecting surface15a; and a half-reflecting surface19bwhich is provided in a position associated with the reflecting surface15band which is in parallel with the reflecting surface15b.

The pick-up11further has a convex lens16and a phase-spatial light modulator17which are provided between the prism blocks15and19in positions associated with the half-reflecting surface15aand reflecting surface19a, and has a spatial light modulator18provided between the prism blocks15and19in a position associated with the reflecting surface15band the half-reflecting surface19b.

The phase-spatial light modulator17has a multiplicity of pixels arranged in the form of a grid and is capable of spatially modulating the phase of light by selecting a phase for light emitted by each of the pixels. A liquid crystal element may be used as the phase-spatial light modulator17. The phase-spatial light modulator17corresponds to the phase modulation means according to the invention.

The spatial light modulator18has a multiplicity of pixels arranged in the form of a grid and is capable of generating information light carrying information by spatially modulating light in terms of intensity by selecting a light transmitting state or a light blocking state for each of the pixels. A liquid crystal element may be used as the spatial light modulator18. The spatial light modulator18constitutes the information light generation means according to the invention.

The pick-up11further has a CCD array20as detection means provided in a direction in which return light from the optical information recording medium1is reflected by the half-reflecting surface19bof the prism block19after being transmitted by the spatial light modulator18.

The pick-up11further has a beam splitter23, a collimator lens24and a light source device25which are provided on the side of the prism block19opposite to the spatial light modulator18in the order listed which is the order of their closeness to the prism block19. The beam splitter23has a half-reflecting surface23awhose normal direction is tilted at an angle of 45° to the direction of the optical axis of the collimator lens24. The light source device25emits coherent linearly polarized light and may be, for example, a semiconductor laser.

The pick-up11further has: a photodetector26provided in a direction in which light from the light source device25is reflected by the half-reflecting surface23aof the beam splitter23; and a convex lens27, a cylindrical lens28and a quadruple photodetector29which are provided on the side of the beam splitter23opposite to the photodetector26in the order listed which is the order of their closeness to the beam splitter23. The photodetector26receives light from the light source device25, and the output of the same is used to adjust the output of the light source device25automatically. As shown inFIG. 3, the quadruple photodetector29has four light-receiving portions29athrough29ddivided by a division line30ain parallel with a direction corresponding to the direction of tracks of the optical information recording medium1and a division line30borthogonal thereto. The cylindrical lens28is provided such that the central axis of the cylindrical surface thereof is at an angle of 45° to the division lines30aand30bof the quadruple photodetector29.

The phase-spatial light modulator17, the spatial light modulator18and the light source device25in the pick-up11are controlled by the controller90inFIG. 2. The controller90has information of a plurality of modulation patterns for spatially modulating the phase of light with the phase-spatial light modulator17. The operating portion91allows selection of any one of the plurality of modulation patterns. The controller90supplies information of a modulation pattern selected by itself or by the operating portion91to the phase-spatial light modulator17in accordance with predetermined conditions, and the phase-spatial light modulator17spatially modulates the phase of light, in accordance with the modulation pattern information supplied by the controller90, in the modulation pattern associated therewith in accordance with the information.

The reflectivity of each of the half-reflecting surfaces15aand19bin the pick-up11is appropriately set, for example, such that information light and reference light for recording incident upon the optical information recording medium1have the same intensity.

FIG. 3is a block diagram of the detection circuit85for detecting the focus error signal FE, the tracking error signal TE and the reproduction signal RF based on the output of the quadruple photodetector29. The detection circuit85has: an adder31for adding the output of each of the diagonal light-receiving portions29aand29dof the quadruple photodetector29; an adder32for adding the output of each of the diagonal light-receiving portions29band29cof the quadruple photodetector29; a subtracter33for calculating the difference between the outputs of the adders31and32to generate the focus error signal FE based on an astigmatic method; an adder34for adding the output of each of the light-receiving portions29aand29bof the quadruple photodetector29which are adjacent to each other in the direction of tracks thereof; an adder35for adding the output of each of the light-receiving portions29cand29dof the quadruple photodetector29which are adjacent to each other in the direction of the tracks thereof; a subtracter36for calculating the difference between the outputs of the adders34and35to generate the tracking error signal TE based on a push-pull method; and an adder37for adding the outputs of the adders34and35to generate the reproduction signal RF. In the present embodiment, the reproduction signal RF is a signal which is the reproduction of the information recorded in the address servo areas6of the optical information recording medium1.

Servo, recording and reproducing operations of the optical information recording/reproducing apparatus according to the present embodiment will now be separately described in that order. In any of the servo, recording and reproducing operations, the optical information recording medium1is rotated by the spindle motor82under control to maintain a predetermined rotating speed.

A servo operation will now be described with reference toFIG. 4. During a servo operation, all pixels of the spatial light modulator18are in a transmitting state. The output of the emission of light from the light source device25is set at a low output for reproduction. The controller90predicts the timing at which light that has exited the objective lens12passes through the address servo areas6based on a basic clock reproduced from a reproduction signal RF and maintains the above-described setting while the light from the objective lens12passes through the address servo areas6.

Light emitted by the light source device25is collimated by the collimator lens24to impinge upon the beam splitter23, and a part of the quantity of light is transmitted by the half-reflecting surface23aand another part is reflected thereby. The light reflected by the half-reflecting surface23ais received by the photodetector26. The light transmitted by the half-reflecting surface23aimpinges upon the prism block19, and a part of the quantity of light is transmitted by the half-reflecting surface19b. The light transmitted by the half-reflecting surface19bpasses through the spatial light modulator18to be reflected by the reflecting surface15bof the prism block15, and a part of the quantity of light is transmitted by the half-reflecting surface15a, passes through the double optically rotating plate14, and is collected by the objective lens12to be projected upon the optical information recording medium1such that it converges at the interface between the hologram layer3and the protective layer4of the optical information recording medium1. This light is reflected by the reflecting film5of the optical information recording medium1, modulated by embossed pits in the address servo areas6while being reflected, and then returned to the objective lens12.

The return light from the optical information recording medium1is collimated by the objective lens12and passes through the double optically rotating plate14again to impinge upon the prism block15, and a part of the quantity of light is transmitted by the half-reflecting surface15a. The return light transmitted by the half-reflecting surface15ais reflected by the reflecting surface15band is transmitted by the spatial light modulator18, and a part of the quantity of light is transmitted by the half-reflecting surface19bof the prism block19. The return light transmitted by the half-reflecting surface19bimpinges upon the beam splitter23, and a part of the quantity of light is reflected by the half-reflecting surface23a, passes through the convex lens27and cylindrical lens28sequentially, and is then detected by the quadruple photodetector29. Based on the output of the quadruple photodetector29, the detection circuit85shown inFIG. 3generates the focus error signal FE, tracking error signal TE and reproduction signal RF based on which focus servo and tracking servo is performed; the basic clock is generated; and addresses are determined.

In the above-described setting for servo, the pick-up11is configured similarly to a configuration of a pick-up for recording on or reproduction from normal optical disks such as CDs (compact disks), DVDs (digital video disks or digital versatile disks) and HSs (hyper storage disks). It is therefore possible to configure the optical information recording/reproducing apparatus10according to the present embodiment to be compatible with normal optical disk devices.

A definition will now be given to terms “A-polarized light” and “B-polarized light” which will be used in the following description. As shown inFIG. 10, A-polarized light is linear polarized light obtained by rotating the polarizing direction of S-polarized light at −45° or by rotating the polarizing direction of P-polarized light at +45°, and B-polarized light is linear polarized light obtained by rotating the polarizing direction of S-polarized light at +45° or by rotating the polarizing direction of P-polarized light at −45°. The polarizing directions of the A-polarized light and B-polarized light are orthogonal to each other. S-polarized light is linear polarized light whose polarizing direction is perpendicular to the plane of incidence (plane ofFIG. 1), and P-polarized light is linear polarized light whose polarizing direction is in parallel with the plane of incidence.

A recording operation will now be described.FIG. 6is an illustration of a state of the pick-up11during recording. During recording, the spatial light modulator18generates information light by selecting a transmitting state (hereinafter also referred to as “on”) or a blocking state (hereinafter also referred to as “off”) for each pixel depending on the information to be recorded to spatially modulate the light that is passing through it. According to the present embodiment, two pixels represent information of one bit, and one of two pixels associated with information of one bit is always on and the other is always off.

The phase-spatial light modulator17generates reference light for recording having a spatially modulated phase by selectively applying a phase difference of 0 (rad) or π (rad) from a predetermined reference phase to each pixel according to a predetermined modulation pattern to spatially modulate the phase of light passing therethrough. The controller90supplies information of a modulation pattern selected by itself or by the operating portion91in accordance with predetermined conditions to the phase-spatial light modulator17which in turn spatially modulates the phase of light passing therethrough according to the modulation pattern information supplied by the controller90.

The output of light emitted by the light source device25is set at a high output to be used for recording in terms of the pulse thereof. Based on the basic clock reproduced from the reproduction signal RF, the controller90predicts timing at which light that has exited the objective lens12passes through the data areas7and maintains the above-described setting while the light from the objective lens12is passing through the data areas7. While the light from the objective lens12is passing through the data areas7, neither focus servo nor tracking servo is performed, and the objective lens12is fixed. The following description is on an assumption that the light source device25emits P-polarized light.

As shown inFIG. 6, P-polarized light emitted by the light source device25is collimated by the collimator lens24to impinge upon the beam splitter23, and a part of the quantity of light is transmitted by the half-reflecting surface23ato impinge upon the prism block19. A part of the light incident upon the prism block19is transmitted by the half-reflecting surface19b, and another part of the quantity of light is reflected by the half-reflecting surface19b. The light transmitted by the half-reflecting surface19bpasses through the spatial light modulator18in which it is spatially modulated into information light according to the information to be recorded. The information light is reflected by the reflecting surface15bof the prism block15, and a part of the quantity of light is transmitted by the half-reflecting surface15ato pass through the double optically rotating plate14. The polarizing direction of light passing through the optically rotating plate14L of the double optically rotating plate14is rotated at +45° to provide A-polarized light, and the polarizing direction of light passing through the optically rotating plate14R is rotated at −45° to provide B-polarized light. The information light having passed through the double optically rotating plate14is collected by the objective lens12and is projected upon the optical information recording medium1such that it converges on the interface between the hologram layer3and the protective layer4, i.e., on the reflecting film5of the optical information recording medium1.

The light reflected by the half-reflecting surface19bof the prism block19is reflected by the reflecting surface19ato pass through the phase-spatial light modulator17in which the phase of light is spatially modulated according to a predetermined modulation pattern to provide reference light for recording. The reference light for recording passes through the convex lens16to become convergent light. A part of the reference light for recording is reflected by the half-reflecting surface15aof the prism block15to pass through the double optically rotating plate14. The polarizing direction of light which has passed through the optically rotating plate14L of the double optically rotating plate14is rotated at +45° to provide A-polarized light, and the polarizing direction of light which has passed through the optically rotating plate14R is rotated at −45° to provide B-polarized light. The reference light for recording which has passed through the double optically rotating plate14is collected by the objective lens12to be projected upon the optical information recording medium1. The light temporarily converges to a minimum diameter before the interface between the hologram layer3and the protective layer4, and thereafter divergingly passes through the hologram layer3.

FIGS. 7 and 8are illustrations of states of light during recording. In those figures, the reference number61represents P-polarized light; the reference number63represents A-polarized light; and the reference number64represents B-polarized light.

As shown inFIG. 7, information light51L which has passed through the optically rotating plate14L of the double optically rotating plate14becomes A-polarized light which illuminates the optical information recording medium1through the objective lens12, passes through the hologram layer3, converges to a minimum diameter on the reflecting film5and passes through the hologram layer3again after being reflected by the reflecting film5. Reference light52L for recording which has passed through the optically rotating plate14L of the double optically rotating plate14becomes A-polarized light which illuminates the optical information recording medium1through the objective lens12, temporarily converges to a minimum diameter before the interface between the hologram layer3and the protective layer4and divergingly passes through the hologram layer3. Interference occurs in the hologram layer3between the A-polarized information light51L reflected by the reflecting film5and the A-polarized reference light52L for recording traveling toward the reflecting film5, so that an interference pattern is formed, and the interference pattern is volumetrically recorded in the hologram layer3when the light emitted by the light source device20is at the high output.

As shown inFIG. 8, information light51R which has passed through the optically rotating plate14R of the double optically rotating plate14becomes B-polarized light which illuminates the optical information recording medium1through the objective lens12, passes through the hologram layer3, converges to a minimum diameter on the reflecting film5and passes through the hologram layer3again after being reflected by the reflecting film5. Reference light52R for recording which has passed through the optically rotating plate14R of the double optically rotating plate14becomes B-polarized light which illuminates the optical information recording medium1through the objective lens12, temporarily converges to a minimum diameter before the interface between the hologram layer3and the protective layer4and divergingly passes through the hologram layer3. Interference occurs in the hologram layer3between the B-polarized information light51R reflected by the reflecting film5and the B-polarized reference light52R for recording traveling toward the reflecting film5, so that an interference pattern is formed, and the interference pattern is volumetrically recorded in the hologram layer3when the light emitted by the light source device20is at the high output.

As shown inFIGS. 7 and 8, according to the present embodiment, the information light and the reference light for recording illuminate the hologram layer3on the same side thereof such that the optical axes of the information light and the reference light for recording are located on the same line.

According to the present embodiment, phase-encoding multiplexing can be performed to record information in the same location of the hologram layer3on a multiplex basis by performing the recording operation a plurality of times in the same location of the hologram layer3with the modulation pattern for the reference light for recording changed.

According to the present embodiment, a reflection type (Lippmann type) hologram is thus formed in the hologram layer3. No interference occurs between the A-polarized information light51L and the B-polarized reference light52R for recording because their polarizing directions are orthogonal to each other and, similarly, no interference occurs between the B-polarized information light51R and the A-polarized reference light52L for recording because their polarizing directions are orthogonal to each other. Thus, the present embodiment makes it possible to prevent the occurrence of any unnecessary interference fringe, thereby preventing any reduction in an SN (signal-to-noise) ratio.

According to the present embodiment, as described above, the information light is projected upon the optical information recording medium1such that it converges to a minimum diameter on the interface between the hologram layer3and the protective layer4, and is reflected by the reflecting film5of the optical information recording medium1to return to the objective lens12. The return light is incident upon the quadruple photodetector29in the same manner as in the servo operation. According to the present embodiment, it is therefore possible to perform focus servo also during recording utilizing the light incident upon the quadruple photodetector29. Since the reference light for recording converges to a minimum diameter before the interface between the hologram layer3and the protective layer4in the optical information recording medium1to become divergent light, it forms no image on the quadruple photodetector29even though it is reflected by the reflecting film5of the optical information recording medium1to return to the objective lens12.

According to the present embodiment, the size of a region (hologram) in which one interference pattern resulting from information light and reference light is volumetrically recorded in the hologram3can be arbitrarily determined by moving the convex lens16back and forth or changing the magnification of the same.

A reproducing operation will now be described with reference toFIG. 9. During reproduction, all pixels of the spatial light modulator18are on. The controller90supplies information of a modulation pattern for the reference light for recording which was supplied at recording of the information which is now to be reproduced to the phase-spatial light modulator17, and the phase-spatial light modulator17spatially modulates the phase of light passing therethrough according to the modulation pattern information supplied by the controller90to generate reference light for reproduction having a spatially modulated optical phase.

The output of the light emitted by the light source device25is set at a low output to be used for reproduction. Based on the basic clock reproduced from the reproduction signal RF, the controller90predicts timing at which light that has exited the objective lens12passes through the data areas7and maintains the above-described setting while the light from the objective lens12is passing through the data areas7. While the light from the objective lens12is passing through the data areas7, neither focus servo nor tracking servo is performed, and the objective lens12is fixed.

As shown inFIG. 9, P-polarized light emitted by the light source device25is collimated by the collimator lens24to impinge upon the beam splitter23, and a part of the quantity of light is transmitted by the half-reflecting surface23ato impinge upon the prism block19. A part of the light incident upon the prism block19is reflected by the half-reflecting surface19b. The reflected light is reflected by the reflecting surface19ato pass through the phase-spatial light modulator17and, at that time, the phase of the light is spatially modulated in a predetermined modulation pattern to provide reference light for reproduction. The reference light for reproduction passes through the convex lens16to become convergent light. A part of the quantity of the reference light for reproduction is reflected by the half-reflecting surface15aof the prism block15to pass through the double optically rotating plate14. The polarizing direction of light passing through the optically rotating plate14L of the double optically rotating plate14is rotated at +45° to provide A-polarized light, and the polarizing direction of light passing through the optically rotating plate14R is rotated at −45° to provide B-polarized light. The reference light for reproduction that has passed through the double optically rotating plate14is collected by the objective lens12and is projected upon the optical information recording medium1. It temporarily converges to a minimum diameter before the interface between the hologram layer3and the protective layer4, and thereafter divergingly passes through the hologram layer3.

FIGS. 10 and 11are illustrations of states of light during reproduction. The reference number61represents P-polarized light; the reference number62represents S-polarized light; the reference number63represents A-polarized light; and the reference number64represents B-polarized light.

As shown inFIG. 10, reference light53L for reproduction which has passed through the optically rotating plate14L of the double optically rotating plate14becomes A-polarized light which illuminates the optical information recording medium1through the objective lens12, temporarily converges to a minimum diameter before the interface between the hologram layer3and the protective layer4, and thereafter divergingly passes through the hologram layer3. As a result, the hologram layer3generates reproduction light54L that is associated with the information light51L for recording. The reproduction light54L travels toward the objective lens12to be collimated by the objective lens12, and passes through the double optically rotating plate14again to become S-polarized light.

As shown inFIG. 11, reference light53R for reproduction which has passed through the optically rotating plate14R of the double optically rotating plate14becomes B-polarized light which illuminates the optical information recording medium1through the objective lens12, temporarily converges to a minimum diameter before the interface between the hologram layer3and the protective layer4, and thereafter divergingly passes through the hologram layer3. As a result, the hologram layer3generates reproduction light54R that is associated with the information light51R for recording. The reproduction light54R travels toward the objective lens12to be collimated by the objective lens12, and passes through the double optically rotating plate14again to become S-polarized light.

The reproduction light which has passed through the double optically rotating plate14impinges upon the prism block15, and a part of the quantity of light is transmitted by the half-reflecting surface15a. The reproduction light transmitted by the half-reflecting surface15ais reflected by the half-reflecting surface15ato pass through the spatial light modulator18, and a part of the quantity of light is reflected by the half-reflecting surface19bof the prism block19to be incident upon and detected by the CCD array20. A pattern originating from an on/off operation of the spatial light modulator18during recording is formed on the CCD array20, and information is reproduced by detecting this pattern.

When a plurality of pieces of information are recorded in the hologram layer3on a multiplex basis by varying the modulation pattern for reference light for recording, only information associated with reference light for recording having the same modulation pattern as that of the reference light for reproduction is reproduced among the plurality of pieces of information.

As shown inFIGS. 10 and 11, according to the present embodiment, the illumination with the reference light for reproduction and the collection of reproduction light is carried out on the same side of the hologram layer3such that the optical axes of the reference light for reproduction and the reproduction light are located on the same line.

According to the present embodiment, a part of the reproduction light impinges upon the quadruple photodetector29similarly to the return light during the servo operation. The present embodiment therefore makes it possible to perform focus servo even during reproduction utilizing the light incident upon the quadruple photodetector29. Since the reference light for reproduction converges to a minimum diameter before the interface between the hologram layer3and the protective layer4of the optical information recording medium1to become divergent light, it forms no image on the quadruple photodetector29when it is reflected by the reflecting film5of the optical information recording medium1to return toward the objective lens12.

When a two-dimensional pattern of reproduction light is detected by the CCD array20, it is required that the reproduction light and the CCD array20are accurately positioned or that a reference position in the pattern of the reproduction light is recognized from data detected by the CCD array20. In the present embodiment, the latter is employed. A description will now be made with reference toFIGS. 12A,12B,13A and13B on a method for recognizing a reference position of a pattern of reproduction light from data detected by the CCD array20. As shown inFIG. 12A, the aperture of the pick-up11is divided by the double optically rotating plate14into two regions71L and71R which are symmetric about the optical axis thereof. Further, as shown inFIG. 12B, the aperture is divided by the spatial light modulator18into a plurality of pixels72. Such a pixel72serves as a minimum unit of two-dimensional pattern data. According to the present embodiment, two pixels represent one bit of digital data “0” or “1”. One of two pixels associated with one bit of information is on, and the other is off. A pair of pixels which are both on or off represent error data. Thus, the representation of one bit of digital data with two pixels provides advantages including an improvement in data detecting accuracy achieved by differential detection.FIG. 13Ashows a pair of pixels73associated with one bit of digital data. The region where such a pair73exists is hereinafter referred to as “data region”. In the present embodiment, reference position information indicating a reference position in a pattern of reproduction light is included in the information light utilizing the fact that a pair of pixels which are both on or off represent error data. Specifically, as shown inFIG. 13B, error data are intentionally provided in a predetermined pattern in a cross-shaped region74constituted by a part in parallel with the division line of the double optically rotating plate14having a width equal to two pixels and a part perpendicular to the division line having a width equal to two pixels. This pattern of error data is hereinafter referred to as “pixel pattern for tracking”. The pixel pattern for tracking serves as the reference position information. InFIG. 13B, the reference number75represents pixels which are on, and the reference number76represents pixels that are off. A region77consisting of four pixels in the middle is always kept off.

A two-dimensional pattern as shown inFIG. 14Ais obtained by combining a pixel pattern for tracking with a pattern associated with data to be recorded. In the present embodiment, regions other than the data regions are off in the upper half of the figure and are on in the lower half, and pixels in the data regions which are contiguous with the regions other than the data regions are in a state which is the reverse of the state of the regions other than the data regions, i.e., they are on if the regions other than the data regions are off, and are off if the regions other than the data regions are on. It is therefore possible to clearly detect the boundary of data regions from data detected by the CCD array20.

During recording, a pattern is recorded in the hologram layer3which originates from interference between information light spatially modulated according to a two-dimensional pattern as shown inFIG. 14Aand reference light for recording. As shown inFIG. 14B, a pattern of reproduction light obtained during reproduction has a contrast and an SN ratio lower than those at recording. During reproduction, a pattern of reproduction light as shown inFIG. 14Bis detected by the CCD array20to determine the data and, at this time, the data are determined by recognizing the pixel pattern for tracking and using the position of the same as a reference position.

FIG. 15Ais a conceptual representation of contents of data determined from a pattern of reproduction light. Each of regions in the figure having reference numbers such as A-1-1represents one bit of data. In the present embodiment, a data region is divided at the cross-shaped region74having a pixel pattern for tracking recorded therein into four regions78A,78B,78C and78D. As shown inFIG. 15B, a rectangular region is formed by combining the diagonal regions78A and78C; another rectangular region is similarly formed by combining the diagonal regions78B and78D; and an ECC table is formed by arranging the two rectangular regions vertically. An ECC table is a table of data formed by adding error-correcting codes (ECCs) such as CRC (cyclic redundancy check) codes to data to be recorded.FIG. 15Bshows an example of an ECC table comprising n rows and m columns, and other arrays may be freely designed. The data array shown inFIG. 15Autilizes a part of the ECC table shown inFIG. 15B, and parts of the ECC table shown inFIG. 15Bwhich are not used in the data array shown inFIG. 15Ahave the same value regardless of the contents of data. During recording, an ECC table as shown inFIG. 15Bis divided into four regions78A,78B,78C and78D as shown inFIG. 15Ato be recorded in the optical information recording medium1and, during reproduction, data arranged as shown inFIG. 15Aare detected and are rearranged to reproduce an ECC table as shown inFIG. 15B, and error correction is carried out based on the ECC table to reproduce the data.

The recognition of a reference position (a pixel pattern for tracking) in a pattern of reproduction light and error correction as described above are performed by the signal processing circuit89inFIG. 2.

As described above, in the optical information recording/reproducing apparatus10according to the present embodiment, the illumination of the optical information recording medium1with reference light for recording and information light during recording and the illumination of the optical information recording medium1with reference light for reproduction and the collection of reproduction light during reproduction are all carried out on the same side of the optical information recording medium1and on the same axis while allowing multiplex recording of information in the optical information recording medium1utilizing phase-encoding multiplexing. This makes it possible to configure the optical system for recording or reproduction smaller than those in prior-art holographic recording systems and eliminates the problem of stray light as encountered in prior-art holographic recording systems. The present embodiment also makes it possible to configure the optical system for recording and reproduction in the form of the pick-up11which is similar to normal optical disk devices. Therefore, random access to the optical information recording medium1can be easily performed.

Further, according to the present embodiment, information required to perform focus servo and tracking servo can be recorded in the optical information recording medium1to allow focus servo and tracking servo to be performed using the information. This makes it possible to position light for recording or reproduction accurately, which results in improved removability, facilitates random access and allows increases in a recording density, recording capacity and transfer rate. Particularly, the present embodiment allows dramatic increases in a recording density, recording capacity and transfer rate as a result of the capability of multiplex recording of information based on phase-encoding multiplexing. For example, when a series of information is recorded in the same location of the hologram layer3on a multiplex basis while changing the modulation pattern for the reference light for recording, the information can be recorded and reproduced at a very high speed.

The present embodiment also makes it possible to achieve copy protection and security easily because information recorded in the optical information recording medium1cannot be reproduced unless reference light for reproduction is used which has the same modulation pattern as that of the reference light for recording used to record the information. The present embodiment also makes it possible to provide services e.g., a service in which a multiplicity of kinds of information (e.g., various kinds of software) with different modulation patterns for reference light are recorded in optical information recording media1; the optical information recording media1themselves are provided to users at a relatively low price; and pieces of information of the reference light modulation patterns to enable reproduction of each of the various kinds of information are separately sold to the users as key information as requested by the users.

With the optical information recording/reproducing apparatus10according to the present embodiment, a pattern of reproduction light can be easily recognized because reference position information indicating a reference position for the pattern of the reproduction light is included in the information light.

The optical information recording/reproducing apparatus10according to the present embodiment is compatible with conventional optical disk devices because information recorded in the form of embossed pits in a recording medium can be reproduced by setting the pick-up11in the servo state shown inFIG. 4.

With the optical information recording/reproducing apparatus10according to the present embodiment, it is quite difficult to copy an optical information recording medium1having information recorded therein because each item of information recorded in the optical information recording medium1on a multiplex basis is associated with a different modulation pattern for the phase of the reference light. This makes it possible to prevent illegal copying.

In the optical information recording medium1according to the present embodiment, since the hologram layer3in which information is recorded utilizing holography is separated from the layer in which information of addresses and the like is recorded in the form of embossed pits, those two layers must be associated with each other to copy the optical information recording medium1having information recorded therein. Copying is difficult also from this point of view, which makes it possible to prevent illegal copying.

A description will now be made on an optical information recording/reproducing apparatus according to a second embodiment of the present invention. The present embodiment is an example in which multiplex recording is enabled by using phase-encoding multiplexing and hole burning type wavelength multiplexing in combination. The general configuration of the optical information recording/reproducing apparatus according to the present embodiment is substantially the same as the configuration of the optical information recording/reproducing apparatus10according to the first embodiment shown inFIG. 2.

First, hole burning type wavelength multiplexing will be briefly described. Hole burning is a phenomenon in which a change in absorbance occurs in an absorption spectrum in the position of the wavelength of incident light and is also referred to as “photochemical hole burning”. Hereinafter, a material that causes hole burning, i.e., a material that causes a change in absorbance in an absorption spectrum in the position of the wavelength of incident light is referred to as “hole burning material”. In general, a hole burning material is a material obtained by dispersing light-absorbing center materials (referred to as “guests”) such as pigment in a medium (referred to as “host”) having an irregular structure, e.g., an amorphous structure. At extremely low temperatures, such a hole burning material exhibits a broad absorption spectrum that is attributable to overlapping of absorption spectra of a multiplicity of guests. When such a hole burning material is illuminated with light such as laser light having a certain wavelength (a wavelength within the absorption band of the hole burning material), since only guests having a resonance spectrum associated with the wavelength jump to a different energy level as a result of a photochemical reaction, a reduction of absorbance occurs in the absorption spectrum of the hole burning material in the position of the wavelength of the illuminating light.

FIG. 16shows a state of the absorption spectrum of a hole burning material in which a reduction of absorbance has occurred in a plurality of wavelength positions as a result of illumination with light having a plurality of wavelengths. The regions of a hole burning material where a reduction of absorbance has occurred when illuminated with light are referred to as “holes”. Since such holes are extremely small, a plurality of pieces of information with different wavelengths can be recorded on a hole burning material on a multiplex basis, and such a method for multiplex recording is referred to as “hole burning type wavelength multiplexing”. Since the size of holes is on the order of 10−2nm, it is assumed that multiplicity on the order of 103to 104can be achieved with a hole burning material. Hole burning is described in detail, for example, in “Fundamentals of Optical Memories” published by Corona Corporation, pp. 104–133, 1990 and the above-cited article “Study on Novel Real Time Recording and Reproduction of Wavelength Multiplex Hologram Utilizing PHB”.

The present embodiment makes it possible to form a plurality of holograms with different wavelengths on a hole burning material utilizing hole burning type wavelength multiplexing as described above. For this purpose, a hologram layer3of an optical information recording medium1used in the optical information recording/reproducing apparatus according to the present embodiment is formed from a hole burning material as described above.

According to the present embodiment, a light source device25in a pick-up11is capable of selectively emitting coherent light having a plurality of wavelengths within the absorption band of the hole burning material from which the hologram layer3is formed. The light source device25may be a wavelength variable laser device having a dye laser and a wavelength selecting element (a prism, diffraction grating or the like) for selecting a wavelength of light emitted by the dye laser; a wavelength variable laser device having a laser and a wavelength selecting element utilizing a non-linear optical element for converting the wavelength of light emitted by the laser; or the like.

An operating portion91according to the present embodiment allows a modulation pattern for reference light to be selected from among a plurality of modulation patterns similarly to that in the first embodiment and allows the wavelength of light emitted by the light source device25to be selected from among a plurality of selectable wavelengths. A controller90supplies information of a wavelength selected by itself or the operating portion91in accordance with predetermined conditions to the light source device25and, according to the wavelength information supplied by the controller90, the light source device25emits light having the wavelength associated therewith. The light source device25of the present embodiment corresponds to the wavelength selection means according to the present invention.

The configuration of the optical information recording/reproducing apparatus according to the present embodiment is otherwise the same as that of the first embodiment.

In the optical information recording/reproducing apparatus according to the present embodiment, when recording is performed, the wavelength of light emitted by the light source device25is selected from among a plurality of selectable wavelengths. As a result, information light and reference light for recording having the selected wavelength are generated. According to the present embodiment, multiplex recording can be carried out utilizing hole burning type wavelength multiplexing by performing a recording operation a plurality of times with the wavelength of the information light and the reference light for recording varied in the same location of the hologram layer3.

With the optical information recording/reproducing apparatus according to the present embodiment, multiplex recording can be carried out which involves both of phase-encoding multiplexing and hole burning type wavelength multiplexing by performing a recording operation a plurality of times with the modulation pattern of the reference light for recording varied at a certain wavelength in the same location of the hologram layer3and further performing the recording operation a plurality of times with the modulation pattern of the reference light varied similarly at a different wavelength. In this case, multiplicity of M×N can be achieved where N represents multiplicity achieved by phase-encoding multiplexing and M represents multiplicity achieved by hole burning type wavelength multiplexing. Therefore, the present embodiment makes it possible to achieve greater increases in the recording density, recording capacity and transfer rate than achievable in the first embodiment.

The present embodiment makes it possible to achieve copy protection and security easily like the first embodiment because information recorded in the optical information recording medium1cannot be reproduced unless reference light for reproduction is used which has the same wavelength as that of the information light and the reference light for recording used to record the information. Further, when multiplex recording is performed as a combination of phase-encoding multiplexing and hole burning type wavelength multiplexing, a higher level of copy protection and security can be achieved because reproduction cannot be performed unless reference light for reproduction is used which has the same wavelength as that of the information light and the reference light for recording used to record the information, and which has the same modulation pattern as that of the reference light for recording.

The present embodiment also makes it possible to provide services e.g., a service in which a multiplicity of kinds of information (e.g., various kinds of software) with different wavelengths of the information light and the reference light for recording or different modulation patterns of reference light are recorded in optical information recording media1; the optical information recording media1themselves are provided to users at a relatively low price; and pieces of information of the wavelengths and the modulation patterns of the reference light to enable reproduction of each of the various kinds of information are separately sold to the users as key information as requested by the users.

The operation and effects of the present embodiment are otherwise substantially the same as those of the first embodiment.

An optical information recording/reproducing apparatus according to a third embodiment of the present invention will now be described. The general configuration of the optical information recording/reproducing apparatus according to the present embodiment is substantially the same as the configuration of the optical information recording/reproducing apparatus10according to the first embodiment shown inFIG. 2except that the configuration of the pick-up is different from that in the first embodiment.

FIG. 17is an illustration of the configuration of the pick-up according to the present embodiment, andFIG. 18is a plan view of a configuration of an optical unit including various elements that form the pick-up.

The pick-up111according to the present embodiment has: a light source device112which emits coherent linearly polarized laser light; and a collimator lens113, a neutral density filter (hereinafter referred to as “ND filter”)114, a rotating optical element115, a polarization beam splitter116, a phase-spatial light modulator117, a beam splitter118and a photodetector119which are provided in the traveling direction of the light emitted by the light source device112in the order listed that is the order of their closeness to the light source device112. The light source device112emits S-polarized linear light or P-polarized linear light. The collimator lens113collimates the light emitted by the light source device112to emit parallel beams. The ND filter114has the property of making the intensity distribution of the light emitted by the collimator lens113uniform. The optically rotating optical element115optically rotates the light emitted by the ND filter114to emit light including S-polarized components and P-polarized components. For example, a ½ wavelength plate or optically rotating plate is used as the rotating optical element115. The polarization beam splitter116has a polarization beam splitter surface116awhich reflects the S-polarized components of the light emitted by the rotating optical element115and which transmits the P-polarized components. The phase-spatial light modulator117is similar to the phase-spatial light modulator17in the first embodiment. The beam splitter118has a beam splitter surface118a. For example, the beam splitter surface118atransmits 20% of the P-polarized components and reflects 80% of the same. The photodetector119is used to monitor the quantity of reference light for automatic power control (hereinafter represented by “APC”) over the reference light. A light-receiving portion of the photodetector119may be divided into a plurality of regions to allow the adjustment of the intensity distribution of reference light.

The pick-up111further has a polarization beam splitter120, a double optically rotating plate121and a raising mirror122which are provided in the traveling direction of the light emitted by the light source device112and reflected by the beam splitter surface118aof the beam splitter118in the order listed that is the order of their closeness to the beam splitter118. The polarization beam splitter120has a polarization beam splitter surface120afor reflecting S-polarized components in light incident thereupon and for transmitting P-polarized components therein. The double optically rotating plate121has an optically rotating plate121R provided on the right side of the optical axis inFIG. 17and an optically rotating plate121L provided on the left side of the optical axis. The optically rotating plates121R and121L are similar to the optically rotating plates14R and14L of the double optically rotating plate14in the first embodiment. The optically rotating plate121R optically rotates a polarizing direction at −45°, and the optically rotating plate121L optically rotates a polarizing direction at +45°. The raising mirror122has a reflecting surface which is tilted at 45° relative to the optical axis of light from the double optically rotating plate121to reflect the light from the double optically rotating plate121in the direction perpendicular to the plane ofFIG. 17.

The pick-up111further has: an objective lens123provided in the direction in which the light from the double optically rotating plate121travels after being reflected by the reflecting surface of the raising mirror122such that it faces a transparent substrate2of an optical information recording medium1when the optical information recording medium1is secured to a spindle81; and has an actuator124(seeFIG. 18) capable of moving the objective lens123in the direction of the thickness of the optical information recording medium1and the direction of tracks thereof.

The pick-up111further has a spatial light modulator125,1aconvex lens126, a beam splitter127and a photodetector128which are provided in the traveling direction of the light emitted by the light source device112and reflected by the polarization beam splitter surface116aof the polarization beam splitter116in the order listed that is the order of their closeness to the polarization beam splitter116. The spatial light modulator125is similar to the spatial light modulator18in the first embodiment. The convex lens126has a function of converging information light before reference light for recording in the optical information recording medium1to form a region of interference between the reference light for recording and the information light. The size of the region of interference between the reference light for recording and the information light can be adjusted by adjusting the position of the convex lens126. The beam splitter127has a beam splitter surface127a. For example, the beam splitter surface127atransmits 20% of S-polarized components and reflects 80% of the same. The photodetector128is used to monitor the quantity of information light to thereby perform APC on the information light. A light-receiving portion of the photodetector128may be divided into a plurality of regions to allow the adjustment of the intensity distribution of information light. Light that impinges upon the beam splitter127from the convex lens126to be reflected by the beam splitter surface127ais incident upon the polarization beam splitter120.

The pick-up111further has a convex lens129, a cylindrical lens130and a quadruple photodetector131which are provided on the side of the beam splitter127opposite to the polarization beam splitter120in the order listed which is the order of their closeness to the beam splitter127. The quadruple photodetector131is similar to the quadruple photodetector29in the first embodiment. The cylindrical lens28is provided such that the center axis of a cylindrical surface thereof defines an angle of 45° to a division line of the quadruple photodetector131.

The pick-up111further has an imaging lens132and a CCD array133which are provided on the side of the beam splitter118opposite to the polarization beam splitter120in the order listed that is the order of their closeness to the beam splitter118.

The pick-up111further has a collimator lens134and a fixing light source device135which are provided on the side of the polarization beam splitter116opposite to the spatial light modulator125in the order listed that is the order of their closeness to the polarization beam splitter116. The fixing light source device135emits light for fixing information recorded in the hologram layer3of the optical information recording medium1, e.g., ultraviolet light having a wavelength of 266 nm. A laser light source, a light source device for passing light emitted by a laser light source through a non-linear optical medium to emit the light with the wavelength thereof converted, or the like may be used as such a fixing light source device135. The collimator lens134collimates light emitted by the fixing light source device135. According to the present embodiment, the fixing light source device135emits S-polarized light.

As shown inFIG. 18, an optical unit140has an optical unit body141.FIG. 18shows only the region of a bottom surface of the optical unit body141. Attached to the optical unit body141are the above-described collimator lens113, ND filter114, rotating optical element115, polarization beam splitter116, phase-spatial light modulator117, beam splitter118, polarization beam splitter120, double optically rotating plate121, raising mirror122, spatial light modulator125, convex lens126, beam splitter127, convex lens129, cylindrical lens130, imaging lens132and collimator lens134.

FIG. 18shows an example of the use of a ½ wavelength plate as the rotating optical element115. In this example, a motor142and a gear143for transmitting the rotation of an output shaft of the motor142to the rotating optical element115are provided in the optical unit body141in order to adjust the ratio between S-polarized components and P-polarized components in light emitted by the rotating optical element115.

FIGS. 19A and 19Bshow an example of the rotating optical element115in which optically rotating plates are used. The rotating optical element115in this example has two wedge-shaped optically rotating plates115aand115bthat are in a face-to-face relationship with each other. At least either of the optically rotating plates115aand115bis displaced by a driving device which is not shown in the directions of the arrows in the figures to change the combined thickness of the optically rotating plates115aand115bat an overlap between the optically rotating plates115aand115bas shown inFIGS. 19A and 19B. This changes a rotating angle of light that passes through the optically rotating plates115aand115b, thereby changing the ratio between S-polarized components and P-polarized components in light emerging from the rotating optical element115. A large combined thickness of the optically rotating plates115aand115bas shown inFIG. 19Aresults in a large rotating angle, and a small combined thickness of the optically rotating plates115aand115bas shown inFIG. 19Bresults in a small rotating angle.

The actuator124is mounted on a top surface of the optical unit body141. The light source device112is integral with a driving circuit145for driving the light source device112and is mounted on a lateral surface of the unit body141along with the driving circuit145. The photodetector119is integral with an APC circuit146and is mounted to a lateral surface of the unit body141along with the APC circuit146. The APC circuit146amplifies the output of the photodetector119to generate a signal APCrefused for APC carried out on reference light. The photodetector128is integral with an APC circuit147and is mounted to a lateral surface of the unit body141along with the APC circuit147. The APC circuit147amplifies the output of the photodetector119to generate a signal APCobjused for APC carried out on information light. A driving circuit148for driving the motor142is mounted to a lateral surface of the unit body141in the vicinity of the motor142for comparing the signals APCrefand APCobjfrom the respective APC circuits146and147to optimize the ratio between S-polarized components and P-polarized components in the light emerging from the rotating optical element115.

The quadruple photodetector131is integral with a detection circuit85(seeFIG. 2) and is mounted to a lateral surface of the unit body141along with the detection circuit85. The CCD array133is integral with a signal processing circuit149for operations such as driving the CCD array133and processing an output signal from the CCD array133and is mounted to a lateral surface of the unit body141along with the signal processing circuit149. The fixing light source device135is integral with a driving circuit150for driving the fixing light source device135and is mounted to a lateral surface of the unit body141along with the driving circuit150. An input/output port151for input and output of various signals between circuits in the optical unit140and the outside of the optical unit140is further mounted to a lateral surface of the unit body141. For example, an optical fiber flexible cable152including an optical fiber for optically transmitting signals is connected to the input/output port151.

Although not shown, a driving circuit for driving the phase-spatial light modulator117and a driving circuit for driving the spatial light modulator125are mounted on an upper surface of the optical unit body141.

FIG. 20shows an example of a configuration of the pick-up111in which the light source device112is capable of transmitting laser beams in three colors, i.e., red (hereinafter represented by “R”), green (hereinafter represented by “G”) and blue (hereinafter represented by “B”) as beams in a plurality of wavelength bands and in which the CCD array133is also capable of detecting beams in the three colors R, G and B.

The light source device112in the example shown inFIG. 20has a color synthesis prism161. The color synthesis prism161has an R-light incidence portion162R, a G-light incidence portion162G and a B-light incidence portion162B. The incidence portions162R,162G and162B are provided with respective correction filters163R,163G and163B. The light source device112further has: semiconductor laser devices (hereinafter represented by “LDs”)164R,164G and164B for emitting R light, G light and B light respectively; and collimator lenses165R,165G and165B for collimating the beams of light emitted by the LDs164R,164G and164B and causing them to impinge upon the respective incidence portions162R,162G and162B. The R light, G light and B light emitted by the respective LDs164R,164G and164B impinge upon the color synthesis prism161through the collimator lenses165R,165G and165B and correction filters163R,163G and163B to be synthesized by the color synthesis prism161and projected upon the ND filter114. In the example shown inFIG. 20, no collimator lens113as shown inFIG. 17is provided.

The CCD array133in the example shown inFIG. 20has a color separation prism171. The color separation prism171has an R-light emerging portion172R, a G-light emerging portion172G and a B-light emerging portion172B. The emerging portions172R,172G and172B are provided with correction filters173R,173G and173B, respectively. The CCD array133further has CCDs174R,174G and174B provided in positions in a face-to-face relationship with the respective emerging portions172R,172G and172B for photographing an R-light image, G-light image and B-light image. Light from the imaging lens132is separated by the color separation prism171into R light, G light and B light which respectively impinge upon the CCDs174R,174G and174B through the correction filters173R,173G and173B.

A description will now be made with reference toFIGS. 21 through 23on a slide-feed mechanism of the optical unit140of the present embodiment.FIG. 21is a plan view of the slide-feed mechanism.FIG. 22is a partially cutaway side view of the slide-feed mechanism in a stationary state.FIG. 23is a partially cutaway side view of the slide-feed mechanism with the optical unit displaced slightly.

The slide-feed mechanism has: two shafts181A and181B arranged in parallel in the moving direction of the optical unit140; two bearings182provided on each of the shafts181A and181B and movable along the respective shafts181A and181B; a plate spring183for elastically coupling each of the bearings182to the optical unit140; and a linear motor184for moving the optical unit140along the shafts181A and181B.

The linear motor184has: a coil185coupled to a lower end of the optical unit140; two yokes186A and186B in the form of frames provided in the moving direction of the optical unit140such that a part thereof penetrates through the coil185; and magnets187A and187B secured to the inner peripheries of the yokes186A and186B in a face-to-face relationship with the coil185.

An operation of the slide-feed mechanism will now be described. When the linear motor184is operated, the optical unit140is displaced. When such a displacement is very small, as shown inFIG. 23, no displacement of the bearings182occurs, and the plate springs183between the bearings182and the optical unit140are transformed. When the displacement of the optical unit140exceeds a predetermined range, the bearings182are displaced to follow the optical unit140. With such a slide-feed mechanism, no displacement of the bearings182occurs when the displacement of the optical unit140is very small, which makes it possible to prevent wear of the bearings182attributable to sliding. As a result, the optical unit140can be driven by the linear motor184to perform tracking servo while maintaining the durability and reliability of the slide-feed mechanism. A seek operation is also performed using the slide-feed mechanism.

The actuator124has a cylindrical actuator body182which holds the objective lens123and which can be rotated about an axis181. The actuator body182is formed with two holes183in parallel with the axis181. A focusing coil184is provided at the outer periphery of the actuator body182. Further, a coil for in-field access which is not shown is provided at a part of the outer periphery of the focusing coil184. The actuator124further has a magnet185inserted in each of the holes183and a magnet which is not shown provided in a face-to-face relationship with the coil for in-field access. The objective lens123is provided such that a line connecting the center of the objective lens123and the axis181is oriented in the direction of tracks when the actuator124is stationary.

A description will now be made with reference toFIGS. 24A through 24CandFIG. 27on a method for positioning (servo) of reference light and information light relative to data areas of the optical information recording medium1according to the present embodiment. The actuator124of the present embodiment is capable of moving the objective lens123in the direction of the thickness of the optical information recording medium1and the direction of tracks thereof.

FIGS. 24A through 24Cshow the operation of moving the objective lens123in the direction of the tracks of the optical information recording medium1with the actuator124. The actuator124is in the state shown inFIG. 24Bwhen it is stationary. When the coil for in-field access which is not shown is energized, the actuator124changes from the state shown inFIG. 24Bto the state shown inFIG. 24Aor24C. Such an operation of moving the objective lens123in the direction of the tracks of the optical information recording medium1is referred to as “in-field access” in the context of the present embodiment.

FIG. 25shows a moving direction of the objective lens123during a seek and a moving direction of the same during in-field access. InFIG. 25, the reference number191represents the moving direction of the objective lens123during a seek, and the reference number192represents the moving direction of the objective lens123during in-field access. The reference number193represents a locus of the center of the objective lens123in the case of a combination of a seeking movement and in-field access. In the case of in-field access, for example, the center of the objective lens123can be moved by about 2 mm.

In the present embodiment, the positioning (servo) of reference light and information light relative to the data areas of the optical information recording medium1is carried out utilizing in-field access.FIGS. 26A and 26Bare illustrations for explaining such positioning. In the optical information recording medium1according to the present embodiment, as shown inFIG. 26A, while a groove201is formed on each track of address servo areas6, no groove201is formed in data areas7. At the ends of an address servo area, there is formed rows of pits202used to reproduce a clock and to indicate the end of a data area7it adjoins (which is referred to as “polarity” in the present embodiment).

InFIG. 26B, the reference number203represents a locus of the center of the objective lens123during recording or reproduction. In the present embodiment, when multiplex recording of information is carried out on a data area7using phase-encoding multiplexing or when the information recorded in the data area7on a multiplex basis is reproduced, the center of the objective lens123is moved using in-field access such that the center of the objective lens123reciprocates within a section including the data area7and a part of the address servo areas6on both sides thereof as shown inFIG. 26B, instead of stopping the center of the objective lens123within the data area7. The rows of pits202are then used to reproduce a clock and to determine the polarity, and the grooves201are used to perform focus servo and tracking servo in sections204in the address servo areas6. No tracking servo is performed in a section205located between the sections204including the data area7, and the state of passage of the sections204is maintained in this section. Turning points in the movement of the center of the objective lens123are determined to be in constant positions based on the reproduced clock. Locations of a data area7where information is recorded on a multiplex basis are also determined to be in constant positions based on the reproduced clock. InFIG. 26B, the reference number206represents a gate signal that indicates timing for recording or reproduction. A high (H) level of this gate signal represents timing for recording or reproduction. To record information in constant locations in a data area7on a multiplex basis, for example, the output of the light source device112may be selectively set at a high output for recording when the gate signal is at the high level. To reproduce information recorded on a multiplex basis in constant locations of a data area7, for example, the light source device112may be selectively caused to emit light when the gate signal is at the high level. In case where the CCD array133has the function of an electronic shutter, images may alternatively be fetched using the function of an electronic shutter when the gate signal is at the high level.

By positioning reference light and information light according to the above-described method, it is possible to prevent any shift of a position of recording or reproduction even when recording or reproduction is performed for a relatively long time in the same location of the optical information recording medium1. Even when the optical information recording medium1is rotated, recording and reproduction can be performed as if the optical information recording medium1is stationary by performing in-field access to follow up the rotation of the optical information recording medium1, which makes it possible to perform recording and reproduction for a relatively long time in the same location of the optical information recording medium1. The use of the technique of positioning reference light and information light utilizing in-field access as described above makes it possible to position reference light and information light easily not only on a disk-shaped optical information recording medium1but also on optical information recording media in other configurations such as a card-like configuration.

FIG. 27shows an example of a locus of the center of the objective lens123in the case of access to a plurality of locations of an optical information recording medium1utilizing a seeking movement and in-field access in combination. In the figure, a straight line in the vertical direction represents a seek; a straight line in the horizontal direction represents a movement to another location in the direction of the tracks; and a region where a reciprocating motion takes place within a short section is a region where recording or reproduction is performed.

A description will now be made with reference toFIGS. 28 and 29on an example of a cartridge that contains an optical information recording medium1.FIG. 28is a plan view of the cartridge, andFIG. 29is a plan view of the cartridge with a shutter thereof opened. A cartridge211in this example has a window portion212where a part of an optical information recording medium1contained therein is exposed and a shutter213for opening and closing the window portion212. The shutter213is urged in the direction of closing the window portion212. While the window portion212is normally closed as shown inFIG. 28, the cartridge211is moved by an optical information recording/reproducing apparatus in the direction of opening the window portion212as shown inFIG. 29when it is mounted in the optical information recording/reproducing apparatus.

A description will now be made with reference toFIGS. 30 through 34on examples of arrangements of optical units140in cases wherein a plurality of pick-ups111are provided in a single optical information recording/reproducing apparatus.

FIG. 30shows an example wherein two optical units140A and140B are provided in a face-to-face relationship with one side of an optical information recording medium1. The optical unit140A has a configuration similar to that of the optical unit140shown inFIG. 21(hereinafter referred to as “type A”). The optical unit140B has a configuration which is in a plane symmetrical relationship with that of the optical unit140shown inFIG. 21(hereinafter referred to as “type B”). The two optical units140A and140B are provided in positions in a face-to-face relationship with the optical information recording medium1exposed at the window portion212of the cartridge211. The slide-feed mechanism of each of the optical units140A and140B is provided such that the center of an objective lens123of each of the optical units140A and140B is moved along a line extending through the center of the optical information recording medium1.

FIG. 31shows an example wherein two optical units are provided in a face-to-face relationship with each side of an optical information recording medium1, i.e., four optical units in total are provided.FIG. 32is a sectional view taken along the line A–A′ inFIG. 31, andFIG. 33is a sectional view taken along the line B—B′ inFIG. 31. In this example, two optical units140A and140B are provided in a face-to-face relationship with one side (back side inFIG. 31), and two optical units140C and140D are provided in a face-to-face relationship with the other side (top side inFIG. 31) of the optical information recording medium1. The optical unit140C is the type A, and the optical unit140D is the type B.

The optical units140A and140B and the slide-feed mechanisms therefor and the optical units140C and140D and the slide-feed mechanisms therefor are arranged in accordance with the same conditions as described with reference toFIG. 30. In order to effectively utilize the four optical units140A,140B,140C and140D, an optical information recording medium1must be used which allows recording and reproduction of information on both sides thereof.

FIG. 34shows an example wherein eight optical units are provided in a face-to-face relationship with each side of an optical information recording medium1, i.e., sixteen optical units are provided in total. In this example, eight optical units1401through1408are provided in a face-to-face relationship with one side (top side inFIG. 34), and eight optical units1409through14016are provided in a face-to-face relationship with the other side (back side inFIG. 34) of the optical information recording medium1. The optical units1401,1403,1405,1407,14010,14012,14014and14016are the type A. The optical units1402,1404,1406,1408,1409,14011,14013and14015are the type B. The slide-feed mechanism of each of the optical units is provided such that the center of the objective lens123of each optical unit is moved along a line extending through the center of the optical information recording medium1. In order to effectively utilize the sixteen optical units, an optical information recording medium1must be used which is not contained in a cartridge and which allows recording and reproduction of information on both sides thereof.

In a system including the optical information recording/reproducing apparatus and the optical information recording medium1according to the present embodiment, an extraordinary amount of information can be recorded in the optical information recording medium1, and such a system is suitable for applications in which an enormous amount of continuous information is recorded. If a system used for such an application is unable to reproduce information during recording of such an enormous amount of continuous information, the system will be very much difficult to use.

Under such circumstances, for example, a plurality of pick-ups111may be provided in a single optical information recording/reproducing apparatus as shown inFIGS. 30 through 34to allow simultaneous recording and reproduction of information using a single optical information recording medium1and to allow simultaneous recording and reproduction of information with the plurality of pick-ups111, which makes it possible to improve the recording and reproducing performance and, particularly, to configure a system which is easy to use even in applications wherein an enormous amount of continuous information is recorded. By providing a plurality of pick-ups111in a single optical information recording/reproducing apparatus, dramatic improvement of performance can be achieved in retrieving a desired item of information from a large amount of information compared to a case in which only a single pick-up111is used.

A description will now be made with reference toFIGS. 35 through 46on an example of a specific structure of an optical information recording medium1according to the present embodiment.

The optical information recording medium1according to the present embodiment has a first information layer (hologram layer) in which information is recorded utilizing holography and a second information layer in which information for servo and address information are recorded in the form of embossed pits or the like. It is necessary to form a region of interference between reference light for recording and information light to a certain size in the first information layer while converging the reference light to a minimum diameter in the second information layer. For this reason, according to the present embodiment, a gap having a certain size is formed between the first and second information layers. This makes it possible to form a region of interference between reference light for recording and information light with a sufficient size in the first layer while converging the reference light to a minimum diameter on the second information layer to allow reproduction of information recorded in the second information layer. Optical information recording media1according to the present embodiment can be classified into an air gap type and a transparent substrate gap type depending on the method for forming such a gap.

FIGS. 35 through 37show an air gap type optical information recording medium1whereinFIG. 35is a sectional view of one half of the optical information recording medium1;FIG. 36is an exploded perspective view of the one half of the optical information recording medium1; andFIG. 37is a perspective view of the one half of the optical information recording medium1. The optical information recording medium1has: a reflecting substrate221one surface of which is a reflecting surface; a transparent substrate222provided in a face-to-face relationship with the reflecting surface of the reflecting substrate221; an outer circumferential spacer223and an inner circumferential spacer224for spacing the reflecting substrate221and transparent substrate222with a predetermined gap therebetween; and a hologram layer225bonded to the surface of the transparent substrate222facing the reflecting substrate221. An air gap having a predetermined thickness is formed between the reflecting surface of the reflecting substrate221and the hologram layer225. The hologram layer225serves as the first information layer. Pre-grooves are formed on the reflecting surface of the reflecting substrate221, and the reflecting surface serves as the second information layer.

FIGS. 38 through 40show a transparent substrate type optical information recording medium1whereinFIG. 38is a sectional view of one half of the optical information recording medium1;FIG. 39is an exploded perspective view of the one half of the optical information recording medium1; andFIG. 40is a perspective view of the one half of the optical information recording medium1. The optical information recording medium1is configured by stacking a transparent substrate231, a hologram layer232to serve as the first information layer and a transparent substrate233in the order listed. Pre-grooves are formed and a reflecting film234is provided on the surface of the transparent substrate231opposite to the hologram layer232. The surface of the transparent substrate231opposite to the hologram layer232serves as the second information layer. A gap having a predetermined thickness is formed by the transparent substrate231between the second information layer and the hologram layer232. The thickness of the transparent substrate233is smaller than that of the transparent substrate231.

Optical information recording media1according to the present embodiment can be classified into a single-sided type and a double-sided type.

FIGS. 41 through 43show single-sided type optical information recording media1whereinFIG. 41is a sectional view of a 1.2 mm thickness type optical information recording medium1;FIG. 42is a sectional view of a 0.6 mm thickness type optical information recording medium1; andFIG. 43is an illustration of how to illuminate a single-sided optical information recording medium1with reference light for recording and information light. The optical information recording media1shown inFIGS. 41 and 42have a structure as shown inFIG. 38. The combined thickness of the transparent substrate231, hologram layer232and transparent substrate233of the optical information recording medium1shown inFIG. 41is 1.2 mm, and the combined thickness of the transparent substrate231, hologram layer232and transparent substrate233of the optical information recording medium1shown inFIG. 42is 0.6 mm.

Reference light241for recording projected upon the optical information recording medium1by the objective lens123converges to a minimum diameter on the surface having pre-grooves formed thereon, and information light242projected upon the optical information recording medium1by the objective lens123converges to a minimum diameter before the hologram layer232. As a result, a region243of interference between the reference light241for recording and the information light242is formed in the hologram layer232.

WhileFIGS. 41 and 42show optical information recording media1belonging to the transparent substrate gap type and the single-sided type, an optical information recording medium1may be configured which belongs to the air-gap type and the single-sided type. In such a case, the combined thickness of the transparent substrate222, hologram layer225and the air gap must be 1.2 mm or 0.6 mm.

FIGS. 44 through 46show double-sided type optical information recording media1whereinFIG. 44is a sectional view of a transparent substrate gap type optical information recording medium1;FIG. 45is a sectional view of an air gap type optical information recording medium1; andFIG. 46is an illustration of how to illuminate a double-sided optical information recording medium1with reference light for recording and information light. The optical information recording medium1shown inFIG. 44has a structure formed of two single-sided type optical information recording media as shown inFIG. 42which are laminated to each other at the reflecting films234thereof. The optical information recording medium1shown inFIG. 45has a structure formed of two single-sided type optical information recording media as shown inFIG. 35which are laminated to each other at the reflecting substrates221thereof. The combined thickness of the transparent substrate222, hologram layer225and the air gap of one side of the optical information recording medium1shown inFIG. 45is 0.6 mm.

Reference light241for recording projected upon the optical information recording medium1by the objective lens123converges to a minimum diameter on the surface having pre-grooves formed thereon, and information light242projected upon the optical information recording medium1by the objective lens123converges to a minimum diameter before the hologram layers232and225. As a result, a region243of interference between the reference light241for recording and the information light242is formed in the hologram layers232and225.

The optical information recording/reproducing apparatus of the present embodiment is capable of recording and reproducing information using conventional optical disks. For example, when a single-sided type optical disk251is used which has pre-grooves formed on one side of a transparent substrate252thereof and which is provided with a reflecting film253as shown inFIG. 47, light projected upon the optical disk251by the objective lens123is converged to a minimum diameter on the surface of the optical disk251formed with pre-grooves, i.e., an information layer, as shown inFIG. 48. For example, the thickness of the transparent substrate252of the optical disk251shown inFIG. 47is 1.2 mm. Optical disks having a structure as shown inFIG. 47include CDs, CD-ROMs, CD-Rs (write once type CDs) and MDs (mini-disks).

When a double-sided type optical disk261is used which has a structure formed by two transparent substrates262formed with pre-grooves and provided with a reflecting film263on one side thereof which are laminated to each other at the reflecting films263as shown inFIG. 49, light projected upon the optical disk261by the objective lens123is converged to a minimum diameter on the surface of the optical disk261formed with pre-grooves, i.e., an information layer, as shown inFIG. 50. For example, the thickness of one of the transparent substrates262of the optical disk261shown inFIG. 49is 0.6 mm. Optical disks having a structure as shown inFIG. 50include DVDs, DVD-ROMS, DVD-RAMs, MOs (magneto-optical disks).

The second information layer of the optical information recording medium1according to the present embodiment may be similar in configuration to information layers of conventional optical disks, for example, as shown inFIGS. 47 and 49, including the contents of information recorded therein. In this case, information recorded in the second information layer can be reproduced by putting the pick-up111in a servo state. Since information for servo and address information are recorded in the information layer of a conventional optical disk, by configuring the second information layer similarly to the information layer of a conventional optical disk, information for servo and address information recorded in the information layer of a conventional optical disk can be used, as it is, to position information light, reference light for recording and reference light for reproduction in the hologram layer for performing recording and reproduction. The second information layer serves a wide range of applications, e.g., high speed retrieval can be performed by recording directory information, directory management information and the like for information recorded in the first information layer (hologram layer) in the second information layer (information layer of a conventional optical disk).

Prior to a description of the operation of the optical information recording/reproducing apparatus according to the present embodiment, a description will now be made on a principle behind phase-encoding multiplexing with reference toFIG. 51andFIGS. 52A through 52C.FIG. 51is a perspective view showing a schematic configuration of a common recording/reproducing system for performing phase-encoding multiplexing. The recording/reproducing system has: a spatial light modulator301for generating information light302based on two-dimensional digital pattern information; a lens303for collecting the information light302from the spatial light modulator301to illuminate a hologram recording medium300with the same; a phase-spatial light modulator304for generating reference light305having a spatially modulated phase to illuminate the hologram recording medium300with the reference light305in a direction substantially orthogonal to the information light302; a CCD array308for detecting reproduced two-dimensional digital pattern information; and a lens307for collecting reproduction light306emitted by the hologram recording medium300and for projecting the same upon the CCD array308.

During recording, the recording/reproducing system shown inFIG. 51digitizes information such as an original image to be recorded and rearranges resultant signals having a value of 0 or 1 on a two-dimensional basis to generate two-dimensional digital pattern information (hereinafter referred to as “page data”). Let us assume here that page data #1through #n are recorded in the same hologram recording medium300on a multiplex basis. Further, different items of two-dimensional digital pattern information #1through #n for phase modulation (hereinafter referred to as “phase data”) are generated for the respective page data #1through #n. First, when the page data #1is recorded, the spatial light modulator301generates spatially modulated information light302based on the page data #1to illuminate the hologram recording medium300through the lens303. Simultaneously, the phase-spatial light modulator304generates reference light305having a spatially modulated phase based on the phase data #1to illuminate the hologram recording medium300. As a result, interference fringes resulting from overlap between the information light302and the reference light305are recorded in the hologram recording medium300. Similarly, to record the page data #2through #n, the spatial light modulator301generates spatially modulated information light302based on the page data #2through #n; the phase-spatial light modulator304generates reference light305having a spatially modulated phase based on the phase data #2through #n; and the hologram recording medium300is illuminated with the information light302and the reference light305. Thus, a plurality of pieces of information are recorded in the same location of the hologram recording medium300on a multiplex basis. Such a hologram having information recorded therein on a multiplex basis is referred to as “stack”. In the example shown inFIG. 51, the hologram recording medium300has a plurality of stacks (stack1, stack2, . . . , stack m, . . . ).

Arbitrary page data can be reproduced from a stack by illuminating the stack with the reference light305having a phase which has been spatially modulated based on the same phase data as used for the recording of the page data. As a result, the reference light305is selectively diffracted by interference fringes associated with the phase data and page data to produce reproduction light306. The reproduction light306impinges upon the CCD array308through the lens307, and the CCD array308detects a two-dimensional pattern of the reproduction light. The detected two-dimensional pattern of the reproduction light is decoded conversely to the process for recording, so that the information such as an original image is reproduced.

FIGS. 52A through 52Cshow how interference fringes are formed in the hologram recording medium300as a result of interference between information light302and reference light305.FIG. 52Ashows how interference fringes3091are formed as a result of interference between information light3021based on the page data #1and reference light3051based on the phase data #1. Similarly,FIG. 52Bshows how interference fringes3092are formed as a result of interference between information light3022based on the page data #2and reference light3052based on the phase data #2.FIG. 52Cshows how interference fringes3093are formed as a result of interference between information light3023based on the page data #3and reference light3053based on the phase data #3.

Servo, recording and reproducing operations of the optical information recording/reproducing apparatus according to the present embodiment will now be separately described in that order.

A servo operation will now be described with reference toFIGS. 53 and 54.FIG. 53is an illustration of a state of the pick-up111during a servo operation. During a servo operation, all pixels of the spatial light modulator125are in a blocking state. The phase-spatial light modulator117is set such that light passing through all pixels have the same phase. The output of the emission of light from the light source device112is set at a low output for reproduction. The controller90predicts the timing at which light that has exited the objective lens123passes through the address servo areas6based on a basic clock reproduced from a reproduction signal RF and maintains the above-described setting while the light from the objective lens123passes through the address servo areas6.

Light emitted by the light source device112is collimated by the collimator lens113to impinge upon the polarization beam splitter116after passing through the ND filter114and rotating optical element115sequentially. S-polarized components in the light incident upon the polarization beam splitter116are reflected by the polarization beam splitter surface116aand are blocked by the spatial light modulator125. P-polarized components in the light incident upon the polarization beam splitter116are transmitted by the polarization beam splitter surface116aand passes through the phase-spatial light modulator117to impinge upon the beam splitter118. A part of the light incident upon the beam splitter118is reflected by the beam splitter surface118aand passes through the polarization beam splitter120to impinge upon the double optically rotating plate121. Light that has passed through the optically rotating plate121R of the double optically rotating plate121becomes B-polarized light, and light that has passed through the optically rotating plate121L becomes A-polarized light. The light that has passed through the double optically rotating plate121is reflected by the raising mirror122, collected by the objective lens123and projected upon the optical information recording medium1so that it converges on the pre-grooves of the optical information recording medium1located further than the hologram layer. This light is reflected on the pre-grooves and, at that time, it is modulated by pits formed on the pre-grooves and then returns to the objective lens123. The raising mirror122is omitted inFIG. 53.

The return light from the optical information recording medium1is collimated by the objective lens123and passes through the double optically rotating plate121to become S-polarized light. The return light is reflected by the polarization beam splitter surface120aof the polarization beam splitter120to impinge upon the beam splitter127. A part of the light is transmitted by the beam splitter surface127aand passes through the convex lens129and cylindrical lens130sequentially to be detected by the quadruple photodetector131. Based on the output of the quadruple photodetector131, the detection circuit85generates a focus error signal FE, tracking error signal TE and reproduction signal RF based on which focus servo and tracking servo are performed; the basic clock is generated; and addresses are determined.

A part of the light incident upon the beam splitter118impinges upon the photodetector119, and a signal APCrefis generated by the APC circuit146based on a signal output by the photodetector119. APC is performed based on the signal APCrefsuch that the optical information recording medium1is illuminated with a constant quantity of light. Specifically, the driving circuit148drives the motor142to adjust the rotating optical element115such that the signal APCrefequals a predetermined value. Alternatively, during the servo operation, APC may be performed by setting the rotating optical element115and adjusting the output of the light source device112such that light which has passed through the rotating optical element115has P-polarized components only. When the light-receiving portion of the photodetector119is divided into a plurality of regions and the phase-spatial light modulator117is capable of adjusting the quantity of light transmitted thereby, the quantity of light transmitted by each pixel of the phase-spatial light modulator117may be adjusted based on a signal output by each of the light-receiving portions of the photodetector119to adjust the light projected upon the optical information recording medium1so as to achieve a uniform intensity distribution.

In the above-described setting for a servo operation, the configuration of the pick-up111is similar to the configuration of a pick-up for recording and reproduction on a normal optical disk. Therefore, the optical information recording/reproducing apparatus according to the present embodiment is capable of recording and reproducing by using a normal optical disk.

FIG. 54is an illustration of a state of light in the vicinity of an optical disk in the case of recording and reproduction using a normal optical disk with the optical information recording/reproducing apparatus according to the present embodiment. A double-sided type optical disk261is illustrated here as an example of a normal optical disk. In the optical disk261, pre-grooves265are formed on the sides of transparent substrates262where reflecting films263are provided, and light from the objective lens123is projected upon the optical disk261such that it converges on the pre-grooves265and is returned to the objective lens123after being modulated by pits formed on the pre-grooves265.

A recording operation will now be described with reference toFIGS. 55 through 57.FIG. 55is an illustration of a state of the pick-up111during recording, and each ofFIGS. 56 and 57is an illustration of a state of light in the vicinity of the optical information recording medium1during recording. The following description will refer to the use of an air gap type optical information recording medium1as an example, as shown inFIG. 56.

During recording, the spatial light modulator125generates information light by selecting a transmitting state (hereinafter also referred to as “on”) or a blocking state (hereinafter also referred to as “off”) for each pixel depending on the information to be recorded to modulate the light that is passing through it. The phase-spatial light modulator117generates reference light for recording having a spatially modulated optical phase by selectively applying a phase difference of 0 (rad) or π (rad) from a predetermined reference phase to each pixel according to a predetermined modulation pattern to modulate the phase of light passing therethrough.

According to the present embodiment, as already described, when multiplex recording of information is carried out on a data area7using phase-encoding multiplexing, the center of the objective lens123is moved using in-field access such that the center of the objective lens123reciprocates within a section including the data area7and a part of the address servo areas6on both sides thereof. When the center of the objective lens123has come to a predetermined position in the data area7, the output of the light source device112is selectively set at a high output for recording.

Light emitted by the light source device112is collimated by the collimator lens113to impinge upon the polarization beam splitter116after passing through the ND filter114and rotating optical element115sequentially. P-polarized components in the light incident upon the polarization beam splitter116are transmitted by the polarization beam splitter surface116ato pass through the phase-spatial light modulator117and, at that time, the phase of the light is spatially modulated to provide reference light for recording. The reference light for recording impinges upon the beam splitter118. A part of the reference light for recording incident upon the beam splitter118is reflected by the beam splitter surface118aand passes through the polarization beam splitter120to impinge upon the double optically rotating plate121. Reference light for recording that has passed through the optically rotating plate121R of the double optically rotating plate121becomes B-polarized light, and reference light for recording that has passed through the optically rotating plate121L becomes A-polarized light. The reference light for recording that has passed through the double optically rotating plate121is reflected by the raising mirror122, collected by the objective lens123and projected upon the optical information recording medium1so that it converges beyond the hologram layer225of the optical information recording medium1. The raising mirror122is omitted inFIG. 55.

S-polarized components in the light incident upon the polarization beam splitter116are reflected by the polarization beam splitter surface116ato pass through the spatial light modulator125and, at that time, the light is spatially modulated according to the information to be recorded to provide information light. The information light impinges upon the beam splitter127. A part of the information light incident upon the beam splitter127is reflected by the beam splitter surface127aand is reflected by the beam splitter surface120aof the polarization beam splitter120to impinge upon the double optically rotating plate121. Information light that has passed through the optically rotating plate121R of the double optically rotating plate121becomes A-polarized light, and information light that has passed through the optically rotating plate121L becomes B-polarized light. The information light that has passed through the double optically rotating plate121is reflected by the raising mirror122, collected by the objective lens123and projected upon the optical information recording medium1so that it temporarily converges before the hologram layer225of the optical information recording medium1and then divergingly passes through the hologram layer225.

As a result, a region313of interference between reference light311for recording and information light312is formed in the hologram layer225, as shown inFIG. 56. The interference region313is in the form of a barrel. As shown inFIG. 55, the converging position of the information light can be adjusted by adjusting the position310of the convex lens126, which makes it possible to adjust the size of the interference region313.

In the hologram layer225, as shown inFIG. 57, interference occurs between A-polarized reference light311A for recording that has passed through the optically rotating plate121L of the double optically rotating plate121and A-polarized information light312A that has passed through the optically rotating plate121R of the double optically rotating plate121; and interference occurs between B-polarized reference light311B for recording that has passed through the optically rotating plate121R of the double optically rotating plate121and B-polarized information light312B that has passed through the optically rotating plate121L of the double optically rotating plate121, resultant interference patterns being volumetrically recorded in the hologram layer225.

By changing the modulation pattern for the phase of the reference light for recording for each item of information to be recorded, a plurality of pieces of information can be recorded in the same location of the hologram layer225on a multiplex basis.

As shown inFIG. 55, a part of the reference light for recording incident upon the beam splitter118impinges upon the photodetector119, and a signal APCrefis generated by the APC circuit146based on a signal output by the photodetector119. A part of the information light incident upon the beam splitter127impinges upon the photodetector128, and a signal APCobjis generated by the APC circuit147based on a signal output by the photodetector128. Based on the signals APCrefand APCobj, APC is performed such that the ratio between the intensity of the reference light for recording and the information light illuminating the optical information recording medium1is set at an optimum value. Specifically, the driving circuit148compares the signals APCrefand APCobjand drives the motor142to adjust the rotating optical element115such that the signals are in a desired ratio. When the light-receiving portion of the photodetector119is divided into a plurality of regions and the phase-spatial light modulator117is capable of adjusting the quantity of light transmitted thereby, the quantity of light transmitted by each pixel of the phase-spatial light modulator117may be adjusted based on a signal output by each of the light-receiving portions of the photodetector119to adjust the light projected upon the optical information recording medium1so as to achieve a uniform intensity distribution. Similarly, when the light-receiving portion of the photodetector128is divided into a plurality of regions and the spatial light modulator125is also capable of adjusting the quantity of light transmitted thereby, the quantity of light transmitted by each pixel of the spatial light modulator125may be adjusted based on a signal output by each of the light-receiving portions of the photodetector128to adjust the light projected upon the optical information recording medium1so as to achieve a uniform intensity distribution.

According to the present embodiment, APC is carried out based on the sum of the signals APCrefand APCobjsuch that the total intensity of the reference light for recording and the information light becomes an optimum value. Methods for controlling the total intensity of the reference light for recording and the information light include control over a peak value of the output of the light source device112and control over an emission pulse width and a profile of the intensity of emitted light over time when light is emitted in the form of pulses.

A fixing operation will now be described with reference toFIGS. 58 and 59.FIG. 58is an illustration of a state of the pick-up111during a fixing operation, andFIG. 59is an illustration of a state of light in the vicinity of the optical information recording medium1during fixing. During a fixing operation, all pixels of the spatial light modulator125are in a blocking state. The phase-spatial light modulator117is set such that light passing through all pixels thereof have the same phase. No light is emitted by the light source device112, and S-polarized ultraviolet light for fixing is emitted by the fixing light source device135.

Light emitted by the fixing light source device135is collimated by the collimator lens134to impinge upon the polarization beam splitter116, reflected by the polarization beam splitter surface116aand passes through the phase-spatial light modulator117to impinge upon the beam splitter118. A part of the light incident upon the beam splitter118is reflected by the beam splitter surface118ato impinge upon the double optically rotating plate121through the polarization beam splitter120. Light that has passed through the optically rotating plate121R of the double optically rotating plate121becomes B-polarized light, and light that has passed through the optically rotating plate121L becomes A-polarized light. The light that has passed through the double optically rotating plate121is reflected by the raising mirror122, collected by the objective lens123and projected upon the optical information recording medium1so that it converges on the pre-grooves of the optical information recording medium1located further than the hologram layer225. This light fixes the interference pattern formed in the interference region313in the hologram layer225. The raising mirror122is omitted inFIG. 58.

The positioning (servo) of fixing light on an optical information recording medium1can be performed similarly to the positioning of reference light for recording and information light during recording.

A part of the light incident upon the beam splitter118impinges upon the photodetector119, and a signal APCrefis generated by the APC circuit146based on a signal output by the photodetector119. Based on the signal APCref, APC is performed such that the quantity of fixing light illuminating the optical information recording medium1is constant. Specifically, the output of the fixing light source device135is adjusted such that the signal APCrefequals a predetermined value. Alternatively, when the light-receiving portion of the photodetector119is divided into a plurality of regions and the phase-spatial light modulator117is capable of adjusting the quantity of light transmitted thereby, the fixing light illuminating the optical information recording medium1may be adjusted to achieve a uniform intensity of light by adjusting the quantity of light transmitted by each of the pixels of the phase-spatial light modulator117based on a signal output by each of the light-receiving portions of the photodetector119.

A reproducing operation will now be described with reference toFIGS. 60 through 62.FIG. 60is an illustration of a state of the pick-up111during reproduction, and each ofFIGS. 61 and 62is an illustration of a state of light in the vicinity of an optical information recording medium1during reproduction.

During reproduction, all pixels of the spatial light modulator125are in a blocking state. The phase-spatial light modulator117generates reference light for reproduction having a spatially modulated optical phase by selectively applying a phase difference of 0 (rad) or π (rad) from a predetermined reference phase to each pixel according to a predetermined modulation pattern to modulate the phase of light passing therethrough. According to the present embodiment, a modulation pattern for the phase of reference light for reproduction is a pattern which is in a point symmetrical relationship with a modulation pattern of the phase of reference light for recording at the time of recording of the information to be reproduced about the center of the phase-spatial light modulator117.

Light emitted by the light source device112is collimated by the collimator lens113to impinge upon the polarization beam splitter116after passing through the ND filter114and the rotating optical element115sequentially. S-polarized components in the light incident upon the polarization beam splitter116are reflected by the polarization beam splitter surface116aand are blocked by the spatial light modulator125. P-polarized components in the light incident upon the polarization beam splitter116are transmitted by the polarization beam splitter surface116ato pass through the phase-spatial light modulator117and, at that time, the phase of the light is spatially modulated to provide reference light for reproduction. The reference light for reproduction impinges upon the beam splitter118. A part of the reference light for reproduction incident upon the beam splitter118is reflected by the beam splitter surface118aand passes through the polarization beam splitter120to impinge upon the double optically rotating plate121. Reference light for reproduction that has passed through the optically rotating plate121R of the double optically rotating plate121becomes B-polarized light, and reference light for reproduction that has passed through the optically rotating plate121L becomes A-polarized light. The reference light for reproduction that has passed through the double optically rotating plate121is reflected by the raising mirror122, collected by the objective lens123and projected upon the optical information recording medium1so that it converges beyond the hologram layer225of the optical information recording medium1. The raising mirror122is omitted inFIG. 60.

The positioning (servo) of reference light for reproduction on an optical information recording medium1can be performed similarly to the positioning of reference light for recording and information light during recording.

As shown inFIG. 62, B-polarized reference light315B for reproduction that has passed through the optically rotating plate121R of the double optically rotating plate121passes through the hologram layer225, and is reflected by the reflecting surface located at a converging position on the further side of the hologram layer225, and then passes through the hologram layer225again. At this time, the reference light315B for reproduction reflected by the reflecting surface passes through the location in the interference region313that was illuminated with the reference light311A for recording during recording, and has the same modulation pattern as that of the reference light311A for recording. Therefore, the reference light315B for reproduction results in the emission of reproduction light316B associated with the information light312A at the time of recording from the interference region313. The reproduction light316B travels toward the objective lens123.

Similarly, A-polarized reference light315A for reproduction that has passed through the optically rotating plate121L of the double optically rotating plate121passes through the hologram layer225, and is reflected by the reflecting surface located at the converging position on the further side of the hologram layer225, and then passes through the hologram layer225again. At this time, the reference light315A for reproduction reflected by the reflecting surface passes through the location in the interference region313that was illuminated with the reference light311B for recording during recording, and has the same modulation pattern as that of the reference light311B for recording. Therefore, the reference light315A for reproduction results in the emission of reproduction light316A associated with the information light312B at the time of recording from the interference region313. The reproduction light316A travels toward the objective lens123.

After passing through the objective lens123, the B-polarized reproduction light316B passes through the optically rotating plate121R of the double optically rotating plate121to become P-polarized light. After passing through the objective lens123, the A-polarized reproduction light316A passes through the optically rotating plate121L of the double optically rotating plate121to become P-polarized light. The reproduction light that has passed through the double optically rotating plate121impinges upon the polarization beam splitter120and is transmitted by the polarization beam splitter surface120ato impinge upon the beam splitter118. A part of the reproduction light incident upon the beam splitter118is transmitted by the beam splitter surface118aand passes through the imaging lens132to impinge upon the CCD array133. As shown inFIG. 60, the state of imaging of the reproduction light on the CCD array133can be adjusted by adjusting the position of the imaging lens132.

A pattern originating from an on/off operation of the spatial light modulator125during recording is formed on the CCD array133, and information is reproduced by detecting this pattern. When a plurality of pieces of information are recorded in the hologram layer225on a multiplex basis by varying the modulation pattern for reference light for recording, only information associated with reference light for recording having a modulation pattern in a point symmetrical relationship with the modulation pattern of the reference light for reproduction is reproduced among the plurality of pieces of information.

A part of the reference light for reproduction incident upon the beam splitter118impinges upon the photodetector119, and a signal APCrefis generated by the APC circuit146based on a signal output by the photodetector119. Based on the signal APCref, APC is performed such that the optical information recording medium1is illuminated with a constant quantity of light. Specifically, the driving circuit148drives the motor142to adjust the rotating optical element115such that the signal APCrefequals a predetermined value. Alternatively, during reproduction, APC may be performed by setting the rotating optical element115and adjusting the output of the light source device112such that light which has passed through the rotating optical element115has P-polarized components only. When the light-receiving portion of the photodetector119is divided into a plurality of regions and the phase-spatial light modulator117is capable of adjusting the quantity of light transmitted thereby, the quantity of light transmitted by each pixel of the phase-spatial light modulator117may be adjusted based on a signal output by each of the light-receiving portions of the photodetector119to adjust the light projected upon the optical information recording medium1so as to achieve a uniform intensity distribution.

The present embodiment may employ: a light source device112capable of emitting laser light in three colors R, G and B; a CCD array133capable of detecting light in three colors R, G and B; and an optical information recording medium1having three hologram layers whose optical characteristics are changed by only light in respective colors R, G and B. In this case, it is possible to record three kinds of information in the same location of the optical information recording medium1using the same modulation pattern for the reference light for recording, which allows multiplex recording of a greater amount of information. For example, recording media having three hologram layers as described above include HRF-700X059-20 (product name) manufactured by DuPont.

When multiplex recording of information is performed using light in three colors R, G and B as described above, information is recorded in each of R, G and B colors on a time division basis in the same location of an optical information recording medium1. In doing so, while the modulation pattern for the information light is varied for each of R, G and B colors, the modulation pattern for the reference light for recording is kept unchanged. When each pixel of information light in each color carries binary information, i.e., when each pixel is rendered bright or dark, multiplex recording of information using light in three colors R, G and B makes it possible to record octal (=23) information for each pixel, for example, R being the MSB (most significant bit), B being the LSB (least significant bit). When the spatial light modulator125is capable of adjusting the quantity of light transmitted thereby in three or more steps and each pixel of information light in each color carries information having n (n is an integer equal to or greater than 3) tones, multiplex recording of information using light in three colors R, G and B makes it possible to record information having n3values for each pixel.

Various methods are possible as described below for reproduction of information when the information is recorded on a multiplex basis using light in three colors R, G and B. Specifically, if the reference light for reproduction is light in any one of R, G and B colors, only information recorded using light in the same color as the reference light for reproduction is reproduced. If the reference light for reproduction is light in any two of R, G and B colors, only two kinds of information recorded using light in the same two colors as the reference light for reproduction are reproduced. The two kinds of information are separated by the CCD array133into information in each color. If the reference light for reproduction is light in three colors R, G and B, three kinds of information recorded using light in the three colors are all reproduced. The three kinds of information are separated by the CCD array133into information in each color. When the optical information recording medium1has a layer for each of R, G and B colors, multiplex recording is performed in the layer in each color using phase-encoding multiplexing. This is advantageous in that it is possible to obtain a reproduction image having a pattern in each of the colors R, G and B for each of phase modulation patterns for the reference light.

A description will now be made with reference toFIGS. 63and64on a direct read after write (hereinafter represented by “DRAW”) function and a write power control (hereinafter represented by “WPC”) function for multiplex recording of the optical information recording/reproducing apparatus according to the present embodiment.

First, the DRAW function will be described. The DRAW function is a function of reproducing recorded information immediately after the information is recorded. This function makes it possible to verify recorded information immediately after the information is recorded.

A principle behind the DRAW function according to the present embodiment will now be described with reference toFIGS. 55 and 57. First, when the DRAW function is used in the present embodiment, a modulation pattern for reference light for recording is used which is in a point symmetrical relationship with the center of the phase-spatial light modulator117. During recording, in the hologram layer225, interference occurs between the A-polarized reference light311A for recording that has passed through the optically rotating plate121L of the double optically rotating plate121and the A-polarized information light312A that has passed through the optically rotating plate121R of the double optically rotating plate121, and interference occurs between the B-polarized reference light311B for recording that has passed through the optically rotating plate121R of the double optically rotating plate121and the B-polarized information light312B that has passed through the optically rotating plate121L of the double optically rotating plate121, resultant interference patterns being volumetrically recorded in the hologram layer225.

Thus, when recording of an interference pattern in the hologram layer225begins, A-polarized reproduction light is generated at the location where the interference pattern is recorded by the reference light311B for recording due to light resulting from the reflection of the A-polarized reference light311A for recording that has passed through the optically rotating plate121L of the double optically rotating plate121at the reflecting surface located in the converging position on the further side of the hologram layer225. This reproduction light travels toward the objective lens123, passes through the objective lens123, and thereafter passes through the optically rotating plate121L of the double optically rotating plate121to become P-polarized light. Similarly, B-polarized reproduction light is generated at the location where the interference pattern is recorded by the reference light311A for recording due to light resulting from the reflection of the B-polarized reference light311B for recording that has passed through the optically rotating plate121R of the double optically rotating plate121at the reflecting surface located in the converging position on the further side of the hologram layer225. This reproduction light travels toward the objective lens123, passes through the objective lens123, and thereafter passes through the optically rotating plate121R of the double optically rotating plate121to become P-polarized light. The reproduction light that has passed through the double optically rotating plate121impinges upon the polarization beam splitter120and is transmitted by the polarization beam splitter surface120ato impinge upon the beam splitter118. A part of the reproduction light incident upon the beam splitter118is transmitted by the beam splitter surface118aand passes through the imaging lens132to impinge upon the CCD array133at which it is detected. Thus, recorded information can be reproduced immediately after the information is recorded.

The reference number321inFIG. 63represents an example of a relationship between the time that has passed after the start of recording of information in one location of an optical information recording medium1and the output level of the CCD array133. As can be seen, the output level of the CCD array133gradually increases after the start of information recording in accordance with the degree of the recording of the interference pattern in the optical information recording medium1, reaches a maximum value at a certain point of time and gradually decreases thereafter. It can be assumed that recorded interference pattern (hereinafter referred to as “recorded pattern”) has higher diffracting efficiency, the higher the output level of the CCD array133. It is therefore possible to form a recorded pattern having desired diffracting efficiency by stopping recording when the CCD array133reaches an output level associated with the desired diffracting efficiency.

In the present embodiment, in order to form a recorded pattern having desired diffracting efficiency using the DRAW unction as described above, an appropriate test area is preferably provided in the optical information recording medium1. A test area is a region where information can be recorded utilizing holography like the data areas7. Preferably, the controller90performs the following operation when information is recorded. Specifically, the controller90performs an operation of recording predetermined test data in the test area in advance and detects a profile of the output level of the CCD array133as shown inFIG. 63. At this time, the operations of recording test data and detecting a profile of the output level of the CCD array133are preferably performed in a plurality of locations in the test area while changing the output of the light source device112and the ratio between reference light for recording and information light. For example, a plurality of profiles are detected as indicated by the reference numbers321through323inFIG. 63; the optimum profile is selected from among them; and the actual information recording operation is performed under conditions in accordance with the selected profile.

Based on the detected profile or selected profile, the controller90identifies the output level associated with desired diffracting efficiency or the time required to reach that output level after the beginning of the recording. In actual recording of information, the controller90monitors the output level of the CCD array133and stops the recording when the output level reaches an output level associated with predefined desired diffracting efficiency. Alternatively, in actual recording of information, the controller90stops the recording when a time spent after the start of the recording agrees with the time required after the start of recording to reach an output level associated with predefined desired diffracting efficiency. Such an operation makes it possible to form a recorded pattern having desired diffracting efficiency in an optical information recording medium1.

As described above, the present embodiment makes it possible to verify recorded information using the DRAW function.FIG. 64shows a configuration of a circuit required to perform such verification in an optical information recording/reproducing apparatus according to the present embodiment. As illustrated, the optical information recording/reproducing apparatus has: an encoder331to which information to be recorded is supplied by the controller90and which encodes the information into data for a modulation pattern of the spatial light modulator (represented by “SLM” inFIG. 64)125; a decoder322for decoding data output by the CCD array133into data in a format adapted to be supplied from the controller90to the encoder331; and a comparing portion333for comparing the data supplied from the controller90to the encoder331and the data obtained by the decoder322and for transmitting the information of the result of the comparison to the controller90. For example, the comparing portion333transmits information of the degree of match between the two items of data to be compared or information of the error rate to the controller90as the information of the comparison result. For example, the controller90continues the recording operation if the information of the comparison result transmitted by the comparing portion333is within a range in which data errors can be corrected, and stops the recording operation if the information of the comparison result is out of the range in which data errors can be corrected.

As described above, since the optical information recording/reproducing apparatus of the present embodiment has the DRAW function, it can perform a recording operation under optimum recording conditions even in the presence of disturbances such as variation of sensitivity of the optical information recording medium1, changes in the ambient temperature and fluctuation of the output of the light source device112.

Further, the present embodiment allows recording at a high speed with high reliability maintained because it has the function of verifying recorded information simultaneously with recording of the information. This function is particularly useful in recording information at a high transfer rate. While the reproduction of unfixed information is unpreferable because it acts similarly to overwrite and can reduce the quality of the recorded information, the verification function of the present embodiment creates no problem because verification of recorded information is completed during the recording operation.

The WPC function during multiplex recording will now be described. When a plurality of pieces of information are recorded on a multiplex basis in the same location of an optical information recording medium1with the modulation pattern of the reference light for recording varied, the diffracting efficiency of an early recorded pattern is gradually decreased by subsequent recording. The WPC function according to the present embodiment is a function of controlling reference light for recording and information light during multiplex recording such that substantially the same diffracting efficiency can be achieved by the recorded pattern of each item of information recorded on a multiplex basis.

The diffracting efficiency of a recorded pattern depends on parameters such as the intensity of the reference light for recording and the information light, the illuminating time of the reference light for recording and the information light, the ratio between the intensity of the reference light for recording and the information light, the modulation pattern of the reference light for recording, the total number of times of the recording in the same location of the optical information recording medium1and the order of the recording of interest. Therefore, the WPC function is required to control at least one of the plurality of parameters. The control can be simplified by controlling the intensity and illuminating time of reference light for recording and information light. When the intensity of reference light for recording and information light is controlled, the intensity is reduced as the recording proceeds. When the illuminating time of reference light for recording and information light is controlled, the illuminating time is decreased as the recording proceeds.

With the WPC function of the present embodiment, reference light for recording and information light are controlled at first through m-th (m is an integer equal to or greater than 2) recording operations based on a profile of the output level of the CCD array133as shown inFIG. 63which has been obtained in advance.FIG. 63shows an example of illuminating times in the case of control over the illuminating time of reference light for recording and information light. Specifically, in the example shown inFIG. 63, it is assumed that recording is performed five times in the same location of an optical information recording medium1, and T1, T2, T3, T4and T5respectively represents the illuminating time of the reference light for recording and the information light at the first, second, third, fourth and fifth recording.

Thus, the present embodiment makes it possible to provide a recorded pattern of each item of information recorded on a multiplex basis with substantially the same diffracting efficiency.

The optical information recording/reproducing apparatus according to the present embodiment makes it possible to record a large amount of information in an optical information recording medium1with a high density. This means that a large amount of information can be lost when a defect or the like occurs in the optical information recording medium1after information is recorded to disable the reproduction of a part of the information. According to the present embodiment, in order to improve reliability by preventing such loss of information, information can be recorded utilizing the RAID (redundant arrays of inexpensive disks) technique as described below.

The RAID technique is a technique for improving reliability of recording by recording data with redundancy using a plurality of hard disk devices. RAIDs are classified into five categories of RAID-1 through RAID-5. The following description will refer to the RAID-1, RAID-3 and RAID-5 which are typical of the technique, by way of example. RAID-1 is a system in which the same contents are written in two hard disk devices and which is also referred to as “mirroring”. RAID-3 is a system in which input data is divided into parts having a predetermined length to be recorded in a plurality of hard disk devices and in which parity data is generated and written in another hard disk device. RAID-5 is a system in which larger units of data division (blocks) are employed; one division of data is recorded in one hard disk device as a data block; parity data for data blocks of the hard disk devices associated with each other is recorded in another hard disk device as a parity block; and the parity block is distributed among all hard disk devices.

A method for recording information utilizing the RAID technique according to the present embodiment (hereinafter referred to as “distributed recording method”) is to record information in an interference region313of an optical information recording medium1which is a substitution for a hard disk device in the context of the above description of RAID.

FIG. 65is an illustration of an example of the distributed recording method according to the present embodiment. In this example, information to be recorded in an optical information recording medium1is a series of data, DATA1, DATA2, DATA3, . . . , and the same data DATA1, DATA2, DATA3, . . . are recorded in a plurality of interference regions313athrough313eof the optical information recording medium1. A plurality of items of data are recorded on a multiplex basis in each of the interference regions313athrough313eusing phase-encoding multiplexing. This method of recording corresponds to RAID-1. According to this method of recording, even if reproduction of data is disabled in any of the plurality of interference regions313athrough313e, the data can be reproduced from other interference regions.

FIG. 66is an illustration of another example of the distributed recording method according to the present embodiment. In this example, information to be recorded in an optical information recording medium1is a series of data, DATA1, DATA2, DATA3, . . . , DATA12; the data are divided and recorded in a plurality of interference regions313athrough313d; parity data for the data recorded in the plurality of interference regions313athrough313dare generated; and the parity data are recorded in an interference region313e. More specifically, according to this method of recording, the data DATA1through DATA4are recorded in the interference regions313athrough313drespectively; parity data PARITY(1–4) for the data DATA1through DATA4are recorded in the interference region313e; the data DATA5through DATA8are recorded in the interference regions313athrough313drespectively; parity data PARITY(5–8) for the data DATA5through DATA8are recorded in the interference region313e; the data DATA9through DATA12are recorded in the interference regions313athrough313drespectively; and parity data PARITY(9–12) for the data DATA9through DATA12are recorded in the interference region313e. A plurality of items of data are recorded on a multiplex basis in each of the interference regions313athrough313eusing phase-encoding multiplexing. This method of recording corresponds to RAID-3. According to this method of recording, even if reproduction of data is disabled in any of the plurality of interference regions313athrough313e, the data can be restored using the parity data recorded in the interference region313e.

FIG. 67is an illustration of another example of the distributed recording method according to the present embodiment. In this example, information to be recorded in an optical information recording medium1is a series of data, DATA1, DATA2, DATA3, . . . , DATA12; the data are divided and recorded in four interference regions among a plurality of interference regions313athrough313e; parity data for the recorded data are generated; and the parity data are recorded in the remaining interference region among the plurality of interference regions313athrough313e. According to this method of recording, the interference region to record the parity data is sequentially changed. More specifically, according to this method of recording, the data DATA1through DATA4are recorded in the interference regions313athrough313drespectively; parity data PARITY(1–4) for the data DATA1through DATA4are recorded in the interference region313e; the data DATA5through DATA8are recorded in the interference regions313athrough313cand313erespectively; parity data PARITY(5–8) for the data DATA5through DATA8are recorded in the interference region313d; the data DATA9through DATA12are recorded in the interference regions313a,313b,313dand313erespectively; and parity data PARITY(9–12) for the data DATA9through DATA12are recorded in the interference region313c. A plurality of items of data are recorded on a multiplex basis in each of the interference regions313athrough313eusing phase-encoding multiplexing. This method of recording corresponds to RAID-5. According to this method of recording, even if reproduction of data is disabled in any of the plurality of interference regions where data are recorded, the data can be restored using the parity data.

For example, the distributed recording methods as shown inFIGS. 65 through 67are carried out under the control of the controller90as control means.

FIG. 68shows an example of an arrangement of a plurality of interference regions used in the distributed recording method as described above. In this example, interference regions used for the distributed recording method are a plurality of interference regions313adjacent to each other in one track. In this case, the plurality of interference regions313used for the distributed recording method are preferably interference regions within a range for which in-field access is possible. The reason is that it allows high speed access to each of the interference regions313.

FIG. 69shows another example of an arrangement of a plurality of interference regions used in the distributed recording method as described above. In this example, interference regions used for the distributed recording method are a plurality of interference regions313which are two-dimensionally adjacent to each other in the radial direction331of the optical information recording medium1and in the direction332of the tracks thereof. In this case, among the plurality of interference regions used for the distributed recording method, a plurality of interference regions313adjacent to each other in the direction332of the tracks are preferably interference regions within a range for which in-field access is possible. The reason is that it allows high speed access to each of the interference regions313which are adjacent to each other in the direction332of the tracks.

According to the distributed recording methods in the present embodiment, a series of data may be recorded in a distributed manner in a plurality of discrete interference regions313instead of recording them in a plurality of interference regions313adjacent to each other.

While a description has been made so far on distributed recording methods for recording a plurality of items of data in a single interference region313on a multiplex basis utilizing phase-encoding multiplexing, a distributed recording method can be implemented also when a plurality of items of data are recorded on a multiplex basis using other methods. By way of example, a description will be made with reference toFIG. 70on a distributed recording method for multiplex recording of a plurality of items of data using a method referred to as “shift multiplexing”. As shown inFIG. 70, shift multiplexing is a method for recording a plurality of pieces of information on a multiplex basis by forming a plurality of interference regions313in an optical information recording medium1such that they are slightly shifted from each other and are partially overlapped with each other in the horizontal direction. WhileFIG. 70shows an example in which a plurality of interference regions313used for the distributed recording method are two-dimensionally arranged, the plurality of interference regions313used for the distributed recording method may be arranged such that they are adjacent to each other in the same track. InFIG. 70, the arrow indicated by the reference number334represents an order of recording. According to the distributed recording method utilizing multiplexing, data and parity data divided from a series of data are recorded in a plurality of interference regions313in a distributed manner.

A distributed recording method can be implemented also when a plurality of items of data are recorded on a multiplex basis using phase-encoding multiplexing and shift multiplexing in combination.FIG. 71shows an example in which interference regions313for multiplex recording of information utilizing phase-encoding multiplexing are formed with no overlap between them in the direction332of the tracks of an optical information recording medium1and in which adjoining interference regions313to be used for shift multiplexing are formed in the radial direction331of the optical information recording medium1such that they are slightly shifted from each other and are partially overlapped with each other in the horizontal direction. Each of the interference regions313in this example is treated similarly to the interference regions313athrough313einFIGS. 65 through 67.

A description will now be made with reference toFIGS. 72 and 73on a juke apparatus utilizing an optical information recording/reproducing apparatus according to the present embodiment as an example of the application of an optical information recording/reproducing apparatus according to the present embodiment. A juke apparatus is an information recording/reproducing apparatus of a large capacity having an auto-changer mechanism for changing recording media.

FIG. 72is a perspective view showing the exterior of the juke apparatus, andFIG. 73is a block diagram of a circuit configuration of the juke apparatus. The juke apparatus has: a front panel block401provided on the front side of the juke apparatus; a robotics block402that forms the interior of the juke apparatus; a rear panel block403provided on the rear side of the juke apparatus; a first disk array404provided inside the juke apparatus and constituted by a plurality of optical information recording/reproducing apparatuses coupled to each other; a second disk array405similarly constituted by a plurality of optical information recording/reproducing apparatuses coupled to each other; and a power supply block406for supplying predetermined power to each part of the juke apparatus.

The front panel block401has a front door407which is opened and closed for purposes such as changing disk arrays404and405, and a front panel408.

On the front panel408, there is provided a keypad409having various operating keys; a display410for displaying modes of operation and the like; a functional switch411for instructing opening and closing of the front door407; a mail slot412which is a port to insert and eject an optical information recording medium1; a transfer motor413for transferring an optical information recording medium1inserted through the mail slot412to a mail box which is not shown and for transferring an optical information recording medium1to be ejected from the main box to the mail slot412; and a full sensor414for detecting that the number of optical information recording media1inserted into the juke apparatus has reached a predefined number.

On the front door407, there is provided a door sensor415for detecting opened and closed states of the front door407; a door lock solenoid416for controlling the opening and closing of the front door407; and an interlock switch417for controlling the opening and closing of the front door407in accordance with operations on the functional switch411.

The robotics block402has: a lower magazine421capable of containing, for example, ten optical information recording media1; an upper magazine422stacked on top of the lower magazine421and capable of containing, for example, ten optical information recording media1; and a controller block423for controlling the juke apparatus as a whole.

The robotics block402further has: a grip operation motor424for controlling a grip operation of a manipulator which is not shown to move an optical information recording medium1inserted into the juke apparatus to a predetermined location; a grip operation motor controller425for controlling the rotating speed and direction of the grip operation motor424under the control of the controller block423; and a grip operation encoder426for detecting the rotating speed and direction of the grip operation motor424and for supplying the detected data to the controller block423. Further, the robotics block402has: a rotating operation motor427for controlling the manipulator for rotation in a clockwise direction, a counterclockwise direction or in both directions; a rotating operation motor controller428for controlling the rotating speed and direction of the rotating operation motor427under the control of the controller block423; and a rotating operation encoder429for detecting the rotating speed and direction of the rotating operation motor427and for supplying the detected data to the controller block423. The robotics block402further has: a vertical operation motor430for controlling upward and downward movements of the manipulator; a vertical operation motor controller431for controlling the rotating speed and direction of the vertical operation motor430under the control of the controller block423; and a vertical operation encoder432for detecting the rotating speed and direction of the vertical operation motor430and for supplying the detected data to the controller block423.

The robotics block402further has: a transfer motor controller433for controlling the rotating speed and direction of the transfer motor413for the operation of inserting and ejecting optical information recording media1through the mail slot412; a clear pass sensor434; and a clear pass emitter420.

The rear panel block403has: an RS232C connector terminal which is an input/output terminal for serial transmission; a UPS (uninterruptible power system) connector terminal436; a first SCSI (small computer system interface) connector terminal437which is an input/output terminal for parallel transmission; a second SCSI connector terminal438which is also an input/output terminal for parallel transmission; and an AC (alternating current) power supply connector terminal439connected to a mains power supply.

Each of the RS232C connector terminal435and UPS connector terminal436is connected to the controller block423. The controller block423converts serial data supplied through the RS232C connector terminal435into parallel data and supplies the data to the disk arrays404and405. It also converts parallel data from disk arrays404and405into serial data and supplies the data to the RS232C connector terminal435.

Each of the SCSI connector terminals437and438is connected to the controller block423and disk arrays404and405. The disk arrays404and405exchange data directly through the SCSI connector terminals437and438, and the controller block423converts parallel data from the disk arrays404and405into serial data and supplies the data to the RS232C connector terminal435.

The AC power supply connector terminal439is connected to the power supply block406. The power supply block406generates power of +5 V, +12 V, +24 V and −24 V based on the mains power supply obtained through the AC power supply connector terminal439and supplies the power to other blocks.

The manipulator which is not shown has a carriage having a gripper for performing operations such as picking up optical information recording media1transferred to the mail box through the mail slot412one by one, a carriage holding portion for holding the carriage, and a driving portion for controlling the carriage for vertical, horizontal, back-and-forth and rotary movements. Inside the juke apparatus, there is provided four columns which define a substantially rectangular configuration on the bottom thereof and which are erected to extend perpendicularly to the bottom from the four corners of the rectangular configuration to the top surface of the juke apparatus. The carriage holding portion holds the carriage such that it can make lateral, back and forth and rotary movements and has column gripping portions on both ends thereof for gripping the columns to allow the carriage holding portion to move vertically along the four columns.

The carriage driving portion generates a driving force to control such a manipulator for vertical movements along the columns, generates a driving force to control the carriage for lateral, back and forth and rotary movements and generates a driving force to pick up an optical information recording medium1with the gripper.

As shown inFIG. 72, the front door407is cantilevered by a hinge450at one end thereof to be able to open and close, and each of the lower magazine421, the upper magazine422and the first and second disk arrays404and405can be pulled out or loaded by opening and closing the front door407. Each of the magazines421and422has a boxy configuration for containing ten optical information recording media1each housed in a cartridge in the form of a stack in parallel with the bottom of the juke apparatus, and an optical information recording medium1is inserted from the rear side of each of the magazines421and422(the side of each of the magazines421and422that is opposite to the front side thereof where the front door407is located when it is mounted in the juke apparatus). Optical information recording media1can be mounted at one time by a user removing the magazines421and422to load it manually and mounting the magazines421and422loaded with the optical information recording media1in the juke apparatus. When optical information recording media1are inserted through the mail slot412, the inserted optical information recording media1are transferred to the mail box, and the optical information recording media1transferred to the mail box are loaded by the manipulator into the magazines421and422. Thus, optical information recording media1can be automatically loaded into the magazines421and422.

Each of the first and second disk arrays404and405has a RAID controller and a drive array formed by coupling first through fifth optical information recording/reproducing apparatuses.

Each of the optical information recording/reproducing apparatuses has a disk insertion/ejection port, and optical information recording media1are inserted in and ejected from each of the optical information recording/reproducing apparatuses through the disk insertion/ejection port. The RAID controllers are connected to the controller block423and control the optical information recording/reproducing apparatuses according to the recording method of RAID-1, RAID-3 or RAID-5 under the control of the controller block423. Each of the recording methods of RAID-1, RAID-3 and RAID-5 is selected through a key operation on the keypad409provided on the front panel408.

In this juke apparatus, data are recorded using the disk arrays404and405in accordance with the recording method of RAID-1, RAID-3 or RAID-5. In order to record data in such a manner, optical information recording media1must be loaded in the juke apparatus in advance. There are two methods for loading the juke apparatus with the optical information recording media1.

As shown inFIG. 72, a first method of loading is a method wherein the front door407is opened to remove the lower magazine421and the upper magazine422and optical information recording media1are manually loaded in the magazines421and422.

A second method of loading is a method wherein optical information recording media1are loaded one by one through the mail slot412as shown inFIG. 73. When an optical information recording medium1is loaded into the mail slot412, the controller block423detects it and controls the driving of the transfer motor413to transfer the optical information recording medium1to the mail box. When the optical information recording medium1is transferred to the mail box, the controller block423controls the driving of the vertical operation motor430to move the manipulator toward the mail box and controls the driving of the grip operation motor424to move the optical information recording medium1picked up by the gripper provided on the manipulator to a vacant disk housing portion of the magazine421or422. The driving of the grip operation motor424is controlled to release the optical information recording medium1held by the gripper in the disk housing portion. The controller block423controls each portion to repeat such a series of operations each time an optical information recording medium1is inserted through the mail slot412.

When the magazines421and422are thus loaded with optical information recording media1according to the first or second method of loading, the controller block423controls the manipulator to transfer the optical information recording media1contained in the lower magazine421or the upper magazine422to the first disk array404or the second disk array405. Each of the disk arrays404and405can be loaded with five optical information recording media1and, therefore, five out of the total of twenty optical information recording media1contained in the magazines421and422are loaded in the first disk array404, and another five are loaded in the second disk array405by the manipulator.

To record data, a user operates the keypad409to select a desired recording method from among the RAID-1, RAID-3 and RAID-5 recording methods and operates the keypad409to instruct the start of data recording. The data to be recorded are supplied to the disk arrays404and405through the RS232C connector terminal435or the first and second SCSI connector terminals437and438. When the start of data recording is instructed, the controller block423controls the disk arrays404and405through the RAID controllers provided at the disk arrays404and405to enable recording of data according to the selected recording method.

In this juke apparatus, five optical information recording/reproducing apparatuses provided for each of the disk arrays404and405are substituted for hard disk devices in a conventional RAID utilizing hard disk devices to record data according to a recording method selected from among the RAID-1, RAID-3 and RAID-5 recording methods. The data interfaces of this juke apparatus are not limited to those mentioned in the above description.

The optical information recording/reproducing apparatus according to the present embodiment makes it possible to achieve copy protection and security easily like the first embodiment.

It is also possible to provide information distribution services e.g., a service in which optical information recording media1having a multiplicity of kinds of information (e.g., various kinds of software) recorded thereon with different modulation patterns for reference light are provided to users and in which pieces of information of the reference light modulation patterns to enable reproduction of each of the various kinds of information are separately sold to the users as key information as requested by the users.

Phase modulation patterns for reference light to serve as the key information to retrieve predetermined information from an optical information recording medium1may be created based on information specific to a person who is a user. Such information specific to a person includes a secret number, a fingerprint, a voiceprint and an iris pattern.

FIG. 74shows an example of a configuration of major parts of an optical information recording/reproducing apparatus according to the present embodiment in which phase modulation patterns for reference light are created based on personal information as described above. In this example, the optical information recording/reproducing apparatus has: a personal information input portion501for inputting information specific to a person such as a fingerprint; a phase modulation pattern encoder502for creating a phase modulation pattern for reference light based on the information input through the personal information input portion501and for supplying information on the created modulation pattern to the phase-spatial light modulator117as desired when information is recorded or reproduced to drive the phase-spatial light modulator117; and a card issuing and input portion503for issuing a card504on which the information on the modulation pattern created by the phase modulation pattern encoder502is recorded and for sending the information on the modulation pattern recorded on the card504to the phase modulation pattern encoder502when the card504is loaded therein.

In the example shown inFIG. 74, when a user inputs information specific to the person such as a fingerprint to the personal information input portion501to record information in an optical information recording medium1using the optical information recording/reproducing apparatus according to the present embodiment, the phase modulation pattern encoder502creates a phase modulation pattern for reference light based on the information input through the personal information input portion501and supplies information on the created modulation pattern to the phase-spatial light modulator117to drive the phase-spatial light modulator117during the recording of the information. As a result, the information is recorded in the optical information recording medium1in association with the phase modulation pattern for reference light created based on the information specific to the person who is the user. The phase modulation pattern encoder502transmits the information on the created modulation pattern to the card issuing and input portion503, and the card issuing and input portion503issues a card504on which the transmitted information on the modulation pattern is recorded.

To reproduce the information recorded as described above from the optical information recording medium1, the user either inputs the information specific to the person to the personal information input portion501as in recording, or loads the card504into the card issuing and input portion503.

When the information specific to the person is input to the personal information input portion501, the phase modulation pattern encoder502creates a phase modulation pattern for reference light based on the information input through the personal information input portion501and supplies information on the created modulation pattern to the phase-spatial light modulator117to drive the phase-spatial light modulator117during the reproduction of the information. At this time, if the phase modulation pattern for the light at recording agrees with the phase modulation pattern for reference light at reproduction, the desired information is reproduced. In order to prevent the phase modulation pattern encoder502from creating different modulation patterns at recording and reproduction in spite of the fact that the same information specific to the person is input to the personal information input portion501, the phase modulation pattern encoder502may be adapted to create the same modulation pattern even if there is some difference between the pieces of information input through the personal information input portion501.

When the card504is loaded into the card issuing and input portion503, the card issuing and input portion503transmits the information on the modulation pattern recorded on the card504to the phase modulation pattern encoder502, and the phase modulation pattern encoder502supplies the transmitted information on the modulation pattern to the phase-spatial light modulator117to drive the phase-spatial light modulator117. Thus, the desired information is reproduced.

The configuration, operation and effects of the present embodiment are otherwise substantially the same as those of the first embodiment.

The present invention is not limited to the above-described embodiments and may be modified in various ways. For example, address information and the like is recorded in advance in the address servo areas6of the optical information recording medium1in the form of embossed pits in the above-described embodiments; however, instead of providing embossed pits in advance, formatting may alternatively be carried out by selectively illuminating regions near the protective layer4of the hologram layer3in the address servo areas6with high power laser light to selectively change the refractivity of such regions, thereby recording address information and the like.

As the element for detecting information recorded in the hologram layer3, a smart optical sensor in which a MOS type solid state image pick-up element and a signal processing circuit are integrated on a single chip (see an article “O plus E, September, 1996, No. 202”, pp. 93–99 by way of example) may be used instead of a CCD array. Since such a smart optical sensor has a high transfer rate and a high speed operating function, the use of such a smart optical sensor allows high speed reproduction, e.g., reproduction at a transfer rate on the order of Gbit/sec.

Especially, when a smart optical sensor is used as the element for detecting information recorded in the hologram layer3, instead of recording address information and the like in the address servo areas6of the optical information recording medium1using embossed pits in advance, address information and the like in a predetermined pattern may be recorded in advance using the same method as for recording in the data areas7utilizing holography, in which case the address information and the like is detected by the smart optical sensor during a servo operation with the pick-up set in the same state as in reproduction. In this case, a basic clock and address can be directly obtained from the data detected by the smart optical sensor. A tracking error signal can be obtained from information of the position of a reproduction pattern on the smart optical sensor. Focus servo can be performed by driving the objective lens12so as to maximize the contrast of the reproduction pattern on the smart optical sensor. Focus servo can be performed also during reproduction by driving the objective lens so as to maximize the contrast of a reproduction pattern on the smart optical sensor.

In the above-described embodiments, information on the modulation pattern of reference light and information on the wavelength thereof may be supplied to the controller90from an external host apparatus.

As described above, in the first optical information recording apparatus or optical information recording method according to the invention, the information recording layer is illuminated with information light carrying information and reference light for recording having a spatially modulated phase on the same side thereof, which is advantageous in that information can be recorded on a multiplex basis utilizing phase-encoding multiplexing and in that the optical system for recording can be configured compactly.

The first optical information recording apparatus according to the invention is further advantageous in that light for recording can be positioned with high accuracy by controlling the positions of information light and reference light for recording relative to the optical information recording medium using information recorded in a positioning region of the optical information recording medium.

In the first optical information recording apparatus according to the invention, the recording optical system projects information light and reference light for recording such that the optical axis of the information light and the optical axis of the reference light for recording are located on the same line, which provides another advantage in that the optical system for recording can be configured more compactly.

In the first optical information recording apparatus according to the invention, the information light generation means generates information light in a plurality of wavelength bands, and the recording reference light generation means generates reference light for recording in the same plurality of wavelength bands as those for the information light, which provides another advantage in that more information can be recorded on a multiplex basis.

The first optical information recording apparatus according to the invention has control means for controlling the information light generation means and the recording reference light generation means such that information is recorded with redundancy in the optical information recording medium, which provides another advantage in that reliability can be improved.

In the first optical information reproducing apparatus or optical information reproducing method according to the invention, the information recording layer is illuminated with reference light for reproduction having a spatially modulated phase; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected. This is advantageous in that information recorded on a multiplex basis utilizing phase-encoding multiplexing can be reproduced and in that the optical system for reproduction can be configured compactly.

The first optical information reproducing apparatus according to the invention is further advantageous in that light for reproduction can be positioned with high accuracy by controlling the position of the reference light for reproduction relative to the optical information recording medium using information recorded in a positioning region of the optical information recording medium.

In the first optical information reproducing apparatus according to the invention, the reproducing optical system projects reference light for reproduction and collects reproduction light such that the optical axis of the reference light for reproduction and the optical axis of the reproduction light are located on the same line, which provides another advantage in that the optical system for reproduction can be configured more compactly.

In the first optical information reproducing apparatus according to the invention, the reproduction reference light generation means generates reference light for reproduction in a plurality of wavelength bands, and the detection means detects reproduction light in the same plurality of wavelength bands as those for the reference light for reproduction, which provides another advantage in that it is possible to reproduce information recorded using reference light for recording and information light in a plurality of wavelength bands.

In the second optical information recording apparatus or optical information recording method according to the invention, the information recording layer is illuminated with information light having a selected wavelength and carrying information and reference light for recording having a selected wavelength on the same side thereof, which is advantageous in that information can be recorded on a multiplex basis utilizing wavelength multiplexing and in that the optical system for recording can be configured compactly.

The second optical information recording apparatus according to the invention is further advantageous in that light for recording can be positioned with high accuracy by controlling the positions of information light and reference light for recording relative to the optical information recording medium using information recorded in a positioning region of the optical information recording medium.

In the second optical information recording apparatus according to the invention, the recording optical system projects information light and reference light for recording such that the optical axis of the information light and the optical axis of the reference light for recording are located on the same line, which provides another advantage in that the optical system for recording can be configured more compactly.

In the second optical information reproducing apparatus or optical information reproducing method according to the invention, the information recording layer is illuminated with reference light for reproduction having a selected wavelength; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected. This is advantageous in that information recorded on a multiplex basis utilizing wavelength multiplexing can be reproduced and in that the optical system for reproduction can be configured compactly.

The second optical information reproducing apparatus according to the invention is further advantageous in that light for reproduction can be positioned with high accuracy by controlling the position of reference light for reproduction relative to the optical information recording medium using information recorded in a positioning region of the optical information recording medium.

In the second optical information reproducing apparatus according to the invention, the reproducing optical system projects reference light for reproduction and collects reproduction light such that the optical axis of the reference light for reproduction and the optical axis of the reproduction light are located on the same line, which provides another advantage in that the optical system for reproduction can be configured more compactly.

In the third optical information recording apparatus or optical information recording method according to the invention, the information recording layer is illuminated with information light having a selected wavelength and carrying information and reference light for recording having a selected wavelength and having a spatially modulated phase on the same side thereof, which is advantageous in that information can be recorded on a multiplex basis utilizing wavelength multiplexing and phase-encoding multiplexing and in that the optical system for recording can be configured compactly.

The third optical information recording apparatus according to the invention is further advantageous in that light for recording can be positioned with high accuracy by controlling the positions of information light and reference light for recording relative to the optical information recording medium using information recorded in a positioning region of the optical information recording medium.

In the third optical information recording apparatus according to the invention, the recording optical system projects information light and reference light for recording such that the optical axis of the information light and the optical axis of the reference light for recording are located on the same line, which provides another advantage in that the optical system for recording can be configured more compactly.

In the third optical information reproducing apparatus or optical information reproducing method according to the invention, the information recording layer is illuminated with reference light for reproduction having a selected wavelength and having a spatially modulated phase; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected. This is advantageous in that information recorded on a multiplex basis utilizing wavelength multiplexing and phase-encoding multiplexing can be reproduced and in that the optical system for reproduction can be configured compactly.

The third optical information reproducing apparatus according to the invention is further advantageous in that light for reproduction can be positioned with high accuracy by controlling the position of reference light for reproduction relative to the optical information recording medium using information recorded in a positioning region of the optical information recording medium.

In the third optical information reproducing apparatus according to the invention, the reproducing optical system projects reference light for reproduction and collects reproduction light such that the optical axis of the reference light for reproduction and the optical axis of the reproduction light are located on the same line, which provides another advantage in that the optical system for reproduction can be configured more compactly.

In the fourth optical information recording apparatus according to the invention, the pick-up device provided in a face-to-face relationship with the optical information recording medium projects information light and reference light for recording upon the information recording layer on the same side thereof to record information in the information recording layer using an interference pattern as a result of interference between the information light and the reference light for recording, which is advantageous in that the optical system for recording can be configured compactly and in that random access to the optical information recording medium can be performed easily.

In the fourth optical information recording apparatus according to the invention, the recording optical system projects information light and reference light for recording such that the optical axis of the information light and the optical axis of the reference light for recording are located on the same line, which provides another advantage in that the optical system for recording can be configured more compactly.

In the fourth optical information recording apparatus according to the invention, the light source emits beams of light in a plurality of wavelength bands, which provides another advantage in that more information can be recorded on a multiplex basis.

In the fourth optical information recording apparatus according to the invention, the pick-up device has first light quantity monitoring means for monitoring the quantity of information light and second light quantity monitoring means for monitoring the quantity of reference light for recording, which provides another advantage in that the quantities of the information light and the reference light for reproduction can be independently monitored and controlled.

In the fourth optical information recording apparatus according to the invention, the pick-up device has reproduction light detection means for detecting reproduction light as a result of diffraction of reference light for recording caused by an interference pattern formed in the information recording layer during the recording of information in the information recording layer, which provides another advantage in that recorded information can be verified immediately after the recording of the information.

The fourth optical information recording apparatus according to the invention has control means for controlling the recording operation based on information on reproduction light detected by reproduction light detection means, which provides another advantage in that the recording operation can be performed in an optimum recording state.

The fourth optical information recording apparatus according to the invention has control means for controlling illuminating conditions for information light and reference light for recording during multiplex recording based on information on reproduction light detected by reproduction light detection means, which provides another advantage in that multiplex recording can be performed under optimum conditions.

In the fourth optical information recording apparatus according to the invention, the pick-up device has fixing means for fixing information recorded using an interference pattern in the information recording layer, which provides another advantage in that information can be fixed.

In the fourth optical information recording apparatus according to the invention, an optical information recording medium is used which has a recording region that allows recording of information using an interference pattern and positioning regions provided on both sides of the recording region for positioning information light and reference light for recording, and control means is provided for reciprocating the illuminating positions of the information light and the reference light for recording by way of the recording region and at least a part of the positioning regions on both sides thereof to position the information light and the reference light for recording relative to the recording region based on information obtained from the positioning regions. This provides another advantage in that it is possible to prevent shift of a recording position even when recording is performed for a relatively long time in the same location of an optical information recording medium.

In the fourth optical information recording apparatus according to the invention, by providing a plurality of pick-up devices, another advantage is achieved in that simultaneous recording can be performed on a single optical information recording medium with the plurality of pick-up devices to improve recording performance.

In the fourth optical information reproducing apparatus according to the invention, the pick-up device provided in a face-to-face relationship with an optical information recording medium projects reference light for reproduction upon the information recording layer; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the reproduction light is detected, which is advantageous in that the optical system for reproduction can be configured compactly and in that random access to the optical information recording medium can be performed easily.

In the fourth optical information reproducing apparatus according to the invention, the reproducing optical system projects the reference light for reproduction and collects reproduction light such that the optical axis of the reference light for reproduction and the optical axis of the reproduction light are located on the same line, which provides another advantage in that the optical system for reproduction can be configured more compactly.

In the fourth optical information reproducing apparatus according to the invention, the light source emits beams of light in a plurality of wavelength bands, and detection means detects reproduction light in the same plurality of wavelength bands as those for the beams of light emitted by the light source. This provides another advantage in that it is possible to reproduce information recorded in an optical information recording medium on a multiplex basis using light in a plurality of wavelength bands.

In the fourth optical information reproducing apparatus according to the invention, the pick-up device has light quantity monitoring means for monitoring the quantity of reference light for reproduction, which provides another advantage in that the quantity of the reference light for reproduction can be monitored and controlled.

In the fourth optical information reproducing apparatus according to the invention, an optical information recording medium is used which has a recording region that allows recording of information using an interference pattern and positioning regions provided on both sides of the recording region for positioning reference light for reproduction, and control means is provided for reciprocating the illuminating position of the reference light for reproduction by way of the recording region and at least a part of the positioning regions on both sides thereof to position the reference light for reproduction relative to the recording region based on information obtained from the positioning regions. This provides another advantage in that it is possible to prevent shift of a reproducing position even when reproduction is performed for a relatively long time in the same location of an optical information recording medium.

In the fourth optical information reproducing apparatus according to the invention, by providing a plurality of pick-up devices, another advantage is achieved in that simultaneous reproduction can be performed on a single optical information recording medium with the plurality of pick-up devices to improve reproducing performance.

In the optical information recording/reproducing apparatus according to the invention, during recording, the pick-up device provided in a face-to-face relationship with the optical information recording medium projects information light and reference light for recording upon the information recording layer on the same side thereof to record information in the information recording layer using an interference pattern as a result of interference between the information light and the reference light for recording. During reproduction, the pick-up device illuminates the information recording layer with reference light for reproduction; reproduction light generated at the information recording layer when illuminated with the reference light for reproduction is collected on the same side of the information recording layer that is illuminated with the reference light for reproduction; and the collected reproduction light is detected. This is advantageous in that the optical system for recording and reproduction can be configured compactly and in that random access to the optical information recording medium can be performed easily.

In the optical information recording/reproducing apparatus according to the invention, by providing a plurality of pick-up devices, another advantage is achieved in that simultaneous recording and reproduction can be performed on a single optical information recording medium with the plurality of pick-up devices to improve recording and reproducing performance.

The optical information recording medium according to the invention has: a first information layer for recording information in the form of an interference pattern as a result of interference between information light and reference light for recording utilizing holography and for generating reproduction light associated with the recorded information when illuminated with reference light for reproduction; and a second information layer which is provided in a position different from the position of the first information layer in the direction of the thickness and in which information is recorded using means different from that for the recording of information in the first information layer. This is advantageous in that the positioning of information light, reference light for recording and reference light for reproduction relative to the first information layer can be performed using the information recorded in the second information layer, and in that directory information, directory management information and the like on the information recorded in the first information layer can be recorded in the second information layer to make it possible to perform random access and high density recording easily.

In the optical information recording medium according to the invention, a gap having a predetermined thickness is formed between the first information layer and the second information layer, which provides another advantage in that a sufficiently large interference region can be formed between reference light for recording and information light in the first information layer while allowing reproduction of information recorded in the second layer.

It will be understood from the above description that the invention may be carried out in various modes and modified modes. Therefore, the present invention may be carried out in modes other than the above-described best modes for carrying out the invention within the scope of equivalence of the appended claims.