JP2011013531A - Information recording method, two-dimensional information creating method, information reproducing method, and information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information recording device having high signal qualities upon reproduction and for recording information in a holographic information recording medium.SOLUTION: The information recording device 100 for recording information in a holographic information recording medium includes a temperature detecting part 25 that detects recording condition information including temperature information of an information recording medium 15. An encoder 10 converts the detected information into two-dimensional information PDT that includes a data information region for storing data information DT and a recording condition storage region for storing the recording condition information TP. The recording condition storage region is disposed at a position where the reproducible region determined by angle selectivity of interference fringes reaches maximum in the two-dimensional information.

Description

  The present invention relates to an information recording method for recording information on a holographic information recording medium, a method for creating the recorded two-dimensional information, an information reproducing method for reproducing information recorded on the holographic information recording medium, and information The present invention relates to a recording medium.

  In holographic recording in which information is recorded using holography, signal light and reference light are superimposed, and interference fringes (holograms) generated by interference of these lights are written on the information recording medium. Specifically, light beams emitted from the same light source are separated into reference light and signal light, and a spatial light modulator performs amplitude modulation corresponding to page data which is two-dimensional information on the signal light. The modulated signal light and reference light are superposed in the hologram recording material, and interference fringes formed at that time are written as refractive index modulation or intensity modulation.

  At the time of reproduction, only the reference light is generated from the light source, and the reference light is applied to the interference fringes recorded in the hologram recording material. By such irradiation, a part of the reference light is diffracted by the recorded interference fringes, and reproduction light having two-dimensional information is generated. The reproduced light is detected by a photodetector such as an image sensor to obtain two-dimensional information, and the recorded information is reproduced by decoding the two-dimensional information.

  As a holographic recording method, an “angle multiplexing method” is well known. In the “angle multiplexing method”, the reference light and the signal light are once branched, and the signal light condensed by the lens and the reference light that is parallel light are superimposed in the hologram recording material.

  In the “angle multiplexing method”, the angle fringe recording can be performed by changing the incident angle of the reference light to record the interference fringes in the same volume of the information recording medium. By recording (multiple recording) a plurality of page data in the same volume, the recording density per unit area on the information recording medium surface is dramatically increased as compared with a conventional optical disc. A series of holograms recorded in a multiplexed manner at the same location is called a “book”. When one book is recorded, the recording position is moved within the surface of the information recording medium and moved to the next position to record the hologram.

  In angle multiplex recording, when a thick hologram recording material is used, recording can be performed with a smaller amount of change in the incident angle of the reference light than when a thin hologram recording material is used. As the thickness increases, the region in which the reference light and signal light overlap in the hologram recording material becomes three-dimensional, and as a result, the hologram reproduction condition (Bragg condition) for the incident angle of the reference light becomes strict. This is because the hologram cannot be reproduced even if the change amount of the incident angle is small.

  An information recording medium generally includes a hologram recording material and a substrate that supports the hologram recording material, and the hologram recording material is sandwiched between the substrates.

  A photopolymer material may be used as the hologram recording material. Photopolymer materials are superior to photorefractive crystals in terms of dynamic range of sensitivity and recording sensitivity (cumulative interference fringe intensity: M number), and are often used in research and development applications. In recent years, thick materials having a thickness of several hundred μm to several mm have been produced, which is an important material for increasing the capacity of holographic recording.

  The photopolymer material is mainly composed of a photopolymerization initiator, a monomer, and a binder polymer. When the photopolymer material is irradiated with interference fringes, the photopolymerization initiator absorbs light in accordance with the light intensity of the interference fringes, the photopolymerization reaction is started, and the monomer polymerization reaction occurs. In the bright part of the interference fringes where the monomer has undergone a polymerization reaction, the monomer concentration decreases and a monomer concentration distribution occurs. According to the concentration distribution of the monomer, the monomer diffuses from the dark part to the bright part of the interference fringes. Thereby, the refractive index distribution of the monomer according to the light intensity of the interference fringes is formed.

  The photopolymer material may expand and contract and change its volume due to a temperature change and a photopolymerization reaction. If there is a temperature difference between the photopolymer material during recording and playback, the shape of the recorded interference fringes will change as the photopolymer material volume changes, and the Bragg condition will change between recording and playback. Sometimes it doesn't match. In this case, there is a problem in that reproduced light cannot be obtained even if reference light is incident under the same conditions as in recording.

  For example, when both the reference light and the signal light used for recording interference fringes are plane waves, the interference fringe inclination angle and the grating interval are both single. Therefore, in this case, the hologram is reproduced even if the shape of the interference fringes changes by changing the incident angle of the reference light at the time of reproduction and correcting the incident angle of the reference light so as to satisfy the Bragg condition. Is possible.

  In angle multiplexing recording, signal fringe that is convergent light and reference light that is parallel light are overlapped to record interference fringes. In this case, since the signal light that is the convergent light includes a plurality of plane wave components having different incident angles, interference fringes having various inclination angles are formed. When the hologram formed in this way is reproduced only by correcting the incident angle of the reference light, the incident angle correction amount of the reference light is different for a plurality of interference fringes having different inclination angles. Therefore, the entire signal light cannot be reproduced, and a part of the reproduced signal light is missing.

  As a method of controlling the lack of the reproduced image, there is a method of correcting the incident light correction amount of the reference light to a plurality of interference fringes having different inclination angles and lattice intervals by correcting the wavelength of the reference light. In other words, by performing both correction of the wavelength of the reference light and correction of the incident angle of the reference light, it becomes possible to reproduce the entire signal light even when a volume change occurs (for example, patent document). 1).

  Here, Patent Document 1 discloses a technique for recording recording conditions and characteristics of a holographic recording material in a header region in an information recording medium. After reading these conditions during reproduction, the wavelength correction amount and the incident angle correction amount of the reference light with respect to the volume change are calculated, and the adjustment process accompanying the reproduction of the entire signal light is speeded up.

  In Patent Document 2, recording conditions and characteristics of a holographic recording material are recorded together with recording information at the time of data recording. Furthermore, the recording tolerance and the like are recorded on the information recording medium with a modulation unit larger than the minimum modulation unit used in information recording, thereby increasing the read tolerance during reproduction.

  In Patent Document 3, during reproduction, temperature information is acquired from header information of an information recording medium, and a temperature detected by a temperature detection unit is acquired. Based on the acquired temperature differences, the reproduction wavelength shift amount for canceling the influence of the interference fringe shape change is determined.

JP 2006-349831 A JP 2007-163643 A JP 2006-267554 A

  However, when the recording condition is recorded by providing the header area, the user usable area of the information recording medium is reduced. In addition, when an external resonator type semiconductor laser is used as a wavelength tunable light source, the state of the recording light source differs between header information recording and data recording due to the effect of semiconductor laser mode hopping or information recording medium temperature drift. . As a result, even if the reference light is corrected using the header information during reproduction, high-quality reproduction signal light cannot be obtained.

  Further, when recording conditions and characteristics of the hologram recording material are recorded together with information, the signal light may be chipped if the temperature changes during reproduction. In this case, even if recording is performed in a modulation unit larger than the minimum modulation unit used in information recording and the reproduction tolerance is increased, there is a possibility that the recording conditions and the like cannot be read out.

  Therefore, an object of the present invention is to record information on a holographic information recording medium capable of reproducing information with high accuracy even if the hologram reproducing condition changes due to expansion and contraction of the information recording medium through temperature change. To provide an information recording method, a method for producing the recorded two-dimensional information, an information reproducing method for reproducing information recorded on a holographic information recording medium, and an information recording medium.

  According to one aspect of the present invention, there is provided an information recording method for recording information on an information recording medium using interference fringes formed by interference between reference light and signal light, the recording including temperature information of the information recording medium A step of detecting condition information, and a step of converting into two-dimensional information including a data information area for storing data information recorded on the information recording medium and a recording condition storage area for storing the detected recording condition information. The recording condition storage area is stored in the two-dimensional information at the position where the reproducible area obtained from the angle selectivity of the interference fringes is maximized, and is modulated based on the reference light and the two-dimensional information. A step of recording interference fringes on the information recording medium by causing the signal light to interfere with the information recording medium.

  Preferably, the position where the reproducible area obtained from the angle selectivity of the interference fringe is maximized is that the angle between the reference light and the signal light incident on the information recording medium during recording is far from 90 degrees in the two-dimensional information. This is a region on the side close to 0 degrees or 180 degrees.

  According to another aspect of the present invention, there is provided a two-dimensional information creation method used for information recording in which interference fringes are recorded as interference between a reference light and a signal light obtained by modulating two-dimensional information, and recorded on an information recording medium Creating a data information area for storing the recorded data information, and creating a recording condition storage area for storing the recording condition information, and the recording condition storage area has an angle of interference fringes in the two-dimensional information. It is arranged at a position where the reproducible area obtained from the selectivity is maximized.

  According to still another aspect of the present invention, there is provided an information reproducing method for reproducing two-dimensional information recorded as interference fringes of reference light and signal light on an information recording medium by irradiation of the reference light, wherein the reference light is the information recording medium. Generating two-dimensional information recorded on the information recording medium by receiving reproduction light generated by irradiating the recording medium, and reading out data information and recording condition information included in the two-dimensional information. The storage area is arranged in the two-dimensional information at a position where the reproducible area obtained from the angle selectivity of the interference fringes is maximized.

  Preferably, the method further includes the step of controlling the incident angle of the reference light to the information recording medium so that the reproducible area in the reproduced two-dimensional information is maximized.

  Preferably, based on the temperature information at the time of reproduction and the temperature information at the time of reproduction and the recording condition information, the incident angle correction amount of the reference light with respect to the signal light having different incident angles modulated by the two-dimensional information Deriving the reference light wavelength correction amount and incident angle correction amount to reduce the change, and controlling the reference light wavelength and reference light incident angle based on the wavelength correction amount and the incident angle correction amount Further comprising the step of:

  According to still another aspect of the present invention, there is provided an information recording medium in which interference between the reference light and the signal light modulated based on the two-dimensional information is recorded as interference fringes, and the two-dimensional information is recorded on the information recording medium. A data information area for storing recorded data information and a recording condition storage area for storing recording condition information, and the recording condition storage area is a reproducible area determined from the angle selectivity of interference fringes in two-dimensional information Is placed at the position where the is the maximum.

  According to the present invention, it is possible to reproduce information with high accuracy even if the hologram reproduction condition changes due to expansion and contraction of the information recording medium through temperature change.

It is the figure which showed the schematic structure of the holographic recording and reproducing apparatus 100, and the operation | movement at the time of recording. It is a figure for demonstrating the relationship between the direction of the signal light SGL and reference light RFL which inject into the information recording medium 15, and the arrangement direction of the recording condition storage area TPp. It is a recording operation procedure flowchart of a holographic recording / reproducing apparatus. FIG. 2 is a diagram showing a schematic configuration of the holographic recording / reproducing apparatus 100 and an operation during reproduction. It is the figure which showed the mode of the signal light SGL and the reference light RFL which inject into the information recording medium 15 at the time of recording. FIG. 6 is a diagram illustrating a state in which signal light SGL having different incident angles interferes with reference light RFL in the information recording medium 15. It is the figure which showed incident angle correction amount (DELTA) (theta) R of the reference light RFL with respect to incident angle (theta) S of signal light SGL. Relationship between diffraction efficiency from hologram and incident angle of reference light RFL to information recording medium when interference fringes with recorded single tilt angle and interference fringe interval are recorded (angle selectivity of reference light RFL) FIG. It is the figure which showed the mode of the signal light SGL and the reference light RFL which inject into the information recording medium 15 at the time of recording. It is the figure which showed angle selectivity and the reproducible area | region in case the signal light SGL from position PA is reproduced | regenerated. It is the figure which showed angle selectivity and the reproducible area | region in case the signal light SGL from the position PB is reproduced | regenerated. It is the figure which showed incident angle correction amount (DELTA) (theta) rc of the reference light RFL with respect to the incident angle (theta) s of the signal light SGL at the time of adding correction | amendment. FIG. 4 is a flowchart showing an operation procedure at the time of reproduction of the holographic recording / reproducing apparatus 100. It is a flowchart which shows the recording condition information acquisition method in case recording condition information TP is recorded on the area | region which becomes the largest of a reproducible area | region. In the information recording medium 15, it is a figure which shows the cross-sectional structure of a hologram recording material and the board | substrate which supports this.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[Configuration and operation during recording]
FIG. 1 is a diagram showing a schematic configuration of a holographic recording / reproducing apparatus 100 during recording and an operation during recording.

  Referring to FIG. 1, holographic recording / reproducing apparatus 100 includes a control system 200 and an optical system 300. The optical system 300 includes a wavelength tunable laser 1, an optical isolator 2, a half-wave plate 3, polarization beam splitters 4 and 7, beam expanding lenses 5 and 6, quarter-wave plates 8 and 21, Spatial light modulator 9, information conversion unit 10, relay lenses 11 and 13, spatial filter 12, objective lens 14, rotation drive mirrors 16 and 22, irradiation position adjusting lenses 19 and 20, and image sensor 23. The control system 200 includes an encoder 10, a decoder 24, a temperature detection unit 25, a memory unit 26, and a control unit 28. Note that the holographic recording / reproducing apparatus 100 may further include a luminance unevenness detector 29 as described later in the operation during reproduction.

  The wavelength tunable laser 1 includes a light source that oscillates a laser beam and a wavelength control unit that controls the oscillation wavelength. As the wavelength tunable laser 1, for example, an external resonator type semiconductor laser can be used. The optical isolator 2 removes reflected light from the optical system after the half-wave plate 3. Thereby, the amount of light returning to the wavelength tunable laser 1 can be reduced, and the oscillation state of the wavelength tunable laser 1 can be further stabilized.

  The holographic recording / reproducing apparatus 100 includes rotation drive mirrors 16 and 22 as an angle deflection unit. The holographic recording / reproducing apparatus 100 records information on the information recording medium 15 and reproduces information from the information recording medium 15. The information recording medium 15 may be either a card type or a rotating disk type. In the following description, the holographic recording / reproducing apparatus 100 that performs recording and reproduction is described. However, as an embodiment, a holographic that performs only recording processing instead of the holographic recording / reproducing apparatus 100 is described. It may be a recording device.

Next, the recording operation of the holographic recording / reproducing apparatus 100 will be described.
The laser beam PL emitted from the wavelength tunable laser 1 passes through the optical isolator 2 and the polarization direction is rotated by the half-wave plate 3. The rotation angle at the half-wave plate 3 is adjusted so that the light intensity ratio between the signal light SGL and the reference light RFL on the information recording medium 15 is optimized. The laser beam PL is separated by the polarization beam splitter 4 into a signal beam SGL passing through the path P1 and a reference beam RFL passing through the path P2.

  The signal light SGL is expanded in beam diameter by the beam expanding lenses 5 and 6 and passes through the polarization beam splitter 7 along the path P3. The transmitted signal light SGL is converted from linearly polarized light to circularly polarized light through the quarter-wave plate 8 and guided to the reflective spatial light modulator 9. The spatial light modulator 9 modulates the light intensity of the signal light SGL based on the page data PDT supplied from the encoder (information conversion unit) 10.

  The temperature detection unit 25 outputs recording condition information TP related to temperature and the like. The temperature detection unit 25 detects the temperature of the hologram recording material (photopolymer material) in the information recording medium 15 by using, for example, a temperature sensor.

  The encoder (information conversion unit) 10 receives the recording condition information TP and the data information DT, and converts the information into two-dimensional page data PDT. In the recording condition information TP, in addition to the temperature information of the hologram recording material at the time of recording, for example, the wavelength at the time of recording by the wavelength tunable laser 1, the incident angle of the reference light RFL, the in-plane direction and the thickness direction of the hologram recording medium 15 Of the linear expansion coefficient, the refractive index of the hologram recording material, the temperature change constant of the refractive index of the hologram recording material, and the linear expansion coefficient in the in-plane direction of the substrate supporting the hologram recording material. Contains information.

  FIG. 15 is a diagram showing a cross-sectional structure of a hologram recording material and a substrate that supports the hologram recording material in the information recording medium 15.

  In the information recording medium 15, the hologram recording material 32 has a structure sandwiched between the substrates 31a and 31b. The substrates 31a and 31b are made of glass, polycarbonate, acrylic resin, or other transparent resin. In the case of the hologram recording material 32 sandwiched between the substrates 31a and 31b as shown in FIG. 15, the amount of expansion or contraction in the thickness direction when a temperature change occurs can be obtained from the linear expansion coefficient of the hologram recording material. As for the amount of expansion or contraction in the direction, since the hologram recording material is sandwiched and supported by the substrate, it is greatly affected by the substrate expansion and contraction, and the amount of expansion and contraction is more accurately obtained from the linear expansion coefficient of the substrate. There are many cases.

  The reproducible area is optimal in accordance with the deformation of the interference light fringe when the temperature of the information recording medium changes between recording and reproduction, and the page data PDT is chipped. It refers to a certain area that can be reproduced without being converted.

  The size of the reproducible area is determined by the relationship between the incident angle of the reference light RFL at the time of recording and the respective incident angles of the collected signal light SGL. The size and position of the reproducible area will be described in detail later in the description of the operation of the hologram recording / reproducing apparatus 100 during reproduction.

  FIG. 2 is a diagram showing an arrangement of page data PDT in the SA-SA ′ cross section of the signal light SGL in FIG. The SA-SA ′ cross section is a focal plane of the relay lens 13 and the objective lens 14 and is optically conjugate with the spatial light modulator surface. The data information DT is arranged in front of the page data PDT, and the recording condition storage area TPp is arranged at a position where the reproducible area is maximized. In this case, even when luminance unevenness occurs during reproduction and a part of the page data PDT cannot be read due to the position of the luminance unevenness, first, the incident angle of the reference light RFL is set so that the width of the reproducible region is maximized. It is possible to read the reproducible area by changing and adjusting. Compared with the case where the recording condition storage area TPp is arranged in an area where the reproducible area is small, it is less likely that the recording condition storage area TPp is not readable, and the recording condition storage area can be easily found. Furthermore, since the area that can be detected at a time becomes large, the amount of recording condition information TP that can be stored can be increased.

  The width of the reproducible region is determined by the angle formed by the reference light RFL and the signal light SGL. Here, the signal light SGL is light collected by the objective lens, and the incident angle of the signal light SGL varies depending on the position in the page data PDT. Therefore, the angle formed by the reference light RFL and the signal light SGL also differs depending on the position of the signal light SGL in the page data PDT, and the width of the reproducible area varies depending on the position in the page data PDT. When angle multiplex recording is performed by changing the incident angle of the reference light RFL, the angle formed by the reference light RFL and the signal light SGL changes according to the incident angle of the reference light RFL, so that the reproducible area is maximized. The position changes in the page data PDT. The width of the reproducible area will be described in the operation during reproduction.

  The recording condition information TP can use information detected and acquired at the start of information recording on the information recording medium 15, but may preferably be updated for each page data PDT. It may be updated every predetermined number of page data PDTs. By sequentially updating in this way, a mode hop occurs in the wavelength tunable laser 1, and even when the recording wavelength changes for each page data PDT or for each predetermined number of page data PDT, more accurate recording condition information TP Can be recorded. Even when the temperature of the information recording medium 15 changes, more accurate recording condition information TP can be recorded.

  Returning to FIG. 1, the signal light SGL that has been intensity-modulated by the spatial light modulator 9 is converted into linearly polarized light having a polarization direction different from that at the time of entering the spatial light modulator 9 by the quarter wavelength plate 8. It is converted and reflected by the polarization beam splitter 7. The reflected signal light SGL passes through the relay lenses 11 and 13 along the path P4. The relay lens 11 is disposed at a position optically separated from the spatial light modulator 9 by a focal length. The relay lens 13 is disposed at a position away from the focal plane of the relay lens 11 by the focal length of the relay lens 13.

  The signal light SGL becomes a Fourier transform image at the focal position of the relay lens 11. The spatial filter 12 inserted in the Fourier transform plane of the relay lens 11 blocks higher-order diffracted light generated by phase modulation from the collected signal light SGL. Thereby, unnecessary high-order diffracted light contained in the signal light SGL can be removed, and the sensitivity of the information recording medium 15 can be used effectively.

  The signal light SGL from which the higher-order diffracted light has been removed is subjected to Fourier transform again by the relay lens 13 and converted into an image conjugate with the image at the spatial light modulator 9 at the focal plane. The objective lens 14 is disposed at a position away from the conjugate image plane by the focal length. The objective lens 14 performs Fourier transform on the signal light SGL and guides it to the information recording medium 15.

  On the other hand, the reference light RFL is guided into the information recording medium 15 by the rotary drive mirror 16 and the irradiation position adjusting lenses 17 and 18 so as to overlap the focal position of the signal light SGL. The rotational drive mirror 16, the irradiation position adjusting lenses 17, 18 and the information recording medium 15 are arranged at positions separated by the focal length of the irradiation position adjusting lenses 17, 18, respectively. That is, these elements are in the “4f optical arrangement”.

  The signal light SGL and the reference light RFL interfere in the information recording medium 15, and the interference fringes are recorded on the hologram recording material 32 in the information recording medium 15. The angle at which the reference light RFL is incident on the information recording medium 15 can be changed by rotating the rotation drive mirror 16 to change the incident angle of the reference light RFL to the irradiation position adjusting lens 17.

  As described above, the holographic recording / reproducing apparatus 100 changes the incident angle of the reference light RFL so that the signal light SGL modulated by the different data information DT and the reference light RFL are in substantially the same region of the information recording medium 15. Interference fringes are recorded by overlapping. Thereby, angle multiplex recording can be performed on the information recording medium 15.

  FIG. 3 is a flowchart showing an operation procedure during recording of the holographic recording / reproducing apparatus 100.

  In the following description, it is assumed that temperature information and wavelength information are updated by detecting the presence or absence of fluctuation for each page data.

  Referring to FIG. 3, in step S101, control unit 28 receives a recording start signal and starts a recording operation.

  In step S102, the temperature detector 25 detects the temperature of the hologram recording material 32 in the current information recording medium (or the temperature in the vicinity thereof or the temperature inside the apparatus), and the controller 28 detects the wavelength of the current light source. Temperature information T and wavelength information λ are acquired.

  In step S103, the control unit 28 drives an information recording medium moving mechanism (not shown) to move the information recording medium 15 to the recording position.

  In step S104, the control unit 28 rotates the rotary drive mirror 16 to set the incident angle of the reference light RFL to an angle for recording. At the time of recording, the light transmitted through the information recording medium 15 is blocked by a light blocking mechanism (not shown) or absorbed by an absorbing member under the control of the control unit 28 and reaches the lens 19. By adopting such a configuration, stray light during recording can be avoided.

  In step S105, the encoder 10 acquires the recording data information DT. In the branch of step S106, the control unit 28 detects whether there is a temperature variation from the temperature acquired in step S102 by the temperature detection unit 25. If there is no temperature fluctuation, the process jumps to step S108. If there is a temperature change, the process proceeds to step S107, and the control unit 28 detects the temperature again by the temperature detection unit 25 and updates the temperature information T stored in the memory unit 26.

  In step S108, the control unit 28 detects whether there is a wavelength variation. If there is no wavelength variation, the process jumps to step S110. If there is a wavelength variation, the control unit 28 detects the wavelength again and updates the wavelength information λ stored in the memory unit 26.

  In the branch of step S110, the control unit 28 determines other information E, for example, the linear expansion coefficient in the in-plane direction of the information recording medium, the linear expansion coefficient in the thickness direction of the information recording medium, according to preset operation conditions, It is determined whether to obtain the temperature change coefficient of the refractive index of the information recording medium or the linear expansion coefficient of the substrate supporting the information recording medium. Other information may be acquired only at the time of the first page data PDT recording in the angle multiplex recording or at the time of the first page data PDT recording to be recorded on the disc. If no other information E is acquired, the process jumps to step S113.

  In step S111, it is checked whether there is a change in the other information E. If there is no change, the process jumps to step S113. If there is a change, the other information E stored in the memory unit 26 is updated.

  In step S113, when there is temperature information T, wavelength information λ, and other information acquired so far, the control unit 28 controls the encoder 10 to store the temperature information T, wavelength information λ, and other information E as recording conditions. The data information D is arranged in the area, the data information D is arranged in the data information area, and the page data PDT is created.

In step S114, holographic recording is performed.
In the branch of step S115, the control unit 28 determines whether or not to end angle multiplex recording. In the case of ending, the control unit 28 advances the process to step S116. If not, the process returns to step S104, the reference light incident angle is changed, and a series of operations from step S105 to step S114 is repeated.

  In the branch of step S116, the control unit 28 determines whether to end the recording. In the case of ending, the control unit 28 advances the process to step S117. If not, the process returns to step S103, and the control unit 28 drives the moving mechanism to shift the recording position by a predetermined amount, and repeats a series of operations from step S104 to step S115 again.

  In step S117, as a post-processing after recording, the control unit 28 performs curing that irradiates light with low coherence to the area where the hologram is recorded. After the curing is completed, the recording operation is finished in step S118.

[Configuration and operation during playback]
Next, the reproducing operation of the holographic recording / reproducing apparatus 100 will be described.

  FIG. 4 is a diagram showing a schematic configuration of the holographic recording / reproducing apparatus 100 and an operation during reproduction. In this case, the following description will be made assuming that the recording / reproducing apparatus 100 is a holographic recording / reproducing apparatus 100. However, in the embodiment, only the reproducing process is executed instead of the holographic recording / reproducing apparatus 100. It may be a holographic playback device.

  Referring to FIG. 4, in holographic recording / reproducing apparatus 100, at the time of reproduction, control unit 28 adjusts the rotation angle of half-wave plate 3 so as to generate only reference light RFL. The reference light RFL passes through the optical isolator 2, the half-wave plate 3, the polarization beam splitter 4, the rotation drive mirror 16, and the irradiation position adjusting lenses 17 and 18 on the same path P2 as in recording, and the information recording medium 15 Incident to. By rotating the rotary drive mirror 16 and changing the incident angle of the reference light RFL to the irradiation position adjusting lens 17, the angle at which the reference light RFL is incident on the information recording medium 15 is changed as in the recording. Can do.

  The reference light RFL transmitted through the information recording medium 15 further passes through the irradiation position adjusting lenses 19 and 20, and is converted into circularly polarized light by the quarter wavelength plate 21 on the path P5. The circularly polarized light is incident on the rotation drive mirror 22. The control unit 28 adjusts the angle of the rotary drive mirror 22 so that the reference light RFL is perpendicularly incident on the rotary drive mirror 22.

  As a result of the operation as described above, the reference light RFL passes through the quarter wavelength plate 21 again through the path P6 opposite to the original path P5, and is converted into linearly polarized light whose polarization direction is rotated by 90 degrees. The As described above, when the incident angle of the reference light RFL to the information recording medium 15 is changed, the reference light RFL is incident on the rotary drive mirror 22 so that the reference light RFL is perpendicularly incident on the rotary drive mirror 22 each time. The angle is adjusted.

  The reference light RFL converted into linearly polarized light by the quarter wavelength plate 21 passes through the irradiation position adjusting lenses 19 and 20 and reenters the information recording medium 15. At this time, since the reference light RFL is incident from the opposite direction to that at the time of recording, the information recording medium 15 is irradiated as light that is phase conjugate with the reference light RFL at the time of recording. Thereby, in the information recording medium 15, the reference light RFL is diffracted by the recorded interference fringes, and as a result, the recorded information is reproduced. The reproduction light CFL generated in this way is Fourier transformed through the objective lens 14. Thereafter, the light passes through the polarization lens splitter 7 through the relay lens 13, the spatial filter 12 and the relay lens 11 on the path P <b> 7 during reproduction.

The reproduction light CFL that has passed through the polarization beam splitter 7 enters the image sensor 23. The image sensor 23 is disposed on the image plane of the relay lens 11. The image sensor 23 receives the reproduction light CFL, reads the intensity modulation given to the reproduction light CFL, and generates two-dimensional page data PDT. The decoder 24 receives the generated two-dimensional page data PDT and reads information including the data information DT and the recording condition information TP therefrom. As the image sensor 23, a CCD (Charge Coupled Device) array or a CMOS (Complementary Metal-Oxide Semiconductor) sensor array can be used.
(Causes and directions of uneven brightness)
When expansion and contraction occur in the hologram recording material 32 during recording and during reproduction, luminance unevenness may occur in the reproduction light. The direction in which the uneven brightness occurs, the reproducible area, and the width of the reproducible area will be described.

  FIG. 5 is a diagram showing the state of the signal light SGL and the reference light RFL incident on the hologram recording material 32 in the information recording medium 15 at the time of recording.

Referring to FIG. 5, the signal light SGL is incident on the objective lens while being diffracted after once forming an image in the SA-SA ′ cross section which is a conjugate surface of the spatial light modulator 9. Light from each position of the signal light SGL passes through the objective lens 14 and enters the information recording medium as parallel light having different incident angles, and the reference light RFL enters the information recording medium 15 at an incident angle θ _R. As shown in FIG. 5, since the incident angle θ _S of the signal light SGL to the information recording medium 15 differs depending on the position of the signal light SGL in the page data PDT, the inclination angle of the interference fringes and the spacing between the fringes are also the signal light SGL. It differs depending on the position in the page data PDT.

  FIG. 6 is a diagram illustrating a state in which the signal light SGL having different incident angles interferes with the reference light RFL by the hologram recording material 32 in the information recording medium 15.

  Referring to FIG. 6, a plurality of interference fringes having different interference fringe intervals and different interference fringe inclination angles corresponding to the respective plane wave components of signal light SGL are recorded on hologram recording material 32 in information recording medium 15. The In the situation where a plurality of interference fringes are recorded at a time, when the hologram recording material 32 expands and contracts, the optimum incident angle correction amount Δθrc of the reference light RFL varies depending on the inclination angle and interval of the interference fringes. . That is, the optimal incident angle correction amount of the reference light RFL differs depending on the position of the signal light SGL in the page data PDT. In such a case, when the reference light RFL is incident at a certain incident angle, the interference fringes recorded by the signal light SGL from a certain position in the page data PDT are reproduced while satisfying the Bragg condition, but from other positions. The interference fringes recorded by the signal light SGL do not satisfy the Bragg condition and are not reproduced. This is the cause of uneven brightness and missing reproduced images.

The direction in which the reproduced image is missing is the direction (X direction) perpendicular to the normal (Y direction) of the surface formed by the optical axis direction of the reference light RFL and the optical axis direction of the signal light SGL. is a diagram showing the incident angle correction amount [Delta] [theta] _R of the reference light RFL with respect to the incident angle theta _S light SGL.

In FIG. 7, the recording wavelength of the tunable laser 1 is 405 nm, the reproducing wavelength is 402 nm, the incident angle of the reference light RFL during recording with respect to the information recording medium 15 is 60 degrees, and the NA (numerical aperture) of the objective lens 14 is set. ) Is assumed to be 0.5. The optical axis of the signal light SGL coincides with the normal direction of the information recording medium 15, and at this time, the incident angle of the signal light SGL to the hologram recording material is -30 degrees to 30 degrees. Assume that a temperature change of about 20 degrees occurs between recording and reproduction. At this time, the required incident angle correction amount Δθrc of the reference light RFL is as shown in the graph of FIG.
(An incident angle correction amount of the reference light RFL)
The incident angle correction amount Δθrc of the reference light RFL is a correction amount from the recording angle. When the incident angle correction amount Δθrc is 0.59 degrees, only the interference fringes within the reproducible angle range θpb centering on 0.59 degrees satisfy the black condition and can be reproduced. If the reproducible angle range θpb is 0.1 degree, the reproducible signal light SGL has an incident angle of 20 ± 5 degrees, and a region corresponding to the incident angle in the page data PDT is reproduced. . This is a reproducible area. Therefore, the reproducible region of the signal light SGL is obtained from the reproducible angle range θpb of the reference light RFL, and the reproducible angle range of the reference light RFL is obtained from the angle selectivity of the reference light RFL.

In general, the angle selectivity of the reference light RFL is determined by the thickness of the hologram recording material, the wavelength of the wavelength tunable laser 1, and the incident angles of the reference light RFL and signal light SGL on the information recording medium 15 during recording.
(Angle selectivity and playable area)
FIG. 8 shows the relationship between the diffraction efficiency from the hologram and the incident angle of the reference light RFL to the information recording medium when the interference fringes having the recorded single tilt angle and interference fringe distance are recorded (the reference light RFL It is the figure which showed angle selectivity.

  Referring to FIG. 8, the range of the incident angle of reference light RFL when the diffraction efficiency of reproduction light CFL is 0.5 is set as a reproducible angle range θpb of reference light RFL. The angle selectivity of the recorded hologram is determined by the thickness of the hologram recording material 32, the wavelength of the wavelength tunable laser 1, and the incident angles of the reference light RFL and signal light SGL on the information recording medium 15 during recording. When the angle formed by the reference light and the signal light SGL is 90 degrees, the full width at half maximum of the angle selectivity is reduced, and the reproducible area is also reduced. When the angle between the reference light RFL and the signal light SGL is 0 degree or 180 degrees, the full width at half maximum of the angle selectivity becomes the largest, and the reproducible area also becomes large. That is, when the wavelength at the time of recording and the wavelength at the time of reproduction are the same, the reproducible area becomes smaller as the angle formed by the reference light and the signal light SGL is closer to 90 degrees, and the reproducible area becomes closer to 0 degrees or 180 degrees. Becomes bigger.

  Referring to FIG. 9, the wavelength of the light source is 405 nm, the reference light incident angle is 30 degrees, the thickness of the hologram recording material is 1.0 mm, the NA of the objective lens for condensing the signal light SGL is 0.5, and the optical axis of the signal light SGL Let us consider a case where the incident angle is −30 degrees. At this time, the incident angle of the signal light SGL to the hologram recording material is 0 degrees to −60 degrees.

  Since the signal light SGL is condensed into the hologram recording material by the objective lens, the incident angle of the signal light SGL varies depending on the position in the page data PDT. That is, the angle selectivity, that is, the reproducible area differs depending on the position in the page data PDT.

  The light from the position PA in the page data PDT in FIG. 9 is collected by the objective lens and enters the hologram recording material at an incident angle of −60 degrees. FIG. 10A shows the angle selectivity at this time, and FIG. 10B shows the corresponding reproducible area. FIG. 10A is a diagram showing angle selectivity when the signal light SGL from the position PA is reproduced. Similarly, the light from the PB position in the page data PDT in FIG. 9 is condensed by the objective lens and enters the hologram recording material at an incident angle of 0 degree. FIG. 11B is a diagram showing the angle selectability at this time and FIG. 11B is a diagram showing the corresponding reproducible area in FIG. In the case of FIG. 11A, the angle selectivity is about twice as large as that in FIG. Therefore, the reproducible area also becomes about twice as large.

  That is, when the wavelength at the time of recording and the wavelength at the time of reproduction are the same, the maximum size of “ An area that can be a “reproducible area” is defined. Therefore, the relationship between such a geometric arrangement and the “maximum reproducible area” is specified by, for example, calculation or experiment in advance, so that the recording condition information TP can be maximized. Place in the area.

  In the example of FIG. 9, by arranging the recording condition information TP in the reproducible area at the position PB, there is a high possibility that the recording condition information TP can be read even when the luminance unevenness of the reproduced image occurs during reproduction. . Further, since the reproducible area is large, more recording condition information TP can be arranged.

  Even when the above-described luminance unevenness occurs, the recording condition information can be easily read by adjusting the incident angle of the reference light so that the reproducible area is maximized. In order to detect the size of the reproducible area, the holographic recording / reproducing apparatus 100 may further include a luminance unevenness detector 29. The luminance unevenness detector 29 may be a line sensor, a multi-division photodiode, or an image sensor such as a CCD camera or a CMOS camera. The luminance unevenness detector 29 detects the reproduction light generated along the path P8 when the reference light RFL passes through the recorded hologram. Further, the size of the reproducible area may be detected using the output of the image sensor.

  Returning to FIG. 3, the reproduction light CFL detected by the image sensor 23 is sent to the decoder 24 as page data PDT. The decoder 24 converts the page data PDT into data information DT and recording condition information TP. The temperature detection unit 25 detects temperature information of the information recording medium 15 and the like. From the temperature information and the recording condition information TP, the linear expansion coefficient and the temperature change constant of the refractive index of the information recording medium 15 are read out. From these pieces of information, the hologram expansion / contraction δx and δz with respect to the temperature change and the refractive index nr of the information recording medium 15 at the time of recording can be obtained.

  Using the above values, the control unit 28 determines the wavelength correction amount and / or the incident angle correction amount of the reference light RFL that makes the incident angle correction amount Δθrc of the reference light RFL substantially constant with respect to the incident angle of the different signal light SGL. calculate. The control unit 28 adjusts the wavelength of the wavelength tunable laser 1 and drives the rotary drive mirror 16 based on the calculated wavelength correction amount and / or incident angle correction amount. As a result, the wavelength of the wavelength tunable laser 1 and the incident angle of the reference light RFL to the information recording medium 15 are corrected.

  FIG. 12 is a diagram illustrating the incident angle correction amount Δθrc of the reference light RFL with respect to the incident angle θs of the signal light SGL when correction is applied.

  As shown in FIG. 12, in addition to the correction of the wavelength of the wavelength tunable laser 1, the incident angle correction amount Δθrc of the reference light RFL can be reproduced by correcting the incident angle of the reference light RFL to the information recording medium 15. It can be contained within θpb. Thereby, it is possible to perform image reproduction without missing page data PDT.

  Note that the amount of temperature change in the information recording medium 15 and / or the holographic recording / reproducing apparatus 100 during recording and reproduction, the wavelength correction amount during reproduction with respect to the wavelength variation of the wavelength tunable laser 1 during recording and reproduction, and wavelength The incident angle correction amount Δθrc of the reference light RFL during reproduction with respect to the wavelength change amount of the variable laser 1 may be recorded in the memory unit 26.

By storing the temperature change amount, the wavelength correction amount, and the incident angle correction amount Δθrc in the memory unit 26 in advance, the wavelength correction amount and the incident amount are obtained based on the recording condition information TP and / or the temperature information at the time of reproduction. The angle correction amount Δθrc can be obtained without calculation. As a result, the above correction and reproduction can be performed at high speed. As described above, according to the holographic recording / reproducing apparatus 100 of the embodiment, the incident angle correction amount Δθrc of the reference light RFL is within the reproducible angle range. By correcting the wavelength of the wavelength tunable laser 1 and the incident angle of the reference light RFL to the information recording medium 15 so as to be within θpb, it is possible to reproduce an image without missing the two-dimensional page data PDT.

  FIG. 13 is a flowchart showing an operation procedure during reproduction of the holographic recording / reproducing apparatus 100.

  The playback method will be described with reference to FIG. In step S201, the control unit 28 receives a reproduction start signal and starts a reproduction operation.

  In step S202, the control unit 28 uses the temperature detection unit 25 to detect the temperature of the hologram recording material 32 in the current information recording medium (or the temperature in the vicinity thereof or the temperature inside the apparatus) and the current light source. Are detected, and temperature information T and wavelength information λ are obtained.

  In step S203, the control unit 28 drives an information recording medium moving mechanism (not shown) to move the information recording medium to a reproduction position.

  In step S204, the control unit 28 rotates the rotary drive mirror 16 to set the reference light incident angle to an angle for reproduction.

  In step S205, the control unit 28 irradiates the position where the information of the information recording medium is recorded with the reference light RFL, reproduces the signal light SGL, and reads the reproduction signal.

  In step S206, the control unit 28 determines whether luminance unevenness has occurred in the read reproduction signal. Judgment of whether or not the luminance unevenness has occurred may be determined from the size of the reproducible region, or by determining the luminance unevenness detection area in the page data PDT and comparing the luminance values thereof. Alternatively, it may be determined from the number of errors or error distribution in the page data PDT.

  If there is no luminance unevenness, the process jumps to step S210. When the luminance unevenness has occurred, the control unit 28 advances the processing to step S207 and reads the recording condition information. In step S208, the control unit 28 derives, from the obtained recording condition information, i) only the reference light incident angle correction information, or ii) the reference light incident angle and light source wavelength correction information, depending on the conditions. .

  Based on the correction information obtained in step S209, the control unit 28 corrects the reference light incident angle and / or the reference light incident angle and the light source wavelength.

  In step S210, the decoder 24 reads the signal again and decodes the obtained signal.

  In the branch of step S211, the control unit 28 confirms whether the angle multiplex reproduction has been completed. When the process ends, the process moves to step S212. When not complete | finishing, the control part 28 returns a process to step S204, and sets a reference light incident angle. The reference light incident angle at this time may be an incident angle corrected by the correction information. Thereafter, the control unit 28 repeats a series of operations from step S205 to step S210. In step S212, it is confirmed whether or not the reproduction is finished. In the case of ending, the control unit 28 moves the process to step S213 and ends the reproduction. If not finished, the control unit 28 returns the process to step S203, changes the playback position, and performs angle-multiplexed playback again.

  FIG. 14 is a flowchart showing a recording condition information acquisition method in the case where the recording condition information TP is recorded in the maximum reproducible area.

The recording condition acquisition method will be described with reference to FIG.
In step S301, the control unit 28 receives the recording condition information read start signal and starts reading. In step S302, the reference light incident angle is set to a predetermined value, and in step S303, the control unit 28 detects the size of the reproducible area, that is, the reproducible area width. If the reproducible area width is maximum in the branch of step S304, the control unit 28 moves the process to step S305. If the reproducible area width is not the maximum, the process returns to step S302, and the control unit 28 changes the reference light incident angle again, and sequentially performs the processes of steps S303 and S304. By performing such repetitive work, the reproducible area width is maximized, and the control unit 28 reads out the recording condition information recorded at the position where the reproducible area width is maximized in step S305. Thereafter, the process proceeds to step S306, and the recording condition information reading is terminated.

  With the configuration as described above, it is possible to read out the recording condition information with certainty and correct the laser wavelength and the incident angle of the reference light, so that it is possible to obtain high-quality reproduced signal light. Become.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  1 tunable laser, 2 optical isolator, 3 1/2 wavelength plate, 4,7 polarization beam splitter, 5,6 beam expanding lens, 8,21 1/4 wavelength plate, 9 spatial light modulator, 10 information conversion unit, DESCRIPTION OF SYMBOLS 11, 13 Relay lens, 12 Spatial filter, 14 Objective lens, 15 Information recording medium, 16, 22 Rotation drive mirror, 19, 20 Irradiation position adjustment lens, 23 Image sensor, 24 decoder, 25 Temperature detection part, 26 Memory part , 28 control unit, 29 luminance unevenness detector, 100 holographic recording / reproducing apparatus.

Claims (7)

An information recording method for recording information on an information recording medium using interference fringes formed by interference between reference light and signal light,
Detecting recording condition information including temperature information of the information recording medium;
Converting to two-dimensional information including a data information area for storing data information recorded on the information recording medium and a recording condition storage area for storing the detected recording condition information,
The recording condition storage area is stored at the position where the reproducible area obtained from the angle selectivity of the interference fringe is maximized in the two-dimensional information,
An information recording method, further comprising: recording the interference fringes on the information recording medium by causing the reference light and the signal light modulated based on the two-dimensional information to interfere with each other in the information recording medium.   The position where the reproducible area obtained from the angle selectivity of the interference fringe is maximized is the angle formed by the reference light and the signal light incident on the information recording medium at the time of recording out of the two-dimensional information. The information recording method according to claim 1, wherein the information recording region is a region far from 90 degrees and near 0 degrees or 180 degrees. A two-dimensional information creation method used for information recording in which interference fringes are recorded as interference between a reference light and a signal light obtained by modulating two-dimensional information,
Creating a data information area for storing data information recorded on the information recording medium;
Creating a recording condition storage area for storing recording condition information,
The recording condition storage area is a two-dimensional information creation method in which the reproducible area determined from the angle selectivity of the interference fringes is arranged in the two-dimensional information at a maximum. An information reproducing method for reproducing two-dimensional information recorded as interference fringes of reference light and signal light on an information recording medium by irradiation of the reference light,
Receiving reproduction light generated by irradiating the information recording medium with the reference light, and generating two-dimensional information recorded on the information recording medium;
Reading data information and recording condition information included in the two-dimensional information,
The information reproducing method, wherein the recording condition storage area is arranged at a position where the reproducible area obtained from the angle selectivity of the interference fringe is maximized in two-dimensional information.   The information reproducing method according to claim 4, further comprising a step of controlling an incident angle of the reference light to the information recording medium so that a reproducible area in the reproduced two-dimensional information is maximized. Detecting temperature information during playback; and
Based on the temperature information at the time of reproduction and the recording condition information, the reference light for reducing the change in the incident angle correction amount of the reference light with respect to the signal light having different incident angles modulated by the two-dimensional information is reduced. Deriving a wavelength correction amount and an incident angle correction amount;
The information reproducing method according to claim 5, further comprising a step of controlling a wavelength of the reference light and an incident angle of the reference light based on the wavelength correction amount and the incident angle correction amount. An information recording medium on which interference between reference light and signal light modulated based on two-dimensional information is recorded as interference fringes,
The two-dimensional information includes a data information area for storing data information recorded on the information recording medium, and a recording condition storage area for storing recording condition information,
The recording condition storage area is an information recording medium arranged in a position where the reproducible area obtained from the angle selectivity of the interference fringes is maximized in the two-dimensional information.

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