WO2017094129A1 - Holographic optical information reproducing device - Google Patents

Holographic optical information reproducing device Download PDF

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Publication number
WO2017094129A1
WO2017094129A1 PCT/JP2015/083835 JP2015083835W WO2017094129A1 WO 2017094129 A1 WO2017094129 A1 WO 2017094129A1 JP 2015083835 W JP2015083835 W JP 2015083835W WO 2017094129 A1 WO2017094129 A1 WO 2017094129A1
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WO
WIPO (PCT)
Prior art keywords
light
reference light
wavefront
angle
reproduction
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Application number
PCT/JP2015/083835
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French (fr)
Japanese (ja)
Inventor
山田　健一郎
健 宇津木
Original Assignee
株式会社日立製作所
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Priority to PCT/JP2015/083835 priority Critical patent/WO2017094129A1/en
Publication of WO2017094129A1 publication Critical patent/WO2017094129A1/en

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/005—Reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector

Definitions

  • the present invention relates to an apparatus for reproducing information from a recording medium using holography.
  • signal light having page data information two-dimensionally modulated by a spatial light modulator is superimposed on reference light inside the recording medium and refracted into the recording medium by the interference fringe pattern generated at that time.
  • This is a technique for recording information on a recording medium by causing rate modulation.
  • the hologram recorded in the recording medium acts like a diffraction grating to generate diffracted light.
  • This diffracted light is reproduced as the same light including the recorded signal light and phase information.
  • the reproduced signal light is detected two-dimensionally at high speed using a photodetector such as a CMOS or CCD.
  • the hologram recording technique enables two-dimensional information to be recorded and reproduced on an optical recording medium by one hologram, and further performs multiplex recording in which a plurality of page data is superimposed on a certain place of the recording medium.
  • a holographic memory uses a photopolymer material as a recording medium in order to record interference fringes. Photopolymer materials expand and contract due to temperature changes and moisture absorption. When the recording medium expands and contracts during hologram reproduction, the angle and interval of the recorded interference fringe changes and is distorted, so that the amount of diffracted light in the reproduction light decreases, and the signal quality deteriorates.
  • Patent Document 1 proposes a method for improving signal quality by controlling a spatial phase of a wavefront of reference light using a genetic algorithm in an adaptive optical system using a wavefront sensor and a wavefront controller.
  • the wavefront of the light detected by the wavefront sensor in the adaptive optical system or the intensity distribution of the light detected by the photodetector is linear with respect to the input signal of the wavefront controller, the wavefront is compensated by feedback control using a transfer function. Is easy. However, in view of hologram reproduction, the response of the wavefront and intensity distribution of the reproduction light to the wavefront shape formed by the wavefront controller is nonlinear, and its transfer function is complicated, making it difficult to perform feedback control.
  • the genotype setting value of the initial population of the genetic algorithm and the population of each generation are set values that can compensate for distortions peculiar to the hologram recording medium.
  • the wavefront shape is optimized by using a setting value that compensates for distortion, for example, the SNR (Signal to Noise Ratio) of the reproduction light.
  • the genetic algorithm must perform calculation for each generation by the size of the population for evaluation. The amount of calculation until the evaluation value converges is extremely large, and optimization takes time even if a high-speed computer is used depending on the group size and evaluation value setting.
  • An object of the present invention is to model the relationship between a camera image and a reference light wavefront in an adaptive optical system using a wavefront controller, and to achieve a wavefront shape capable of compensating for interference fringe distortion caused by expansion or contraction of a hologram recording medium at high speed. Deriving and realizing high reproduction quality while maintaining a high transfer rate.
  • the present invention it is possible to achieve high quality reproduction quality while maintaining a high transfer speed even when the interference fringes are distorted due to expansion or contraction of the hologram recording medium.
  • regenerating apparatus of this invention The schematic diagram showing the pickup at the time of recording of the hologram optical information reproducing
  • regenerating apparatus of this invention Schematic diagram showing the playback image and hologram playback in an ideal state
  • Flow chart showing wavefront compensation method 7 is a schematic diagram showing the distribution of the amount of diffracted light with respect to the pitch angle for searching the pitch angle in step S702.
  • FIG. 7 is a schematic diagram showing the distribution of the amount of diffracted light with respect to the Bragg angle for searching for the Bragg angle in step S704.
  • regeneration apparatus 10 in Example 1 The schematic diagram which showed distribution of the exclusive overlap area
  • the flowchart which showed the optimization process of the wavefront shape of the reference light of this invention The result of calculating the reference light wavefront optimization of the present invention by optical simulation under the condition that the expansion rate in the thickness direction of the hologram recording medium 1 is 0.105%
  • FIG. 1 is a block diagram showing an optical information reproducing apparatus of a hologram recording medium for reproducing digital information using holography.
  • the hologram optical information reproducing device 10 is connected to an external control device 91 via an input / output control circuit 90.
  • the hologram reproducing device 10 receives an information signal to be recorded from the external control device 91 by the input / output control circuit 90.
  • the hologram reproducing device 10 transmits the reproduced information signal to the external control device 91 by the input / output control circuit 90.
  • the hologram optical information reproducing apparatus 10 includes a pickup 11, a reproduction reference light optical system 12, a cure optical system 13, a disk rotation angle detection sensor 14, a radial position detection sensor 15, a spindle motor 50, and a radial direction conveyance unit 51.
  • the spindle motor 50 has a medium attaching / detaching portion (not shown) that allows the hologram recording medium 1 to be attached to and detached from its rotation axis.
  • the hologram recording medium 1 is configured to be rotatable by the spindle motor 50. At the same time, the hologram recording medium 1 is configured to be movable in the radial direction by the radial transport unit 51 with reference to the position of the pickup 11.
  • the position where the signal light and / or the reference light is irradiated is determined by the position of the pickup 11 described later, and is a position fixed to the apparatus.
  • the spindle motor 50, the movable part of the radial transport part 51, and the moving stage 51 function as means for changing the position on the hologram recording medium 1 to which the signal light and / or the reference light is irradiated.
  • the rotation angle detection sensor 14 is used for detecting the rotation angle of the hologram recording medium 1.
  • the rotation angle detection sensor 14 detects the rotation angle of the hologram recording medium 1 using, for example, an angle detection mark provided on the hologram recording medium 1.
  • An output signal of the rotation angle detection sensor 14 is input to the rotation angle control circuit 21.
  • the rotation angle control circuit 21 When changing the rotation angle irradiated with the signal light and the reference light, the rotation angle control circuit 21 generates a drive signal based on the output signal of the rotation angle detection sensor 14 and the command signal from the controller 80 to drive the spindle.
  • the spindle motor 50 is driven via the circuit 22. Thereby, the rotation angle of the hologram recording medium 1 can be controlled.
  • the radial position detection sensor 15 is used to detect the position of the movable part of the radial direction transport part 51.
  • the radial position detection sensor 15 detects the position of the movable part of the radial direction transport part 51 using, for example, a position detection pattern in which a scale having a predetermined pattern is fixed.
  • An output signal of the radial position detection sensor 15 is input to the radial position control circuit 23.
  • the radial position control circuit 23 When the radial position irradiated with the signal light and the reference light is changed, the radial position control circuit 23 generates a drive signal based on the output signal of the radial position detection sensor 15 and the command signal from the controller 80 to drive the radial position.
  • the radial conveyance unit 51 is driven via the circuit 24. Thereby, the hologram recording medium 1 is conveyed in the radial direction, and the radial position irradiated with the signal light and the reference light can be controlled.
  • the pickup 11 plays a role of irradiating the hologram recording medium 1 with reference light and signal light and recording digital information on the recording medium using holography.
  • the information signal to be recorded is sent by the controller 80 to a spatial light modulator (described later) in the pickup 11 via the signal generation circuit 81, and the signal light is modulated by the spatial light modulator.
  • the reproduction reference light optical system 12 When reproducing the information recorded on the hologram recording medium 1, the reproduction reference light optical system 12 generates a light wave that causes the reference light emitted from the pickup 11 to enter the hologram recording medium 1 in the direction opposite to that during recording. To do.
  • the reproduction light reproduced by the reproduction reference light is detected by a photodetector described later in the pickup 11, and the signal is reproduced by the signal processing circuit 82.
  • an incident angle serving as a multiple angle of the page data of the reference light is generated.
  • a drive signal is generated by the Bragg angle control circuit 32, and will be described later in the pickup 11 via the Bragg angle drive circuit 33.
  • the actuator 222 generates a drive signal by the pitch angle control circuit 35 for the angle of reference light incident on the surface substantially perpendicular to the surface including the optical axis of the signal light and the normal line of the recording medium. Control is performed by driving an actuator 220 described later in the pickup 11 and an actuator 225 described later in the reproduction reference light optical system 12 through the pitch angle driving circuit 36.
  • the Bragg angle control signal generation circuit 31 generates a signal for use in controlling the Bragg angle from the output signal of at least one of the pickup 11 and the reproduction reference light optical system 12.
  • the Bragg angle control circuit 32 performs control using the output signal of the Bragg angle control signal generation circuit 31 in accordance with an instruction from the controller 80.
  • the pitch angle control signal generation circuit 34 generates a signal to be used for controlling the pitch angle from the output signals of at least one of the pickup 11 and the reproduction reference light optical system 12.
  • the pitch angle control circuit 34 performs control using the output signal of the Bragg angle control signal generation circuit 31 in accordance with an instruction from the controller 80.
  • the irradiation time of the reference light and the signal light applied to the hologram recording medium 1 can be adjusted by controlling the opening / closing time of the shutter 203 in the pickup 11 via the shutter control circuit 37 by the controller 80.
  • the cure optical system 13 plays a role of generating a light beam used for pre-curing and post-curing of the hologram recording medium 1.
  • Pre-curing is a pre-process for irradiating a predetermined light beam in advance before irradiating the reference light and signal light to the desired position when recording information at the desired position in the hologram recording medium 1.
  • Post-cure is a post-process for irradiating a predetermined light beam after recording information at a desired position in the hologram recording medium 1 so that additional recording cannot be performed at the desired position.
  • the light beam used for pre-cure and post-cure is preferably incoherent light, that is, light with low coherence.
  • a predetermined light source driving current is supplied from the light source driving circuit 38 to the light sources in the pickup 11 and the cure optical system 13, and each light source can emit a light beam with a predetermined light quantity.
  • the pickup 11 and the cure optical system 13 may be simplified by combining several optical system configurations or all optical system configurations into one.
  • “reproduction” in the hologram reproduction apparatus 10 of the present invention means having a hologram reproduction function, and does not mean that the hologram recording function is not provided. That is, an apparatus having both a reproducing function and a recording function is also included in the concept of the hologram reproducing apparatus 10 of the present invention.
  • FIG. 2 shows a recording principle in an example of a basic optical system configuration of the pickup 11 and the reproducing reference light optical system 12 in the hologram reproducing apparatus 10.
  • the reproduction reference light optical system 12 includes an optical element 232, a lens 233, an actuator 235, and a mirror 234, which will be described later.
  • the light beam emitted from the light source 201 passes through the collimator lens 202 and enters the shutter 203.
  • the optical element 204 composed of, for example, a half-wave plate or the like, adjusts the light quantity ratio of p-polarized light and s-polarized light to a desired ratio.
  • the light beam enters a PBS (Polarization Beam Splitter) prism 205.
  • the light beam that has passed through the PBS prism 205 functions as signal light 206, and after the light beam diameter is expanded by the beam expander 208, the light beam passes through the phase mask 209, the relay lens 210, and the PBS prism 211 and passes through the spatial light modulator 212. Is incident on. Phase information is added to the signal light 206 by passing through the phase mask 209. The signal light to which information is added by the spatial light modulator 212 reflects the PBS prism 211 and propagates through the relay lens 213 and the spatial filter 214. Thereafter, the signal light is condensed on the hologram recording medium 1 by the objective lens 215.
  • the light beam reflected from the PBS prism 205 works as reference light 207, and is set to a predetermined polarization direction according to recording or reproduction by the polarization direction conversion element 216, and then reflected by the PBS prism 217 to pass through the optical element 218.
  • the optical element 218 is composed of, for example, a quarter wave plate.
  • the light is reflected by a wavefront modifier 219 having a reflection surface that is an ideal planar shape, and is again transmitted through the optical element 218 and the PBS prism 217 to enter the optical element 220.
  • a deformable mirror can be used as the wavefront changer.
  • the optical element 220 is formed of, for example, a half-wave plate whose polarization direction can be changed, and in FIG. 2 at the time of recording, the angle formed by the azimuth angle of the incident reference light polarization and the optical axis of the optical element 220 is zero. Is set such that the polarization state of the reference light does not change.
  • the reference light transmitted through the optical element 220 is reflected by the PBS prism 221, passes through the optical element 225, and then enters the optical element 226.
  • the optical element 225 is formed of, for example, a half-wave plate whose polarization direction can be changed, and is set so that the polarization of the reference light does not change in FIG.
  • the optical elements 220 and 225 are not limited to the setting of the optical axis that is polarized so that the reference light does not branch to the wavefront sensor 224 side, but are polarized so that the reference light branches to the wavefront sensor 224 side during reproduction.
  • the optical axis may be set.
  • the reflection angle of the optical element 226 can be adjusted in the pitch angle direction by the actuator 227.
  • the reference light reflected by the optical element 226 enters the optical element 228.
  • the reflection angle of the optical element 228 can be adjusted in the Bragg angle direction by an actuator 229.
  • the reference light reflected by the optical element 228 passes through the lens 230 and the lens 231 and then enters the hologram recording medium 1.
  • the optical element 226 may be a reflective prism
  • the optical element 228 may be a mirror
  • the actuator 227 and the actuator 229 may be galvanometers.
  • the signal light and the reference light are incident on the hologram recording medium 1 so as to overlap each other, whereby an interference fringe pattern is formed in the recording medium, and information is recorded by writing this pattern on the recording medium.
  • the Bragg angle of the reference light incident on the hologram recording medium 1 can be changed by the actuator 229, recording by angle multiplexing is possible.
  • FIG. 20 shows the geometric relationship between the hologram area formed when recording on the hologram recording medium 1 and the optical axis of the objective lens 215.
  • a line segment 2001 represents the optical axis of the objective lens 215.
  • the Bragg angle represents an angle defined in a plane 2002 including the normal line of the optical axis 2001 and the recording medium 1.
  • the surface 2002 is an incident surface. Of the signal light collected by the objective lens 215 in the incident surface 2002, the light beam closest to the incident angle of the reference light indicated by 2003 in the figure is the closest light beam.
  • the region of the reference light through which the plane 2004 including the closest light ray 2003 among the surfaces perpendicular to the incident surface 2002 passes is hereinafter referred to as a region (i).
  • a region (i) holograms corresponding to each Bragg angle are called pages, and a set of pages angle-multiplexed in the same area is called a book.
  • FIG. 3 shows a reproduction principle in an example of a basic optical system configuration of the pickup 11 and the reproduction reference light optical system 12 in the hologram light information reproduction apparatus 10.
  • the wavefront modifier 219 adds desired phase information to the reference light, changes the wavefront shape, and enters the optical element 220.
  • the azimuth angle for changing the incident reference light in FIG. 3 during reproduction and the optical axis of the optical element 220 are arranged with a predetermined angle.
  • the reference light transmitted through the PBS prism 221 passes through the lens 222 and the lens 223 and is optimal for detection.
  • the light is incident on the wavefront sensor 224 with a light beam diameter.
  • the reference light reflected from the PBS prism 221 is incident on the recording medium 1 in the same manner as during recording.
  • the light beam incident on the hologram recording medium 1 and transmitted through the hologram recording medium 1 passes through the optical element 232, and is collected by the lens 233 on the reflecting surface of the optical element 234.
  • the optical element 232 is composed of, for example, a quarter wave plate.
  • the optical element 234 can adjust the position before and after the desired reflecting surface and the reflection angle with respect to the pitch direction and the Bragg direction by the actuator 235, and reflects the reference light collected by the lens 233.
  • the light reflected by the optical element 234 passes through the same optical path as the incident light and passes through the lens 233 and the optical element 232.
  • the reflected light is a phase-conjugate light beam having the same angle as that at the time of incidence and the incident direction being different from the pitch direction and the Bragg direction.
  • the phase conjugate light beam is referred to as reproduction reference light. Since the reproduction reference light is phase conjugate light, the wavefront shape changed by the wavefront changer 219 is reversed in the optical element 234 with respect to both the Bragg direction and the pitch direction.
  • the wavefront shape given by the wavefront modifier 219 is point-symmetric with respect to the center point of the effective diameter of the reference light, the wavefront shape of the reference light for reproduction is exactly the same as that at the time of incidence and is incident on the medium from the back surface. Can do.
  • the light beam incident on the hologram recording medium 1 from the surface and diffracted to the side opposite to the reproduction reference light is detected by the photodetector 236.
  • the light detector 236 is positioned so that the amount of light detected by the light detector 236 is also maximized when the light amount of the light detector 237 that detects the reference light for reproduction is at the maximum Bragg angle.
  • the wavefront shape of the reference light needs to be point-symmetric with respect to the center point of the effective diameter of the reference light. This is because the reproduction reference light is phase conjugate light reflected by the optical element 234 as described above.
  • a light detection element such as a photodiode can be used.
  • any element may be used as long as the amount of light diffracted toward the light detector 236 can be detected.
  • Reproduction light that is incident as reproduction reference light and reproduced on the recording medium propagates through the objective lens 215, the relay lens 213, and the spatial filter 214. Thereafter, the reproduction light passes through the PBS prism 211 and enters the photodetector 237, and the recorded signal can be reproduced.
  • an image sensor such as a CMOS image sensor or a CCD image sensor can be used, but any element may be used as long as page data can be reproduced.
  • the Bragg angle control signal generation circuit 32 receives an output signal of an angle detection sensor (not shown) provided in the actuator 229 as an input and generates a signal used for controlling the Bragg angle of the optical element 228.
  • the pitch angle control signal generation circuit 34 receives an output signal of an angle detection sensor (not shown) provided in the actuator 227 as an input, and generates a signal used for controlling the pitch angle of the optical element 221.
  • the relative position of the lens 233 and the optical element 234 is important.
  • the actuator 235 is moved in the Bragg direction, the pitch direction, and the total light quantity of the reproduction light in the photodetector 237 so that the reflection surface of the optical element 234 is positioned perpendicular to the optical axis of the incident light and at the focal point of the convergent light.
  • the angle and position are adjusted by scanning in the order of the focal direction. The adjustment is performed before the information is reproduced, and thereafter, the adjustment angle and the position are not changed.
  • an optical encoder can be used as the angle detection sensor provided in the actuator 227 and the actuator 229.
  • the recording technology using the principle of angle multiplexing of holography tends to have a very small tolerance for the deviation of the reference beam angle. Therefore, without using the angle detection sensor provided in the actuator 229, a mechanism for detecting the deviation amount of the reference light angle is separately provided in the pickup 11, and the Bragg angle control signal generation circuit 85 inputs the output signal of the mechanism. As a configuration, a signal for use in controlling the reference light angle may be generated.
  • FIGS. 4 to 6 are schematic views showing the relationship between the reproduction reference beam and the hologram recording area during reproduction, and the upper diagram shows a reproduced image obtained by simulation. Since the reproduction reference light incident from the back side of the medium is a plane wave, the reference light vector is represented by a single arrow as shown in the figure. The wavefront of the reference light is indicated by a straight line perpendicular to and parallel to the reference light vector as shown in the figure.
  • the hologram vector formed in the medium exists for each pixel of the SLM, and the region is defined for each pixel. However, in the drawing, only one hologram vector is shown in the entire hologram region for simplicity.
  • the reproduction light can be considered as a collection of reproduction light vectors diffracted by each hologram. In the figure, among all the reproduction light vectors, three of (i) on the highest angle side with respect to the Bragg angle direction, (ii) on the center side and (iii) on the lowest angle side are indicated by arrows. .
  • the horizontal axis on the paper surface represents the Bragg direction
  • the vertical axis on the paper surface represents the pitch direction.
  • FIG. 4 shows how the hologram is reproduced in an ideal state where the hologram recording medium 1 is not expanded or contracted at all.
  • a high amount of diffracted light can be obtained in all angular directions from (i) to (iii).
  • FIG. 5 shows a state of reproduction when the temperature is lower than that during recording and the hologram recording medium 1 contracts.
  • the shrinkage direction is anisotropic shrinkage only in the thickness direction of the medium. As the interval and angle of the recorded holograms change with shrinkage, the length and direction of the hologram vector also change.
  • the Bragg diffraction condition is satisfied only at some Bragg angles, and the amount of diffracted light decreases at other Bragg angles. Therefore, the reproduced image is bright only at some Bragg angles, and a figure with bright lines in the vertical direction of the paper surface as shown in the upper diagram of FIG. 5 is obtained.
  • FIG. 6 shows the state when the hologram recording medium 1 contracts, as in FIG.
  • the state after optimizing the Bragg angle of the reference light used for reproduction to an angle that maximizes the total light amount of the reproduced image is shown.
  • the diffracted light has the largest amount of diffracted light near the center of the reproduced image with respect to the Bragg direction as shown in the upper diagram of FIG.
  • the dark area can be biased toward the high angle side in the Bragg direction of the camera image as shown in the broken line area in FIG. I understand.
  • wavefront compensation in the present embodiment will be described on the assumption that the dark region is biased to the high angle side by optimization of the Bragg angle.
  • the light quantity detected by the photodetector 236 is actually used as an index for optimization, not the diffracted light quantity of the reproduced image.
  • the total light amount is detected from the detected image image. This is because calculation time is required to calculate.
  • it is desirable to optimize the pitch angle in advance This is because when the pitch angle is not optimal, the bright line is inclined toward the Bragg direction, so that even if the Bragg angle is optimized in this state, the dark region cannot necessarily be biased to the high angle side. .
  • FIG. 7 shows a flowchart of the wavefront compensation method.
  • the hologram light information reproducing apparatus 10 drives the actuator 227 and scans the pitch angle of the reference light to search for the optimum pitch angle (step S702).
  • the detected light amount of the photodetector 236 when the pitch angle is scanned from the minimum angle to the maximum angle of the predetermined scanning range is acquired at a constant sampling period, as shown in FIG. Become a graph.
  • a quadratic function approximation is performed based on this plot, and the apex pitch angle ⁇ peak is set as the optimum pitch angle. Note that ⁇ peak does not necessarily need to be a vertex of quadratic function approximation, and the maximum value of the measured sample values may be used as it is.
  • the target angle of the actuator 227 is set to the derived optimum pitch angle ⁇ peak (step S703).
  • the actuator 229 is driven to scan the Bragg angle of the reference light to search for the optimum Bragg angle (step S704).
  • a quadratic function approximation is performed based on the plot, and the Bragg angle ⁇ peak at the vertex is set as the optimum Bragg angle. Similarly to ⁇ peak, ⁇ peak may be the maximum sample value. Alternatively, quadratic function approximation using only sample values near the vertex may be used.
  • step S705 the target angle of the actuator 229 is set to the derived optimum pitch angle ⁇ peak (step S705).
  • step S706 a later-described reference light wavefront optimization routine is performed.
  • the optimum Bragg angle ⁇ peak transitions. Therefore, the optimum Bragg angle is searched again by sweeping the Bragg angle similarly to Step S704 (Step S707).
  • the target angle of the actuator 229 is set to the new optimum Bragg angle ⁇ peak found in step S707 (step S708), and the wavefront compensation process ends (step S709).
  • the optimum pitch angle ⁇ peak may be searched and set again not only for the Bragg angle but also for the pitch angle after the reference light wavefront optimization routine.
  • the left diagram in FIG. 10 is a schematic diagram showing the geometrical relationship among the photodetector 237, the objective lens 215, and the reproduction reference light during reproduction in the hologram light information reproducing apparatus 10.
  • the focal position of the objective lens 215 is adjusted so that it is exactly in the center with respect to the thickness direction of the hologram recording medium 1, and the optical axis of the objective lens 215 is in the normal line of the recording medium 1 with respect to the Bragg direction.
  • it is designed to be inclined to the opposite side to the reproduction reference beam.
  • (i) represents a region equal to the region (i). Due to the geometric relationship of the optical system, the light beam (i) on the high angle side overlaps with almost the entire region of the reproduction reference light, and the overlap is considered when the projection surface of the reference light onto the hologram recording medium 1 is considered.
  • the region is the region indicated by (1).
  • the central (ii) ray is an area (2) that is narrower than (1), and the overlapping area of the (iii) ray on the low angle side is only a narrower central part than (2). This is the area (3).
  • the inclusion relationship of the overlap areas is (3) ⁇ (2) ⁇ (1).
  • This overlap region is exclusively divided and defined as (a), (b), and (c) as shown in the left diagram of FIG. These areas are hereinafter referred to as exclusive overlap areas.
  • exclusive overlap areas when the reference light is viewed on a plane perpendicular to the normal line of the hologram recording medium 1, it has a rectangular effective diameter as shown by the broken line in the upper right diagram of FIG. Note that the effective diameter of the reference light is not limited to a rectangular shape, and can take any shape.
  • the reproduced image is viewed from the side opposite to the incident direction of the reproduction light with respect to the photodetector, the lower right diagram in FIG. 10 is obtained.
  • Table 1 shows each of the exclusive overlapping regions. The reproduced image area affected by changing the wavefront is shown.
  • the dark region is biased toward the high angle side of the reproduced image as shown in the left diagram of FIG. I can do it. It can be confirmed that the dark region overlaps only the reproduced image region (i) as shown in FIG.
  • the relationship between the exclusive overlap areas (a), (b), and (c) and the areas (i), (ii), and (iii) with respect to the Bragg direction of the reproduced image is represented again on the effective diameter of the reference light. And as shown on the right side of FIG.
  • the area (i) of the reproduced image having the dark area has an influence on the entire overlapping area (a), (b), (c) of the effective diameter of the reference light, but the area (c) is affected as described above. Focusing only on the area (i) can be affected without affecting other areas. That is, in order to improve the amount of diffracted light in the dark region in the left diagram of FIG. 12, only the wavefront of the region (c), which is the region at both ends of the reference light wavefront, is optimized, and conversely the other (a) and (b) This means that there is no need to change the wavefront of the region.
  • the wavefront shape of the reference light to be applied to the region (c) is expressed using a function that continuously changes in the Bragg direction. This is apparent from the boundary conditions between the regions (b) and (c) and the continuity of the wave front.
  • a function having a vertex at the boundary between the (b) region and the (c) region and secondarily increasing or decreasing in the Bragg direction is used. This is because the difference in the position in the Bragg direction at the effective diameter of the reference light is equal to the difference in the angle of the overlapping signal light.
  • the degree of phase modulation is not limited as an optimization parameter.
  • the temperature at the time of reproduction at the reproduction position of the hologram recording medium 1 is measured by a non-contact type temperature sensor or estimated based on a conversion formula from the surface temperature.
  • the value may be determined based on a table value prepared in advance.
  • phase application start point can be obtained geometrically from a position where the signal light corresponding to the pixel on the lowest angle side intersects within the effective diameter of the reference light when the signal light is collected by the objective lens 215.
  • the optimization parameter is used.
  • the optimization parameter is not limited, and a geometrically derived value may be used as it is.
  • the optimization parameters in the derivation of the optimum wavefront shape in the present embodiment are two points, the phase modulation degree and the phase application start point.
  • the wavefront shape optimization will be described in detail with reference to FIG.
  • the upper diagram of FIG. 13 shows the effective diameter of the reference light and the phase shape within the effective diameter in a three-dimensional manner.
  • black represents a phase of zero
  • white represents a phase of 2 ⁇
  • the phase in between is represented by black and white gradation colors.
  • the lower diagram of FIG. 13 is a schematic diagram in which the horizontal axis represents the effective diameter of the reference light in the Bragg direction, and the vertical axis represents the phase application amount.
  • a lower diagram ( ⁇ ) in FIG. 13 is a schematic diagram showing a state where the phase application start point, which is an optimization parameter, is equal to the center of the effective reference beam diameter. In this state, the phase modulation degree, which is another optimization parameter, is shaken for each predetermined value, and the amount of light detected by the photodetector 236 at that time is confirmed.
  • the phase modulation degree on both sides from the effective diameter center of the reference light is always equal to the Bragg direction so that the wavefront shape is point-symmetric with respect to the effective diameter center.
  • the focal position of the objective lens 215 is the center of the hologram recording medium 1 in the thickness direction, so that the formed hologram is ideally point-symmetric with respect to the focal point of the objective lens 215. is there.
  • the degree of phase modulation on both sides is not always limited to the same value.
  • the phase application start point is further moved by a predetermined distance from the center of the effective diameter of the reference light to both sides in the Bragg direction as shown in the lower diagrams ( ⁇ ) and ( ⁇ ) of FIG. Like ( ⁇ ), the value is shaken for each predetermined value, and the value of the photodetector 236 at that time is confirmed. At this time, the distance from the center of the effective diameter of the reference light to the phase start points on both sides is made equal. This is due to the fact that the focal position of the objective lens 215 is at the center in the thickness direction of the hologram recording medium 1 as with the degree of phase modulation. However, the phase application amount on both sides is not always limited to the same value in the present invention. .
  • the wavefront shape with respect to the pitch direction of the effective diameter of the reference light in this embodiment is the same shape with respect to the pitch direction. This is because the signal light is convergent light by the objective lens 215, and the hologram area formed in the hologram recording medium 1 gradually decreases regardless of whether it travels in the positive or negative direction with respect to the pitch direction. This is because the sensitivity of wavefront compensation is low. In other words, this is to prevent a decrease in transfer speed during reproduction due to the time required to optimize the wavefront shape with respect to the pitch direction.
  • the wavefront shape with respect to the pitch direction is not limited to the same.
  • FIG. 14 shows a flowchart of the reference light wavefront optimization shown in step S706 of FIG.
  • step S1401 the phase application start point index i is initialized to zero (step S1402), and the phase modulation index j is also initialized to zero (step S1403).
  • step S1404 the value of the phase application start point is set to a value corresponding to the current index i in the parameter table prepared in advance (step S1404).
  • step S1407 it is determined whether the index j is Njmax, which is the maximum index value in the parameter table. If NO is determined in step S1407, the process proceeds to step S1408, and the index j is incremented by 1, and then the process proceeds to step S1404. If it is determined as Yes in step S1407, the process proceeds to step S1409, and it is determined whether or not the index i is Nimax that is the index maximum value of the parameter table.
  • step S1409 If NO is determined in step S1409, the process proceeds to step S1410, and the index i is incremented by 1, and then the process proceeds to step S1403.
  • step S1410 the index i is incremented by 1
  • step S1403 the process proceeds to step S1411, and the phase application start point and the phase modulation degree of the combination in which the diffracted light quantity acquired by the photodetector 236 is the largest in the created i ⁇ j two-dimensional map.
  • step S1411 the phase application start point and the phase modulation degree of the combination in which the diffracted light quantity acquired by the photodetector 236 is the largest in the created i ⁇ j two-dimensional map.
  • the reference light wavefront optimization ends. In the following, description will be made using results obtained by a specific optical simulation assuming that wavefront compensation is performed for distortion at the time of expansion of the hologram recording medium.
  • FIG. 15 shows the result of calculation of the reference light wavefront optimization shown in FIG. 14 by optical simulation under the condition that the expansion rate in the thickness direction of the hologram recording medium 1 is 0.105%.
  • the horizontal axis represents the value of the phase application start point at the effective diameter ratio with respect to the Bragg direction of the reference light, the difference between the markers represents the difference in the phase modulation degree of the 2 ⁇ ratio, and the vertical axis represents the amount of diffracted light in the wavefront shape of each parameter combination. Each is shown.
  • the broken line in FIG. 15 represents the amount of diffracted light when only the Bragg angle of the reference light is optimized after expansion.
  • the focal position of the objective lens 215 is adjusted so as to be exactly in the center with respect to the thickness direction of the hologram recording medium 1 has been described. Since the optimum wavefront shape of the reference light according to the present invention is derived based on the optical geometric relationship in the hologram optical information reproducing apparatus 10, a model for identifying the optimum wavefront shape if there is a difference in the optical system. Must be changed. In this embodiment, a case where the focal position of the objective lens 215 is designed as the medium surface of the hologram recording medium 1 will be described.
  • the left diagram in FIG. 16 is a schematic diagram showing a geometrical relationship among the photodetector 237, the objective lens 215, and the reproduction reference light during reproduction in the hologram light information reproducing apparatus 10.
  • the focal position of the objective lens 215 is adjusted so that it is exactly the surface position with respect to the thickness direction of the hologram recording medium 1, and the optical axis of the objective lens 215 is normal to the recording medium 1 with respect to the Bragg direction.
  • it is designed to be inclined to the opposite side to the reproduction reference beam.
  • This overlap area is divided exclusively and defined as (a), (b) and (c) as shown in the left figure of FIG.
  • Table 2 shows reproduced image regions that are affected by changing the wavefront of each of the exclusive overlap regions.
  • Table 2 is exactly the same as Table 1 of the first embodiment, changing the area (a) or (b) affects a plurality of reproduced image areas, but when changing (c), the Bragg angle It can be seen that only the high-angle side region (i) can be changed.
  • the effective diameter of the reference light and the exclusive overlap regions (a), (b), and (c) defined above are superimposed on the effective diameter of the reference light shown in the left diagram of FIG. 17, the right diagram of FIG. It becomes a relationship like this.
  • the Bragg angle is optimized so that the total light amount of the reproduced image is maximized, the dark region can be biased toward the high angle side of the reproduced image as shown in the left diagram of FIG.
  • the dark region overlaps only the reproduced image region (i) as shown in FIG.
  • the relationship between the exclusive overlap areas (a), (b), and (c) and the areas (i), (ii), and (iii) with respect to the Bragg direction of the reproduced image is represented again on the effective diameter of the reference light.
  • the area (i) of the reproduced image having the dark area has an influence on the entire overlapping area (a), (b), (c) of the effective diameter of the reference light, but the area (c) is affected as described above. Focusing only on the area (i) can be affected without affecting other areas. That is, in order to improve the amount of diffracted light in the dark region in the left diagram of FIG. 18, only the wavefront of the region (c), which is the region at both ends of the reference light wavefront, is optimized, and conversely the other (a) and (b) This means that there is no need to change the wavefront of the region.
  • the exclusive overlap region (c) used for compensation of the dark region is at both ends as shown in FIG. 12, so that the phase is searched for the boundary between the regions (b) and (c).
  • the application start point was searched from the center of the effective diameter of the reference beam toward both ends.
  • the exclusive overlap region (c) exists only at one end of the effective diameter as shown in FIG. 18, so the phase application start point is set as the reference light effective diameter as shown in FIG. The search will start from the end of the image toward the opposite end. Note that optimization of the wavefront shape of the reference light in this embodiment is the same as in FIG.
  • SYMBOLS 1 Hologram recording medium, 10 ... Hologram optical information reproducing

Abstract

In a holographic optical information reproducing device which combines two optical elements to change a reference light angle, the present invention achieves high-quality reproduction while maintaining a high transfer speed even when a deviation from the orthogonal angle is occurring in the two optical elements due to installation error or the like. Provided is a holographic optical information reproducing device that reproduces information from a recording medium on which the information has been recorded by means of irradiation with signal light and reference light, and that is provided with: an objective lens that collects the signal light; a first reference light angle alteration unit that alters the angle of the reference light irradiated on the recording medium in a Bragg angle direction; a wave surface alteration unit that is disposed in the optical path of the reference light and that alters the wave surface shape of the reference light; and a reproduction luminance information acquisition unit that acquires luminance information of reproduction light for the recording medium, wherein the first reference light angle alternation unit performs control on the Bragg angle of the reference light in accordance with the light quantity of reproduction light detected by the reproduction luminance information acquisition unit, and the wave surface alteration unit performs control, on the basis of the information obtained by the reproduction luminance information acquisition unit, on the wave surface shape that corresponds to a portion of an exclusive overlap region where the reference light and the signal light overlap with each other.

Description

ホログラム光情報再生装置Hologram optical information reproducing apparatus
　本発明は、ホログラフィを用いて記録媒体から情報を再生する装置に関する。 The present invention relates to an apparatus for reproducing information from a recording medium using holography.
　ホログラム記録技術は、空間光変調器により２次元的に変調されたページデータの情報を有する信号光を、記録媒体の内部で参照光と重ね合わせ、その時に生じる干渉縞パターンによって記録媒体内に屈折率変調を生じさせることで情報を記録媒体に記録する技術である。
  情報の再生時には、記録時に用いた参照光を記録媒体に照射すると、記録媒体中に記録されているホログラムが回折格子のように作用して回折光を生じる。この回折光が記録した信号光と位相情報を含めて同一の光として再生される。
  再生された信号光は、ＣＭＯＳやＣＣＤなどの光検出器を用いて２次元的に高速に検出される。このようにホログラム記録技術は、１つのホログラムによって２次元的な情報を光記録媒体に記録、再生することを可能とし、さらに記録媒体のある場所に複数のページデータを重ねた多重記録をすることで、大容量かつ高速な情報の記録再生を果たすことができる。
  しかし、ホログラフィックメモリでは干渉縞を記録する為に記録媒体にフォトポリマー材料を用いる。フォトポリマー材料は温度変化や吸湿により膨張および収縮する。ホログラムの再生において記録媒体の膨張および収縮が起こると、記録された干渉縞の角度や間隔が変化、歪んでしまうために再生光の回折光量が低下、ひいては信号品質が劣化する。この問題に対し、干渉縞の歪みを補償する方法として波面補償技術が提案されている。特許文献１では波面センサと波面制御器を用いた適応光学系において遺伝的アルゴリズムを用いて参照光の波面の空間的な位相を制御することで信号品質を改善する方法を提案している。 In hologram recording technology, signal light having page data information two-dimensionally modulated by a spatial light modulator is superimposed on reference light inside the recording medium and refracted into the recording medium by the interference fringe pattern generated at that time. This is a technique for recording information on a recording medium by causing rate modulation.
At the time of reproducing information, if the recording medium is irradiated with the reference light used at the time of recording, the hologram recorded in the recording medium acts like a diffraction grating to generate diffracted light. This diffracted light is reproduced as the same light including the recorded signal light and phase information.
The reproduced signal light is detected two-dimensionally at high speed using a photodetector such as a CMOS or CCD. As described above, the hologram recording technique enables two-dimensional information to be recorded and reproduced on an optical recording medium by one hologram, and further performs multiplex recording in which a plurality of page data is superimposed on a certain place of the recording medium. Thus, large-capacity and high-speed information recording / reproducing can be achieved.
However, a holographic memory uses a photopolymer material as a recording medium in order to record interference fringes. Photopolymer materials expand and contract due to temperature changes and moisture absorption. When the recording medium expands and contracts during hologram reproduction, the angle and interval of the recorded interference fringe changes and is distorted, so that the amount of diffracted light in the reproduction light decreases, and the signal quality deteriorates. In response to this problem, a wavefront compensation technique has been proposed as a method for compensating for distortion of interference fringes. Patent Document 1 proposes a method for improving signal quality by controlling a spatial phase of a wavefront of reference light using a genetic algorithm in an adaptive optical system using a wavefront sensor and a wavefront controller.
特開２００９－８６２４８JP2009-86248
　適応光学系において波面センサにより検出される光の波面や、光検出器により検出される光の強度分布が波面制御器の入力信号に対して線形ならば伝達関数を用いたフィードバック制御により波面の補償が容易である。しかし、ホログラムの再生を鑑みると、波面制御器により形成される波面形状に対する再生光の波面や強度分布の応答は非線形であり、その伝達関数が複雑となりフィードバック制御を行うことが困難である。 If the wavefront of the light detected by the wavefront sensor in the adaptive optical system or the intensity distribution of the light detected by the photodetector is linear with respect to the input signal of the wavefront controller, the wavefront is compensated by feedback control using a transfer function. Is easy. However, in view of hologram reproduction, the response of the wavefront and intensity distribution of the reproduction light to the wavefront shape formed by the wavefront controller is nonlinear, and its transfer function is complicated, making it difficult to perform feedback control.
　この問題に対して、上記特許文献１では遺伝的アルゴリズムの初期集団の遺伝型の設定値および各世代の集団を、ホログラム記録媒体特有の歪みを補償し得る設定値とし、適応度として干渉縞の歪みを補償するような設定値、例えば再生光のＳＮＲ（Ｓｉｇｎａｌ　ｔｏ　Ｎｏｉｓｅ　Ｒａｔｉｏ）とすることで波面形状の最適化を行う。しかし、遺伝的アルゴリズムは評価の為に集団のサイズだけ毎世代において計算を行わなくてはならない。評価値が収束するまでの計算量は非常に膨大となり、集団サイズや評価値の設定によっては高速な計算機を用いても最適化に時間を要する。ホログラム光情報再生装置として波面補償に伴う再生時の転送速度の低下を防ぐためには、波面形状の最適化に要する時間は出来る限り短くなければならない。また特許文献１で用いられる遺伝的アルゴリズムは、その初期値の設定によっては局所解に陥ってしまい、真に最適な波面形状が得られないこともある。 In order to solve this problem, in Patent Document 1 described above, the genotype setting value of the initial population of the genetic algorithm and the population of each generation are set values that can compensate for distortions peculiar to the hologram recording medium. The wavefront shape is optimized by using a setting value that compensates for distortion, for example, the SNR (Signal to Noise Ratio) of the reproduction light. However, the genetic algorithm must perform calculation for each generation by the size of the population for evaluation. The amount of calculation until the evaluation value converges is extremely large, and optimization takes time even if a high-speed computer is used depending on the group size and evaluation value setting. In order to prevent a decrease in transfer speed during reproduction accompanying wavefront compensation as a hologram optical information reproducing apparatus, the time required for optimizing the wavefront shape must be as short as possible. Moreover, the genetic algorithm used in Patent Document 1 falls into a local solution depending on the setting of the initial value, and a truly optimal wavefront shape may not be obtained.
　本発明の目的は、波面制御器を用いた適応光学系においてカメラ画像と参照光波面の関係をモデル化し、ホログラム記録媒体の膨張または収縮に伴う干渉縞の歪みを補償し得る波面形状を高速に導出し、高い転送速度を維持しつつ、かつ高品質な再生品質を実現することである。 An object of the present invention is to model the relationship between a camera image and a reference light wavefront in an adaptive optical system using a wavefront controller, and to achieve a wavefront shape capable of compensating for interference fringe distortion caused by expansion or contraction of a hologram recording medium at high speed. Deriving and realizing high reproduction quality while maintaining a high transfer rate.
　上記課題は、例えば請求項の範囲に記載の発明により解決される。 The above problem is solved by, for example, the invention described in the scope of claims.
　本発明によれば、ホログラム記録媒体の膨張または収縮に伴い干渉縞に歪みが生じた場合でも高い転送速度を維持しつつ、かつ高品質な再生品質を実現することができる。 According to the present invention, it is possible to achieve high quality reproduction quality while maintaining a high transfer speed even when the interference fringes are distorted due to expansion or contraction of the hologram recording medium.
本発明のホログラム光情報再生装置を示すブロック図The block diagram which shows the hologram optical information reproducing | regenerating apparatus of this invention 本発明のホログラム光情報再生装置の記録時のピックアップを表す模式図The schematic diagram showing the pickup at the time of recording of the hologram optical information reproducing | regenerating apparatus of this invention 本発明のホログラム光情報再生装置の再生時のピックアップを表す模式図The schematic diagram showing the pickup at the time of reproduction | regeneration of the hologram optical information reproducing | regenerating apparatus of this invention 理想状態における再生画像およびホログラムの再生の様子を表す模式図Schematic diagram showing the playback image and hologram playback in an ideal state 収縮が生じた際の再生画像およびホログラム再生の様子を表す模式図Schematic diagram showing the playback image and hologram playback when shrinkage occurs 収縮が生じた際に参照光角度を最適化した際の再生画像およびホログラム再生の様子を表す模式図Schematic diagram showing the playback image and hologram playback when the reference beam angle is optimized when shrinkage occurs 波面補償の方法を示したフローチャートFlow chart showing wavefront compensation method 図７ステップＳ７０２におけるピッチ角度探索のためのピッチ角度に対する回折光量の分布を示した模式図7 is a schematic diagram showing the distribution of the amount of diffracted light with respect to the pitch angle for searching the pitch angle in step S702. 図７ステップＳ７０４におけるブラッグ角度探索のためのブラッグ角度に対する回折光量の分布を示した模式図7 is a schematic diagram showing the distribution of the amount of diffracted light with respect to the Bragg angle for searching for the Bragg angle in step S704. 実施例１におけるホログラム光情報再生装置１０における再生時の光検出器２３７および対物レンズ２１５および再生用参照光の幾何的関係を表した模式図The schematic diagram showing the geometric relationship of the photodetector 237, the objective lens 215, and the reference light for reproduction | regeneration at the time of reproduction | regeneration in the hologram optical information reproduction | regeneration apparatus 10 in Example 1 実施例１における参照光有効径での排他的オーバーラップ領域の分布を示した模式図The schematic diagram which showed distribution of the exclusive overlap area | region in the reference beam effective diameter in Example 1 実施例１における排他的オーバーラップ領域の分布と再生画像の分割領域の関係を示した模式図Schematic diagram showing the relationship between the distribution of exclusive overlap regions and the divided regions of a reproduced image in Example 1 参照光の有効径および有効径内の位相形状および実施例１におけるブラッグ方向に対する波面形状のパラメータ最適化の様子を示した模式図Schematic diagram showing the parameter optimization of the effective diameter of the reference light, the phase shape within the effective diameter, and the wavefront shape in the Bragg direction in the first embodiment 本発明の参照光の波面形状の最適化処理を示したフローチャートThe flowchart which showed the optimization process of the wavefront shape of the reference light of this invention 本発明の参照光波面最適化をホログラム記録媒体１の厚み方向の膨張率＝０．１０５％の条件で光学シミュレーションにより計算した結果The result of calculating the reference light wavefront optimization of the present invention by optical simulation under the condition that the expansion rate in the thickness direction of the hologram recording medium 1 is 0.105% 実施例２におけるホログラム光情報再生装置１０における再生時の光検出器２３７および対物レンズ２１５および再生用参照光の幾何的関係を表した模式図The schematic diagram showing the geometric relationship of the photodetector 237 and the objective lens 215 at the time of reproduction | regeneration in the hologram optical information reproduction | regeneration apparatus 10 in Example 2, and the reference light for reproduction | regeneration 実施例２における参照光有効径での排他的オーバーラップ領域の分布を示した模式図The schematic diagram which showed distribution of the exclusive overlap area | region in the reference beam effective diameter in Example 2 実施例２における排他的オーバーラップ領域の分布と再生画像の分割領域の関係を示した模式図Schematic diagram showing the relationship between the distribution of the exclusive overlap region and the divided region of the reproduced image in Example 2 参照光の有効径および有効径内の位相形状および実施例１におけるブラッグ方向に対する波面形状のパラメータ最適化の様子を示した模式図Schematic diagram showing the parameter optimization of the effective diameter of the reference light, the phase shape within the effective diameter, and the wavefront shape in the Bragg direction in the first embodiment 記録を行った際に形成されるホログラム領域と対物レンズ２１５の光軸の幾何的関係図Geometrical relationship between the hologram area formed when recording and the optical axis of the objective lens 215
　以下、本発明の実施例について図面を用いて説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
　本発明の実施形態を添付図面にしたがって説明する。　　図１はホログラフィを利用してデジタル情報を再生するホログラム記録媒体の光情報再生装置を示すブロック図である。
  ホログラム光情報再生装置１０は、入出力制御回路９０を介して外部制御装置９１と接続されている。ホログラム記録媒体１に情報を記録する場合には、ホログラム再生装置１０は外部制御装置９１から記録する情報信号を入出力制御回路９０により受信する。ホログラム記録媒体１から情報を再生する場合には、ホログラム再生装置１０は再生した情報信号を入出力制御回路９０により外部制御装置９１に送信する。 Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an optical information reproducing apparatus of a hologram recording medium for reproducing digital information using holography.
The hologram optical information reproducing device 10 is connected to an external control device 91 via an input / output control circuit 90. When recording information on the hologram recording medium 1, the hologram reproducing device 10 receives an information signal to be recorded from the external control device 91 by the input / output control circuit 90. When reproducing information from the hologram recording medium 1, the hologram reproducing device 10 transmits the reproduced information signal to the external control device 91 by the input / output control circuit 90.
　ホログラム光情報再生装置１０は、ピックアップ１１、再生用参照光光学系１２、キュア光学系１３、ディスク回転角度検出センサ１４、半径位置検出センサ１５及びスピンドルモータ５０、半径方向搬送部５１を備えている。
  スピンドルモータ５０は、その回転軸に対してホログラム記録媒体１を着脱可能な媒体着脱部（図示しない）を有しており、ホログラム記録媒体１はスピンドルモータ５０によって回転可能な構成となっている。同時にホログラム記録媒体１は半径方向搬送部５１によって、ピックアップ１１の位置を基準として、半径方向に移動可能な構成となっている。
  信号光及び／または参照光が照射される位置は後述するピックアップ１１の位置によって決まり、装置に固定された位置である。本実施例においては、スピンドルモータ５０及び半径方向搬送部５１の可動部及び移動ステージ５１が、信号光及び／または参照光が照射されるホログラム記録媒体１上の位置を変更する手段として機能する。 The hologram optical information reproducing apparatus 10 includes a pickup 11, a reproduction reference light optical system 12, a cure optical system 13, a disk rotation angle detection sensor 14, a radial position detection sensor 15, a spindle motor 50, and a radial direction conveyance unit 51. .
The spindle motor 50 has a medium attaching / detaching portion (not shown) that allows the hologram recording medium 1 to be attached to and detached from its rotation axis. The hologram recording medium 1 is configured to be rotatable by the spindle motor 50. At the same time, the hologram recording medium 1 is configured to be movable in the radial direction by the radial transport unit 51 with reference to the position of the pickup 11.
The position where the signal light and / or the reference light is irradiated is determined by the position of the pickup 11 described later, and is a position fixed to the apparatus. In the present embodiment, the spindle motor 50, the movable part of the radial transport part 51, and the moving stage 51 function as means for changing the position on the hologram recording medium 1 to which the signal light and / or the reference light is irradiated.
　回転角度検出センサ１４は、ホログラム記録媒体１の回転角度を検出するために用いられる。回転角度検出センサ１４は例えばホログラム記録媒体１に設けられた角度検出用マークを用いて、ホログラム記録媒体１の回転角度を検出する。回転角度検出センサ１４の出力信号は回転角度制御回路２１に入力される。信号光及び参照光の照射される回転角度を変更する場合には、回転角度制御回路２１が回転角度検出センサ１４の出力信号及びコントローラ８０からの指令信号に基づいて駆動信号を生成し、スピンドル駆動回路２２を介してスピンドルモータ５０を駆動する。これにより、ホログラム記録媒体１の回転角度を制御する事が出来る。
  また、半径位置検出センサ１５は、半径方向搬送部５１の可動部の位置を検出するために用いられる。半径位置検出センサ１５は例えば所定パターンを有するスケールが固定されている位置検出パターンを用いて半径方向搬送部５１の可動部の位置を検出する。半径位置検出センサ１５の出力信号は半径位置制御回路２３に入力される。信号光及び参照光の照射される半径位置を変更する場合は、半径位置制御回路２３が半径位置検出センサ１５の出力信号及びコントローラ８０からの指令信号に基づいて駆動信号を生成し、半径位置駆動回路２４を介して半径方向搬送部５１を駆動する。これにより、ホログラム記録媒体１が半径方向に搬送され、信号光及び参照光の照射される半径位置を制御する事が出来る。 The rotation angle detection sensor 14 is used for detecting the rotation angle of the hologram recording medium 1. The rotation angle detection sensor 14 detects the rotation angle of the hologram recording medium 1 using, for example, an angle detection mark provided on the hologram recording medium 1. An output signal of the rotation angle detection sensor 14 is input to the rotation angle control circuit 21. When changing the rotation angle irradiated with the signal light and the reference light, the rotation angle control circuit 21 generates a drive signal based on the output signal of the rotation angle detection sensor 14 and the command signal from the controller 80 to drive the spindle. The spindle motor 50 is driven via the circuit 22. Thereby, the rotation angle of the hologram recording medium 1 can be controlled.
The radial position detection sensor 15 is used to detect the position of the movable part of the radial direction transport part 51. The radial position detection sensor 15 detects the position of the movable part of the radial direction transport part 51 using, for example, a position detection pattern in which a scale having a predetermined pattern is fixed. An output signal of the radial position detection sensor 15 is input to the radial position control circuit 23. When the radial position irradiated with the signal light and the reference light is changed, the radial position control circuit 23 generates a drive signal based on the output signal of the radial position detection sensor 15 and the command signal from the controller 80 to drive the radial position. The radial conveyance unit 51 is driven via the circuit 24. Thereby, the hologram recording medium 1 is conveyed in the radial direction, and the radial position irradiated with the signal light and the reference light can be controlled.
　ピックアップ１１は、参照光と信号光をホログラム記録媒体１に照射してホログラフィを利用してデジタル情報を記録媒体に記録する役割を果たす。この際、記録する情報信号はコントローラ８０によって信号生成回路８１を介してピックアップ１１内の後述する空間光変調器に送られ、信号光は空間光変調器によって変調される。 The pickup 11 plays a role of irradiating the hologram recording medium 1 with reference light and signal light and recording digital information on the recording medium using holography. At this time, the information signal to be recorded is sent by the controller 80 to a spatial light modulator (described later) in the pickup 11 via the signal generation circuit 81, and the signal light is modulated by the spatial light modulator.
　ホログラム記録媒体１に記録した情報を再生する場合は、ピックアップ１１から出射された参照光を記録時とは逆の向きにホログラム記録媒体１に入射させる光波を再生用参照光光学系１２にて生成する。再生用参照光によって再生される再生光をピックアップ１１内の後述する光検出器によって検出し、信号処理回路８２によって信号を再生する。 When reproducing the information recorded on the hologram recording medium 1, the reproduction reference light optical system 12 generates a light wave that causes the reference light emitted from the pickup 11 to enter the hologram recording medium 1 in the direction opposite to that during recording. To do. The reproduction light reproduced by the reproduction reference light is detected by a photodetector described later in the pickup 11, and the signal is reproduced by the signal processing circuit 82.
　参照光の角度は、参照光のページデータの多重角度を担う入射角度をブラッグ角度θについてはブラッグ角度制御回路３２により駆動信号を生成し、ブラッグ角度駆動回路３３を介してピックアップ１１内の後述するアクチュエータ２２２を、信号光の光軸と記録媒体の法線を含む面に対して略垂直方向の面での参照光の入射角度をピッチ角度φについてはピッチ角度制御回路３５により駆動信号を生成し、ピッチ角度駆動回路３６を介してピックアップ１１内の後述するアクチュエータ２２０を、そして再生用参照光光学系１２内の後述するアクチュエータ２２５を駆動することで制御される。ブラッグ角度制御信号生成回路３１ではピックアップ１１及び再生用参照光光学系１２の少なくとも一方の出力信号からブラッグ角度の制御に用いるための信号を生成する。ブラッグ角度制御回路３２は、コントローラ８０からの指示に従ってブラッグ角度制御信号生成回路３１の出力信号を用いて制御を行う。同様にピッチ角度制御信号生成回路３４ではピックアップ１１及び再生用参照光光学系１２の少なくとも一方の出力信号からピッチ角度の制御に用いるための信号を生成する。ピッチ角度制御回路３４は、コントローラ８０からの指示に従ってブラッグ角度制御信号生成回路３１の出力信号を用いて制御を行う。 As for the angle of the reference light, an incident angle serving as a multiple angle of the page data of the reference light is generated. For the Bragg angle θ, a drive signal is generated by the Bragg angle control circuit 32, and will be described later in the pickup 11 via the Bragg angle drive circuit 33. The actuator 222 generates a drive signal by the pitch angle control circuit 35 for the angle of reference light incident on the surface substantially perpendicular to the surface including the optical axis of the signal light and the normal line of the recording medium. Control is performed by driving an actuator 220 described later in the pickup 11 and an actuator 225 described later in the reproduction reference light optical system 12 through the pitch angle driving circuit 36. The Bragg angle control signal generation circuit 31 generates a signal for use in controlling the Bragg angle from the output signal of at least one of the pickup 11 and the reproduction reference light optical system 12. The Bragg angle control circuit 32 performs control using the output signal of the Bragg angle control signal generation circuit 31 in accordance with an instruction from the controller 80. Similarly, the pitch angle control signal generation circuit 34 generates a signal to be used for controlling the pitch angle from the output signals of at least one of the pickup 11 and the reproduction reference light optical system 12. The pitch angle control circuit 34 performs control using the output signal of the Bragg angle control signal generation circuit 31 in accordance with an instruction from the controller 80.
　ホログラム記録媒体１に照射する参照光と信号光の照射時間は、ピックアップ１１内のシャッタ２０３の開閉時間をコントローラ８０によってシャッタ制御回路３７を介して制御することで調整できる。
  キュア光学系１３は、ホログラム記録媒体１のプリキュア及びポストキュアに用いる光ビームを生成する役割を果たす。プリキュアとは、ホログラム記録媒体１内の所望の位置に情報を記録する際、所望位置に参照光と信号光を照射する前に予め所定の光ビームを照射する前工程である。ポストキュアとは、ホログラム記録媒体１内の所望の位置に情報を記録した後、該所望の位置に追記不可能とするために所定の光ビームを照射する後工程である。プリキュア及びポストキュアに用いる光ビームは、インコヒーレントな光、即ち可干渉性（コヒーレンス）の低い光である必要があることが好ましい。
  光源駆動回路３８からは所定の光源駆動電流がピックアップ１１、キュア光学系１３内の光源に供給され、各々の光源からは所定の光量で光ビームを発光することができる。 The irradiation time of the reference light and the signal light applied to the hologram recording medium 1 can be adjusted by controlling the opening / closing time of the shutter 203 in the pickup 11 via the shutter control circuit 37 by the controller 80.
The cure optical system 13 plays a role of generating a light beam used for pre-curing and post-curing of the hologram recording medium 1. Pre-curing is a pre-process for irradiating a predetermined light beam in advance before irradiating the reference light and signal light to the desired position when recording information at the desired position in the hologram recording medium 1. Post-cure is a post-process for irradiating a predetermined light beam after recording information at a desired position in the hologram recording medium 1 so that additional recording cannot be performed at the desired position. The light beam used for pre-cure and post-cure is preferably incoherent light, that is, light with low coherence.
A predetermined light source driving current is supplied from the light source driving circuit 38 to the light sources in the pickup 11 and the cure optical system 13, and each light source can emit a light beam with a predetermined light quantity.
　また、ピックアップ１１、キュア光学系１３は、いくつかの光学系構成または全ての光学系構成をひとつに纏めて簡素化しても構わない。
  なお、本発明のホログラム再生装置１０における「再生」とは、ホログラム再生機能を有することを表すものであり、ホログラムの記録機能を備えていないということではない。すなわち、再生機能と記録機能の両方を有する装置も本発明のホログラム再生装置１０の概念に含まれる。 Further, the pickup 11 and the cure optical system 13 may be simplified by combining several optical system configurations or all optical system configurations into one.
Note that “reproduction” in the hologram reproduction apparatus 10 of the present invention means having a hologram reproduction function, and does not mean that the hologram recording function is not provided. That is, an apparatus having both a reproducing function and a recording function is also included in the concept of the hologram reproducing apparatus 10 of the present invention.
　図２は、ホログラム再生装置１０におけるピックアップ１１及び再生用参照光光学系１２の、基本的な光学系構成の一例における記録原理を示したものである。再生用参照光光学系１２は、後述する光学素子２３２とレンズ２３３とアクチュエータ２３５とミラー２３４から成る。 FIG. 2 shows a recording principle in an example of a basic optical system configuration of the pickup 11 and the reproducing reference light optical system 12 in the hologram reproducing apparatus 10. The reproduction reference light optical system 12 includes an optical element 232, a lens 233, an actuator 235, and a mirror 234, which will be described later.
　光源２０１を出射した光ビームはコリメートレンズ２０２を透過し、シャッタ２０３に入射する。シャッタ２０３が開いている時は、光ビームはシャッタ２０３を通過した後、例えば２分の１波長板などで構成される光学素子２０４によってｐ偏光とｓ偏光の光量比が所望の比になるようになど偏光方向が制御された後、ＰＢＳ（Ｐｏｌａｒｉｚａｔｉｏｎ　Ｂｅａｍ　Ｓｐｌｉｔｔｅｒ）プリズム２０５に入射する。
  ＰＢＳプリズム２０５を透過した光ビームは、信号光２０６として働き、ビームエキスパンダ２０８によって光ビーム径が拡大された後、位相マスク２０９、リレーレンズ２１０、ＰＢＳプリズム２１１を透過して空間光変調器２１２に入射する。
  信号光２０６は位相マスク２０９を通過することによって位相情報が付加される。空間光変調器２１２によって情報が付加された信号光は、ＰＢＳプリズム２１１を反射し、リレーレンズ２１３ならびに空間フィルタ２１４を伝播する。その後、信号光は対物レンズ２１５によってホログラム記録媒体１に集光する。 The light beam emitted from the light source 201 passes through the collimator lens 202 and enters the shutter 203. When the shutter 203 is open, after the light beam passes through the shutter 203, the optical element 204 composed of, for example, a half-wave plate or the like, adjusts the light quantity ratio of p-polarized light and s-polarized light to a desired ratio. After the polarization direction is controlled, the light beam enters a PBS (Polarization Beam Splitter) prism 205.
The light beam that has passed through the PBS prism 205 functions as signal light 206, and after the light beam diameter is expanded by the beam expander 208, the light beam passes through the phase mask 209, the relay lens 210, and the PBS prism 211 and passes through the spatial light modulator 212. Is incident on.
Phase information is added to the signal light 206 by passing through the phase mask 209. The signal light to which information is added by the spatial light modulator 212 reflects the PBS prism 211 and propagates through the relay lens 213 and the spatial filter 214. Thereafter, the signal light is condensed on the hologram recording medium 1 by the objective lens 215.
　一方、ＰＢＳプリズム２０５を反射した光ビームは参照光２０７として働き、偏光方向変換素子２１６によって記録時または再生時に応じて所定の偏光方向に設定された後、ＰＢＳプリズム２１７により反射され光学素子２１８を透過する。光学素子２１８は例えば４分の１波長板などで構成される。その後、反射面を理想的な平面形状とした波面変更器２１９により反射され再び光学素子２１８およびＰＢＳプリズム２１７を透過し光学素子２２０に入射する。波面変更器は例えばデフォーマブルミラーを用いることができる。光学素子２２０は例えば偏光方向が変更可能な２分の１波長板で構成され、記録時の図２においては入射した参照光の偏光の方位角と光学素子２２０の光学軸のなす角がゼロとなる角度、すなわち参照光の偏光状態が変わらないように設定される。次に光学素子２２０を透過した参照光はＰＢＳプリズム２２１により反射され、光学素子２２５を通過した後に光学素子２２６に入射する。光学素子２２５は例えば偏光方向が変更可能な２分の１波長板で構成され、光学素子２２０と同じく記録時の図２では参照光の偏光が変わらないように設定される。なお、光学素子２２０および２２５は波面センサ２２４側に参照光が分岐しない偏光となる光学軸の設定に限定されるものでなく、再生時において波面センサ２２４側に参照光が分岐する偏光となるよう光学軸を設定であっても構わない。 On the other hand, the light beam reflected from the PBS prism 205 works as reference light 207, and is set to a predetermined polarization direction according to recording or reproduction by the polarization direction conversion element 216, and then reflected by the PBS prism 217 to pass through the optical element 218. To Penetrate. The optical element 218 is composed of, for example, a quarter wave plate. Thereafter, the light is reflected by a wavefront modifier 219 having a reflection surface that is an ideal planar shape, and is again transmitted through the optical element 218 and the PBS prism 217 to enter the optical element 220. For example, a deformable mirror can be used as the wavefront changer. The optical element 220 is formed of, for example, a half-wave plate whose polarization direction can be changed, and in FIG. 2 at the time of recording, the angle formed by the azimuth angle of the incident reference light polarization and the optical axis of the optical element 220 is zero. Is set such that the polarization state of the reference light does not change. Next, the reference light transmitted through the optical element 220 is reflected by the PBS prism 221, passes through the optical element 225, and then enters the optical element 226. The optical element 225 is formed of, for example, a half-wave plate whose polarization direction can be changed, and is set so that the polarization of the reference light does not change in FIG. The optical elements 220 and 225 are not limited to the setting of the optical axis that is polarized so that the reference light does not branch to the wavefront sensor 224 side, but are polarized so that the reference light branches to the wavefront sensor 224 side during reproduction. The optical axis may be set.
　光学素子２２６はアクチュエータ２２７によってピッチ角度方向に反射角度を調整可能である。光学素子２２６により反射された参照光は光学素子２２８に入射する。光学素子２２８はアクチュエータ２２９によってブラッグ角度方向に反射角度を調整可能である。光学素子２２８により反射された参照光は、レンズ２３０とレンズ２３１を通過した後にホログラム記録媒体１に入射する。例えば光学素子２２６は反射型プリズム、光学素子２２８はミラー、アクチュエータ２２７およびアクチュエータ２２９はガルバノメータを用いることができる。 The reflection angle of the optical element 226 can be adjusted in the pitch angle direction by the actuator 227. The reference light reflected by the optical element 226 enters the optical element 228. The reflection angle of the optical element 228 can be adjusted in the Bragg angle direction by an actuator 229. The reference light reflected by the optical element 228 passes through the lens 230 and the lens 231 and then enters the hologram recording medium 1. For example, the optical element 226 may be a reflective prism, the optical element 228 may be a mirror, and the actuator 227 and the actuator 229 may be galvanometers.
　このように信号光と参照光とをホログラム記録媒体１において、互いに重ね合うように入射させることで、記録媒体内には干渉縞パターンが形成され、このパターンを記録媒体に書き込むことで情報を記録する。また、アクチュエータ２２９によってホログラム記録媒体１に入射する参照光のブラッグ角度を変化させることができるため、角度多重による記録が可能である。 In this way, the signal light and the reference light are incident on the hologram recording medium 1 so as to overlap each other, whereby an interference fringe pattern is formed in the recording medium, and information is recorded by writing this pattern on the recording medium. . In addition, since the Bragg angle of the reference light incident on the hologram recording medium 1 can be changed by the actuator 229, recording by angle multiplexing is possible.
　図２０にホログラム記録媒体１に記録を行った際に形成されるホログラム領域と対物レンズ２１５の光軸の幾何的関係を示す。線分２００１は対物レンズ２１５の光軸を表す。ブラッグ角度は光軸２００１と記録媒体１の法線を含む面２００２内で規定される角度を表す。当該面２００２を入射面とする。入射面２００２内における前記対物レンズ２１５で集光される信号光のうち、図中２００３で示される最も参照光の入射角度に近い光線を最近接光線とする。前記入射面２００２に垂直な面のうち最近接光線２００３を含む平面２００４が通過する参照光の領域を以降、領域（ｉ）と呼ぶ。
  以降、同じ領域に参照光角度を変えて記録されたホログラムにおいて、１つ１つのブラッグ角度に対応したホログラムをページと呼び、同領域に角度多重されたページの集合をブックと呼ぶことにする。 FIG. 20 shows the geometric relationship between the hologram area formed when recording on the hologram recording medium 1 and the optical axis of the objective lens 215. A line segment 2001 represents the optical axis of the objective lens 215. The Bragg angle represents an angle defined in a plane 2002 including the normal line of the optical axis 2001 and the recording medium 1. The surface 2002 is an incident surface. Of the signal light collected by the objective lens 215 in the incident surface 2002, the light beam closest to the incident angle of the reference light indicated by 2003 in the figure is the closest light beam. The region of the reference light through which the plane 2004 including the closest light ray 2003 among the surfaces perpendicular to the incident surface 2002 passes is hereinafter referred to as a region (i).
Hereinafter, in holograms recorded in the same area with different reference light angles, holograms corresponding to each Bragg angle are called pages, and a set of pages angle-multiplexed in the same area is called a book.
　図３は、ホログラム光情報再生装置１０におけるピックアップ１１及び再生用参照光光学系１２の、基本的な光学系構成の一例における再生原理を示したものである。記録した情報を再生する場合は、波面変更器２１９では参照光に所望の位相情報を付加し、波面形状を変更して光学素子２２０に入射する。再生時の図３において入射した参照光の変更の方位角と光学素子２２０の光学軸は所定の角度をもって配置される。光学素子２２０によりｐ偏光とｓ偏光の光量比が所望の比になるようになど偏光方向が制御された後、ＰＢＳプリズム２２１を透過した参照光はレンズ２２２とレンズ２２３を通過し、検出に最適な光ビーム径で波面センサ２２４に入射する。一方、ＰＢＳプリズム２２１を反射した参照光は記録時と同様に記録媒体１に入射する。前述したように参照光をホログラム記録媒体１に入射し、ホログラム記録媒体１を透過した光ビームは、光学素子２３２を通過し、レンズ２３３により光学素子２３４の反射面状に集光される。光学素子２３２は例えば４分の１波長板により構成される。光学素子２３４はアクチュエータ２３５によって所望の反射面の前後の位置およびピッチ方向およびブラッグ方向に対する反射角度を調整可能であり、レンズ２３３により集光された参照光を反射する。光学素子２３４で反射された光は入射時と同一の光路を通り、レンズ２３３および光学素子２３２を通過する。該反射光は入射時とは同一角度で入射方向がピッチ方向およびブラッグ方向に対して異なる位相共役の光ビームである。該位相共役の光ビームを再生用参照光と呼ぶ。再生用参照光は位相共役な光なので、波面変更器２１９で変更した波面形状は光学素子２３４においてブラッグ方向およびピッチ方向の両方向に対して逆転した形状となる。しかし、波面変更器２１９で与える波面形状が参照光の有効径の中心点に対して点対称であれば、再生用参照光における波面形状は入射時と全く同じ形状で媒体に裏面から入射することができる。 FIG. 3 shows a reproduction principle in an example of a basic optical system configuration of the pickup 11 and the reproduction reference light optical system 12 in the hologram light information reproduction apparatus 10. When reproducing the recorded information, the wavefront modifier 219 adds desired phase information to the reference light, changes the wavefront shape, and enters the optical element 220. The azimuth angle for changing the incident reference light in FIG. 3 during reproduction and the optical axis of the optical element 220 are arranged with a predetermined angle. After the polarization direction is controlled by the optical element 220 such that the light quantity ratio between p-polarized light and s-polarized light becomes a desired ratio, the reference light transmitted through the PBS prism 221 passes through the lens 222 and the lens 223 and is optimal for detection. The light is incident on the wavefront sensor 224 with a light beam diameter. On the other hand, the reference light reflected from the PBS prism 221 is incident on the recording medium 1 in the same manner as during recording. As described above, the light beam incident on the hologram recording medium 1 and transmitted through the hologram recording medium 1 passes through the optical element 232, and is collected by the lens 233 on the reflecting surface of the optical element 234. The optical element 232 is composed of, for example, a quarter wave plate. The optical element 234 can adjust the position before and after the desired reflecting surface and the reflection angle with respect to the pitch direction and the Bragg direction by the actuator 235, and reflects the reference light collected by the lens 233. The light reflected by the optical element 234 passes through the same optical path as the incident light and passes through the lens 233 and the optical element 232. The reflected light is a phase-conjugate light beam having the same angle as that at the time of incidence and the incident direction being different from the pitch direction and the Bragg direction. The phase conjugate light beam is referred to as reproduction reference light. Since the reproduction reference light is phase conjugate light, the wavefront shape changed by the wavefront changer 219 is reversed in the optical element 234 with respect to both the Bragg direction and the pitch direction. However, if the wavefront shape given by the wavefront modifier 219 is point-symmetric with respect to the center point of the effective diameter of the reference light, the wavefront shape of the reference light for reproduction is exactly the same as that at the time of incidence and is incident on the medium from the back surface. Can do.
　一方でホログラム記録媒体１に表面から入射し、再生用参照光とは逆側に回折した光ビームは光検出器２３６によって検出される。光検出器２３６は再生用参照光を検出する光検出器２３７の光量が最大となるブラッグ角度のときに光検出器２３６で検出する光量も最大となるように位置付けされている。ただし、光検出器２３６と光検出器の２３７の光量をともに最大とするには参照光の波面形状が参照光の有効径の中心点に対して点対称である必要がある。これは既述のように、再生用参照光が光学素子２３４で反射された位相共役光である為である。なお、検出器２３６としては例えばフォトダイオードなどの光検出素子を用いることができるが、光検出器２３６側に回折した光量を検出可能であればどのような素子であっても構わない。 On the other hand, the light beam incident on the hologram recording medium 1 from the surface and diffracted to the side opposite to the reproduction reference light is detected by the photodetector 236. The light detector 236 is positioned so that the amount of light detected by the light detector 236 is also maximized when the light amount of the light detector 237 that detects the reference light for reproduction is at the maximum Bragg angle. However, in order to maximize both the light amounts of the photodetector 236 and the photodetector 237, the wavefront shape of the reference light needs to be point-symmetric with respect to the center point of the effective diameter of the reference light. This is because the reproduction reference light is phase conjugate light reflected by the optical element 234 as described above. As the detector 236, for example, a light detection element such as a photodiode can be used. However, any element may be used as long as the amount of light diffracted toward the light detector 236 can be detected.
　再生用参照光として入射し、記録媒体にて再生された再生光は、対物レンズ２１５、リレーレンズ２１３ならびに空間フィルタ２１４を伝播する。その後、再生光はＰＢＳプリズム２１１を透過して光検出器２３７に入射し、記録した信号を再生することができる。光検出器２３７としては例えばＣＭＯＳイメージセンサーやＣＣＤイメージセンサーなどの撮像素子を用いることができるが、ページデータを再生可能であれば、どのような素子であっても構わない。 Reproduction light that is incident as reproduction reference light and reproduced on the recording medium propagates through the objective lens 215, the relay lens 213, and the spatial filter 214. Thereafter, the reproduction light passes through the PBS prism 211 and enters the photodetector 237, and the recorded signal can be reproduced. As the photodetector 237, an image sensor such as a CMOS image sensor or a CCD image sensor can be used, but any element may be used as long as page data can be reproduced.
　なお本実施例において、ブラッグ角度制御信号生成回路３２はアクチュエータ２２９に備え付けられた角度検出センサ（図示しない）の出力信号を入力として、光学素子２２８のブラッグ角度の制御に用いるための信号を生成する。同様にピッチ角度制御信号生成回路３４はアクチュエータ２２７に備え付けられた角度検出センサ（図示しない）の出力信号を入力として、光学素子２２１のピッチ角度の制御に用いるための信号を生成する。 In this embodiment, the Bragg angle control signal generation circuit 32 receives an output signal of an angle detection sensor (not shown) provided in the actuator 229 as an input and generates a signal used for controlling the Bragg angle of the optical element 228. . Similarly, the pitch angle control signal generation circuit 34 receives an output signal of an angle detection sensor (not shown) provided in the actuator 227 as an input, and generates a signal used for controlling the pitch angle of the optical element 221.
　再生用参照光光学系１２における光学素子２３４に関しては、レンズ２３３と光学素子２３４の相対位置が重要となる。光学素子２３４の反射面は入射光の光軸と垂直かつ収束光の焦点に位置付くよう、光検出器２３７における再生光の総光量が最大となるよう、アクチュエータ２３５をブラッグ方向、ピッチ方向、そして焦点方向の順に走査することで角度および位置の調整を行う。該調整は情報の再生前までに実施され、以降、該調整角度および位置から変更しない。 Regarding the optical element 234 in the reproduction reference light optical system 12, the relative position of the lens 233 and the optical element 234 is important. The actuator 235 is moved in the Bragg direction, the pitch direction, and the total light quantity of the reproduction light in the photodetector 237 so that the reflection surface of the optical element 234 is positioned perpendicular to the optical axis of the incident light and at the focal point of the convergent light. The angle and position are adjusted by scanning in the order of the focal direction. The adjustment is performed before the information is reproduced, and thereafter, the adjustment angle and the position are not changed.
　アクチュエータ２２７、アクチュエータ２２９に備え付けられた角度検出センサは、例えば、光学式エンコーダを用いることができる。 For example, an optical encoder can be used as the angle detection sensor provided in the actuator 227 and the actuator 229.
　ところで、ホログラフィの角度多重の原理を利用した記録技術は、参照光角度のずれに対する許容誤差が極めて小さくなる傾向がある。そのため、アクチュエータ２２９に備え付けられた角度検出センサを用いずに、ピックアップ１１内に参照光角度のずれ量を検出する機構を別に設けて、ブラッグ角度制御信号生成回路８５が該機構の出力信号を入力として参照光角度の制御に用いるための信号を生成する構成としても構わない。 By the way, the recording technology using the principle of angle multiplexing of holography tends to have a very small tolerance for the deviation of the reference beam angle. Therefore, without using the angle detection sensor provided in the actuator 229, a mechanism for detecting the deviation amount of the reference light angle is separately provided in the pickup 11, and the Bragg angle control signal generation circuit 85 inputs the output signal of the mechanism. As a configuration, a signal for use in controlling the reference light angle may be generated.
　図４から図６を用いて、ホログラム記録媒体１に膨張収縮が生じた際に、参照光の位相情報を変更せず平面波のまま、すなわち波面補償を用いない参照光の角度のみの補償方法を説明する。図４から図６の下図は再生時の再生用参照光およびホログラム記録領域の関係を表した模式図を、上図はシミュレーションにより得られる再生画像をそれぞれ示している。メディアの裏面より入射された再生用参照光は平面波であるため参照光ベクトルは図中のように一本の矢印で表される。参照光の波面は図中のように参照光ベクトルに垂直かつ平行な直線で示される。媒体中に形成されたホログラムベクトルはＳＬＭのピクセルごとに存在し、その領域はピクセルごとに定義されるが、図中では簡単のために全ホログラム領域に１つのホログラムベクトルのみを表記している。再生光は各ホログラムで回折された再生光ベクトルの集まりとして考えられる。図中では全再生光ベクトルの内、ブラッグ角度方向に対して最も高角度側の（ｉ）、中央の（ｉｉ）および最も低角度側の（ｉｉｉ）の３つを代表として矢印で示している。なお再生画像において紙面横軸がブラッグ方向を、紙面縦軸がピッチ方向をそれぞれ表す。 4 to 6, a method for compensating only the angle of the reference light without changing the phase information of the reference light without changing the phase information of the reference light, that is, using the wavefront compensation when the hologram recording medium 1 is expanded or contracted is used. explain. The lower diagrams of FIGS. 4 to 6 are schematic views showing the relationship between the reproduction reference beam and the hologram recording area during reproduction, and the upper diagram shows a reproduced image obtained by simulation. Since the reproduction reference light incident from the back side of the medium is a plane wave, the reference light vector is represented by a single arrow as shown in the figure. The wavefront of the reference light is indicated by a straight line perpendicular to and parallel to the reference light vector as shown in the figure. The hologram vector formed in the medium exists for each pixel of the SLM, and the region is defined for each pixel. However, in the drawing, only one hologram vector is shown in the entire hologram region for simplicity. The reproduction light can be considered as a collection of reproduction light vectors diffracted by each hologram. In the figure, among all the reproduction light vectors, three of (i) on the highest angle side with respect to the Bragg angle direction, (ii) on the center side and (iii) on the lowest angle side are indicated by arrows. . In the reproduced image, the horizontal axis on the paper surface represents the Bragg direction, and the vertical axis on the paper surface represents the pitch direction.
　図４はホログラム記録媒体１に膨張収縮が全くない理想状態におけるホログラムの再生の様子を示したものである。この場合、（ｉ）から（ｉｉｉ）の全角度方向に対して高い回折光量が得られる。また、図４上図に示したように再生画像の全面においても高い回折光量が得られる。図５は記録時よりも温度が低くなり、ホログラム記録媒体１が収縮した際の再生の様子を示している。ただし、収縮方向は媒体の厚み方向のみの非等方な収縮とする。収縮に伴い、記録されたホログラムの間隔および角度が変化するので、ホログラムベクトルの長さおよび方向も変化する。この場合、一部のブラッグ角度でのみブラッグの回折条件が成り立ち、それ以外のブラッグ角度では回折光量が低下する。その為、再生画像も一部のブラッグ角度でのみ明るく図５上図のように紙面の縦方向に対して輝線が入ったような図が得られる。 FIG. 4 shows how the hologram is reproduced in an ideal state where the hologram recording medium 1 is not expanded or contracted at all. In this case, a high amount of diffracted light can be obtained in all angular directions from (i) to (iii). Further, as shown in the upper diagram of FIG. 4, a high amount of diffracted light can be obtained over the entire surface of the reproduced image. FIG. 5 shows a state of reproduction when the temperature is lower than that during recording and the hologram recording medium 1 contracts. However, the shrinkage direction is anisotropic shrinkage only in the thickness direction of the medium. As the interval and angle of the recorded holograms change with shrinkage, the length and direction of the hologram vector also change. In this case, the Bragg diffraction condition is satisfied only at some Bragg angles, and the amount of diffracted light decreases at other Bragg angles. Therefore, the reproduced image is bright only at some Bragg angles, and a figure with bright lines in the vertical direction of the paper surface as shown in the upper diagram of FIG. 5 is obtained.
　図６は図５と同じくホログラム記録媒体１が収縮した際の様子である。ただし、図５と異なり、再生の用いる参照光のブラッグ角度を再生画像の総光量が最大となる角度へと最適化した後の様子を示している。再生画像の総光量が最大となるようにブラッグ角度を最適化すると回折光は図６上図のようにブラッグ方向に対して再生画像の中心付近での回折光量が最大となる。ここで、再生画像の総光量が最大となるようにブラッグ角度を最適化すると、図６上図の破線領域に示すようにカメラ画像のブラッグ方向の高角度側に暗領域を偏らせることができることが分かる。以降、ブラッグ角度の最適化により暗領域を高角度側に偏らせた状態を前提として本実施例における波面補償を説明する。なお、最適化における指標は実際には再生画像の回折光量ではなく、光検出器２３６で検出される光量を用いる。これは再生用参照光とは逆側に回折した光ビームの総光量が直接検出できる光検出器２３６に対して、二次元イメージセンサーを用いる光検出器２３７の場合、検出した画像イメージから総光量を計算するまでに演算時間を要する為である。また、ブラッグ角度に対して最適化をする際には事前にピッチ角度について最適化を実施していることが望ましい。これはピッチ角度が最適でない状態では前記輝線がブラッグ方向側に傾いて入ってしまう為、その状態でブラッグ角度を最適化しても暗領域を必ずしも高角度側に偏らせることが出来ない為である。 FIG. 6 shows the state when the hologram recording medium 1 contracts, as in FIG. However, unlike FIG. 5, the state after optimizing the Bragg angle of the reference light used for reproduction to an angle that maximizes the total light amount of the reproduced image is shown. When the Bragg angle is optimized so that the total light amount of the reproduced image is maximized, the diffracted light has the largest amount of diffracted light near the center of the reproduced image with respect to the Bragg direction as shown in the upper diagram of FIG. Here, if the Bragg angle is optimized so that the total amount of light in the reproduced image is maximized, the dark area can be biased toward the high angle side in the Bragg direction of the camera image as shown in the broken line area in FIG. I understand. Hereinafter, wavefront compensation in the present embodiment will be described on the assumption that the dark region is biased to the high angle side by optimization of the Bragg angle. Note that the light quantity detected by the photodetector 236 is actually used as an index for optimization, not the diffracted light quantity of the reproduced image. In contrast to the photodetector 236 that can directly detect the total light amount of the light beam diffracted to the side opposite to the reproduction reference light, in the case of the photodetector 237 using a two-dimensional image sensor, the total light amount is detected from the detected image image. This is because calculation time is required to calculate. Further, when optimizing the Bragg angle, it is desirable to optimize the pitch angle in advance. This is because when the pitch angle is not optimal, the bright line is inclined toward the Bragg direction, so that even if the Bragg angle is optimized in this state, the dark region cannot necessarily be biased to the high angle side. .
　本実施例における波面補償の方法について図７を用いて詳細に説明する。図７は波面補償の方法のフローチャートを示したものである。波面補償を開始すると（ステップＳ７０１）、ホログラム光情報再生装置１０はアクチュエータ２２７を駆動して参照光のピッチ角度を走査して最適ピッチ角度を探索する（ステップＳ７０２）。ピッチ角度を所定の走査レンジの最小角度から最大角度まで走査した際の光検出器２３６の検出光量を一定のサンプリング周期で取得すると、図８に示すようにピッチ角度φに対して白丸のようなグラフになる。該プロットを基に二次関数近似を行い、頂点となるピッチ角度φｐｅａｋを最適ピッチ角度とする。なお、φｐｅａｋは必ずしも二次関数近似の頂点である必要はなく、測定したサンプル値における最大値をそのまま用いても構わない。 The wavefront compensation method in the present embodiment will be described in detail with reference to FIG. FIG. 7 shows a flowchart of the wavefront compensation method. When wavefront compensation is started (step S701), the hologram light information reproducing apparatus 10 drives the actuator 227 and scans the pitch angle of the reference light to search for the optimum pitch angle (step S702). When the detected light amount of the photodetector 236 when the pitch angle is scanned from the minimum angle to the maximum angle of the predetermined scanning range is acquired at a constant sampling period, as shown in FIG. Become a graph. A quadratic function approximation is performed based on this plot, and the apex pitch angle φpeak is set as the optimum pitch angle. Note that φpeak does not necessarily need to be a vertex of quadratic function approximation, and the maximum value of the measured sample values may be used as it is.
　また、走査レンジによっては全サンプル値を用いずに頂点付近のサンプル値のみを用いた二次関数近似としても構わない。次に、導出した最適ピッチ角度φｐｅａｋへとアクチュエータ２２７の目標角度を設定する（ステップＳ７０３）。ステップＳ７０３に続いてはアクチュエータ２２９を駆動して参照光のブラッグ角度を走査して最適ブラッグ角度を探索する（ステップＳ７０４）。ブラッグ角度を所定の走査レンジの最小角度から最大角度まで走査した際の光検出器２３６の検出光量を一定のサンプリング周期で取得すると、図９に示すようにブラッグ角度θに対して白丸のようなグラフになる。該プロットを基に二次関数近似を行い、頂点となるブラッグ角度θｐｅａｋを最適ブラッグ角度とする。θｐｅａｋもφｐｅａｋと同様、サンプル値における最大値を用いても構わない。また、頂点付近のサンプル値のみを用いた二次関数近似としても構わない。 Also, depending on the scanning range, it is possible to use quadratic function approximation using only sample values near the apex without using all sample values. Next, the target angle of the actuator 227 is set to the derived optimum pitch angle φpeak (step S703). Following step S703, the actuator 229 is driven to scan the Bragg angle of the reference light to search for the optimum Bragg angle (step S704). When the detected light amount of the photodetector 236 when the Bragg angle is scanned from the minimum angle to the maximum angle of the predetermined scanning range is acquired at a constant sampling period, as shown in FIG. Become a graph. A quadratic function approximation is performed based on the plot, and the Bragg angle θpeak at the vertex is set as the optimum Bragg angle. Similarly to φpeak, θpeak may be the maximum sample value. Alternatively, quadratic function approximation using only sample values near the vertex may be used.
　次に、導出した最適ピッチ角度θｐｅａｋへとアクチュエータ２２９の目標角度を設定する（ステップＳ７０５）。ステップＳ７０６では後述する参照光波面最適化ルーチンが実施される。該参照光波面最適化ルーチンが実施されると最適ブラッグ角度θｐｅａｋが遷移する為、ステップＳ７０４と同様に再びブラッグ角度をスイープして最適ブラッグ角度を探索する（ステップＳ７０７）。その後、ステップＳ７０７で判明した新たな最適ブラッグ角度θｐｅａｋへとアクチュエータ２２９の目標角度を設定し（ステップＳ７０８）、波面補償の処理は終了する（ステップＳ７０９）。なお、参照光波面最適化ルーチン後にブラッグ角度だけでなくピッチ角度についても最適ピッチ角度φｐｅａｋの探索および設定を再度行っても構わない。 Next, the target angle of the actuator 229 is set to the derived optimum pitch angle θpeak (step S705). In step S706, a later-described reference light wavefront optimization routine is performed. When the reference light wavefront optimization routine is executed, the optimum Bragg angle θpeak transitions. Therefore, the optimum Bragg angle is searched again by sweeping the Bragg angle similarly to Step S704 (Step S707). After that, the target angle of the actuator 229 is set to the new optimum Bragg angle θpeak found in step S707 (step S708), and the wavefront compensation process ends (step S709). Note that the optimum pitch angle φpeak may be searched and set again not only for the Bragg angle but also for the pitch angle after the reference light wavefront optimization routine.
　図１０を用いて参照光と再生画像の光学的な幾何的関係を説明する。図１０左図はホログラム光情報再生装置１０における再生時の光検出器２３７、対物レンズ２１５、再生用参照光の幾何的関係を表した模式図である。本実施例では対物レンズ２１５の焦点位置はホログラム記録媒体１の厚み方向に対してちょうど中央の位置となるように位置調整され、対物レンズ２１５の光軸はブラッグ方向に関して記録媒体１の法線に対して再生用参照光とは逆側に傾いて設計されている。 The optical geometric relationship between the reference light and the reproduced image will be described with reference to FIG. The left diagram in FIG. 10 is a schematic diagram showing the geometrical relationship among the photodetector 237, the objective lens 215, and the reproduction reference light during reproduction in the hologram light information reproducing apparatus 10. In this embodiment, the focal position of the objective lens 215 is adjusted so that it is exactly in the center with respect to the thickness direction of the hologram recording medium 1, and the optical axis of the objective lens 215 is in the normal line of the recording medium 1 with respect to the Bragg direction. On the other hand, it is designed to be inclined to the opposite side to the reproduction reference beam.
　今、カメラに受光される回折光のうち、参照光角度方向に対して最も高角度側の（ｉ）、中央の（ｉｉ）、最も低角度側の（ｉｉｉ）と再生用参照光のオーバーラップする領域を考える。ここで（ｉ）は前記領域（ｉ）と等しい領域を表している。上記光学系の幾何的関係から、高角度側の（ｉ）の光線は再生用参照光のほぼ全領域とオーバーラップし、参照光のホログラム記録媒体１への投影面で考えると、そのオーバーラップ領域は（１）で示される領域となる。同様に考えると、中央の（ｉｉ）の光線は（１）よりも狭い（２）の領域となり、低角度側の（ｉｉｉ）の光線のオーバーラップ領域は（２）よりもさらに狭い中心部分のみの（３）の領域となる。オーバーラップ領域の包含関係は（３）⊂（２）⊂（１）となる。このオーバーラップ領域を排他的に区切り、図１０左図のようにそれぞれ（ａ）、（ｂ）、（ｃ）と定義する。これら領域を以下、排他的オーバーラップ領域と呼ぶ。ここで参照光をホログラム記録媒体１の法線に対して垂直な平面上で見ると、図１０右上図の破線で示されるような矩形の有効径をもった形となる。なお、参照光の有効径は矩形に限定するものでなく、任意の形状を取ることが出来る。一方で光検出器に対して再生光の入射方向と反対側から再生画像を見ると図１０右下図になる。 Now, among the diffracted light received by the camera, (i) at the highest angle side with respect to the reference light angle direction, (ii) at the center, and (iii) at the lowest angle side overlap with the reference light for reproduction. Think about the area to do. Here, (i) represents a region equal to the region (i). Due to the geometric relationship of the optical system, the light beam (i) on the high angle side overlaps with almost the entire region of the reproduction reference light, and the overlap is considered when the projection surface of the reference light onto the hologram recording medium 1 is considered. The region is the region indicated by (1). In the same way, the central (ii) ray is an area (2) that is narrower than (1), and the overlapping area of the (iii) ray on the low angle side is only a narrower central part than (2). This is the area (3). The inclusion relationship of the overlap areas is (3) ⊂ (2) ⊂ (1). This overlap region is exclusively divided and defined as (a), (b), and (c) as shown in the left diagram of FIG. These areas are hereinafter referred to as exclusive overlap areas. Here, when the reference light is viewed on a plane perpendicular to the normal line of the hologram recording medium 1, it has a rectangular effective diameter as shown by the broken line in the upper right diagram of FIG. Note that the effective diameter of the reference light is not limited to a rectangular shape, and can take any shape. On the other hand, when the reproduced image is viewed from the side opposite to the incident direction of the reproduction light with respect to the photodetector, the lower right diagram in FIG. 10 is obtained.
　再生画像のブラッグ方向に対する領域（ｉ）、（ｉｉ）、（ｉｉｉ）に対してオーバーラップする参照光の領域における波面がそれぞれ影響を与えるという考えに基づき、表１に排他的オーバーラップ領域それぞれの波面を変更することで影響を受ける再生画像領域を示す。 Based on the idea that the wavefronts in the regions of the reference light that overlap the regions (i), (ii), and (iii) with respect to the Bragg direction of the reproduced image each have an influence, Table 1 shows each of the exclusive overlapping regions. The reproduced image area affected by changing the wavefront is shown.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
表１から領域（ａ）または（ｂ）を変更すると複数の再生画像領域に影響を与えてしまうが，（ｃ）を変更する場合はブラッグ角度に対して高角側の領域（ｉ）だけを変更することができることが分かる。ここで、改めて参照光の有効径と先ほど定義した排他的オーバーラップ領域（ａ）、（ｂ）、（ｃ）を図１１左図で示す参照光の有効径に重ねると、図１１右図のような関係になる。 Changing the area (a) or (b) from Table 1 affects multiple playback image areas, but when changing (c), only the area (i) on the high angle side with respect to the Bragg angle is changed. You can see that you can. Here, when the effective diameter of the reference light and the exclusive overlap regions (a), (b), and (c) defined above are overlapped with the effective diameter of the reference light shown in the left diagram of FIG. 11, the right diagram of FIG. It becomes a relationship like this.
　ここで、図６の説明で述べたように、再生画像の総光量が最大となるようにブラッグ角度を最適化すると図１２左図のように再生画像の高角度側に暗領域を偏らせることが出来る。暗領域は図１２中図のように再生画像領域（ｉ）とのみ重なっていることが確認できる。一方で、排他的オーバーラップ領域（ａ）、（ｂ）、（ｃ）と再生画像のブラッグ方向に対する領域（ｉ）、（ｉｉ）、（ｉｉｉ）の関係を改めて参照光の有効径上で表すと図１２右図のようになる。暗領域のある再生画像の領域（ｉ）は参照光有効径の排他的オーバーラップ領域（ａ）、（ｂ）、（ｃ）全領域において影響があるが、前述のように領域（ｃ）にのみ着目すると、他の領域に影響を与えずに領域（ｉ）のみに影響を与えることが出来る。すなわち、図１２左図の暗領域における回折光量を改善させる場合には参照光波面の両端の領域である領域（ｃ）の波面のみを最適化し、逆に他の（ａ）および（ｂ）の領域の波面を変化させる必要がないことを意味する。 Here, as described in the explanation of FIG. 6, when the Bragg angle is optimized so that the total light amount of the reproduced image is maximized, the dark region is biased toward the high angle side of the reproduced image as shown in the left diagram of FIG. I can do it. It can be confirmed that the dark region overlaps only the reproduced image region (i) as shown in FIG. On the other hand, the relationship between the exclusive overlap areas (a), (b), and (c) and the areas (i), (ii), and (iii) with respect to the Bragg direction of the reproduced image is represented again on the effective diameter of the reference light. And as shown on the right side of FIG. The area (i) of the reproduced image having the dark area has an influence on the entire overlapping area (a), (b), (c) of the effective diameter of the reference light, but the area (c) is affected as described above. Focusing only on the area (i) can be affected without affecting other areas. That is, in order to improve the amount of diffracted light in the dark region in the left diagram of FIG. 12, only the wavefront of the region (c), which is the region at both ends of the reference light wavefront, is optimized, and conversely the other (a) and (b) This means that there is no need to change the wavefront of the region.
　次に最適波面形状の導出について説明する。上述した内容から波面形状を変更すべき参照光の領域は（ｃ）領域であると判明した。ここで、（ｃ）領域に印加すべき参照光の波面形状は、ブラッグ方向に対して連続的に変化する関数を用いて表現する。これは（ｂ）領域と（ｃ）領域の境界条件および波面の連続性から明らかである。また、該波面形状を表す連続的に変化する関数としては（ｂ）領域と（ｃ）領域の境界において頂点をもち、ブラッグ方向に対して二次的に増加あるいは減少する関数を用いる。これは、参照光の有効径においてブラッグ方向の位置の違いはオーバーラップする信号光の角度の違いと等しい為である。すなわち、ブラッグ方向の位置に応じて、必要とされる波面ベクトルの方向は一定ではなく常に変化する為である。一方で、関数のブラッグ方向に対する二次的な変化率はホログラム記録媒体１の膨張率および収縮率に依存する為、本実施例においては最適化パラメータとする。以降、この変化率のことを位相変調度と呼ぶ。本発明において位相変調度は最適化パラメータとして限定するものではなく、例えば非接触型温度センサによりホログラム記録媒体１の再生箇所における再生時の温度を測定あるいは表面温度からの変換式に基づき推定することで、予め用意したテーブル値に基づいてその値を決定してもよい。 Next, the derivation of the optimum wavefront shape will be described. From the above description, it has been found that the reference light region whose wavefront shape is to be changed is the region (c). Here, the wavefront shape of the reference light to be applied to the region (c) is expressed using a function that continuously changes in the Bragg direction. This is apparent from the boundary conditions between the regions (b) and (c) and the continuity of the wave front. As the continuously changing function representing the wavefront shape, a function having a vertex at the boundary between the (b) region and the (c) region and secondarily increasing or decreasing in the Bragg direction is used. This is because the difference in the position in the Bragg direction at the effective diameter of the reference light is equal to the difference in the angle of the overlapping signal light. That is, according to the position in the Bragg direction, the direction of the required wavefront vector is not constant but always changes. On the other hand, since the secondary change rate of the function with respect to the Bragg direction depends on the expansion rate and contraction rate of the hologram recording medium 1, it is set as an optimization parameter in this embodiment. Hereinafter, this rate of change is referred to as a phase modulation degree. In the present invention, the degree of phase modulation is not limited as an optimization parameter. For example, the temperature at the time of reproduction at the reproduction position of the hologram recording medium 1 is measured by a non-contact type temperature sensor or estimated based on a conversion formula from the surface temperature. Thus, the value may be determined based on a table value prepared in advance.
　また、（ｃ）領域と（ｂ）領域の具体的な境界が不明である。この（ｃ）領域と（ｂ）領域の境界を以降、位相印加開始点と呼ぶ。位相印加開始点は、理想的には最も低角度側のピクセルに相当する信号光が対物レンズ２１５によって集光される際に参照光の有効径内で交わる位置から幾何的に求めることが出来るが、本実施例においては最適化パラメータとする。しかし、本発明においては最適化パラメータとして限定するものではなく、幾何的に導出した値をそのまま使用してもよい。 Also, the specific boundary between (c) region and (b) region is unknown. Hereinafter, the boundary between the (c) region and the (b) region is referred to as a phase application start point. Ideally, the phase application start point can be obtained geometrically from a position where the signal light corresponding to the pixel on the lowest angle side intersects within the effective diameter of the reference light when the signal light is collected by the objective lens 215. In this embodiment, the optimization parameter is used. However, in the present invention, the optimization parameter is not limited, and a geometrically derived value may be used as it is.
　以上から、本実施例における最適波面形状の導出における最適化パラメータは位相変調度と位相印加開始点の２点である。図１３を用いて波面形状の最適化について詳しく説明する。図１３上図は参照光の有効径および有効径内の位相形状を三次元的に示したものである。図１３上図有効径内において、黒色は位相ゼロを、白色は位相２πを、その間の位相は黒と白の階調色で表される。 From the above, the optimization parameters in the derivation of the optimum wavefront shape in the present embodiment are two points, the phase modulation degree and the phase application start point. The wavefront shape optimization will be described in detail with reference to FIG. The upper diagram of FIG. 13 shows the effective diameter of the reference light and the phase shape within the effective diameter in a three-dimensional manner. In the upper effective diameter in FIG. 13, black represents a phase of zero, white represents a phase of 2π, and the phase in between is represented by black and white gradation colors.
　続いて、図１３上図内の二重線上でブラッグ方向に対して二次元化した様子を図１３下図によって表現する。図１３下図は横軸にブラッグ方向の参照光有効径を、縦軸に位相印加量を示した模式図である。図１３下図（α）は最適化パラメータである位相印加開始点が参照光有効径の中心に等しい様子を表した模式図である。この状態でもう一つの最適化パラメータである位相変調度を所定の値ごとに振って、その際の光検出器２３６の検出光量を確認する。このとき、ブラッグ方向に対して参照光の有効径中心から両側の位相変調度は常に等しくし、波面形状が有効径中心に点対称の関係となるようにする。これは本実施例において、対物レンズ２１５の焦点位置がホログラム記録媒体１の厚み方向中心であることから、形成されるホログラムが理想的には対物レンズ２１５の焦点に対して点対称である為である。しかし、本発明に関しては両側の位相変調度は常に等しい値に限定するものではない。 Subsequently, the state of two-dimensionalization with respect to the Bragg direction on the double line in the upper diagram of FIG. 13 is expressed by the lower diagram of FIG. The lower diagram of FIG. 13 is a schematic diagram in which the horizontal axis represents the effective diameter of the reference light in the Bragg direction, and the vertical axis represents the phase application amount. A lower diagram (α) in FIG. 13 is a schematic diagram showing a state where the phase application start point, which is an optimization parameter, is equal to the center of the effective reference beam diameter. In this state, the phase modulation degree, which is another optimization parameter, is shaken for each predetermined value, and the amount of light detected by the photodetector 236 at that time is confirmed. At this time, the phase modulation degree on both sides from the effective diameter center of the reference light is always equal to the Bragg direction so that the wavefront shape is point-symmetric with respect to the effective diameter center. This is because, in this embodiment, the focal position of the objective lens 215 is the center of the hologram recording medium 1 in the thickness direction, so that the formed hologram is ideally point-symmetric with respect to the focal point of the objective lens 215. is there. However, in the present invention, the degree of phase modulation on both sides is not always limited to the same value.
　波面形状の最適化ではさらに、位相印加開始点を図１３下図（β）や（γ）のように参照光の有効径中心からブラッグ方向の両側に所定の距離だけ移動し、かつ位相変調度を（α）と同じく所定の値ごとに振って、その際の光検出器２３６の値を確認する。このとき参照光の有効径中心から両側の位相開始点までの距離は等しくする。これは位相変調度と同様に対物レンズ２１５の焦点位置がホログラム記録媒体１の厚み方向中心であることに起因するが、本発明に関しては両側の位相印加量は常に等しい値に限定するものではない。 In the optimization of the wavefront shape, the phase application start point is further moved by a predetermined distance from the center of the effective diameter of the reference light to both sides in the Bragg direction as shown in the lower diagrams (β) and (γ) of FIG. Like (α), the value is shaken for each predetermined value, and the value of the photodetector 236 at that time is confirmed. At this time, the distance from the center of the effective diameter of the reference light to the phase start points on both sides is made equal. This is due to the fact that the focal position of the objective lens 215 is at the center in the thickness direction of the hologram recording medium 1 as with the degree of phase modulation. However, the phase application amount on both sides is not always limited to the same value in the present invention. .
　なお、図１３の説明では参照光有効径のブラッグ方向に対する波面形状についてのみ説明した。一方で本実施例における参照光有効径のピッチ方向に対する波面形状は、ピッチ方向に対して同一形状とする。これは、信号光が対物レンズ２１５による収束光であり、ホログラム記録媒体１において形成されるホログラム領域がピッチ方向に対して正負どちらの方向に進行しても、徐々に少なくなることからピッチ方向に対する波面補償の感度が低い為である。すなわち、ピッチ方向に対しての波面形状の最適化に要する時間に伴う再生時の転送速度の低下を防ぐためである。しかし、本発明においてピッチ方向に対しての波面形状は同一に限定されるものではない。 In the description of FIG. 13, only the wavefront shape with respect to the Bragg direction of the effective diameter of the reference light has been described. On the other hand, the wavefront shape with respect to the pitch direction of the effective diameter of the reference light in this embodiment is the same shape with respect to the pitch direction. This is because the signal light is convergent light by the objective lens 215, and the hologram area formed in the hologram recording medium 1 gradually decreases regardless of whether it travels in the positive or negative direction with respect to the pitch direction. This is because the sensitivity of wavefront compensation is low. In other words, this is to prevent a decrease in transfer speed during reproduction due to the time required to optimize the wavefront shape with respect to the pitch direction. However, in the present invention, the wavefront shape with respect to the pitch direction is not limited to the same.
　参照光の波面形状の最適化について、図１４を用いて詳しく説明する。図１４は図７のステップＳ７０６で示された参照光波面最適化のフローチャートを示したものである。参照光波面の最適化を開始すると（ステップＳ１４０１）、位相印加開始点のインデックスｉをゼロに初期化し（ステップＳ１４０２）、位相変調度のインデックスｊもゼロに初期化する（ステップＳ１４０３）。次に位相印加開始点の値を予め用意したパラメータテーブルのうち、現在のインデックスｉに相当する値に設定する（ステップＳ１４０４）。次に位相変調度を予め用意したパラメータテーブルのうち、現在のインデックスｊに相当する値に設定する（ステップＳ１４０５）、光検出器２３６により得られる回折光量を取得する（ステップＳ１４０６）。次にステップＳ１４０７ではインデックスｊがパラメータテーブルのインデックス最大値であるＮｊｍａｘであるかを判定する。ステップＳ１４０７においてＮｏと判断された場合、ステップＳ１４０８へと移行し、インデックスｊは１だけインクリメントされた後にステップＳ１４０４へと移行する。ステップＳ１４０７においてＹｅｓと判定された場合、ステップＳ１４０９へ移行し、インデックスｉがパラメータテーブルのインデックス最大値であるＮｉｍａｘであるかを判定する。ステップＳ１４０９においてＮｏと判断された場合、ステップＳ１４１０へと移行し、インデックスｉは１だけインクリメントされた後にステップＳ１４０３へと移行する。ステップＳ１４０９においてＹｅｓと判定された場合、ステップＳ１４１１へ移行し、作成したｉ×ｊの二次元マップにおいて光検出器２３６で取得された回折光量が最も大きくなる組み合わせの位相印加開始点および位相変調度のパラメータを設定し、参照光波面最適化は終了する。
  以下、ホログラム記録媒体の膨張時の歪みに対して波面補償を行うことを想定した、具体的な光学シミュレーションにより得られた結果を用いて説明する。 The optimization of the wavefront shape of the reference light will be described in detail with reference to FIG. FIG. 14 shows a flowchart of the reference light wavefront optimization shown in step S706 of FIG. When optimization of the reference light wavefront is started (step S1401), the phase application start point index i is initialized to zero (step S1402), and the phase modulation index j is also initialized to zero (step S1403). Next, the value of the phase application start point is set to a value corresponding to the current index i in the parameter table prepared in advance (step S1404). Next, the phase modulation degree is set to a value corresponding to the current index j in the parameter table prepared in advance (step S1405), and the amount of diffracted light obtained by the photodetector 236 is acquired (step S1406). In step S1407, it is determined whether the index j is Njmax, which is the maximum index value in the parameter table. If NO is determined in step S1407, the process proceeds to step S1408, and the index j is incremented by 1, and then the process proceeds to step S1404. If it is determined as Yes in step S1407, the process proceeds to step S1409, and it is determined whether or not the index i is Nimax that is the index maximum value of the parameter table. If NO is determined in step S1409, the process proceeds to step S1410, and the index i is incremented by 1, and then the process proceeds to step S1403. When it is determined Yes in step S1409, the process proceeds to step S1411, and the phase application start point and the phase modulation degree of the combination in which the diffracted light quantity acquired by the photodetector 236 is the largest in the created i × j two-dimensional map. The reference light wavefront optimization ends.
In the following, description will be made using results obtained by a specific optical simulation assuming that wavefront compensation is performed for distortion at the time of expansion of the hologram recording medium.
　図１５は図１４で示した参照光波面最適化をホログラム記録媒体１の厚み方向の膨張率＝０．１０５％の条件で光学シミュレーションにより計算した結果である。横軸は参照光のブラッグ方向に対する有効径比での位相印加開始点の値を、マーカーの違いは２π比の位相変調度の違いを、縦軸は各パラメータの組み合わせの波面形状における回折光量をそれぞれ示す。図１５中の破線は膨張後に参照光のブラッグ角度のみ最適化した際の回折光量を表す。すなわち、該破線を回折光量が上回っている場合、波面補償により膨張に伴う回折光量劣化を改善できており、該破線を回折光量が下回っている場合、波面補償により回折光量が劣化していることを表す。結果として、本実施例における波面補償を適用することで回折光量が改善することが確認できる。また、位相印加開始点１５％、位相変調度＋１．５０（＝３π）の最適化パラメータの組み合わせが最も回折光量を改善する最適波面形状として導出できたことが確認できる。 FIG. 15 shows the result of calculation of the reference light wavefront optimization shown in FIG. 14 by optical simulation under the condition that the expansion rate in the thickness direction of the hologram recording medium 1 is 0.105%. The horizontal axis represents the value of the phase application start point at the effective diameter ratio with respect to the Bragg direction of the reference light, the difference between the markers represents the difference in the phase modulation degree of the 2π ratio, and the vertical axis represents the amount of diffracted light in the wavefront shape of each parameter combination. Each is shown. The broken line in FIG. 15 represents the amount of diffracted light when only the Bragg angle of the reference light is optimized after expansion. That is, when the amount of diffracted light exceeds the broken line, deterioration of the amount of diffracted light due to expansion can be improved by wavefront compensation, and when the amount of diffracted light falls below the broken line, the amount of diffracted light is degraded by wavefront compensation. Represents. As a result, it can be confirmed that the amount of diffracted light is improved by applying the wavefront compensation in this embodiment. Further, it can be confirmed that the combination of the optimization parameters of the phase application start point 15% and the phase modulation degree + 1.50 (= 3π) can be derived as the optimum wavefront shape that most improves the diffracted light quantity.
　このように、再生画像の総光量が最大となるようにブラッグ角度を最適化することで再生画像の高角度側に暗領域を偏らせ、参照光有効径の排他的オーバーラップ領域の特定の領域の波面形状を最適化することで、干渉縞の歪みを補償できる波面形状を高速に導出し、高い転送速度を維持しつつ、高品質な再生品質を実現できる。 In this way, by optimizing the Bragg angle so that the total light amount of the reproduced image is maximized, the dark area is biased to the high angle side of the reproduced image, and a specific area of the exclusive overlapping area of the reference light effective diameter By optimizing the wavefront shape, a wavefront shape capable of compensating for interference fringe distortion can be derived at high speed, and high-quality reproduction quality can be realized while maintaining a high transfer rate.
　実施例１では、対物レンズ２１５の焦点位置はホログラム記録媒体１の厚み方向に対してちょうど中央の位置となるように位置調整された場合について説明した。本発明の参照光の最適波面形状はホログラム光情報再生装置１０における光学的幾何学関係を基に導出しているので、光学系に差異がある場合は最適な波面形状を同定する為のモデルを変更しなくてはならない。本実施例では、対物レンズ２１５の焦点位置はホログラム記録媒体１の媒体表面として設計した場合について説明する。 In the first embodiment, the case where the focal position of the objective lens 215 is adjusted so as to be exactly in the center with respect to the thickness direction of the hologram recording medium 1 has been described. Since the optimum wavefront shape of the reference light according to the present invention is derived based on the optical geometric relationship in the hologram optical information reproducing apparatus 10, a model for identifying the optimum wavefront shape if there is a difference in the optical system. Must be changed. In this embodiment, a case where the focal position of the objective lens 215 is designed as the medium surface of the hologram recording medium 1 will be described.
　図１６を用いて参照光と再生画像の光学的な幾何的関係を説明する。図１６左図はホログラム光情報再生装置１０における再生時の光検出器２３７、対物レンズ２１５、再生用参照光の幾何的関係を表した模式図である。本実施例では対物レンズ２１５の焦点位置はホログラム記録媒体１の厚み方向に対してちょうど表面の位置となるように位置調整され、対物レンズ２１５の光軸はブラッグ方向に関して記録媒体１の法線に対して再生用参照光とは逆側に傾いて設計されている。実施例１と同様に再生画像のうち、参照光のブラッグ角度方向に対して最も高角度側の（ｉ）、中央の（ｉｉ）、最も低角度側の（ｉｉｉ）と再生用参照光のオーバーラップする領域を考える。高角度側の（ｉ）の光線は再生用参照光のほぼ全領域とオーバーラップし、参照光のホログラム記録媒体１への投影面で考えると、そのオーバーラップ領域は（１）で表される。同様に考えると、中央の（ｉｉ）の光線は（１）よりも狭い（２）の領域となり、低角度側の（ｉｉｉ）の光線のオーバーラップ領域は（２）よりもさらに狭い端の部分のみの（３）の領域となる。オーバーラップ領域の包含関係は（３）⊂（２） ⊂（１）となる。 The optical geometric relationship between the reference light and the reproduced image will be described with reference to FIG. The left diagram in FIG. 16 is a schematic diagram showing a geometrical relationship among the photodetector 237, the objective lens 215, and the reproduction reference light during reproduction in the hologram light information reproducing apparatus 10. In this embodiment, the focal position of the objective lens 215 is adjusted so that it is exactly the surface position with respect to the thickness direction of the hologram recording medium 1, and the optical axis of the objective lens 215 is normal to the recording medium 1 with respect to the Bragg direction. On the other hand, it is designed to be inclined to the opposite side to the reproduction reference beam. In the same manner as in the first embodiment, among the reproduced images, (i) at the highest angle side with respect to the Bragg angle direction of the reference light, (ii) at the center, (iii) at the lowest angle side and the reference light for reproduction are over. Consider the area to wrap. The light beam (i) on the high angle side overlaps with almost the entire region of the reproduction reference light, and the overlap region is expressed by (1) when considered on the projection surface of the reference light onto the hologram recording medium 1. . In the same way, the central (ii) ray is a region (2) that is narrower than (1), and the overlap region of the (iii) ray on the low angle side is an end portion that is narrower than (2). This is the only area (3). The inclusion relationship of the overlap areas is (3) ⊂ (2) ⊂ (1).
　このオーバーラップ領域を排他的に区切り、図１６左図のようにそれぞれ（ａ）、（ｂ）、（ｃ）と定義する。表２に排他的オーバーラップ領域それぞれの波面を変更することで影響を受ける再生画像領域を示す。 This overlap area is divided exclusively and defined as (a), (b) and (c) as shown in the left figure of FIG. Table 2 shows reproduced image regions that are affected by changing the wavefront of each of the exclusive overlap regions.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
表２は実施例１の表１と全く等しいので、領域（ａ）または（ｂ）を変更すると複数の再生画像領域に影響を与えてしまうが，（ｃ）を変更する場合はブラッグ角度に対して高角側の領域（ｉ）だけを変更することができることが分かる。ここで、改めて参照光の有効径と先ほど定義した排他的オーバーラップ領域（ａ）、（ｂ）、（ｃ）を図１７左図で示す参照光の有効径に重ねると、図１７右図のような関係になる。ここで、実施例１と同じく、再生画像の総光量が最大となるようにブラッグ角度を最適化すると図１８左図のように再生画像の高角度側に暗領域を偏らせることが出来る。暗領域は図１８中図のように再生画像領域（ｉ）とのみ重なっていることが確認できる。一方で、排他的オーバーラップ領域（ａ）、（ｂ）、（ｃ）と再生画像のブラッグ方向に対する領域（ｉ）、（ｉｉ）、（ｉｉｉ）の関係を改めて参照光の有効径上で表すと図１８右図のようになる。暗領域のある再生画像の領域（ｉ）は参照光有効径の排他的オーバーラップ領域（ａ）、（ｂ）、（ｃ）全領域において影響があるが、前述のように領域（ｃ）にのみ着目すると、他の領域に影響を与えずに領域（ｉ）のみに影響を与えることが出来る。すなわち、図１８左図の暗領域における回折光量を改善させる場合には参照光波面の両端の領域である領域（ｃ）の波面のみを最適化し、逆に他の（ａ）および（ｂ）の領域の波面を変化させる必要がないことを意味する。 Since Table 2 is exactly the same as Table 1 of the first embodiment, changing the area (a) or (b) affects a plurality of reproduced image areas, but when changing (c), the Bragg angle It can be seen that only the high-angle side region (i) can be changed. Here, when the effective diameter of the reference light and the exclusive overlap regions (a), (b), and (c) defined above are superimposed on the effective diameter of the reference light shown in the left diagram of FIG. 17, the right diagram of FIG. It becomes a relationship like this. Here, as in the first embodiment, when the Bragg angle is optimized so that the total light amount of the reproduced image is maximized, the dark region can be biased toward the high angle side of the reproduced image as shown in the left diagram of FIG. It can be confirmed that the dark region overlaps only the reproduced image region (i) as shown in FIG. On the other hand, the relationship between the exclusive overlap areas (a), (b), and (c) and the areas (i), (ii), and (iii) with respect to the Bragg direction of the reproduced image is represented again on the effective diameter of the reference light. As shown in the right figure of FIG. The area (i) of the reproduced image having the dark area has an influence on the entire overlapping area (a), (b), (c) of the effective diameter of the reference light, but the area (c) is affected as described above. Focusing only on the area (i) can be affected without affecting other areas. That is, in order to improve the amount of diffracted light in the dark region in the left diagram of FIG. 18, only the wavefront of the region (c), which is the region at both ends of the reference light wavefront, is optimized, and conversely the other (a) and (b) This means that there is no need to change the wavefront of the region.
　対物レンズ２１５の焦点位置によって排他的オーバーラップ領域の分布は変化する為、最適波面形状を同定する際のパラメータも再考慮しなくてはならない。焦点位置が媒体中央にあった場合、暗領域の補償に利用する排他的オーバーラップ領域（ｃ）は図１２のように両端だったため，領域（ｂ）と（ｃ）の境界を探すために位相印加開始点は参照光有効径の中心から両端に向かって探索を行った。しかしフーリエ面が媒体表面の場合，図１８のように排他的オーバーラップ領域（ｃ）は有効径の片側の端にのみ存在するので，図１９で示すように位相印加開始点を参照光有効径の端から逆の端に向かって探索していくこととなる。なお、本実施例における参照光の波面形状の最適化は図１４と等しい為、省略する。 Since the distribution of the exclusive overlap region varies depending on the focal position of the objective lens 215, parameters for identifying the optimum wavefront shape must be reconsidered. When the focal position is in the center of the medium, the exclusive overlap region (c) used for compensation of the dark region is at both ends as shown in FIG. 12, so that the phase is searched for the boundary between the regions (b) and (c). The application start point was searched from the center of the effective diameter of the reference beam toward both ends. However, when the Fourier plane is the surface of the medium, the exclusive overlap region (c) exists only at one end of the effective diameter as shown in FIG. 18, so the phase application start point is set as the reference light effective diameter as shown in FIG. The search will start from the end of the image toward the opposite end. Note that optimization of the wavefront shape of the reference light in this embodiment is the same as in FIG.
　これにより、対物レンズ２１５の焦点位置がホログラム記録媒体１の媒体表面として設計した場合であっても、干渉縞の歪みを補償できる波面形状を高速に導出し、高い転送速度を維持しつつ、高品質な再生品質を実現することが可能となる。 Thereby, even when the focal position of the objective lens 215 is designed as the medium surface of the hologram recording medium 1, a wavefront shape capable of compensating for interference fringe distortion can be derived at high speed while maintaining a high transfer speed, It becomes possible to realize a high reproduction quality.
１・・・ホログラム記録媒体、１０・・・ホログラム光情報再生装置、１１・・・ピックアップ
１２・・・再生用参照光光学系、１３・・・ディスクＣｕｒｅ光学系、
１４・・・ディスク回転角度検出用光学系、１５・・・半径位置検出光学系
２１・・・回転角度制御回路、２２・・・スピンドル駆動回路、２３・・・半径位置制御回路
２４・・・半径位置駆動回路、３１・・・ブラッグ角度制御信号生成回路
３２・・・ブラッグ角度制御回路、３３・・・ブラッグ角度駆動回路、３４・・・ピッチ角度制御信号生成回路
３５・・・ピッチ角度制御回路、３６・・・ピッチ角度駆動回路、３７・・・シャッタ制御回路
３８・・・光源駆動回路、８０・・・コントローラ
８１・・・信号生成回路、８２・・・信号処理回路、９０…入出力制御回路、９１…外部制御装置 DESCRIPTION OF SYMBOLS 1 ... Hologram recording medium, 10 ... Hologram optical information reproducing | regenerating apparatus, 11 ... Pickup 12 ... Reference light optical system for reproduction | regeneration, 13 ... Disc Cure optical system,
DESCRIPTION OF SYMBOLS 14 ... Optical system for disc rotation angle detection, 15 ... Radial position detection optical system 21 ... Rotation angle control circuit, 22 ... Spindle drive circuit, 23 ... Radial position control circuit 24 ... Radial position drive circuit, 31 ... Bragg angle control signal generation circuit 32 ... Bragg angle control circuit, 33 ... Bragg angle drive circuit, 34 ... Pitch angle control signal generation circuit 35 ... Pitch angle control Circuit 36... Pitch angle drive circuit 37 37 shutter control circuit 38 light source drive circuit 80 controller 81 signal generation circuit 82 signal processing circuit 90 input Output control circuit, 91 ... external control device

Claims (19)

  1. 信号光と参照光の照射により記録を行った記録媒体より情報を再生するホログラム再生装置であって、
    前記信号光を集光する対物レンズと、
    ブラッグ角度方向で前記参照光の前記記録媒体への照射角度を変更する第１の参照光角度変更部と、
    前記参照光の光路中に配置され前記参照光の波面形状を変更する波面変更部と、
    前記記録媒体の再生光の輝度情報を取得する再生光輝度情報取得部と、を備え、
    前記第１の参照光角度変更部は前記参照光のブラッグ角度を前記再生光輝度情報取得部で検出した再生光の光量に応じて制御し、
    前記波面変更部は、前記再生光輝度情報取得部より得られる情報を基に、前記参照光と前記信号光が重なった排他的オーバーラップ領域の一部に対応した前記波面形状を制御することを特徴とするホログラム再生装置。     A hologram reproducing apparatus for reproducing information from a recording medium on which recording is performed by irradiation with signal light and reference light,
    An objective lens for condensing the signal light;
    A first reference light angle changing unit that changes an irradiation angle of the reference light to the recording medium in a Bragg angle direction;
    A wavefront changing unit that is arranged in the optical path of the reference light and changes a wavefront shape of the reference light;
    A reproduction light luminance information acquisition unit that acquires luminance information of reproduction light of the recording medium,
    The first reference light angle changing unit controls the Bragg angle of the reference light according to the amount of reproduction light detected by the reproduction light luminance information acquisition unit,
    The wavefront changing unit controls the wavefront shape corresponding to a part of an exclusive overlap region where the reference light and the signal light overlap based on information obtained from the reproduction light luminance information acquisition unit. A featured hologram reproducing apparatus.
  2. 請求項１に記載のホログラム再生装置であって、
    前記対物レンズの光軸と前記記録媒体の法線を含む面を入射面とし、
    前記入射面内における前記対物レンズで集光される信号光を構成する光線のうち入射角度が前記参照光の入射角度に最も近い光線を最近接光線とし、
    前記入射面に垂直な面のうち前記最近接光線を含む平面が前記記録媒体と交差する領域を通過する前記参照光の前記排他的オーバーラップ領域を所定の領域としたとき、
    前記波面変更部は、前記再生光輝度情報取得部より得られる情報を基に前記所定の領域以外の領域に略対応した前記波面形状を制御することを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 1,
    The surface including the optical axis of the objective lens and the normal line of the recording medium is an incident surface,
    Of the light beams constituting the signal light collected by the objective lens in the incident surface, the light beam closest to the incident angle of the reference light is the closest light beam,
    When the exclusive overlap region of the reference light passing through a region where a plane including the closest ray among surfaces perpendicular to the incident surface intersects the recording medium is a predetermined region,
    The hologram reproduction apparatus characterized in that the wavefront changing unit controls the wavefront shape substantially corresponding to a region other than the predetermined region based on information obtained from the reproduction light luminance information acquisition unit.
  3. 請求項１に記載のホログラム再生装置であって、
    前記再生光輝度情報取得部とは再生光を検出する光検出器であることを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 1,
    The hologram reproduction apparatus characterized in that the reproduction light luminance information acquisition unit is a photodetector for detecting reproduction light.
  4. 請求項１に記載のホログラム再生装置であって、
    前記再生光輝度情報取得部とは前記記録媒体を透過せず前記記録媒体に対して前記再生光と逆側へ回折した光を検出する光検出器であることを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 1,
    The hologram reproduction apparatus according to claim 1, wherein the reproduction light luminance information acquisition unit is a photodetector that detects light diffracted to the recording medium opposite to the reproduction light without passing through the recording medium.
  5. 請求項４に記載のホログラム再生装置であって、
    前記再生光輝度情報取得部は、
    　前記記録媒体を透過した前記参照光を反射する可動ミラーと、
    　前記可動ミラーを駆動させるミラー駆動部と、
    　前記記録媒体を透過した光を前記可動ミラー面へ集光する集光レンズと、を備え、
    前記再生光輝度情報取得部で検出される光量が略最大となるとき前記再生光の光量も略最大となることを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 4, wherein
    The reproduction light luminance information acquisition unit
    A movable mirror that reflects the reference light transmitted through the recording medium;
    A mirror driving unit for driving the movable mirror;
    A condensing lens that condenses the light transmitted through the recording medium onto the movable mirror surface,
    A hologram reproducing apparatus, wherein when the amount of light detected by the reproducing light luminance information acquisition unit becomes substantially maximum, the amount of light of the reproducing light also becomes substantially maximum.
  6. 請求項１に記載のホログラム再生装置であって、
    ピッチ角度方向で前記参照光の前記記録媒体への照射角度を変更する第２の参照光角度変更部と、を有し、
    前記再生光輝度情報取得部において検出される光量が略最大となるように前記第２の参照光角度変更部が前記参照光のピッチ角度を制御した後に、前記波面変更部が前記排他的オーバーラップ領域の一部に対応した波面形状を制御することを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 1,
    A second reference light angle changing unit that changes an irradiation angle of the reference light to the recording medium in a pitch angle direction,
    After the second reference light angle changing unit controls the pitch angle of the reference light so that the amount of light detected by the reproduction light luminance information acquisition unit is substantially maximized, the wavefront changing unit performs the exclusive overlap. A hologram reproducing apparatus that controls a wavefront shape corresponding to a part of a region.
  7. 請求項６に記載のホログラム再生装置であって、
    前記再生光輝度情報取得部において検出される光量が最大となるように前記第１の参照光角度変更部が前記参照光のブラッグ角度を制御した後に、前記波面変更部が前記排他的オーバーラップ領域の一部に対応した波面形状を制御することを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 6,
    After the first reference light angle changing unit controls the Bragg angle of the reference light so that the amount of light detected in the reproduction light luminance information acquisition unit is maximized, the wavefront changing unit is configured to use the exclusive overlap region. A hologram reproducing apparatus that controls a wavefront shape corresponding to a part of the hologram.
  8. 請求項７に記載のホログラム再生装置であって、
    前記第２の参照光角度変更部が前記参照光のピッチ角度を制御した後に、前記第１の参照光角度変更部が前記参照光のブラッグ角度を制御することを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 7, wherein
    The hologram reproducing apparatus, wherein the first reference light angle changing unit controls the Bragg angle of the reference light after the second reference light angle changing unit controls the pitch angle of the reference light.
  9. 請求項２に記載のホログラム再生装置であって、
    前記所定の領域とは前記排他的オーバーラップ領域の一部以外の領域であり、
    前記波面変更部は前記所定の領域に対応した前記波面形状を制御した後に、前記排他的オーバーラップ領域の一部に対応した前記波面形状を制御することを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 2,
    The predetermined area is an area other than a part of the exclusive overlap area,
    The hologram reproducing apparatus according to claim 1, wherein the wavefront changing unit controls the wavefront shape corresponding to a part of the exclusive overlap region after controlling the wavefront shape corresponding to the predetermined region.
  10. 請求項１に記載のホログラム再生装置であって、
    前記再生光輝度情報取得部とはＣＭＯＳやＣＣＤの二次元センサであることを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to claim 1,
    The reproduction light luminance information acquisition unit is a two-dimensional sensor such as a CMOS or a CCD.
  11. 前記請求項２乃至１０に記載のホログラム再生装置であって、
    前記波面変更部は、前記排他的オーバーラップ領域における位相印加開始点及び位相変化量の絶対値を制御することで、前記排他的オーバーラップ領域の一部に対応した前記波面形状を制御することを特徴とするホログラム再生装置。     The hologram reproducing apparatus according to any one of claims 2 to 10,
    The wavefront changing unit controls the wavefront shape corresponding to a part of the exclusive overlap region by controlling an absolute value of a phase application start point and a phase change amount in the exclusive overlap region. A featured hologram reproducing apparatus.
  12. 請求項１に記載のホログラム再生装置であって、
    前記再生光輝度情報取得部とは前記記録媒体の再生箇所における温度を検出する温度検出器であることを特徴とするホログラム再生装置     The hologram reproducing apparatus according to claim 1,
    The reproduction light luminance information acquisition unit is a temperature detector that detects a temperature at a reproduction position of the recording medium.
  13. 請求項１に記載のホログラム再生装置であって、
    前記波面変更部は、前記対物レンズの光軸と前記記録媒体の法線を含む所定の面に略平行な方向に対して位相変化量の絶対値を二次的に変更することを特徴とするホログラム再生装置     The hologram reproducing apparatus according to claim 1,
    The wavefront changing unit secondarily changes an absolute value of a phase change amount in a direction substantially parallel to a predetermined plane including an optical axis of the objective lens and a normal line of the recording medium. Hologram playback device
  14. 請求項６に記載のホログラム再生装置の前記波面変更部の形状を調整する波面調整方法であって、
    前記第１の参照光角度変更部の制御を行う第１のステップと、
    前記第２の参照光角度変更部の制御を行う第２のステップと、
    前記排他的オーバーラップ領域における位相変化量の絶対値を変更する際、前記変化量の変調度および位相の印加を開始する位置を変更する第３のステップを備えることを特徴とする波面調整方法。     A wavefront adjusting method for adjusting the shape of the wavefront changing unit of the hologram reproducing apparatus according to claim 6,
    A first step of controlling the first reference light angle changing unit;
    A second step of controlling the second reference light angle changing unit;
    A wavefront adjustment method comprising: a third step of changing a modulation degree of the change amount and a position where the application of the phase is started when changing the absolute value of the phase change amount in the exclusive overlap region.
  15. 請求項１４に記載の波面調整法であって、
    前記対物レンズの光軸と前記記録媒体の法線を含む所定の面に略平行な方向に対して位相変化量の絶対値を二次的に変更することを特徴とする波面調整方法。     The wavefront adjustment method according to claim 14,
    2. A wavefront adjustment method, wherein an absolute value of a phase change amount is secondarily changed with respect to a direction substantially parallel to a predetermined plane including an optical axis of the objective lens and a normal line of the recording medium.
  16. 請求項１４に記載の波面調整方法であって、
    前記第１のステップ及び前記第２のステップ及び前記第３のステップは、記録媒体に記録された情報を再生する前に実施することを特徴とする波面調整方法。     The wavefront adjusting method according to claim 14,
    The wavefront adjusting method, wherein the first step, the second step, and the third step are performed before reproducing information recorded on a recording medium.
  17. 請求項１４または１６に記載の波面調整方法であって、
    前記第１のステップ及び前記第２のステップ及び前記第３のステップは、
    前記光検出器において検出される光量が略最大となるように実施されることを特徴とする波面調整方法。     The wavefront adjusting method according to claim 14 or 16,
    The first step, the second step, and the third step are:
    The wavefront adjustment method is performed such that the amount of light detected by the photodetector is substantially maximized.
  18. 前記請求項１７に記載の波面調整方法であって、
    前記第２のステップは前記第１のステップよりも先に実施されることを特徴とする波面調整方法。     The wavefront adjusting method according to claim 17,
    The wavefront adjusting method, wherein the second step is performed prior to the first step.
  19. 前記請求項１８に記載の波面調整方法であって、
    前記光検出器において検出される光量が略最大となるように前記第１の参照光角度変更部の制御を行う第４のステップを備え、
    前記第４のステップは前記第１のステップ及び前記第２のステップ及び前記第３のステップの後に実施されることを特徴とする波面調整方法。     The wavefront adjusting method according to claim 18, wherein
    A fourth step of controlling the first reference light angle changing unit so that the amount of light detected by the photodetector becomes substantially maximum;
    4. The wavefront adjusting method according to claim 4, wherein the fourth step is performed after the first step, the second step, and the third step.
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