WO2017094129A1 - Dispositif de reproduction d'informations optiques holographiques - Google Patents

Dispositif de reproduction d'informations optiques holographiques 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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WIPO (PCT)
Prior art keywords
light
reference light
wavefront
angle
reproduction
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PCT/JP2015/083835
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English (en)
Japanese (ja)
Inventor
山田　健一郎
健 宇津木
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株式会社日立製作所
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Priority to PCT/JP2015/083835 priority Critical patent/WO2017094129A1/fr
Publication of WO2017094129A1 publication Critical patent/WO2017094129A1/fr

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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

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Abstract

Dans un dispositif de reproduction d'informations optiques holographiques qui combine deux éléments optiques pour changer un angle de lumière de référence, la présente invention réalise une reproduction de grande qualité tout en maintenant une vitesse de transfert élevée même lorsqu'un écart par rapport à l'angle orthogonal se produit dans les deux éléments optiques en raison d'une erreur d'installation ou autre. L'invention concerne un dispositif de reproduction d'informations optiques holographiques qui reproduit des informations provenant d'un support d'enregistrement sur lequel les informations ont été enregistrées par exposition à une lumière de signal et une lumière de référence, et qui comprend : une lentille d'objectif qui collecte la lumière de signal ; une première unité de modification d'angle de lumière de référence qui modifie l'angle de la lumière de référence dirigée sur le support d'enregistrement dans une direction d'angle de Bragg ; une unité de modification de surface d'onde qui est disposée sur le trajet optique de la lumière de référence et qui modifie la forme de surface d'onde de la lumière de référence ; et une unité d'acquisition d'informations de luminance de reproduction qui acquiert des informations de luminance de lumière de reproduction pour le support d'enregistrement, la première unité de modification d'angle de lumière de référence exerçant une commande sur l'angle de Bragg de la lumière de référence en fonction de la quantité de lumière de la lumière de reproduction détectée par l'unité d'acquisition d'informations de luminance de reproduction, et l'unité de modification de surface d'onde exerçant une commande, sur la base des informations obtenues par l'unité d'acquisition d'informations de luminance de reproduction, sur la forme de surface d'onde qui correspond à une partie d'une région de chevauchement exclusif où la lumière de référence et la lumière de signal se chevauchent.
PCT/JP2015/083835 2015-12-02 2015-12-02 Dispositif de reproduction d'informations optiques holographiques WO2017094129A1 (fr)

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US10678053B2 (en) 2009-04-27 2020-06-09 Digilens Inc. Diffractive projection apparatus
US11175512B2 (en) 2009-04-27 2021-11-16 Digilens Inc. Diffractive projection apparatus
US11726332B2 (en) 2009-04-27 2023-08-15 Digilens Inc. Diffractive projection apparatus
US11487131B2 (en) 2011-04-07 2022-11-01 Digilens Inc. Laser despeckler based on angular diversity
US11287666B2 (en) 2011-08-24 2022-03-29 Digilens, Inc. Wearable data display
US11256155B2 (en) 2012-01-06 2022-02-22 Digilens Inc. Contact image sensor using switchable Bragg gratings
US11448937B2 (en) 2012-11-16 2022-09-20 Digilens Inc. Transparent waveguide display for tiling a display having plural optical powers using overlapping and offset FOV tiles
US11443547B2 (en) 2013-07-31 2022-09-13 Digilens Inc. Waveguide device incorporating beam direction selective light absorber
US11106048B2 (en) 2014-08-08 2021-08-31 Digilens Inc. Waveguide laser illuminator incorporating a despeckler
US11307432B2 (en) 2014-08-08 2022-04-19 Digilens Inc. Waveguide laser illuminator incorporating a Despeckler
US11709373B2 (en) 2014-08-08 2023-07-25 Digilens Inc. Waveguide laser illuminator incorporating a despeckler
US11726323B2 (en) 2014-09-19 2023-08-15 Digilens Inc. Method and apparatus for generating input images for holographic waveguide displays
US11726329B2 (en) 2015-01-12 2023-08-15 Digilens Inc. Environmentally isolated waveguide display
US11740472B2 (en) 2015-01-12 2023-08-29 Digilens Inc. Environmentally isolated waveguide display
US11703645B2 (en) 2015-02-12 2023-07-18 Digilens Inc. Waveguide grating device
US11194098B2 (en) 2015-02-12 2021-12-07 Digilens Inc. Waveguide grating device
US11281013B2 (en) 2015-10-05 2022-03-22 Digilens Inc. Apparatus for providing waveguide displays with two-dimensional pupil expansion
US11754842B2 (en) 2015-10-05 2023-09-12 Digilens Inc. Apparatus for providing waveguide displays with two-dimensional pupil expansion
US11604314B2 (en) 2016-03-24 2023-03-14 Digilens Inc. Method and apparatus for providing a polarization selective holographic waveguide device
US11513350B2 (en) 2016-12-02 2022-11-29 Digilens Inc. Waveguide device with uniform output illumination
US11586046B2 (en) 2017-01-05 2023-02-21 Digilens Inc. Wearable heads up displays
US11194162B2 (en) 2017-01-05 2021-12-07 Digilens Inc. Wearable heads up displays
US12092914B2 (en) 2018-01-08 2024-09-17 Digilens Inc. Systems and methods for manufacturing waveguide cells
US10732569B2 (en) 2018-01-08 2020-08-04 Digilens Inc. Systems and methods for high-throughput recording of holographic gratings in waveguide cells
WO2019217453A1 (fr) * 2018-05-07 2019-11-14 Digilens Inc. Procédés et appareils pour copier une variété de prescriptions d'hologramme à partir d'un maître commun
US11402801B2 (en) 2018-07-25 2022-08-02 Digilens Inc. Systems and methods for fabricating a multilayer optical structure
CN112805781B (zh) * 2018-10-05 2022-11-18 索尼半导体解决方案公司 再现装置以及再现方法
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US11543594B2 (en) 2019-02-15 2023-01-03 Digilens Inc. Methods and apparatuses for providing a holographic waveguide display using integrated gratings
US11378732B2 (en) 2019-03-12 2022-07-05 DigLens Inc. Holographic waveguide backlight and related methods of manufacturing
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US11442222B2 (en) 2019-08-29 2022-09-13 Digilens Inc. Evacuated gratings and methods of manufacturing
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