JP2008112107A - Hologram reproducing apparatus - Google Patents

Hologram reproducing apparatus Download PDF

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JP2008112107A
JP2008112107A JP2006296507A JP2006296507A JP2008112107A JP 2008112107 A JP2008112107 A JP 2008112107A JP 2006296507 A JP2006296507 A JP 2006296507A JP 2006296507 A JP2006296507 A JP 2006296507A JP 2008112107 A JP2008112107 A JP 2008112107A
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hologram
light
recording
image sensor
reference light
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Masaaki Hara
Kenji Tanaka
Mitsuru Toishi
雅明 原
満 外石
健二 田中
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Sony Corp
ソニー株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for removing noises when recorded-data are reproduced from a hologram recording/reproducing medium. <P>SOLUTION: A hologram reproducing apparatus is equipped with an image sensor 25 having pixels which are arrayed in two-dimension and receive diffraction light generated by irradiating a hologram recording/reproducing medium 50 with reference light and a control section 60 for reproducing the recorded data by processing electrical signals from the image sensor 25. The control section 60 changes wavelength of the reference light when an area, where hologram is formed, of the hologram recording/reproducing medium 50 is irradiated with the reference light. Thereby, reproducing processing exhibiting the effect of noises reduction can be carried out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hologram reproducing apparatus.

  2. Description of the Related Art In recent years, a hologram recording / reproducing apparatus, which is a recording / reproducing apparatus capable of recording and reproducing recorded data at a high transfer speed while achieving a high recording density, has attracted attention. In the hologram recording / reproducing apparatus, the thickness direction of the recording medium is also utilized, and at the time of recording, the interference fringes between the reference light and the signal light are hologram-recorded / reproduced based on the page data corresponding to the recorded data with two-dimensional information as one page unit. It is formed in the form of a hologram (diffraction grating) in a medium, and page data is recorded three-dimensionally. Further, at the time of reproduction, recorded data is reproduced by obtaining diffracted light generated by irradiating the hologram formed in this way with reference light (see Patent Document 1 and Non-Patent Document 1).

  In a hologram recording / reproducing apparatus, two-dimensional information is displayed on a spatial light modulator (SLM) for each page at the time of recording to generate a signal light and a reference light, and a hologram is formed at the time of reproduction. In order to capture diffracted light by irradiating and capturing an electric signal corresponding to a reproduced image formed by the diffracted light by a two-dimensional image sensor typified by a CSD (CCD) or Cmos (CMOS) image sensor, There are many sources of noise that were not possible with conventional optical disc recording / reproducing apparatuses. There is a need for a technique for reducing noise from such noise sources.

  Up to now, as a known noise reduction technique in a related technical field, a noise reduction technique in the field of solid-state imaging devices has been known (see Patent Document 2). This technology outputs dark data from a solid-state imaging device using a light-shielding jig when manufacturing a solid-state imaging device, and outputs this dark-time data to a CPU in the solid-state imaging device. The fixed pattern noise of the image sensor is detected, and the detected fixed pattern noise is compressed and stored in the nonvolatile memory. When the solid-state imaging device is actually used, the fixed pattern noise is transferred from the nonvolatile memory to the memory in the image processing circuit. Information is moved and stored, and the fixed pattern noise is removed from the image pickup signal by adding and subtracting the image pickup signal output from the solid-state image pickup device and the fixed pattern noise read from the memory.

Here, the process of generating noise in the hologram recording / reproducing apparatus is different from the process of generating noise in the solid-state imaging apparatus described above. Research on noise in a hologram recording / reproducing apparatus has been advanced in recent years, and for example, simulation results have been reported on the influence of noise from an optical system on SNR (Signal to Noise Ratio) as recording / reproducing characteristics ( (See Non-Patent Document 2).
Japanese Patent Laid-Open No. 2004-226821 JP 2003-18475 A Nikkei Electronics January 17, 2005, pages 106-114 Stella Romaine LAMBOURDIERE, et al "Simulation of Holographic Data Storage for the Optical Collinear System" Japanese Journal of Applied Physics Vol. 45, No. 2B, 2006, pp. 1246-1252

  Noise in this hologram recording / reproducing apparatus is very difficult to remove because it exists spatially randomly due to the pixel pattern at the time of recording, but this noise is the performance of the hologram recording / reproducing apparatus, that is, Significantly affects recording and playback characteristics. For example, in the case of performing multiplexing, which is a technique peculiar to hologram recording, which is a technique for performing volume recording of a plurality of holograms by sharing one recording area, the degree of multiplexing can be determined by such noise. . This means that the influence of noise in such hologram recording / reproduction cannot be ignored for large-capacity recording. However, as described above, there are few known techniques for removing noise peculiar to holograms. As a next-generation recording / reproducing technology, the most promising hologram recording / reproducing technology is put into practical use, and recording from a hologram recording / reproducing medium is performed from the viewpoint of achieving higher recording density recording using multiplexing or the like. A technique for removing noise generated during data reproduction is required.

  Therefore, an object of the present invention is to provide a technique for removing noise in hologram recording / reproduction.

  The hologram reproducing apparatus of the present invention records the recording light from the hologram formed on the recording layer of the hologram recording / reproducing medium by causing the signal light modulated according to the recording data to interfere with the signal light and the reference light having the same light source. A hologram reproducing apparatus for reproducing data, comprising: a reference light generating unit that generates the reference light; and a two-dimensionally arranged pixel that receives diffracted light generated by irradiating the hologram with the reference light A sensor and a control unit that performs processing for capturing an electrical signal from the image sensor and reproducing recorded data, wherein the reference light generation unit generates the reference light having different wavelengths a plurality of times, and The sensor receives each of the diffracted lights corresponding to each of the reference lights having the different wavelengths from the same hologram, and the control unit It is intended to reproduce the recorded data by a process of averaging each of said electrical signals from the image sensor corresponding to each of the diffracted light.

  The hologram reproducing apparatus includes a reference light generation unit, an image sensor, and a control unit. The reference light generator generates reference light having different wavelengths a plurality of times. This reference light is applied to the same hologram, and different diffracted light is generated a plurality of times. Further, the image sensor receives the diffracted light from the same hologram and sends an electric signal corresponding to the diffracted light to the control unit. The control unit reproduces recorded data by performing a process of averaging each electric signal from the image sensor corresponding to each of a plurality of different diffracted lights.

  ADVANTAGE OF THE INVENTION According to this invention, the technique which can remove the noise in hologram recording reproduction | regeneration can be provided. As a result, it is possible to provide a hologram reproducing apparatus that enables high-density hologram recording.

  Embodiments of the present invention will be described below. In describing the embodiment, first, the principle of hologram recording / reproducing will be described with respect to a coaxial optical system as one embodiment of an optical system for hologram recording / reproducing, a hologram recording / reproducing medium will be described, and such a coaxial optical system will be described. A hologram recording / reproducing apparatus having a system will be described, and thereafter, a characteristic part of the embodiment will be described. Here, the coaxial optical system is a general optical system characterized in that each of signal light and reference light, which will be described later, are arranged coaxially (coaxially) and share a part of the optical path of the light beam. It is a name.

(Coaxial optical system)
The outline of the coaxial optical system 10 having a recording action will be described with reference to FIG. 1, and the outline of the coaxial optical system 11 having a reproducing action will be described with reference to FIG.

  A coaxial optical system 10 shown in FIG. 1 includes a laser light source 20, a spatial light modulator 22 composed of transmissive liquid crystal, a beam splitter 23, and an objective lens 24 as main optical components.

  The light beam emitted from the laser light source 20 passes through the spatial light modulator 22. Then, the spatial light modulator 22 includes a signal light spatial light modulator 46 (see FIG. 2) that displays a signal light pattern based on the recording data and a reference light spatial light modulator 47 (see FIG. 2) that displays a reference light pattern. And a transmission region of two light beams. A light beam that passes through each of the regions of the spatial light modulator 22 divided into two regions is a beam splitter as a signal beam 40 and a reference beam 41 that are coaxially arranged with the same center line. 23 and the common optical component of the objective lens 24, that is, the signal light 40 and the reference light 41 are incident on the recording layer 50a (see FIG. 4) of the hologram recording / reproducing medium 50 with a common optical path. The signal light 40 generated by the signal light spatial light modulator 46 and the reference light 41 generated by the reference light spatial light modulator 47 interfere in the recording layer 50a. Then, the refractive index in the minute region of the recording layer 50a changes according to this interference mode, and the recording data is recorded as a diffraction grating (hologram) corresponding to the refractive index pattern.

  FIG. 2 shows an example of the signal light pattern and the reference light pattern displayed on the spatial light modulator 22. In this pattern, the signal light spatial light modulator 46, which is closer to the center, has a signal light pattern (a signal light spatial light modulator according to a combination of a color portion (white portion) and a black portion (black portion) on the paper). 46 is displayed, and the reference light spatial light modulation unit 47 around the reference light pattern (the pattern generated in the reference light spatial light modulation unit 47 due to the combination of the white part and the black part) is displayed. It is in shape. In FIG. 2, the black portion is a portion that blocks the light beam, and the white portion is a portion that transmits the light beam, and the modes of the signal light and the reference light change according to the arrangement of the black portion and the white portion. Here, the white portion and the black portion can be controlled to be either the white portion or the black portion for each minute region (hereinafter referred to as a pixel) finely divided in two dimensions.

  Here, the recording data is developed as a two-dimensional signal light pattern in the signal light spatial light modulator 46. That is, the recording data is encoded as a block code in which “1” and “0” are distributed two-dimensionally, and the pixel of the signal light spatial light modulation unit 46 corresponding to “1” corresponds to the white portion and corresponds to “0”. The pixels of the signal light spatial light modulation unit 46 to be made correspond to black portions.

  In addition, as an example of the reference light pattern, not only the spoke-shaped pattern shown in FIG. 2 (a mode in which a white portion and a black portion are separated by a line extending concentrically), for example, a random number is generated in advance. A random pattern that is a pattern in which white portions and black portions are randomly arranged may be used.

  FIG. 3 shows a conceptual diagram of a coaxial optical system 11 used in a coaxial hologram reproducing apparatus. In the coaxial hologram reproducing apparatus, in addition to the laser light source 20, the spatial light modulator 22, the beam splitter 23, and the objective lens 24 described above, a charge coupled device (CCD) or a sea moss (CMOS) sensor, etc. The image sensor 25 comprised by these is provided.

  In reproduction, only the reference light pattern is displayed on the reference light spatial light modulation unit 47 of the spatial light modulator 22, and the signal light spatial light modulation unit 46 displays an all-black pattern (a pattern of only the black part that blocks transmission of the light beam). ). The reference light 41 from the reference light spatial light modulator 47 passes through the beam splitter 23 and the objective lens 24 and is incident on the hologram formed on the recording layer 50a of the hologram recording / reproducing medium 50, thereby reproducing the recorded data. That is, diffracted light 42 corresponding to the hologram is generated by the reference light, and the traveling direction of the diffracted light 42 as a light beam is changed by the beam splitter 23, and the image sensor 25 is used as the diffracted light 43. Irradiate. Then, the light is received by an image sensor 25 having a light receiving portion (pixel terminology is used similarly to the spatial light modulator 22) divided into two-dimensionally arranged minute regions. The electric signal from each pixel is a signal corresponding to the shape of the hologram, that is, the recording data, and the recording data can be reproduced from the electric signal in a reproduction signal processing unit (not shown). As shown in FIG. 4, the characteristic feature of the coaxial optical system is that signal light, reproduction light, and diffracted light are arranged coaxially.

(Structure of hologram recording / reproducing medium)
FIG. 4 schematically shows the structure cut in the cross-sectional area direction of the hologram recording / reproducing medium 50 described above. Further, the signal light 40 (passes through the inside of the broken line and the spatial light modulator 22 (see FIG. 1)). Light beam from the recording layer 50a to the beam splitter 23 (see FIG. 3)) and reference light 41 (light beam from the recording layer 50a to the beam splitter 23 (see FIG. 3)). It is generated between the spatial light modulator 22 (see FIG. 1) and the light beam from the spatial light modulator 22 (see FIG. 1) to the recording layer 50a and the servo light beam (servo optical system 30 (see FIG. 5)). It is a figure which shows typically how the light beam which passes the inner side of a dashed-dotted line) injects into the objective lens 24. FIG. The hologram recording / reproducing medium 50 includes a protective film 50d, a recording layer 50a, a recording / reproducing light beam reflecting film 50b, and an address groove 50c.

  At the time of recording, a hologram is formed on the recording layer 50a according to the shape of interference fringes generated by the interference between the signal light 40 and the reference light 41. At the time of reproduction, only the reference light 41 is irradiated on the hologram, so that the diffracted light 42 corresponding to the hologram is reflected by the reflective film 50b in the substantially same area as the signal light 40 at the time of recording, and the objective lens. An image (reproduced image) is generated on the image sensor 25 through 24. On the other hand, the servo light beam is transmitted through the reflective film 50b having wavelength selection characteristics, reflected by the aluminum reflective film on which the address groove 50c is formed, and used in a CD (Compact Disc) and a DVD (Digital Vaseail Disc). Based on the same principle as above, on the basis of the electrical signal detected from the photodetector of the servo optical system, the control unit, for each servo required for the processing of the focus servo, radial servo and spindle servo described above. Error signal, and further, an address signal for specifying the position of the recording layer 50a of the hologram recording / reproducing medium 50 irradiated with the light beam in the hologram recording / reproducing medium 50 is obtained.

  The light beam for recording / reproducing is, for example, a light beam (blue light beam) from a blue laser diode, and the light beam for servo is, for example, a light beam (red light beam) from a red laser diode. The mutual positional relationship between the optical paths through which both light beams pass is specified in advance by specifying the arrangement of the optical components. As a result, by performing servo using the red light beam, the position where the hologram is formed by the blue beam (signal light 40 and reference light 41) is specified by the action of this servo, and the blue light beam (reference light 41, diffraction light) The position where the recording data is reproduced from the hologram is specified by the action of the servo by the light 42 and the diffracted light 43), and the hologram recording / reproduction can be set to a predetermined position of the recording layer 50a of the hologram recording / reproducing medium 50.

(Hologram recording / reproducing device using coaxial optical system)
In a hologram recording / reproducing apparatus using a coaxial optical system (hereinafter referred to as a coaxial hologram recording apparatus), the signal light, the reference light, and the diffracted light are shared by sharing a part of the optical path of the light beam. Since the objective lens can be used for recording and reproduction, the optical system can be simplified. Further, since it is relatively easy to be compatible with conventional optical discs such as CD and DVD, it attracts attention as a future recording / reproducing apparatus.

  FIG. 5 is a schematic diagram of the hologram recording / reproducing apparatus 100 centering on the optical unit as an embodiment of the hologram recording apparatus. The same reference numerals are given to the same parts as those quoted in the above description, and the description is omitted.

  The hologram recording / reproducing apparatus 100 is provided with a servo optical system 30. Only the main optical components constituting the servo optical system 30 will be described with reference numerals. The servo light source 28 emits a servo light beam. The servo light beam is different from the wavelength of the light beam from the laser light source 20 for recording and reproduction, and the servo light beam and recording are performed as a longer wavelength light beam (for example, a light beam from a red laser). The reproduction light beam can be separated. Further, since the photopolymer does not react to the red light beam, the recording layer 50a (see FIG. 4) is not affected by the red light beam.

  The beam splitter 27 is for guiding the return light from the hologram recording / reproducing medium 50 to the photo detector 29. The photo detector 29, for example, for focus servo (position control in the direction indicated by symbol F in FIG. 5), The stigma method and the radial (tracking) servo (position control in the direction indicated by the symbol T in FIG. 5) have a configuration in which the detector is divided into a plurality so as to correspond to the push-pull method. The dichroic mirror 34 is an optical component common to the servo optical system 30 and the recording / reproducing optical system, and is a wavelength separation element that separates the servo light beam and the recording / reproducing light beam. Further, the reflection mirror 56 changes the traveling direction of the servo light beam and the recording / reproducing light beam and guides it to the objective lens 24, and from the address groove 50c (see FIG. 5) of the hologram recording / reproducing medium 50 and the hologram. The traveling direction of each diffracted light is changed and guided to the servo optical system 30 and the recording / reproducing optical system. The reflection mirror 56 also functions as a mechanism unit for performing angle multiplexing.

  The spindle motor 51 rotates around the geometrical center of the disk shape of the hologram recording / reproducing medium 50 having the same outer shape as that of a conventional optical disk such as a CD or DVD. The rotational position of the hologram recording / reproducing medium 50 is controlled by the signal. Further, the temperature detector 70 is disposed in contact with the hologram recording / reproducing medium 50 so as to have a low thermal conductivity or in the vicinity of the hologram recording / reproducing medium 50.

  The control unit 60 controls the operation of the hologram recording / reproducing apparatus 100, for example, control of the laser light source 20, control of the reference light pattern and signal light pattern displayed on the spatial light modulator 22, control of the reflection mirror 56, Control of servo light source 28, processing of servo signal from photodetector 29, control of focus servo and radial servo using servo actuator 54, control of spindle motor 51, hologram recording detected by temperature detector 70 Control of recording / reproduction by detecting the temperature of the reproduction medium 50 is performed. The image sensor actuator 125 is also controlled. The image sensor actuator 125 is an actuator that changes the position of the image sensor 25, and changes the separation distance between the beam splitter 23 and the image sensor 25. The position of the image sensor 25 is controlled by the image sensor actuator 125 according to the wavelength of the light beam from the laser light source 20, and the reproduced image in the image sensor 25 is made the most clear. The SNR can be made good. Here, the position of the image sensor 25 with respect to the wavelength of the light beam is stored in advance in a ROM arranged in the control unit 60, and the control unit 60 controls the image sensor actuator 125 with reference to this ROM. A signal can be output. Furthermore, the control unit 60 performs noise reduction processing as a main part of the present embodiment.

  FIG. 6 is a diagram schematically showing the laser light source 20 of the embodiment. The laser light source 20 of the embodiment will be described in more detail with reference to FIG. The laser light source 20 includes a multimode semiconductor laser 211, a collimating lens 212, a diffraction grating 213, a mirror 214, a rotating shaft 227, a rotating motor 241a, a gear 241b, and a gear 241c. In principle, the laser light source 20 is a so-called Littrow type laser device.

  Here, the mirror 214 and the diffraction grating 213 are fixed, and can rotate in the direction indicated by the arrow in the drawing with the rotation axis 227 as the center. Here, the rotation shaft 227 is provided at the point where the extension line between the diffraction grating forming surface 213a and the mirror surface 214a intersects. In order to rotate around the rotation shaft 227, a rotation motor 241a, a gear 241b, and a gear 241c are provided as rotation mechanisms. That is, the mirror 214 and the diffraction grating 213 rotate while keeping the angle formed by the diffraction grating forming surface 213a and the mirror surface 214a constant according to the rotation of the rotary motor 241a.

  The laser light source control circuit 230 receives the laser wavelength control signal for controlling the laser wavelength from the control unit 60 and controls the rotary motor 241a. The rotation angle of the rotation motor 241 a is detected by a rotation angle detector (not shown) and input to the laser light source control circuit 230. The laser light source control circuit 230 can set the rotation angle of the rotation motor 241a, that is, the rotation angle between the mirror 214 and the diffraction grating 213, to a desired angle by using the rotation angle detector and the rotation motor 241a.

  The operation of the laser light source 20 shown in FIG. 6 will be described. The light beam emitted from the semiconductor laser 211 is converted into parallel light by the collimator lens 212, and the light beam converted into parallel light is reflected by the diffraction grating 213 and is 0th-order light that is diffracted light that travels in different directions for each wavelength. And primary light. The diffraction grating 213 diffracts in a different direction for each wavelength. Among these primary lights, there is also primary light that returns to the semiconductor laser 211, and the resonator is caused by the action of the primary light that returns to the semiconductor laser 211. Composed. The wavelength of oscillation of the semiconductor laser 211 according to the resonator composed of the diffraction grating 213 and the mirror 214 and the semiconductor laser 211, that is, according to the angle between the mirror 214 and the diffraction grating 213 rotating around the rotation axis 227. Is different. Since the oscillation wavelength of the semiconductor laser 211 with respect to the angle between the mirror 214 and the diffraction grating 213 is known in advance, the control unit 60 can control the laser light source 20 so as to obtain a desired light beam wavelength.

  The hologram recording / reproducing apparatus 100 described above has all functions as a hologram recording / reproducing apparatus capable of recording and reproducing holograms. However, the hologram recording / reproducing apparatus 100 is configured as a hologram recording apparatus having only components related to hologram recording, and is used for hologram reproduction. Even when it is configured as a hologram reproducing apparatus having only such components, the respective functions can be achieved without any problem.

(Noise removal in the embodiment)
A noise reduction technique when using the above-described hologram recording / reproducing apparatus 100 and the above-described hologram recording / reproducing medium 50 will be described.

  FIG. 7 shows a reproduced image of a hologram formed on the light receiving surface of the image sensor 25 of the hologram recording / reproducing apparatus 100 shown in FIG. In FIG. 7, square white portions arranged at equal intervals are sync information, which is two-dimensional information for specifying the position of a reproduced image. Further, FIG. 8 shows an enlarged view of the end portion of the signal component of the reproduced image (the portion surrounded by the lower right square in FIG. 7). From the enlarged view shown in FIG. 8, it can be seen that there are fine light and dark patterns. This fine light and dark pattern is noise, and is based on the non-uniformity of the hologram recording / reproducing medium 50 or the recording layer 50a, or in the hologram recording / reproducing medium, a diffused light beam and a light beam incident from the objective lens 24 Interference fringes caused by the interference, or the influence of diffracted light from other holograms when multiplexed.

  The fine light and dark pattern as the noise component is a light and dark pattern in which the positions of the noise are irregularly distributed as shown in FIG. 8, and thereby the signal-to-noise ratio of the electric signal obtained from the image sensor. (SNR) is reduced. Since this noise is integrated according to the multiplexing of the hologram, the SNR deteriorates as the number of multiplexing of holograms (multiplicity) increases, and the multiplicity is limited by this SNR.

  Each of FIG. 9A to FIG. 9E shows a reproduced image in the image sensor 25 when the wavelength of the light beam from the laser light source 20 is changed. 9A shows a case where reproduction is performed at the same light beam wavelength used during recording, and FIG. 9B shows a case where reproduction is performed while changing the wavelength of the light beam used during recording by 0.5 nm (nanometer). FIG. 9C shows a case where reproduction is performed by changing the wavelength of the light beam used at the time of recording by 1 nm. FIG. 9D shows a case where reproduction is performed by changing the wavelength of the light beam used at the time of recording by 1.5 nm. In this case, (E) of FIG. 9 shows each case where reproduction is performed by changing the wavelength of the light beam used for recording by 2.0 nm. For recording, the recording was performed by irradiating the reference light and the signal light for 1 Sec (seconds).

  10 differs from the case shown in FIG. 7 in that the reference beam is 50 .mu.m (micrometer) and the tracking direction in the plane of the recording layer 50a (the direction indicated by T in FIG. 1) for the same hologram. 2 shows a reproduced image generated in the image sensor 25 when shifted to. Each of FIG. 11A to FIG. 11E is an enlarged view of a part shown in FIG. 10 (a part surrounded by a lower right square in FIG. 10), and FIG. When reproducing with the same light beam wavelength as used sometimes, FIG. 11B shows the case where reproduction is performed by changing the wavelength of the light beam used for recording by 0.2 nm (nanometer), and FIG. When reproduction is performed by changing the wavelength of the light beam used sometimes by 1 nm, FIG. 11D shows the case where reproduction is performed by changing the wavelength of the light beam used for recording by 1.5 nm. ) Shows each of cases where reproduction is performed by changing the wavelength of the light beam used for recording by 2.0 nm.

  FIG. 9 (A) to FIG. 9 (E) and FIG. 11 (A) to FIG. 11 (E) are compared, and the following findings are obtained by the inventors of the present application (hereinafter referred to as the invention). Omitted). First, the reproduced images shown in FIGS. 9A to 9E could not be found visually. The noise component included in the reproduced image shown in FIGS. 11A to 11E is caused by scattering of the light beam. For this reason, a noise component is generated even when the reference light is shifted in the 50 μm tracking direction. This noise component has a substantially constant brightness when the wavelength of the light beam is varied, but the position of the light and dark distribution changes as shown in FIGS. 11A to 11E. You can see that

  In addition, as shown in FIG. 12, the inventors obtained experimental results of wavelength selectivity of signals and crosstalk noise. This shows the relationship between the spatial correlation coefficient of the reproduced image from the hologram and the spatial correlation coefficient of the noise component image and the wavelength displacement. The horizontal axis in FIG. 12 represents the difference between the wavelength of the light beam during recording and the wavelength of the light beam during reproduction, and the vertical axis represents the spatial correlation coefficient. As can be seen from FIG. 12, as the wavelength of the light beam at the time of reproduction changes from the wavelength at the time of recording, the noise component has a smaller correlation coefficient value than the signal component. In other words, when the wavelength of the light beam is changed during reproduction, the change in the reproduced image formed by the hologram in response to the signal component is small, but the change in the reproduced image formed by the hologram in accordance with the noise component is large. ing.

  From the above findings, the following conclusions can be drawn. In order to remove the influence of noise components from the reproduced image, reference beams having mutually different wavelengths are generated a plurality of times, and the image sensor 25 performs the diffraction corresponding to each of the plurality of reference beams from the same hologram. If the recording data is reproduced by receiving the light a plurality of times and averaging the electrical signals from the image sensor 25 corresponding to each of the diffracted lights obtained a plurality of times, the original signal component is generated by the reference light. The noise components are added according to the number of times, and the noise components are averaged without being added. In other words, the noise component has a smaller spatial correlation coefficient value when the wavelength of the light beam at the time of recording is different from that at the time of reproduction. A process close to is performed.

  Here, in the experimental results of the wavelength selectivity of the signal and the crosstalk noise in FIG. 12, the correlation coefficient value is 0 even when the wavelength at the time of reproducing the light beam is changed by about 3 nm from the wavelength at the time of recording. The reason is that the contrast ratio of the spatial light modulator 22 (the luminance ratio between the white part and the black part) is not so good, and a uniform noise component is generated regardless of the wavelength of the light beam. The inventors think that it is because of this. Here, signal 1 and signal 2 are correlation coefficients when a certain hologram is reproduced, and noise is a phase when the spot of the blue light beam is condensed at a position 50 μm away from the hologram corresponding to signal 1. The number of relationships.

  FIG. 13 is a calculation result of wavelength selectivity of signals and crosstalk noise calculated using the calculation method disclosed in Non-Patent Document 2 shown in the background art.

  From the above experimental results and calculation results, when adding the electrical signal obtained from the image sensor 25 by a plurality of times of diffracted light, the noise component is averaged according to the change in wavelength, while the signal component is The inventors have found that processing close to spatial synchronous addition is performed according to changes. Based on this knowledge, the main part of the present embodiment will be described in more detail. This embodiment is divided into a first embodiment (wavelength shift individual reproduction method) and a second embodiment (continuous wavelength shift reproduction method), and each will be described in turn.

First Embodiment (Wavelength Shift Individual Regeneration Method)
In this method, each time the wavelength of the light beam is changed, an electrical signal corresponding to a reproduced image generated by diffracted light for one page is obtained a plurality of times for the same hologram, and processing is performed. In this method, when the noise is reduced, the wavelength of the light beam (reference light) is changed after the control unit 60 takes in the electrical signals from all the two-dimensionally arranged pixels of the image sensor 25. is there. That is, the amount of data as an electrical signal obtained is the number of changes in the wavelength of the light beam multiplied by the number of pixels. In this method, as described above, a large amount of information is used for processing in order to obtain recording data with reduced noise for a plurality of pages per page, and the effect of noise reduction is high. On the other hand, since it is necessary to capture reproduced images for a plurality of pages, the reproduction transfer speed is slow.

  The reproduction procedure performed by the control unit 60 when the wavelength shift individual reproduction method is used is as follows. The following shows the procedure for reproducing one page. In the following description, continuous pixel address information is sequentially given to all pixels in two-dimensionally arranged pixels, and this pixel address information has a one-to-one correspondence with the RAM address of the control unit 60. Is.

  (1) Using the servo optical system 30 described above, the red light beam is condensed by the objective lens 24 by the action of the focus servo described above to form a light spot on the recording layer 50a. Also, tracking servo along the address groove 50c is performed by the action of the tracking servo, the address information is reproduced by an address decoder arranged in the control unit 60, and a predetermined area (on the hologram recording / reproducing medium) (with reference to this address information) For example, the reproduction reference information recorded in the innermost peripheral area) is read out. The reproduction standard information is, for example, the number N of changes in the wavelength of the light beam (reference light) from the laser light source 20, the wavelength of each reference light, or the degree of difference between the wavelengths of the reference light (for example, 5 Pnm (pico・ Information such as every nanometer) is recorded.

  (2) Using the servo optical system 30, the address information is reproduced by the address decoder disposed in the control unit 60, and the red light beam is applied to the recording layer 50a for reproducing the recording data from the hologram on the basis of the address information. To form a light spot. In addition, the contents of the RAM that stores the electrical signal from the image sensor 25 arranged in the control unit 60 are cleared. The value of the wavelength change counter that stores the number of changes in wavelength is set to 1.

  (3) A control signal for controlling the rotary motor 241a disposed in the laser light source 20 is output, and the wavelength of the light beam from the laser light source 20 is set to the nth wavelength represented by the value n of the wavelength change counter. To do. In this case, the wavelength of the light beam changes stepwise. Further, the position of the image sensor 25 corresponding to the wavelength of the light beam from the laser light source 20 is read from the ROM of the control unit 60, and the image sensor actuator 125 is arranged so that the image sensor 25 is arranged at a predetermined position indicated by the ROM information. To control. Further, a predetermined pattern is displayed on the reference light spatial light modulator 47 of the spatial light modulator 22.

  (4) A control signal (not shown) is output to emit a light beam from the semiconductor laser 211 of the laser light source 20. Obtains electrical signals from all pixels of the image sensor, reads the previously stored data from the corresponding addresses in the RAM corresponding to each pixel, and adds the electrical signals from each pixel currently applicable to the value. And stored in the RAM of the corresponding address (average processing). Instead of controlling the emission of the light beam by controlling the semiconductor laser 211 of the laser light source 20, all the pixels of the spatial light modulator 22 are made black to create the same state as when the blue beam is stopped, In the case of emission, a predetermined pixel of the spatial light modulator 22 can be set as a white portion, and an operation equivalent to emission of a light beam from the semiconductor laser 211 can be performed.

  (5) It is determined whether the number of wavelength changes is N. If the number of wavelength changes is N, the process ends. If the number of wavelength changes is not N, the process returns to (3) above.

  The above is the process of reproducing one page. However, when a plurality of pages are processed, the process may be continued again by returning to the above-described process (1). It is also possible to return to the process and continue the process.

  In this way, for each pixel for one page, the wavelength can be changed continuously or in a stepwise manner, and an electrical signal can be taken into the control unit 60 a plurality of times for reproduction processing.

Second embodiment (continuous wavelength shift regeneration method)
As a method of increasing the transfer rate of reproduction, the wavelength of the light beam (reference light) is changed after taking in an electric signal from a part of the pixels arranged in two dimensions of the image sensor 25. That is, the amount of data obtained as an electrical signal is equal to the number of pixels. In this case, the wavelength may be sequentially changed while part of the electrical signal for one page is read from the image sensor 25 into the control unit 60. When the laser light source 20 is used, the wavelength can be changed stepwise. With this method, the transfer rate of playback can be increased.

  The reproduction procedure performed by the control unit 60 when the continuous wavelength shift reproduction method is used is as follows. The following shows the procedure for reproducing one page. In the following description, two-dimensional pixels are assigned one-dimensional pixel address information to all the pixels, and the pixel address information has a one-to-one correspondence with the RAM address of the control unit 60. .

  (1) Using the servo optical system 30 described above, the red light beam is condensed by the objective lens 24 by the action of the focus servo described above to form a light spot on the recording layer 50a. Also, tracking servo along the address groove 50c is performed by the action of the tracking servo, the address information is reproduced by an address decoder arranged in the control unit 60, and a predetermined area (on the hologram recording / reproducing medium) (with reference to this address information) For example, the reproduction reference information recorded in the innermost peripheral area) is read out. The reproduction standard information is, for example, the number M of continuous pixels that is the number of pixels that continuously read an electrical signal without changing the wavelength of the light beam (reference light) from the laser light source 20, and the reference light of each continuous pixel. The degree of mutual difference in wavelength or wavelength of reference light between each successive pixel (eg, every 5 Pnm (pico-nanometer)).

  (2) Using the servo optical system 30, the address information is reproduced by the address decoder disposed in the control unit 60, and the red light beam is applied to the recording layer 50a for reproducing the recording data from the hologram on the basis of the address information. Irradiate the light spot. The contents of the RAM that stores the electrical signal from the image sensor 25 arranged in the control unit 60 are cleared. The value of the wavelength change counter that stores the number of changes in wavelength is set to 1. Further, the value of the total pixel counter that counts the cumulative sum of the continuous pixel number M is set to zero.

  (3) A control signal for controlling the rotary motor 241a disposed in the laser light source 20 is output, and the wavelength of the light beam from the laser light source 20 is set to the nth wavelength represented by the value n of the wavelength change counter. To do. In this case, the wavelength of the light beam changes stepwise. Further, the position of the image sensor 25 corresponding to the wavelength of the light beam from the laser light source 20 is read from the ROM of the control unit 60, and the image sensor actuator 125 is arranged so that the image sensor 25 is arranged at a predetermined position indicated by the ROM information. To control. Further, a predetermined pattern is displayed on the reference light spatial light modulator 47 of the spatial light modulator 22.

  (4) A control signal (not shown) is output to emit a light beam from the semiconductor laser 211 of the laser light source 20. Electrical signals from successive pixels of the pixel address information of the image sensor 25 that accumulates sequentially (for example, when the electrical signals are read up to the Lth pixel last time, consecutive M pixels from L + 1 to L + M). And the electric signal from each pixel is stored in the corresponding address of the RAM corresponding to each pixel. Instead of controlling the emission of the light beam by controlling the semiconductor laser 211 of the laser light source 20, all the pixels of the spatial light modulator 22 are made black to create the same state as when the blue beam is stopped, In the case of emission, a predetermined pixel of the spatial light modulator 22 can be set as a white portion, and an operation equivalent to emission of a light beam from the semiconductor laser 211 can be performed.

  (5) It is determined from the pixel address information whether or not the electric signals from all the pixels have been taken into the RAM, and the process ends when the electric signals from all the pixels have been taken into the RAM. If the electrical signals from all the pixels are not taken into the RAM, the processing returns to the above (3).

  The above is the process of reproducing one page. However, when processing a plurality of pages, the process may be resumed by returning to the process (1) described above, or the process (2) described above. You may return to processing and continue processing.

  In this way, while the data for one page is captured, the control unit 60 can perform reproduction processing so as to change the wavelength continuously or stepwise.

  Regardless of whether the wavelength shift individual reproduction method or the continuous wavelength shift reproduction method is used, in the reproduction process of the recorded data in the control unit 60 after taking in the electric signal from the pixel of the image sensor 25, the above-mentioned hologram is recorded. By using the sync information, the two-dimensional information can be accurately aligned in the reproduction information decoding.

  Each of the above-described embodiments is merely one embodiment of the present invention, and the present invention is not limited to the above-described embodiment. For example, in the above description, the coaxial method in which the signal light and the reference light are coaxially arranged has been described. However, in the two-beam method in which the signal light and the reference light are incident on the hologram recording / reproducing medium via different optical components. Can be implemented based on the same technical idea. Also, for example, the spatial light modulator can be implemented using either a transmission type or a reflection type.

It is a figure which shows the concept of the coaxial optical system in a hologram recording device. It is a drawing substitute photograph showing an example of a signal light pattern and a reference light pattern displayed on a spatial light modulator. It is a figure which shows the concept of the coaxial optical system in a hologram reproduction apparatus. 1 schematically shows a structure cut in a cross-sectional area direction of a hologram recording / reproducing medium. 1 is a schematic diagram of a hologram recording / reproducing apparatus of an embodiment showing an optical part as a center. It is a figure which shows typically the laser light source 20 of embodiment. 3 is a drawing-substituting photograph showing a reproduced image of a hologram formed on a light receiving surface of an image sensor. 3 is a drawing-substituting photograph showing a reproduced image of a hologram formed on a light receiving surface of an image sensor. 3 is a drawing-substituting photograph showing a reproduced image of a hologram formed on a light receiving surface of an image sensor. 3 is a drawing-substituting photograph showing a reproduced image formed on the light receiving surface of the image sensor. 3 is a drawing-substituting photograph showing a reproduced image formed on the light receiving surface of the image sensor. It is a figure which shows the experimental result of the wavelength selectivity of a signal and crosstalk noise. It is a figure which shows the calculation result of the wavelength selectivity of a signal and crosstalk noise.

Explanation of symbols

  10, 11 Coaxial optical system, 20 Laser light source, 22 Spatial light modulator, 23 Beam splitter, 24 Objective lens, 25 Image sensor, 27 Beam splitter, 28 Servo light source, 29 Photo detector, 30 Servo optical system, 34 Dichroic mirror , 40 Signal light, 41 Reference light, 42, 43 Diffracted light, 46 Signal light spatial light modulator, 47 Reference light spatial light modulator, 50 Hologram recording / reproducing medium, 50a Recording layer, 50b Reflective film, 50c Address groove, 50d Protective film, 51 spindle motor, 54 servo actuator, 56 reflecting mirror, 60 control unit, 70 temperature detector, 100 hologram recording / reproducing device, 125 image sensor actuator, 211 semiconductor laser, 212 collimating lens, 213 Diffraction grating, 213a diffraction grating formation surface, 214 mirror, 214a mirror surface, 227 rotary shaft, 230 a laser light source control circuit, 241a rotating motor, 241b, 241c gear

Claims (7)

  1. A hologram reproducing apparatus that reproduces the recording data from a hologram formed on a recording layer of a hologram recording / reproducing medium by interfering with the signal light modulated according to the recording data and the reference light having the same signal light and the same light source. There,
    A reference light generator for generating the reference light;
    An image sensor having two-dimensionally arranged pixels for receiving diffracted light generated by irradiating the hologram with the reference light;
    A control unit that takes in an electrical signal from the image sensor and performs a process of reproducing recorded data;
    With
    The reference light generator generates the reference light having different wavelengths a plurality of times,
    The image sensor receives each of the diffracted lights corresponding to each of the reference lights having the different wavelengths from the same hologram,
    The control unit reproduces the recording data by performing a process of averaging each of the electrical signals from the image sensor corresponding to each of the diffracted lights.
    A hologram reproducing apparatus characterized by that.
  2.   2. The hologram reproducing apparatus according to claim 1, wherein the number of different wavelengths of the reference light is determined by reading information recorded in a predetermined area of the hologram recording / reproducing medium.
  3.   The hologram reproducing apparatus according to claim 1, wherein a position of the image sensor with respect to a direction in which the diffracted light is incident is changed according to a difference in wavelength of the reference light.
  4.   2. The hologram reproducing apparatus according to claim 1, wherein the degree of difference in wavelength of the reference light is determined by reading information recorded in a predetermined area of the hologram recording / reproducing medium.
  5.   The hologram reproducing apparatus according to claim 1, wherein the wavelength of the reference light is changed after the control unit captures the electrical signals from all of the pixels of the image sensor.
  6.   The hologram reproducing apparatus according to claim 1, wherein the wavelength of the reference light is changed after taking in the electrical signal from a part of the pixels of the image sensor.
  7.   The sync information recorded in the hologram in advance is used in the reproduction process of the recorded data in the control unit after taking in the electrical signals from a part of the two-dimensionally arranged pixels of the image sensor. The hologram reproducing apparatus according to claim 1, wherein:
JP2006296507A 2006-10-31 2006-10-31 Hologram reproducing apparatus Pending JP2008112107A (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004219672A (en) * 2003-01-14 2004-08-05 Sony Corp Hologram recording method, method for reproducing hologram recording, hologram recording and reproducing device and hologram reproducing device
JP2004310957A (en) * 2003-04-10 2004-11-04 Optware:Kk Optical information reproducing device, and recording medium stored with program usable to realize the same and readable by computer
JP2006215191A (en) * 2005-02-02 2006-08-17 Toshiba Corp Optical recording method, optical reproducing method, optical recording medium, and optical recording and reproducing device
JP2006267827A (en) * 2005-03-25 2006-10-05 Toshiba Corp Hologram recording and reproducing method, hologram recording medium, and hologram recording and reproducing device
JP2006267554A (en) * 2005-03-24 2006-10-05 Sony Corp Device and method for hologram recording and reproduction

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004219672A (en) * 2003-01-14 2004-08-05 Sony Corp Hologram recording method, method for reproducing hologram recording, hologram recording and reproducing device and hologram reproducing device
JP2004310957A (en) * 2003-04-10 2004-11-04 Optware:Kk Optical information reproducing device, and recording medium stored with program usable to realize the same and readable by computer
JP2006215191A (en) * 2005-02-02 2006-08-17 Toshiba Corp Optical recording method, optical reproducing method, optical recording medium, and optical recording and reproducing device
JP2006267554A (en) * 2005-03-24 2006-10-05 Sony Corp Device and method for hologram recording and reproduction
JP2006267827A (en) * 2005-03-25 2006-10-05 Toshiba Corp Hologram recording and reproducing method, hologram recording medium, and hologram recording and reproducing device

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