JP4506329B2 - Hologram recording apparatus, information processing apparatus, and hologram recording method - Google Patents

Description

  The present invention relates to a hologram recording apparatus, an information processing apparatus, and a hologram recording method.

  Development of hologram recording devices that record data using holography is in progress.

In hologram recording, signal light modulated by a spatial light modulator (hereinafter referred to as SLM) is separated into reference light that has passed through another optical path not including SLM, and these are condensed on a recording medium. These interference patterns are recorded (for example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2004-139023

  By the way, in such a hologram recording apparatus, when a liquid crystal device is used as the spatial light modulator, the signal light modulated by the liquid crystal device is extracted from positive light or negative light by, for example, a polarization beam splitter. The light is condensed on the recording medium and the other component is discarded.

  In addition, when a grating light valve is used as the spatial light modulator, for example, light other than the 0th-order diffracted light is discarded.

  For this reason, in the conventional hologram recording apparatus, the amount of light applied to the recording medium is very small compared to the amount of light from the laser light source. In particular, in the case of high speed recording, it is necessary to irradiate a recording medium with a high amount of light. That is, particularly when performing high-speed recording, there is a problem in that an improvement in the ratio of the surface light amount to the laser light amount is required.

  In view of the circumstances as described above, an object of the present invention is to provide a hologram recording apparatus, an information processing apparatus, and a hologram recording method capable of performing hologram recording at high speed even using a low-power laser light source.

  A. In view of the above, the hologram recording apparatus according to the present invention includes a laser light source that emits laser light, spatial modulation means that spatially modulates the laser light emitted from the laser light source, and a signal for the modulated laser light. Separating means for separating light into reference light, a first lens for condensing the separated signal light on a recording medium, and uniforming the separated reference light onto the recording medium And a spatial filter.

  In the present invention, the modulated laser beam is separated into the signal beam and the reference beam, and the separated reference beam is made uniform and guided onto the recording medium. Only laser light can be used effectively. Therefore, according to the present invention, hologram recording can be performed at high speed even using a low-power laser light source.

  Here, the spatial filter may include a second lens that Fourier transforms the separated reference light, and shielding means that shields the Fourier transformed reference light other than the 0th-order diffracted light.

  Thereby, the uniform reference light can be obtained with a simple configuration.

  In the present invention, the hologram recording apparatus can be used alone or as a storage means such as a personal computer.

  (1) The spatial modulation means is a spatial modulator that selectively polarizes laser light emitted from the laser light source in accordance with a signal to be modulated, and the separation means is modulated by the spatial modulator. The laser light is separated into negative light which is one of the signal light and the reference light and positive light which is the other of the signal light and the reference light, and the shielding means transmits only the 0th-order diffracted light. It may be a shielding plate having a pinhole.

  Thereby, two-dimensional modulation can be realized in accordance with the spirit of the present invention.

  Here, as the separating means, a polarization beam splitter is suitable.

  (2) The spatial modulation means and the separation means, according to the signal to be modulated, use the 0th order diffracted light and the 1st order diffracted light of the laser light emitted from the laser light source as the reference light in the first direction. It may be a spatial modulator that selectively separates the signal light in a second direction, and the shielding means may be a shielding plate having a slit that transmits only the 0th-order diffracted light.

  Thereby, one-dimensional modulation can be realized in accordance with the spirit of the present invention.

  Here, a grating light valve is preferable as the spatial modulator.

  B. In view of the above, the hologram recording method according to the present invention spatially modulates laser light emitted from a laser light source, separates the modulated laser light into signal light and reference light, and separates the separated signal light. Is collected on a recording medium, and the separated reference light is made uniform and guided onto the recording medium.

  In the present invention, the modulated laser beam is separated into the signal beam and the reference beam, and the separated reference beam is made uniform and guided onto the recording medium. Only laser light can be used effectively. Therefore, according to the present invention, hologram recording can be performed at high speed even using a low-power laser light source.

  Here, the homogenization of the separated reference light may be performed by subjecting the separated reference light to Fourier transform to shield other than the 0th-order diffracted light.

  Thereby, the uniform reference light can be obtained with a simple configuration.

  As described above, according to the present invention, the laser beam can be effectively used by the amount of the reference light that has been discarded in the past, so that hologram recording is performed at high speed even with a low-power laser light source. be able to.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)

  FIG. 1 is a block diagram showing a hologram recording / reproducing apparatus 10 according to the first embodiment of the present invention.

  The hologram recording / reproducing apparatus 10 includes a laser light source 11, a spatial light modulator 12, a polarization beam splitter 13, a lens 14, a lens 15, a shielding plate 16, a lens 17, a mirror 18, a HWP 19, a mirror 20, and a lens 21. , CCD sensor 22 and recording medium 23.

  As the laser light source 11, for example, a green laser with a wavelength of 532 nm can be used.

  The spatial light modulator 12 spatially modulates the laser light emitted from the laser light source 11. Here, as the spatial light modulator 12, a two-dimensional spatial light modulator is used which is configured by a modulation element arranged in a lattice shape in two directions orthogonal to each other. An example of this is a liquid crystal device (LCD). The two-dimensional spatial light modulator has an advantage that the amount of data processed by one recording / reproducing operation can be easily increased as compared with the one-dimensional spatial light modulator.

  2A shows the light intensity distribution of the cross section of the laser light incident on the spatial light modulator 12, and FIG. 2B shows the laser light after passing through the spatial light modulator 12. FIG. The cross-sectional light intensity distribution is shown. As shown in FIG. 2B, the laser light after passing through the spatial light modulator 12 also has a uniform light intensity distribution, and the signal appears as rotation of the polarization plane. That is, 0 and 1 are modulated as polarized light.

  The polarization beam splitter 13 distributes the laser light spatially modulated by the spatial light modulator 12 to the light intensity corresponding to the signals 0 and 1 as shown in FIG. FIG. 2C shows laser light (positive light) that has passed through the polarizing beam splitter 13. For example, this is used as signal light, and FIG. 2D shows the laser light (negative light) reflected by the polarizing beam splitter 13. For example, this is used as reference light.

  The lens 14 is an optical element that condenses the signal light on the recording medium 23. An image (real image) displayed on the spatial light modulator 12 is converted into a Fraunhofer diffraction image (Fourier transform image) at the focal position of the lens 14 to form an image. FIG. 2E shows the light intensity distribution in the cross section of the imaged diffraction image.

  The lens 15 and the shielding plate 16 are spatial filters that normalize a laser beam carrying a signal to a Gaussian distribution like the light intensity distribution shown in FIG.

  The lens 15 is an optical element that condenses the laser light reflected by the polarization beam splitter 13 on the shielding plate 16. By this lens 15, the laser beam reflected from the polarization beam splitter 13 is converted into a Fraunhofer diffraction image (Fourier transform image) at the focal position of the lens 15 and imaged.

  As shown in FIG. 3, the shielding plate 16 is provided with a pinhole 16a. The pinhole 16a has a size that allows the 0th-order light 16b of the diffraction image formed on the shielding plate 16 to pass and shields the first-order light and the subsequent 16c.

  The lens 17 converts the laser light that has passed through the pinhole 16a into parallel light. The light intensity distribution of the parallel light is made uniform as shown in FIG.

  The mirrors 18 and 20 guide the parallel light to the recording medium 23 as reference light. The angle of the reference light is adjusted by the mirrors 18 and 20 so as to enter the recording medium 23 at an angle of 90 ° with respect to the signal light.

  The HWP (half-wave plate) 19 is an optical element for causing the polarization direction of the reference light to coincide with the signal light, and rotating the polarization plane of the incident reference light by 90 °. This is because if the HWP (half-wave plate) 19 is not inserted, the signal light and the reference light are orthogonal to each other, so that optical interference (hologram recording) does not occur between the signal light and the reference light.

  The lens 21 condenses the diffracted light reproduced from the recording medium 23 on the CCD sensor 22. At this time, a real image displayed on the spatial light modulator 12 is formed on the detection surface of the CCD sensor 22 as shown in FIG. That is, the lens 21 is an inverse Fourier transform lens that forms an image on the CCD sensor 22 by performing inverse Fourier transform on the Fourier transform image of the spatial light modulator 12 recorded on the recording medium 23.

  The CCD sensor 22 is a light receiving element that detects the reproduced signal light, and is a two-dimensional light receiving element in which the light receiving elements are arranged in two directions.

  The recording medium 23 is a recording medium that has a recording layer and records interference fringes due to signal light and reference light. That is, a real image Fraunhofer diffraction image (Fourier transform image) displayed on the spatial light modulator 12 is formed and recorded on the recording layer. The recording medium 23 is installed so as to include a crossing portion of the signal light and the reference light in the recording layer.

The recording layer of the recording medium 23 records the interference fringes as a change in refractive index (or transmittance), and is a material that changes the refractive index (or transmittance) in accordance with the intensity of light. If there is, it can be used regardless of whether it is an organic material or an inorganic material. As the inorganic material, for example, a photorefractive material whose refractive index changes according to the exposure amount by an electro-optic effect such as lithium niobate (LiNbO ₃ ) can be used. As the organic material, for example, a photopolymerization type photopolymer can be used. In the photopolymerization type photopolymer, in the initial state, monomers are uniformly dispersed in the matrix polymer. When this is irradiated with light, the monomer is polymerized at the exposed portion. As the polymer is formed, the monomer moves from the surroundings, and the concentration of the monomer changes depending on the location.

  The hologram recording / reproducing apparatus 10 configured as described above irradiates the recording medium 23 with both signal light and reference light at the time of recording, and the modulation pattern of the signal light is recorded in the recording layer as interference fringes of two beams. .

Further, at the time of reproduction by the hologram recording / reproducing apparatus 10, the signal light is shielded by a shutter (not shown), and only the reference light is irradiated to the recording medium 23. The interference fringes generated in the recording medium 23 function as a diffraction grating, and the modulated signal light is reproduced (diffracted).
(Effective use of laser light)

  Next, the reason why laser light is used effectively in the hologram recording / reproducing apparatus 10 configured as described above will be described.

  FIG. 4 shows a configuration example of a normal hologram recording / reproducing apparatus 40. In FIG. 4, the same components as those in FIG.

  In the hologram recording / reproducing apparatus 40 shown in FIG. 4, a polarization beam splitter 41 is disposed in front of the spatial light modulator 12 to extract the reference light, and reflected by the polarization beam splitter 13 disposed in the subsequent stage of the spatial light modulator 12. Light is thrown away as unnecessary light.

  On the other hand, in the hologram recording / reproducing apparatus 10 according to the present embodiment, the reflected light from the polarization beam splitter 13 is used as reference light without being discarded. Thereby, it becomes possible to use a laser beam effectively.

  However, since a signal is carried in the reflected light by the polarization beam splitter 13, it cannot be used as a reference light as it is. Therefore, in this hologram recording / reproducing apparatus 10, the reflected light from the polarization beam splitter 13 can be used as the reference light by using a spatial filter that normalizes the laser light carrying the signal into a Gaussian distribution.

Therefore, the hologram recording / reproducing apparatus 10 configured as described above has an effect that hologram recording can be performed at high speed even if the laser light source 11 has low power.
(Second Embodiment)

  FIG. 5 is a block diagram showing a hologram recording / reproducing apparatus 50 according to the second embodiment of the present invention.

  The hologram recording / reproducing device 50 includes a laser light source 51, a spatial light modulator 52, a lens 53, a lens 54, a shielding plate 55, a lens 56, a mirror 57, a lens 58, a CCD sensor 59, and a recording medium 60. Is done.

  As the laser light source 51, for example, a green laser having a wavelength of 532 nm can be used.

  The spatial light modulator 52 spatially modulates the laser light emitted from the laser light source 51. Here, as the spatial light modulator 52, one-dimensional spatial light modulation in which modulation elements are arranged in one direction, light is modulated in only one direction, and there is no modulation signal component in the other direction. It is a vessel. An example of this is GLV (Grating Light Valve) manufactured by Silicon Light Machine. The one-dimensional spatial light modulator has advantages that the response speed can be increased and the element size can be easily reduced. In this spatial light modulator 52, a first direction (a direction in which incident light is axisymmetric with respect to the normal of the incident surface of the spatial light modulator 52) and a signal with zero-order light and primary light as reference lights The light is selectively separated in the second direction (normal direction of the incident surface of the spatial light modulator 52).

  FIG. 6A shows the light intensity distribution of the cross section of the laser light incident on the spatial light modulator 52. This light intensity distribution is uniform. FIGS. 6B and 6C show light intensity distributions of the cross sections of the above-described zeroth-order light and first-order light, respectively.

  The lens 53 is an optical element that condenses the signal light on the recording medium 60. The primary light modulated by the spatial light modulator 60 is converted into a Fraunhofer diffraction image (Fourier transform image) at the focal position of the lens 53 to form an image. FIG. 6D shows the light intensity distribution in the cross section of the imaged diffraction image. Note that the image formed may be a defocused image or a real image.

  The lens 54 and the shielding plate 55 are spatial filters that normalize 0th-order light on which signals are carried to a Gaussian distribution.

  The lens 54 is an optical element that collects zero-order light on the shielding plate 55. By this lens 54, the zero-order light is converted into a Fraunhofer diffraction image (Fourier transform image) at the focal position of the lens 54 and imaged.

  As shown in FIG. 7, the shielding plate 55 is provided with a slit 55a. The slit 55a has a size and shape that allows the 0th-order light 55b of the diffraction image formed on the shielding plate 55 to pass through and shields the first-order light and the subsequent 55c.

  The lens 56 converts the laser light that has passed through the slit 55a into parallel light. The light intensity distribution of the parallel light is made uniform as shown in FIG.

  The mirror 57 guides this parallel light to the recording medium 60 as reference light. The angle of the reference light is adjusted by the mirror 57 so as to enter the recording medium 60 at an angle of 45 ° with respect to the signal light. The reference light and the signal light are optimally incident on the recording medium 60 at an angle of 45 °, but may of course be at an angle other than 45 °.

  The lens 58 collects the diffracted light reproduced from the recording medium 60 on the CCD sensor 59. At this time, a real image displayed on the spatial light modulator 52 is formed on the detection surface of the CCD sensor 59 as shown in FIG. That is, the lens 58 is an inverse Fourier transform lens that forms an image on the CCD sensor 59 by performing inverse Fourier transform on the Fourier transform image of the spatial light modulator 52 recorded on the recording medium 60.

  The CCD sensor 59 is a light receiving element that detects the reproduced signal light, and is a one-dimensional light receiving element in which the light receiving elements are arranged in one direction.

  The recording medium 60 is a recording medium that has a recording layer and records interference fringes due to signal light and reference light, and is the same as that described in the first embodiment.

  The hologram recording / reproducing apparatus 50 configured in this way also irradiates the recording medium 60 with both the signal light and the reference light during recording, and the modulation pattern of the signal light is recorded in the recording layer as interference fringes of two beams. .

Further, at the time of reproduction by the hologram recording / reproducing apparatus 50, the signal light is shielded by a shutter (not shown), and only the reference light is irradiated to the recording medium 60. The interference fringes generated in the recording medium 60 function as a diffraction grating, and the modulated signal light is reproduced (diffracted).
(Effect unique to the apparatus according to the second embodiment)

In the hologram recording / reproducing apparatus 50 configured as described above, the laser beam can be used effectively. In addition to this, the following effects can be obtained.
(1) Since the polarization direction of the reference light and the polarization direction of the signal light coincide with each other, an optical element such as HWP is not necessary.
(2) The GLV can operate at a higher speed than the liquid crystal device.
(3) GLV also serves as a separating means, and an optical element such as a polarizing beam splitter is not necessary.
(Other embodiments)
(1) Although the above GLV is a blazed type, each ribbon is inclined and the direction in which the diffracted light is emitted is different from that of the incident light, it is possible to use a GLV that is not a blazed type. In this case, since the light incident on the GLV and the signal light are coaxial, and the signal light becomes the 0th order light, either ± 1st order light or both may be used as the reference light.
(2) The above GLV is premised on one dimension, but can be used in the present invention if a two-dimensional GLV can also be realized.

  Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.

1 is a block diagram showing a hologram recording / reproducing apparatus according to a first embodiment of the present invention. It is a figure which shows the light intensity distribution of the cross section of the laser beam in each part which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the shielding board which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the hologram recording / reproducing apparatus to which this invention is not applied. It is a block diagram which shows the hologram recording / reproducing apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the light intensity distribution of the cross section of the laser beam in each part which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the shielding board which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hologram recording / reproducing apparatus 11 Laser light source 12 Spatial light modulator 13 Polarization beam splitters 14 and 15 Lens 16 Shielding plate 16a Pinhole 17 Lens 23 Recording medium

Claims (9)

A laser light source for emitting laser light;
Spatial modulation means for spatially modulating laser light emitted from the laser light source;
Separating means for separating the modulated laser light into signal light and reference light;
A first lens for condensing the separated signal light on a recording medium;
And a spatial filter for making the separated reference light uniform and guiding it onto the recording medium. The hologram recording apparatus according to claim 1,
The spatial filter is
A second lens for Fourier transforming the separated reference light;
A hologram recording apparatus, comprising: shielding means for shielding non-zero order light among the Fourier-transformed reference light. The hologram recording apparatus according to claim 2,
The spatial modulation means is a spatial modulator that selectively polarizes laser light emitted from the laser light source according to a signal to be modulated,
The separation means separates the laser light modulated by the spatial modulator into a negative light that is one of the signal light and the reference light and a positive light that is the other of the signal light and the reference light. Yes,
The hologram recording apparatus, wherein the shielding means is a shielding plate having a pinhole that transmits only zeroth-order light. The hologram recording apparatus according to claim 3, wherein
The hologram recording apparatus, wherein the separating means is a polarization beam splitter. The hologram recording apparatus according to claim 2,
The spatial modulation means and the separation means use the 0th order light and the 1st order light of the laser light emitted from the laser light source according to the signal to be modulated as the reference light in the first direction and the signal light, respectively. As a spatial modulator that selectively separates in the second direction as
The hologram recording apparatus, wherein the shielding means is a shielding plate having a slit that transmits only zeroth-order light. The hologram recording device according to claim 5,
The hologram recording apparatus, wherein the spatial modulator is a grating light valve. A laser light source for emitting laser light;
Spatial modulation means for spatially modulating laser light emitted from the laser light source;
Separating means for separating the modulated laser light into signal light and reference light;
A first lens for condensing the separated signal light on a recording medium;
An information processing apparatus comprising: a hologram recording apparatus comprising: a spatial filter for making the separated reference light uniform and guiding the separated reference light onto the recording medium. Spatially modulates the laser light emitted from the laser light source,
Separating the modulated laser light into signal light and reference light;
Condensing the separated signal light on a recording medium;
The hologram recording method, wherein the separated reference light is made uniform and guided onto the recording medium. The hologram recording method according to claim 8, comprising:
The homogenization of the separated reference light is performed by Fourier-transforming the separated reference light and shielding other than the 0th order light.

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