JP4475031B2 - Hologram recording apparatus, hologram reproducing apparatus, and information processing apparatus - Google Patents

Description

  The present invention relates to a hologram recording device, a hologram reproducing device, and an information processing device.

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 crossed on a recording medium with reference light that has passed through another optical path that does not include the SLM, and these interference patterns are holograms. Record as.
A technique for reducing a noise component during information recording by blocking a predetermined diffraction image component is disclosed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2004-139023

In the hologram recording apparatus, the signal light modulated by the SLM is formed as a Fraunhofer diffraction image (Fourier transform image) by passing through a recording lens and recorded on a recording medium. At this time, the Fraunhofer diffraction image on the recording medium is composed of a zero-order diffraction image on the center of the optical axis and a high-order diffraction image centered on the zero-order diffraction image.
In such a hologram recording apparatus, if the relative position between the + side and the − side of the high-order diffraction image is shifted for some reason, noise is generated in the reproduction signal, which causes deterioration of the signal contrast and reduction of the S / N ratio. . Causes of this positional deviation include recording lens aberration, recording medium deformation / shrinkage, optical axis deviation, and the like.
In order to reduce this misalignment, methods such as the introduction of a lens with good visual field characteristics, improvement in the positional accuracy of the optical system, and reduction in the deformation / shrinkage of the media can be considered, but this increases the cost and size of the system. Will be invited.
In view of the circumstances as described above, it is an object of the present invention to provide a hologram recording device, a hologram reproducing device, and an information processing device which are intended to reduce noise generated due to the effect of positional deviation of diffraction images.

  A. In view of the above, a hologram recording apparatus according to the present invention is modulated by a laser light source that emits laser light, a spatial modulator that spatially modulates the laser light emitted from the laser light source, and the spatial modulator. A first lens for condensing a laser beam on a recording medium; and a shielding unit that is disposed between the lens and the recording medium and shields one of positive and negative of a part of the diffraction image from the spatial modulator. It is characterized by comprising.

  If position asymmetry occurs in the positive and negative components of the diffraction image, beat noise may occur due to interference between these diffraction images. In such a case, noise during recording of the hologram can be reduced by excluding one of the positive and negative diffraction images in which the position asymmetry has occurred with the shielding plate.

(1) The shielding means may shield either the positive or negative first-order diffraction image, or all of the positive or negative first-order diffraction images.
Low-order diffraction images are generally high in intensity, and often have a large influence on beat noise caused by the occurrence of asymmetry between positive and negative diffraction images.

(2) The hologram recording apparatus further includes a branch element that branches the laser light emitted from the laser light source, and a second lens that focuses the laser light branched by the branch element on the recording medium. May be.
By irradiating the recording medium with the reference light together with the signal light, recording on the recording medium can be performed.

  B. In view of the above, the hologram reproducing apparatus according to the present invention includes a laser light source that emits laser light, a lens that condenses the laser light emitted from the laser light source on a recording medium on which the hologram is recorded, and the light condensing device. A light receiving element that receives a diffraction image obtained by diffracting the laser beam diffracted by the hologram; and a light receiving element that is disposed between the recording medium and the light receiving element and shields one of positive and negative of a part of the diffraction image from the hologram. And a shielding means.

  If position asymmetry occurs in the positive and negative components of the diffraction image, beat noise may occur due to interference between these diffraction images. In such a case, noise during reproduction of the hologram can be reduced by excluding one of the positive and negative diffracted images having asymmetry with the shielding plate.

Here, the shielding means may shield any positive or negative primary diffraction image, for example, any positive or negative primary diffraction image.
Low-order diffraction images are generally high in intensity, and have a great influence on beat noise due to position asymmetry that occurs between positive and negative diffraction images.

  As described above, according to the present invention, it is possible to provide a hologram recording apparatus, a hologram reproducing apparatus, and an information processing apparatus that are capable of reducing noise generated due to the influence of the positional deviation of a diffraction image.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
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 filter 12, shutters 13 and 14, half-wave plates HWP1 and HWP2, a polarization beam splitter PBS, a spatial light modulator SLM, lenses LZ1 to LZ3, It comprises a shielding plate 15, a mirror M, a recording medium D, and a sensor 16.

As the laser light source 11, for example, a green laser with a wavelength of 532 nm can be used.
The spatial filter 12 is composed of lenses 1221 and 122 and a pinhole 123, and is an optical element for removing high-frequency noise components contained in the laser light emitted from the laser light source 11.

The shutters 13 and 14 are optical elements that control the passage and shielding of laser light.
Among these, the shutter 13 controls the operation / stop of the hologram recording / reproducing apparatus 10. By opening the shutter 13, the hologram recording / reproducing apparatus 10 can perform either information recording or reproduction.
On the other hand, the shutter 14 switches between recording and reproduction of the hologram recording / reproducing apparatus 10. At the time of recording, the shutter 13 is opened, and both the signal light and the reference light are irradiated onto the recording medium D. At the time of reproduction, the shutter 14 is closed and only the reference light is irradiated to the recording medium D.

The half-wave plates HWP1 and HWP2 are optical elements that rotate the polarization plane of incident signal light by 90 °.
Of these, the half-wave plate HWP1 adjusts the polarization direction of the laser light incident on the deflection beam splitter PBS.
On the other hand, the half-wave plate HWP2 is for making the polarization direction of the reference light coincide with the signal light.
The deflection beam splitter PBS is an optical element that splits the laser beam emitted from the half-wave plate HWP1 into two beams. The laser light is branched into signal light that passes through the deflecting beam splitter PBS and reference light that is reflected by the deflecting beam splitter PBS.

The spatial light modulator SLM spatially modulates the laser light transmitted through the deflecting beam splitter PBS.
As the spatial light modulator SLM, a one-dimensional SLM and a two-dimensional SLM can be used.
The one-dimensional SLM is a spatial light modulator SLM in which modulation elements are arranged in one direction, light is modulated in only one direction, and does not have a modulation signal component in the other direction. An example of this is GLV (Grating Light Valve) manufactured by Silicon Light Machine. The one-dimensional SLM has an advantage that the response speed can be increased and the element size can be easily reduced.
The two-dimensional SLM is a spatial light modulator SLM configured with modulation elements arranged in two directions. For example, the modulation elements are arranged in a lattice shape in two directions orthogonal to each other. Examples of this include a liquid crystal element and DMD (Deformable Mirror Device). The two-dimensional SLM has an advantage that the amount of data processed by one recording / reproducing operation can be easily increased as compared with the one-dimensional SLM.

  The lens LZ1 (recording lens) is an optical element that condenses the recording light emitted from the spatial light modulator SLM on the recording medium D. An image (real image) displayed on the spatial light modulator SLM is converted into a Fraunhofer diffraction image (Fourier transform image) at the focal position of the recording lens LZ1 to form an image.

The mirror M is an optical element that reflects the reference light emitted from the half-wave plate HWP2 and changes its direction. As a result, the angle of the reference light is adjusted so as to enter the recording medium D at an angle of 45 ° with respect to the signal light.
The lens LZ2 is an optical element that condenses the reference light reflected by the mirror M on the recording medium D.

The recording medium D is a recording medium that has a recording layer and records interference fringes due to the signal light and the reference light from the lenses LZ1 and LZ2. That is, the interference fringes generated at the intersection of the real image Fraunhofer diffraction image (Fourier transform image) displayed on the spatial light modulator SLM and the reference light are recorded in the recording layer.
The recording medium D is installed in the recording layer so as to include a crossing portion of the signal light and the reference light. The reference beam is shaped as necessary so as to overlap the signal beam at this intersection.

The recording layer of the recording medium D records the interference fringes as a change in refractive index (or transmittance), and may be a material in which the refractive index (or transmittance) changes depending on the intensity of light. For example, 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.
As described above, when the refractive index (or transmittance) of the recording layer changes according to the exposure amount, interference fringes caused by the reference light and the signal light are applied to the recording medium D as changes in the refractive index (or transmittance). Can record. This interference fringe is called a hologram.

As described above, at the time of recording by the hologram recording / reproducing apparatus 10, the shutters 13 and 14 are opened, both the signal light and the reference light are irradiated onto the recording medium D, and the modulation pattern of the signal light is an interference between the two beams. It is recorded in the recording layer as a stripe (hologram).
Further, at the time of reproduction by the hologram recording / reproducing apparatus 10, only the reference light is irradiated to the recording medium D by opening the shutter 13 and closing the shutter 14. The hologram generated in the recording medium D functions as a diffraction grating, and the modulated signal light is reproduced (diffracted).

  The shielding plate 15 is an optical element that is disposed between the lens LZ1 and the recording medium D and shields a part of the Fraunhofer diffraction image from the spatial light modulator SLM. The shielding plate 15 shields the first-order or higher-order diffraction image on one side with the zero-order diffracted light from the spatial light modulator SLM as the center. As a result, the S / N ratio of the signal recorded on the recording medium D is improved. Details of this will be described later.

  The lens LZ3 focuses the diffraction image reproduced from the recording medium D on the sensor 16. At this time, a real image displayed on the spatial light modulator SLM is formed on the detection surface of the sensor 16. The lens LZ1 is a Fourier transform lens that forms an image on the recording medium D by performing a Fourier transform on the real image of the spatial light modulator SLM. On the other hand, the lens LZ3 is an inverse Fourier transform lens that forms an image on the sensor 16 by performing inverse Fourier transform on the Fourier transform image of the spatial light modulator SLM recorded on the recording medium D.

  The sensor 16 is a light receiving element that detects the reproduced signal light. There may be a one-dimensional light receiving element in which the light receiving elements are arranged in one direction and a two-dimensional light receiving element in which the light receiving elements are arranged in two directions. When the spatial light modulator SLM is two-dimensional, a two-dimensional light receiving element such as a CCD is used. However, when the spatial light modulator SLM is one dimensional, a one-dimensional light receiving element can be used.

(Details of shielding plate 15)
The reason why the S / N ratio is improved by the shielding plate 15 will be described below.
A. Reduction of S / N ratio in the case where there is no shielding plate 15 The cause of the decrease in S / N ratio in the case where there is no shielding plate 15 will be described.
As described above, in the hologram recording apparatus 10, the signal light modulated by the spatial light modulator SLM is formed on the recording medium D as a Fraunhofer diffraction image (Fourier transform image) by the lens LZ1.

The Fraunhofer diffraction image on the recording medium D corresponds to a zero-order diffraction image on the center of the optical axis and a highly symmetrical distribution centered on the zero-order diffraction image corresponding to the periodicity of the element arrangement of the spatial light modulator SLM. And a next diffraction image. The imaging position of the high-order diffraction image is determined by the spatial frequency of the modulation signal, the low-frequency component is closer to the 0th-order diffraction image, and the high-frequency component is formed at a position further away from the 0th-order diffraction image. Further, when the element arrangement of the spatial light modulator SLM has periodicity in a plurality of directions, a symmetrical diffraction image is formed in each direction, and the entire diffraction image has a radial structure centered on the 0th-order diffraction image. It becomes.
At this time, if the relative position between the + side and the − side of the diffraction image is shifted for some reason in the hologram recording apparatus, noise is generated in the reproduction signal, which causes deterioration of the signal contrast and reduction of the S / N ratio.

  FIG. 2 is a diagram illustrating a correspondence relationship between the spatial light modulator SLM, the recording medium D, the sensor 16, and the intensity pattern of the recording light when the shielding plate 15 is not provided. 2A is a schematic diagram in which a part of the hologram recording / reproducing apparatus 10 is enlarged. FIGS. 2B, 2C, and 2D are diagrams on the spatial light modulator SLM, the recording medium D, 3 is a graph showing an intensity pattern of recording light imaged on a sensor 16;

  As shown in FIG. 2A, here, it is assumed that a one-dimensional SLM is used as the spatial light modulator SLM, and the modulation elements alternately repeat bright and dark. As a result, as shown in FIG. 2B, the real image of the spatial light modulator SLM becomes a single frequency modulation pattern.

As shown in FIG. 2C, the Fourier image of the spatial light modulator SLM on the recording medium D is a Fourier transform image of a single frequency modulation pattern. This figure shows ± 1st order diffraction images δy _{± 1} , ± 2nd order diffraction images δy _{± 2} and ± 3rd order diffraction images δy _{± 3} . A broken line is an ideal Fourier image, and a solid line is a Fourier transform image including distortion. In a Fourier image including distortion, the relative positions of the + side diffraction image and the − side diffraction image, which are essentially the same frequency components, are shifted, and therefore the distances of the positive and negative diffraction images δy from the 0th order diffraction image do not match ( | δy ₊₁ | ≠ | δy _-1 |, | δy ₊₂ | ≠ | δy _-2 |, | δy ₊₃ | ≠ | δy _-3 |).
As shown in FIG. 2D, when a Fourier transform image including distortion is reproduced, the intensity pattern of the recording light on the spatial light modulator SLM is not reproduced and an optical beat appears. This is because a slight difference occurs in the frequency of the positive and negative diffraction images due to the distortion of the Fourier transform image.

B. Improvement of S / N ratio by the shielding plate 15 As described above, the shielding plate 15 has a first-order or higher-order diffraction image on one side (positive or negative) centered on the zero-order diffraction image from the spatial light modulator SLM. Shield. For this reason, even if there is a difference in frequency between the positive and negative diffraction images, the occurrence of an optical beat is prevented and the S / N ratio is improved.

(1) In the case of a one-dimensional SLM FIG. 3 is a schematic diagram illustrating a correspondence relationship between the spatial light modulator SLMa and the shielding plate 15a when the spatial light modulator SLM is a one-dimensional SLM. 3A and 3B respectively show the spatial light modulator SLMa and the shielding plate 15a.
The elements of the spatial light modulator SLMa are periodically arranged along the direction Dsa, and a diffraction image is distributed along the direction Dfa corresponding to the direction Dsa. A zero-order diffraction image S0 is arranged at the center of the diffraction image.
The shielding plate 15a shields the first-order or higher-order diffraction image on one side (one of positive and negative) centering on the zero-order diffraction image S0 from the spatial light modulator SLMa.

In the spatial light modulator SLMa that is a one-dimensional SLM, the diffraction image is distributed in one direction. For this reason, the shielding plate 15a has a semi-planar shape having one side 151 of a linear knife edge.
Note that a one-dimensional sensor having a smaller pixel size than the modulation pixel of the spatial light modulator SLMa is used as the sensor 16 as a light receiving element of the diffraction image that has passed through the shielding plate 15, and the sensor 16 is used as one pixel of the spatial light modulator SLMa. The plurality of light receiving pixels correspond to each other.

(2) Case of Two-Dimensional SLM Next, a case where a two-dimensional SLM is used as the spatial light modulator SLM will be described.
4 to 8 are schematic diagrams illustrating an example of a correspondence relationship between the spatial light modulators SLMb to SLMf and the shielding plates 15b to 15f when the spatial light modulator SLM is a two-dimensional SLM. Specifically, A correspondence relationship among the arrangement pattern of the modulation elements of the spatial light modulator SLM, the distribution direction of the diffraction image, the shape of the shielding plate, and the installation position thereof is shown. 4 to 8A and 4B respectively show the spatial light modulators SLMb to SLMf and the shielding plates 15b to 15f.

  As shown in FIGS. 4 to 8, the modulation signal of the spatial light modulators SLMb to SLMf is modulated in the directions Dfb1 to Dff3 corresponding to the periodic directions Dsb1 to Dsf3 with the zero-order diffraction image S0 as the center. The Fraunhofer diffraction image is distributed linearly. The shielding plates 15b to 15f shield one of positive and negative high-order diffraction images other than the zero-order diffraction image in all the directions Dfb1 to Dff3 corresponding to the periodicity of the element arrangement.

  Further, the sides 151b to 151f of the shielding plates 15b to 15f have a knife edge shape, and have a square shape that is slightly concave on the opening side with the 0th-order diffraction image S0 as the center. It can be seen that the sides 151b to 151f are bent in the vicinity of the 0th-order diffraction image S0 as compared to the one-dot chain line (straight line) shown in FIGS. 4 (B) to 8 (B). Note that the sides 151b to 151f may be composed of a combination of two straight lines or a curved line.

  If one side 151b to 151f is a straight line (for example, the one-dot chain line in the figure: a straight line passing through the center of the 0th-order diffraction image S0), the components of the diffraction image distributed in the direction parallel to the one side 151b to 151f are the shielding plates 15b to 15f. Will pass. That is, if the diffraction image is distributed in parallel directions, it passes through the shielding plates 15b to 15f regardless of the sign, and becomes a factor that generates beat noise. By forming the sides 151b to 151f in a dogleg shape, only one of the positive and negative components of the diffraction image passes through the shielding plates 15b to 15f, and the occurrence of beat noise in the sensor 16 is prevented.

(Second Embodiment)
The second embodiment of the present invention will be described below.
In the first embodiment, when recording modulated signal light by the spatial light modulator SLM, beat noise is removed by shielding all half of the signal light on the Fourier plane.
Depending on conditions, beat noise can be removed by shielding only a part of the positive and negative sides of the signal light Fourier image. For example, when beat noise is generated only by the relative position shift of only a specific order diffraction image, the beat noise can be removed by shielding only the positive or negative of the corresponding diffraction. Note that the diffraction image that causes beat noise may include a plurality of orders of diffraction.

FIG. 9 is a schematic diagram showing a case where beat noise is removed by shielding only a diffraction image of a specific order, and is a partially enlarged view of FIG. 9A is a schematic diagram in which a part of the hologram recording / reproducing apparatus 10 is enlarged. FIGS. 9B to 9F are diagrams on the spatial light modulator SLM, on the recording medium D, and on the sensor 16. It is a graph showing the intensity | strength pattern of the recording light condensed.
In the present embodiment, a region variable shielding plate capable of changing the shielding region (shielding mask pattern), for example, a transmissive liquid crystal element is used as the shielding plate 15h. By doing in this way, according to noise conditions, the shielding mask pattern of the shielding board 15h can be changed suitably.
As shown in FIG. 9A, here, it is assumed that a one-dimensional SLM is used as the spatial light modulator SLM, and the modulation elements alternately repeat bright and dark. As a result, as shown in FIG. 9B, the real image of the spatial light modulator SLM becomes a single frequency modulation pattern.

The removal of beat noise in this embodiment is performed as follows.
(1) Detection of signal light in a non-shielded state First, signal light that has passed through the lens LZ1 (Fourier transform lens), the recording medium D (media), and the lens LZ2 (inverse Fourier transform lens) is detected by the sensor 16 (CCD camera). It detects (FIG. 9 (D)). At this time, the reference light is not irradiated, and the shielding plate 15h is in an open state (a state in which there is no shielding region).

(2) Calculation of frequency of beat noise included in detected signal Beat noise may be mixed in the signal detected by the sensor 16. By applying Fourier transform to the signal detected by the sensor 16 (FIG. 9D), the frequency component of beat noise can be calculated.

(3) Control of shielding plate 15h based on calculated beat noise frequency Recording operation is performed in a state where a shielding pattern for shielding a diffraction image at a position corresponding to the beat noise frequency is generated by shielding plate 15h. The calculated frequency corresponds to the position of the diffraction image (Fourier transform image) on the recording medium D (Fourier plane of the lens LZ1), and this opposing relationship is defined by the characteristics of the lens LZ1.

By controlling the shielding plate 15h, beat noise can be removed from the modulation signal recorded on the recording medium D (see FIGS. 9E and 9F).
In FIG. 9, the relative positions of the ± 1st order diffraction images are shifted (see FIG. 9C), and beat noise is removed by shielding the + 1st order diffraction image (see FIG. 9E). (See FIGS. 9D and 9F).
Here, a one-dimensional SLM is used as the spatial modulator SLM, but noise can be similarly removed even when a two-dimensional SLM is used as the spatial modulator SLM. In this case, the shielding portion (the shielding target portion in the diffraction image) is two-dimensionally distributed in the plane of the shielding plate 15. For this reason, the shielding region of the shielding plate 15 is changed two-dimensionally according to the distribution of the shielding portion.
As the shielding plate 15 (device for generating a shielding pattern), a reflective liquid crystal, a DMD (mirror array), or the like may be used instead of the transmissive liquid crystal.

(Third embodiment)
The third embodiment of the present invention will be described below.
In the first and second embodiments, when recording the modulated signal light by the spatial light modulator SLM, beat noise is removed by shielding the signal light.
In contrast, in the present embodiment, the signal light is not shielded during recording on the recording medium D, and the reference light is shielded during reproduction from the recording medium D. Therefore, the shielding plate 15 can be inserted and removed between the lens LZ1 and the recording medium D. Except for this point, the present embodiment is substantially the same as the first embodiment (FIG. 1), and the illustration is omitted.

When recording the Fourier transform image on the recording medium D, the shielding plate 15 is removed from the optical path, and the entire Fourier transform image (Fraunhofer diffraction image) is recorded on the recording medium D.
At the time of reproducing a signal from the recording medium D, the shielding plate 15 is inserted into the optical path, and the reproduction light is irradiated to only one half from the 0th-order diffraction image recorded on the recording medium D. In this case, the relative position of the recording medium D and the shielding plate 15 is adjusted according to the position of the recording mark (diffraction image) to be reproduced.
In this way, only one of the positive and negative components of the diffraction image is generated from the recording medium D, and the occurrence of beat noise in the reproduction signal imaged by the sensor 16 is prevented.

(Modification of the third embodiment)
Hereinafter, a modification of the third embodiment of the present invention will be described.
FIG. 10 is a block diagram showing a hologram recording / reproducing apparatus 10b according to a modification of the third embodiment of the present invention.
In the present modification, the shielding plate 15k is disposed not between the lens LZ1 and the recording medium D but between the lens LZ2 and the recording medium D.
At the time of recording on the recording medium D, the entire Fraunhofer diffraction image (Fourier transform image) is recorded on the recording medium D.
During reproduction of a signal from the recording medium D, reproduction light is irradiated so as to irradiate the entire recording mark, and half of the diffracted reproduction signal is shielded. In this case, the relative position of the recording medium D and the shielding plate 15k is adjusted according to the position of the recording mark (diffraction image) to be reproduced.
By doing so, only one of the positive and negative components of the diffraction image passes through the shielding plate 15k, and the occurrence of beat noise in the sensor 16 is prevented.

(Example)
FIGS. 11 and 12 are graphs showing detection results of the sensor 16 when only one of the positive and negative components of the diffraction image is passed by the shielding plate 15 and when the shielding plate 15 is not used. The graph shown here corresponds to a case where a one-dimensional SLM is used as the spatial light modulator SLM, and the modulation elements alternately repeat bright and dark. That is, the shielding plate 15a shown in FIG.
11 and 12, the horizontal axis corresponds to the position of the individual element of the sensor 16, and the vertical axis corresponds to the signal intensity.
In FIG. 11 (example) using the shielding plate 15a, beat noise does not appear, whereas in FIG. 12 (comparative example) where the shielding plate 15a is not used, beat noise appears.
By shielding a part of the diffraction image using the shielding plate 15 in this way, noise at the sensor 16 can be reduced.

(Other embodiments)
As described above, in the above embodiment, the noise in the sensor 16 can be reduced by shielding a part of the diffraction image using the shielding plate 15. As a result, the following advantages can be enjoyed.
Even when a recording lens with poor field-of-view characteristics is used for the lens LZ1, the quality of the recording signal can be improved. For this reason, it is possible to reduce the cost of the hologram recording / reproducing apparatus 10. Noise can be removed without reducing the amount of information of the original signal.
The size of the recording mark on the recording medium can be further reduced to improve the recording density of the recording medium. Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and changed. Such embodiments are also included in the technical scope of the present invention.

1 is a block diagram showing a hologram recording / reproducing apparatus 10 according to a first embodiment of the present invention. It is a figure showing the correspondence of a spatial light modulator, a recording medium, a sensor, and the intensity pattern of recording light when there is no shielding board. It is a schematic diagram showing an example of the correspondence between a spatial light modulator and a shielding plate when the spatial light modulator is one-dimensional. It is a schematic diagram showing an example of the correspondence of a spatial light modulator and a shielding board in case a spatial light modulator is two-dimensional. It is a schematic diagram showing an example of the correspondence of a spatial light modulator and a shielding board in case a spatial light modulator is two-dimensional. It is a schematic diagram showing an example of the correspondence of a spatial light modulator and a shielding board in case a spatial light modulator is two-dimensional. It is a schematic diagram showing an example of the correspondence of a spatial light modulator and a shielding board in case a spatial light modulator is two-dimensional. It is a schematic diagram showing an example of the correspondence of a spatial light modulator and a shielding board in case a spatial light modulator is two-dimensional. It is a schematic diagram showing the case where beat noise is removed by shielding only the diffracted light of a specific order. It is a block diagram which shows the hologram recording / reproducing apparatus which concerns on the modification of the 3rd Embodiment of this invention. It is a graph showing the detection result with the sensor at the time of using a shielding board. It is a graph showing the detection result with the sensor when not using a shielding board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hologram recording / reproducing apparatus 11 Laser light source 12 Spatial filter 13, 14 Shutter 15 Shielding plate 16 Sensor D Recording medium HWP1, HWP2 1/2 wavelength plate LZ1-LZ3 Lens M Mirror PBS Polarization beam splitter SLM Spatial light modulator

Claims (9)

A laser light source for emitting laser light;
A spatial modulator for spatially modulating laser light emitted from the laser light source;
A first lens for condensing the laser light modulated by the spatial modulator on a recording medium;
A shielding unit that is disposed between the first lens and the recording medium and shields only one of positive and negative of a partial diffraction image from the spatial modulator;
A holographic recording apparatus comprising: The hologram recording apparatus according to claim 1, wherein the shielding unit shields either a positive or negative first-order diffraction image. 3. The hologram recording apparatus according to claim 2, wherein the shielding means shields all first-order and higher-order diffraction images. A branch element for branching the laser light emitted from the laser light source;
A second lens for condensing the laser beam branched by the branch element onto the recording medium;
The hologram recording apparatus according to claim 1, further comprising: A laser light source for emitting laser light;
A lens that focuses laser light emitted from the laser light source onto a recording medium on which a hologram is recorded;
A light receiving element for receiving a diffraction image obtained by diffracting the focused laser beam by the hologram;
A shielding unit disposed between the recording medium and the light receiving element, and shielding only one of positive and negative of a part of the diffraction image from the hologram;
A hologram reproducing apparatus comprising: 6. The hologram reproducing apparatus according to claim 5, wherein the shielding means shields a positive or negative first-order diffraction image. 7. The hologram reproducing apparatus according to claim 6, wherein the shielding means shields all first-order or higher-order diffraction images. A laser light source for emitting laser light;
A spatial modulator for spatially modulating laser light emitted from the laser light source;
A first lens for condensing the laser light modulated by the spatial modulator on a recording medium;
A shielding unit that is disposed between the first lens and the recording medium and shields only one of positive and negative of a partial diffraction image from the spatial modulator;
An information processing apparatus comprising: a hologram recording apparatus comprising: A laser light source for emitting laser light;
A lens that focuses laser light emitted from the laser light source onto a recording medium on which a hologram is recorded;
A light receiving element for receiving a diffraction image obtained by diffracting the focused laser beam by the hologram;
A shielding unit disposed between the recording medium and the light receiving element, and shielding only one of positive and negative of a part of the diffraction image from the hologram;
An information processing apparatus comprising: a hologram reproducing apparatus comprising:

Images