JP4581841B2 - Hologram recording apparatus and hologram recording method - Google Patents

Description

  The present invention relates to a hologram recording apparatus and a hologram recording method, and more particularly, to a hologram recording apparatus and a hologram recording method for performing multiple recording of holograms at the same location of a hologram recording medium.

  The holographic storage is a volume type recording that records also in the depth direction of the recording medium. According to the holographic storage, a large capacity recording is possible. Moreover, the recording capacity of the holographic memory (recording medium) can be further increased by multiplex recording a plurality of holograms in the same volume.

  Conventionally, as a hologram multiplex recording method, “angle multiplexing” for performing multiplex recording while changing the incident angle of the reference light, “shift multiplex” for performing multiplex recording while moving the hologram recording medium relative to the recording head, etc. Various multiplex recording methods have been proposed. For example, in the case of angle multiplexing, when irradiating the hologram recording medium with signal light and reference light, by sequentially changing the incident angle of the reference light for each hologram, a plurality of holograms can be placed in the same volume of the hologram recording medium. Multiple recording is possible. Further, at the time of hologram reproduction, any hologram can be selectively reproduced from among the multiplex-recorded holograms by irradiating the reference light used for recording.

  However, the above angle multiplexing and shift multiplexing require a mechanical drive means such as changing the angle of the mirror or moving the recording medium, and there is a problem that the control mechanism of the apparatus becomes complicated. For this reason, various methods for easily performing multiplex recording without using mechanical driving means (non-moving) have been studied. As a method of performing multiplex recording without moving, there is “phase correlation multiplexing” in which multiplex recording is performed while changing the phase of the reference light (Patent Document 1). In phase correlation multiplexing, a plurality of holograms can be multiplexed and recorded in the same volume of the hologram recording medium by using reference light having a random phase and low correlation with each other.

Further, phase code multiplexing is one of phase correlation multiplexing (Non-patent Document 1). In phase code multiplexing, multiple recording is performed while changing the phase distribution (phase code) of the reference light. By using a two-dimensional phase distribution of 0 and π corresponding to the Walsh-Hadamard function as the phase code, destructive interference due to the orthogonality of the phase distribution is used to reproduce any hologram without crosstalk. can do. That is, when signal light is hologram-recorded using reference light in which the phases of 0 and π are spatially distributed, when the reference light having another phase distribution is irradiated, the reproduced light cancels out due to interference, As a result, the signal light is not reproduced.
JP 2005-84401 A Holographic data storage, Springer, p419-428.

  However, in the conventional phase multiplexing recording, there is a problem that it is difficult to generate completely non-correlated reference light, and it is difficult to reproduce the multiplexed recording hologram without crosstalk. Further, in phase code multiplexing, there is a problem that even if the phase distribution of the reference light is slightly deviated from 0 and π, the destructive interference condition collapses and crosstalk occurs, so that stable multiple recording cannot be performed. there were.

  The present invention has been made to solve the above problems, and an object of the present invention is to reduce crosstalk in a hologram recording apparatus and method for performing non-moving multiplex recording by phase correlation multiplexing.

  To achieve the above object, the hologram recording method of the present invention irradiates the optical recording medium with the signal light and the reference light at the same time while changing the wavefront of the reference light, so that the information of the signal light is transmitted to a plurality of holograms. A hologram recording method for performing multiplex recording on the optical recording medium as described above, in the case of multiplex recording of the data of a plurality of pages, using reference light having a random pattern with uneven phases and / or intensities, A DC component is removed from the converted image, and the optical recording medium is irradiated with signal light and reference light from which the DC component has been removed, and a plurality of pages of data are multiplexed and recorded by phase correlation multiplexing.

  In the hologram recording method of the present invention, when the information of the signal light is recorded as a hologram of a plurality of pages, the wavefront of the reference light is changed. Therefore, a plurality of holograms are multiplexed and recorded in the same volume without being moved by phase correlation multiplexing. be able to. In addition, by removing the DC component from the Fourier transform image of the reference light having a random pattern with irregular phases and / or intensities using a filter, the Fourier transform image of the reference light for recording each page becomes completely different, and the phase correlation Multiple crosstalk can be prevented.

  Further, the hologram recording apparatus of the present invention is a hologram recording apparatus that records information of signal light as a plurality of pages of holograms on an optical recording medium using the hologram recording method of the present invention, and a light source for irradiating coherent light A light separating optical path changing means for changing the optical path so that the optical recording medium is simultaneously irradiated with the reference light and the signal light after separating the coherent light into the light for the reference light and the light for the signal light; Signal light generating means arranged in the optical path of the signal light and modulating the signal light according to the supplied recording signal for each page to generate the signal light, and the information of the signal light The recording signal supply means for supplying the recording signal for each page to the signal light generation means, and the optical signal for the reference light are arranged and supplied so as to be multiplexed and recorded as a hologram of a plurality of pages. Randa Reference light generating means for modulating the light for the reference light according to a pattern and generating a reference light having a random pattern with irregular phase and / or intensity, and information of the signal light is multiplexed and recorded by phase correlation multiplexing In addition, a random pattern supply unit that supplies a different random pattern for each page to the reference light generation unit, an imaging optical system that Fourier transforms the reference light, and a reference light irradiation side of the optical recording medium, And a filter that blocks a DC component of a Fourier transform image of the reference light.

  As described above, according to the present invention, there is an effect that crosstalk can be reduced when non-moving multiplex recording is performed by phase correlation multiplexing.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic diagram showing an example of the configuration of a hologram recording apparatus. In this example, a case where digital data over a plurality of pages is recorded for each page will be described. The hologram recording apparatus is provided with a light source 10 that oscillates laser light that is coherent light. A beam splitter 12 for separating the laser light into signal light and reference light is disposed on the laser light irradiation side of the light source 10.

  On the light transmission side of the beam splitter 12, a shutter 14 for blocking the laser light for signal light transmitted through the beam splitter 12 is disposed so as to be able to be inserted into and retracted from the optical path. On the light transmission side of the shutter 14, a lens system including collimator lenses 16 a and 16 b and a Fourier transform lens 20 is arranged in this order. A transmissive spatial light modulator 18 is disposed between the collimator lens 16 b and the Fourier transform lens 20. The spatial light modulator 18 is composed of a liquid crystal display element or the like, and a laser beam for signal light is modulated in accordance with digital data supplied from a computer (not shown), and a digital image (signal light) is generated for each page. The

  On the light reflection side of the beam splitter 12, a reflection mirror 24 is disposed for reflecting the laser light for reference light reflected by the beam splitter 12 and changing the optical path. On the light reflection side of the reflection mirror 24, a lens system including collimator lenses 26a and 26b and a Fourier transform lens 30 is arranged in this order. A transmissive spatial light modulator 28 is disposed between the collimator lens 26 b and the Fourier transform lens 30. The spatial light modulator 28 is composed of a liquid crystal display element or the like, and the reference light laser light is modulated in accordance with digital data supplied from a computer (not shown) to generate reference light having a different random pattern for each page. Is done.

  On the light transmission side of the Fourier transform lens 30, a filter 32 for removing a direct current component from the reference light is disposed. The filter 32 is disposed on the Fourier transform plane of the reference light. On the light transmitting side of the filter 32, a lens system including a collimator lens 34 and a Fourier transform lens 36 is arranged in this order. On the light transmission side of the Fourier transform lens 36, a reflection mirror 38 for reflecting the reference light collected by the Fourier transform lens 36 and changing its optical path toward the optical recording medium 22 is disposed.

  Next, hologram recording using the above hologram recording apparatus will be described. First, the shutter 14 is retracted from the optical path by a driving device (not shown) so that the laser beam can pass. Laser light oscillated from the light source 10 is separated into signal light and reference light by a beam splitter 12. The laser light that has passed through the beam splitter 12 is collimated into a large-diameter beam by the collimator lenses 16a and 16b, and is applied to the spatial light modulator 18 as laser light for signal light.

  Digital data is input to the spatial light modulator 18 from a computer (not shown). In the spatial light modulator 18, the intensity of the laser light for signal light is modulated in accordance with the supplied digital data, and signal light of a predetermined page is generated. The generated signal light is Fourier transformed by the Fourier transform lens 20 and applied to the optical recording medium 22.

  At the same time, the laser beam reflected by the beam splitter 12 is reflected by the reflection mirror 24, collimated into a large-diameter beam by the collimator lenses 26a and 26b, and irradiated to the spatial light modulator 28 as laser light for reference light. The Digital data is input to the spatial light modulator 28 from a computer (not shown). In the spatial light modulator 28, the reference light laser light is intensity-modulated in accordance with the supplied digital data, and reference light having a pseudo-random pattern is generated.

  For example, by using a chaos function, it is possible to generate a random pattern having a low correlation with each other. By using reference light having a pseudo-random pattern, the principle of phase correlation multiplexing can be used instead of a multiplexing method using Bragg conditions such as angle multiplexing. Also, by using the Walsh-Hadamard function used in phase code multiplexing, it is possible to generate a pattern that is not random but has a low correlation with each other.

  The generated reference light is Fourier transformed by the Fourier transform lens 30 and the direct current component is removed by the filter 32. The reference light from which the DC component has been removed is collimated into a large-diameter beam by the collimator lens 34 and Fourier-transformed by the Fourier transform lens 36. The Fourier-transformed reference light is reflected by the reflection mirror 38 and is irradiated as reference light having a random wavefront with non-uniform phases on the region of the optical recording medium 22 where the signal light is irradiated.

  As a result, the signal light after Fourier transform interferes with the reference light in the optical recording medium 22, and the signal light of a predetermined page is recorded as a hologram. Further, by sequentially recording the signal light of each page using the reference light having a different random wavefront for each page, a plurality of holograms are recorded in the same volume without movement by phase correlation multiplexing. Reference lights having different random wavefronts mean reference lights having a random phase and low correlation with each other. Since the reference light for recording each page has a low correlation with each other, the hologram cannot be completely reproduced with light other than the reference light used at the time of recording.

  Here, the filtering function of the filter 32 will be described in more detail. FIG. 2 is a diagram illustrating an example of a random pattern generated by the spatial light modulator 28. In this figure, binary digital data “0, 1” is digitalized as “bright, dark”. The laser beam for reference light whose intensity is modulated in accordance with the random pattern is subjected to Franforfer diffraction (Fourier transform) by the Fourier transform lens 30. As a result, the Francophor diffraction image shown in FIG. 3 is obtained on the Fourier transform plane.

  As shown in FIG. 2, when the random pattern is converted into a digital image and the spatial frequency takes a normalized value, as shown in FIG. It is a regular diffraction grating having components, and becomes a Fourier transform image itself. Therefore, in the following, the francopha diffraction image is referred to as a Fourier transform image. The order here is the order of the bright spots appearing at each distance of ζ = fλ / d from the 0th order (center) on the Fourier transform plane, and the distance ζ is the focal length f of the lens and the recording wavelength λ. The value is determined by the pixel pitch d of the spatial light modulator 28.

  4A and 4B are diagrams showing Fourier transform spectra. As shown in FIG. 4A, the Fourier transform spectrum has a peak corresponding to the direct current component of each order for each bright spot. Even if the random patterns generated by the spatial light modulator 28 are different, each of the reference lights has a common DC component as long as the values of f, λ, and d are constant. As described above, when the reference light has a common component, when reproducing an arbitrary hologram from a plurality of holograms recorded in a multiplexed manner, other holograms are partially reproduced and crosstalk occurs. On the other hand, as shown in FIG. 4B, a specific spatial frequency component corresponding to the random pattern is included between the bright spots of the Fourier transform image. That is, when the random patterns are different, these spatial frequency components are also different.

  FIG. 5 is a diagram illustrating an example of a filter that removes a DC component of a Fourier transform image. As shown in FIG. 5, the filter 32 is a light transmitting body in which a light shielding portion 44 is formed so as to face each bright spot of the Fourier transform image. The light transmissive body is made of a material that is transparent to the reference light. By disposing the filter 32 on the Fourier transform plane of the reference light, the direct current component of the reference light is blocked. That is, the filter 32 functions as a band pass filter that transmits only the spatial frequency components other than the DC component. In this way, by removing the direct current component, which is a common component, from the reference light by the filter 32, the Fourier transform image of the reference light for recording each page becomes completely different. Thereby, crosstalk in phase correlation multiplexing can be prevented.

  FIG. 6 is a diagram showing an example of the configuration of the hologram reproducing device. This hologram reproducing apparatus is obtained by adding a Fourier transform lens 40 and a two-dimensional photodetector 42 such as a photodetector array such as a CCD or CMOS array to the hologram recording apparatus shown in FIG. On the optical recording medium 22, digital data over a plurality of pages is multiplexed and recorded for each page by the method described above.

  At the time of reproducing the hologram, the shutter 14 is inserted into the optical path by a driving device (not shown) to block the laser light for signal light. Thereby, only the laser light for reference light is modulated by the spatial light modulator 28, the direct current component is removed from the generated reference light by the filter 32, and the reference light from which the direct current component has been removed is applied to the optical recording medium 22. Irradiated. The irradiated reference light is diffracted by the hologram recorded on the optical recording medium 22, and diffracted light is emitted from the optical recording medium 22.

  Since a Fourier transform image of the signal light is recorded on the optical recording medium 22, the reproduced image can be observed on the focal plane of the Fourier transform lens 40 by performing inverse Fourier transform on the diffracted light by the Fourier transform lens 40. . This reproduced image can be detected by the photodetector 42 and digital data included in the signal light can be read.

  At the time of reproduction, by using reference light having a specific random wavefront used at the time of hologram recording, an arbitrary hologram can be selectively reproduced from a plurality of holograms that are multiplexed and recorded in the same volume.

  As described above, in the first embodiment, when recording each page of the digital data, the reference light having a different random wavefront is used for each page. A hologram can be recorded. Also, by removing the DC component by the filter, reference light with completely different random wavefronts can be obtained, and crosstalk in phase correlation multiplexing can be prevented. Also, compared with phase code multiplexing using a light distribution of two phases of 0 and π, the robustness is high and multiplex recording can be performed stably.

(Second Embodiment)
In the first embodiment, the example in which the signal light and the reference light are irradiated from different directions has been described. In the second embodiment, an example in which the signal light and the reference light are irradiated coaxially will be described.

  FIG. 7 shows an example of a hologram recording / reproducing apparatus having a coaxial configuration. The hologram recording / reproducing apparatus is provided with a light source 52 that oscillates laser light that is coherent light. Collimator lenses 54 and 56 are arranged on the laser light irradiation side of the light source 52. A polarization beam splitter 58 that transmits only polarized light in a predetermined direction is disposed on the light transmission side of the collimator lenses 54 and 56. A reflective spatial light modulator 60 is disposed on the light reflection side of the polarization beam splitter 58.

  The laser light oscillated from the light source 52 is collimated into a large-diameter beam by the collimator lenses 54 and 56, enters the polarization beam splitter 58, and is reflected in the direction of the spatial light modulator 60. Digital data is input to the spatial light modulator 60 from a computer (not shown), and the intensity of the laser light is modulated in accordance with the supplied digital data, and the digital image (signal light) for each page is different from each page. Reference light having a random pattern is generated.

  For example, as shown in FIG. 8, the left half of the spatial light modulator 60 is used for data display, and the intensity of the portion of the incident light 74 incident on the left half of the spatial light modulator 60 is modulated. The light reflected by the left half is signal light 1, while the right half of the spatial light modulator 60 is intensity-modulated or phase-modulated with reference light data (such as a random pattern) and reflected by the right half. Is a reference beam 2. The signal light and reference light reflected by the spatial light modulator 60 enter the polarization beam splitter 58 and pass through the polarization beam splitter 58.

  A Fourier transform lens 62 is disposed on the light transmission side of the polarization beam splitter 58. A reflective spatial light modulator 64 is arranged as a programmable filter on the light transmission side of the Fourier transform lens 62.

  The signal light and reference light transmitted through the polarization beam splitter 58 are Fourier transformed by the Fourier transform lens 62. The Fourier-transformed signal light and reference light are applied to the spatial light modulator 64. The spatial light modulator 64 arranged as a programmable filter functions as a bandpass filter that removes a DC component from each of the signal light and the reference light and transmits only a spatial frequency component other than the DC component. The filtered signal light and reference light are reflected in the direction of the Fourier transform lens 62, are subjected to inverse Fourier transform by the lens 62, enter the polarization beam splitter 58 again, and are reflected by the polarization beam splitter 58.

  An objective lens 66 having a high NA is disposed on the light reflection side of the polarizing beam splitter 58. The signal light and the reference light reflected by the polarization beam splitter 58 are Fourier-transformed by the objective lens 66 and are irradiated onto the optical recording medium 68 simultaneously and coaxially. The reference light is irradiated to the area where the signal light after Fourier transform is irradiated. As a result, the signal light after Fourier transform interferes with the reference light in the optical recording medium 68, and the signal light of a predetermined page is recorded as a hologram. Further, by sequentially recording the signal light of each page using reference light having a different random wavefront for each page, a plurality of holograms are recorded in the same volume by phase correlation multiplexing.

  Note that a high NA objective lens 70 and a two-dimensional photodetector 72 such as a CMOS array are disposed on the reproducing light emission side of the optical recording medium 68, and only the reference light is reproduced when reproducing the hologram. An area where 68 holograms are recorded is irradiated. The irradiated reference light is diffracted by the hologram. By performing inverse Fourier transform on the diffracted light by the objective lens 70, a reproduced image in which the image edge portion of the signal light is emphasized can be observed on the focal plane of the objective lens 70. This reproduced image can be detected by the photodetector 72 and the digital data possessed by the image edge portion of the signal light can be read.

  As described above, in the case of coaxial recording as in the second embodiment, the reference light and the signal light pass through a common optical system, are simultaneously Fourier transformed by the lens, and are simultaneously filtered by the programmable filter. The configuration becomes simple and the mounting becomes easy.

  By the above filtering, a direct current component that causes noise is removed from the signal light, and only a Fourier spectrum necessary for data recording is extracted, so that the S / N is improved. In addition, the DC component, which is a common component, is removed from the reference light, and the Fourier transform image of the reference light that records each page becomes completely different, so that crosstalk in phase correlation multiplexing can be prevented, and phase code multiplexing Compared to the above, robustness is high and multiple recording can be performed stably. Further, unnecessary components such as the direct current component and the higher order component of the reference light and the signal light are not used for the exposure, so that the dynamic range of the hologram recording medium is not lost, and recording of about V / λ3 bits is performed near the limit of volume recording. Capacity can be realized.

  In the above-described embodiment, a random pattern digitally imaged by a spatial light modulator is generated, and laser light is intensity-modulated according to the random pattern, so that a reference having a random pattern with uneven phase and / or intensity is obtained. Although an example of generating light has been described, reference light can also be generated by other methods. For example, it is possible to generate reference light having a random pattern with uneven phases and / or intensities by scattering laser light that is coherent light using a light diffuser such as frosted glass or frosted glass. In this case, since the degree of randomization becomes high, the Francophor diffraction image (again, synonymous with the Fourier transform image) has a bright spot corresponding to the 0th-order component as shown in FIG. Have only. Therefore, as a filter for removing the direct current component of the Fourier transform image, as shown in FIG. 9B, a light transmitting body in which the light shielding portion 46 is formed facing the bright spot of the Fourier transform image can be used. .

  In the above embodiment, an example in which digital data is recorded has been described. However, the present invention can also be applied to a case where analog data is recorded as a hologram.

It is the schematic which shows an example of a structure of a hologram recording device. It is a figure which shows an example of the random pattern produced | generated by a spatial light modulator. It is a figure which shows an example of the Francophor diffraction image of reference light. (A) is a figure which shows a Fourier-transform spectrum, (B) is the partial enlarged view. It is a figure which shows an example of the filter which removes the direct current | flow component of a Fourier-transform image. It is a figure which shows an example of a structure of a hologram reproduction apparatus. An example of the hologram recording / reproducing apparatus of a coaxial structure is shown. It is a figure which shows the structure of the spatial light modulator which produces | generates signal light and reference light simultaneously. (A) is a figure which shows the other example of the Francophor diffraction image of reference light, (B) is a figure which shows an example of the filter according to (A).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Signal light 2 Reference light 10 Light source 12 Beam splitter 14 Shutter 16a Collimator lens 16b Collimator lens 18 Spatial light modulator 20 Fourier transform lens 22 Optical recording medium 24 Reflection mirror 26a Collimator lens 26b Collimator lens 28 Spatial light modulator 30 Fourier transform lens 32 Filter 34 Collimator lens 36 Fourier transform lens 38 Reflective mirror 40 Fourier transform lens 42 Photo detector 44 Light shield unit 46 Light shield unit 52 Light source 54 Collimator lens 58 Polarizing beam splitter 60 Spatial light modulator 62 Fourier transform lens 62 Lens 64 Spatial light modulation Instrument 66 objective lens 68 optical recording medium 70 objective lens 72 photodetector 74 incident light

Claims (19)

A hologram recording method for multiplex-recording information of the signal light as a hologram of a plurality of pages on the optical recording medium by simultaneously irradiating the optical recording medium with the signal light and the reference light while changing the wavefront of the reference light. ,
When multiple pages of data are to be recorded in a multiplexed manner, a reference beam having a random pattern with uneven phase and / or intensity is used, and a DC component is removed from a Fourier transform image of the reference beam, thereby removing a signal beam and a DC component. A hologram recording method of irradiating an optical recording medium with the reference light thus recorded, and recording multiple pages of data by phase correlation multiplexing.   2. The hologram recording according to claim 1, wherein a filter that blocks a direct current component in at least the 0th order of the Fourier transform image is disposed on a reference light irradiation side of the optical recording medium, and the direct current component is removed from the Fourier transform image by the filter. Method.   A filter that cuts off a direct current component in the 0th order to the nth order (n is an integer of 1 or more) of the Fourier transform image is disposed on the reference light irradiation side of the optical recording medium, and the direct current component is removed from the Fourier transform image by the filter. The hologram recording method according to claim 1 to be removed.   4. The hologram recording method according to claim 2, wherein a direct current component is removed from the Fourier transform image by a filter in which a light shielding portion is formed in advance so as to face the bright spot of the Fourier transform image.   4. The hologram recording method according to claim 2, wherein a direct current component is removed from the Fourier transform image by a variable filter that is sequentially formed at a position where a light-shielding portion is opposed to each other between bright spots of the Fourier transform image.   The hologram recording method according to claim 5, wherein the variable filter is configured by a spatial light modulator.   The hologram recording method according to any one of claims 1 to 6, wherein a random pattern in which binary digital data is represented by a bright and dark image is used as the random pattern.   The hologram recording method according to claim 7, wherein the random pattern is generated by a spatial light modulator.   9. The hologram recording method according to claim 7, wherein the random pattern is generated based on a chaos function.   An image edge portion is extracted from a Fourier transform image of signal light representing binary digital data as a light and dark image, and the signal light from which the image edge portion has been extracted and the reference light are simultaneously irradiated onto the optical recording medium. The hologram recording method according to claim 1, wherein the image edge portion is recorded as a hologram on the optical recording medium.   The hologram recording method according to claim 10, wherein a filter that transmits only an image edge portion of the Fourier transform image is disposed on the signal light irradiation side of the optical recording medium, and the image edge portion is extracted from the Fourier transform image by the filter. .   The hologram recording method according to claim 1, wherein the signal light and the reference light are irradiated coaxially.   A hologram recording apparatus that records information on signal light as a hologram of a plurality of pages on an optical recording medium using the hologram recording method according to claim 1. A light source that emits coherent light;
After separating the coherent light into light for reference light and light for signal light, a light separation optical path changing means for changing the optical path so that the reference recording light and the signal light are simultaneously irradiated onto the optical recording medium;
A signal light generating unit that is disposed in the optical path of the signal light, modulates the signal light according to the supplied recording signal for each page, and generates signal light;
Recording signal supply means for supplying a recording signal for each page to the signal light generation means so that information of the signal light is multiplexed and recorded as a hologram of a plurality of pages;
Reference light generating means arranged in the optical path of the light for reference light, which modulates the light for reference light according to the supplied random pattern, and generates a reference light having a random pattern with uneven phase and / or intensity When,
Random pattern supply means for supplying the reference light generation means with a different random pattern for each page so that the information of the signal light is multiplexed and recorded by phase correlation multiplexing;
An imaging optical system for Fourier transforming the reference light;
A filter disposed on the reference light irradiation side of the optical recording medium and blocking a DC component of a Fourier transform image of the reference light;
Hologram recording apparatus comprising:   The hologram recording apparatus according to claim 14, wherein the filter blocks a DC component in at least the 0th order of the Fourier transform image.   The hologram recording apparatus according to claim 14, wherein the filter blocks a direct current component in a 0th order to an nth order (n is an integer of 1 or more) of the Fourier transform image.   17. The hologram recording apparatus according to claim 14, wherein the filter is a light transmission body in which a light shielding portion is formed in advance so as to face a bright spot of the Fourier transform image.   17. The hologram recording apparatus according to claim 14, wherein the filter is a variable filter in which light shielding portions are sequentially formed at different positions so as to face each other between the bright spots of the Fourier transform image.   The hologram recording apparatus according to claim 18, wherein the variable filter is configured by a spatial light modulator.