JP2006234990A - Hologram recording device and optical component - Google Patents

Hologram recording device and optical component Download PDF

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Publication number
JP2006234990A
JP2006234990A JP2005046371A JP2005046371A JP2006234990A JP 2006234990 A JP2006234990 A JP 2006234990A JP 2005046371 A JP2005046371 A JP 2005046371A JP 2005046371 A JP2005046371 A JP 2005046371A JP 2006234990 A JP2006234990 A JP 2006234990A
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Japan
Prior art keywords
light
optical component
hologram recording
spatial modulator
signal light
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JP2005046371A
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Japanese (ja)
Inventor
Tomoki Kanesaka
Nobuhiro Kihara
Norihiro Tanabe
Hisayuki Yamatsu
智樹 兼坂
久行 山津
信宏 木原
典宏 田部
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Sony Corp
ソニー株式会社
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Priority to JP2005046371A priority Critical patent/JP2006234990A/en
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Abstract

<P>PROBLEM TO BE SOLVED: To suppress a DC component of signal light without increasing the S/N of a recorded image. <P>SOLUTION: The DC component of the signal light is suppressed by arranging a diffusion plate 12 which diffuses light adjacently to a spatial modulator 11 thereby spreading an intensity distribution of the signal light on a hologram recording material as usual. In addition, it is known by experiment that, when the width of diffusion units of the light such as unevenness of the diffusion plate 12 is made, for example, twice as large as the pixel width of the spatial modulator 11, deterioration in S/N of the recording image due to use of the diffusion plate 12 can be suppressed, and noise caused by the diffusion plate 12 is prevented from being superposed on the signal light to keep the S/N of the recorded image excellent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a holographic recording apparatus that records interference fringes between signal light and reference light on a hologram recording material, and in particular, a diffusion plate that suppresses a DC component of signal light (sometimes referred to as a diffuser or a phase mask). It relates to optical parts.

  In recent years, there has been proposed a holographic data storage system that records and reproduces large-capacity data using a hologram technique that records in volume the interference fringes of signal light and reference light spatially modulated by information on a hologram recording material.

  In the conventional holographic data storage system, a coherent laser beam 50 emitted from a light source (not shown) is branched into a signal beam 100 and a reference beam 200 as shown in FIG. When the signal light 100 obtained in this way passes through a spatial modulator (SLM) 1, it is spatially modulated by information (data pattern) displayed on the SLM 1. The signal light 100 spatially modulated by the SLM 1 is condensed in the vicinity of the recording material 3 by the lens 2, and a hologram is recorded by causing the recording material 3 to be separately irradiated with the reference light 200.

  At this time, the laser light 50 incident on the SLM 1 is diffracted according to the pixel pattern of the SLM 1 and the displayed data pattern. As a result, the signal light 100 has a certain extent on the recording material 3. According to the theory of wave optics, this spread is related to the Fourier transform pattern of the image displayed on the SLM 1, and the size of the spread is proportional to the pixel size displayed on the SLM 1 and the focal length of the lens. A simulation example of the spread of the signal light 100 on the recording material 3 is shown in FIG.

  As can be seen from FIG. 4, the light on the recording material 3 has a strong intensity near the origin, and the light intensity in other parts is weak. A strong intensity component near the origin is called a DC component. The occurrence of such non-uniform distribution is known as a problem of the DC component when the SLM 1 that performs only intensity modulation is used. Such non-uniformity is known to cause various problems during hologram recording, and some countermeasures have been proposed (see Non-Patent Document 1, for example).

As one of such measures, there is a method using an optical component called a random phase mask or a diffusion plate. This is, for example, an optical component having a random pattern with the same pitch as the pixel pitch of SLM1 and a phase difference of 0 and π. This optical component transmits this light so that the random pattern matches the pixel of SLM1. It is a method of diffusing light by being arranged. This optical component having a random pattern with a phase difference of 0 and π is called a diffusion plate. When light is diffused in this way, the light distribution on the recording material 3 becomes uniform, and the recording characteristics are greatly improved. FIGS. 5A and 5B are a front view and a side view comparing the pitches of the diffusion plate and the SLM. As described above, the diffusion plate is an optical component having a random pattern with the same pitch as the pixel pitch of the SLM 1 and a phase difference of 0 and π.
Holographic Data Storage; HJCoufal, D.Psaltis, GTSincerbox ED; Springer; p.259-269 Beam Conditioning Techniques for Holographic Recording Systems

  However, in order to prevent the signal light from concentrating on the recording material to reduce the use efficiency of the hologram recording material or to reduce the S / N, a diffusion plate that removes a DC component from the signal light is used as a signal light optical system. When introduced inside, the noise caused by the diffusion plate rides on the signal light, and conversely, the S / N ratio decreases. This noise is generated because the intensity component is applied to the image of the diffusion plate, which is essentially only the phase component, due to the aberration of the hologram recording / reproducing optical system and the imperfection of the hologram recording itself.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is an optical component capable of suppressing the DC component of signal light without deteriorating the S / N of a recorded image, and the optical component. An object of the present invention is to provide a hologram recording apparatus using parts.

  In order to achieve the above object, the present invention is a signal light generated by modulating a part of light emitted from a coherent light source with a spatial modulator, and another part of the light emitted from the light source. A hologram recording apparatus for recording interference fringes with reference light on a hologram recording material, comprising an optical component that diffuses light in an optical system through which the signal light passes, and a diffusion angle of light by the optical component is It is smaller than the light diffusion angle by the spatial modulator.

  In addition, the light diffusion unit of the optical component of the present invention has a period that is at least twice as long as a pixel period of the spatial modulator.

  Further, the present invention is an optical component that diffuses light modulated by a spatial modulator, and includes an unevenness or a refractive index changing structure for diffusing the light, and the unevenness or the refractive index changing structure. The period of the light diffusing unit is at least twice as long as the pixel period of the spatial modulator.

  As described above, the optical component for diffusing the light of the present invention, for example, the diffusion plate, is disposed adjacent to the spatial modulator, for example, so that the intensity distribution of the signal light in the hologram recording material can be expanded as in the conventional manner. The effect of effectively using the dynamic range of the material can be obtained, and when the width of the light diffusion unit such as the unevenness of the diffusion plate is doubled compared to the pixel width of the spatial modulator, for example, this diffusion plate is used. It has been experimentally found that the S / N of the recorded image is prevented from deteriorating, and the DC component can be removed from the signal light without the noise caused by the diffuser being placed on the signal light.

According to the present invention, the light diffusion unit width of an optical component such as a diffusing plate that suppresses the DC component of signal light is set to an integer multiple of twice or more the pixel width of the spatial modulator. The DC component can be suppressed, and the S / N increase of the recorded image can also be suppressed.
As a result, a sufficient S / N can be obtained even when the multiplicity of recorded images is increased as compared with the prior art, so that the recording capacity of the recording material can be improved.
Further, as a result of suppressing the S / N of the recorded image, the amount of information per page can be increased as compared with the conventional case, and as a result, the data transfer rate can be improved.

  For the purpose of suppressing the DC component of the signal light without deteriorating the S / N of the recorded image, the light diffusion unit width of an optical component such as a diffusion plate for suppressing the DC component of the signal light is set to the pixel width of the spatial modulator. Realized by making it an integer multiple compared to.

  FIG. 1 is a block diagram showing a configuration of a main part of a hologram recording apparatus according to an embodiment of the present invention. The hologram recording apparatus has a recording signal light optical system 301. The recording signal light optical system 301 forms a spatial light modulator (SLM) 11, a diffusion plate 12 disposed adjacent to the SLM 11, and a signal light optical system. The lens 13, 14, 15, an aperture 16 inserted between the lenses 13 and 14 to remove unnecessary light, and a hologram recording material 80 on which a hologram is recorded are included. However, a portion (diffuser plate) indicated by a broken line in the drawing will be described later.

  Next, the operation of this embodiment will be described. The signal light 100 branched from the laser light emitted from a laser light source (not shown) is spatially modulated by the SLM 11, further diffused by the diffusion plate 12, and then collected on the hologram recording material 80 through the lenses 13, 14, and 15. At that time, the aperture 16 cuts unnecessary light such as higher-order light generated when passing through the SLM 11. At this time, reference light (not shown) branched from the laser light is applied to the hologram recording material 80, and interference fringes between the reference light and the signal light 100 are recorded on the hologram recording material 80.

  2A and 2B are a front view and a side view showing the configuration of the diffusion plate 12 and the SLM 11 shown in FIG. The diffusion plate 12 has irregularities formed on the surface, and diffuses light by the irregularities. This concave or convex is one unit of light diffusion. The width of these irregularities formed on the diffusion plate 12 is twice the pixel width of the SLM 11. In other words, the period of the diffusion unit of the diffusion plate 12 is twice the pixel period of the SLM 11.

  When the hologram recording material 80 on which the hologram is recorded as described above is irradiated with the reference light similar to that at the time of recording, diffracted light due to the interference fringes recorded on the hologram recording material 80 is generated, and the reproduced signal light which is this diffracted light Is received by an image sensor (not shown) through a reproducing light optical system (not shown), and a reproduced image is obtained.

  According to the present embodiment, by using the diffusion plate 12 whose period is twice that of the SLM 11, the diffusion effect of the DC component of the signal light 100 and the noise reduction effect due to the insertion of the diffusion plate 12 by experiment. Since the intensity distribution of the signal light 100 in the hologram recording material 80 is expanded and the DC component of the signal light is suppressed, the dynamic range of the hologram recording material 80 can be effectively utilized, and S / N good hologram recording can be performed.

  The optical component that suppresses the DC component of the signal light may be an optical component that changes the phase of light by a change in refractive index instead of unevenness on the surface. In this case, the diffusion unit period for diffusing the light is the pixel period of the SLM 11. 2 times or more is sufficient.

  In addition, the present invention is not limited to the above-described embodiment, and can be implemented in various other forms in specific configurations, functions, operations, and effects without departing from the gist thereof. In the present embodiment, the SLM and the diffuser plate are described in consideration of being arranged adjacent to each other. However, the SLM and the diffuser plate are arranged at positions where they are in an imaging relationship with each other (positions indicated by broken lines in FIG. 1). May be. In this case, naturally, the period of the SLM and the diffusion plate needs to be determined including the mutual imaging magnification. For example, when the SLM is imaged on the diffusion plate at a magnification of 1/2, it is clear that the same effect as in this embodiment can be obtained even if the actual period of the SLM and the diffusion plate is the same. .

  Further, although the diffusion plate of the present embodiment shown in FIG. 2 has a structure that takes only binary values of the concave portion and the convex portion, the same effect can be obtained even with a multi-value diffusion plate. Furthermore, although the diffusion plate of this embodiment diffuses light using unevenness, the same effect can be obtained even if light is diffused by a change in refractive index that does not depend on unevenness.

It is the block diagram which showed the structure of the principal part of the hologram recording apparatus which concerns on one Embodiment of this invention. It is the front view and side view which showed the structure of the diffuser plate and SLM which were shown in FIG. It is the block diagram which showed a part of conventional hologram recording device. It is the figure which showed intensity distribution in the recording material of signal light. It is the front view and side view which showed the structure of the conventional diffusion plate and SLM.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Spatial modulator (SLM), 12 ... Diffusing plate, 13, 14, 15 ... Lens, 16 ... Aperture, 80 ... Hologram recording material, 301 ... Signal optical system for recording.

Claims (7)

  1. Hologram recording material for interference fringes between signal light generated by modulating a part of light emitted from a coherent light source with a spatial modulator and reference light which is another part of the light emitted from the light source A hologram recording device for recording on
    The optical system through which the signal light passes includes an optical component that diffuses the light,
    A hologram recording apparatus, wherein a light diffusion angle by the optical component is smaller than a light diffusion angle by the spatial modulator.
  2.   The hologram recording apparatus according to claim 1, wherein the optical component diffuses light by changing a phase of light by surface irregularities or a change in refractive index.
  3.   2. The optical component according to claim 1, wherein the optical component includes a diffusing unit that is disposed in a position close to or in an imaging relationship with the spatial modulator and has a width that is a natural number multiple of the pixel width of the spatial modulator. 2. The hologram recording apparatus according to 2.
  4.   4. The hologram recording apparatus according to claim 3, wherein the light diffusion unit of the optical component has a period at least twice as long as a pixel period of the spatial modulator.
  5.   The hologram recording apparatus according to claim 2, wherein the unevenness or refractive index change of the optical component is binary.
  6. An optical component that diffuses light modulated by a spatial modulator,
    Containing unevenness that diffuses the light, or a refractive index changing structure,
    An optical component characterized in that a period of a light diffusing unit due to the unevenness or refractive index changing structure is at least twice as long as a pixel period of the spatial light modulator.
  7.   The optical component according to claim 6, wherein the optical component is a diffusion plate, and the light diffusion unit has a period of at least twice as long as a pixel period of the spatial modulator.
JP2005046371A 2005-02-23 2005-02-23 Hologram recording device and optical component Pending JP2006234990A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006276373A (en) * 2005-03-29 2006-10-12 Sony Corp Hologram recording device and phase mask
JP2007164862A (en) * 2005-12-12 2007-06-28 Fuji Xerox Co Ltd Hologram recording method and hologram recording device
JP2009026352A (en) * 2007-07-17 2009-02-05 Toshiba Corp Optical information recording device
JP2010067300A (en) * 2008-09-09 2010-03-25 Sony Corp Reproducing device and reproducing method
JP2014086102A (en) * 2012-10-22 2014-05-12 National Institute Of Advanced Industrial & Technology Random phase mask for fourier transform hologram

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH1091056A (en) * 1996-08-15 1998-04-10 Lucent Technol Inc Method for performing recording inside laminated medium
JP2000039831A (en) * 1998-07-10 2000-02-08 Lucent Technol Inc Method and device of storing holography data

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH1091056A (en) * 1996-08-15 1998-04-10 Lucent Technol Inc Method for performing recording inside laminated medium
JP2000039831A (en) * 1998-07-10 2000-02-08 Lucent Technol Inc Method and device of storing holography data

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006276373A (en) * 2005-03-29 2006-10-12 Sony Corp Hologram recording device and phase mask
JP2007164862A (en) * 2005-12-12 2007-06-28 Fuji Xerox Co Ltd Hologram recording method and hologram recording device
US7835052B2 (en) 2005-12-12 2010-11-16 Fuji Xerox Co., Ltd. Hologram recording method and hologram recording device
JP4696890B2 (en) * 2005-12-12 2011-06-08 富士ゼロックス株式会社 Hologram recording method and hologram recording apparatus
JP2009026352A (en) * 2007-07-17 2009-02-05 Toshiba Corp Optical information recording device
JP2010067300A (en) * 2008-09-09 2010-03-25 Sony Corp Reproducing device and reproducing method
JP4569692B2 (en) * 2008-09-09 2010-10-27 ソニー株式会社 Playback device and playback method
JP2014086102A (en) * 2012-10-22 2014-05-12 National Institute Of Advanced Industrial & Technology Random phase mask for fourier transform hologram

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