JP2008242023A - Hologram-reproducing device and hologram recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram-reproducing device and a hologram recording and reproducing device which are capable of significantly the improving S/N ratio of a reproduced image of page data, by reducing moire patterns superimposed on the reproduced image. <P>SOLUTION: Page data input to a reproduced image division means 21 from a recording medium 12 are stored in a storage area 102, when it is decided as being white display page data by a page data evaluator 101, and are successively input to a division operator 103, when it is decided as being signal coded page data. Signal coded page data are divided by page data stored in the storage area 102. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hologram reproducing apparatus and hologram recording / reproducing apparatus capable of high-density multiplex recording, and more particularly to an apparatus for reproducing signals from holographic memory of discrete digital data (for example, large-capacity archive data for storage). Is.

In recent years, optical information recording media such as optical discs are becoming popular in information recording. In addition, research and development of next-generation optical information recording media aiming at higher speed and larger capacity is being actively conducted.
Among them, various multiplex recording / reproducing apparatuses using a hologram recording / reproducing method have been proposed from the viewpoint that the recording capacity can be significantly increased (for example, Patent Document 1 below).

Hereinafter, a conventional hologram recording / reproducing apparatus will be described with reference to FIG.
The coherent laser beam emitted from the laser light source 301 is expanded in beam diameter by a beam expander including a diverging lens 302 and a collimator lens 303, and is split into two beams by a beam splitter including a polarization beam splitter 305, Each of them functions as signal light (object light: actually, it is made into signal light by the spatial light modulation element 309) and reference light.
The signal light branched by the polarization beam splitter 305 is applied to the spatial light modulator 309 via the polarization beam splitter 308.

  Digital information to be recorded is arranged in a two-dimensional array called page data, and is sequentially displayed on the spatial light modulation element 309, thereby spatially modulating light passing (reflecting). The polarization direction of the signal light emitted from the spatial light modulation element 309 is changed from that of the incident light, is reflected by the polarization beam splitter 308, optically Fourier transformed by the Fourier transform lens 311, and hologram recording medium 312. Is irradiated. At this time, if the reference light branched by the polarization beam splitter 305 is simultaneously irradiated from a different angle to the place where the signal light in the hologram recording medium 312 passes, interference fringes are generated in the volume inside the recording medium 312, and this fringe distribution is expressed. Hologram recording is performed by transferring to a recording area of the recording medium 312 in the form of a refractive index distribution or the like. Then, different page data is displayed on the spatial light modulator 309 and the incident angle of the reference light on the hologram recording medium 312 is changed little by little to multiplex-record different page data on the same area in the recording medium 312. It becomes possible to store information at high density.

  In the optical path, reflection mirrors 304 and 306 for deflecting the light beam and shutters 307 and 310 for appropriately passing / blocking the light beam are provided.

  On the other hand, when reproducing the page data recorded on the hologram recording medium 312, the same recording area is obtained by irradiating the recording medium 312 with the reference light at the same angle as the incident angle at the time of recording as described above. Even when a plurality of page data are recorded in a multiplexed manner, only desired page data can be selectively taken out and imaged by a CCD (imaging device) 314 via a Fourier transform lens (imaging lens) 313.

JP 2004-272268 A Japanese Patent Laid-Open No. 5-19187

  By the way, since laser light has extremely high coherence, moire interference fringes (hereinafter simply referred to as moire) are likely to occur due to interference caused by reflection on the surfaces of mirrors and lenses in the optical path. It is also known that interference occurs due to reflection inside the light receiving element, and moire is likely to occur. When such moire occurs, a reproduced image of the page data on which the moire pattern is superimposed is captured, and the reproduced image is extremely deteriorated.

  FIG. 2 shows a reproduced image captured when the entire screen is displayed in white, and a moire pattern is superimposed on the entire screen.

  FIG. 3 shows a reproduced image of page data in which a moire pattern is superimposed and a signal is encoded. The reproduced image is extremely deteriorated due to the superimposition of the moiré pattern. Thus, the moire pattern reduces the signal to noise ratio (SNR) of the reproduced page data. For this reason, in the hologram recording / reproducing technique, it is an important issue to reduce the moire pattern in order to achieve high density and large recording capacity of recorded information.

  Reflection of laser light can be reduced by coating AR mirror (Anti Reflection Coating: anti-reflection coating) on reflective mirrors and lenses placed in the optical path, as well as protective glass inside the image sensor. Thus, the occurrence of moiré can be suppressed to some extent, but since the reflection of the laser beam cannot be completely prevented, a certain amount of moiré occurs.

  In addition, as described in Patent Document 2, it is conceivable to insert a ground glass immediately before the image pickup element to diffuse the laser light so that interference does not occur. However, the reproduced image is blurred due to the diffusion effect of the ground glass. End up.

  Furthermore, it is conceivable to remove the moire component by performing signal processing on the captured reproduced image, but it is difficult in practice because the moire pattern includes various frequency components.

  The present invention has been made in view of the above circumstances, and a hologram reproducing apparatus and hologram recording / reproducing that can significantly reduce the signal-to-noise ratio of the reproduced image by reducing the moire pattern superimposed on the reproduced image of the page data. The object is to provide an apparatus.

The hologram reproducing apparatus of the present invention reproduces page data information from a hologram recording medium in which interference fringes obtained by causing interference between signal light carrying data information and reference light are holographically recorded as page data information In the hologram reproducing apparatus to
When reproducing the page data information, a first reproduced image that is a reproduced image of any page data on which a moire is superimposed and a signal is encoded, and a moire superimposed on the first reproduced image. Reproduction image acquisition means for acquiring a second reproduction image that is a reproduction image of all-pixel white page data on which the same moire is superimposed, and a reproduction image that divides the first reproduction image by the second reproduction image The division means is provided.

  The reproduced image dividing means receives the first reproduced image and a memory unit for storing the second reproduced image, and the inputted first reproduced image is sequentially stored in the memory unit. It is possible to provide a signal processing unit that divides by the second reproduced image.

  Further, the reproduced image dividing means includes a data adding unit for adding a plurality of the first reproduced images, a memory unit for storing a result of addition by the data adding unit as the second reproduced image, and the first It is possible to provide a signal processing unit that receives one reproduced image and sequentially divides the input first reproduced image by the second reproduced image stored in the memory unit.

Further, the hologram recording / reproducing apparatus of the present invention holographically records the interference fringes due to the interference light on the hologram recording medium as page data by causing the signal light carrying the data information and the reference light to interfere with each other, and the recorded page In a hologram recording / reproducing apparatus for reproducing data information,
When reproducing the page data information, a first reproduced image that is a reproduced image of any page data on which a moire is superimposed and a signal is encoded, and a moire superimposed on the first reproduced image. Reproduction image acquisition means for acquiring a second reproduction image that is a reproduction image of all-pixel white page data on which the same moire is superimposed, and a reproduction image that divides the first reproduction image by the second reproduction image The division means is provided.

  In the hologram reproducing apparatus and the hologram recording / reproducing apparatus of the present invention, a first reproduced image that is a reproduced image of any page data in which a moire is superimposed and a signal is encoded, and a moire identical to the moire are superimposed. The second reproduced image, which is the reproduced image of the page data of all pixels white, is obtained, and the first reproduced image is divided by the second reproduced image, and the moire portion is 1 (or a constant). On the other hand, since the information of the page data in which the signal is encoded is maintained without being equalized, the other part maintains the information of the page data in which the signal is encoded. Thus, moire can be reduced. As a result, it is possible to achieve higher recording information density and higher recording capacity.

  Hereinafter, a hologram recording / reproducing apparatus according to an embodiment of the present invention will be described separately for an information recording function and an information reproducing function with reference to the drawings. In addition, the hologram reproducing apparatus according to the embodiment of the present invention is represented by an information reproducing function part of a hologram recording / reproducing apparatus according to the following embodiment, and this information reproducing function part is referred to as a hologram reproducing apparatus. Includes an information recording function part and a part having only an information reproduction function part.

  FIG. 1 is a schematic diagram showing a main optical system of a hologram recording / reproducing apparatus according to an embodiment of the present invention. In FIG. 1, some members for controlling the optical system are not shown.

<Information recording function>
As shown in FIG. 1, the coherent laser beam emitted from the laser light source 1 is expanded in beam diameter by a beam expander including a diverging lens 2 and a collimating lens 3, reflected by a reflection mirror 4, and then a polarized beam. The light is split into two light beams by a beam splitter including the splitter 5 and the like, and functions as signal light (object light: actually signal light by a spatial light modulation element) and reference light, respectively.
The reference light (longitudinal linearly polarized light in the present embodiment: the same applies hereinafter) is reflected by the reflecting mirror 6 and irradiated onto a predetermined area on the hologram recording medium 12 via the shutter 7.

On the other hand, the signal light (horizontal linearly polarized light in the present embodiment: the same applies hereinafter) is applied to the spatial light modulator 9 via the polarization beam splitter 8.
As the spatial light modulator 9, a light valve such as a liquid crystal display panel or DMD (Digital Micromirror Device) is used. Each pixel on the spatial light modulator 9 passes light (reflects in the example of FIG. 1) / blocks light according to binary digital information on the page data, thereby spatially modulating the light. By this modulation processing, signal light carrying page data information is generated.

  The polarization direction of the signal light emitted from the spatial light modulator 9 is changed from the incident state (horizontal linearly polarized light → vertical linearly polarized light), reflected by the polarizing beam splitter 8, and passed through the shutter 7. Optically Fourier-transformed by a post-Fourier transform lens (FTL: Fourier Transform Lens) 11 is applied to the hologram recording medium 12. At this time, since the reference light is simultaneously irradiated from another angle to the place where the signal light in the hologram recording medium 12 passes, interference fringes are generated in the volume inside the recording medium 12, and this fringe distribution is changed to the refractive index distribution. Hologram recording is performed by transferring to the recording area of the recording medium 12 in a form such as. Then, different page data is displayed on the spatial light modulation element 9 and the incident angle of the reference light on the hologram recording medium 12 is changed little by little to multiplex-record different page data on the same area in the recording medium 12. It becomes possible to store information at high density.

  By the way, in this embodiment, page data in which a signal is encoded is recorded on the hologram recording medium 12 as in the prior art. Before that, all pixels displayed on the spatial light modulation element 9 are first displayed. White page data is recorded.

  In this case, instead of holographically recording page data of all pixels white on the hologram recording medium 12, the spatial light modulator 9 displays all pixels in white, and the light is directly imaged by the CCD 14, and a reproduced image dividing means 21 described later. May be stored in the white display page data storage area 102 (see FIG. 5).

<Information playback function>
Further, at the time of information reproduction, the reference light that has passed through the shutter 7 is applied to a predetermined region of the hologram recording medium 12 at the same incident angle and position as at the time of information recording. The shutter 10 is in a closed state.

  In other words, when reproducing the desired page data, the diffracted light carrying the desired page data information is set by setting the same reference light incident conditions as when the information was recorded when the desired page data was recorded. Is output from the hologram recording medium 12, and the diffracted light is incident on the image pickup device including the CCD 14 via the Fourier transform lens 13 and is imaged.

  By the way, since the laser light has extremely high coherence, moire is likely to occur due to reflection of a mirror or a lens in the optical path and further due to reflection inside the image sensor. When such moire occurs, a reproduction image of page data on which the moire pattern is superimposed is picked up, and the reproduction image is extremely deteriorated. Therefore, in the present embodiment, when the page data information is reproduced, the first reproduced image of the arbitrary page data obtained by encoding the signal and the same moire superimposed on the first reproduced image. A reproduction image acquisition unit 20 that acquires a second reproduction image of page data of all pixels white on which moiré is superimposed, and a reproduction image division unit 21 that divides the first reproduction image by the second reproduction image are provided. .

  That is, when the page data information is reproduced, a first reproduction image of arbitrary page data and a second reproduction image of all-pixel white page data on which the same moire as this moire is superimposed are obtained. One reproduced image is divided by the second reproduced image, and the moire portion is uniformized to 1 (or a constant), while the other portions are in a state where the information of the page data in which the signal is encoded is maintained. Therefore, moire can be reduced while maintaining the information of the page data in which the signal is encoded.

  The Fourier transform lens (imaging lens) 13 and the CCD 14 constitute a reproduced image acquisition means 20.

Hereinafter, the reproduced image dividing means 21 will be described with reference to FIG.
As shown in FIG. 1, the reproduction image of the page data captured by the reproduction image acquisition unit 20 (CCD 14) is first sequentially input to the page data evaluator 101 of the reproduction image division unit 21.
By the way, in this embodiment, as described above, page data in which a signal is encoded is recorded on the hologram recording medium 12, but at the same time, page data of all pixels white is also recorded.

  When data recorded on the hologram recording medium 12 is reproduced, first, a reproduced image of white page data of all pixels is read, and the page data evaluator 101 determines whether or not the reproduced image is white display page data. Is judged. The page data determined by the page data evaluator 101 as white display page data is stored in the white display page data storage area 102.

  Next, a reproduced image of the page data encoded with the signal is read out, and the page data evaluator 101 determines whether or not the signal is a reproduced image of the page data encoded. The page data determined by the page data evaluator 101 to be encoded page data is sequentially input to the division calculator 103.

In the division calculator 103, each pixel of the page data image in which the signal is encoded is assigned to each pixel of the page data image stored in the white display page data storage area 102 corresponding to the pixel. Each pixel is divided to reduce the moire for each pixel.
Thereafter, the page data is decoded by the decoder 104 using a conventionally known method such as the LDPC method.

  The contents of the LDPC method are described in detail in “Haruo Sugawara,“ Turbo Code and LDPC Code ”, IEICE Technical Report CS2004-33, pp. 25-32” and the like.

  FIG. 3 shows a first reproduced image of page data obtained by encoding a signal on which moire is superimposed. Due to the superimposition of the moiré pattern, the reproduced image of the portion that is originally white is extremely deteriorated.

  On the other hand, FIG. 4 shows the first reproduction image of the page data on which the moire pattern is superimposed as shown in FIG. 3, and the white color of all the pixels on which the same moire pattern as the first reproduction image is superimposed is shown in FIG. The reproduction image obtained by dividing by the second reproduction image of the page data is shown. As a result of the above division processing, the same moire pattern in both reproduced images becomes 1 (or a constant) and is uniformed. Therefore, in FIG. 4, pixels that should be white should be white and black. The pixels are black, and a desired reproduced image can be obtained. Thereby, the signal-to-noise ratio (SN ratio) of the reproduced image of the page data can be greatly improved.

  The hologram reproducing apparatus and hologram recording / reproducing apparatus of the present invention are not limited to those of the above-described embodiment, and various other aspects can be changed. For example, in the above embodiment, the reproduced image dividing means having the configuration as shown in FIG. 5 is used, but the reproduced image dividing means is not limited to the configuration shown in FIG. Various other configurations may be employed. For example, it may be configured as a reproduced image dividing unit 21A shown in FIG. That is, in this modification, it is only necessary to record page data in which signals are encoded on the hologram recording medium 12, and it is not necessary to record page data of all pixels white as in the above embodiment. .

Then, the page data in which the signal is encoded is reproduced from the hologram recording medium 12 and is sequentially input to the addition calculator 201 of the reproduced image dividing means 21A. Since the white arrangement of the page data is random, by adding a large number of page data so as to overlap each other, an image of all-pixel white page data on which moire is superimposed can be obtained. That is, the reproduction image of the page data of all pixels white can be obtained in the addition calculator 201 and stored in the white display page data storage area 202.
Next, the page data in which the signal is encoded is reproduced again from the hologram recording medium 12, and sequentially input to the division calculator 203 of the reproduced image dividing means 21A.

In this division computing unit 203, as in the above-described embodiment, a white display page data storage area corresponding to each pixel of each pixel of the page data image in which the signal is encoded is positioned. Each pixel of the page data image stored in 202 can be divided to reduce the moire for each pixel.
Thereafter, the page data is decoded by the decoder 204 using a conventionally known method such as the LDPC method, as in the above-described embodiment.

  Note that each component of the above-described reproduced image dividing means 21 and 21A is generally configured by a program stored in a CPU and a memory such as a ROM, but may be configured only by hardware.

1 is a schematic diagram showing a main optical system of a hologram recording / reproducing apparatus according to an embodiment of the present invention. The figure which shows an example of the 2nd reproduction | regeneration image imaged in the state on which the moire pattern of all pixels white (when the whole screen was displayed white) was superimposed. The figure which shows the 1st reproduction image of signal coding page data on which the moire pattern shown in FIG. 2 was superimposed. The figure which shows the image of the state which divided the 1st reproduction image shown in FIG. 3 by the 2nd reproduction image shown in FIG. 1 is a block diagram showing a configuration of a reproduced image dividing unit according to an embodiment of the present invention. The block diagram which shows the structure of the change aspect of the reproduction | regeneration image division means shown in FIG. Schematic showing the main optical system of a hologram recording and reproducing apparatus according to the prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,301 Laser light source 2,302 Divergence lens 3,303 Collimate lens 4,6,304,306 Reflection mirror 5,8,305,308 Polarization beam splitter 7,10,307,310 Shutter 9,309 Spatial light modulation element 11 , 13, 311, 313 Lens 12, 312 Hologram recording medium 14, 314 CCD
20 reproduction image acquisition means 21, 21A reproduction image division means 101 page data evaluator 102, 202 white display page data storage area 103, 203 division calculator 104, 204 decoder 201 addition calculator

Claims (4)

In a hologram reproducing apparatus for reproducing the page data information from a hologram recording medium in which interference fringes obtained by causing the signal light carrying the data information and the reference light to interfere with each other are holographically recorded as page data information,
When reproducing the page data information, a first reproduced image that is a reproduced image of any page data on which a moire is superimposed and a signal is encoded, and a moire superimposed on the first reproduced image. Reproduction image acquisition means for acquiring a second reproduction image that is a reproduction image of all-pixel white page data on which the same moire is superimposed, and a reproduction image that divides the first reproduction image by the second reproduction image A hologram reproducing apparatus comprising a dividing means.   The reproduced image dividing means receives the first reproduced image and a memory unit that stores the second reproduced image, and the input first reproduced image is sequentially stored in the memory unit. 2. The hologram reproducing apparatus according to claim 1, further comprising a signal processing unit that divides by the second reproduced image.   The reproduction image dividing means includes a data addition unit for adding a plurality of the first reproduction images, a memory unit for storing the result of addition by the data addition unit as the second reproduction image, and the first reproduction image 2. The hologram reproduction according to claim 1, further comprising a signal processing unit that receives an image and sequentially divides the inputted first reproduced image by a second reproduced image stored in the memory unit. apparatus. In the hologram recording / reproducing apparatus for causing the signal light carrying the data information to interfere with the reference light and holographically recording the interference fringes due to the interference light on the hologram recording medium as page data, and reproducing the recorded page data information,
When reproducing the page data information, a first reproduced image that is a reproduced image of any page data on which a moire is superimposed and a signal is encoded, and a moire superimposed on the first reproduced image. Reproduction image acquisition means for acquiring a second reproduction image that is a reproduction image of all-pixel white page data on which the same moire is superimposed, and a reproduction image that divides the first reproduction image by the second reproduction image A hologram recording / reproducing apparatus comprising a dividing means.