JP2007179596A - Position detection marker and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a marker to find the position of the data areas contained in reproduced images even when hologram images are recording under cutting off the DC components, and a method to detect the position of the data areas contained in reproduced images by using this marker. <P>SOLUTION: The position detection marker has the components of the same spatial frequency as the signal light expressing binary digital data in a black-and-white image consisting of many pixels arranged in a matrix and is attached to a data area. This marker is recorded and reproduced as a hologram together with the signal light to detect the position of the data area included in reproduced images. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a position detection marker and a position detection method, and in particular, records a hologram by simultaneously irradiating an optical recording medium with signal light from which a direct current component has been removed and reference light, and reproduces the recorded hologram. In a hologram recording / reproducing system, a position detection marker used for detecting the position of a data area included in a reproduced image, and a position detection method for detecting the position of the data area included in the reproduced image using the position detection marker.

  In the holographic data storage, binary digital data “0, 1” is converted into a digital image (signal light) as “bright, dark”, and the signal light is Fourier-transformed by a lens and applied to an optical recording medium. . A Fourier transform image is recorded as a hologram on the optical recording medium. However, since the Fourier transform image of digital data has an extremely strong peak intensity in the 0th order, in the holographic data storage, the dynamic range of the optical recording medium is wasted due to this 0th order component (DC component). If an attempt is made to increase the multiplicity (the number of holograms that are multiplexed and recorded), the S / N (signal-noise ratio) of the reproduced image is greatly reduced. Therefore, there is a problem that the multiplicity cannot be increased.

In order to solve this problem, various methods for blocking the zero-order component of the Fourier transform image of the signal light have been proposed (Patent Documents 1 and 2). For example, in the method described in Patent Document 1, a light shield is disposed between a lens and an optical recording medium, and the 0th-order component of signal light is blocked by this light shield. Then, only the components of the specific order of the signal light pass through the aperture formed in the light shielding body, and the image edge portion of the signal light is recorded as a hologram. According to this method, waste of the dynamic range can be prevented by suppressing useless exposure due to the zeroth-order component, and the recording area of each data page can be reduced.
JP 2000-66565 A JP 2004-198816 A

  However, when the hologram is recorded while blocking the zeroth-order component, there is a problem that the position detection marker disappears from the reproduced image reproduced from the hologram, or the position detection marker is partially lost. This position detection marker is added to the digital data in order to detect the position of the digital data. For this reason, when the position detection marker disappears or is partially missing, the position cannot be properly detected, and as a result, the SNR (signal-noise ratio) deteriorates.

  The present invention has been made to solve the above problems, and an object of the present invention is to detect the position of a data area included in a reproduced image even when a hologram is recorded with a DC component cut off. Another object of the present invention is to provide a position detection marker that can detect the position and a position detection method that uses this to detect the position of a data area included in a reproduced image.

  In order to achieve the above object, the position detection marker according to the present invention removes a direct current component from signal light representing binary digital data as a bright and dark image in which a large number of pixels are arranged in a matrix, and the direct current component is removed. In a hologram recording / reproducing system for recording a hologram on the optical recording medium by simultaneously irradiating the optical recording medium with signal light and reference light, and reproducing the recorded hologram, the position of the data area included in the reproduced image is determined. A position detection marker used for detection, which is added to the data area, has the same component as the spatial frequency of the signal light, and is recorded and reproduced as a hologram together with the signal light Yes.

  In addition, the position detection method of the present invention removes a DC component from signal light representing binary digital data as a bright and dark image in which a large number of pixels are arranged in a matrix, and the signal light and reference light from which the DC component has been removed. Position detection method for detecting the position of a data area included in a reproduced image in a hologram recording / reproducing system that records a hologram on the optical recording medium and reproduces the recorded hologram The signal light and a position detection marker having the same component as the spatial frequency of the signal light are recorded as a hologram, a reproduced image is obtained from the recorded hologram, and the position detection marker included in the reproduced image And detecting the position of the data area included in the reproduced image based on the position of the detected position detection marker. There.

  The position detection marker of the present invention is added to the data area and recorded and reproduced as a hologram together with the signal light. However, since it has the same component as the spatial frequency of the signal light, the direct current component is removed from the signal light. Even when a hologram is recorded by simultaneously irradiating the optical recording medium with signal light and reference light from which a direct current component has been removed, the position detection marker disappears from the reproduced image, or the position detection marker is partially missing The position of the data area included in the reproduced image can be detected.

  As described above, according to the present invention, even when the hologram is recorded with the DC component cut off, the position detection marker does not disappear from the reproduced image, or the position detection marker is not partially lost. It is possible to detect the position of the data area included in the.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

(Position detection marker)
FIG. 1 is a diagram showing an image of a data page to be recorded as a hologram.
In this data page 50, binary digital data “0, 1” is represented as “white pixels, black pixels”, and a large number of pixels are arranged in a matrix. By recording this data image as a hologram, binary digital data can be recorded for each page. In this case, the size of one pixel corresponds to 1-bit data. The four corners of the data page 50, upon detection of a reproduced image from the hologram, the position detection marker 52 ₁ to 52 ₄ for detecting the position of the data page 50 is located.

FIG. 2 is an enlarged view of the position detection marker.
Position detection marker 52 ₁ is represented by white pixels, has a straight portion extending straight portion and the column extending in the row direction of the matrix, extending straight portion and the column extending in rows The straight portions intersect each other. The width d of the straight line portion is in a range satisfying the following relationship, where a is the length of one side of the data pixel.

                              a / 2 ≦ d ≦ 2a

Position detection marker 52 ₁ satisfying the above relationship will have the same component as the spatial frequency of the data page 50. Incidentally, each of the position detection marker 52 ₂ to 52 ₄ also has the same shape as the position detection marker 52 _1.

(First embodiment)
FIG. 3 is a diagram showing a schematic configuration of the hologram recording / reproducing apparatus according to the first embodiment. As shown in the figure, the recording / reproducing apparatus can irradiate the optical recording medium with the signal light and the reference light coaxially.

  The hologram recording / reproducing apparatus is provided with a light source 10 that oscillates laser light that is coherent light. A beam expander 15 including lenses 12 and 14 is disposed on the laser light irradiation side of the light source 10. On the light transmission side of the beam expander 15, a polarization beam splitter 16 that transmits only polarized light in a predetermined direction and reflects other polarized light is disposed. In the following description, it is assumed that the polarizing beam splitter 16 transmits P-polarized light and reflects S-polarized light.

  A reflective spatial light modulator 18 is disposed on the light reflection side of the polarization beam splitter 16. The spatial light modulator 18 is connected to the personal computer 30 via the pattern generator 32. The pattern generator 32 generates a pattern to be displayed on the spatial light modulator 18 according to the digital data supplied from the personal computer 30, and the spatial light modulator 18 modulates the incident laser light according to the display pattern. A digital image (signal light) and reference light for each page are generated. The generated signal light and reference light are reflected in the direction of the polarization beam splitter 16 and pass through the polarization beam splitter 16.

  On the signal light transmitting side of the polarizing beam splitter 16, a quarter wavelength plate 20, lenses 22, 24, and a Fourier transform lens 26 are arranged in this order along the optical path. In addition, a mask 38 for removing a direct current component from the Fourier transform images of the signal light and the reference light is disposed between the lens 22 and the lens 24. As the mask 38, for example, a micromirror that reflects only the DC component of the Fourier transform image can be used. Also, a filter that absorbs only the DC component of the Fourier transform image can be used.

  When reproducing the hologram, when the optical recording medium 28 is irradiated with the reference light, the irradiated reference light is diffracted by the hologram, and the diffracted light is reflected by the reflection layer 28a of the optical recording medium 28 in the direction of the Fourier transform lens 26. The The reflected diffracted light enters the polarization beam splitter 16. On the diffracted light reflecting side of the polarization beam splitter 16, a photodetector 36 is arranged which is composed of an image sensor such as a CCD or CMOS array and converts the received reproduction light (diffracted light) into an electric signal and outputs it. . The photodetector 36 is connected to the personal computer 30.

Next, the hologram recording process will be described.
The laser light oscillated from the light source 10 is collimated into a large-diameter beam by the beam expander 15, enters the polarization beam splitter 16, and is reflected in the direction of the spatial light modulator 18. When digital data is input from the personal computer 30, the pattern generator 32 generates a signal light pattern (data page) according to the supplied digital data, and combines it with the reference light pattern to generate the spatial light modulator 18. A pattern to be displayed is generated.

As described above, the four corners of the data page 50, upon detection of a reproduced image from the hologram, the position detection marker 52 ₁ to 52 ₄ for detecting the position of the data page 50 is located (Figure 1 reference). In the spatial light modulator 18, the laser light is polarization-modulated according to the displayed pattern, and signal light and reference light are generated.

  For example, as shown in FIG. 4, the central portion of the spatial light modulator 18 is used for data display (for signal light), and the peripheral portion of the spatial light modulator 18 is used for reference light. The laser light incident on the central portion of the spatial light modulator 18 is polarization-modulated according to the display pattern to generate signal light. On the other hand, the laser light incident on the peripheral portion of the spatial light modulator 18 is polarization-modulated according to the display pattern to generate reference light.

  The signal light and the reference light that have been polarization-modulated by the spatial light modulator 18 are applied to the polarization beam splitter 16 and transmitted through the polarization beam splitter 16 to be converted into linearly polarized amplitude distribution. Thereafter, the light is converted into circularly polarized light by the quarter-wave plate 20 and Fourier-transformed by the lens 22. The signal light and the reference light subjected to the Fourier transform are irradiated onto the mask 38, and the DC component is removed from the Fourier transform images of the signal light and the reference light.

  The signal light and the reference light that are not blocked by the mask 38 are subjected to inverse Fourier transform by the lens 24, subjected to Fourier transform again by the lens 26, and irradiated onto the optical recording medium 28 simultaneously and coaxially. As a result, the signal light and the reference light interfere with each other in the optical recording medium 28, and the interference pattern is recorded as a hologram.

Next, playback image acquisition processing will be described.
As shown in FIG. 5, a light-shielding pattern (all black pixels) is displayed at the central portion of the spatial light modulator 18, and the same reference light pattern as that during recording is displayed at the peripheral portion of the spatial light modulator 18. As a result, only the laser light incident on the peripheral portion of the spatial light modulator 18 is polarized and modulated to generate the reference light, which is transmitted through the polarization beam splitter 16 and converted into an amplitude distribution, and then the ¼ wavelength plate 20 Through the lenses 22, 24, and 26, only the reference light is irradiated to the area where the hologram of the optical recording medium 28 is recorded.

  The irradiated reference light is diffracted by the hologram, and the diffracted light is reflected in the direction of the lens 26 by the reflection layer 28 a of the optical recording medium 28. The reflected diffracted light is subjected to inverse Fourier transform from the lens 26, relayed by the lenses 24 and 22, converted to S-polarized light by the quarter-wave plate 20, and incident on the polarization beam splitter 16. Reflected in the direction. A reproduced image can be observed on the focal plane of the lens 22.

  In this embodiment, the direct current component is removed from the Fourier transform images of the signal light and the reference light, and the hologram is recorded. However, since the position detection marker has the same component as the spatial frequency of the data page, The detection marker disappears and the position detection marker is not partially lost, and is reproduced together with the data page.

  This reproduced image is detected by the photodetector 36. The detected analog data is A / D converted by the photodetector 36, and the image data of the reproduced image is input to the personal computer 30 and held in the RAM (not shown). The luminance value (image data) detected by each pixel of the photodetector 36 is input to the personal computer 30 in association with each pixel of the spatial light modulator 18.

Next, data page position detection processing will be described.
The image data of the reproduced image held in the RAM of the personal computer 30 is read, and the position of the position detection marker is detected by a method such as template matching. When detecting the position of the marker, it is preferable not to match the entire held image but to search only a part of the region where the marker is expected. Specifically, when there are position detection markers at the four corners, the search area is set to an area about twice as large as the area where the marker position can be shifted due to misalignment of the optical system. Since the search area depends on the device, it is determined experimentally. The marker detection time can be reduced by the above operation.

  When the position of the marker is detected, the address corresponding to the data page is assigned to the held reproduction image. For example, if the data page is 1000 × 1000 bits, the area surrounded by the markers is divided into 1000 × 1000. Then, the average luminance of each divided area is obtained. Alternatively, the maximum luminance of each divided area can be selected. Next, these luminance values are compared with threshold values and assigned to binary digital data, and a 1000 × 1000 bit data page is decoded.

Actually, a reproduction experiment of the position detection marker was performed under the following conditions.
As the light source 10, a second harmonic cw of 532 nm of YAG laser was used. As the spatial light modulator 18, a reflection type liquid crystal panel was used. The pixel size is 19 μm square and is 1024 × 768 pixels. On the other hand, the photodetector 36 has a pixel size of 6 μm and uses a 2048 × 2048 CCD camera. In this configuration, one pixel of the spatial light modulator 18 can be detected by about 3 × 3 pixels of the CCD. One bit of digital data is represented by 2 × 2 pixels of the spatial light modulator, and a data page is constructed. Therefore, one bit of the signal light is detected (sampled) by about 6 × 6 pixels of the CCD. The line width of the marker was 8 pixels, 4 pixels, 2 pixels, and 1 pixel of the spatial light modulator.

  As shown in FIG. 6, experiments were performed using cross-shaped markers 1 to 4 with respective line widths. The width d of the straight line portion is 4 times (4a) for the marker 1 and 2 times (2a) for the marker 2 where a is the length of one side of the data pixel (in this case, two pixels of the spatial light modulator 18). The marker 3 has four types, which is 1 (a) and the marker 4 has a half (1 / 2a). The position detection marker has a linear portion extending in the row direction and a linear portion extending in the column direction with respect to a data page in which a large number of pixels are arranged in a matrix, and a linear portion extending in the row direction; The straight portions extending in the column direction cross each other.

FIG. 7 is a diagram showing an image reproduced from a hologram in which a data page and a position detection marker are recorded. It can be seen that the position detection marker having a wider straight line portion deteriorates the image. On the other hand, the light intensity becomes insufficient as the width of the straight line portion becomes narrower. In order to detect the position detection marker even when the hologram is recorded while blocking the zero-order component of the Fourier transform image, the width d of the straight line portion is preferably in a range satisfying the following relationship.
a / 2 ≦ d ≦ 2a

  As described above, in the present embodiment, even when the hologram is recorded by blocking the direct current component of the Fourier transform image, the position detection marker does not disappear from the reproduced image or is not partially lost, and the position is appropriately set. Detection can be performed.

  In the above embodiment, an example of the position detection marker having a relatively short straight portion with respect to the matrix has been described. However, as shown in FIG. 8, the position detection marker 52 is provided along the outer periphery of the data page 50. You can also.

It is a figure which shows the image of the data page recorded as a hologram. It is an enlarged view of a position detection marker. It is a figure which shows schematic structure of the hologram recording / reproducing apparatus which concerns on 1st Embodiment. It is a figure which shows the display image of a spatial light modulator. It is a figure which shows the display image of a spatial light modulator in the case of acquiring a reproduced image. It is a figure which shows a data page and the cross-shaped position detection marker added to this. It is a figure which shows the reproduction | regeneration image from the hologram which recorded the data image shown in FIG. It is a figure which shows the other example of a position detection marker.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light source 12 Lens 15 Beam expander 16 Polarizing beam splitter 18 Spatial light modulator 20 Wave plate 22 Lens 24 Lens 26 Fourier transform lens 26 Lens 28 Optical recording medium 28a Reflective layer 30 Personal computer 32 Pattern generator 36 Photo detector 38 Mask 50 Data page 52 Position detection marker

Claims (8)

A direct current component is removed from signal light representing binary digital data as a bright and dark image in which a large number of pixels are arranged in a matrix, and the optical recording medium is irradiated with the signal light from which the direct current component has been removed and the reference light simultaneously. In the hologram recording / reproducing system for recording a hologram on the optical recording medium and reproducing the recorded hologram, a position detection marker used for detecting the position of the data area included in the reproduced image,
A position detection marker that is added to the data area, has the same component as the spatial frequency of the signal light, and is recorded and reproduced as a hologram together with the signal light.   The position detection marker according to claim 1, comprising a straight line portion extending in a row direction or a column direction of the matrix. The position detection marker according to claim 1 or 2, wherein the width d of the straight line portion satisfies the following relationship, where a is the length of one side of one pixel of the bright and dark image.
a / 2 ≦ d ≦ 2a   The position detection marker of Claim 2 or 3 containing the linear part extended in the row direction and column direction of the said matrix.   The position detection marker according to claim 4, wherein a linear portion extending in a row direction and a linear portion extending in a column direction of the matrix intersect.   The position detection marker of any one of Claims 1 thru | or 5 arrange | positioned at the four corners of the said data area. A direct current component is removed from signal light representing binary digital data as a bright and dark image in which a large number of pixels are arranged in a matrix, and the optical recording medium is irradiated with the signal light from which the direct current component has been removed and the reference light simultaneously. In the hologram recording / reproducing system for recording a hologram on the optical recording medium and reproducing the recorded hologram, a position detecting method for detecting the position of a data area included in a reproduced image,
Recording the signal light and a position detection marker having the same component as the spatial frequency of the signal light as a hologram,
Obtain a reconstructed image from the recorded hologram,
Detecting the position of the position detection marker included in the reproduced image,
A position detection method for detecting a position of a data area included in the reproduced image based on a position of a detected position detection marker.   An optical recording medium on which a hologram is recorded is irradiated with the reference light as readout light, and the reproduction light reproduced from the hologram by irradiation of the readout light is imaged on a light receiving element, and the reproduction light is imaged. The position detection method according to claim 7, wherein the reproduced image is received by the light receiving element, and the reproduced image is acquired from the recorded hologram.