JP4697812B2 - Hologram recording / reproducing apparatus and hologram recording apparatus - Google Patents

Description

  The present invention relates to a hologram recording / reproducing apparatus and a hologram recording apparatus.

  As a conventional hologram recording device, a device that investigates a noise pattern in advance and performs reproduction in consideration of the noise pattern has been proposed (see Patent Document 1). In this document, a noise pattern is obtained by irradiating signal light onto an unrecorded hologram recording medium and imaging the signal light transmitted through the hologram recording medium. When reproducing the data recorded on the hologram recording medium, reproduction with good SN is realized by removing noise from the image data obtained by imaging the reproduction signal light based on the noise pattern obtained as described above. is doing.

JP 2005-70675 A

However, since recording is performed at a large number of recording positions in the hologram recording medium, there is a problem that if the noise patterns for all the recording positions are stored, the storage amount becomes enormous. In addition, a method has been proposed (see Patent Document 1, paragraph 0045) in which noise patterns are not investigated for all recording positions by interpolating and predicting noise patterns from the positional relationship of the recording positions. According to this method, the amount of noise pattern to be stored can be suppressed, but there is a problem that interpolation prediction cannot cope with a local defect or non-uniformity of the hologram recording medium. Furthermore, since the hologram recording device that investigates a noise pattern in an unrecorded hologram recording medium and the hologram reproducing device that reproduces data from the recorded hologram recording medium are not necessarily the same device, hologram reproduction There has been a problem that the apparatus cannot obtain noise pattern data.
An object of the present invention is to provide a hologram recording / reproducing apparatus and a hologram recording apparatus capable of realizing high reproduction quality even if a hologram recording medium has a defect or the like.

  In order to solve the above-mentioned problems, a second aspect of the invention relates to a two-dimensional recording electronic data to be recorded in a hologram recording apparatus that records an interference pattern by irradiating a hologram recording medium with light by a predetermined optical system. Modulation means for modulating the binary image into page data, shift means for relatively moving the optical system and the hologram recording medium, and at each recording position of the hologram recording medium shifted by the shift means Recording means for irradiating the recording reference light and the recording signal light obtained by spatially modulating the page data to record the interference pattern, and the recording signal light emitted by the recording means at each recording position. Imaging means for imaging the media light transmitted or reflected by the hologram recording medium by the imaging device, and the imaging means for imaging the media light A determination means for determining pass / fail of each recording position based on the image data obtained in this manner, and an invalidating means for invalidating the interference pattern at the recording position determined to be defective by the determination means. It is as.

  In the invention of claim 2 configured as described above, the modulating means modulates the recording electronic data to be recorded into page data representing a two-dimensional binary image. A shift means relatively moves the optical system and the hologram recording medium, thereby recording a large amount of the recording data on the hologram recording medium. Furthermore, multiple recording may be performed by shift multiplexing or the like. The recording means records the interference pattern by irradiating recording reference light and recording signal light at each recording position of the hologram recording medium shifted by the shifting means. The recording signal light is a light beam obtained by optical spatial modulation of the page data.

  When the recording means irradiates the recording reference light and the recording signal light at each recording position, the imaging means receives media light obtained by transmitting or reflecting the recording signal light on the hologram recording medium. An image is picked up by the image sensor. The determination means determines pass / fail of each recording position based on image data obtained by the image pickup means picking up the media light. Further, the invalidating means invalidates the interference pattern at the recording position determined by the determining means to be defective. For example, if the fact that the interference pattern recorded at the recording position is invalid is recorded on the hologram recording medium, it is possible to prevent electronic data from being reproduced from the interference pattern during reproduction.

The invention according to claim 3 is configured such that the determination means performs the quality determination based on luminance information of the image data.
In the invention of claim 3 configured as described above, the quality determination is performed based on the luminance information of the image data. When the recording position is normal, it can be considered that the brightness of the media light obtained by reflecting or transmitting the recording signal light from the recording position is stable. Accordingly, when the luminance information indicates abnormal luminance, it is possible to determine that the recording position is defective.

Furthermore, in the invention according to claim 4, the determination means performs the pass / fail determination based on the degree of coincidence between the binarized image data obtained by binarizing the image data and the page data.
In the invention of claim 4 configured as described above, binarized image data is first obtained by binarizing the image data. Since the binarized image data and the page data are both binary images, the pass / fail judgment can be performed based on the degree of coincidence between the two. In the evaluation of the degree of coincidence, the coincidence of each pixel may be evaluated, or the coincidence of each block obtained by dividing the binarized image data and the page data may be evaluated.

On the other hand, in the invention according to claim 5, the determination means performs the pass / fail determination based on demodulated electronic data obtained by demodulating the binarized image data obtained by binarizing the image data into electronic data. It is as.
As in the invention of claim 5 configured as described above, the pass / fail judgment is performed based on demodulated electronic data obtained by demodulating the binarized image data obtained by binarizing the image data into electronic data. Can also be done. Even when error correction is performed in the demodulation, the quality determination is performed based on the electronic data after error correction. In addition, in the electronic data with parity, the above pass / fail judgment can be performed by a parity check.

In the invention according to claim 6, the determination means performs the pass / fail determination based on a degree of coincidence between the demodulated electronic data and the recorded electronic data.
In the invention of claim 6 configured as described above, according to the comparison between the demodulated electronic data and the recorded electronic data, it is possible to make a pass / fail judgment based on more effective data reproducibility.

On the other hand, in the invention according to claim 7, the imaging means is configured to perform imaging for a predetermined period from the start of irradiation in which the recording means irradiates the recording reference light and the recording signal light at each recording position.
8. The hologram recording medium according to claim 7, wherein the recording unit starts forming the interference pattern by irradiating the recording reference light and the recording signal light at each recording position. Photosensitivity starts. Therefore, by performing imaging for a predetermined period immediately after the start of irradiation of the recording reference light and the recording signal light, the influence of the media light due to the exposure of the hologram recording medium can be suppressed as much as possible. Therefore, this method is suitable for purely evaluating defects or the like of the hologram recording medium.

Furthermore, in the invention according to claim 8, the image pickup means supplies reproduction signal light as diffracted light, which is obtained by irradiating the interference reference light to the interference pattern, to the image pickup element during reproduction of the hologram recording medium. In addition, the imaging condition is different between when the media light is captured by the imaging element and when the reproduction signal light is captured by the imaging element.
In the invention of claim 8 configured as described above, reproduction signal light as diffracted light obtained by irradiating the interference reference light to the interference pattern at the time of reproduction of the hologram recording medium is imaged by the imaging element. To do. That is, the hologram recording apparatus is a recording / reproducing apparatus having a reproducing function, and the imaging element images not only the media light but also the reproduced signal light. It is not necessary to provide a plurality of image sensors, and the apparatus can be simplified. However, since the media light is direct light and the reproduction signal light is diffracted light, the intensities of both are remarkably different. Therefore, it is desirable that the imaging conditions be different between when the recording medium light is captured and when the reproduction signal light is captured.

In the invention according to claim 9, the image pickup means makes the shutter opening time different between when the media light is picked up by the image pickup device and when the reproduction signal light is picked up by the image pickup device. As a configuration.
In the invention of claim 9 configured as described above, the shutter opening time is varied as a specific method for varying the imaging conditions. Thereby, even when the media light has a difference in intensity of the reproduction signal light, the amount of light incident on the image sensor can be optimized.

In the invention according to claim 10, the image pickup means supplies reproduction signal light as diffracted light obtained by irradiating the interference reference light to the interference pattern when reproducing the hologram recording medium to the image pickup element. The recording means is configured to vary the intensity of the recording signal light in a period in which the media light is imaged by the imaging element and in other recording periods.
In the invention of claim 10 configured as described above, the intensity of the medium light is suitable for imaging by the imaging device during the period of imaging by the imaging device, and the hologram is used during other recording periods. The intensity is suitable for exposing the recording medium. This also makes it possible to optimize the amount of light incident on the image sensor.

  Furthermore, as a more specific configuration example, the invention according to claim 1 is a holographic recording / reproducing apparatus that records an interference pattern by irradiating light onto a holographic recording medium by a predetermined optical system. Modulation means for modulating the image data into page data representing a two-dimensional binary image, shift means for relatively moving the optical system and the hologram recording medium, and each of the hologram recording medium shifted by the shift means A recording means for recording the interference pattern by irradiating a recording reference beam and a recording signal beam obtained by optical spatial modulation of the page data at a recording position; and an illumination reference beam for reproducing the hologram recording medium. The reproduction signal light as the diffracted light obtained by irradiating the interference pattern is imaged by the image sensor, and the recording means records each recording signal. An image pickup means for picking up an image by the image pickup element with a shutter opening time different from that during the reproduction of the medium light transmitted or reflected by the hologram recording medium by the recording signal light irradiated at a position; A determination unit for determining pass / fail of each recording position based on the degree of coincidence between the binarized image data obtained by binarizing the image data captured by the unit and the page data, and determining that the determination unit is defective Invalidation means for invalidating the interference pattern at the recording position.

As described above, according to the first and second aspects of the present invention, it is possible to provide a hologram recording / reproducing apparatus and a hologram recording apparatus capable of realizing high reproduction quality even if the hologram recording medium has a defect or the like. it can.
According to the invention of claim 3, it is possible to make a pass / fail judgment at high speed.
According to the invention of claim 4, it is possible to accurately determine whether the product is good or bad.
According to the fifth aspect of the present invention, it is possible to make a pass / fail judgment directly related to the reproduction quality.

According to the invention of claim 6, it is possible to make a pass / fail determination based on the reproducibility of the electronic data.
According to the seventh aspect of the present invention, it is possible to purely evaluate defects or the like of the hologram recording medium.
According to the invention concerning Claim 8, while being able to serve as an image pick-up element, the malfunction at that time can be prevented.
According to the invention concerning Claim 9 and Claim 10, the intensity | strength of the light which injects into an image pick-up element can be optimized.

Hereinafter, embodiments of the present invention will be described in the following order.
(1) Configuration of hologram recording / reproducing apparatus:
(2) Recording process:
(3) Reproduction processing:
(4) Modification:

(1) Configuration of Hologram Recording / Reproducing Device Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the hologram recording / reproducing apparatus 100 capable of recording and reproducing electronic data will be described as an example. However, it is needless to say that the present invention can be realized in a recording-dedicated apparatus and also in a multi-function machine having other functions. Can be realized. Hereinafter, the configuration of the hologram recording / reproducing apparatus 100 will be described with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing a schematic configuration of a collinear hologram recording / reproducing apparatus that performs recording / reproduction on a transmissive recording medium, and FIG. 2 is a collinear that performs recording / reproduction on a transmissive recording medium. It is a block diagram which shows schematic structure of the optical system 50 of the hologram recording / reproducing apparatus of a system. The collinear method is characterized in that the signal light and the reference light are arranged on the same optical axis, and the optical system can be configured more compactly compared to the two-beam interference method or the like. The hologram recording / reproducing apparatus 100 includes a drive system 70, an optical system 50, and a control unit 30. The present invention is not limited to recording / reproducing on a transmissive recording medium by the collinear method, but can also be applied to a recording / reproducing on a two-beam interference method or a reflective recording medium.

  The optical system 50 includes a laser light source 10, a DMD [Digital Micro-mirror Device] 12, an objective lens 14, condenser lenses 18 and 22, a light shielding plate 20, a magnification adjustment lens 24, an optical sensor 26, It is comprised including. The control unit 30 includes a driver 30a for controlling the output of the laser light source 10, an encoder 30b as modulation means of the present invention that modulates the input recording electronic data into predetermined page data and outputs the image data to the DMD 12, and an optical sensor. 26. The decoder 30d that binarizes the image data obtained at 26 and further demodulates it into demodulated electronic data, a driver 30c that controls the optical sensor 26, and a microcomputer 30f that executes various control processes according to a predetermined control program. ing. The microcomputer 30f includes a CPU, a RAM, a ROM, and the like (not shown), and the CPU executes a calculation necessary for processing to be described later while expanding a control program read from the ROM in the RAM.

  The laser light source 10 amplifies light (electromagnetic wave) to generate, for example, green coherent light and makes it incident on the DMD 12. The laser light incident on the DMD 12 is made into parallel light matched to the shape of the incident surface of the DMD 12 by a collimator lens (not shown) or the like. Any laser light source 10 may be used as long as it generates laser light such as a solid-state laser, a liquid laser, a gas laser, or a semiconductor laser.

  The DMD 12 is configured by a plurality of micromirrors arranged in a dot matrix, and individually controls the orientation angle of the micromirrors. The DMD 12 generates recording signal light and recording reference light obtained by spatially modulating the incident light for each micromirror (in this embodiment, two-dimensionally). Since the signal light and the reference light are generated simultaneously by one spatial light modulator, the relative positional relationship between the two is always constant because it is determined by the spatial light modulator. The modulation in this case means that uniform laser light is processed by performing on / off control in units of micromirrors based on, for example, page data input to the DMD 12. That is, by switching the orientation angle of each micromirror of the DMD 12 in accordance with the image data, either the direction in which the incident laser light is reflected by the objective lens 14 at the subsequent stage or the direction in which it is not reflected by the objective lens 14. And spatially modulate the laser beam. Therefore, the DMD 12 forms a spatial light modulator. In this embodiment, the DMD 12 is employed as the spatial light modulator, but a reflective liquid crystal, a transmissive liquid crystal, a magneto-optical spatial modulator [MOSLM], or the like can also be used.

  The objective lens 14 focuses the light incident from the DMD 12 on the recording layer of the hologram recording medium 16. The recording layer of the hologram recording medium 16 is made of a light-sensitive material, and the intensity distribution of interference fringes formed by the interference between the recording signal light and the illumination reference light during recording indicates the refractive index of the hologram recording medium 16 or Recorded as a change in transmittance. This change in refractive index or transmittance behaves as a diffraction grating. As the recording layer, for example, a photosensitive material such as a lithium niobate single crystal or a photopolymer can be used.

  In the hologram recording medium 16, the change in refractive index or transmittance formed during recording is stably maintained against light irradiation after recording and other environmental fluctuations. At the time of reproduction, when illumination reference light is incident on the hologram recording medium 16, the recorded change in refractive index or transmittance acts as a diffraction grating to generate diffracted light. The hologram recording medium 16 can adopt various shapes, and may be a bulk shape or a disk shape. Regardless of the shape, the imaging position of the interference pattern can be changed. For example, a large amount of recorded electronic data can be recorded by shift multiplexing. Further, by changing the imaging depth and imaging angle in the recording layer, more recording electronic data can be recorded in a multiplexed manner.

  In the present embodiment, a disc-shaped hologram recording medium 16 is employed, and a drive system 70 is provided as a shift unit that relatively moves the optical system 50 and the hologram recording medium 16. Specifically, the optical system 50 and the hologram recording medium 16 are rotationally moved in the circumferential direction of the hologram recording medium 16 by a spindle motor or the like, and the optical system 50 and the hologram recording medium 16 are moved by the tracking motor or the like. By combining driving that linearly moves in the radial direction, the driving system 70 can irradiate light to any recording position / reproducing position in the hologram recording medium 16. In this embodiment, a spiral track is formed on the hologram recording medium 16, and data is continuously recorded / reproduced by sequentially shifting the recording position / reproduction position along the track.

  The condenser lens 18 condenses the reproduction light that has passed through the hologram recording medium 16 during recording and reproduction and converts it into parallel rays. The condensing lens 22 condenses again the parallel light beam converted by the condensing lens 18 at a predetermined focal point. The light shielding plate 20 is disposed in a section that is a parallel light beam between the condenser lens 18 and the condenser lens 22 at the time of recording and reproduction, and blocks light unnecessary for quality determination and reproduction of the hologram recording medium 16. .

  The magnification adjusting lens 24 collects the light emitted from the condenser lenses 18 and 22 and diffused again beyond a predetermined focal point, and forms an image within a predetermined range of the light receiving surface of the optical sensor 26. That is, in the optical system 50, the magnification adjustment lens 24 condenses the light incident on the magnification adjustment lens 24 so that it falls within a predetermined range of the light receiving surface, and forms an image of the light that has passed through the magnification adjustment lens 24. It arrange | positions so that a surface may become the light-receiving surface of the optical sensor 26. FIG.

  The optical sensor 26 is a sensor in which a plurality of photoelectric elements are arranged in a dot matrix, and an electric charge is generated according to light intensity (luminance) incident on each photoelectric element, and a luminance image obtained by digitizing the amount of the electric charge. Data is generated and output to the decoder 30b. As the optical sensor 26, for example, a CCD sensor or a CMOS sensor can be used. A plurality of photoelectric elements constituting the optical sensor 26 constitute an imaging element for imaging the reproduction light. The optical sensor 26 is controlled by a driver 30c, and the opening time of the shutter (electronic shutter) can be adjusted.

(2) Recording Process FIG. 3 schematically shows the main part of the hologram recording / reproducing apparatus 100 during recording. At the time of recording, for example, electronic data read from another recording medium or acquired via a communication medium is input to the encoder 30b. The encoder 30b acquires the electronic data as recorded electronic data. The encoder 30b attaches an error correcting code [ECC: Error Correcting Code] to the recorded electronic data. Further, the encoder 30b modulates (encodes), for example, binary recording electronic data into binary (on / off or light / dark) two-dimensional image data. For example, as shown in FIG. 4, “0” of the recorded electronic data corresponds to “off” + “on” of the image pattern, and “1” of the recorded electronic data corresponds to “on” + “off” of the image pattern. Thus, by arranging the image pattern in accordance with the bit arrangement in the recorded electronic data, each pixel can be modulated into two-dimensional page data having binary information.

  FIG. 5 shows the page data converted by the encoder 30b. In the drawing, page data (actual data area A1) based on recorded electronic data is substantially circular. The encoder 30b combines the actual data area A1 with the central part of the invariant data area A2 whose outer shape is rectangular. The actual data area A1 reflects the recorded electronic data and the pattern changes, but the invariant data area A2 is constant image data that does not depend on the electronic data, and the on / off ratio is substantially equal to the actual data area A1. A fixed random pattern is set (shown in gray that the on / off ratio is 1: 1). Image data obtained by combining the actual data area A1 (page data) and the invariant data area D1 is output to the DMD 12. Each pixel of the image data corresponds to each micromirror of the DMD 12, and the orientation angle of the micromirror is controlled by the value (on / off) of each pixel.

  That is, the micromirror corresponding to the ON pixel in the image data causes the reflected light to enter the objective lens 14, and the micromirror corresponding to the OFF pixel does not cause the reflected light to enter the objective lens 14. When the laser light from the laser light source 10 is irradiated to the DMD 12 in which the orientation angle of each micromirror is controlled as described above, the laser light is modulated in accordance with the image data described above, and the hologram recording medium 16 Is irradiated.

  FIG. 6 shows in detail the state of the optical system during recording. As shown in the figure, the reflected light from the actual data area A1 and the invariant data area A2 enters the objective lens 14 from the DMD 12 and is condensed and irradiated on the hologram recording medium 16. Here, the reflected light from the actual data area A1 is referred to as recording signal light WS, and the reflected light from the invariant data area A2 is referred to as recording reference light WR. The optical axes of the recording signal light WS and the recording reference light WR are a common line, and the optical system of this embodiment is a collinear method. When the recording signal light WS and the recording reference light WR are collected, interference occurs, and an interference pattern is formed on the hologram recording medium 16. Thereby, the recording electronic data modulated by the recording signal light WS can be recorded on the hologram recording medium 16 as an interference pattern. By sequentially recording the above interference pattern at each recording position of each hologram recording medium 16, a large amount of data can be recorded.

  While the recording signal light WS and the recording reference light WR contribute to the formation of the interference pattern, the transmitted light (referred to as media light in the present invention) that has passed through the hologram recording medium 16 is generated as it is. This media light is received by the optical sensor 26 via the condenser lens 18, the light shielding plate 20, and the condenser lens 22. Note that the media light transmitted through the hologram recording medium 16 by the recording signal light WS is denoted as media signal light MS, and the media light transmitted through the hologram recording medium 16 by the recording reference light WR is denoted as media reference light MR. Similar to the relationship between the recording signal light WS and the recording reference light WR, the media reference light MR is distributed on the outer periphery of the media signal light MS. The media reference light MR on the outer periphery is blocked by the light shielding plate 20, and the media signal light MS on the inner side is imaged by the optical sensor 26.

  FIG. 7 shows a detailed flow of the recording process. The recording cycle shown in the figure is repeated until recording of the recording electronic data is completed. In step S100, the encoder 30b acquires the recording electronic data, and generates page data corresponding to the recording electronic data. The microcomputer 30f stores the generated page data in a RAM or the like. In step S110, the drive system 70 moves (tracks) the recording position. In step S120, the page data generated in step S110 is output to the DMD 12, and the laser light source 10 emits light. Thereby, the recording signal light WS and the recording reference light WR are irradiated onto the hologram recording medium 16 (irradiating means). The optical axes of the recording signal light WS and the recording reference light WR in the hologram recording medium 16 are the predetermined recording positions moved in advance by the drive system 70 in step S110. During the irradiation of the recording signal light WS and the recording reference light WR, the optical sensor 26 images the media signal light MS (step S130). In step S140, the optical sensor 26 generates image data corresponding to the image of the media signal light MS.

  FIG. 8 shows the irradiation time of the recording signal light WS and the recording reference light WR in step S120, and the shutter opening time of the optical sensor 26 in step S130. In this figure, the irradiation time of the recording signal light WS and the recording reference light WR is defined. During this period, the recording signal light WS and the recording reference light WR are irradiated to form an interference pattern on the hologram recording medium 16. Can be recorded. On the other hand, the shutter opening by the optical sensor 26 is controlled by an electronic shutter by the driver 30c, and imaging starts (shutter opening) with the start of irradiation of the recording signal light WS and the recording reference light WR, and the recording signal light WS and the recording reference light. Imaging is terminated (shutter shut off) at a time earlier than the end of WR irradiation. That is, in the present embodiment, imaging is performed at the initial stage of the irradiation time, and the shutter opening time is shorter than the irradiation time.

  By shortening the shutter opening time by the optical sensor, the amount of received media signal light MS in the optical sensor 26 can be limited, and the saturation of the luminance in the image data generated by the optical sensor 26 can be prevented. Note that the sensitivity of the optical sensor 26, the light transmittance of the hologram recording medium 16, and the intensities of the recording signal light WS and the recording reference light WR vary depending on the design of each device. It is desirable to set. Further, by performing imaging together with the start of irradiation of the recording signal light WS and the recording reference light WR, transmitted light (media) before the interference pattern is recorded on the hologram recording medium 16 by the irradiation of the recording signal light WS and the recording reference light WR. Signal light MS) can be imaged. Therefore, it can be determined by the media signal light MS whether or not the hologram recording medium 16 can transmit light normally.

  In step S150, the decoder 30b binarizes the image data to generate binarized image data. For example, at the time of step S140, the luminance of each pixel is expressed in 256 gradations in the image data, and binarization is performed by comparing the luminance of each pixel with a predetermined threshold value. When binarization is performed, image size conversion is performed in advance so that the image size becomes the same as the page data described above. In step S160, the binarized image data generated in step S150 is compared with the page data stored in step S100. In any data, each pixel has a binary gradation of “0” or “1”, and it is summed up whether or not the gradation of each pixel is the same. A value obtained by dividing the number of non-matching pixels by the total number of pixels is calculated as an error rate.

  Here, the binary image data is obtained by imaging the media signal light MS through which the light spatially modulated based on the page data passes through the hologram recording medium 16. Therefore, if it is assumed that the current recording position of the hologram recording medium 16 is a flat and homogeneous transparent body, the binary image data should show the same image as the page data, and the error rate should be 0%. However, when the thickness of the current recording position on the hologram recording medium 16 is abnormal or contains foreign matter, the error rate becomes high. If the error rate exceeds a certain error rate, a sufficient SN cannot be obtained during reproduction even if an interference pattern is recorded at the recording position.

  In step S170 (determination means), the error rate is compared with the threshold value. If the error rate is below the threshold value, the current recording position is determined to be good, and the process returns to step S100 to generate the next page data. In S110, it moves to the next recording position. On the other hand, if the error rate exceeds the threshold, it is determined that the current recording position is defective, and the recording position is stored in the RAM as a defective recording position in step S180. In step S110, it moves (slips) to the next recording position. Here, no new page data is generated, and the interference pattern based on the page data to be recorded at the previous recording position is recorded again. By repeating the above recording cycle, it is possible to sequentially record new recording electronic data as an interference pattern while sequentially shifting the recording position, while avoiding recording at the defective recording position and other normal recording positions. Slip recording. In the RAM, a plurality of defective recording positions are accumulated and stored.

  When the recording of the recording electronic data is completed by the above recording cycle, a list of defective recording positions stored in the RAM is recorded as TOC information near the inner periphery of the hologram recording medium 16, for example (invalidating means). The list of defective recording positions may be recorded by a hologram or may be recorded by other optical recording methods such as direct exposure with light.

(3) Reproduction processing:
FIG. 9 schematically shows the main part of the hologram recording / reproducing apparatus 100 during reproduction. At the time of reproduction, the hologram recording medium 16 on which the above-described interference pattern is recorded in a multiplexed manner is set, and the hologram recording medium 16 is read. First, the encoder 30b creates a real data area A1 that is all off. The encoder 30b combines the actual data area A1 with the central part of the invariant data area A2. The invariant data area A2 here is also the same fixed random pattern image data as at the time of recording. This image data is output to the DMD 12. FIG. 10 shows image data output to the DMD 12 during reproduction. As shown in the figure, the pixels in the actual data area A1 are set to an off (dark) state, and the pixels in the invariant data area A2 are set to an on / off (light / dark) state according to a fixed random pattern. The image data is output to the DMD 12. The laser light from the laser light source 10 is reflected by the DMD 12 in which the orientation angle of each micromirror is controlled by the image data described above.

  FIG. 11 shows in detail the state of the optical system during reproduction. As shown in the figure, the reflected light from the real data area A1 and the invariant data area A2 having the same optical axis from the DMD 12 is incident on the objective lens 14 and is condensed and irradiated onto the hologram recording medium 16. However, since the micromirror corresponding to the actual data area A1 does not allow the reflected light to enter the objective lens 14, the light beam reflected by the actual data area A1 does not reach the hologram recording medium 16, but is reflected only by the invariable data area A2. Only the emitted light beam reaches the hologram recording medium 16. Here, the light beam reflected by the invariant data area A2 at the time of reproduction is referred to as illumination reference light LR.

  When the illumination reference light LR is irradiated onto the hologram recording medium 16, the reproduction light R transmitted through the hologram recording medium 16 is generated. As shown in FIG. 11, when the illumination reference light LR passes through the hologram recording medium 16, diffraction occurs using the interference pattern recorded on the hologram recording medium 16 as a diffraction grating, and recording is performed when the interference pattern is recorded. Diffracted and transmitted light similar to the signal light WS (media signal light MS) can be reproduced. This diffracted transmitted light is referred to as reproduction signal light RS. The reproduction signal light RS is once converted into parallel rays by the condenser lens 18 and further received by the optical sensor 26 via the condenser lens 22 and the magnification adjustment lens 24. The optical sensor 26 generates image data indicating an image of the reproduction signal light RS, binarizes the image data, and outputs it to the decoder 30d. The decoder 30d performs a decoding process reverse to the encoding process in the encoder 30b. Specifically, demodulated electronic data is reproduced by demodulating two-dimensional binarized image data into demodulated electronic data and performing error correction based on ECC.

  FIG. 12 shows the detailed flow of the reproduction process. The reproduction cycle shown in the figure is repeated until the reproduction of electronic data is completed. In step S200, the TOC information recorded near the inner periphery of the hologram recording medium 16, for example, is read. As described above, since the list of defective recording positions determined at the time of recording is recorded in the TOC information, the microcomputer 30f acquires the defective recording positions and stores them in the RAM. In step S210, the drive system 70 moves the recording position. In step S220, it is determined whether or not the current recording position is a defective recording position. If it is not a defective recording position, the illumination reference light LR is irradiated in step S230, and the reproduction signal light RS obtained thereby is used. The optical sensor 26 images in step S240.

  Here, the shutter opening time of the optical sensor 26 is different from the shutter opening time of the optical sensor 26 at the time of recording described above (step S130). The output of the laser light source 10 is different at the time of reproduction and at the time of recording. At the time of recording, the media signal light MS that is not diffracted is imaged, whereas the reproduction signal light RS generated by diffraction at the time of reproduction is captured. This is because the light intensity of the two is different. In this way, by differentiating the shutter opening time between reproduction and recording (step S130), the optical sensor 26 can be shared between reproduction and recording, and the recording / reproducing apparatus can be simplified. Can do.

  In step S250, the decoder 30b binarizes the image data as in step S150, thereby generating binarized image data. Here, since the amount of received light and the shutter opening time are different from those in step S150, the binarization determination may be performed using different threshold values. In step S160, the binarized image data is demodulated into demodulated electronic data. Here, a conversion process reverse to that in FIG. 4 may be performed. Further, in step S270, error correction of the demodulated demodulated electronic data is performed.

  On the other hand, if it is determined in step S220 that the current recording position is a defective recording position, the process returns to step S210 to move (slip) to the next recording position. By doing so, it is possible to reproduce only the interference pattern recorded at the recording position where the interference pattern can be normally recorded without reproducing the interference pattern recorded at the defective recording position. At the time of recording, since the interference pattern that should have been recorded at the defective recording position is recorded by slipping to another recording position, the recorded electronic data corresponding to the interference pattern is not lost.

  As described above, in the present embodiment, when recording is performed at each recording position, the quality determination of each recording position is performed. Record. In addition, information for identifying a defective recording position determined to be defective is recorded on the hologram recording medium 16 as TOC information and read during reproduction, so that the defective recording position is slipped even during reproduction. Playback can be performed. As a result, only the interference pattern recorded at a good recording position can be read and reproduced, and a good SN ratio and error rate can be realized.

(4) Modification In the above embodiment, the amount of light received by the optical sensor 26 at the time of recording is optimized by adjusting the shutter opening time, but the output of the laser light source 10 during the period of imaging the media signal light MS. The amount of light received by the optical sensor 26 may be optimized by adjusting. FIG. 13 shows the transition of the output of the laser light source 10. As shown in the figure, the output of the laser light source 10 is weakened in the initial irradiation of the recording signal light WS and the recording reference light WR. The optical sensor 26 performs imaging corresponding to a period in which the output of the laser light source 10 is weakened. In this modification, the shutter opening time of the optical sensor 26 is fixed, and the shutter opening time is the same during reproduction. However, since the output of the laser light source 10 is weakened, the optical sensor 26 saturates during imaging during recording. Can be prevented. Note that there may be a case where the reproduction signal light RS received during reproduction has a higher intensity than the media signal light MS received during recording. In this case, as indicated by a broken line, the output of the laser light source 10 during the period for imaging the media signal light MS may be increased.

  In the above embodiment, as illustrated in FIG. 3, the example in which the pass / fail judgment of each recording position is performed based on the degree of coincidence (error rate) between the page data and the binarized image data obtained by imaging is illustrated. The quality of each recording position may be determined by other determination methods. For example, as shown in FIG. 14, the recorded electronic data before ECC attachment and the demodulated electronic data after error correction (the electronic data demodulated based on the image data captured by the optical sensor 26 at the time of recording are indicated as demodulated electronic data). It is also possible to make a pass / fail judgment based on the (bit) error rate. By doing in this way, it is possible to realize an effective pass / fail judgment that takes into account the effect of error correction to some extent. Further, when ECC or parity is added to the recorded electronic data in advance, the error rate of the demodulated electronic data can be grasped by performing a parity check or the like without performing comparison with the original recorded electronic data.

  In the above embodiment, it is possible to determine whether or not the recording position is good based on multi-tone image data before binarization is performed on the image data captured by the optical sensor 26 during recording. For example, according to the image modulation processing shown in FIG. 4, it can be considered that the number of “on” and “off” pixels is 1: 1 in the page data after image modulation in any recording electronic data. Therefore, as shown in FIG. 15, a histogram relating to the luminance value of multi-tone image data is created, and the current recording position is good if the number of bright pixels and the number of dark pixels are approximately 1: 1. It can be determined that there is. Of course, it is also possible to make a determination by other statistical methods. For example, the determination may be made based on whether or not the average value ave is substantially intermediate to the luminance range Ra. The determination may be made based on whether or not the standard deviations σ1 and σ2 of the luminance groups are not unnatural. Furthermore, it may be determined that the luminance difference between the mode values p1 and p2 of each group is good when it is equal to or higher than a predetermined luminance.

  Note that the image modulation processing shown in FIG. 4 is merely an example, and the number of pixels “ON” and “OFF” is not limited to 1: 1. For example, it is possible to perform unequal image modulation in which the number of pixels of “ON” and “OFF” is 1: 3 or 3:13. In this case, since preferable distributions for the above-described histogram are different, it is necessary to perform pass / fail determination based on a statistical index suitable for each modulation method. In addition, the histogram shown in FIG. 15 is created for each of a plurality of blocks obtained by dividing the image data, the pass / fail judgment is performed for each block, and the pass / fail of each block is totaled to determine the overall pass / fail. May be. For example, when the number of normal blocks exceeds a predetermined ratio, it may be determined that the whole is good.

1 is a block diagram illustrating a schematic configuration of a collinear hologram recording / reproducing apparatus that performs recording / reproduction with respect to a transmission type recording medium. FIG. 1 is a configuration diagram illustrating a schematic configuration of an optical system of a collinear hologram recording / reproducing apparatus that performs recording / reproduction with respect to a transmission type recording medium. It is a schematic diagram explaining the mode of the hologram recording / reproducing apparatus at the time of recording. It is a figure explaining encoding. It is a figure which shows the image data output to DMD at the time of recording. It is a schematic diagram explaining the mode of the optical system at the time of recording. It is a flowchart which shows the detail of a recording process. It is a timing chart at the time of recording. It is a schematic diagram explaining the mode of the hologram recording / reproducing apparatus at the time of reproduction | regeneration. It is a figure which shows the image data output to DMD at the time of reproduction | regeneration. It is a schematic diagram explaining the mode of the optical system at the time of reproduction | regeneration. It is a flowchart which shows the detail of a reproduction | regeneration process. It is a graph which shows transition of the laser output at the time of recording concerning a modification. It is a schematic diagram explaining the mode of the hologram recording / reproducing apparatus at the time of recording of a modification. It is a histogram explaining the quality determination in another modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Laser light source, 12 ... DMD, 14 ... Objective lens, 16 ... Hologram recording medium, 18 ... Condensing lens, 20 ... Light shielding plate, 22 ... Condensing lens, 24 ... Magnification adjustment lens, 26 ... Optical sensor, 30 ... Control unit, 30a ... driver, 30b ... encoder, 30c ... driver, 30d ... decoder, 30f ... microcomputer, 100 ... hologram recording / reproducing apparatus.

Claims (10)

In a hologram recording / reproducing apparatus for recording an interference pattern by irradiating light onto a hologram recording medium with a predetermined optical system,
Modulation means for modulating recording electronic data to be recorded into page data representing a two-dimensional binary image;
Shift means for relatively moving the optical system and the hologram recording medium;
Recording means for recording the interference pattern by irradiating recording reference light and recording signal light obtained by optical spatial modulation of the page data at each recording position of the hologram recording medium shifted by the shifting means; ,
The reproduction signal light as the diffracted light obtained by irradiating the interference reference light to the interference pattern at the time of reproduction of the hologram recording medium is imaged by the imaging element, and the recording means irradiates at each recording position Image pickup means for picking up an image by the image pickup device with a shutter opening time different from that at the time of reproduction of the medium light having the recording signal light transmitted or reflected by the hologram recording medium;
Determining means for determining pass / fail of each recording position based on the degree of coincidence between binary image data obtained by binarizing image data captured by the image capturing unit with the media light and the page data;
A hologram recording / reproducing apparatus, comprising: invalidating means for invalidating the interference pattern at the recording position where the judging means is judged to be defective. In a hologram recording apparatus for recording an interference pattern by irradiating a hologram recording medium with light by a predetermined optical system,
Modulation means for modulating recording electronic data to be recorded into page data representing a two-dimensional binary image;
Shift means for relatively moving the optical system and the hologram recording medium;
Recording means for recording the interference pattern by irradiating recording reference light and recording signal light obtained by optical spatial modulation of the page data at each recording position of the hologram recording medium shifted by the shifting means; ,
An image pickup means for picking up an image of the medium light transmitted or reflected by the hologram recording medium with the recording signal light emitted by the recording means at each recording position;
Determination means for determining pass / fail of each recording position based on image data obtained by imaging the media light by the imaging means;
A hologram recording apparatus comprising: invalidating means for invalidating the interference pattern at the recording position where the determining means is determined to be defective.   The hologram recording apparatus according to claim 2, wherein the determination unit performs the quality determination based on luminance information of the image data.   3. The hologram recording apparatus according to claim 2, wherein the determination unit performs the pass / fail determination based on a degree of coincidence between the binarized image data obtained by binarizing the image data and the page data.   3. The determination unit according to claim 2, wherein the determination unit performs the pass / fail determination based on demodulated electronic data obtained by demodulating binarized image data obtained by binarizing the image data into electronic data. Hologram recording device.   6. The hologram recording apparatus according to claim 5, wherein the determination unit performs the pass / fail determination based on a degree of coincidence between the demodulated electronic data and the recorded electronic data.   3. The hologram recording apparatus according to claim 2, wherein the imaging unit performs imaging for a predetermined period from the start of irradiation in which the recording unit irradiates the recording reference light and the recording signal light at each recording position. . The imaging means is
At the time of reproduction of the hologram recording medium, the reproduction signal light as diffracted light obtained by irradiating the interference reference light to the interference pattern is imaged by the imaging element, and
8. The imaging condition according to claim 2, wherein the imaging condition is different between when the media light is imaged by the imaging element and when the reproduction signal light is imaged by the imaging element. The hologram recording apparatus according to item. The imaging means is
9. The hologram recording apparatus according to claim 8, wherein the shutter opening time is different between when the media light is picked up by the image pickup device and when the reproduction signal light is picked up by the image pickup device. The imaging means is
At the time of reproduction of the hologram recording medium, the reproduction signal light as diffracted light obtained by irradiating the interference reference light to the interference pattern is imaged by the imaging element, and
The recording means is
8. The intensity of the recording signal light is made different between a period in which the media light is imaged by the image sensor and a recording period other than that period. 8. Hologram recording device.