JP4154365B2 - Information reproducing apparatus and information reproducing method - Google Patents

Description

  The present invention relates to an information reproducing apparatus and information reproducing method for reproducing information recorded as a hologram on a recording medium.

  Conventionally, an optical information recording apparatus is known as an information recording apparatus capable of recording large-capacity data such as a high-density image. As optical information recording devices, magneto-optical information recording devices, optical phase change information recording devices, CD-Rs, and the like have been put into practical use, and demands for increasing the amount of information recorded on optical recording media are still increasing. It is.

  In order to realize such high-capacity optical information recording, a hologram type optical information recording apparatus using holography, particularly digital volume holography has been proposed.

  A hologram type optical information recording apparatus is generally an apparatus that superimposes information light provided with information as a two-dimensional pattern and reference light inside an optical recording medium and records information as an interference pattern.

  For example, Horime et al. Disclose a technique capable of accurately reproducing information by a reflective polarization coaxial interference method (see, for example, Patent Document 1).

  When the recorded information is played back, only the reference light is irradiated to the area where the information inside the optical recording medium is recorded with the same spatial arrangement as during recording, so that the information light is given as diffracted light from the interference pattern. Information can be obtained as a reproduced image.

  In particular, in a hologram type optical information recording apparatus using digital volume holography, the diffraction direction is increased by actively utilizing the thickness direction of the optical information recording medium to record the interference pattern in three dimensions, thereby increasing the inside of the optical information recording medium. In the same area, multiple recording is possible, and the recording capacity can be increased.

JP 2002-123949 A

  An optical recording apparatus using holography applies a two-dimensional pattern information to recording light and records it on an optical recording medium. At the time of reproduction, information is extracted as a two-dimensional image. Thus, since information can be recorded and reproduced two-dimensionally, there is an advantage that information can be input and output at high speed.

  However, in order to take advantage of this advantage, it is essential to have a method for two-dimensionally modulating information light with high contrast and a method for accurately processing a two-dimensional image obtained as a reproduced image and converting it into digital data. It is.

  Currently, CCD image sensors, CMOS image sensors, and the like are known as photodetectors used for reproduction in optical recording apparatuses using holography. When converting a two-dimensional image obtained by these photodetectors into digital data, generally, a histogram of the horizontal axis brightness and the vertical axis pixel number is created for the two-dimensional image. Thereafter, a predetermined lightness is set as a threshold value, and a calculation is performed such that a pixel having a lightness value equal to or higher than the threshold value is determined as “1”, and a pixel having a lightness value equal to or lower than the threshold value is determined as “0”.

  However, originally, recording light (information light and reference light) and reproduction light have a lightness distribution such that the central part is bright and the peripheral part is dark in the cross section of the beam. For this reason, the spread occurs when the histogram is created. Furthermore, when a threshold value is set for lightness and “1” and “0” of data are determined, there is a problem that reading errors frequently occur.

  In addition, in an optical recording medium using holography, information is recorded and reproduced by utilizing light interference. However, the recording medium and the recording / reproducing apparatus have different optical characteristics for each individual. Therefore, the value of the light interference varies due to the characteristics of the recording medium and the recording / reproducing apparatus. This is a big problem when considering portability and compatibility.

  The present invention has been made in view of the above, and an object of the present invention is to provide an information reproducing apparatus and an information reproducing method capable of efficiently obtaining a reproduced image with higher accuracy.

In order to solve the above-described problems and achieve the object, the present invention is an information reproducing apparatus for reproducing information recorded as a hologram on a recording medium, and irradiates reproduction light for reading the information from the recording medium Among the reproduction lights irradiated by the reproduction light irradiation means, the diffracted light receiving means for receiving the diffracted light diffracted by the hologram formed on the recording medium, and the reproduction light, The information is reproduced based on the transmitted light receiving means for receiving the transmitted light transmitted through the recording medium, the diffracted light received by the diffracted light receiving means, and the transmitted light received by the transmitted light receiving means. reproducing means, and the light intensity of the diffracted light which the diffracted light receiving means has received, a second arithmetic means for the transmitted light receiving unit calculates the sum of the light intensity of the transmitted light received, the second arithmetic And 3rd calculating means for correcting a light intensity value of at least one of the light intensity of the diffracted light and the light intensity of the transmitted light based on the sum of the light intensities obtained by the stage, and the reproducing means The information is reproduced based on the light intensity corrected by the third calculating means .

The present invention also provides an information reproducing apparatus for reproducing information recorded as a hologram on a recording medium, the reproducing light irradiating means for irradiating the reproducing light for reading the information from the recording medium, and the reproducing light irradiating means. Receiving the diffracted light receiving means for receiving the diffracted light diffracted by the hologram formed on the recording medium, and the transmitted light transmitted through the recording medium among the reproduced light. a transmitted light receiving unit, and reproducing means for the light intensity of the diffracted light the diffracted light receiving means has received, on the basis of the light intensity of the transmitted light which the transmitted light receiving unit has received, to reproduce the information, wherein First calculation means for calculating a difference between the light intensity of the diffracted light received by the diffracted light receiving means and the light intensity of the transmitted light received by the transmitted light receiving means, and the first light received by the diffracted light receiving means Second computing means for calculating the sum of the light intensity of the folded light and the transmitted light received by the transmitted light receiving means; and the second computing means based on the sum of the light intensities obtained by the second computing means. 4th calculating means for correcting the difference value of the light intensity obtained by one calculating means, and the reproducing means reproduces information based on the difference in light intensity corrected by the fourth calculating means. characterized in that it.

  Since the information reproducing apparatus and the information reproducing method according to the present invention use not only diffracted light but also transmitted light, there is an effect that a reproduced image with higher accuracy can be obtained efficiently.

  Embodiments of an information reproducing apparatus and an information reproducing method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a diagram for explaining a process of recording information on the optical recording medium 1 in the optical recording / reproducing apparatus according to the first embodiment. Here, the optical recording / reproducing apparatus corresponds to the information reproducing apparatus described in the claims. The optical recording / reproducing apparatus according to the first embodiment records information on the optical recording medium 1 by the reflective coaxial interferometry.

  As shown in FIG. 1, information light 110 and reference light 120 are irradiated onto the optical recording medium 1 from a direction that is symmetrical with respect to the plane of the optical recording medium 1. Thereby, the reflection type hologram 200 is formed. When information light that has been spatially information-modulated and reference light (in particular, a plane wave or a spherical wave that is not information-modulated) are simultaneously irradiated onto the optical recording medium 1, the information light and the reference light in the optical recording medium 1 interfere with each other. An optical change occurs in the portion where the light intensity is strengthened. This optical change is recorded three-dimensionally on the optical recording medium 1 as an interference pattern according to the information signal. According to this method, a plurality of interference patterns can be recorded in a multiple manner on the same area of the optical recording medium 1.

  FIG. 2 is a diagram for explaining the process of reproducing the information. By transmitting only the reference light 120 at the time of reproduction, the transmitted light 130 and the diffracted light 140 are obtained.

  Specifically, the light irradiated to the position where the hologram 200 is formed in the reference light 120 is diffracted by the hologram 200 and emitted from the optical recording medium 1 as the diffracted light 140. On the other hand, the light irradiated to the position where the hologram 200 is not formed in the reference light 120 is transmitted through the optical recording medium 1 as transmitted light 130 without being diffracted.

  The optical recording / reproducing apparatus according to the first embodiment reads information based on the transmitted light 130 and the diffracted light 140. This process will be described with reference to FIGS. 3, 4-1 and 4-2.

  FIG. 3 shows an outline of the modulation pattern 25 applied to the information light 110 irradiated to the optical recording medium 1. FIGS. 4A and 4B schematically show a diffraction image 26 and a transmission image 27 obtained with respect to the modulation pattern 25 shown in FIG.

  The modulation pattern 25 shown in FIG. 3 includes bright pixels 28 and dark pixels 29. Reference numeral 30 denotes a beam contour of the information beam 110 or the reference beam 120.

  In hologram recording using the reflective coaxial interferometry, the information beam 110 and the reference beam 120 are incident on the optical recording medium 1 in contrast. Further, the transmitted light 130 and the diffracted light 140 are emitted to the optical recording medium 1 in contrast. Therefore, as shown in FIGS. 4A and 4B, the bright part 31a in the diffraction image 26 becomes the dark part 31b in the transmission image 27, and the dark part 32a in the diffraction image 26 becomes the bright part 32b in the transmission image 27. That is, the diffraction image 26 and the transmission image 27 are in a positive / negative relationship.

  The optical recording / reproducing apparatus according to the first embodiment performs data discrimination using both the light intensity distribution of the diffraction image 26 and the light intensity distribution of the transmission image 27. Specifically, the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27 is calculated. Then, the light intensity of the diffraction image 26 is divided by the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27. A threshold value is set for the result thus obtained to discriminate between a bright part and a dark part.

  Similarly, the light intensity of the transmission image 27 may be divided by the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27. Also in this case, a threshold value is set for the result obtained thereby to discriminate between a bright part and a dark part.

  FIG. 5A is a graph showing the light intensity distribution on the straight line 41 passing through the beam center 42 in the diffraction image 26 shown in FIG. 4A. FIG. 5B is a graph showing the light intensity distribution on the straight line 43 passing through the beam center 44 in the transmission image 27 shown in FIG.

  From the respective graphs shown in FIGS. 5A and 5B, it can be seen that the light intensity increases as the distance from the beam center increases in both the diffraction image 26 and the transmission image 27.

  FIG. 6 is a graph showing the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27. When the modulation pattern irradiated by the diffraction image 26 and the transmission image 27 is accurately reproduced, the sum of these light intensities is expected to show a constant value.

  On the other hand, as shown in FIG. 6, the light intensity tends to increase as it approaches the beam center. Such a tendency of light intensity is presumed to reflect the light intensity distribution of the reference light 120 irradiated when reproducing information. That is, it is estimated that a more accurate pattern can be obtained by removing the influence of the reference beam 120.

  FIG. 7A is a graph showing the result of dividing the light intensity of the diffraction image 26 by the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27. FIG. 7B is a graph showing the result of dividing the light intensity of the transmission image 27 by the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27.

  Thus, by dividing the light intensity of the diffracted image 26 by the sum of the light intensity of the diffracted image 26 and the light intensity of the transmitted image 27, the diffracted image 26 from which the influence of the light intensity of the reference light 120 is removed is obtained. Can do. Similarly, by dividing the light intensity of the transmission image 27 by the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27, the transmission image 27 is obtained by removing the influence of the light intensity of the reference light 120 and the like. be able to.

  In the first embodiment, as described above, a threshold is set for the diffracted light or the transmitted light after the influence of the light intensity of the reference light 120 is removed, and the bright part and the dark part are discriminated based on the threshold. I do. Accordingly, reading errors due to the influence of light intensity and the like can be reduced.

  Conventionally, the transmitted image 27 is not used, and the bright and dark portions of the pattern are discriminated using only the diffraction image 26. Specifically, as shown in FIG. 8, a certain threshold value 50 is set. Then, the bright part and the dark part of the pattern recorded as information are determined with the threshold value 50 as a boundary.

  However, as described above, the recorded information pattern changes due to the influence of the apparatus and the influence of the measurement environment, for example, the light intensity is stronger as it is closer to the beam center. For this reason, a mismatch between the written information pattern and the reproduced information pattern occurs. That is, there is a problem that reading errors frequently occur, such as being a dark part, although it is a part corresponding to a bright pixel.

  In hologram recording / reproduction, disturbance of light in the optical element or the optical recording medium is reflected in the hologram. For this reason, when the optical recording medium 1 is once removed and then attached and reproduced, the position of the optical recording medium 1 is shifted, so that the light intensity changes due to the influence of the positional shift, and reading errors frequently occur. was there.

  On the other hand, in the first embodiment, such an error in light intensity can be corrected, so that information recorded on the recording medium can be reproduced with higher accuracy. Further, it is possible to correct a change in light intensity caused by characteristics of the recording medium or the like. Therefore, the optical recording / reproducing apparatus according to the present embodiment is excellent in portability and compatibility between apparatuses.

  Next, the optical recording medium 1 according to the first embodiment will be described in detail with reference to FIG. FIG. 9 shows an optical recording medium 1 formed in a disk shape. The optical recording medium 1 according to the first embodiment is optically recorded and reproduced by the reflective coaxial interferometry.

  The optical recording medium 1 has a transparent substrate 4 formed of glass, polycarbonate or the like. Further, the recording layer 3 is provided on the main surface of the transparent substrate 4 and the reflective layer 5 is provided on the other main surface. Further, a protective layer 2 is provided on the light incident side of the recording layer 3. The protective layer 2 may not be provided depending on the usage environment of the optical recording medium 1.

  The recording layer 3 is formed of a material whose optical characteristics such as an extinction coefficient and a refractive index change according to its intensity when irradiated with electromagnetic waves. The hologram recording material used for the recording layer 3 may be an organic material. Moreover, an inorganic material may be sufficient.

  Examples of the organic material include a photopolymer, a photorefractive polymer, a photochromic dye dispersion polymer, and the like. Examples of the inorganic material include lithium niobate and barium titanate.

  The reflective layer 5 is made of a material having a high reflectance at the recording light wavelength, such as aluminum.

  The recording light irradiated on the optical recording medium 1 by the objective lens 7 is reflected on the surface of the reflective layer 5 and forms a reflection type hologram 200 by interference between the incident light and the reflected light.

  The optical recording medium 1 according to the first embodiment is provided in a disc shape, but the shape of the optical recording medium 1 is not limited to the present embodiment, and may be a card shape, a block shape, or the like. There may be.

  Next, an optical recording / reproducing apparatus using reflective polarization coaxial holography will be described. In the conventional reflective coaxial holography, when the reference light is irradiated during reproduction, the diffracted light as the reproduced light and the remaining transmitted light that has been diffracted are coaxially incident on the photodetector, so that the signal-to-noise ratio is poor and reproduction is performed. There was a problem that it was difficult. Such a problem can be solved by the reflective polarization coaxial interference system. (For details, refer to JP 2002-123949 A).

  FIG. 10 is a schematic diagram of an optical recording / reproducing apparatus 100 using the reflective polarization coaxial interferometry. As the light source device 8, a laser that outputs linearly polarized light is desirable because of coherence or the like. Specific examples of the laser include a semiconductor laser, a He—Ne laser, an argon laser, and a YAG laser. The beam expander 9 is installed so that the light emitted from the light source device 8 is expanded and emitted as a parallel light beam.

  The optical rotatory optical element 10 rotates the light emitted from the beam expander 9 to generate light including an S-polarized component and a P-polarized component. The optical rotatory optical element 10 is, for example, a half-wave plate or a quarter-wave plate. Of the light transmitted through the optical rotatory optical element 10, the P-polarized component passes through the polarization beam splitter 11 and becomes information light. The S-polarized component is reflected by the polarization beam splitter 11 and becomes reference light.

  The information light transmitted through the polarization beam splitter 11 passes through the electromagnetic shutter 12 and the polarization beam splitter 13 and then enters the reflective spatial light modulator 14. The reflective spatial light modulator 14 has a plurality of pixels arranged two-dimensionally in a lattice shape. The reflective spatial light modulator 14 imparts information to the information light as a two-dimensional pattern by polarizing the reflected light for each pixel to be P-polarized light or S-polarized light.

  The information light reflected by the reflective spatial light modulator 14 is incident on the beam splitter 13 again. The information light is reflected by the polarization beam splitter 13 in accordance with the polarization modulation pattern provided by the reflective spatial light modulator 14. Thereby, intensity modulation is performed two-dimensionally.

  Information light reflected by the polarization beam splitter 13 is rotated in its polarization direction by the half-wave plate 15. Thereafter, the light passes through the polarization beam splitter 16 and enters the optical element 17 for split optical rotation. The information light incident on the two-part optical rotatory optical element 17 is rotated by + 45 ° for the half polarization direction of the light beam and by −45 ° for the other half polarization direction. Thereafter, the optical recording medium 1 is irradiated by the objective lens 7 and condensed on the surface of the reflective layer 5 of the optical recording medium 1 so that the beam diameter is minimized.

  On the other hand, the reference light reflected by the polarizing beam splitter 11 passes through the electromagnetic shutter 18 and is then reflected by the polarizing beam splitter 19. The reference light reflected by the polarizing beam splitter 19 passes through the half-wave plate 20 and is reflected by the polarizing beam splitter 16 and enters the optical element 17 for two-part optical rotation. The reference light incident on the two-part optical rotatory optical element 17 has its polarization direction half rotated by + 45 ° and the other half polarization direction rotated by −45 °. Thereafter, like the information light, the optical recording medium 1 is irradiated by the objective lens 7 and condensed on the surface of the reflection layer 5 of the optical recording medium 1 so that the beam diameter is minimized.

  As described above, the information light and the reference light are irradiated onto the optical recording medium 1 through the optical element 17 for two-part optical rotation so that the reflected information light, the reference light, and the reference light are reflected inside the recording layer 3. The light and the information light are in the same polarization direction, and the reflection hologram 200 is formed on the optical recording medium 1.

  When reproducing the recorded information, the information light is blocked by closing the electromagnetic shutter 12. Then, the hologram 200 recorded on the optical recording medium 1 is irradiated with only the reference light. Part of the reference light enters the optical recording medium 1 and is diffracted by the hologram 200 to become diffracted light.

  The diffracted light passes through the optical element 17 for two-part optical rotation, then is reflected by the polarization beam splitter 16, and the polarized light is rotated by the half-wave plate 20. Further, a part of the light passes through the polarization beam splitter 19 and is imaged as a diffraction image on the two-dimensional photodetector 22 by the imaging lens 21.

  Further, the transmitted light that has not been diffracted by the hologram 200 is transmitted again through the two-split optical rotatory optical element 17, and as a result, the polarization direction is rotated by 90 ° and transmitted through the polarizing beam splitter 16. Therefore, the transmitted light does not enter the two-dimensional photodetector 22. Further, the polarization direction is rotated by the half-wave plate 15 and is incident on the secondary photodetector 24. Thereby, the transmitted light and the diffracted light can be completely separated.

  The calculation described with reference to FIGS. 5A to 8 is performed on the light intensity distribution detected by the two-dimensional detector 22 and the light intensity distribution detected by the two-dimensional detector 24. Then, the light intensity obtained as a result of the calculation is converted into an electric signal, thereby reproducing the information.

(Embodiment 2)
Next, FIG. 11 for explaining the optical recording / reproducing apparatus according to the second embodiment is a diagram for explaining a process of recording information on the optical recording medium 41 in the optical recording / reproducing apparatus according to the second embodiment. It is.

  The optical recording / reproducing apparatus according to the second embodiment records information on the optical recording medium 41 by the transmission type two-beam interference method. In hologram recording using the transmission type two-beam interference method, it is possible to configure the diffraction image and the transmission image to have a positive / negative relationship, similar to the reflection type polarization coaxial holography described in the first embodiment. is there.

  As shown in FIG. 11, the optical recording medium 41 is irradiated with information light 110 and reference light 120 from different directions. Thereby, the transmission hologram 300 is formed.

  FIG. 12 is a diagram for explaining a process of reproducing information in the optical recording / reproducing apparatus according to the second embodiment. During reproduction, the transmitted light 130 and the diffracted light 140 are obtained by irradiating the optical recording medium 41 only with the reference light 120.

  Specifically, the light irradiated to the position where the hologram 300 is formed in the reference light 120 is diffracted by the hologram 300 and emitted from the optical recording medium 1 as the diffracted light 140. On the other hand, light irradiated to a position where the hologram 300 is not formed in the reference light 120 passes through the optical recording medium 41 as transmitted light 130 without being diffracted.

  Note that the process of reading information in the optical reproduction recording apparatus according to the second embodiment is the same as the process of reading information in the optical reproduction recording apparatus according to the first embodiment, and a description thereof will be omitted.

  Next, the optical recording medium 41 according to the second embodiment will be described in detail with reference to FIG. FIG. 13 shows an optical recording medium 41 formed in a disk shape.

  The transmissive optical recording medium 41 includes a transparent substrate 4 formed of glass, polycarbonate or the like. Further, the recording layer 3 is provided on the main surface of the transparent substrate 4. Further, a protective layer 2 is provided on the main surface of the recording layer 3. The protective layer 2 may not be provided depending on the usage environment of the optical recording medium 1. The recording layer 3 is formed of the same material as the recording layer 3 in the optical recording medium 1 according to the first embodiment.

  FIG. 14 is a schematic diagram of a transmissive optical recording / reproducing apparatus 102. The light source device 8 is preferably a laser that outputs linearly polarized light. The beam expander 9 expands the emitted light from the light source device 8 and emits it as a parallel light beam. The optical rotatory optical element 10 rotates the light emitted from the beam expander 9 to generate light including an S-polarized component and a P-polarized component.

  The optical rotatory optical element 10 is, for example, a half-wave plate or a quarter-wave plate. Of the light transmitted through the optical rotatory optical element 10, the P-polarized component is transmitted through the polarizing beam splitter 11 to become information light, and the S-polarized component is reflected by the polarizing beam splitter 11 to become reference light.

  The information light transmitted through the polarization beam splitter 11 passes through the electromagnetic shutter 12 and the polarization beam splitter 13 and then enters the reflective spatial light modulator 14. The reflective spatial light modulator 14 has a plurality of pixels arranged two-dimensionally in a lattice shape. The reflective spatial light modulator 14 imparts information to the information light as a two-dimensional pattern by polarizing the reflected light for each pixel to make it P-polarized light or S-polarized light.

  The information light reflected by the reflective spatial light modulator 14 is incident on the beam splitter 13 again. The information light is reflected by the polarization beam splitter 13 in accordance with the polarization modulation pattern provided by the reflective spatial light modulator 14. Thereby, intensity modulation is performed two-dimensionally. The information light reflected by the polarization beam splitter 13 is applied to the transmission optical recording medium 41 by the objective lens 33.

  On the other hand, the reference light reflected by the polarization beam splitter 11 passes through the electromagnetic shutter 18, is reflected by the mirror 36, and is irradiated by the objective lens 37 so as to overlap the information light in the recording layer of the transmissive optical recording medium 41. .

  When reproducing the recorded information, the information light is blocked by closing the electromagnetic shutter 12, and only the reference light is irradiated on the hologram recorded on the transmission type optical recording medium 41. A part of the reference light is diffracted by the recorded hologram and becomes diffracted light toward the imaging lens 34 when passing through the transmissive optical recording medium 41. The diffracted light is imaged as a diffracted image on the two-dimensional photodetector 35 by the imaging lens 34.

  On the other hand, of the reference light irradiated to the transmission type optical recording medium 41 during reproduction, the transmitted light that has not been diffracted by the hologram is formed as a transmission image on the two-dimensional photodetector 39 by the imaging lens 38.

  From the viewpoint of positive and negative relation between the diffraction image obtained by the two-dimensional photodetector 35 and the transmission image obtained by the two-dimensional photodetector 39 in hologram recording using the transmission type two-beam interference method, information light It is desirable for the reference light and the reference light to be incident as light having a symmetrical wavefront curvature.

  Further, from the viewpoint of making the reproduced image and the transmitted image have a positive / negative relationship, in the optical recording / reproducing apparatus 102 according to the second embodiment shown in FIG. 14, the objective lens 33 and the objective lens 37 have the same shape. It is desirable. In order to make the diffraction image and the transmission image have the same size in the imaging optical system, it is desirable that the imaging lens 34 and the imaging lens 38 have the same shape. Furthermore, when the thickness of the optical recording medium 1 is large, the relationship between positive and negative is not symmetric. Accordingly, it is desirable that the optical recording medium 1 be provided with a thickness that allows a positive / negative relationship to be formed.

  The diffraction image and the transmission image obtained in the optical recording / reproducing apparatus 102 according to the second embodiment are positive and negative in the same manner as described with reference to FIGS. 4A and 4B in the first embodiment. It has become.

  Note that, in any of the reflection type coaxial interference method and the transmission type two-beam interference method, the diffraction image and the transmission image may not be exactly positive or negative depending on the arrangement of the optical element and the optical recording medium. However, in this case, a positive / negative relationship may be obtained by arbitrarily rotating, inverting, enlarging, and reducing the transmission image.

  As described above, a control function for adjusting the relationship between positive and negative may be provided, and as another example, the relationship between positive and negative may be set during manufacturing.

  As described above, the present invention has been described using the embodiment, but various changes or improvements can be added to the above embodiment.

  As such a first modification, information may be calculated based on the difference in light intensity between the diffraction image 26 and the transmission image 27. FIG. 15 is a graph showing the difference in light intensity between the diffraction image 26 and the transmission image 27. Thus, by taking the difference in light intensity between the diffracted image 26 and the transmitted image 27, the difference in light intensity between the bright part and the dark part can be increased. That is, the contrast in the bright part and the dark part can be increased. Also, by taking the difference, the influence of the error can be reduced. Therefore, as shown in FIG. 15, by reproducing information based on the light intensity obtained as the difference in light intensity between the diffraction image 26 and the transmission image 27, the information can be reproduced with higher accuracy.

  Furthermore, as a second modification, the difference between the light intensities of the diffraction image 26 and the transmission image 27 may be divided by the sum of the light intensities of the diffraction image 26 and the transmission image 27. FIG. 16 is a graph showing the result of dividing the difference in light intensity between the diffraction image 26 and the transmission image 27 by the sum of the light intensity of the diffraction image 26 and the transmission image 27.

  As shown in FIG. 16, the difference in light intensity between the diffracted image 26 and the transmitted image 27 is further divided by the sum of the light intensities of the diffracted image 26 and the transmitted image 27, thereby eliminating the influence of the light intensity of the reference light 120 and the like. High light intensity can be obtained. Therefore, information can be reproduced more accurately by reproducing information using this light intensity.

  When the light intensity obtained as a difference between the light intensities of the diffraction image 26 and the transmission image 27 includes a negative value, the light intensity obtained as the difference is translated so that all of the light intensity becomes a positive value. May be. In this case, the light intensity after the parallel movement is divided by the sum of the light intensities of the diffraction image 26 and the transmission image 27. As a result, even when the light intensity obtained as the difference in light intensity between the diffraction image 26 and the transmission image 27 includes a negative value, the difference between the light intensity and the sum of the light intensities can be used for more accuracy. Information can be reproduced well.

  As described above, the obtained diffracted light and transmitted light may be corrected based on both diffracted light and transmitted light, and the calculation method used for this purpose is not limited to the present embodiment.

  As a third modified example, in this embodiment, adjustment is performed so that the relationship between positive and negative is accurately maintained. However, in order to obtain a reproduced image and a transmitted image, the positive and negative are not necessarily obtained. It is not necessary to make adjustments so that the relationship is accurately maintained.

1. Production of Optical Recording Medium In Example 1, the reflective optical recording medium 1 according to the first embodiment shown in FIG. 1 was produced by the following method. First, 3.86 g vinyl carbazole and 2.22 g vinyl pyrrolidone were mixed. Next, 0.19 g of Irgacure 784 (Ciba Specialty Chemicals) was added and stirred.

  After all was dissolved, 0.04 g of perbutyl H (manufactured by NOF Corporation) was mixed to prepare monomer solution A. Next, 10.1 g of 1,4-butanediol diglycidyl ether and 3.6 g of diethylenetriamine were mixed to prepare an epoxy solution B. An optical recording medium precursor was prepared by mixing 1.5 ml of A monomer solution and 8.5 ml of B epoxy solution and degassing.

  Next, a square quartz glass substrate 4 having a thickness of 0.5 mm and a side of 5 cm was prepared. An aluminum layer having a thickness of 200 nm is formed as a reflective layer 5 on one surface of the glass substrate 4 by sputtering. A spacer made of a fluororesin and having a thickness of 250 μm was placed on the surface of the prepared quartz glass substrate 4 opposite to the aluminum layer 5. In the meantime, the mixed solution was cast.

  After casting, a separately prepared quartz glass substrate 2 was placed oppositely, and further the uniform solution was applied to stretch the mixed solution to a thickness of 250 μm. Finally, it was heated at 50 ° C. for 10 hours to produce an optical recording medium 1 having a recording area with a thickness of 250 μm. In the optical recording medium 1 produced in this example, the upper quartz glass substrate forms the protective layer 2.

  In this embodiment, a series of operations were performed in a room where light shorter than a wavelength of 600 nm was shielded so that the recording area was not exposed.

2. Recording of Information Next, the optical recording medium 1 manufactured by the above method was mounted on the reflection type optical recording / reproducing apparatus 100 shown in FIG. 10, and information was actually recorded.

  As the coherent light output from the light source 8, the second harmonic (wavelength: 532 nm) of a neodymium YAG laser was used. A half wave plate was used as the optical element 10 for optical rotation. A liquid crystal light modulator was used as the reflective spatial light modulator 14.

  Further, the direction of the half-wave plate used as the optical rotatory optical element 10 was adjusted so that the information light and the reference light had the same intensity on the surface of the optical recording medium 1. Furthermore, here, the light intensity of the information light and the reference light on the surface of the optical recording medium 1 is both 0.1 mW.

  In this case, the spot size of the laser beam on the upper surface of the recording layer 3 was 500 μm. As the liquid crystal light modulator 14, an area of 150 × 150 22500 pixels was used, and as shown in FIG. 17, adjacent 3 × 3 9 pixels were used as unit panels, and a total of 2500 panels were used. As the input of information, a 9: 5 modulation method was used in which 5 out of 9 3 × 3 panels were bright panels (transmitting light).

3. Reproduction of information Next, the information recorded on the optical recording medium 1 by the above-described method was read using the recording / reproducing apparatus 100 shown in FIG. At the time of reading, the orientation of the half-wave plate used as the optical rotatory optical element 10 was adjusted. Specifically, the intensity of the reference light on the surface of the optical recording medium 1 was 0.02 mW. As the two-dimensional photodetectors 22 and 24, CCD arrays were used.

4). Discrimination of information Next, the recording / reproducing performance of the optical recording / reproducing apparatus was evaluated by the following method. Using the diffraction image and transmission image obtained by the method of “3. Reproduction of information”, the following calculation (Equation 1) was performed for each pixel obtained by the CCD.
Reconstructed image intensity after calculation = Diffraction image intensity / (Diffraction image intensity + Transmission image intensity) (Equation 1)

FIG. 18 shows a histogram showing the relationship between the post-computation reproduced image intensity of each pixel and the number of pixels obtained by (Equation 1).

As shown in FIG. 18 , a threshold was set between the peaks of the number of pixels. The light panel and the dark panel were discriminated on the basis of the threshold. Then, the output patterns of the bright panel and the dark panel determined by the threshold and the pattern input to the liquid crystal light modulator 14 were compared. As a result, the number of panels that caused a discrimination error was 0 out of 2500 panels.

(Comparative Example 1)
As Comparative Example 1, a reflective optical recording medium was produced by the same method as in Example 1, and information was recorded.

1. Information reproduction Next, the recorded information was reproduced. Reproduction was performed in the same manner as in Example 1, but only the CCD array 22 was used as the two-dimensional photodetector.

2. Discrimination of information Next, the recording / reproducing performance of the optical recording / reproducing apparatus was evaluated by the following method. Using only the diffraction image obtained from the CCD array 22, the output of each pixel by the CCD was obtained. FIG. 19 shows a histogram showing the relationship between the output of each pixel by the CCD and the number of pixels.

  Next, as shown in FIG. 19, a threshold value was set between the peaks of the number of pixels. Based on the threshold value, a bright panel and a dark panel were distinguished. That is, the output patterns of the bright panel and the dark panel determined by the threshold and the pattern input to the liquid crystal light modulator 14 were compared. As a result, 120 panels out of 2500 panels had a discrimination error.

  As described above, by using the transmission image in addition to the diffraction image for data discrimination, it is possible to read information with fewer errors than in the case of reading information from the diffraction image alone as in the prior art.

1. Production of Optical Recording Medium In this example, a transmissive optical recording medium 41 according to the second embodiment shown in FIG. 13 was produced by the following method.

  A mixed solution for forming a recording area was prepared by the same method as described in Example 1. Next, this mixed solution was cast between spacers having a thickness of 250 μm made of a fluororesin and placed on a square quartz glass substrate 4 having a thickness of 0.5 mm and a side of 5 cm as shown in FIG.

  After casting, a separately prepared quartz glass substrate 4 was placed oppositely, and a uniform pressure was further applied to stretch the mixed solution to a thickness of 250 μm. Finally, it was allowed to stand at room temperature for 24 hours to produce an optical recording medium 41 having a recording area with a thickness of 250 μm. In the optical recording medium prepared in this example, the upper quartz glass substrate forms the protective layer 2 shown in FIG.

  In this embodiment, a series of operations were performed in a room where light shorter than a wavelength of 600 nm was shielded so that the recording area was not exposed.

2. Recording of Information Next, the optical recording medium 41 manufactured by the above method was mounted on the transmission optical recording / reproducing apparatus 102 shown in FIG. 14, and information was actually recorded. Here, the second harmonic (wavelength: 532 nm) of a neodymium YAG laser was used as the coherent light output from the light source 8. A half wave plate was used as the optical element 10 for optical rotation. A liquid crystal light modulator was used as the reflective spatial light modulator 14.

  The direction of the half-wave plate used as the optical rotatory optical element 10 was adjusted so that the information light and the reference light had the same intensity on the surface of the optical recording medium 41. Furthermore, here, the light intensity of the information light and the reference light on the surface of the optical recording medium 41 is both 0.1 mW. In this case, the spot size of the laser beam on the upper surface of the recording layer 3 was 2 mm.

  As the liquid crystal light modulator 14, an area of 150 × 150 22500 pixels was used, and adjacent 3 × 3 9 pixels were used as a unit panel, and a total of 2500 panels were used. As the input of information, a 9: 5 modulation method was used in which 5 out of 9 3 × 3 panels were bright panels (transmitting light).

3. Reproduction of information Next, the information recorded on the optical recording medium 41 by the above method was read using the transmission type optical recording / reproducing apparatus 102 shown in FIG. At the time of this reading, the intensity of the reference light on the surface of the optical recording medium 41 was set to 0.02 mW by adjusting the direction of the half-wave plate used as the optical rotatory optical element 10. As the two-dimensional photodetectors 35 and 39, CCD arrays were used.

4). Discrimination of information Next, the recording / reproducing performance of the optical recording / reproducing apparatus was evaluated by the following method. Using the diffraction image and transmission image obtained by the method of “3. Reproduction of information” above, the calculation of (Equation 1) in Example 1 was performed on each pixel obtained by the CCD.

The results obtained after calculation diffraction image intensity calculation, setting the threshold value in the same manner as shown in FIG 8. Based on the threshold, a threshold is set for the calculated diffraction image intensity, and a bright panel and a dark panel are discriminated based on the threshold. Then, the output patterns of the bright panel and the dark panel determined by the threshold and the pattern input to the liquid crystal light modulator 14 were compared. As a result, the number of panels that caused a discrimination error was 0 out of 2500 panels.

(Comparative Example 2)
In this comparative example, a transmissive optical recording medium 41 was produced by the same method as in Example 2, and information was recorded.

1. Information reproduction Next, the recorded information was reproduced. Reproduction was performed in the same manner as in Example 1, but only the CCD array 35 was used as the two-dimensional photodetector.

2. Discrimination of information Next, the recording / reproducing performance of the optical recording / reproducing apparatus was evaluated by the following method. Using only the diffraction image obtained from the CCD array 35, a threshold value is set for the output of the CCD, and based on the threshold value, a light panel and a dark panel are discriminated to form an output pattern, and liquid crystal light modulation is performed. Comparison was made with the pattern input to the instrument 14. As a result, 25 of the 2500 panels were identified.

  As described above, it has been shown that even in transmission optical recording / reproduction, it is possible to read information with few errors by using a diffraction image and a transmission image for data discrimination.

  As described above, the information reproducing apparatus and the information reproducing method according to the present invention are useful for reading information recorded on an optical recording medium, and are particularly suitable for reading information with high accuracy.

FIG. 4 is a diagram for explaining a process of recording information on the optical recording medium 1 in the optical recording / reproducing apparatus according to the first embodiment. It is a figure for demonstrating the process which reproduces | regenerates the said information. 2 is a diagram showing an outline of a modulation pattern 25 applied to information light 110 irradiated on the optical recording medium 1. FIG. It is a figure which shows the outline of the diffraction image 26 obtained with respect to the modulation pattern 25 shown in FIG. It is a figure which shows the outline of the transmission image 27 obtained with respect to the modulation pattern 25 shown in FIG. It is a figure which shows the graph which shows the light intensity distribution on the straight line 41 which passes along the beam center 42 among the diffraction images 26 shown to FIGS. It is a figure which shows the graph which shows the light intensity distribution on the straight line 43 which passes along the beam center 44 among the transmission images 27 shown to FIGS. 4-2. FIG. 6 is a graph showing the sum of the light intensity of a diffraction image 26 and the light intensity of a transmission image 27. 6 is a graph showing a result of dividing the light intensity of a diffraction image 26 by the sum of the light intensity of the diffraction image 26 and the light intensity of a transmission image 27. FIG. FIG. 6 is a graph showing the result of dividing the light intensity of the transmission image 27 by the sum of the light intensity of the diffraction image 26 and the light intensity of the transmission image 27. It is a figure which shows the threshold value 50. FIG. 1 is a diagram showing an optical recording medium 1 according to a first embodiment. 1 is a schematic diagram of an optical recording / reproducing apparatus 100 using a reflective polarization coaxial interferometry. FIG. 10 is a diagram for explaining a process of recording information on an optical recording medium 41 in the optical recording / reproducing apparatus according to the second embodiment. FIG. 10 is a diagram for explaining a process of reproducing information in the optical recording / reproducing apparatus according to the second embodiment. FIG. 6 is a diagram illustrating an optical recording medium 41 according to a second embodiment. 1 is a schematic diagram of a transmissive optical recording / reproducing apparatus 102. FIG. It is a figure which shows the graph which shows the difference of the light intensity of the diffraction image 26 and the transmission image 27. FIG. 6 is a graph showing a result of dividing a difference in light intensity between a diffraction image 26 and a transmission image 27 by a sum of light intensity in the diffraction image 26 and the transmission image 27. FIG. It is a figure for demonstrating a unit panel. It is a figure which shows the histogram which shows the relationship between the reproduced image intensity | strength after a calculation, and the number of pixels. It is a figure which shows the histogram which shows the relationship between the output of each pixel by CCD, and the number of pixels.

Explanation of symbols

1,41 Optical recording medium 2 Protective layer 3 Recording layer 4 Transparent substrate 5 Reflective layer 7 Objective lens 8 Light source device 9 Beam expander 10 Optical element for optical rotation 11 Polarizing beam splitter 12 Electromagnetic shutter 13 Polarizing beam splitter 14 Reflective spatial light modulation Device 15 Half-wave plate 16 Polarizing beam splitter 17 Split optical rotation element 18 Electromagnetic shutter 19 Polarizing beam splitter 20 Half-wave plate 21 Imaging lens 22 Two-dimensional photodetector 25 Modulation pattern 26 Diffraction image 27 Transmission image 28 Bright pixel 29 Dark pixel 31 Dark part 33 Objective lens 34 Imaging lens 35 Two-dimensional photodetector 36 Mirror 37 Objective lens 38 Imaging lens 39 Two-dimensional photodetector 100, 102 Optical recording / reproducing apparatus 110 Information beam 120 Reference beam 130 Transmission Light 140 Diffracted light 200, 300 Hologram

Claims (6)

An information reproducing apparatus for reproducing information recorded as a hologram on a recording medium,
Reproduction light irradiating means for irradiating reproduction light for reading the information from the recording medium;
Of the reproduction light irradiated by the reproduction light irradiation means, diffracted light receiving means for receiving diffracted light diffracted by a hologram formed on the recording medium;
Of the reproduction light, transmitted light receiving means for receiving the transmitted light transmitted through the recording medium;
Reproducing means for reproducing the information based on the light intensity of the diffracted light received by the diffracted light receiving means and the light intensity of the transmitted light received by the transmitted light receiving means;
Second calculating means for calculating the sum of the light intensity of the diffracted light received by the diffracted light receiving means and the light intensity of the transmitted light received by the transmitted light receiving means;
Third calculating means for correcting the value of at least one of the light intensity of the diffracted light and the light intensity of the transmitted light based on the sum of the light intensities obtained by the second calculating means;
The information reproducing apparatus, wherein the reproducing means reproduces information based on the light intensity corrected by the third calculating means.   The third computing means divides at least one of the light intensity of the diffracted light and the light intensity of the transmitted light by the sum of the light intensities obtained by the second computing means. The information reproducing apparatus according to claim 1. An information reproducing apparatus for reproducing information recorded as a hologram on a recording medium,
Reproduction light irradiating means for irradiating reproduction light for reading the information from the recording medium;
Of the reproduction light irradiated by the reproduction light irradiation means, diffracted light receiving means for receiving diffracted light diffracted by a hologram formed on the recording medium;
Of the reproduction light, transmitted light receiving means for receiving the transmitted light transmitted through the recording medium;
Reproducing means for reproducing the information based on the light intensity of the diffracted light received by the diffracted light receiving means and the light intensity of the transmitted light received by the transmitted light receiving means;
First calculation means for calculating a difference between the light intensity of the diffracted light received by the diffracted light receiving means and the light intensity of the transmitted light received by the transmitted light receiving means;
Second calculating means for calculating the sum of the light intensity of the diffracted light received by the diffracted light receiving means and the light intensity of the transmitted light received by the transmitted light receiving means;
A fourth computing means for correcting the difference value of the light intensity obtained by the first computing means based on the sum of the light intensities obtained by the second computing means,
The information reproducing apparatus, wherein the reproducing means reproduces information based on the difference in light intensity corrected by the fourth calculating means. The fourth computing means divides the difference value of the light intensity obtained by the first computing means by the sum value of the light intensity obtained by the second computing means. Item 4. The information reproducing apparatus according to Item 3. Further comprising control means for controlling the diffracted light emitted from the recording medium and the transmitted light to have a negative-positive relationship,
5. The information reproduction according to claim 1, wherein the reproduction unit reproduces the information based on the diffracted light and the transmitted light after being processed by the control unit. apparatus. It said reproducing means, the information reproducing apparatus according to any one of claims 1 to 4, characterized in that for reproducing the information based on said diffracted light in the relationship of negative-positive and the transmitted light.

Images