Hologram reproduction method and apparatus

Abstract

A hologram reproduction method for reproducing a hologram from an optical recording medium in which the hologram is recorded by Fourier transforming a signal light, in which digital data is represented by an image of intensity distribution, and a reference light, and simultaneously irradiating the lights in a state in which a direct current component is removed from at least the Fourier transformed signal light onto the optical recording medium is provided. The method including: irradiating a read out reference light onto the optical recording medium, and generating a diffracted light from the recorded hologram; generating all or a part of a direct current component contained in a Fourier transformed image of the signal light; combining the diffracted light and the generated all or a part of the direct current component, and generating a combined beam; and reproducing the signal light by inverse-Fourier transforming the combined beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a diagram showing a schematic configuration of a hologram recording and reproduction apparatus according to a first and a fifth exemplary embodiment of the present invention;

FIG. 2 is a flowchart showing a processing routine of record/reproduction processing in the first exemplary embodiment;

FIG. 3 is a diagram showing a display image of a spatial light modulator at the time of record processing;

FIG. 4 is a diagram showing a display image of the spatial light modulator at the time of reproduction processing;

FIG. 5 is a flowchart showing a processing routine of record/reproduction processing in a second exemplary embodiment;

FIG. 6 is a diagram showing a schematic configuration of a hologram recording and reproduction apparatus according to a third and a sixth exemplary embodiment;

FIG. 7A is a diagram showing the configuration of a pixel block of a signal light having a high white proportion, FIG. 7B is a negative image of FIG. 7A, and FIG. 7C is a positive image of FIG. 7A;

FIG. 8A illustrates a pattern displayed on the spatial light modulator in the third and the sixth exemplary embodiment, and FIG. 8B illustrates a signal light pattern displayed at the center of the pattern in FIG. 8A;

FIG. 9A is a diagram expressing a reproduced image when a 0-order component is not added, and FIG. 9B is a diagram expressing a reproduced image when the 0-order component is added;

FIG. 10 is a diagram showing a schematic configuration of a hologram recording and reproduction apparatus according to a fourth exemplary embodiment;

FIG. 11 is a flowchart showing a processing routine of record/reproduction processing of the fifth exemplary embodiment;

FIG. 12A is a diagram showing a display image of the spatial light modulator when a first reproduced image is obtained, and FIG. 12B is a diagram showing a display image of the spatial light modulator when a second reproduced image is obtained;

FIG. 13A illustrates a first reproduced image obtained in the sixth exemplary embodiment, FIG. 13B illustrates a second reproduced image, and FIG. 13C illustrates an image after subtraction processing;

FIG. 14 is a diagram for explaining a decoding principle of digital data; and

FIGS. 15A and 15B are graphs showing results of computer experiments.

Claims

1. A hologram reproduction method for reproducing a hologram from an optical recording medium in which the hologram is recorded by Fourier transforming a signal light, in which digital data is represented by an image of intensity distribution, and a reference light, and simultaneously irradiating the lights in a state in which a direct current component is removed from at least the Fourier transformed signal light onto the optical recording medium, the method comprising: irradiating a read out reference light onto the optical recording medium, and generating a diffracted light from the recorded hologram;generating all or a part of a direct current component contained in a Fourier transformed image of the signal light;combining the diffracted light and the generated all or a part of the direct current component, and generating a combined beam; andreproducing the signal light by inverse-Fourier transforming the combined beam.

2. The hologram reproduction method according to claim 1, wherein the combining further comprises combining the diffracted light and the direct current component so as to increase the contrast of the intensity of the combined beam.

3. The hologram reproduction method according to claim 1, wherein the combining further comprises combining the diffracted light and the direct current component so that a phase θ of the direct current component and a phase φ of the diffracted light satisfy the following equation (1): 0≦|θ−φ|<π/2   Equation (1).

4. The hologram reproduction method according to claim 3, wherein the combining further comprises combining the diffracted light and the direct current component so that a phase θ of the direct current component and a phase φ of the diffracted light satisfy the following equation (2): |θ−φ|=0   Equation (2).

5. The hologram reproduction method according to claim 1, wherein the combining further comprises combining the diffracted light and the direct current component so that a phase θ of the direct current component and a phase φ of the diffracted light satisfy the following equation (3): π/2<|θ−φ|≦π  Equation (3).

6. The hologram reproduction method according to claim 5, wherein the combining further comprises combining the diffracted light and the direct current component so that a phase θ of the direct current component and a phase φ of the diffracted light satisfy the following equation (4): |θ−φ|=π  Equation (4)

7. The hologram reproduction method according to claim 1, wherein the generating of the combined beam further comprises combining the diffracted light and the direct current component of the signal light, and generating one or more combined beams;and the reproducing of the signal light further comprisesobtaining two types of image data by (a) detecting each of an inverse-Fourier transformed image of the diffracted light and the combined beam, or (b) detecting each of an inverse-Fourier transformed image of two types of combined beams; andsubtracting any one of the two types of image data from the other for each pixel of the image of intensity distribution.

8. The hologram reproduction method according to claim 7, further comprising decoding the digital data based on a value obtained by the subtraction.

9. The hologram reproduction method according to claim 7, wherein the generating of one more combined beams further comprises generating a first combined beam by combining the diffracted light and a first direct current component, and generating a second combined beam by combining the diffracted light and a second direct current component of a phase different from that of the first direct current component.

10. The hologram reproduction method according to claim 9, wherein a phase of the first direct current component and a phase of the second direct current component are made to be different, so that the first image data and the second image data become mutually reversed images.

11. The hologram reproduction method according to claim 8, wherein the decoding further comprises, when a 1 of the digital data corresponds to a light portion and a 0 of the digital data corresponds to a dark portion, determining a sign of a pixel for which the calculated difference is positive as a 1, and determining a sign of a pixel for which the calculated difference is negative as a 0.

12. A hologram reproduction apparatus for reproducing a hologram from an optical recording medium in which the hologram is recorded by Fourier transforming a signal light, in which digital data is represented by an image of intensity distribution, and a reference light, and simultaneously irradiating the lights in a state in which a direct current component is removed from at least the Fourier transformed signal light onto the optical recording medium, the apparatus comprising: an irradiating section that irradiates a read out reference light onto the optical recording medium on which the hologram is recorded;a generating section that generates all or a part of a direct current component contained in a Fourier transformed image of the signal light; andan optical system that inverse-Fourier transforms a combined beam of diffracted light, obtained by irradiating the read out reference light onto the optical recording medium, and the generated all or a part of the direct current component.

13. The hologram reproduction apparatus according to claim 12 further comprising: a combined beam generating section that generates a combined beam by combining the direct current component of the signal light with diffracted light diffracted by the recorded hologram;an image data obtaining section that obtains reproducing image data by detecting an inverse-Fourier transformed image of the diffracted light or the combined beam;a control section for controlling the irradiating section, the combined beam generating section, and the image data obtaining section, so as to irradiate the read out reference light onto the optical recording medium, generate the diffracted light from the recorded hologram, and combine the direct current component of signal light with the diffracted light to generate one or more combined beams, and obtain two types of image data by (a) detecting each of an inverse-Fourier transformed image of the diffracted light and the combined beam, or (b) detecting each of an inverse-Fourier transformed image of two types of the combined beams; anda computing section for subtracting any one of the two types of image data from the other for each pixel of the image of intensity distribution.

14. The hologram reproduction apparatus according to claim 13, further comprising a decoding section that decodes the digital data based on a value obtained by the subtraction by the computing section.

15. The hologram reproduction apparatus according to claim 12, wherein the combined beam is formed by combining the diffracted light and the direct current component so as to increase the contrast of the intensity of the combined beam.

16. The hologram reproduction apparatus according to claim 12, wherein the combined beam is formed by combining the diffracted light and the direct current component so that a phase θ of the direct current component and a phase φ of the diffracted light satisfy the following equation (1): 0≦|θ−φ|<π/2   Equation (1).

17. The hologram reproduction apparatus according to claim 12, wherein the combined beam is formed by combining the diffracted light and the direct current component so that a phase θ of the direct current component and a phase φ of the diffracted light satisfy the following equation (3): π/2<|θ−φ|≦π  Equation (3).

18. The hologram reproduction apparatus according to claim 13, wherein the control section controls the generating of the one more combined beams so as to generate a first combined beam by combining the diffracted light and a first direct current component, and generate a second combined beam by combining the diffracted light and a second direct current component of a phase different from that of the first direct current component.

19. The hologram reproduction apparatus according to claim 18, wherein the control section controls the phase of the first direct current component and the phase of the second direct current component to be different, so that the first image data and the second image data become mutually reversed images.

20. The hologram reproduction apparatus according to claim 14, wherein the decoding section determines, when a 1 of the digital data corresponds to a light portion and a 0 of the digital data corresponds to a dark portion, a sign of a pixel for which the calculated difference is positive as a 1, and a sign of a pixel for which the calculated difference is negative as a 0.