JP2009252303A - Optical reproducing method and optical reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical reproducing method and an optical reproducing apparatus by which two reproduced images corresponding to a positive image and a negative image can be obtained simultaneously from recorded one fourier transform hologram by reproducing operation of one time. <P>SOLUTION: The high order component of diffraction light diffracted from a hologram recorded in an optical recording medium can be separated into an S polarization component (S<SB>H</SB>) vibrating in a direction vertical to the progress direction of light (optical axis direction) and a P polarization component (P<SB>H</SB>) vibrating in a direction horizontal to the optical axis. In the same way, a given DC component can be separated into an S polarization component (S<SB>DC</SB>) and a P polarization component (P<SB>DC</SB>). The S polarization component (S<SB>H</SB>) of the high order component of the diffracted light and S polarization component (S<SB>DC</SB>) of the DC component have the same phase, and both are combined and the positive image is reproduced as a first reproduced image. The P polarization component (P<SB>H</SB>) of the high order component of the diffracted light and P polarization component (P<SB>DC</SB>) of the DC component have the opposite phase to each other, and both are combined and the negative image is reproduced as a second reproduced image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical reproduction method and an optical reproduction apparatus.

  In holographic data storage, a signal light pattern representing digital data per page as a bright and dark image is displayed on a spatial light modulator to generate signal light modulated for each pixel, and this signal light is converted into a lens. Is Fourier-transformed to irradiate the optical recording medium together with the reference light. Due to the interference between the signal light and the reference light, a Fourier transform hologram of a data page is recorded on the optical recording medium. For example, a plurality of pages of holograms can be multiplexed and recorded by various multiplexing methods such as an angle multiplexing method in which the incident angle of the reference light is changed.

  The present applicant takes two reconstructed images of a positive image and a negative image from the same hologram, and compares them to cancel the noise common to both of them, so that the SNR (signal-to-noise ratio) of the reconstructed image is obtained. Have proposed a “hologram reproduction method” (Patent Documents 1 and 2). By improving the SNR of the reproduced image, it is possible to increase the multiplicity and increase the amount of data per page, thereby realizing a high recording density. In addition, this reproduction method can be applied to both reproduction of a hologram recorded with the DC component removed and reproduction of a hologram recorded without removing the DC component.

  In these “hologram reproduction methods”, a photopolymer having the same phase of the intensity distribution of the interference fringes of the recording light and the refractive index distribution formed thereby is used as the hologram recording medium, and the reference light for reading is used as the recording medium. A positive image is reproduced by applying a direct current component having the same phase as that of the diffracted light to the diffracted light obtained from the hologram by irradiation. Further, a negative image is reproduced by adding a direct current component having a phase opposite to that of the diffracted light to the diffracted light obtained from the hologram. If the phase of the diffracted light is shifted by π / 2 from the phase of the reference light for reading, the phase of the direct current component to be applied is shifted by π / 2 with respect to the reference light, so that the diffracted light and the direct current component to be applied are in phase. Or it becomes an antiphase.

  Recently, a "coaxial recording method (collinear method)" has been proposed as a recording / reproducing method for a holographic memory. In this collinear method, the signal light and the reference light are generated by being modulated by the same spatial light modulator. The generated signal light and reference light are collected by the same lens as a common optical axis. Due to the interference between the signal light and the reference light, a hologram is recorded on the optical recording medium. By irradiating the reference light as the readout light, the signal light is reproduced from the recorded hologram.

  Using the above collinear method, when performing a hologram reconstruction method to obtain a reconstructed image by applying a DC component to diffracted light, the reference light and the DC component to be applied are generated by the same spatial light modulator during reproduction. Will do. For this reason, in order to give direct current components having different phases between the positive image and the negative image, it is necessary to perform the reproduction operation twice.

Japanese Patent Laid-Open No. 2007-179597 JP 2007-335056 A

  The present invention relates to an improvement of the above invention, and an object of the present invention is to reproduce two reproduced images corresponding to a positive image and a negative image from one recorded Fourier transform hologram in one reproduction operation. It is an object to provide an optical recording / reproducing method capable of simultaneously obtaining the above.

  In order to achieve the above object, the optical reproduction method according to claim 1 is characterized in that the signal light representing the digital data as a bright and dark image and the reference light are simultaneously condensed on the optical recording medium to obtain the signal light and the reference light. A hologram recorded on an optical recording medium by interference is irradiated with the reference light as readout light, and a first polarization component having a first polarization plane and a second polarization plane orthogonal to the first polarization plane are obtained. Generating diffracted light that is polarized light each having two polarization components, and a third polarization component having the first polarization plane that is orthogonal to the diffracted light and has the same phase as the diffracted light. And generating a combined light by applying a direct current component composed of polarized light each having a second polarization component having the second polarization plane opposite in phase to the diffracted light to the diffracted light; The diffracted light and the added direct current component are synthesized. The component light is separated into a fifth polarization component composed of the first polarization component and the third polarization component, and a sixth polarization component composed of the second polarization component and the fourth polarization component. And a step of reproducing a first reproduction image from the separated fifth polarization component and a step of reproducing a second reproduction image from the separated sixth polarization component. A list of polarization components is shown in Table 1 below.

  The optical reproduction method according to claim 2 is the optical reproduction method according to claim 1, wherein the first reproduction image and the second reproduction image are compared to acquire a luminance difference value for each pixel. The method further includes the step of acquiring a third reproduced image from the positive and negative of the difference value and decoding the digital data superimposed on the signal light based on the acquired third reproduced image.

  The optical regeneration method according to claim 3 is the optical regeneration method according to claim 1 or 2, wherein the diffracted light is one of linearly polarized light, elliptically polarized light, and circularly polarized light. .

  The optical regeneration method according to claim 4 is the optical regeneration method according to any one of claims 1 to 3, wherein when the diffracted light is linearly polarized light, the polarization plane of the diffracted light and the first The first polarization plane of the polarized light component intersects, and the polarization plane of the diffracted light and the second polarization plane of the second polarization component intersect.

  The optical regeneration method according to claim 5 is the optical regeneration method according to claim 4, wherein when the diffracted light is linearly polarized light, the polarization plane of the diffracted light and the first polarized light of the first polarized component. The plane intersects at 45 °, and the polarization plane of the diffracted light and the second polarization plane of the second polarization component intersect at 45 °.

  The optical reproducing device according to claim 6 is composed of a light source that emits coherent light, a plurality of pixel units arranged two-dimensionally, and a signal light region that generates signal light or a direct-current component to be applied, and A reference light region disposed so as to surround the signal light region and generating a reference light coaxial with the signal light, and displaying a transmission pattern with uniform luminance in the signal light region of the spatial light modulator and the space. A spatial light modulator that displays a reference light pattern in a reference light region of the light modulator, modulates light incident from the light source for each pixel according to the display pattern, and generates reference light and a direct-current component to be applied; The first polarization component having a first polarization plane from the hologram recorded in the recording area by condensing the reference light generated by the spatial light modulator and the direct current component to be applied to the recording area of the optical recording medium And the first polarization plane The diffracted light, which is polarized light each having a second polarization component having a second polarization plane orthogonal to each other, is generated, and the first polarized light having a polarization direction orthogonal to the diffracted light and having the same phase as the diffracted light. Generating a direct current component composed of polarized light having a third polarization component having a surface and a fourth polarization component having the second polarization surface having the opposite phase to the diffracted light, and composed of the polarized light. A combined optical system that combines the dc light with the diffracted light to generate a combined light, and a combined light generated by the combined optical system from the first polarized component and the third polarized component. A polarization beam splitter that separates the fifth polarization component into a sixth polarization component composed of the second polarization component and the fourth polarization component, and a first reproduction from the separated fifth polarization component. A first photodetector for detecting an image and the separated sixth polarization component; A second photodetector for detecting the second reproduction image from that comprising the.

  The optical reproduction device according to claim 7 is the optical reproduction device according to claim 6, wherein the first reproduction image and the second reproduction image are compared to obtain a luminance difference value for each pixel. And a controller that executes a decoding process for acquiring a third reproduced image from the positive and negative of the difference value and decoding the digital data superimposed on the signal light based on the acquired third reproduced image. It is characterized by that.

  The optical regenerator according to claim 8 is the optical regenerator according to claim 6 or 7, wherein the combining optical system converts the reference light generated by the spatial light modulator and the direct-current component to be applied into parallel light. A collimating lens system, a DC component modulation element that rotates a polarization plane of the DC component to be applied that has been collimated, and generates a DC component whose polarization direction is orthogonal to the diffracted light, and a collimated beam And a condensing lens for condensing the reference light and the applied direct current component, the polarization plane of which is rotated by the direct current component modulation element, in a recording area of the optical recording medium.

  The optical reproducing apparatus according to claim 9 is the optical reproducing apparatus according to claim 6 or 7, wherein the combining optical system collimates the reference light generated by the spatial light modulator and the direct current component to be applied. The collimator lens system that rotates and the plane of polarization of the reference light that has been collimated are rotated to rotate the plane of polarization of the higher-order component of the diffracted light, and a DC component whose polarization direction is orthogonal to the diffracted light is generated A high-order component modulation element, the direct-current component to be applied that has been collimated, and the direct-current component to which the polarization plane has been rotated by the high-order component modulation element are collected in a recording area of the optical recording medium. And a condensing lens that emits light.

  The optical reproducing apparatus according to claim 10 is the optical reproducing apparatus according to claim 6 or 7, wherein the combining optical system converts the reference light generated by the spatial light modulator and the direct-current component to be applied into parallel light. A collimator lens system, a collimated reference beam and a direct-current component to be applied to the recording region of the optical recording medium, and a focal plane of the condensing lens on the recording region. A direct current component modulation element for generating a direct current component whose polarization direction is orthogonal to the diffracted light by rotating a polarization plane of a direct current component to be applied generated from a recorded hologram, and the diffracted light generated from the hologram And a collimator lens system for collimating the applied direct current component whose polarization plane is rotated by the direct current component modulation element.

  The optical reproducing device according to claim 11 is the optical reproducing device according to claim 6 or 7, wherein the combining optical system converts the reference light generated by the spatial light modulator and the direct-current component to be applied into parallel light. A collimator lens system, a collimated reference beam and a direct-current component to be applied to the recording region of the optical recording medium, and a focal plane of the condensing lens on the recording region. A high-order component that rotates the polarization plane of the diffracted light generated from the recorded hologram to rotate the polarization plane of the higher-order component of the diffracted light and generates a DC component whose polarization direction is orthogonal to the diffracted light A collimator lens system for collimating a modulation element, the direct-current component to be applied generated from the hologram, and the higher-order component of the diffracted light whose polarization plane is rotated by the higher-order component modulation element; It is characterized by having .

  According to the first aspect of the present invention, two reproduced images corresponding to a positive image and a negative image can be obtained simultaneously from one recorded Fourier transform hologram in one reproduction operation. There is an effect that the reproduction processing speed is improved as compared with the case where the reproduction operation is performed.

  According to the second aspect of the invention, it is possible to improve the SNR of the reproduced image by canceling noise common to the two reproduced images corresponding to the positive image and the negative image acquired simultaneously. effective.

  According to the invention of claim 3, there is an effect that the present invention can be applied regardless of the type of polarization of the diffracted light.

  According to the invention of claim 4, there is an effect that two reproduced images corresponding to the positive image and the negative image can be obtained with a predetermined intensity.

  According to the fifth aspect of the invention, there is an effect that two reproduced images corresponding to a positive image and a negative image can be obtained with the same intensity.

  According to the sixth aspect of the present invention, even when a hologram is recorded with linearly polarized light, two sheets corresponding to a positive image and a negative image are recorded from one recorded Fourier transform hologram by one reproduction operation. There is an effect that a reproduced image can be obtained simultaneously.

  According to the invention of claim 7, even when a hologram is recorded with circularly polarized light, two sheets corresponding to a positive image and a negative image are recorded from one recorded Fourier transform hologram by one reproduction operation. There is an effect that a reproduced image can be obtained simultaneously.

  According to the eighth aspect of the present invention, there is an effect that the “direct current component to be applied” before irradiating the optical recording medium can be polarization-modulated.

  According to the ninth aspect of the invention, there is an effect that the “reference light” before irradiating the optical recording medium can be polarization-modulated.

  According to the tenth aspect of the invention, there is an effect that the “direct current component to be applied” after passing through the optical recording medium can be polarization-modulated.

  According to the invention of claim 11, there is an effect that the “diffracted light” diffracted by the optical recording medium can be polarization-modulated.

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

<First Embodiment>
In the first embodiment, a case will be described in which a direct current component is removed during recording to record a hologram, and during reproduction, a direct current component is applied to reproduce the hologram. More specifically, during recording, the direct current component of the signal light and the reference light is removed, and the hologram is recorded by interference between the signal light from which the direct current component has been removed and the reference light. Further, at the time of reproduction, a reference beam for reading is irradiated on the hologram, and a direct current component is given to the diffracted light diffracted from the hologram. Divides the diffracted light with a direct current component into two polarization components that are orthogonal to each other, reproduces the light and dark image of the original signal light from one polarization component, and reproduces the inverted image of the original signal light from the other polarization component To do.

  In some cases, an inverted image cannot always be obtained due to the white ratio (ratio of bright pixels in the entire light / dark image), but in this case as well, noise caused by the reproduction optical system can be removed. In this specification, for convenience, the two reproduced images are referred to as a “positive image” and a “negative image”.

  The light reproduction method of the present invention can be carried out regardless of whether the diffracted light is linearly polarized light or circularly polarized light. In the first embodiment, linearly polarized signal light and linearly polarized reference light are used. The case of recording and reproducing the hologram will be described.

(Schematic configuration of optical recording / reproducing apparatus)
FIG. 1 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to an embodiment of the present invention. This optical recording / reproducing apparatus is an optical recording / reproducing apparatus of “coaxial recording system (collinear system)” that irradiates an optical recording medium with a signal beam having a common optical axis and a reference light as recording light of one light beam from the same direction. It is. In the present embodiment, a “coaxial transmission type” optical recording / reproducing apparatus using a reflection type spatial light modulator (SLM) and a transmission type optical recording medium will be described.

  The optical recording / reproducing apparatus is provided with a light source 10 that oscillates laser light that is coherent light. As the light source 10, for example, a laser light source that oscillates green laser light having an oscillation wavelength of 532 nm is used. On the light exit side of the light source 10, a shutter 12 that can be inserted into or retracted from the optical path (open / close), a half-wave plate 14 that gives a half-wave optical path difference between orthogonal linearly polarized light components, and a predetermined polarization A polarizing plate 16 that transmits light in the direction, a beam expander 18 that is an expansion / collimating optical system, and a reflection mirror 20 are arranged in this order along the optical path from the light source 10 side.

  The shutter 12, the half-wave plate 14 and the polarizing plate 16 can be omitted. In the present embodiment, as shown in FIG. 1, the light having a polarization plane (first polarization plane: parallel to the plane of FIG. 1 in this embodiment) that transmits a polarization beam splitter 40 described later. Is assumed to be “P-polarized light”, and light having a polarization plane reflected by the polarization beam splitter 40 (second polarization plane: in this embodiment, a direction perpendicular to the paper surface of FIG. 1) will be described as “S-polarized light”.

  The light source 10 is connected to the control device 46 via the drive device 48. The control device 46 is constituted by a personal computer or the like provided with a CPU, ROM, RAM, external storage device, input device, and output device. The light source 10 is driven by the driving device 48 in accordance with a control signal input from the control device 46 to the driving device 48. The shutter 12 is connected to the control device 46 via the drive device 50. In response to a control signal input from the control device 46 to the drive device 50, the shutter 12 is driven by the drive device 50 to open and close.

  On the light reflection side of the reflection mirror 20, a transmissive spatial light modulator 22 that polarizes and modulates incident light for each pixel is disposed. As the transmissive spatial light modulator 22, a liquid crystal spatial light modulator such as a liquid crystal shutter array can be used. The spatial light modulator 22 is connected to the control device 46 via the pattern generator 52. Each pixel unit of the spatial light modulator 22 is driven and controlled by the control device 46.

  The pattern generator 52 represents the digital data supplied from the control device 46 as a bright and dark image, and generates a signal light pattern to be displayed on the spatial light modulator 22. The signal light pattern is, for example, a digital pattern in which binary digital data “0, 1” is expressed as “dark (black pixels), light (white pixels)”. In addition to the signal light pattern, the spatial light modulator 22 displays a reference light pattern. The reference light pattern is, for example, a random pattern. The spatial light modulator 22 modulates the incident laser light according to the displayed signal light pattern or reference light pattern, and generates signal light or reference light. The spatial light modulator 22 emits the generated signal light and reference light to the lens 24 described later.

  FIG. 2A is a plan view showing an example of a display area set on the display surface 22A of the spatial light modulator 22 and a recording pattern displayed in the area. On the display surface 22A of the spatial light modulator 22, a signal light region 22S and a reference light region 22R are preset according to the size of the display surface 22A and the like. The shapes and sizes of the signal light region 22S and the reference light region 22R can be changed as appropriate.

  As shown in FIG. 2A, in the present embodiment, the display surface 22A of the spatial light modulator 22 has a rectangular signal light region 22S and a ring-shaped reference light region surrounding the signal light region 22S. 22R are arranged respectively. During recording, a signal light pattern for generating signal light is displayed in the signal light region 22S. At the time of recording, a reference light pattern for generating reference light is displayed in the reference light region 22R.

  FIG. 2B is a plan view showing an example of a reproduction pattern displayed on the display surface 22 </ b> A of the spatial light modulator 22. During reproduction, a reference light pattern for generating reference light is displayed in the reference light region 22R. At the time of reproduction, a transmission pattern for generating a DC component to be applied is displayed in the signal light region 22S. The transmission pattern is composed of a group of pixels having the same luminance other than the luminance of zero. With this transmission pattern, the amplitude and phase of the laser light incident on the signal light region 22S are uniformly modulated, and a DC component to be applied is generated.

  As described above, in the hologram reproduction method for obtaining a reproduction image of two positive images and two negative images, a positive image is reproduced by adding a DC component having the same phase as the diffracted light to the diffracted light obtained from the hologram. Further, a negative image is reproduced by adding a direct current component having a phase opposite to that of the diffracted light to the diffracted light obtained from the hologram. When a photopolymer in which the intensity distribution of the interference fringes of the recording light and the refractive index distribution formed thereby has the same phase (phase shift amount = 0) is used as the hologram recording medium, the phase of the diffracted light is It is shifted by π / 2 from the phase of the reference light for reading. In this case, if the phase of the direct current component to be applied is shifted by π / 2 with respect to the reference light, the diffracted light and the direct current component to be imparted have the same or opposite phase.

If the phase shift amount between the intensity distribution of the interference fringes of the recording light and the refractive index distribution formed thereby is θ, the value of the shift amount θ differs depending on the hologram recording material. Examples of the recording medium in which the phase difference between the readout reference light and the diffracted light is different include photorefractive crystals (lithium niobate (LiNbO ₃ ), barium titanate (BaTiO _3, etc.), and θ = π / In the case of an azo polymer, θ = π, and in the case of a hologram formed only by a light absorptivity distribution such as a silver salt material, θ = π.

  In these cases, the phase difference between the reference light for reading and the diffracted light from the hologram is π / 2 + θ. Also in this case, as described above, a positive image or a negative image can be obtained by determining the phase of the DC component to be applied so as to be in phase or opposite phase to the diffracted light. In the following, for the sake of simplicity, a case where a photopolymer is used as a recording medium will be described as an example. That is, it is a case where θ = 0. However, as will be described later, the recording medium of the present invention is not limited to a photopolymer, and any recording medium can be used.

  In this embodiment, as described above, a photopolymer is used as the recording medium, and the phase of the DC component to be applied is assumed on the assumption that the phase of the diffracted light is shifted by π / 2 from the phase of the reference light for reading during reproduction. The spatial light modulator 22 modulates the amplitude and phase of the incident laser light so as to shift by π / 2 with respect to the phase of the reference light. Further, the polarization direction of the laser beam incident thereon is controlled by the spatial light modulator 22. The polarization modulation by the spatial light modulator 22 will be described later.

  On the light transmission side of the spatial light modulator 22, a lens 24, a DC component removing element 26 that can be inserted into or retracted from the optical path, a lens 28, a DC component modulating element 30 that can be inserted into or retracted from the optical path, and a lens 32 are arranged in this order along the optical path from the spatial light modulator 22 side. The lens 24, the lens 28, and the lens 32 are Fourier transform lenses. The lens 24 condenses the incident light by Fourier transform and irradiates the direct current component removing element 26. The lens 28 converts the incident light into parallel light by inverse Fourier transform and relays it to the lens 32. The lens 32 condenses the incident light by Fourier transform and irradiates an optical recording medium 36 described later.

  The direct current component removing element 26 is arranged in a Fourier transform plane of the lens 24, that is, in a frequency space between the lens 24 and the lens 28. The direct current component removing element 26 is inserted into the optical path during recording, and removes the direct current component (0th-order diffracted light component) in the frequency space. The DC component removing element 26 is connected to the control device 46 via the drive device 54. In response to a control signal input from the control device 46 to the drive device 54, the DC component removal element 26 is driven and moved by the drive device 54.

  Examples of the direct current component removing element 26 include a light absorption filter that absorbs only direct current components, such as a transparent substrate coated with a black pigment on the optical path of the direct current component (near the optical axis), an ND filter disposed near the optical axis, and the like. A partially reflecting mirror that reflects only the direct current component, such as a transparent substrate coated with a reflective film in the vicinity of the optical axis, can be used.

  The direct current component modulation element 30 is disposed between the lens 28 and the lens 32. Since the direct current component applied at the time of reproduction is generated in the signal light region 22S of the spatial light modulator 22, it passes through the signal light optical path in the same manner as the signal light. Therefore, the DC component modulation element 30 is arranged on the optical path of the DC component to be applied, that is, on the signal light optical path. The DC component modulation element 30 is inserted into the optical path during reproduction, and rotates the polarization plane of the DC component to be applied. The DC component modulation element 30 is connected to the control device 46 via the drive device 56. In response to a control signal input from the control device 46 to the drive device 56, the DC component modulation element 30 is driven and moved by the drive device 56.

  As the direct current component modulation element 30, for example, a ½ wavelength plate can be used. When a half-wave plate is used as the DC component modulation element 30, the plane of polarization of the DC component to be applied is rotated by 90 ° during reproduction. A method for arranging the DC component modulation element 30 will be described later.

  A holding stage 34 that holds the optical recording medium 36 is provided on the light emitting side of the lens 32. The holding stage 34 is connected to the control device 46 via the drive device 58. The holding stage 34 is driven in accordance with a control signal input from the control device 46 to the driving device 58, and moves in the optical axis direction or a plane direction perpendicular to the optical axis. For example, the holding stage 34 holds the optical recording medium 36 at a reference position where the center position in the film thickness direction of the optical recording medium 36 is the focal position of the lens 32.

  The optical recording medium 36 is an optical recording medium capable of recording a hologram by a change in refractive index due to light irradiation. Examples of such an optical recording medium 36 include an optical recording medium using a recording material such as a photopolymer material, a photorefractive material, or a silver salt photosensitive material. In this embodiment, as described above, a case where an optical recording medium using a photopolymer material is used will be described.

  On the light transmission side of the optical recording medium 36, a lens 38 and a polarization beam splitter 40 that reflects light in a predetermined polarization direction and transmits light in a polarization direction orthogonal thereto are arranged. Here, the polarization beam splitter 40 reflects the S polarization component and transmits the P polarization component orthogonal thereto. A sensor array 42 is disposed on the light reflection side of the polarization beam splitter 40. The sensor array 42 receives the S-polarized component. A sensor array 44 is also arranged on the light transmission side of the polarization beam splitter 40. The sensor array 44 receives the P-polarized component.

  The sensor arrays 42 and 44 are composed of a two-dimensional image sensor such as a CCD or a CMOS array, and convert the received light into an electrical signal and output it. Each of the sensor arrays 42 and 44 is connected to a control device 46. Each of the sensor arrays 42 and 44 captures a reproduction image formed on the light receiving surface during reproduction, converts it into image data, and outputs the image data to the control device 46.

  The control device 46 compares the first reproduced image captured by the sensor array 42 with the second reproduced image captured by the sensor array 44 to obtain a luminance difference value for each pixel, and the obtained difference value. To generate a third reconstructed image. The control device 46 decodes the digital data superimposed on the signal light based on the third reproduced image.

(Polarization direction of outgoing light from spatial light modulator)
In the optical recording / reproducing apparatus shown in FIG. 1, the polarization plane of linearly polarized light emitted from the spatial light modulator 22 is the polarization plane of any polarization component (S-polarized component, P-polarized component) emitted from the polarization beam splitter 40. Are also designed not to be vertical or parallel. That is, the polarized light emitted from the spatial light modulator 22 includes both the S-polarized component and the P-polarized component.

  As will be described in detail later, the diffracted light from the hologram and the imparted direct current component are incident on the polarization beam splitter 40, separated into an S-polarized component and a P-polarized component, and emitted. These form a positive reproduction image and a negative reproduction image. In order to generate these reproduced images with high contrast, it is desirable that the applied DC component and the higher-order component that is diffracted light are phase-matched (in phase or in phase). For this purpose, the plane of polarization of the outgoing light from the spatial light modulator 22 is preferably designed to make an angle of about 45 ° relative to the plane of polarization of the outgoing light from the polarizing beam splitter 40. .

(Recording operation of optical recording / reproducing device)
Next, the recording operation of the optical recording / reproducing apparatus shown in FIG. 1 will be described.
When recording a hologram, first, the shutter 12 is opened, the direct current component removing element 26 is inserted, the direct current component modulating element 30 is retracted, and laser light is emitted from the light source 10. At the same time, a recording pattern is displayed on the spatial light modulator 22 (see FIG. 2A). Instead of retracting the DC component modulation element 30, a half-wave plate 14 or the like may be used to make it unmodulated. The laser light oscillated from the light source 10 passes through the shutter 12, and the polarization direction is adjusted by the half-wave plate 14 and the polarizing plate 16 as necessary. An unmodulated state can also be achieved by rotating the optical axis of the DC component modulation element 30 so as to be parallel to the polarization direction of the incident light.

  The light that has passed through the polarizing plate 16 is converted into large-diameter parallel light by the beam expander 18, reflected by the reflection mirror 20, and irradiated on the spatial light modulator 22. In the spatial light modulator 22, the laser light is modulated in accordance with the displayed recording pattern, and signal light and reference light are generated. As will be described in detail in the description of the reproducing operation, as described above, the signal light and the reference light generated from the spatial light modulator 22 include both the S-polarized component and the P-polarized component. When the polarization plane of the outgoing light from the spatial light modulator 22 is a plane rotated by 45 ° relative to both the P-polarized light and the S-polarized light, the S-polarized component and the P-polarized light included in the outgoing light The components have the same amplitude and the same phase.

  In the present embodiment, as shown in FIG. 2A, the spatial light modulator 22 is set with a signal light region 22S and a reference light region 22R. The laser light incident on the signal light region 22S is modulated in accordance with the displayed signal light pattern, and signal light is generated. Further, the laser light incident on the reference light region 22R is modulated according to the displayed reference light pattern, and the reference light is generated.

  The recording light (signal light and reference light) generated by the spatial light modulator 22 is collected by the lens 24 and applied to the DC component removing element 26. In the recording light condensed by the lens 24, an unnecessary frequency component is cut by the DC component removing element 26, and the remaining part passes through the DC component removing element 26. That is, in the direct current component removing element 26, the zero-order diffraction component is blocked (the direct current component is removed), and the first-order or higher diffraction component is transmitted. The recording light that has passed without being removed by the direct current component removing element 26 is converted into parallel light by the lens 28.

  The recording light converted into parallel light by the lens 28, that is, the signal light from which the direct current component has been removed and the reference light are subjected to Fourier transform by the lens 32, collected, and irradiated onto the optical recording medium 36 simultaneously and coaxially. The Interference fringes formed by the interference between the signal light and the reference light are recorded on the optical recording medium 36 as a hologram at a position where the signal light and the reference light are collected.

(Reproducing operation of optical recording / reproducing device)
Next, the reproducing operation of the optical recording / reproducing apparatus shown in FIG. 1 will be described.
When reading data recorded on the optical recording medium 36 (during reproduction), the shutter 12 is opened, the DC component removing element 26 is retracted, the DC component modulating element 30 is inserted, and laser light is emitted from the light source 10. Irradiate. At the same time, a reproduction pattern is displayed on the spatial light modulator 22 (see FIG. 2B). The laser light oscillated from the light source 10 passes through the shutter 12 in the same manner as in recording, the light intensity and the polarization direction are adjusted by the half-wave plate 14 and the polarizing plate 16, and the beam expander 18 The light is converted into large-diameter parallel light, reflected by the reflection mirror 20, and applied to the spatial light modulator 22. In the spatial light modulator 22, the laser light is modulated in accordance with the displayed reproduction pattern, and the reference light and the direct current component to be applied are generated.

  In the present embodiment, as shown in FIG. 2B, the spatial light modulator 22 is set with a signal light region 22S and a reference light region 22R. The laser light incident on the reference light region 22R is modulated in accordance with the displayed reference light pattern, and read reference light is generated. Further, the laser light incident on the signal light region 22S is modulated according to the displayed transmission pattern, and a DC component having a phase difference of π / 2 with respect to the reference light is generated.

  The reference light and the direct current component generated by the spatial light modulator 22 are relayed by the lenses 24 and 28 and converted into parallel light by the lens 28. The direct current component converted into parallel light by the lens 28 passes through the signal light optical path, and is incident on the lens 32 with the plane of polarization rotated by 90 degrees by the direct current component modulation element 30 disposed on the signal light optical path. When the polarization plane is rotated by 90 °, the phase difference of the S polarization component with respect to the P polarization component is π. The reference light converted into parallel light by the lens 28 passes through the reference light optical path and enters the lens 32. The reference light and the direct current component incident on the lens 32 are subjected to Fourier transform by the lens 32 and collected, and are irradiated onto the area where the hologram of the optical recording medium 36 is recorded.

  That is, the optical recording medium 36 is irradiated with the reference light as the readout light, and with a direct current component whose phase is shifted by π / 2 from the reference light and whose polarization direction is orthogonal to the reference light. The irradiated reference light is diffracted by the hologram when passing through the optical recording medium 36, and transmitted diffracted light whose phase is shifted by π / 2 from the reference light is emitted to the lens 38 side. Further, the applied direct current component passes through the optical recording medium 36 without being diffracted. As a result, a direct current component whose phase is shifted by π / 2 from the reference light is emitted to the lens 38 side.

  3A and 3B are diagrams illustrating the polarization state of the reference light and the direct-current component to be applied. As shown in FIG. 3A, the reference light and the DC component generated by the spatial light modulator 22 are an electric field and a magnetic field in the “space A” between the spatial light modulator 22 and the lens 24. Is a "linearly polarized light 1" with a constant vibration direction. The direction of vibration of “linearly polarized light 1” is inclined 45 ° with respect to the direction perpendicular to the paper surface of FIG. 1 in accordance with the rotation angle of the spatial light modulator 22 with respect to the optical axis. That is, it has a polarization plane inclined by 45 ° with respect to both the polarization planes of P polarization and S polarization.

  In the “space B” obtained by removing the space downstream of the DC component modulation element 30 from the space between the lens 28 and the lens 32, the reference light and the DC component are “linearly polarized light 1”. On the other hand, in the “space C” on the downstream side of the direct current component modulation element 30, the direct current component to be applied has its polarization plane rotated by 90 ° by the direct current component modulation element 30, and “linear polarization 1” and the polarization direction Are converted into “linearly polarized light 2” orthogonal to each other. In FIG. 3A, “linearly polarized light 1” is indicated by a solid line, and “linearly polarized light 2” is indicated by a dotted line.

  As shown in FIG. 3B, the diffracted light emitted from the optical recording medium 36 and the direct current component to be applied are higher-order components of the diffracted light in “space D” on the downstream side of the optical recording medium 36. Becomes linearly polarized light having the same polarization direction as that of “linearly polarized light 1”, and the applied DC component is linearly polarized light having the same polarization direction as that of “linearly polarized light 2”. That is, the higher-order component of the diffracted light and the direct current component to be applied are linearly polarized light whose polarization directions are orthogonal to each other. The linearly polarized light can be separated into an S-polarized light component perpendicular to the paper surface of FIG. 1 and a P-polarized light component parallel to the paper surface of FIG.

  The diffracted light emitted from the optical recording medium 36 and the direct current component to be applied are inverse Fourier transformed by the lens 38 to be collimated, and enter the polarization beam splitter 40. The diffracted light and the s-polarized light component to be imparted are reflected by the polarization beam splitter 40 and enter the sensor array 42. On the light receiving surface of the sensor array 42, a first reproduced image based on the S-polarized component is formed. The diffracted light and the P component of the direct-current component to be imparted pass through the polarization beam splitter 40 and enter the sensor array 44. On the light receiving surface of the sensor array 44, a second reproduced image is formed by the P-polarized component.

  When the hologram is recorded by interference between the signal light from which the direct current component has been removed and the reference light, when the reference light for reading is irradiated onto the hologram, the signal light from which the direct current component has been removed is reproduced as diffracted light. By applying a DC component having the same phase to the diffracted light, the original signal light is restored, and a light and dark image (positive image) of the original signal light is reproduced. On the other hand, a reverse image (negative image) of a light / dark image of the original signal light is reproduced by applying a DC component having an opposite phase to the diffracted light.

  The phase of the diffracted light is shifted by π / 2 from the phase of the reference light, and the phase of the DC component is shifted by π / 2 from the phase of the reference light. There may occur a case where the phase is the same as the phase and a case where the phase of the higher-order component of the diffracted light is opposite to the phase of the DC component to be applied. In the case of the same phase, the positive amplitude increases due to the interference between the diffracted light (higher order component) and the DC component, and a positive image is reproduced. When the phase is reversed, the negative amplitude increases due to the interference between the diffracted light and the DC component, and a negative image is reproduced.

  In the present embodiment, the S-polarized component of the higher-order component of the diffracted light and the S-polarized component of the DC component to be applied have the same phase. Therefore, the S-polarized component of the higher-order component of the diffracted light and the S-polarized component of the DC component in phase with this are combined, and a positive image is reproduced as the first reproduced image. Further, the P-polarized component of the higher-order component of the diffracted light and the P-polarized component of the direct current component to be applied are in opposite phases. Therefore, the high-order component P-polarized component of the diffracted light and the direct-current component P-polarized component having the opposite phase are combined to reproduce the negative image as the second reproduced image.

This will be described from the polarization state of the diffracted light and the direct-current component imparted. 4A is a diagram illustrating a polarization state of a higher-order component of diffracted light in the space D, and FIG. 4B is a diagram illustrating a polarization state of a direct-current component applied in the space D. As shown in FIG. 4A, the higher-order component of the diffracted light in the space D is S-polarized light that vibrates in the direction perpendicular to the light traveling direction (optical axis direction) (perpendicular to the plane of FIG. 1). The component (S _H ) can be separated into a P-polarized component (P _H ) that vibrates in the horizontal direction with respect to the optical axis direction (the horizontal direction with respect to the paper surface of FIG. 1). Similarly, as shown in FIG. 4B, the direct-current component applied in the space D is an S-polarized component (S _DC ) that vibrates in a direction perpendicular to the optical axis direction (perpendicular to the paper surface of FIG. 1). And a P-polarized component (P _DC ) that vibrates in the horizontal direction with respect to the optical axis direction (the horizontal direction with respect to the paper surface of FIG. 1).

As can be seen from FIGS. 4A and 4B, the S-polarized component (S _H ) of the higher-order component of the diffracted light and the S-polarized component (S _DC ) of the applied _DC component are in phase, Are combined to reproduce a positive image as the first reproduced image. The high-order component P-polarized component (P _H ) of the diffracted light and the P-polarized component (P _DC ) of the direct-current component to be applied are in opposite phases, and they are combined to reproduce a negative image as the second reproduced image. The

  Each of the sensor arrays 42 and 44 captures a reconstructed image formed on the light receiving surface at the time of reproduction, converts it into image data, and outputs the image data to the control device 46. In the sensor arrays 42 and 44, it is preferable to perform oversampling in which one pixel of the signal light data is received by a plurality of light receiving elements. For example, 1-bit data is received by four (2 × 2) light receiving elements.

  The control device 46 subtracts the image data of the second reproduction image from the image data of the first reproduction image, and calculates a luminance difference for each pixel of the light and dark image representing the signal light. The difference when the luminance of the second reproduced image (negative image) is subtracted from the luminance of the first reproduced image (positive image) is positive in the bright part of the original bright / dark image and negative in the dark part of the original bright / dark image. . Since the second reproduced image is an inverted image of the first reproduced image, the contrast after the subtraction process (third reproduced image) is more emphasized than the first reproduced image and the second reproduced image.

  Further, in the third reproduced image, noise common to the first reproduced image and the second reproduced image is canceled out, so that the third reproduced image has a higher SNR than each of the first reproduced image and the second reproduced image. The control device 46 decodes the digital data superimposed on the signal light based on the third reproduced image. That is, since the SNR of the third reproduced image is improved, binary digital data is decoded with high accuracy.

<Second Embodiment>
In the second embodiment, hologram reproduction is performed using circularly polarized signal light and reference light. Other than this, as in the first embodiment, during recording, the direct current component of the signal light and the reference light is removed, and the hologram is recorded by interference between the signal light from which the direct current component has been removed and the reference light. . Further, at the time of reproduction, a reference beam for reading is irradiated on the hologram, and a direct current component is given to the diffracted light diffracted from the hologram. Divides the diffracted light with a direct current component into two polarization components that are orthogonal to each other, reproduces the light and dark image of the original signal light from one polarization component, and reproduces the inverted image of the original signal light from the other polarization component To do.

(Schematic configuration of optical recording / reproducing apparatus)
FIG. 5 is a schematic diagram showing the configuration of an optical recording / reproducing apparatus according to the second embodiment of the present invention. In this optical recording / reproducing apparatus, a pair of lenses 70, a lens 72, and a quarter wavelength plate 74 are added between the spatial light modulator 22 and the lens 24 in order to convert linearly polarized light into circularly polarized light. Has the same configuration as that of the optical recording / reproducing apparatus according to the first embodiment shown in FIG. 1, and therefore, the same components are denoted by the same reference numerals and description thereof is omitted.

(Recording operation of optical recording / reproducing device)
Next, the recording operation of the optical recording / reproducing apparatus shown in FIG. 5 will be described.
When recording a hologram, first, the shutter 12 is opened, the direct current component removing element 26 is inserted, the direct current component modulating element 30 is retracted, and laser light is emitted from the light source 10. At the same time, a recording pattern is displayed on the spatial light modulator 22 (see FIG. 2A). The laser light oscillated from the light source 10 passes through the shutter 12, and the light intensity and the polarization direction are adjusted by the half-wave plate 14 and the polarizing plate 16. For example, the polarizing plate 16 is arranged to transmit only the S-polarized light, and the light intensity of the S-polarized light is adjusted by controlling the polarization direction of the laser light by the half-wave plate 14.

  The light that has passed through the polarizing plate 16 is converted into large-diameter parallel light by the beam expander 18, reflected by the reflection mirror 20, and irradiated on the spatial light modulator 22. In the spatial light modulator 22, the laser light is modulated in accordance with the displayed recording pattern, and signal light and reference light are generated. The signal light and the reference light generated by the spatial light modulator 22 are linearly polarized light whose polarization plane is rotated by a predetermined angle (here, 45 °) around the optical axis.

  The linearly polarized recording light generated by the spatial light modulator 22 is relayed by the lens 70 and the lens 72 and converted into circularly polarized light by the quarter wavelength plate 74. When the light is converted into circularly polarized light by the quarter wavelength plate 74, an optical path difference of 1/4 wavelength (π / 2 phase difference) is imparted between the S polarization component and the P polarization component of the recording light. The The recording light converted into circularly polarized light by the ¼ wavelength plate 74 is collected by the lens 24 and irradiated to the DC component removing element 26. In the recording light condensed by the lens 24, an unnecessary frequency component is cut by the DC component removing element 26, and the remaining part passes through the DC component removing element 26. That is, in the direct current component removing element 26, the zero-order diffraction component is blocked (the direct current component is removed), and the first-order or higher diffraction component is transmitted. The recording light that has passed through the direct current component removing element 26 is converted into parallel light by the lens 28.

  The recording light converted into parallel light by the lens 28, that is, the signal light from which the direct current component has been removed and the reference light are collected by being Fourier-transformed by the lens 32 while being circularly polarized, and simultaneously collected on the optical recording medium 36. And it is irradiated coaxially. Interference fringes formed by the interference between the signal light and the reference light are recorded on the optical recording medium 36 as a hologram at a position where the signal light and the reference light are collected.

(Reproducing operation of optical recording / reproducing device)
Next, the reproducing operation of the optical recording / reproducing apparatus shown in FIG. 5 will be described.
When reading data recorded on the optical recording medium 36 (during reproduction), the shutter 12 is opened, the DC component removing element 26 is retracted, the DC component modulating element 30 is inserted, and laser light is emitted from the light source 10. Irradiate. At the same time, a reproduction pattern is displayed on the spatial light modulator 22 (see FIG. 2B). The laser light oscillated from the light source 10 passes through the shutter 12 in the same manner as in recording, the light intensity and the polarization direction are adjusted by the half-wave plate 14 and the polarizing plate 16, and the beam expander 18 The light is converted into large-diameter parallel light, reflected by the reflection mirror 20, and applied to the spatial light modulator 22.

  In the spatial light modulator 22, the laser light is modulated in accordance with the displayed reproduction pattern, and the reference light and the direct current component to be applied are generated. As a direct current component to be applied, a direct current component having a phase difference of π / 2 with respect to the reference light is generated. The signal light and the DC component generated by the spatial light modulator 22 are linearly polarized light whose polarization plane is rotated by a predetermined angle (here, 45 °) around the optical axis with respect to the incident plane. The linearly polarized reference light and direct current component generated by the spatial light modulator 22 are relayed by the lens 70 and the lens 72 and converted to circularly polarized light by the quarter wavelength plate 74. When being converted into circularly polarized light by the quarter wavelength plate 74, an optical path difference of ¼ wavelength (phase difference of π / 2) between the reference light and the S and P polarization components of the direct current component. Is granted. The recording light converted into circularly polarized light by the quarter wavelength plate 74 is relayed by the lenses 24 and 28 and converted into parallel light by the lens 28.

  The direct current component converted into parallel light by the lens 28 passes through the signal light optical path, is converted into reverse circularly polarized light by the direct current component modulation element 30 disposed on the signal light optical path, and enters the lens 32. The reference light converted into parallel light by the lens 28 passes through the reference light optical path and enters the lens 32. The reference light and the direct current component incident on the lens 32 are circularly polarized while being Fourier-transformed by the lens 32 and collected, and are applied to the area where the hologram of the optical recording medium 36 is recorded.

  That is, the optical recording medium 36 is irradiated with the reference light as the readout light, and the direct current is shifted in phase by π / 2 from the reference light and the polarization direction is orthogonal to the reference light (the rotation direction is reverse). The component is irradiated. The irradiated reference light is diffracted by the hologram when passing through the optical recording medium 36, and transmitted diffracted light whose phase is shifted by π / 2 from the reference light is emitted to the lens 38 side. Further, the applied direct current component passes through the optical recording medium 36 without being diffracted. As a result, a direct current component whose phase is shifted by π / 2 from the reference light is emitted to the lens 38 side.

  FIG. 6 is a diagram for explaining the polarization state of the reference light and the DC component to be applied. As shown in FIG. 6, the linearly polarized reference light and the direct current component generated by the spatial light modulator 22 are converted into circularly polarized light by the ¼ wavelength plate 74. In the “space A ′” between the quarter-wave plate 74 and the lens 24, “circularly polarized light 1” in which the vibration direction of the electric and magnetic fields rotates in a certain direction around the optical axis.

  Further, in “space B ′” obtained by removing the space downstream of the DC component modulation element 30 from the space between the lens 28 and the lens 32, the reference light and the DC component are “circularly polarized light 1”. . On the other hand, in the “space C ′” on the downstream side of the DC component modulation element 30, the direct current component to be applied has its polarization plane rotated by 90 ° by the DC component modulation element 30 and is opposite to “Circular polarization 1”. It is converted into surrounding “circularly polarized light 2”. In FIG. 6, “circularly polarized light 1” is indicated by a solid line, and “circularly polarized light 2” is indicated by a dotted line.

  As shown in FIG. 6, the diffracted light emitted from the optical recording medium 36 and the direct-current component to be applied are “space D ′” on the downstream side of the optical recording medium 36, and the higher-order component of the diffracted light is “ The circularly polarized light has the same rotational direction as that of “Circularly polarized light 1”, and the applied DC component is circularly polarized light having the same rotational direction as that of “Circularly polarized light 2”. That is, the high-order component of the diffracted light and the direct-current component to be imparted are circularly polarized light whose rotation directions are opposite to each other. Similar to linearly polarized light, circularly polarized light can be separated into an S-polarized component whose vibration direction is perpendicular to the paper surface of FIG. 5 and a P-polarized component whose vibration direction is parallel to the paper surface of FIG. .

  The diffracted light emitted from the optical recording medium 36 and the direct current component to be applied are inverse Fourier transformed by the lens 38 to be collimated, and enter the polarization beam splitter 40 as circularly polarized light. The diffracted light and the s-polarized light component to be applied are reflected by the polarization beam splitter 40 and enter the sensor array 42. On the light receiving surface of the sensor array 42, a first reproduced image based on the S-polarized component is formed. The diffracted light and the P component of the direct-current component to be imparted pass through the polarization beam splitter 40 and enter the sensor array 44. On the light receiving surface of the sensor array 44, a second reproduced image is formed by the P-polarized component.

  When the hologram is recorded by interference between the signal light from which the direct current component has been removed and the reference light, when the reference light for reading is irradiated onto the hologram, the signal light from which the direct current component has been removed is reproduced as diffracted light. By applying a DC component having the same phase to the diffracted light, the original signal light is restored, and a light and dark image (positive image) of the original signal light is reproduced. On the other hand, a reverse image (negative image) of a light / dark image of the original signal light is reproduced by applying a DC component having an opposite phase to the diffracted light.

  In the present embodiment, the S-polarized component of the higher-order component of the diffracted light and the S-polarized component of the DC component to be applied have the same phase. Therefore, the S-polarized component of the higher-order component of the diffracted light and the S-polarized component of the DC component in phase with this are combined, and a positive image is reproduced as the first reproduced image. Further, the P-polarized component of the higher-order component of the diffracted light and the P-polarized component of the direct current component to be applied are in opposite phases. Therefore, the high-order component P-polarized component of the diffracted light and the direct-current component P-polarized component having the opposite phase are combined to reproduce the negative image as the second reproduced image.

This will be described from the polarization state of the diffracted light and the direct-current component imparted. FIG. 7A is a diagram illustrating a polarization state of a higher-order component of diffracted light in the space D ′, and FIG. 7B is a diagram illustrating a polarization state of a direct-current component to be applied in the space D ′. As shown in FIG. 7A, the higher-order component of the diffracted light in the space D ′ vibrates in a direction perpendicular to the light traveling direction (optical axis direction) (perpendicular to the plane of FIG. 5). The polarization component (S _H ) can be separated from the P polarization component (P _H ) that vibrates in the horizontal direction with respect to the optical axis direction (the horizontal direction with respect to the paper surface of FIG. 5). Since the diffracted light is circularly polarized light, there is a 1/4 wavelength optical path difference (π / 2 phase difference) between the S-polarized component and the P-polarized component of the higher-order component of the diffracted light.

Similarly, as shown in FIG. 7B, the direct-current component to be applied in the space D ′ is an S-polarized component (S _DC ) that vibrates in a direction perpendicular to the optical axis direction (perpendicular to the paper surface of FIG. 5). ) And a P-polarized component (P _DC ) that vibrates in the horizontal direction with respect to the optical axis direction (the horizontal direction with respect to the paper surface of FIG. 5). Since the direct current component to be imparted is also circularly polarized light, there is an optical path difference (π / 2 phase difference) of ¼ wavelength between the S polarization component and the P polarization component of the direct current component to be imparted.

As can be seen from FIGS. 7A and 7B, the S-polarized component (S _H ) of the higher-order component of the diffracted light and the S-polarized component (S _DC ) of the _DC component to be applied are in phase, Are combined to reproduce a positive image as the first reproduced image. The high-order component P-polarized component (P _H ) of the diffracted light and the P-polarized component (P _DC ) of the direct-current component to be applied are in opposite phases, and they are combined to reproduce a negative image as the second reproduced image. The

  Each of the sensor arrays 42 and 44 captures a reconstructed image formed on the light receiving surface at the time of reproduction, converts it into image data, and outputs the image data to the control device 46. The control device 46 subtracts the image data of the second reproduction image from the image data of the first reproduction image, and calculates a luminance difference for each pixel of the light and dark image representing the signal light. The control device 46 decodes the digital data superimposed on the signal light based on the subtracted image (third reproduced image). That is, since the SNR of the third reproduced image is improved, binary digital data is decoded with high accuracy.

  In the first and second embodiments, the “coaxial transmission type” optical recording / reproducing apparatus and method using a transmission type optical recording medium have been described. However, the present invention relates to a recording layer made of an optical recording material. The present invention can also be applied to a “coaxial reflection type” optical recording / reproducing apparatus and method using a reflection type optical recording medium provided with a reflection layer.

  In the first and second embodiments described above, a case where a direct current component is removed during recording to record a hologram and a direct current component is applied during reproduction to reproduce the hologram has been described. It is also possible to record a hologram without removing it and reproduce the hologram by applying a direct current component only during reproduction. Also in this case, the signal light is reproduced as diffracted light when the reading reference light is irradiated onto the hologram. By applying a DC component having the same phase to the diffracted light, a bright and dark image (positive image) of the original signal light is reproduced. On the other hand, a reverse image (negative image) of a light / dark image of the original signal light is reproduced by applying a DC component having an opposite phase to the diffracted light.

  In the first and second embodiments, the example in which the polarization of the DC component to be applied is modulated (the polarization plane is rotated) during reproduction has been described. However, the polarization of the reference light for reading can be modulated instead of the DC component to be applied. For example, in the optical recording / reproducing apparatus shown in FIG. 1, a wave plate (high-order component modulation element) that rotates the polarization of only the reference light by 90 ° is arranged instead of the DC component modulation element 30. Only the light passing through the reference light path is modulated by the high-order component modulation element. As a result, it is possible to simultaneously acquire a negative image and a positive image as a reproduced image by modulating the polarization of the reference light for reading. Note that the principle of forming a reproduced image is as described with reference to FIG.

  In the first and second embodiments, the example in which the DC component modulation element is arranged on the light incident side of the hologram has been described. However, the DC component modulation element can be arranged on the light emission side of the hologram. is there. FIG. 8 is a schematic diagram showing the configuration of an optical recording / reproducing apparatus in which a DC component modulation element is arranged on the light emission side of a hologram. In the optical recording / reproducing apparatus shown in FIG. 1, the DC component modulation element 30 is removed, and a pair of lenses 80 and 84 and a DC component modulation element 82 are disposed between the lens 38 and the polarization beam splitter 40. Since the configuration is the same as that of the optical recording / reproducing apparatus according to the first embodiment, the same components are denoted by the same reference numerals, and description thereof is omitted.

  In other words, a pair of lenses 80 and 84 constituting a relay system (4f system) are arranged on the light emitting side of the lens 38. A DC component modulation element 82 is disposed between the lens 80 and the lens 84. A polarizing beam splitter 40 is disposed on the light exit side of the lens 84. The DC component modulation element 82 is arranged in the Fourier transform plane of the lens 80, that is, in a frequency space between the lens 80 and the lens 84. The DC component modulation element 82 modulates only the polarization of the DC component (0th order diffracted light component) in the frequency space during reproduction.

Next, the reproducing operation of the optical recording / reproducing apparatus shown in FIG. 8 will be described.
When reading data recorded on the optical recording medium 36 (during reproduction), the shutter 12 is opened, the DC component removing element 26 is retracted, and laser light is emitted from the light source 10. At the same time, a reproduction pattern is displayed on the spatial light modulator 22 (see FIG. 2B). The laser light oscillated from the light source 10 passes through the shutter 12 in the same manner as in recording, the light intensity and the polarization direction are adjusted by the half-wave plate 14 and the polarizing plate 16, and the beam expander 18 The light is converted into large-diameter parallel light, reflected by the reflection mirror 20, and applied to the spatial light modulator 22. In the spatial light modulator 22, the laser light is modulated in accordance with the displayed reproduction pattern, and the reference light and the direct current component to be applied are generated. In the present embodiment, as in the first embodiment, a reference light for reading and a direct current component having a phase difference of π / 2 between the reference light are generated.

  The reference light and the direct current component generated by the spatial light modulator 22 are relayed by the lenses 24 and 28 and converted into parallel light by the lens 28. The reference light and the direct current component converted into parallel light by the lens 28 enter the lens 32. The reference light and the direct current component incident on the lens 32 are subjected to Fourier transform by the lens 32 and collected, and are irradiated onto the area where the hologram of the optical recording medium 36 is recorded.

  That is, the optical recording medium 36 is irradiated with the reference light as the readout light and with a direct current component whose phase is shifted by π / 2 from the reference light. The irradiated reference light is diffracted by the hologram when passing through the optical recording medium 36, and transmitted diffracted light whose phase is shifted by π / 2 from the reference light is emitted to the lens 38 side. Further, the applied direct current component passes through the optical recording medium 36 without being diffracted. As a result, a direct current component whose phase is shifted by π / 2 from the reference light is emitted to the lens 38 side.

  The diffracted light emitted from the optical recording medium 36 and the direct current component to be applied are subjected to inverse Fourier transform by the lens 38 and relayed, condensed by the lens 80, and irradiated to the direct current component modulation element 82. The direct current component modulation element 82 modulates only the polarization of the zeroth-order diffraction component (polarizes and modulates only the direct current component) and transmits the first-order or higher diffraction component (the higher-order component of the diffracted light) without polarization modulation. . The direct current component whose polarization is modulated by the direct current component modulation element 82 and the higher-order component of the diffracted light transmitted through the direct current component modulation element 82 are converted into parallel light by the lens 84 and are incident on the polarization beam splitter 40.

  The diffracted light and the s-polarized light component to be applied are reflected by the polarization beam splitter 40 and enter the sensor array 42. On the light receiving surface of the sensor array 42, a first reproduced image based on the S-polarized component is formed. The diffracted light and the P component of the direct-current component to be imparted pass through the polarization beam splitter 40 and enter the sensor array 44. On the light receiving surface of the sensor array 44, a second reproduced image is formed by the P-polarized component.

  In this case, the polarization state of the reference light and the direct-current component to be applied will be described. As shown in FIG. 9A, the reference light and the DC component generated by the spatial light modulator 22 are an electric field and a magnetic field in the “space A” between the spatial light modulator 22 and the lens 24. Is a "linearly polarized light 1" with a constant vibration direction. The direction of vibration of “linearly polarized light 1” is inclined 45 ° with respect to the direction perpendicular to the paper surface of FIG. 1 in accordance with the rotation angle of the spatial light modulator 22 with respect to the optical axis. That is, it has a polarization plane inclined by 45 ° with respect to both the polarization planes of P polarization and S polarization. In the “space B” between the lens 28 and the lens 32, the reference light and the direct current component are “linearly polarized light 1”.

  As shown in FIG. 9B, the diffracted light emitted from the optical recording medium 36 and the direct current component to be applied are the direct current to be applied to the diffracted light in “space E” on the downstream side of the optical recording medium 36. The component is linearly polarized light having the same polarization direction as that of “linearly polarized light 1”. On the other hand, in the “space F” on the downstream side of the DC component modulation element 82, as shown in FIG. 9C, the applied DC component has its plane of polarization rotated by 90 ° by the DC component modulation element 82. Thus, it is converted into linearly polarized light having the same polarization direction as that of “linearly polarized light 2” whose polarization direction is orthogonal to “linearly polarized light 1”.

  The high-order component of the diffracted light passes through the DC component modulation element 82 without being subjected to polarization modulation, and remains linearly polarized light having the same polarization direction as that of “linearly polarized light 1”. That is, in the “space F”, the high-order component of the diffracted light and the direct-current component to be imparted are linearly polarized light whose polarization directions are orthogonal to each other. Note that linearly polarized light can be separated into an S-polarized light component perpendicular to the paper surface of FIG. 8 and a P-polarized light component parallel to the paper surface of FIG. The high-order component of the diffracted light and the direct-current component to be applied enter the polarization beam splitter 40 and are separated into an S-polarized component and a P-polarized component.

  As described above, instead of the DC component modulation element (DC component modulation element 82 in FIG. 8) that modulates the polarization of only the DC component of the reproduced image (diffracted light and the DC component to be applied), the higher-order component of the reproduced image. It is also possible to arrange a high-order component modulation element that modulates only polarized light. Also in this case, the higher-order component of the diffracted light and the direct-current component to be imparted are linearly polarized light whose polarization directions are orthogonal to each other. Therefore, the higher-order component of the diffracted light and the direct-current component to be applied enter the polarization beam splitter 40 and are separated into the S-polarized component and the P-polarized component.

It is the schematic which shows the structure of the optical recording / reproducing apparatus which concerns on embodiment of this invention. (A) is a top view which shows an example of the display area | region set on the display surface of the spatial light modulator, and the recording pattern displayed on this area | region, (B) is displayed on the display surface of a spatial light modulator. It is a top view which shows an example of the pattern for reproduction | regeneration which is. (A) And (B) is a figure explaining the polarization state of the direct-current component provided with reference light. (A) is a figure showing the polarization state of the high-order component of the diffracted light in the space D, (B) is a figure showing the polarization state of the direct-current component provided in the space D. It is the schematic which shows the structure of the optical recording / reproducing apparatus which concerns on the 2nd Embodiment of this invention. It is a figure explaining the polarization state of the direct-current component provided with reference light. (A) is a figure showing the polarization state of the high-order component of the diffracted light in space D ', (B) is a figure showing the polarization state of the direct-current component to provide in space D'. It is the schematic which shows the structure of the modification of the optical recording / reproducing apparatus which concerns on embodiment of this invention. (A)-(C) is a figure explaining the polarization state of a direct-current component given with reference light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light source 12 Shutter 14 1/2 wavelength plate 16 Polarizing plate 18 Beam expander 20 Reflection mirror 22 Spatial light modulator 22R Reference light area 22S Signal light area 22A Display surface 24 Lens 26 DC component removal element 28 Lens 30 DC component modulation element 32 Lens 34 Holding stage 36 Optical recording medium 38 Lens 40 Polarizing beam splitter 42 Sensor array 44 Sensor array 46 Control device 48 Drive device 50 Drive device 52 Pattern generator 54 Drive device 56 Drive device 58 Drive device 70 Lens 72 Lens 74 1 / 4 wavelength plate 80 lens 82 DC component modulation element 84 lens

Claims (11)

Signal light representing digital data as a dark and dark image and reference light are simultaneously condensed on an optical recording medium, and recorded on the optical recording medium by interference between the signal light and the reference light, the reference light is used as readout light. To generate diffracted light that is polarized light each having a first polarization component having a first polarization plane and a second polarization component having a second polarization plane orthogonal to the first polarization plane When,
A third polarization component having the first polarization plane orthogonal to the diffracted light and having the same phase as that of the diffracted light, and a fourth polarization component having the second polarization plane opposite in phase to the diffracted light. Applying a direct current component composed of polarized light having each of the above to the diffracted light to generate combined light;
A synthesized light obtained by synthesizing the diffracted light and the applied DC component is converted into a fifth polarized light component including the first polarized light component and the third polarized light component, the second polarized light component, and the fourth polarized light. Separating to a sixth polarization component comprising the polarization components of:
Reconstructing a first reconstructed image from the separated fifth polarization component and reconstructing a second reconstructed image from the separated sixth polarization component;
An optical regeneration method including:   The first reconstructed image and the second reconstructed image are compared to obtain a luminance difference value for each pixel, and a third reconstructed image is obtained from the sign of the obtained difference value. The optical reproduction method according to claim 1, further comprising: decoding digital data superimposed on the signal light based on an image.   The optical reproduction method according to claim 1, wherein the diffracted light is one of linearly polarized light, elliptically polarized light, and circularly polarized light.   When the diffracted light is linearly polarized light, the polarization plane of the diffracted light and the first polarization plane of the first polarization component intersect, and the polarization plane of the diffracted light and the second polarization component of the second polarization component The optical reproduction method according to claim 1, wherein the two polarization planes intersect each other.   When the diffracted light is linearly polarized light, the polarization plane of the diffracted light and the first polarization plane of the first polarization component intersect at 45 °, and the polarization plane of the diffracted light and the second polarization The optical reproduction method according to claim 4, wherein the second polarization plane of the component intersects at 45 °. A light source that emits coherent light;
A signal light region that generates a signal light or a direct current component to be applied, and a reference light that is arranged to surround the signal light region and coaxial with the signal light. A reference light area to be generated, displaying a uniform transmission pattern of luminance in the signal light area of the spatial light modulator, and displaying a reference light pattern in the reference light area of the spatial light modulator, from the light source A spatial light modulator that modulates incident light for each pixel according to a display pattern and generates a reference light and a direct-current component to be applied;
A reference light generated by the spatial light modulator and a direct-current component to be applied are condensed on a recording area of the optical recording medium, and a first polarization component having a first polarization plane from a hologram recorded in the recording area; Generates diffracted light that is polarized light each having a second polarization component having a second polarization plane orthogonal to the first polarization plane, and has a polarization direction orthogonal to the diffracted light and the same as the diffracted light. Generating a DC component composed of polarized light each having a third polarization component having the first polarization plane in phase and a fourth polarization component having the second polarization plane in phase opposite to the diffracted light; A multiplexing optical system that combines the diffracted light with a DC component composed of the polarized light to generate combined light;
The synthesized light generated by the multiplexing optical system is composed of a fifth polarization component composed of the first polarization component and the third polarization component, and a second polarization component and the fourth polarization component. A polarization beam splitter that separates into a sixth polarization component;
A first photodetector for detecting a first reproduced image from the separated fifth polarization component;
A second photodetector for detecting a second reproduced image from the separated sixth polarization component;
An optical reproducing apparatus comprising:   The first reconstructed image and the second reconstructed image are compared to obtain a luminance difference value for each pixel, and a third reconstructed image is obtained from the sign of the obtained difference value. The optical reproduction device according to claim 6, further comprising a control device that performs a decoding process for decoding the digital data superimposed on the signal light based on an image. The synthetic optical system is
A collimator lens system that collimates the reference light generated by the spatial light modulator and the DC component to be applied; and
A DC component modulation element that rotates a polarization plane of the DC component to be applied that has been converted into parallel light, and generates a DC component whose polarization direction is orthogonal to the diffracted light;
A condensing lens that condenses the reference light that has been collimated and the direct current component that is imparted with the plane of polarization rotated by the direct current component modulation element in a recording region of the optical recording medium;
An optical regenerator according to claim 6 or 7, comprising: The synthetic optical system is
A collimator lens system that collimates the reference light generated by the spatial light modulator and the DC component to be applied; and
A high-order component modulation element that rotates a polarization plane of the reference light that has been collimated to rotate a polarization plane of a high-order component of the diffracted light and generates a DC component whose polarization direction is orthogonal to the diffracted light When,
A condensing lens that condenses the direct-current component to be applied, which has been converted into parallel light, and the direct-current component to which the polarization plane has been rotated by the higher-order component modulation element, onto a recording region of the optical recording medium;
An optical regenerator according to claim 6 or 7, comprising: The synthetic optical system is
A collimator lens system that collimates the reference light generated by the spatial light modulator and the DC component to be applied; and
A condensing lens that condenses the collimated reference light and the direct current component to be applied to the recording area of the optical recording medium;
A DC component that generates a DC component whose polarization direction is orthogonal to the diffracted light by rotating the polarization plane of the DC component to be applied generated from the hologram recorded in the recording area at the focal plane of the condenser lens A modulation element;
A collimator lens system that collimates the diffracted light generated from the hologram and the imparted direct current component whose polarization plane is rotated by the direct current component modulation element;
An optical regenerator according to claim 6 or 7, comprising: The synthetic optical system is
A collimator lens system that collimates the reference light generated by the spatial light modulator and the DC component to be applied; and
A condensing lens that condenses the collimated reference light and the direct current component to be applied to the recording area of the optical recording medium;
By rotating the polarization plane of the diffracted light generated from the hologram recorded in the recording area at the focal plane of the condenser lens, rotating the polarization plane of the higher-order component of the diffracted light, what is the diffracted light? A high-order component modulation element that generates a direct-current component having orthogonal polarization directions;
A collimator lens system that collimates the direct-current component to be applied generated from the hologram and the higher-order component of the diffracted light whose polarization plane is rotated by the higher-order component modulation element;
An optical regenerator according to claim 6 or 7, comprising:

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