JP2009104037A - Hologram recording device and hologram recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-resolution reconstructed image, in a hologram recording device. <P>SOLUTION: The hologram recording device 1 has a spatial light modulator 50 for modulating light, according to information to be recorded; divides the coherent light from a light source 11 to information light and reference light; and records a hologram based on interference between the information light and the reference light, by emitting the information light and the reference light to overlap them with a hologram recording medium 100. The spatial light modulator having a plurality of pixel areas 50P is provided with a mask 52, which has a grid pattern for optically dividing a pixel that emits the reference light to an emission face side, into a plurality of divided pixels so that the area of a single divided pixel, emitting the reference light, becomes substantially smaller than the area of one pixel emitting the information light. The hologram recording device is also provided with an aperture plate 42 for blocking a diffraction light peak of the reference light, in an optical path between the spatial light modulator and the hologram recording medium. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hologram recording apparatus that records holograms by irradiating information light and reference light so as to overlap a hologram recording medium.

Japanese Patent Application Laid-Open No. 7-20765 describes a hologram recording apparatus. The hologram recording apparatus records a hologram on a hologram recording medium by a phase code multiplexing method. In the hologram recording apparatus, laser light emitted from a light source is separated into signal light (signal beam) and reference light (reference beam) by a beam splitter, and the signal light is a pixel pattern corresponding to recording information by a spatial light modulator. The hologram recording medium is irradiated with the modulated light. The reference light is modulated into light having an appropriate phase pattern by a phase encoding multiplexer, and a phase code is given. A phase-encoding multiplexer consists of a transmissive liquid crystal device with a large number of cells. It gives a predetermined phase difference for each cell to the incident reference light, and modulates the reference light into transmitted light with a desired phase pattern. And exit. The reference light subjected to the phase modulation is irradiated on the hologram recording medium so as to overlap with the signal light, and as a result, a hologram composed of interference fringes (page pattern) between the signal light and the reference light is recorded. At this time, if the modulation pattern (pixel pattern or phase pattern) of the signal light and the reference light is changed without displacing the irradiation part of the hologram recording medium, various page patterns corresponding to the modulation pattern are displayed on the irradiation part. Multiple holograms are recorded.
Japanese Patent Laid-Open No. 7-20765

Japanese Patent Application Laid-Open No. 2006-107633 describes a holographic recording / reproducing apparatus using a phase correlation multiplex recording method. In the holographic recording / reproducing apparatus, a signal phase modulation unit having a phase mask structure that applies phase modulation to signal light and a reference light phase modulation unit having a phase mask structure that applies phase modulation to reference light have one phase. The modulation element is arranged in a plane.
JP 2006-107663 A

Japanese Laid-Open Patent Publication No. 2006-338851 describes a hologram recording apparatus. In the hologram recording apparatus, the filter is a light shielding body in which a pinhole is formed facing the position between the 0th order and the 1st order on the x axis of the Fourier transform image. By disposing this filter on the upstream side of the optical recording medium and on the Fourier transform plane, only a specific spatial frequency component between the bright spot and the bright spot is transmitted through the filter, and other spatial frequency components including a DC component are transmitted. Is cut off. As a result, useless exposure due to a direct current component is prevented, S / N is improved, and only the image edge portion of the signal light is efficiently recorded.
JP 2006-338851 A

  In the above-described hologram recording apparatus, each cell of the liquid crystal device through which the reference light is transmitted is given electro-optical characteristics that cause a phase difference according to the driving voltage using birefringence. In order to form an arbitrary phase pattern using birefringence, complicated application voltage control is performed for each cell, so that the configuration for phase modulation is complicated.

  For example, in the case of a transmissive liquid crystal device using general nematic liquid crystal molecules, the applied voltage of each cell must be finely variably controlled so that gradation display is performed every time the phase pattern is changed. Further, since the response speed of the liquid crystal molecules is not so high, the recording speed of each hologram page is slow.

  An object of the present invention is to realize a hologram recording apparatus having a high recording speed with a simple configuration.

  Another object of the present invention is to obtain a high-resolution reproduced image in a hologram recording apparatus.

  According to a feature of the present invention, a hologram recording apparatus that records a hologram by interference between information light and reference light modulates coherent light from a light source according to information to be recorded, and includes information light and reference light. And an irradiation unit that irradiates the information light and the reference light so as to overlap the hologram recording medium. The spatial light modulator has a plurality of pixel regions, and emits light so that an area of one divided pixel that emits the reference light is substantially smaller than an area of one pixel that emits the information light. A mask having a lattice pattern for optically dividing the pixel emitting the reference light into a plurality of divided pixels on the surface side. The hologram recording apparatus further includes an aperture plate for blocking a diffracted light peak of the reference light in an optical path between the spatial light modulator and the hologram recording medium.

  According to another feature of the present invention, a hologram recording apparatus for recording a hologram by interference between information light and reference light has a plurality of pixel regions formed by optical elements, and records coherent light from a light source. The spatial light modulator that modulates the information light and separates the information light and the reference light, and the pixel area of the spatial light modulator has an area of one divided pixel that emits the reference light. A lattice pattern for optically dividing the pixel emitting the reference light into a plurality of divided pixels on the light emitting surface side of the reference light so as to be smaller than the area of one pixel emitting the information light. A mask having the optical phase modulation means for generating a predetermined phase difference for each pixel of the spatial light modulator, and the diffracted light of the information light passes through an optical path between the spatial light modulator and the hologram recording medium. Let the It includes a aperture plate for blocking at least one of the diffracted light peaks of illuminating, and irradiating means for irradiating to overlap and the reference light and the information light to the hologram recording medium.

  The present invention also relates to a hologram recording method used in the above-described hologram apparatus.

  According to the present invention, a hologram recording apparatus with a high recording speed can be realized with a simple configuration, and a high-resolution reproduced image can be obtained in the hologram recording apparatus.

  Non-limiting embodiments of the present invention will be described with reference to the drawings. In the drawings, similar components are given the same reference numerals.

  FIG. 1 shows a hologram recording apparatus 1 according to an embodiment of the present invention.

  The hologram recording apparatus 1 includes a light source 11, a collimator lens 12, a spatial light modulator 50 to which almost all coherent light from the light source 11 is incident, and a mesh mask or grating disposed on the reflective surface side of the spatial light modulator 50. A mask 52, a first relay lens 40, 41, a light selection plate 42 which is disposed at a focal position between the first relay lenses 40 and 41 and has an opening or an aperture having a predetermined diameter (for example, 1 mm), Beam splitter 16 and objective lens 17 for recording and reproduction, second relay lenses 80 and 81, beam splitter 18 for reproducing light separation, light receiving sensor 19 for reproduction, condenser lens 21 and light receiving sensor 20, and spatial light modulation A modulation control unit 300 for controlling the device (SLM) 50 is provided.

  The light source 11 is made of, for example, a semiconductor laser element, and emits laser light or coherent light having a relatively narrow band and high coherence. Laser light emitted from the light source 11 is converted into parallel light by the collimator lens 12, and almost all of the parallel light emitted from the collimator lens 12 enters the spatial light modulator 50. The spatial light modulator 50 is composed of a deformable mirror device having a plurality of movable reflecting elements arranged in a matrix of, for example, 1024 × 1024. The spatial light modulator 50 partially functions as optical phase modulation (DPM) means.

  In this case, the hologram recording medium 100 is a reflection type, and has a structure in which a support substrate layer, a reflection layer, a hologram recording layer, and a transparent substrate layer are laminated in this order from the bottom, and has a disc shape. The hologram recording layer is irradiated with information light and reference light so as to overlap each other, whereby a hologram composed of interference fringes (page pattern) is recorded. Embossed pits are formed in the reflective layer, and servo control such as track control, focus control, and tilt control is performed by the servo light receiving sensor 20 detecting changes in reflected light caused by the embossed pits. Is called.

  FIG. 2 shows a hologram recording apparatus 3 according to another embodiment of the present invention.

  In the hologram recording apparatus 3, second relay lenses 80 and 81 and a light receiving sensor 9 for reproduction are provided on the opposite side of the recording medium B. In this case, the hologram recording medium 100 is a transmission type, has a structure in which a support substrate layer, a hologram recording layer, and a transparent substrate layer are laminated in this order, and has a disc shape. Other configurations are the same as those of the hologram recording apparatus 1 of FIG.

  FIGS. 3A, 3B and 3C show a front view of a spatial light modulator 50 having a mesh mask 52 in a lattice pattern, and side views of two different forms of spatial light modulator 50, respectively. FIGS. 4A, 4B, and 4C show a front view of a spatial light modulator 50 having another lattice-patterned mesh mask 52, and side views of two different forms of spatial light modulator 50, respectively.

  The spatial light modulator 50 is a reflective spatial light modulator, and includes a first light modulation region 51A and a second light modulation region 51B. The spatial light modulator 50 of FIGS. 3A and 3B has a first light modulation region 51A in the central portion of the light reflection surface of the spatial light modulator 50, and the first light modulation region 51A outside the central portion has a first light modulation region 51A. It has two light modulation areas 51B. On the spatial light modulator 50, a mesh mask or a lattice mask 52 is arranged in the second light modulation region 51B. As shown in FIG. 3B, in one form of spatial light modulator 50, mesh mask 52 has an opening in first light modulation region 51A. As shown in FIG. 3C, in another form of the spatial light modulator 50, a phase element 53 including, for example, frosted glass for scattering is disposed on the opening of the first light modulation region 51A. It may be.

  The first light modulation area 51A modulates incident central part of light into pixel pattern light corresponding to recording information, and emits the light as information light or signal light. The second light modulation region 51B phase-modulates the incident other surrounding light into light of a desired phase pattern P, and emits this as reference light. The information light and the reference light are guided to the first relay lenses 40 and 41 along the same coaxial optical path, and further overlap each other at a predetermined portion of the hologram recording medium 100 via the beam splitter 16 and the objective lens 17. Irradiated.

  As an alternative configuration, a second light modulation region for reference light may be provided at the center of the light reflection surface, and a first light modulation region for information light may be provided around the light reflection surface outside the center portion. Further, as an alternative configuration, for example, one half of the light reflecting surface may be the first light modulation region, and the other half of the light reflecting surface may be the second light modulation region.

  In the second light modulation region 51B, a large number of phase patterns P indicated by thick dashed frames are arranged. The spatial light modulator 50 is disposed at a predetermined angle with respect to these optical axes so that the information light and the reference light are incident on the objective lens 17 and the hologram recording medium 100 perpendicularly. Further, the light receiving sensor 19 for reproduction is also arranged at a predetermined angle so as to capture a correct image according to the inclination degree of the spatial light modulator 50.

  The modulation control unit 300 controls the pixel 50p of the first light modulation region 51A to generate information light having a desired pixel pattern, and generates the reference light having a desired phase pattern for the pixel 50p of the second light modulation region 51B. Control as follows.

  The light reflection surface 50A of the spatial light modulator 50 is divided into a first light modulation region 51A and a second light modulation region 51B, and reference light having a desired phase pattern is generated by the second light modulation region 51B. The pixel 50p can be modulated into reference light having a desired phase pattern simply by turning the pixel 50p on / off (ie, on / off mode), and the on / off control of each pixel 50p can be easily performed. Therefore, the hologram recording apparatus 1 or 3 having the phase modulator 50 can realize phase modulation by the phase code multiplexing method with a simple configuration, and can increase the hologram recording speed.

  Since a single spatial light modulator 50 generates both information light having a desired pixel pattern and reference light having a phase pattern, the configuration of the apparatus is simplified, the apparatus can be miniaturized, and the cost can be reduced.

  5A and 5B show a front view and a side view of a schematic configuration of the phase modulator 50 when a DMD (Deformable Mirror Device) is used as the phase modulator 50. FIG. As an alternative configuration, the phase modulator 50 may be LCoS (Liquid Crystal on Silicon).

  The phase modulator 50 has a plurality of movable reflective elements 50p that are respectively changed to a predetermined inclination angle ± φ with respect to the normal line Ln of the light reflecting surface 50A serving as a reference, and the plurality of movable reflective elements 50p are They are arranged in a grid or matrix. The pitch d of the vertical and horizontal arrangements of the movable reflective elements 50p is, for example, 13.7 μm. Each movable reflecting element 50p has a rotation axis that coincides with the diagonal line Ld, and is swung to an inclination angle + φ / −φ around the rotation axis by on / off control. The inclination angle φ of each movable reflective element 50p is, for example, about 12 °.

  For example, as shown by a solid line in FIG. 5B, when the movable reflective element 50p is turned on and the reference light is incident on the movable reflective element 50p at an incident angle θi with respect to the light reflecting surface 50A, the reference light is inclined by the movable reflective element 50p. The reference light is reflected according to the angle φ, and the reference light is emitted in the direction of the emission angle θo with respect to the light reflecting surface 50A. On the other hand, in the movable reflecting element 50p in the off state, as shown by a broken line in the figure, the reference light incident on the movable reflecting element 50p is a direction indicated by a white arrow (a certain direction different from the direction of the emission angle θo). ). As for the movable reflective element 50p, for example, unit sections arranged 10 × 10 in length and width are used as cells.

  In such a phase modulator 50 composed of the movable reflective element 50p, a phase difference is given by appropriately designing the incident angle θi of the reference light with respect to the light reflecting surface 50A, the pitch d between the elements, and the like. A phase pattern is formed. Specifically, the movable reflective element 50p having a phase difference of 0 and the movable reflective element 50p having a phase difference of π are alternately arranged by satisfying the following conditional expression. Here, the wavelength of the light emitted from the light source is λ, the pitch between the movable reflecting elements 50p is d, and m is an integer.

The following relational expression is established among the tilt angle φ, the incident angle θi, and the outgoing angle θo of the movable reflective element 50p.
θi + θo = 2φ

  For example, when a light source that emits green light is used and λ = 0.532 μm, d = 13.7 μm, and φ = 12 °, the incident angle θi when adjusted to m = 7 is about 19.27 °. The emission angle θo is about 4.73 °. That is, the reference light incident on the light reflecting surface 50A at the incident angle θi is reflected by the movable movable element 50p in the on state and is emitted in the direction in which the emission angle becomes θo. As shown in FIG. When viewed along a direction orthogonal to Ld (vertical direction in the drawing), the movable reflective elements 50p having a phase difference of 0 and the movable reflective elements 50p having a phase difference of π are alternately arranged. By turning on only the movable reflective element 50p having such a phase difference of 0, a zero-type cell is formed, and by turning on only the movable reflective element 50p having a phase difference of π, a π-type cell is formed. The When all the movable reflective elements 50p having the phase difference 0 and the phase difference π are turned off, a light shielding type cell is formed.

  Further, for example, when a light source that emits blue light is used and λ = 0.405 μm and other conditions are the same as above, as an example, the incident angle θi when adjusted to m = 9 is about 28.96 °. The emission angle θo is approximately −4.96 ° (on the side opposite to the incident angle θi with the normal Ln of the light reflecting surface 50A as the axis of symmetry).

  The reference light emitted from the phase modulator 50 as reflected light having an outgoing angle θo passes through the beam splitter 16 and is irradiated onto the hologram recording medium 100.

  The movable reflective element 50p is mechanically driven, but is ultra-compact, and therefore has a very fast response speed compared to ferroelectric liquid crystal molecules. Therefore, the phase pattern can be switched at high speed, and the recording speed of each hologram page can be further increased. For example, the page recording speed of the hologram recording apparatus using the phase modulator 50 is approximately 7000 pages / second, and the advantages of the phase code multiplexing method can be further enhanced.

  Therefore, the hologram recording apparatus 1 or 3 having the phase modulator 50 can simplify the configuration for phase modulation by the phase code multiplexing method, and can further increase the hologram recording speed.

  FIG. 6 shows a block diagram of a recording / reproducing control unit for supplying data to be recorded to the hologram recording apparatus 1 or 3 and taking out data reproduced from the hologram recording apparatus 1 or 3.

  In FIG. 6, the recording / reproducing control unit includes a controller interface (I / F) that forms an interface with the outside, and a recording data holding unit 302 and a recording data holding unit 302 as a recording control unit or modulation control unit 300. The data encoder 304 that encodes the data and supplies coded data for information light (signal light) to the spatial light modulator 50, and generates reference data for reference light to generate the spatial light modulator 50. A reference data generator 312 to be supplied to the recording medium 100, a driving device 320 for driving the recording medium 100, and a reproduction control unit 340 for reading and decoding data from the light receiving sensor 19 including a two-dimensional image sensor. Decoder 344 and a reproduction data holding unit that holds the decoded data as reproduction data And it includes a 42.

  The reference data pattern is generated by being randomly changed for each recording page. At the time of reproduction, the same reference data pattern as that for recording is supplied to the spatial light modulator 50. The recording medium 100 is moved when changing a book which is a collection of pages.

  When the mesh mask 52 is not disposed on the spatial light modulator 50, in the DPM (digital phase mask) system or the phase code multiplexing system, the laser light reflected or transmitted through the spatial light modulator 50 is converted into the spatial light modulator. Diffraction is performed by 50 matrix or lattice pixel division structures. The diffracted light is generated by the structure of the spatial light modulator 50 and does not depend on the pixel pattern. Therefore, when such diffracted light is used for recording, crosstalk occurs in the reproduction light, and sufficient multiplex recording cannot be performed.

In the embodiment of FIGS. 1 and 2, as shown in FIG. 3 or 4, a mesh mask 52 is disposed on the reflective surface side of the second light modulation region 51 </ b> B of the spatial light modulator 50. The lattice-like pattern on the mesh mask 52 is formed of a plurality of light-shielding lines (black lines) having a predetermined lattice-like parallel pitch on the transparent plate. The central portion of the mesh mask 52 has an opening for the first light modulation region 51A. The pitch p _MG of the lattice pattern of the mesh mask 52 is equal to the vertical and horizontal pitches p _RE of the adjacent pixels 50p (FIG. 4) or an integral fraction of the pitch p _RE (FIG. 3 or 4). It is desirable that the distance between adjacent pixels 50p or the area of the region be small. It is also desirable that the area of the light shielding lines of the mesh mask 52 is small.

The grid lines of the mesh mask 52 are desirably aligned so as to overlap the pixel dividing lines between the pixels 50 of the spatial light modulator 50 as shown in FIG. 3A. In this case, the lattice pattern of the mesh mask 52 has a vertical and horizontal pitch p _MG smaller than the vertical and horizontal pitches p _RE of the matrix-like pixels 50p. The pitch p _MG of the mesh mask 52 is an integral number, preferably half (for example, 6.85 μm) or one third (for example, 4.56 μm) of the vertical and horizontal pitches p _RE of the adjacent pixels 50 p. It is.

  The lattice pattern provides an effect that each original pixel of the second light modulation region 51B is divided into a plurality of divided pixels having substantially the same area. The grid pattern on the mesh mask 52 is obtained by dividing the original non-divided pixel that emits the reference light in the second light modulation region 51B by an integer (for example, 1/2) in the X direction and an integer in the Y direction. The area of one divided pixel that emits the reference light is divided or optically divided into 1 (for example, half) of the area of one pixel that emits the information light. It acts so as to be 1 (for example, one-fourth or one-nine in two dimensions).

When the grid lines of the mesh mask 52 do not overlap the pixel dividing lines between the pixels 50 of the spatial light modulator 50 as shown in FIG. 4A, the grid pattern and the pixel dividing line pattern of the mesh mask 52 are used. And the composite lattice pattern with the vertical and horizontal composite pitches p _MG ′ smaller than the vertical and horizontal pitches p _RE of the matrix-like pixels 50p. The composite pitch p _MG ′ of the composite lattice pattern of the mesh pattern of the mesh mask 52 and the pixel dividing line pattern is an integer, preferably 1/2 (for example, 6) of the vertical and horizontal pitches p _RE of the adjacent pixels 50p. .85 μm) or one third (eg, 4.56 μm).

Due to the narrow grating pitch p _MG , the distribution of the peaks of the m-th order diffracted light of the reference light and the m + 1-order diffracted light (m is an integer or an integer multiple of 0.5) on the optical axis, m + 1 than the light amount distribution of the diffracted light, can be moved largely to the outside of the reference light, for example, mesh when the pitch p _MG mask 52 is one-half of the pitch p _RE adjacent pixels m order diffracted light and the m + 1 The peak interval of the next diffracted light can be doubled. The dynamic range of the hologram recording medium 100 is uniformly used within a range having linearity by blocking the mth-order diffracted light and m + 1st-order diffracted light peak of the reference light by the light selection plate 42 to prevent the passage of the diffracted light peak Alternatively, it can be consumed, thereby increasing the resolution of the recorded image, thereby improving the quality of the reproduced signal.

  Diffracted light between the m-th order diffracted light and the (m + 1) th order diffracted light of the pixel division structure of the spatial light modulator 50 (for example, diffracted light between the m + 0th order diffracted light and the m + 1st order diffracted light, and between the m-1st order diffracted light and the m + 0th order diffracted light) Diffracted light or diffracted light between m + 0.5th order diffracted light and m−0.5th order diffracted light) is used as reference light. The diffracted light is generated by alternately giving 0 and π phases to the spatial light modulator 50.

  In the case of using the hologram recording device 1 or 3 of the coaxial optical system, it is necessary for the information light to have a high resolution so that the reproduced image can identify data. In order to obtain the resolution, the light selection plate 42 must be opened. Even if the hole is narrowed down to the smallest size, it is necessary to pass a plurality of diffracted light peaks such as m + 0 order diffracted light and m ± 1st order diffracted light through the opening of the light selection plate 42. When a phase element or phase mask 53 including polished glass and a light diffusing plate is applied to the information light, the diffracted light peak disappears as a result of phase mismatch, but it is necessary to obtain the necessary resolution to obtain the required resolution. The size of the hole does not change. Therefore, in a coaxial optical system that coaxially irradiates information light and reference light, it is necessary to remove the diffracted light peak for the reference light, but for the information light, the portion of the diffracted light peak is required for high resolution. The amount of light is necessary.

  7A and 7C show the optical path of information light (signal light) and the optical path of reference light from the spatial light modulator 50 to the recording medium 100 in the hologram recording apparatus 1 or 3, respectively. 7B and 7D respectively show the light amount distributions of the diffracted light of the information light and the reference light from the spatial light modulator 50 in the vicinity of the optical axis in front of the light selection plate 42.

  Referring to FIGS. 7A and 7B, the information light from the first light modulation region 51A of the spatial light modulator 50 is centered on the peaks of the mth order diffracted light and the m + 1st order diffracted light that are separated by a normal predetermined distance on the optical axis. Exists on both sides. When this light is passed through the aperture 42a of the light selection plate 42, most of the information light including the peaks of the mth order diffracted light and the m + 1st order diffracted light and the center m + 0.5th order diffracted light can be passed.

  Referring to FIGS. 7C and 7D, the reference light from the second light modulation region 51B is formed by a narrow pitch grating formed on the mesh mask 52 disposed on the second light modulation region 51B of the spatial light modulator 50. , The peaks of m + 0 order diffracted light and m + 1 order diffracted light move far from the center (for example, twice as far as information light). By passing this light through the aperture 42a of the light selection plate 42 having a diameter narrower than the peak interval between the m + 0th order diffracted light and the m + 1st order diffracted light, the area around the peaks of the m + 0th order diffracted light and the m + 1st order diffracted light is shielded. Only m + 0.5th order diffracted light having a low peak at the center and widely distributed can be passed.

  8A, 8B, 8C, and 8D show the optical paths of the reference light and information light from the spatial light modulator 50 to the recording medium 100 when the spatial light modulator 50, the mesh mask 52, and the light selection plate 42 are used. The diffracted light distribution of reference light at each position on the optical axis, the diffracted light distribution of information light at each position on the optical axis, and the distribution of information light and reference light above a predetermined level near the optical axis FIG.

  8B shows the light amount distribution (a) of the reference light near the optical axis in front of the light selection plate 42, the light amount distribution (b) of the reference light in the vicinity of the optical axis after the light selection plate 42, and the front of the light selection plate 42. 2 shows the two-dimensional diffracted light distribution pattern of the reference light, the arrangement (c) of the apertures 42 a of the light selection plate 42, and the light quantity distribution (d) of the reference light in the recording medium 100.

  From FIG. 8B, the (m, m) order, (m, m + 1) order, (m + 1, m) order, (m + 1, m) order, (m + 1) on the (X, Y) coordinates outside the optical axis of the reference light by the light selection plate 42. , M + 1) the diffracted light peak is removed, and only the m + 0.5th diffracted light in the X-axis direction and the m + 0.5th diffracted light in the Y-axis direction at the center of the reference light are selected and applied to the recording medium 100. I understand.

  8C shows the light amount distribution (a) of information light near the optical axis in front of the light selection plate 42, the light amount distribution (b) of information light in the vicinity of the optical axis after the light selection plate 42, and the front of the light selection plate 42. 2 shows the two-dimensional diffracted light distribution pattern of information light, the arrangement (c) of the apertures 42a of the light selection plate 42, and the light quantity distribution (d) of information light in the recording medium 100.

  From FIG. 8C, the light selection plate 42 causes the (m, m−1) -th order, (m−1, m) -th order, (m, m + 2) on the (X, Y) coordinates outside the optical axis of the information light. ), (M + 2, m), (m + 1, m-1), (m-1, m + 1), (m + 1, m + 2), (m + 2, m + 1) diffracted light peaks are removed, and information is removed. (M + 0.5, m + 0.5) order diffracted light on the (X, Y) coordinates near the center of the optical axis of light, and (m, m), (m, m + 1), (m + 1, m) orders It can also be seen that the (m + 1, m + 1) th order diffracted light peak is selected and applied to the recording medium 100. The light quantity ratio or intensity ratio between the information light and the reference light in the recording medium 100 is desirably 1: 1 or close to 1: 1. When a DMD is used as the spatial light modulator 50, typically m = 8. When LCoS is used as the spatial light modulator 50, typically m = 0.

  FIGS. 9A, 9B, 9C, and 9D show the spatial light modulator 50 to the recording medium 100 when the spatial light modulator 50, the mesh mask 52, the phase element or phase mask 53, and the light selection plate 42 are used. The optical path of the reference light and the information light, the diffracted light distribution of the reference light at each position on the optical axis, the diffracted light distribution of the information light at each position on the optical axis, and information above a predetermined level near the optical axis The enlarged view of the light quantity distribution of light and reference light is shown. In this case, the phase element or phase mask 53 is disposed on the reflection surface side of the first light modulation region 51A of the spatial light modulator 50 and scatters information light. The phase element or phase mask 53 includes polished glass, a light diffusion plate, and the like.

  FIG. 9B relating to the reference light is similar to FIG. 8B and will not be described again.

  FIG. 9C shows a light amount distribution (a) of information light near the optical axis in front of the light selection plate 42, a light amount distribution (b) of information light in the vicinity of the optical axis after the light selection plate 42, and in front of the light selection plate 42. 2 shows the two-dimensional diffracted light distribution pattern of information light, the arrangement (c) of the apertures 42a of the light selection plate 42, and the light quantity distribution (d) of information light in the recording medium 100.

  In this case, the information light is scattered by the phase element 53 arranged in the first light modulation region 51A of the spatial light modulator 50. Therefore, as shown in FIG. 9C (a), the information light has a substantially uniform light amount distribution with a clear peak disappearing in a region near the center on the optical axis. As shown in FIG. 9C (b), the information light is selected only in the vicinity of the center through the opening 42a of the light selection plate 42, and a substantially rectangular light amount distribution is obtained. In the information light, the (m, m) -order, (m, m + 1) -order, (m + 1, m) -order and (m + 1, m + 1) -order diffracted light peaks are blurred, and there is no clear diffracted light peak. Therefore, as shown in FIG. 9C (c), the information light can obtain a uniform rectangular light amount distribution in the vicinity of the center of the recording medium 100. The light quantity ratio or intensity ratio between the information light and the reference light in the recording medium 100 is desirably 1: 1 or close to 1: 1. When a DMD is used as the spatial light modulator 50, typically m = 8. When LCoS is used as the spatial light modulator 50, typically m = 0.

  As shown in FIG. 9D, in the recording medium 100, the substantially uniform reference light having a peak at the center and the uniform information light are superimposed. As a result, the dynamic range of the hologram recording medium 100 can be uniformly used or consumed within a range having linearity, thereby increasing the resolution of the recorded image and thereby improving the quality of the reproduced signal.

  According to the hologram recording / reproducing apparatus 1 or 3, a digital phase modulation (DPM) system is used for a coaxial optical hologram recording / reproducing apparatus by using a mesh mask for the spatial light modulator and a phase element for light scattering. Can be used to obtain a high resolution reconstructed image and simplify the hologram recording optical system. Furthermore, highly accurate alignment (alignment) between the information beam and the reference beam becomes unnecessary, and the number of adjustment steps during manufacturing can be greatly reduced.

  Although the present invention has been described with reference to a hologram recording apparatus using a reflective spatial light modulator, the present invention is directed to a transmissive spatial light modulator that transmits light from a light source (for example, a liquid crystal device comprising a plurality of liquid crystal elements). ) May be applied to a hologram recording apparatus using the above.

  The embodiments described above are merely given as typical examples, and it is obvious to those skilled in the art to combine the components of each embodiment, and variations and variations thereof will be apparent to those skilled in the art. Obviously, various modifications may be made to the above-described embodiments without departing from the scope of the invention as set forth in the scope.

FIG. 1 shows a hologram recording apparatus according to an embodiment of the present invention. FIG. 2 shows a hologram recording apparatus according to another embodiment of the present invention. FIGS. 3A, 3B and 3C show a front view and two different side views, respectively, of a spatial light modulator having a mesh mask with a lattice pattern. 3A, 3B and 3C show a front view and two different side views, respectively, of a spatial light modulator having a mesh mask with another grid pattern. 5A and 5B show a front view and a side view of a schematic configuration of a phase modulator when DMD is used as the phase modulator. FIG. 6 shows a block diagram of a recording / reproduction control unit for supplying data to be recorded to the hologram recording apparatus and taking out the reproduced data from the hologram recording apparatus. 7A and 7C respectively show the optical path of information light and the optical path of reference light from the spatial light modulator to the recording medium in the hologram recording apparatus. FIGS. 7B and 7D respectively show the light quantity distributions of the diffracted light of the information light and the reference light from the spatial light modulator near the optical axis in front of the light selection plate. 8A, 8B, 8C, and 8D show the optical paths of the reference light and the information light from the spatial light modulator to the recording medium and the optical axis when the spatial light modulator, the mesh mask, and the light selection plate are used. The diffracted light distribution of reference light at each position, the diffracted light distribution of information light at each position on the optical axis, and an enlarged view of the distribution of information light and reference light above a predetermined level near the optical axis are shown. Yes. 9A, 9B, 9C, and 9D show the reference light and information light from the spatial light modulator to the recording medium when the spatial light modulator, mesh mask, phase element or phase mask, and light selection plate are used. The optical path, the diffracted light distribution of reference light at each position on the optical axis, the diffracted light distribution of information light at each position on the optical axis, and the amount of information light and reference light above a predetermined level near the optical axis An enlarged view of the distribution is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hologram recording device 11 Light source 17 Objective lens 40, 41 1st relay lens 50 Spatial light modulator (SLM)
52 mesh mask 42 light selection plate 100 hologram recording medium 19 light receiving sensor 80, 81 second relay lens 300 modulation control unit

Claims (9)

In a hologram recording apparatus for recording a hologram by interference between information light and reference light,
A spatial light modulator that modulates coherent light from a light source according to information to be recorded and separates into information light and reference light;
An irradiation unit that irradiates the information light and the reference light so as to overlap the hologram recording medium;
The spatial light modulator has a plurality of pixel regions, and emits light so that an area of one divided pixel that emits the reference light is substantially smaller than an area of one pixel that emits the information light. A mask having a lattice pattern for optically dividing the pixel emitting the reference light on the surface side into a plurality of divided pixels;
The hologram recording apparatus further comprises an aperture plate for blocking a diffracted light peak of the reference light in an optical path between the spatial light modulator and the hologram recording medium. The pixel that emits the reference light in the spatial light modulator includes an on state that reflects or transmits the reference light in a predetermined direction toward the hologram recording medium, and an off state that guides or shields the reference light out of the predetermined direction. It takes two states
The hologram recording apparatus according to claim 1, wherein the spatial light modulator further includes an optical phase modulation unit that gives a predetermined phase difference for each pixel.   The lattice pattern is formed in a form in which the mask optically divides one pixel that emits the reference light into at least two divided pixels having the same area. The hologram recording apparatus according to 1 or 2.   The plurality of pixels are optical elements, and are arranged such that pixels having a phase difference of 0 and pixels having a phase difference of π are alternately arranged as the predetermined phase difference. The hologram recording apparatus described in 1.   5. The spatial light modulator according to claim 1, further comprising a phase element that scatters the information light on an emission surface side of a pixel that emits the information light. Hologram recording device. In a hologram recording apparatus for recording a hologram by interference between information light and reference light,
A spatial light modulator that has a plurality of pixel regions configured by optical elements, modulates coherent light from a light source according to information to be recorded, and separates the information light and the reference light;
The pixel region of the spatial light modulator has the reference light emitting surface side so that an area of one divided pixel that emits the reference light is smaller than an area of one pixel that emits the information light. A mask having a lattice pattern for optically dividing a pixel emitting reference light into a plurality of divided pixels;
Optical phase modulation means for producing a predetermined phase difference for each pixel of the spatial light modulator;
An aperture plate for allowing the diffracted light of the information light to pass through the optical path between the spatial light modulator and the hologram recording medium and blocking at least one diffracted light peak of the reference light;
Irradiation means for irradiating the information light and the reference light so as to overlap the hologram recording medium;
A hologram recording apparatus comprising: A hologram recording method for recording a hologram by interference between information light and reference light,
A spatial light modulator for modulating light according to information to be recorded, and separating coherent light from a light source into information light and reference light via the spatial light modulator;
A mask having a lattice pattern is provided on the emission surface side of the region emitting the reference light of the spatial light modulator having a plurality of pixel regions, and the information light is emitted from one pixel emitting the reference light. Smaller than the area of one pixel
By the aperture provided in the optical path between the spatial light modulator and the hologram recording medium, the diffracted light of the reference light is blocked,
A hologram recording method comprising irradiating the information light and the reference light so as to overlap a hologram recording medium. The pixels that emit the reference light of the spatial light modulator have two states, an on state in which the reference light is reflected or transmitted in a predetermined direction toward the hologram recording medium, and an off state in which the reference light is guided or shielded from the predetermined direction. Take one state,
The hologram recording method according to claim 7, wherein the spatial light modulator performs phase modulation so that a predetermined phase difference is generated for each pixel.   9. The hologram recording method according to claim 7, wherein the mask optically divides one pixel that emits the reference light into at least two pixels having the same area.

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