JP2008046248A - Spatial light modulator, information recording device, and information reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spatial light modulator without needing position adjustment of an optical element so much by having light use efficiency, and to provide an information recording device and an information reproducing apparatus thereof. <P>SOLUTION: A polarization direction of emission light of amplitude SLM2 rotates up to 90 degrees to incident light of an optical beam 13A and becomes the same polarization direction as a director 19. A half-wavelength plate 14 being a polarizing element is installed in an emission side of the amplitude SLM2. The amplitude modulated emission light 13B is obtained in response to a transmission polarization direction of the half-wavelength plate 14 by passing the half-wavelength plate 14 by the emission light of the amplitude SLM2. Emission polarization 16 of the emission light 13B is matched with incident polarization 15 of the optical beam 13A in the polarization direction. Emission light 13C of a phase SLM3 maintains the polarization direction of a direction equal to the optical beam 13A. In other words, emission polarization 17 of the emission light 13C is matched with incident polarization 15 of the optical beam 13A in the polarization direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a spatial light modulator, an information recording device, and an information reproducing device, and more specifically, a spatial light modulator using a liquid crystal element, an information recording device for recording information by a hologram, and reproducing information from the hologram. The present invention relates to an information reproducing apparatus.

  For high-density optical recording, volume holography, particularly digital volume holography, has been developed at a practical level and attracts attention. Volume holography is a method of writing interference fringes (holograms) three-dimensionally by causing object light carrying information and reference light not carrying information to interfere in the recording medium and actively utilizing the thickness direction of the recording medium. It is a method. Volume holography is characterized in that the diffraction efficiency can be increased by increasing the thickness and the recording capacity can be increased by using multiple recording.

  Digital volume holography is a computer-oriented holographic recording method that uses a recording medium and a recording method similar to those used for volume holography, but in which the recorded image information is limited to a binary digital pattern. In digital volume holography, for example, analog image information such as a picture is once digitized and developed into two-dimensional digital pattern information (two-dimensional page data), which is recorded as image information. At the time of reproduction, the two-dimensional digital pattern information is read out and decoded so that the two-dimensional digital pattern information is restored to the original information and displayed.

  In digital volume holography, even if the signal-to-noise ratio (signal-to-noise ratio) is somewhat poor at the time of reproduction, the original information can be faithfully reproduced by differential detection or error correction by encoding binary data. Can be reproduced. In order to realize large-capacity recording in such an information recording system using holograms, it is necessary to record a large number of holograms in a predetermined recording area. For that purpose, it is necessary to narrow the pitch of each hologram to be recorded. As a method of narrowing the pitch of each hologram to be recorded, there is a method of applying phase modulation to reference light (for example, see Patent Document 1).

  FIG. 8 is a cross-sectional view showing a schematic configuration of a conventional spatial light modulator 100. Referring to FIG. 8, a spatial light modulator (hereinafter also referred to as SLM (Spatial Light Modulator)) 100 includes an amplitude modulation spatial light modulator (hereinafter also referred to as amplitude SLM) 101 having pixel 103A, and pixel 103B. And a spatial light modulation element for phase modulation (hereinafter also referred to as a phase SLM) 102. The amplitude SLM 101 and the phase SLM 102 are formed almost integrally and are spatially connected in series so that the pixels 103A and 103B correspond to each other.

  The spatial light modulator 100 applies amplitude modulation to the object light and applies phase modulation to the reference light. In the spatial light modulator 100, although depending on the coherence length of the light source to be used, the pixels 103A, 103a, and 103b have an optical length shorter than the coherence length in order to superimpose the modulation points of the amplitude and the phase without disturbing the phase. 103B is superimposed.

  FIG. 9 is a cross-sectional view showing a schematic configuration of a conventional spatial light modulator 200. Referring to FIG. 9, the spatial light modulator 200 includes an amplitude SLM 201 having a liquid crystal layer 203A, a phase SLM 202 having a liquid crystal layer 203B, polarizing plates 204A and 204B, substrates 205A and 205B, and a liquid crystal layer 206. Including. The spatial light modulator 200 is a TFT liquid crystal SLM in which a thin film transistor (TFT) is used as an active element and arranged in each pixel of the liquid crystal layers 203A and 203B.

  The amplitude SLM 201 modulates the amplitude of the light source light 208, and a polarizing plate 204A is disposed on the output side. The light source light 208 is linearly polarized laser light and is incident on the amplitude SLM 201 as linearly polarized light polarized in the direction set in the amplitude SLM 201. A further polarizing element may be provided on the incident side or the emission side of the spatial light modulator 200.

  The phase SLM 202 is disposed in close proximity to the amplitude SLM 201 with the polarizing plate 204A, the substrate 205A, the liquid crystal layer 206, the substrate 205B, and the polarizing plate 204B interposed therebetween. Thin polarizing plates are used for the polarizing plates 204A and 204B. Further, thin glass substrates are used for the substrates 205A and 205B.

  By using a thin polarizing plate and a glass substrate as described above, the optical length between the amplitude SLM 201 and the phase SLM 202 can be made shorter than the coherence length of the light source light 208, and the modulation point of the amplitude and phase can be reduced. The optical path difference can be extremely shortened. In the liquid crystal layer 203 </ b> A having the amplitude SLM 201, each pixel corresponds to the liquid crystal layer 203 </ b> B of the phase SLM 202. In the simplest case, the liquid crystal layers 203A and 203B are arranged so as to correspond to each other at equal intervals and in the same shape, and amplitude and phase modulation information is given to each pixel.

  The liquid crystal layer 203A having the amplitude SLM 201 and the liquid crystal layer 203B having the phase SLM 202 use different modes. For the liquid crystal layer 203A, a twisted nematic (TN) mode used in a liquid crystal display device is used. Here, the phase difference (retardation) Δnd is set large to reduce the phase change applied to the amplitude modulation. The liquid crystal layer 203B uses an electrically controlled birefringence (ECB) mode. Here, the phase modulation of 2π or more is possible by aligning the liquid crystal layer 203B in parallel and adjusting the phase difference Δnd.

  FIG. 10 is a diagram for explaining the polarization directions (electric field vibration planes) on the incident side and the emission side of the conventional optical modulation structure 300. FIG. 10 shows a liquid crystal molecule direction (hereinafter also referred to as a director) which is a polarization direction in a state where no electric field is applied. Referring to FIG. 10, the optical modulation structure 300 includes liquid crystal layers 308 and 309. The liquid crystal layer 308 corresponds to the liquid crystal layer 203A of the amplitude SLM 201 in FIG. The liquid crystal layer 309 corresponds to the liquid crystal layer 203B of the phase SLM 202 in FIG.

  The light beam 311 is incident on the liquid crystal layer 308 with incident polarized light 301 parallel to the director 302 having the amplitude SLM 201 and orthogonal to the director 312. Since the liquid crystal layer 308 adopts the TN mode, the light emitted from the liquid crystal layer 308 becomes polarized light 303 rotated by 90 degrees with respect to the incident light of the light beam 311.

  On the light exit side of the liquid crystal layer 308, a linearly polarizing plate 304 that is a polarizing element is provided. When the light emitted from the liquid crystal layer 308 passes through the linear polarizing plate 304, a light beam 311 of the linearly polarized light 306 that is amplitude-modulated according to the transmission polarization direction 305 of the linear polarizing plate 304 is obtained. The light beam 311 is incident on the liquid crystal layer 309 in parallel with the director 307 of the phase SLM 202. Thus, the optical modulation structure 300 emits the light beam 311 of the polarized light 310 whose amplitude and phase are separately modulated.

  FIG. 11 is a cross-sectional view showing a schematic configuration of a conventional optical device 400 that simultaneously applies amplitude modulation and phase modulation. Referring to FIG. 11, optical device 400 includes a TN mode liquid crystal element 402, an ECB mode liquid crystal element 406, and flat microlens arrays 411 and 413.

  The optical device 400 uses an afocal optical system composed of a pair of flat microlens arrays 411 and 413 to connect the two liquid crystal elements 402 and 406. In FIG. 11, a Fourier transform plane FS is an image side focal plane of the front-stage flat microlens array 411 and an object-side focal plane with respect to the rear-stage flat microlens array 413 as indicated by a focal length f.

The pair of flat microlens arrays 411 and 413 optically connect the corresponding pixels of the two liquid crystal elements 402 and 406. In the optical device 400, in order to compensate the phase change generated in the TN mode liquid crystal element 402 at the ECB mode liquid crystal element 406, the transmission axis of the output side polarizing plate (not shown) of the TN mode liquid crystal element 402 is used. Must be parallel to the liquid crystal molecular direction (director) of the liquid crystal element 406 in the ECB mode.
Japanese Patent No. 3141440

  When the amplitude SLM 101 and the phase SLM 102 are spatially connected in series as in the spatial light modulator 100 of FIG. 8, it is necessary to arrange the pixels 103A and 103B so as to correspond to each other. Further, when information is recorded by hologram using the amplitude SLM 201 and the phase SLM 202 as in the spatial light modulator 200 of FIG. 9, the light beam is emitted as described in the optical modulation structure 300 of FIG. Light utilization efficiency is poor because it passes through two SLMs. Furthermore, when the configuration like the optical device 400 of FIG. 11 is adopted, there is a problem that the position adjustment of the flat microlens arrays 411 and 413 installed between the two liquid crystal elements 402 and 406 must be strictly performed. was there.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a spatial light modulator, an information recording apparatus, and an information reproducing apparatus that have high light utilization efficiency and do not require much positional adjustment of optical elements.

  The present invention is a spatial light modulator that spatially modulates a light beam, and is arranged in parallel with an amplitude modulation spatial light modulation device that modulates the amplitude of the light beam, and the amplitude modulation spatial light modulation device, and the phase of the light beam And a spatial light modulation element for phase modulation that modulates.

Preferably, the spatial light modulator applies amplitude modulation and phase modulation to the light beam at the same time.
Preferably, the phase modulation spatial light modulation element is disposed around the amplitude modulation spatial light modulation element.

  Preferably, the spatial light modulation element for amplitude modulation and the spatial light modulation element for phase modulation are controlled independently.

Preferably, the spatial light modulator has a thickness in the light beam direction shorter than the coherence length of the light beam.
Preferably, the amplitude modulation spatial light modulation element and the phase modulation spatial light modulation element are constituted by liquid crystal elements of different modes.

  Preferably, the spatial light modulator for amplitude modulation is composed of a twisted nematic mode liquid crystal element.

  Preferably, the spatial light modulation element for phase modulation is composed of a liquid crystal element of an electric field control birefringence mode.

Preferably, a half-wave plate is provided on the emission side of the spatial light modulator for amplitude modulation.
According to another aspect of the present invention, there is provided an information recording apparatus for recording information on a recording medium by a hologram, a light source that emits light, and a space that generates object light and reference light from light emitted from the light source The optical modulator includes an optical system that causes object light and reference light to interfere with each other in a recording medium. The spatial light modulator is disposed in parallel with the spatial light modulation element for amplitude modulation that generates object light by modulating the amplitude of the light emitted from the light source, and the spatial light modulation element for amplitude modulation that is emitted from the light source. And a spatial light modulator for phase modulation that generates reference light by modulating the phase of the light.

Preferably, the spatial light modulation element for amplitude modulation gives two-dimensional page data to the object light.
Preferably, the spatial light modulator for phase modulation gives random phase modulation to the reference light.

  Preferably, the spatial light modulator simultaneously applies amplitude modulation and phase modulation to the light beam, and the spatial light modulation element for phase modulation is disposed around the spatial light modulation element for amplitude modulation, and the spatial light modulation element for amplitude modulation And the spatial light modulator for phase modulation are controlled independently, and the spatial light modulator has a thickness in the light beam direction shorter than the coherence length of the light beam, and a spatial light modulator for amplitude modulation and a spatial light modulator for phase modulation. Are composed of liquid crystal elements of different modes.

Preferably, the recording medium is made of a photorefractive material.
According to another aspect of the present invention, there is provided an information reproducing apparatus for reproducing information from a recording medium using a hologram, a light source that emits light, and a spatial light modulator that generates reference light from the light emitted from the light source; And an optical system for condensing the reference light on the recording medium, and a photodetector for detecting reproduction light generated from the recording medium by the reference light. The spatial light modulator is disposed in parallel with the spatial light modulation element for amplitude modulation that blocks light emitted from the light source and the spatial light modulation element for amplitude modulation, and modulates the phase of the light emitted from the light source. And a spatial light modulation element for phase modulation that generates reference light.

  Preferably, the spatial light modulation element for phase modulation gives the reference light the same random phase modulation as that during recording.

  Preferably, a light shielding plate is further provided for blocking transmitted reference light generated from the recording medium by the reference light.

  Preferably, the spatial light modulator simultaneously applies amplitude modulation and phase modulation to the light beam, and the spatial light modulation element for phase modulation is disposed around the spatial light modulation element for amplitude modulation, and the spatial light modulation element for amplitude modulation And the spatial light modulator for phase modulation are controlled independently, and the spatial light modulator has a thickness in the light beam direction shorter than the coherence length of the light beam, and a spatial light modulator for amplitude modulation and a spatial light modulator for phase modulation. Are composed of liquid crystal elements of different modes.

  Preferably, the recording medium is made of a photorefractive material.

  According to the present invention, the light use efficiency can be increased, and the position adjustment of the optical element is not so necessary.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a front view showing a schematic configuration of a spatial light modulator 1 according to Embodiment 1 of the present invention. FIG. 2 is a side view showing a schematic configuration of the spatial light modulator 1 according to the first embodiment of the present invention.

  Referring to FIGS. 1 and 2, spatial light modulator 1 of the first embodiment includes an amplitude modulation spatial light modulation element (amplitude SLM) 2 and a phase modulation spatial light modulation element (phase SLM) 3. . The amplitude SLM2 is provided in a circular shape near the center of the spatial light modulator 1. The phase SLM3 is provided in a ring shape around the amplitude SLM2. The amplitude SLM2 and the phase SLM3 are provided in parallel with the traveling direction of the light beam 4.

  In the amplitude SLM2 and the phase SLM3, the modes used in the liquid crystal layer are different as in the spatial light modulator 200 of FIG. In the amplitude SLM2, the twisted nematic (TN) mode used in the liquid crystal display device is used for the liquid crystal layer. In the phase SLM3, an electric field control birefringence (ECB) mode is used for the liquid crystal layer. In the phase SLM3, in order to suppress the change in the amplitude accompanying the phase modulation as much as possible, the pretilt angle of the alignment is set to be high and the lateral twist of the liquid crystal is regulated.

  FIG. 3 is a diagram for explaining the polarization directions (electric field vibration planes) on the incident side and the emission side of the spatial light modulator 1. FIG. 3 shows the liquid crystal molecule direction (director), which is the polarization direction when no electric field is applied, as in the optical modulation structure 300 of FIG. Referring to FIG. 3, spatial light modulator 1 includes an amplitude SLM 2, a phase SLM 3, and a half-wave plate 14. The light beam 13A is incident on the amplitude SLM2 and phase SLM3 with an incident polarization 15 that is parallel to the director 11 of amplitude SLM2 and the director 12 of phase SLM3 and orthogonal to the director 19 of amplitude SLM2.

  Since the amplitude SLM2 employs the TN mode, the output light of the amplitude SLM2 has a polarization direction rotated by 90 degrees with respect to the incident light of the light beam 13A, and has the same polarization direction as that of the director 19. A half-wave plate 14 which is a polarizing element is installed on the emission side of the amplitude SLM2. When the outgoing light with the amplitude SLM2 passes through the half-wave plate 14, the outgoing light 13B that is amplitude-modulated according to the transmitted polarization direction of the half-wave plate 14 is obtained. The outgoing polarized light 16 of the outgoing light 13B has the same polarization direction as the incident polarized light 15 of the light beam 13A.

  Since the phase SLM3 employs the ECB mode, the outgoing light 13C of the phase SLM3 maintains a polarization direction equal to that of the light beam 13A. That is, the polarization direction of the outgoing polarized light 17 of the outgoing light 13C coincides with the incident polarized light 15 of the light beam 13A. Also in the phase SLM3, as in the case of the half-wave plate 14 having the amplitude SLM2, a linearly polarizing element for aligning the polarization on the emission side of the spatial light modulator 1 may be installed as necessary.

  As described above, in the spatial light modulator of the first embodiment, the amplitude SLM2 and the phase SLM3 are arranged in parallel with respect to the direction of the light beam. As a result, the amplitude and phase are modulated by different SLMs in the same light beam, so that light having a uniform polarization direction as a whole can be emitted by arranging a linearly polarizing element or the like on the emission side. Further, the thickness can be reduced as compared with the conventional spatial light modulator, and no extra microlens or spatial filter is required.

  Moreover, since the spatial light modulator of Embodiment 1 controls the amplitude and the phase independently, the amplitude and the wavefront can be arbitrarily controlled. Further, since the total length of the spatial light modulator in the light beam direction is shorter than the coherence length of the light beam, the apparatus can be miniaturized. Further, since information can be rewritten in real time, it can be widely applied as an active optical element in hologram recording / reproduction. Furthermore, by providing a half-wave plate on the emission side of the amplitude SLM2, the polarization of the light beam that passes through the amplitude SLM2 can be controlled.

  Further, in the spatial light modulator of the first embodiment, the amplitude SLM2 and the phase SLM3 are formed from liquid crystal elements in different modes. Since the amplitude SLM2 is composed of a twisted nematic (TN) mode liquid crystal element, amplitude modulation with little phase change can be performed. Since the phase SLM3 includes a liquid crystal element in an electric field controlled birefringence (ECB) mode, a phase exceeding 2π can be controlled. In the first embodiment, a general TN mode is used for the amplitude SLM2 and an ECB mode is used for the phase SLM3. However, the present invention is not limited to these.

[Embodiment 2]
In the second embodiment, a configuration and operation for recording two-dimensional page data as a Fourier transform hologram using a spatial light modulator will be described in detail.

  FIG. 4 is a front view showing a schematic configuration of a spatial light modulator 1A according to Embodiment 2 of the present invention. Referring to FIG. 4, spatial light modulator 1 </ b> A of the second embodiment includes amplitude SLM <b> 2 and phase SLM <b> 3, similarly to spatial light modulator 1 of the first embodiment. The amplitude SLM2 is provided in a circular shape near the center of the spatial light modulator 1A. The phase SLM3 is provided in a ring shape around the amplitude SLM2.

  FIG. 4 shows how the light beam incident on the spatial light modulator 1A is modulated during data recording. As shown in FIG. 4, in the amplitude SLM2, the light transmission state (ON) and the light blocking state (OFF) are controlled, and two-dimensional page data is given to the light beam 22 passing through the amplitude SLM2. On the other hand, in the phase SLM3, random phase modulation is given to the light beam 23 passing through the phase SLM3.

  As described above, in the spatial light modulator 1A of the second embodiment, the light beam 22 that has passed through the amplitude SLM2 serves as so-called object light in hologram recording / reproduction, and the light beam 23 that has passed through the phase SLM3 serves as so-called reference light in hologram recording / reproduction. .

  FIG. 5 is a sectional view showing a schematic configuration of an information recording apparatus 40A according to Embodiment 2 of the present invention. Referring to FIG. 5, the information recording apparatus 40A according to the second embodiment includes a spatial light modulator 1A described in FIG. 4, a light source 41, a collimator lens 42, a condenser lens 45, an objective lens 47, A light shielding plate 50 and a photodetector 51 are provided. The photodetector 51 is constituted by, for example, a CCD (Charge Coupled Device) array, a CMOS (Complementary Metal-Oxide-Semiconductor) sensor, or the like. The information recording device 40A records the two-dimensional page data of the light beam 22 described in FIG. 4 on the recording medium 46 as a hologram.

  The laser light emitted from the light source 41 is converted into a parallel light beam by the collimator lens 42 and then irradiated to the spatial light modulator 1A. As described with reference to FIG. 4, the spatial light modulator 1A includes the amplitude SLM2 and the phase SLM3. The amplitude SLM2 amplitude-modulates the laser light from the light source 41 to generate the object light 43 to which the two-dimensional page data is added. The phase SLM 3 generates reference light 44 by phase-modulating the laser light from the light source 41.

  The object light 43 and the reference light 44 are condensed on the recording medium 46 by the condenser lens 45. If the polarization state and energy density of the object light 43 are substantially equal to the reference light 44 near the condensing point of the recording medium 46, the object light 43 and the reference light 44 interfere near the condensing point. At this time, the two-dimensional page data carried by the object beam 43 is recorded as interference fringes (holograms) in the photorefractive crystal of the recording medium 46.

  As described above, the information recording apparatus 40A according to the second embodiment records two-dimensional page data as a Fourier transform hologram by using the spatial light modulator 1A having the amplitude SLM2 and the phase SLM3 arranged in parallel. be able to. In the information recording apparatus 40A, the object beam 43 and the reference beam 44 are generated by one spatial light modulator 1A and collected by the same condenser lens 45. Thereby, the apparatus can be reduced in size. In the second embodiment, a photorefractive crystal is used as the material of the recording medium 46, but the material is not limited to this as long as the refractive index changes with the light intensity.

[Embodiment 3]
In the third embodiment, a configuration and operation for reproducing the two-dimensional page data recorded as a hologram on the recording medium 46 in the second embodiment will be described in detail.

  FIG. 6 is a front view showing a schematic configuration of a spatial light modulator 1B according to Embodiment 3 of the present invention. Referring to FIG. 6, spatial light modulator 1B of the third embodiment includes an amplitude SLM2B and a phase SLM3. The amplitude SLM2B is provided in a circular shape near the center of the spatial light modulator 1B. The phase SLM3 is provided in a ring shape around the amplitude SLM2B.

  FIG. 6 shows a state of a light beam incident on the spatial light modulator 1B during data reproduction. As shown in FIG. 6, the incident light beam 22 is blocked at the amplitude SLM2B. On the other hand, the phase SLM 3 is formed with the same phase modulation pattern as when the phase modulation was applied to the light beam 23 during recording. In this manner, the spatial light modulator 1B generates ring-shaped reference light by transmitting only the light beam 23 that has passed through the phase SLM3 in the incident light.

  FIG. 7 is a sectional view showing a schematic configuration of an information reproducing apparatus 40B according to Embodiment 3 of the present invention. The information reproducing device 40B of the third embodiment is different from the information recording device 40A of the second embodiment in that the spatial light modulator 1A is replaced with the spatial light modulator 1B. Therefore, description of portions overlapping with those of Embodiment 2 will not be repeated here. The information reproducing device 40B reproduces the two-dimensional page data recorded as a hologram from the recording medium 46 using the reference light of the light beam 23 described in FIG.

  The laser light emitted from the light source 41 is converted into a parallel light beam by the collimator lens 42 and then irradiated to the spatial light modulator 1B. As described with reference to FIG. 6, the spatial light modulator 1B includes the amplitude SLM2B and the phase SLM3. The amplitude SLM2B blocks the laser light from the light source 41. The phase SLM 3 generates a ring-shaped reference light 44 by phase-modulating the laser light from the light source 41. In the phase SLM3, by applying random phase modulation to the reference beam 44 and performing speckle shift multiplex recording, noise due to crosstalk during data reproduction can be suppressed and the shift pitch in shift multiplex recording can be reduced. Can do.

  The ring-shaped reference light 44 is condensed on the hologram recording area of the recording medium 46 by the condenser lens 45. When the reference light 44 is applied to the hologram recording area, reproduction light 48 is generated in addition to the transmitted reference light 49. The reproduction light 48 is converted into parallel light by the objective lens 47 and then detected by the photodetector 51. Thereby, the two-dimensional page data recorded on the recording medium 46 is reproduced. The transmitted reference light 49 is also converted into parallel light by the objective lens 47 and then blocked by the ring-shaped light shielding plate 50 in front of the photodetector 51.

  As described above, the information reproducing apparatus 40B according to the third embodiment reproduces two-dimensional page data recorded as a hologram by using the spatial light modulator 1B3 having the amplitude SLM2B and the phase SLM3 arranged in parallel. be able to. Further, in the information recording apparatus 40B, the reproduction light 48 to which the same phase modulation as the recording reference light 44 (see FIG. 5) is given is generated. Thereby, the information recorded on the recording medium 46 can be accurately reproduced.

  In the second and third embodiments, the recording and reproduction of the transmission hologram have been described. Similarly, the recording and reproduction of the reflection hologram can be performed by recording and reproducing two-dimensional page data as a hologram. Further, although the information recording device 40A of the second embodiment and the information reproducing device 40B of the third embodiment have been described separately, they can be integrated as an information recording / reproducing device.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

It is the front view which showed schematic structure of the spatial light modulator 1 by Embodiment 1 of this invention. 1 is a side view showing a schematic configuration of a spatial light modulator 1 according to Embodiment 1 of the present invention. FIG. FIG. 4 is a diagram for explaining polarization directions on the incident side and the emission side of the spatial light modulator 1. It is the front view which showed schematic structure of 1 A of spatial light modulators by Embodiment 2 of this invention. It is sectional drawing which showed schematic structure of 40 A of information recording apparatuses by Embodiment 2 of this invention. It is the front view which showed schematic structure of the spatial light modulator 1B by Embodiment 3 of this invention. It is sectional drawing which showed schematic structure of the information reproduction apparatus 40B by Embodiment 3 of this invention. FIG. 6 is a cross-sectional view illustrating a schematic configuration of a conventional spatial light modulator 100. FIG. 6 is a cross-sectional view showing a schematic configuration of a conventional spatial light modulator 200. It is a figure for demonstrating the polarization direction of the incident side of the conventional optical modulation structure 300, and an output side. It is sectional drawing which showed schematic structure of the conventional optical apparatus 400 which provides amplitude modulation and phase modulation simultaneously.

Explanation of symbols

  1, 1A, 1B, 100, 200 Spatial light modulator, 2, 2B, 101, 201 Amplitude SLM, 3, 102, 202 Phase SLM, 14 1/2 wavelength plate, 40A information recording device, 40B information reproducing device, 41 Light source, 42 collimator lens, 45 condenser lens, 46 recording medium, 47 objective lens, 50 light shielding plate, 51 photodetector, 103A, 103B pixel, 203A, 203B liquid crystal layer, 204A, 204B polarizing plate, 205A, 205B substrate, 206, 308, 309 Liquid crystal layer, 400 Optical device, 402, 403 Liquid crystal element, 411, 413 Flat microlens array.

Claims (19)

A spatial light modulator for spatially modulating a light beam,
A spatial light modulator for amplitude modulation for modulating the amplitude of the light beam;
A spatial light modulator comprising: a phase modulation spatial light modulation element which is arranged in parallel with the amplitude modulation spatial light modulation element and modulates the phase of the light beam.   The spatial light modulator according to claim 1, wherein the spatial light modulator simultaneously applies amplitude modulation and phase modulation to the light flux.   The spatial light modulator according to claim 1, wherein the phase modulation spatial light modulation element is arranged around the amplitude modulation spatial light modulation element.   The spatial light modulator according to claim 1, wherein the spatial light modulator for amplitude modulation and the spatial light modulator for phase modulation are controlled independently.   The spatial light modulator according to claim 1, wherein the spatial light modulator has a thickness in the light beam direction shorter than a coherence length of the light beam.   2. The spatial light modulator according to claim 1, wherein the spatial light modulator for amplitude modulation and the spatial light modulator for phase modulation are composed of liquid crystal elements of different modes.   The spatial light modulator according to claim 6, wherein the amplitude modulation spatial light modulation element includes a twisted nematic mode liquid crystal element.   The spatial light modulator according to claim 6, wherein the phase modulation spatial light modulation element includes a liquid crystal element in an electric field control birefringence mode.   The spatial light modulator according to claim 1, wherein a half-wave plate is provided on an emission side of the spatial light modulator for amplitude modulation. An information recording apparatus for recording information on a recording medium by a hologram,
A light source that emits light;
A spatial light modulator that generates object light and reference light from light emitted from the light source;
An optical system for causing the object light and the reference light to interfere with each other in the recording medium,
The spatial light modulator is
A spatial light modulation element for amplitude modulation that generates the object light by modulating the amplitude of light emitted from the light source;
An information recording apparatus comprising: a phase modulation spatial light modulation element that is arranged in parallel with the amplitude modulation spatial light modulation element and generates the reference light by modulating a phase of light emitted from the light source.   The information recording apparatus according to claim 10, wherein the spatial light modulation element for amplitude modulation gives two-dimensional page data to the object light.   The information recording apparatus according to claim 10, wherein the phase modulation spatial light modulation element applies random phase modulation to the reference light.   The information recording apparatus according to claim 10, wherein the spatial light modulator is the spatial light modulator according to claim 2.   The information recording apparatus according to claim 10, wherein the recording medium is made of a photorefractive material. An information reproducing apparatus for reproducing information from a recording medium by a hologram,
A light source that emits light;
A spatial light modulator that generates reference light from the light emitted from the light source;
An optical system for condensing the reference light on the recording medium;
A photodetector for detecting reproduction light generated from the recording medium by the reference light,
The spatial light modulator is
A spatial light modulator for amplitude modulation that blocks light emitted from the light source;
An information reproducing apparatus including: a phase modulation spatial light modulation element that is arranged in parallel with the amplitude modulation spatial light modulation element and generates the reference light by modulating a phase of light emitted from the light source.   The information reproducing apparatus according to claim 15, wherein the spatial light modulator for phase modulation gives the reference light the same random phase modulation as that during recording.   The information reproducing apparatus according to claim 15, further comprising a light shielding plate that blocks transmitted reference light generated from the recording medium by the reference light.   The information reproducing apparatus according to claim 15, wherein the spatial light modulator is the spatial light modulator according to claim 3.   The information reproducing apparatus according to claim 15, wherein the recording medium is the recording medium according to claim 10.

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