JP2006243760A - Spatial light modulating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spatial light modulating device with high efficiency of using light by the help of a reflection type spatial light modulator. <P>SOLUTION: The readout light in the spatial light modulating device using the reflection type spatial light modulator is P polarized light which is made diagonally incident on a light reflection layer 17. The liquid crystal in the light reflection layer 17 is so oriented that liquid crystal molecules incline within the plane inclusive of both optical axes of readout light which is incident light and modulation light which is exit light i.e. the plane parallel to the normal plane by accompanying the voltage application by a driving circuit 12, for example, to attain horizontal orientation or perpendicular orientation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spatial light modulation device using liquid crystal as a light modulation material, and more particularly to a spatial light modulation device using a reflective spatial light modulator.

  There are two types of spatial light modulators: intensity modulation type and phase modulation type. The former intensity modulation type is a type used for a light valve of a liquid crystal television or a projector, and many spatial light modulation devices are of this type. On the other hand, the latter phase modulation type is considered promising in fields such as optical information processing and hologram processing. This is because, unlike the intensity modulation type, the phase modulation type can increase the light use efficiency. A system using such a phase modulation type spatial light modulator is disclosed in J. Gruxstadt et al. In "Loseless Light Projection", Optics Letters Vol.22, No.18.

  In the case of a reflective spatial light modulation device, unlike the transmission type, the incident surface of the readout light and the exit surface of the modulated light are the same surface. Therefore, the modulated light is usually separated from the readout light using a half mirror. . As a result, the light utilization efficiency is lowered, and the merit of the phase modulation type is lost. As a system that does not use a half mirror, there is a method in which the optical axis of the readout light and the modulated light is shifted by making the readout light incident obliquely on the incident surface, but when the light is incident obliquely on the liquid crystal layer Since the polarization plane of the modulated light rotates, only a low diffraction efficiency can be obtained as compared with normal incidence. As a result, there is a problem that only low light utilization efficiency can be obtained.

  In view of the above problems, an object of the present invention is to provide a spatial light modulator that uses a reflective spatial light modulator and has high light utilization efficiency.

  In order to solve the above-mentioned problem, a light modulation layer using a liquid crystal as a light modulation material and a light reflection layer are provided, and readout light incident on the light modulation layer from the opposite side of the light reflection layer is reflected by the light reflection layer. In order to write the image information in the reflection type spatial light modulator and the phase modulation type reflection type spatial light modulator that performs the light modulation twice and outputs the modulated light from the incident surface side by passing the light modulation layer again. Linearly polarized light having a polarization direction within a normal plane that is disposed on the incident surface side of the reflective spatial light modulator and includes the optical axis of the readout light and the normal of the incident surface of the reflective spatial light modulator Reading light incident means for making the reflected light enter the reflective spatial light modulator, and the modulated light is also linearly polarized light having a polarization direction in the normal plane, and the liquid crystal in the light modulation layer Is a plane that includes the optical axes of both the readout light and the modulated light when a voltage is applied. Liquid crystal molecules in the line plane is characterized in that it is oriented to be inclined.

  According to this, when linearly-polarized readout light having a polarization direction is incident obliquely within a normal plane including the optical axis of the readout light and the normal of the entrance surface of the spatial light modulator, the readout light is The light has a polarization direction within the normal plane including the normal axis of the optical axis and the incident surface of the spatial light modulator. Since the liquid crystal in the light modulation layer is arranged so as to be inclined in this normal plane with voltage application, the polarization plane of the readout light and the orientation direction of the liquid crystal molecules are not twisted. Phase modulation can be performed without any problem. Since the reflected light is the same, the polarization plane of the finally output modulated light is the same as the incident light, and is output as linearly polarized light having a polarization direction within the normal plane. Therefore, it is possible to maintain high diffraction efficiency as in the case of normal incidence.

  It is preferable to further include a Fourier transform lens that is arranged on the outgoing light path of the modulated light and that performs Fourier transform on the modulated light.

  A spatial light modulation device that switches connection between elements between a first parallel operation board including an information output laser diode array and a second parallel operation board including an information input light receiver array, The laser diode array for information output of one parallel operation board is read light incident means for causing the read light to enter the reflective spatial light modulator, and the read light output from the first parallel operation board is reflected to the reflective spatial light. It is preferable to further include a prism that allows the modulated light to be incident on the information input light receiver array of the second parallel operation board and a Fourier transform lens that performs Fourier transform on the read light and the modulated light.

  The writing means includes a writing light source that emits writing light, a liquid crystal television that writes predetermined image information to the writing light when the writing light passes, and a control means that controls the image information written to the writing light. Is preferred.

  The reading light incident means causes P-polarized light having a polarization direction in the normal plane to enter the reflective spatial light modulator as read light, and the modulated light is also P-polarized light having a polarization direction in the normal plane. May be.

  The reading light incident means is preferably a laser.

  The liquid crystal in the light modulation layer is preferably subjected to vertical alignment or horizontal alignment treatment. Liquid crystal molecules are arranged in a predetermined plane without twisting by subjecting the liquid crystal to vertical alignment or horizontal alignment treatment. By aligning the predetermined plane with the slope, it becomes easy to perform phase modulation without rotation of the polarization plane.

  The reading light incident means preferably causes the reading light to enter the light reflection layer of the reflective spatial light modulator obliquely.

  According to the present invention, the linearly polarized light having the polarization direction in the normal plane is used for the read light at an oblique incidence, and the liquid crystal in the light modulation layer of the spatial light modulator is a plane parallel to the normal plane of the read light when a voltage is applied. Since the liquid crystal molecules are aligned so as to be inclined, the plane of polarization of light does not rotate during light modulation. Since the light is obliquely incident and reflected on the spatial light modulator, the incident optical axis and the outgoing optical axis are separated, the degree of freedom of arrangement of the incident and outgoing optical systems is increased, and the light use efficiency is increased.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a light modulation layer of a spatial light modulation device according to the present invention, and FIG. 2 is a schematic cross-sectional view showing a configuration of a light modulator portion having this light modulation layer. FIG. 3 is a schematic diagram showing a first embodiment of a spatial light modulation device according to the present invention having this light modulator.

  First, the structure of the spatial light modulator used in the spatial light modulation device according to the present invention will be described with reference to FIGS.

  The spatial light modulator (SLM) 1 shown in FIG. 2 has ITO 13 on the surface opposite to the incident surface of the glass substrate 12 on which the AR coating 11 that prevents unnecessary reflection of incident light is applied to the incident surface of the writing light. A photoconductive layer 14 made of amorphous silicon (a-Si) whose resistance changes according to the intensity of incident light and a mirror layer 15 made of a dielectric multilayer film are laminated. On the other hand, on the reading light side, ITO 20 is laminated on the surface opposite to the incident surface of the glass substrate 21 similarly provided with the AR coating 22, and the alignment layers 16 and 19 are provided on the mirror layer 15 and the ITO 20, respectively. The alignment layers 16 and 19 are connected to each other through a frame-shaped spacer 18, and a liquid crystal layer is provided by filling a frame of the spacer 18 with a nematic liquid crystal to form a light modulation layer 17. . By the alignment layer 16, the nematic liquid crystal in the light modulation layer 17 is aligned parallel or perpendicular to the surface of the alignment layer 16. And the drive apparatus 2 is connected to ITO13 and 20, and the predetermined voltage is applied between both.

  Here, the alignment of the liquid crystal in the light modulation layer 17 will be described with reference to FIG. FIG. 1A shows a case where a parallel alignment liquid crystal type is used as the light modulation layer 17, and FIG. 1B shows a case where a vertical alignment liquid crystal type is used.

  As shown in FIGS. 1A and 1B, the direction perpendicular to the paper surface in the figure is the X direction, the paper surface is the YZ plane, and the thickness direction of the light modulation layer 17 is the Z direction. In the spatial light modulation device according to the present invention, as described later, the light incident on the light modulation layer 17 has the YZ plane in FIGS. 1A and 1B as a slope. Here, the normal plane refers to a plane including any of the incident optical axis, the reflected optical axis, and the mirror normal when linearly polarized light is incident on the mirror and reflected. The incident light is P-polarized light, that is, linearly polarized light having a polarization direction within the normal. The liquid crystal in the light modulation layer 17 is aligned so that the alignment direction is inclined in a plane parallel to the normal plane when a voltage is applied to the light modulation layer 17. By aligning the liquid crystal molecules in the light modulation layer 17 in this way, the polarization plane of the incident light is not rotated, and the polarization direction of the emitted light is maintained as P-polarized light.

  Next, a first embodiment of the light modulation device according to the present invention will be described with reference to FIG. A light source 3 for writing light, a transmissive liquid crystal television 5 for displaying an image of the writing light, and an image signal included in the writing light on the photoconductive layer 14 of the SLM 1 on the writing light incident surface side of the SLM 1 shown in FIG. An imaging lens 6 that forms an image is disposed, and a writing electric signal generator 4 that controls image display is connected to the transmissive liquid crystal television 6.

  On the other hand, on the reading light incident surface side of the SLM 1, a He—Ne laser 7 serving as a reading light source, a lens 8, and a spacer are disposed on an optical axis inclined at an angle θ with respect to the normal line within the normal surface of the incident surface. A Schal filter 9 and a collimating lens 10 are arranged, and a Fourier transform lens 30 is arranged on the outgoing optical path.

  Next, the operation of this embodiment will be described. In the writing light emitted from the light source 3 on the writing light side, predetermined image information is written under the control of the electric signal generator 4 when passing through the liquid crystal television 5. The writing light having this image information is imaged on the photoconductive layer 14 of the SLM 1 by the imaging lens 6. An AC voltage of several volts is applied between the ITOs 13 and 20 of the SLM 1 by the driving device 2, but the electrical impedance of the photoconductive layer 14 varies depending on the pixel position depending on the image written on the photoconductive layer 14. . As a result, the divided voltage applied to the light modulation layer 17 varies depending on the pixel position. In this case, the light source 3, the liquid crystal television 5, and the electric signal generator (control means) 4 function as writing means for writing image information into the SLM 1.

  On the other hand, the linearly polarized light emitted from the He—Ne laser 7 is adjusted to parallel light by the lens 8, the spatial filter 9 and the collimating lens 9, and enters the light modulation layer 17 of the SLM 1 as P-polarized light. As described above, since the divided voltage applied to the light modulation layer 17 varies depending on the pixel position, the inclination of the liquid crystal molecules changes according to this voltage. At this time, the orientation direction of the liquid crystal molecules changes within the slope. As a result, the refractive index of the light modulation layer 17 changes depending on the pixel position. The readout light incident on the light modulation layer 17 is phase-modulated by this refractive index change, reflected by the mirror layer 15, and output again from the incident surface. At this time, since the polarization plane does not rotate, efficient phase modulation can be performed. A predetermined hologram image can be displayed by Fourier transforming the emitted readout light with the Fourier transform lens 30. In this case, the He—Ne laser 7, the lens 8, the spatial filter 9, and the collimating lens 10 function as reading light incident means that causes the reading light to enter the SLM 1.

  The present inventors conducted a comparative experiment for confirming the improvement of the light utilization efficiency of the spatial light modulation device according to the present invention.

  In the apparatus shown in FIG. 3, when the vertical stripe image is displayed on the liquid crystal television 6 and the number of vertical stripes to be displayed, that is, the spatial frequency and the incident / exit angle θ of the readout light is changed, the readout light emitted from the SLM 1 is used. The intensity ratio of the first-order diffracted light, that is, the diffraction efficiency was measured. In the experiment, parallel alignment liquid crystal was used as the light modulation layer 17 of the SLM 1, and the embodiment using the alignment shown in FIG. 1A according to the present invention and the S-polarized light as shown in FIG. Comparison was made with a comparative example in which the alignment direction of the liquid crystal was arranged orthogonal to the slope of the readout light.

  FIG. 5 shows the experimental results of the diffraction efficiency of the example, and FIG. 6 shows the experimental results of the diffraction efficiency of the comparative example.

  In the example, even when the incident / exit angle θ changes, the diffraction efficiencies are almost the same and show high efficiency, whereas in the comparative example, the diffraction efficiency decreases as the incident / exit angle θ increases. confirmed. In the first embodiment according to the present invention, that is, in the first embodiment of the present invention, the incident / exit angle θ can be increased while maintaining the diffraction efficiency, that is, the light utilization efficiency high. For this reason, the incident optical path and the outgoing optical path of the readout light can be completely separated without using an additional optical member. Therefore, high light utilization efficiency can be obtained. Further, there is an advantage that the degree of freedom in designing the incident optical path and the outgoing optical path is increased.

  FIG. 7 is a schematic diagram showing a second embodiment of the spatial light modulation device according to the present invention. This device is an optical interconnection device 60 that switches connections between elements between parallel operation boards 40 and 50 that exchange information with light.

  Both parallel operation boards 40 and 50 include light receiving arrays 41 and 51 for information input and laser diode arrays 42 and 52 for information output, respectively. The optical interconnection device 60 is disposed between the laser diode array 42 of the parallel calculation board 40 and the light receiver array 51 of the parallel calculation board 50.

  The interconnection device 60 includes the SLM 1 having the structure shown in FIGS. 1 and 2, and the Fourier transform lens 30 and the prism 61 are disposed on the reading light incident surface side from the incident surface side. On the other hand, an imaging lens 6, a transmissive liquid crystal television 5 for displaying a written image, and a light source 3 are arranged on the writing light incident surface side, and the liquid crystal television 5 is connected to the writing image control device 4. .

  Next, the operation of the optical interconnection device 60 will be described. When the controller 4 is controlled to display a hologram pattern for switching the optical path on the liquid crystal television 5 and write light is emitted from the light source 3, the hologram pattern displayed on the liquid crystal television 5 is converted into the SLM 1 via the imaging lens 6. An image is formed on the photoconductive layer 14. In this case, the light source 3, the liquid crystal television 5, the control device (control means) 4, and the imaging lens 6 function as writing means for writing image information to the SLM 1.

  The output signal of the parallel operation board 40 is output as two-dimensional or one-dimensional image information by the laser diode array 42. This image is reflected by the prism 61 and guided to the SLM 1 via the Fourier transform lens 30. And it injects into the light modulation layer 17 of SLM1. The readout light undergoes predetermined light modulation in accordance with the optical path switching hologram pattern displayed on the liquid crystal television 5. The image thus modulated is reflected again by the prism 61 through the Fourier transform lens 30 and is incident on the light receiver array 51 of the parallel calculation board 50. By changing the hologram image displayed on the liquid crystal television 6, it is possible to switch the connection between arbitrary pixels of the laser diode array 42 of the parallel calculation board 40 and the light receiver array of the parallel calculation board 50. In this case, the parallel calculation board 40 and the laser diode array 42 function as read light incident means for causing the read light to enter the SLM 1.

  Since linearly polarized light is used as the readout light and the liquid crystal alignment direction of the SLM 1 is set as shown in FIG. 1A or 1B, high diffraction efficiency can be obtained. Can be connected to.

  The spatial light modulation device of the present invention is not limited to the embodiment described above, and can be applied to various spatial light modulation devices using phase modulation. For example, it can be applied to computer synthesized holograms, optical computing, and the like. Various lasers can be used as the linearly polarized light source.

  Further, the alignment direction of the liquid crystal is not limited to the horizontal alignment and the vertical alignment shown in FIGS. 1A and 1B, and may be a hybrid alignment or a tilt alignment. However, it goes without saying that the liquid crystal molecules need to be aligned in a direction inclined in the normal plane when a voltage is applied.

It is a figure explaining the liquid crystal arrangement | positioning in the light modulation layer of the spatial light modulation apparatus which concerns on this invention. It is a figure which shows the structure of the spatial light modulator used for the spatial light modulation apparatus which concerns on this invention. 1 is a diagram showing a first embodiment of a spatial light modulation device according to the present invention. It is a figure explaining the liquid crystal arrangement | positioning in the light modulation layer of the spatial light modulation apparatus of a comparative example. It is a graph which shows the measurement result of the diffraction efficiency in 1st Embodiment. It is a graph which shows the measurement result of the diffraction efficiency in a comparative example. It is a figure which shows 2nd Embodiment of the spatial light modulation apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Spatial light modulator, 2 ... Drive apparatus, 3 ... Light source, 5 ... Liquid crystal television, 6 ... Imaging lens, 7 ... Laser, 13, 20 ... ITO, 14 ... Photoconductive layer, 15 ... Mirror layer, 17 ... Light modulation layer, 30 ... Fourier transform lens.

Claims (8)

A light modulation layer comprising a liquid crystal as a light modulation material; and a light reflection layer, wherein the light reflection layer reflects the read light incident on the light modulation layer from the opposite side of the light reflection layer. A phase modulation type reflective spatial light modulator that performs light modulation twice by passing the light again and outputs the modulated light from the incident surface side, and
Writing means for writing image information to the reflective spatial light modulator;
Linearly polarized light disposed on the incident surface side of the reflective spatial light modulator and having a polarization direction within a normal plane including the optical axis of the readout light and the normal of the incident surface of the reflective spatial light modulator Read light incident means for making the light of the above incident on the reflective spatial light modulator as the read light,
The modulated light is also linearly polarized light having a polarization direction in the normal plane,
The liquid crystal in the light modulation layer is oriented so that liquid crystal molecules are tilted in a plane parallel to a plane including the optical axes of both the readout light and the modulated light in accordance with voltage application. Spatial light modulation device.   The spatial light modulation device according to claim 1, further comprising a Fourier transform lens arranged on an emission optical path of the modulated light and performing Fourier transform on the modulated light. A spatial light modulation device that switches connection between elements between a first parallel operation board including an information output laser diode array and a second parallel operation board including an information input light receiver array,
The information output laser diode array of the first parallel operation board is the read light incident means for causing the read light to be incident on the reflective spatial light modulator.
A prism that causes the readout light output from the first parallel computing board to enter the reflective spatial light modulator and causes the modulated light to enter the information input light receiver array of the second parallel computing board. When,
The spatial light modulation device according to claim 1, further comprising a Fourier transform lens that Fourier transforms the readout light and the modulated light.   The writing means includes a writing light source that emits writing light, a liquid crystal television that writes predetermined image information to the writing light when the writing light passes, and a control means that controls the image information to be written to the writing light. The spatial light modulation device according to claim 1, wherein The readout light incident means causes P-polarized light having a polarization direction in the normal plane to enter the reflective spatial light modulator as the readout light,
The spatial light modulator according to claim 1, wherein the modulated light is also P-polarized light having a polarization direction in the normal plane.   6. The spatial light modulation device according to claim 1, wherein the reading light incident means is a laser.   The spatial light modulation device according to claim 1, wherein the liquid crystal in the light modulation layer is subjected to a vertical alignment process or a horizontal alignment process. The spatial light modulation device according to claim 1, wherein the readout light incident unit obliquely enters the readout light into the light reflection layer of the reflective spatial light modulator.

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