JPH06250205A - Spatial optical modulator - Google Patents

Abstract

PURPOSE:To provide the spatial optical modulator capable of spatially modulating light in paralle, writing images at an extremely high speed and reading out the images after amplifying the images. CONSTITUTION:This spatial optical modulator is constituted by arranging an optical transmission film 106, a dielectric mirror 105 and a liquid crystal oriented film 104b deposited on a glass substrate 101d having a transparent electrode 103b, arranging a liquid crystal oriented film 104a on another glass substrate 101c having a transparent electrode 103a, disposing both liquid crystal oriented films 104a, 104b opposite to each other and packing a liquid crystal 102 of a twisted chiral smectic C phase therebetween.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator capable of spatially modulating light in parallel to write an image at an extremely high speed and amplify and read the image.

[0002]

2. Description of the Related Art The function of a spatial light modulator (hereinafter abbreviated as "SLM") is that a two-dimensional pattern (for example, an image) is written on an SLM by writing light and written by another light (reading light). The dimensional pattern is read out. This makes it possible to perform threshold processing of image light, inversion or incoherent / coherent conversion between read light and write light, wavelength conversion, and the like.

As a structure of a conventional SLM, for example, a liquid crystal light valve will be described with reference to FIG. Figure 7
FIG. 4 is a cross-sectional view of a liquid crystal light valve. In the figure, 11 is a power source, 12a and 12b are glass plates, 13a and 13b are transparent electrodes, 14a and 14b are alignment films, 15 is a dielectric mirror,
Reference numeral 16 is a photoconductive film, 18 is a sealant, 19 is a light-shielding film, and 20 is a twisted nematic liquid crystal (hereinafter abbreviated as "TN liquid crystal").

The operating principle of this element is as follows.
During operation, an AC voltage is applied from the power source 11 to each layer by the transparent electrodes 13a and 13b. That is, the current is transparent electrode 13a, photoconductive film 16, light-shielding film 19, dielectric mirror 15, alignment film 14a, TN liquid crystal 20, alignment film 14.
b, then the transparent electrode 13b.

Further, the light pattern simultaneously written in the element is the glass substrate 12 as the writing light L _a from the right side in the drawing.
It is incident on the photoconductive film 16 via b. Further, the read light L _b enters from the left side of the drawing, is modulated by the TN liquid crystal 20, is reflected by the dielectric mirror 15, is again modulated by the TN liquid crystal 20, and is emitted to the left side. At this time, the photoconductive film 1
The resistance of the photoconductive film changes according to the light intensity at each point depending on the light pattern irradiated on the light.

[0006]

By the way, the photoconductive film 1 is used.
For example, CdS is known as 6, but this material is
When irradiated with (especially visible light), the resistance value decreases. this
Modulation of current by light, and eventually applied voltage to TN liquid crystal 20.
Causes a change in pressure, which causes the writing light L _aIlluminating
The optical rotatory power of the liquid crystal can be controlled by the presence or absence of the irradiation. Reflective
No voltage is applied to the TN liquid crystal used in the device.
If not, keep the spiral structure that rotates 45 ° in the cell.
Hold, but if a voltage exceeding the threshold is applied,
The child stands perpendicular to the cell plane. Therefore, the read light L_bTo
If you set it to linearly polarized light, it will read according to the writing pattern.
Light out L_bThe polarization of can be modulated.

However, although this liquid crystal light valve is used in projection displays and the like,
The TN liquid crystal 20 has a drawback that the switching time is as long as several tens to several hundreds ms and it does not sufficiently support moving images.
In order to solve this problem, an SLM using a surface-stabilized ferroelectric liquid crystal (abbreviated as SSFLC) has been developed, but the gradation important for image display quality is not sufficiently displayed, or gradation expression is not performed. However, there was a drawback that the driving became extremely complicated.

The present invention has been made in view of such a background, and an object thereof is to provide a high-speed spatial light modulator capable of optically analog-modulating (gradation-modulating) two-dimensional data such as an image. And

[0009]

The structure of the spatial light modulator according to the present invention to achieve the above-mentioned object is a photoconductive film, a dielectric mirror and a liquid crystal alignment film deposited on one glass substrate having a transparent electrode. A liquid crystal alignment film is arranged on the other glass substrate having a transparent electrode, the liquid crystal alignment films are opposed to each other, and the gap between them is filled with a liquid crystal of twisted chiral smectic C phase. And

Further, in the above configuration, the twist
Chiral smectic C phase liquid crystal twist angle is 4
It is characterized in that it is 5 ° or 90 °.

[0011]

Function: The liquid crystal molecules of the chiral smectic C phase are originally arranged so as to naturally draw a spiral, but in the past, this liquid crystal unwound the spiral structure by pushing the molecules into a narrow gap of several microns. It is used as "surface-stabilized ferroelectric liquid crystal". This surface-stabilized ferroelectric liquid crystal is characterized by artificially deciding the arrangement of molecules, and thereby exhibiting a bright and dark bistable state and a memory property. Therefore, it is very difficult to reproduce a gradation image including a halftone. On the other hand, the liquid crystal of the chiral smectic C phase used in the present invention undergoes the alignment treatment according to the helical pitch peculiar to the material even though it is in the gap, so that it can be in an intermediate state. That is, when applied to a spatial light modulator as in the present invention, analog modulation can be easily performed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a spatial light modulator (SLM), 2 is an SLM
White writing light source, which acts as a writing light source to
Reference numeral 3 is an image (mask) which is a writing pattern to the SLM, 4 is a read laser light source which functions as a read light source of the SLM, and 5 is a light source from the laser light source 4.
A magnifying collimator that expands to the aperture of 6a, a polarizer that linearly polarizes the read laser light, and an analyzer 7 that makes the read light reflected from the SLM into orthogonal Nicols,
Reference numeral 8 is a semi-transparent mirror (half mirror) that separates the incident and the emission of the readout light, 9 is a lens that forms an image between the SLM 1 and the screen 10, and 10 is a screen that projects the readout image.
Is a drive power source for the SLM, and 12 is a shutter.

Next, the operation principle of the liquid crystal of the twisted chiral smectic C phase (hereinafter abbreviated as "TCC") will be described with reference to FIG. FIG. 2A shows the orientation state of molecules when a voltage is not applied (voltage off), and FIG. 2B shows the orientation state of molecules when a voltage is applied (voltage on). In the figure, 101a and 101b are glass substrates, 102a is a molecule of twisted chiral smectic C phase liquid crystal (hereinafter abbreviated as "TCC liquid crystal"), and 120 is a mirror. The arrows shown on the glass substrates 101a and 101b are the orientation directions by rubbing or the like. Although transparent electrodes are vapor-deposited on the inner surface of each of the two glass substrates 101a and 101b, they are not shown in the figure. The reading light L _b enters from the glass substrate 101a on the upper surface, is reflected by the mirror 120 on the lower surface, and exits from the upper surface again.

The relationship between the orientation direction and the polarization of the readout light will be described with reference to FIG. With respect to the orientation direction, the orientation of the upper surface is used as a reference, and the orientation of the lower surface is shifted by 45 °. As shown in FIG. 2A, when no voltage is applied, the TCC liquid crystal molecules 10
The orientations of 2a are arranged in a spiral shape from the top to the bottom in the figure along with the orientation direction applied to the glass substrate. Since the pitch of this spiral is matched with the pitch of the TCC liquid crystal molecules 102a used, the thickness of the cell is set to about 1/4 of the pitch. Further, the tilt angle of the liquid crystal is preferably about 22.5 °. If the polarization of the incident light is matched with the orientation of the upper surface, the polarization of the emitted light becomes a linearly polarized light that is exactly 90 ° apart while passing through the reciprocating twice by the optical rotation of the liquid crystal.

On the other hand, if a voltage is applied between the substrates as shown in FIG. 2 (b), TC is caused by the interaction between the spontaneous polarization having a component parallel to the shortening of the TCC liquid crystal molecule 102a and the electric field.
All the C liquid crystal molecules 102a are aligned in the alignment direction on the upper surface.
However, in a small area under the substrate, the anchoring energy of the orientation restrains the switching. In this state, the polarization of the incident light does not change even if it passes through the liquid crystal. Therefore, according to the liquid crystal cell having this structure, the polarization of the read light L _b can be freely modulated by controlling the applied voltage due to the optical activity of the molecule. Further, when this read out emitted light is observed through an analyzer, intensity modulation is applied.

The following Table 1 shows the relationship between the applied voltage and the brightness of the read light in the optical system using the polarizer and the analyzer.

[0018]

[Table 1]

In order from the above list, the state name, voltage, alignment state of liquid crystal, and light and dark in the crossed Nicols and parallel Nicols arrangement of the reading optical system are shown. According to this "Table 1", in the state of applying a negative voltage (a), the liquid crystal molecules are all aligned in the same direction due to the interaction between the spontaneous polarization and the electric field, and the polarization of the passing light is not changed. That is, at this time, the crossed Nicols arrangement is dark and the parallel Nicols arrangement is bright. In the state (a) when no voltage is applied, the liquid crystal molecules are aligned while rotating between the substrates according to the alignment treatment. In this state, the molecule has optical rotatory power, so bright in crossed Nicols,
It is dark in parallel Nicols. When positive voltage is applied (c),
Although different from (a), all molecules are oriented in the same direction. That is, it is dark in crossed Nicols and bright in parallel Nicols.

The present embodiment is a spatial light modulator using this TCC liquid crystal, and its structure is shown in FIG. 3A is a top view, and FIG. 3B is a sectional view taken along line BB ′ shown in FIG. In the figure, 101c and 101d are quartz glass substrates, and 103a to 103c are indium tin oxides (IT
O) a transparent electrode, 104a and 104b are polyimide alignment films, 105 is a dielectric mirror composed of alternating films of TiO ₂ and SiO ₂ , and 106 is a hydrogenated amorphous film.
Silicon photoconductive film, 107 is silver paste, 108a is epoxy sealing material, 109a and 109b are lead electrodes, 1
Reference numerals 10a and 110b respectively denote ceramic spacers.

The detailed structure of the SLM is as follows.

On the writing side, the glass substrate 101
Transparent electrodes 103b and 103c made of indium tin oxide (ITO) sputter-deposited film on d, photoconductive film 106a of undoped hydrogenated amorphous silicon made by plasma CVD method, and a dielectric made of alternating volumes of TiO ₂ and SiO _2. The mirror 105 is deposited in order, and the polyimide alignment film 1
04b was spin coated. The alignment film 104b was subjected to alignment treatment by rubbing.

On the other hand, on the read side, the transparent electrode 1
03a was deposited and the alignment film 104a was spin-coated. The alignment film 104a was also subjected to the alignment treatment by rubbing, but the angle was shifted by 45 ° from the alignment film 104b side.
After that, two ceramic sphere spacers 110a and 110b were scattered on the alignment films 104a and 104b in order to maintain the gap between the glass substrates 101a and 101b. After printing the silver paste 107 for wiring the transparent electrodes 103a to 103c, the glass substrates 101c and 101d are printed.
We put together. After the TCC liquid crystal 102 was sealed in the gap between the substrates, a sealing treatment with a sealant 108 was performed to prevent deterioration of the device.

Now, each of the above-mentioned thin films must satisfy both optical and electrical conditions. TC
The C liquid crystal 102 has a tilt angle close to 22.5 degrees, and its thickness d is preferably 1/4 of the pitch peculiar to the material. In addition, from the electrical requirements, the thinner the layer, the easier the switching, depending on the selection of the liquid crystal material.

Amorphous silicon having no rectifying property is desirable as the photosensitive layer on the writing side from the viewpoint of response speed and simplicity of manufacturing method. It is appropriate and practical to have a thickness of 2 to 7 μm in view of the matching of electric capacity. The optical length n · d of the dielectric mirror 105a is (1 /
4) to obtain a TiO _2, an SiO ₂ with a total of 14 layers alternately stacked reflectivity of 99% of the mirror with a thickness of the wavelength.

With the SLM manufactured as described above, FIG.
With the configuration described above, an image can be written, amplified, and read out. The driving method will be described below.

FIG. 4 is a diagram showing pulses applied to the SLM. In order from the top, (a) applied voltage, (b) writing light intensity, (c) incident side reading light intensity, and (d) emitting side reading light intensity are shown. As described above, in the TCC liquid crystal, the intensity of the read light is determined not by the positive or negative of the applied voltage but by the magnitude of the voltage. Therefore, the SLM is applied with pulses for switching between positive and negative as shown in FIG.
By applying voltages of different polarities alternately, the average voltage to the liquid crystal can be set to 0, and the deterioration of the liquid crystal can be prevented. As an example, the writing light intensity diagram (b) shows that the first two pulses are dark and the second two pulses are bright.

Now, in FIG. 1, the reading light L _b is incident on the SLM 1 only at the time of reading in synchronization with the applied voltage by the shutter 12 arranged after the laser light source 4. This can increase the contrast. Although an acousto-optic modulator is used as the shutter 12 in this embodiment, an electro-optic modulator, a liquid crystal shutter, or the like may be used instead. FIG. 4D is a diagram showing the emission-side readout light intensity when the SLM 1 is operated under these conditions and in the parallel Nicol arrangement.

Next, the operating state will be described in correspondence with the four pulses applied to the SLM.

Write when the first positive pulse is applied
Miko L_aIs not irradiated. At this time, the applied voltage is SLM
In FIG. 1, mainly the photoconductive film 106, the dielectric mirror 105a, T
The voltage is divided by the CC liquid crystal 102. However, the photoconductive film 10
Write light L on 6_aIs not irradiated, the liquid crystal layer
Sufficient voltage to cause switching
Absent. That is, the TCC liquid crystal molecules 102 are in a twisted state.
And read light L _bIs not output to the output side.

The polarity of the second pulse is also opposite to that of the first pulse, but switching does not occur and the read light L
_b is not output.

On the other hand, when the writing light L _a is applied to the SLM ₁ as in the case of applying the third pulse, the resistance of the photoconductive film is small due to the photoconductive effect, and most of the applied voltage is applied to the liquid crystal layer. Like At this time, the read light is output brightly.

Similar results are obtained with the fourth pulse.

Actually, the prepared SLM having an effective surface of about 1 cm ²
Regarding No. 1, a white halogen lamp (15w) was used as the writing light source 2 and a helium neon laser (wavelength 633 μm, output 20 mw) was used as the reading laser light source 4, and writing and reading of images were confirmed.

In this embodiment, the writing light L _a is applied to the mask 3 on which the image pattern is recorded, and the transmitted light is SL.
The light was incident on the writing side (photoconductive film surface) of M1. By disposing the mask 3 and the SLM 1 in close contact with each other, it is possible to prevent blurring without using an imaging optical system. Further, the reading light L emitted from the reading laser light source 4
_The beam _b passes through the shutter 12 and is collimated by the magnifying collimator 5. The polarization of the readout is parallel Nicol,
Both the polarizer 6 and the analyzer 7 are arranged so as to be horizontally polarized. The readout incident light that has passed through the polarizer 6 passes through a semitransparent mirror (half mirror) 8 and is incident on the readout side (TCC liquid crystal surface) of the SLM 1a. On the other hand, the readout outgoing light reflected by the SLM 1 is reflected by the semi-transparent mirror 8 and then the analyzer 7
Pass through. The lens 9 is arranged so that the SLM 1 and the screen 10 image each other.

Voltage pulse (voltage V _SLM = ±
When 10 V, ON time 500 μs, OFF time 500 μs) were applied, it was possible to read with a contrast of 50: 1 and a resolution of 50 lines / mm.

The relationship between the writing light intensity and the reading light intensity at this time was as shown in FIG. 5A, and the reading light intensity also monotonically increased as the writing light intensity increased. Further, when the analyzer 7 was rotated 90 degrees and arranged in the orthogonal Nicol arrangement, the read light intensity monotonically decreased as shown in FIG. 5B, and the read pattern became a negative pattern. It should be noted that although the contrast is lowered, the light pattern can be written and read in the same manner even in a device in which the shutter is simplified and removed. Furthermore, the operation was confirmed even when the applied pulse was a simple square wave or sine wave.

In addition to the above embodiment, the twist angle is set to 90.
The transmission type element (S
LM) was also produced. Although the structural diagram of the SLM is omitted, TC
The behavior of the state of the C liquid crystal 102 will be described with reference to FIG.

FIG. 6A shows the orientation state of molecules when no voltage is applied, and FIG. 6B shows the orientation state of molecules when voltage is applied. In the figure, 6 is a polarizer,
7 is an analyzer, 101e and 101f are glass substrates, 102
b is a TCC liquid crystal molecule. Glass substrate 101e, 10
The arrow shown in 1f is the alignment direction by rubbing or the like. Although transparent electrodes are vapor-deposited on the inner surfaces of the two glass substrates, they are not shown in the figure.

The reading light L _b is emitted from the glass substrate 101 on the lower surface.
The light enters from f and is emitted to the glass substrate 101e on the upper surface.
The helical pitch of the TCC liquid crystal molecules 102b is set so that the cell thickness is about ¼ of the pitch, as in the case of the reflection type. Also, the tilt angle of the liquid crystal is preferably about 45 ° for the transmissive type.

In FIG. 6A, no voltage is applied,
The liquid crystal is aligned on the helix according to the alignment treatment. At this time, since the linearly polarized readout light has optical rotatory power,
In the case of the orthogonal Nicols as shown in this figure, the readout light L _b passes through the analyzer 7. On the other hand, when a voltage is applied (FIG. 6B), the TCC liquid crystal molecules 102 are all aligned in the same direction, so that the read light L _b is not output.

According to the SLM 1b having this structure, it was possible to perform writing with white light and read with infrared light. Also in this case, writing and reading of images were performed as planned, and good images could be obtained.

[0043]

As is apparent from the above description, according to the spatial light modulator of the present invention, it is possible to rapidly amplify or invert an image pattern having gradation. INDUSTRIAL APPLICABILITY The present invention can be widely applied as a projection type display in a high-resolution display device of HDTV, image measurement, optical computing and the like.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a diagram showing an operation of liquid crystals of TCC liquid crystal molecules in a reflective cell.

FIG. 3 is a structural diagram (a: top view, b: sectional view) of a spatial light modulator SLM in an example.

FIG. 4 is a diagram showing a pulse shape applied to an SLM.

FIG. 5 is a diagram showing write / read characteristics of an SLM.

FIG. 6 is a diagram showing an operation of liquid crystals of TCC liquid crystal molecules in a transmission cell.

FIG. 7 is a cross-sectional view of a conventional liquid crystal light valve.

[Explanation of symbols]

 1 Spatial light modulator (SLM) 2 Writing light source 3 Image (mask) 4 Reading laser light source 5 Magnifying collimator 6 Polarizer 7 Analyzer 8 Semi-transparent mirror (half mirror) 9 Lens 10 Screen 11 Driving power supply 12 Shutters 101a to 101f Glass Substrate 102 Smectic C liquid crystal (TCC liquid crystal) 102a, 102b TCC liquid crystal molecule 103a to 103c Transparent electrodes 104a, 104b Alignment film 105 Dielectric mirror 106 Photoconductive film 107 Silver paste 108 Sealant 109a, 109b Lead electrode 110 Spacer

Claims (2)

[Claims] 1. A photoconductive film, a dielectric mirror, and a liquid crystal alignment film deposited on one glass substrate having a transparent electrode, and a liquid crystal alignment film disposed on the other glass substrate having a transparent electrode, A spatial light modulator characterized in that the liquid crystal alignment films are opposed to each other, and a gap between them is filled with a liquid crystal of twisted chiral smectic C phase. 2. The spatial light modulator according to claim 1, wherein the liquid crystal twist angle of the twist chiral smectic C phase is 45 ° or 90 °.