JPH0750280B2 - Liquid crystal spatial light modulator and driving method thereof - Google Patents

Description

The present invention relates to a liquid crystal spatial light modulator used for optical information processing and a driving method thereof.

(Prior Art) Since the liquid crystal spatial light modulator can process two-dimensional optical information in parallel and simultaneously, it can be applied to a parallel optical logic element or an image processing element, which is an important key in constructing an optical computer in the future. It has the potential to become a device.

6 (a) and 6 (b) are diagrams showing a structure of a conventional liquid crystal spatial light modulator and an equivalent circuit, respectively. As shown in FIG. 6 (a), the conventional liquid crystal spatial modulator has a transparent electrode A601,
The nematic liquid crystal 608 is sandwiched between the glass substrate A605 on which the photoconductor layer 602, the light shielding film 603, and the reflection film 604 are formed, and the glass substrate B607 on which the transparent electrode B606 is formed. The structure is connected as shown.
The nematic liquid crystal normally adopts a twisted nematic (hereinafter abbreviated as TN) mode and is twisted. In FIG. 6A, the layer of the alignment treatment material for obtaining the twist alignment is omitted. This is because it is not directly involved in the operation of the liquid crystal spatial light modulator.

The equivalent circuit is, as shown in FIG. 6 (b), a resistor 612 of the photoconductor layer and a resistor 613 of the liquid crystal layer connected in series by an AC power source. The resistance of the photoconductor layer is shown as a variable resistance because its resistance value changes depending on the intensity of input light.

The operation principle and driving method of the liquid crystal spatial light modulator will be described below.

In FIG. 6, the photoconductor layer resistance 612 when the input light 610 is irradiated and when the input light 610 is not irradiated is respectively a light resistance R _ph and a dark resistance R _d.
And the resistance 613 of the liquid crystal layer is R _LC , R _ph , R _d , R
_The following relationships have been established between the _LCs .

R _ph << R _LC << R _d (1) Therefore, when the input light is not irradiated, most of the applied voltage supplied from the AC power source 609 is applied to the photoconductor layer, and the liquid crystal layer has no electro-optical effect. Does not happen. On the contrary, when the input light is irradiated, the resistance of the photoconductor layer decreases and most of the applied voltage is applied to the liquid crystal layer, and the liquid crystal is switched. That is, the liquid crystal can be turned on / off by turning on / off the input light, and an optical input / output system is established.

As shown in FIG. 6A, the input light 610 is input from the glass substrate A side, and the output light 611 is read out as the light emitted from the glass substrate B side and reflected by the reflection film.
At this time, the polarizing plates installed on both sides of the liquid crystal spatial light modulator
A614 and polarizing plate B615 are set to balanced Nicols whose polarization directions are the same or crossed Nicols orthogonal to each other.In the former case, bright true Logic (Brig
ht True Logic (hereinafter referred to as BTL), and in the latter case, dark true logic (hereinafter referred to as Dark True Logic, which indicates that the output light is dark when the input light is applied.
It is expressed as DTL).

The element that holds the key in constructing an optical computer is said to be an optical bistable element. An optical bistable element is an element having two stable states as output light for a certain input state in an optical input / output system. An optical flip-flop element is one of the more specific optical functional elements developed from the optical bistable element.

A liquid crystal spatial light modulator can be used to make an optical flip-flop device. FIG. 7 shows a conventional method of realizing a set / reset (SR) optical flip-flop device using the liquid crystal spatial light modulator (APPLIED OPTI).
CS vol.2, No.13 (1984) pp.2163). This method uses two liquid crystal spatial light modulators, a liquid crystal spatial light modulator A701 and a liquid crystal spatial light modulator B702. The set optical signal 114 is input to the liquid crystal spatial light modulator A, and the reset optical signal 113 is input to the liquid crystal spatial light modulator B. The output light of the liquid crystal spatial light modulator A is the Glanton Thompson prism 703 and the half mirror 7.
A part of the light is extracted as output light Q711 via 04, and a part of the light is used as the read light of the liquid crystal spatial light modulator B.
Liquid crystal spatial light modulator B read by the reading
The output light of is added to the set light signal as feedback light using the optical system of the mirror 705, the polarizing plate B709, and the mirror C707, thereby realizing an SR optical flip-flop element. This optical flip-flop element can switch the state of the liquid crystal by giving a set optical signal and a reset optical signal in pulses, and can be directly used as an optical storage element.

(Problems to be Solved by the Invention) In the SR optical flip-flop element using the conventional liquid crystal spatial light modulator described above, nematic liquid crystal is used as the liquid crystal material. The electro-optical response time of the nematic liquid crystal is several tens to several hundreds of msec, and the response time of the liquid crystal spatial light modulator is limited by the response time of the nematic liquid crystal. That is, the response time of the conventional liquid crystal spatial light modulator is as slow as several tens to several hundreds of msec, and the above problems become a major bottleneck in performing optical information processing at higher speed using the liquid crystal spatial light modulator. There is.

Further, in the conventional method of realizing the optical flip-flop using the liquid crystal spatial light modulator, two liquid crystal spatial light modulators are required and the method of feeding back the output light Q to the set optical signal is adopted. This method requires two liquid crystal spatial light modulators, and for optical feedback,
It requires one Gran Thompson prism, one half mirror, and three mirrors, and a space to install them.
A space is required to secure the feedback optical path. This is a factor of making the device large and increasing the manufacturing cost.

Ferroelectric chiral smectic liquid crystals respond faster to electric fields than nematic liquid crystals. That is, the nematic liquid crystal has a response time of several tens to several hundreds msec, while the ferroelectric liquid crystal shows a high-speed response of several tens to several hundreds μsec which is two to three orders of magnitude faster than that. Therefore, if a ferroelectric liquid crystal is used as the liquid crystal material of the liquid crystal spatial light modulator, it is possible to realize a high-speed liquid crystal spatial light modulator that responds in tens to hundreds of microseconds. In addition to high-speed characteristics, ferroelectric liquid crystals also have the characteristics of electro-optical bistability, and by utilizing this effect, an SR optical flip-flop device that does not require an optical feedback system can be realized. You can

However, since the TN liquid crystal switches by ON / OFF of the electric field, the ferroelectric liquid crystal switches by inversion,
The conventional liquid crystal spatial light modulator structure cannot switch the ferroelectric liquid crystal.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal spatial light modulator which is capable of high-speed response and which is small in size and low in cost, and a method of driving the same, which solves the above-mentioned problems of the conventional art.

(Means for Solving the Problems) A liquid crystal spatial light modulator according to the present invention includes one or a plurality of pixel electrodes and first and second photoconductor layers respectively formed at different ends of the pixel electrodes. And a first transparent insulating substrate comprising first and second conductive light-shielding films formed so as to respectively cover the first and second photoconductor layers without contacting the pixel electrode. , A second transparent insulating substrate on which a counter electrode is formed, and a ferroelectric liquid crystal is sandwiched between the counter electrode and the second transparent insulating substrate so that the first and second conductive light-shielding films are reverse biased with respect to the counter electrode. It is characterized in that the first and second DC power supplies are connected.

In addition, one or a plurality of pixel electrodes, first and second photoconductor layers respectively formed at different ends of the pixel electrodes, and the first and second pixel electrodes without contacting the pixel electrodes.
A first transparent insulating substrate comprising first and second conductive light-shielding films formed so as to respectively cover the photoconductor layers of
Ferroelectric liquid crystal is sandwiched between a second transparent insulating substrate having a counter electrode formed thereon, and the first and second conductive light-shielding films are reversely biased with respect to the counter electrode. In the method of driving a liquid crystal spatial light modulator to which first and second DC power supplies are connected, in one of the first and second photoconductor layers,
A set light pulse signal is input from the second transparent insulating substrate side, and the second light is applied to the other of the first and second photoconductor layers.
Input the reset light pulse signal from the transparent insulating substrate side of
The liquid crystal spatial light modulator is driven by irradiating the first transparent insulating substrate side as read-out light.

(Operation) When the liquid crystal spatial light modulator of the present invention and the counter electrode are used as a reference, the potential of the pixel electrode is inverted when the set light signal is input and when the reset light signal is input. The switching of the ferroelectric liquid crystal can be controlled by the set optical signal and the reset optical signal. When neither the set optical signal nor the reset optical signal is input, the potential of the pixel electrode is 0 V, and the ferroelectric liquid crystal has electro-optical bistability, so the set optical signal and the reset optical signal are You can retain the state when you entered.

Therefore, a high-speed SR optical flip-flop element using the liquid crystal spatial light modulator can be realized, and optical information can be processed at a higher speed. Further, since the SR optical flip-flop element can be realized by only one liquid crystal spatial light modulator, and does not require an optical feedback system, an SR optical flip-flop using the liquid crystal spatial light modulator is not required. It is also possible to reduce the size and cost of the device.

(Example) Below, the Example of this invention is described in detail.

(Embodiment 1) FIG. 1 is a diagram showing an embodiment of a liquid crystal spatial light modulator of the present invention. FIG. 1A shows a sectional structure of the liquid crystal spatial light modulator. In this embodiment, the number of pixels is one. A pixel electrode 101, a photoconductor layer A102 formed so as to cover an end portion of the pixel electrode, and a conductive light-shielding film A103 formed so as to cover the photoconductor layer A without making contact with the pixel point. , A photoconductor layer B104 formed so as to cover an end different from the end of the pixel electrode, and a conductive light-shielding film B1 so as to cover the photoconductor layer B without contacting the pixel electrode.
The structure is such that the ferroelectric liquid crystal 109 is sandwiched between the glass substrate A106 having the number 05 and the glass substrate B108 on which the counter electrode 107 is formed. The external power source is connected to the counter electrode with a direct current power source A110 and a direct current power source B111 so that the conductive light-shielding films A and B have a negative bias and a positive bias, respectively.

In order to provide the ferroelectric liquid crystal with electro-optical bistability, the cell gap is controlled to about 1.5 μm by the spacer 112.

Here, a plan view and a sectional view of a glass substrate A on which a photoconductor layer, which can be said to be the heart of the liquid crystal spatial light modulator of the present invention, are shown in FIGS. 2 (a) and 2 (b), respectively. In this embodiment, the photoconductor layer A102, and the photoconductor layer B104,
The conductive light-shielding film A103 and the conductive light-shielding film B105 are formed in a corner portion sharing one side of the pixel electrode 101, and are formed so as to cover the photoconductor layer A and the photoconductor layer B, respectively. . The photoconductor layer A102 and the photoconductor layer B104 may be formed at diagonal portions as long as the two layers do not overlap.

A cross-sectional view of the glass substrate A106 cut along the line segment AB is shown in FIG. A-Si: H was adopted as the photoconductor material. The reason why a-Si: H is used is that the a-Si: H material exhibits high-speed response as a photoconductor material and has high sensitivity in the visible light region. The high sensitivity in the visible light region means that the liquid crystal spatial light modulator can process a visible image. As the photoconductor layer, zinc sulfide (ZnS), zinc oxide (ZnO), cadmium sulfide (CdS),
It is also possible to use selenium (Se).

The photoconductor layers A and B are the pixel electrode and the conductive light-shielding film A,
In order to make ohmic contact with B, n ⁺ layer 201-i layer 202-
Although the three-layer structure of the n ⁺ layer 203 is used and Cr204 is used as the conductive light-shielding film, Al can also be applied. The photoconductor layers A and B formed on the glass substrate A are formed symmetrically with respect to the center line 205 in FIG. 2B, and both show the same photoconductive characteristics.

FIG. 1 (b) is a diagram showing an equivalent circuit of the liquid crystal spatial light modulator of the present invention. The resistance 119 of the photoconductor layer A and the resistance 120 of the photoconductor layer B change with the ON / OFF state of the reset optical signal 113 and the set optical signal 114, respectively. ing. In addition, the liquid crystal layer has a resistance of 12
It is known to be shown by parallel connection of 1 and capacity 122,
It is connected between contacts A and B as shown in FIG. 1 (b).

The operation principle of the liquid crystal spatial light modulator of the present invention will be described below with reference to the equivalent circuit of FIG.

The resistance of the liquid crystal layer is R _LC , the resistance of the photoconductor layer A when the photoconductor layer A is irradiated with the reset light signal is R _pha , the resistance of the photoconductor layer A when it is not irradiated is R _da , and the set light is set. The resistance of the photoconductor layer B when the signal resistance layer is irradiated onto the photoconductor layer B is R _phb ,
If the resistance of the photoconductor layer B when not irradiated is R _db , it is premised that the film thickness and impurity concentration of each layer are selected so that the following relationship is established.

R _pha = R _phb << R _LC << R _da = R _db (2) Further, the voltages of the DC power supply A and the DC power supply B are equal to V _B.

Below, under the above conditions, the ferroelectric liquid crystal layer in three states, that is, when the set optical signal is emitted, when the reset signal is emitted, and when neither the set optical signal nor the reset optical signal is emitted. Find the voltage applied to.

(A) When the set optical signal is applied When the set optical signal is applied to the photoconductor layer B, the voltage applied to the liquid crystal layer is based on A, and the equivalent circuit and the equation (2) give + V. It becomes _B V.

(B) When the reset light signal is applied When the reset light signal is applied to the photoconductor layer A, the voltage applied to the liquid crystal layer is based on the point A. From the equivalent circuit and the equation (2), , −V _B V.

(C) When neither the set light signal nor the reset light signal is irradiated: When neither the set light signal nor the reset light signal is irradiated, the voltage applied to the liquid crystal layer is 0 V according to the equivalent circuit and the formula (2). Becomes

Therefore, the electric field applied to the liquid crystal layer can be switched between positive and negative depending on the set optical signal and the reset optical signal, and the ferroelectric liquid crystal that causes switching by inversion of the electric field can be driven.

Based on the above operation principle, in FIG. 1 (a), the reset optical signal 113 is applied to the photoconductor layer A from the glass substrate A side, and the set optical signal 114 is applied to the photoconductor layer B from the glass substrate A side. Then, the read light 115 is transmitted through the polarizing plate A117, the liquid crystal spatial light modulator, and the polarizing plate B118 in this order, and when it is used as the output light, the optical output controlled by the set optical signal and the reset optical signal can be obtained. At this time, the polarizing plates A and B installed on both sides of the liquid crystal spatial light modulator are set to be crossed Nicols.

Next, a method of driving the liquid crystal spatial light modulator of this embodiment will be described below with reference to FIGS.

FIGS. 3A to 3D are diagrams illustrating the light input / output characteristics of the liquid crystal spatial light modulator of this embodiment. (A), (b)
Figures, (c) and (d) are BTL and D, respectively.
The case of TL is shown, which can be mutually converted by rotating the polarizing plate A and the polarizing plate B set to the crossed Nicols by the tilt angle of the ferroelectric liquid crystal, which is 45 degrees.

In FIG. 3A, the xy plane and the −y plane are on the same plane, and the set / reset light intensity dependency of the liquid crystal applied voltage is shown, and the yz plane is the liquid crystal applied voltage of the output light intensity. Shows dependency.

In the xy plane, as the set optical signal intensity increases,
The liquid crystal application voltage from 0V to + V _B V changes substantially linearly. On the −y plane, the liquid crystal applied voltage changes almost linearly from 0 V to −V _B V as the reset light signal intensity increases. On the other hand, in the liquid crystal spatial light modulator of this embodiment, since the ferroelectric liquid crystal exhibits electro-optical bistability, the electro-optical characteristics of the liquid crystal are as shown on the yz plane.

From the three-dimensional coordinates shown in FIG. 3 (a), the xz plane and the −z plane are represented on the same plane, and the set / reset light input / output characteristics are obtained, as shown in FIG. 3 (b). , When neither the set light signal nor the reset light signal is emitted,
A kind of optical bistable state is realized in which the output light has two stable states.

In the case of DTL, the light input / output characteristics shown in FIG. 3 (d) can be obtained from the three-dimensional coordinates shown in FIG. 3 (c).

FIG. 4 is a diagram showing the optical response characteristics of the liquid crystal spatial light modulator of the present embodiment showing the set / reset light input / output characteristics shown in FIGS. 3 (b) and 3 (d).

In the present embodiment, outside the set time and outside the set time, both the set optical signal and the reset optical signal are cut off, the liquid crystal applied voltage is 0 V during that time, and the ferroelectric liquid crystal having electro-optical bistability is It retains its previous state. During the set time, a set optical signal as shown in FIG. 4 (a) is transmitted from the glass substrate A side of FIG. 1 (a) to the photoconductor layer B.
To enter. Even after the set light pulse is turned off, the output light remains in the set state for a period of T1 until the next reset light pulse is input as shown in FIG. 4 (c).

During the reset time, a reset light signal as shown in FIG. 4 (b) is input to the photoconductor layer A from the glass substrate A side in FIG. 1 (a). Even after the reset light pulse is turned off, the output light retains the state at reset for the T2 period until the next set light pulse is input as shown in FIG. 4 (c).

On the other hand, in the case of DTL, when the set / reset optical signals of FIGS. 4 (a) and 4 (b) are input, an optical response in which the output light of FIG. 4 (c) is inverted is obtained as shown in FIG. 4 (d). To be

As described above, in the liquid crystal spatial light modulator of this embodiment,
The set / reset light input / output characteristic shows optical bistability, and the state of output light can be switched by the set light pulse and the reset light pulse by the driving method. The optical pulse width of 200 μsec is sufficient for switching the ferroelectric liquid crystal, and high-speed operation can be obtained. The fact that the BTL and DTL can be easily obtained by rotating two polarizing plates by 45 degrees is a very advantageous point when the present liquid crystal spatial light modulator is applied to an optical logic element.

(Embodiment 2) FIGS. 5A and 5B are views showing an embodiment of the liquid crystal spatial light modulator of the present invention. Although the number of pixels is 1 in the first embodiment, this embodiment shows an example in which the number of pixels is 16 (4 × 4).

FIG. 5A shows a pixel electrode 101, a photoconductor layer A102, a photoconductor layer B104, a conductive light shielding film A103, and a conductive light shielding film B1.
FIG. 13 is a plan view of the glass substrate A106 on which 05 is formed, viewed from the pixel electrode side. Further, FIG. 5B is an enlarged view of the periphery of the pixel electrode, and also shows the photoconductor layer A and the photoconductor layer B formed under the conductive light shielding films A and B, respectively.

In FIG. 5A, the conductive light-shielding film A formed so as to cover the photoconductor layer A at the upper left corner of the pixel electrode is a connection terminal.
The conductive light-shielding film B, which is connected to A501 and is formed in the lower left corner of the pixel electrode so as to cover the photoconductor layer B, has a connection terminal B5.
It is connected to 02. Further, the connection terminal A and the connection terminal B are a counter electrode, a DC power supply A110, and a DC power supply B1, respectively.
They are connected via 11 in the bias direction shown in FIG.

The sectional view of the glass substrate A taken along the line AB in FIG. 5B is the same as FIG. 2B in the first embodiment.

In this embodiment, each pixel is independent of the first pixel.
It is represented by the equivalent circuit shown in FIG. 6B, and therefore each pixel can be driven independently. That is, this embodiment is superior to the first embodiment in parallel processing capability.

(Effects of the Invention) As described above, when the liquid crystal spatial light modulator of the present invention is applied, an SR optical flip-flop that does not require optical feedback and is composed of only one liquid crystal spatial light modulator is provided. Can be realized. This does not require the optical components such as the Glan-Thompson prism and the mirror which are required in the conventional optical feedback system, the space of the feedback optical path can be eliminated, and one liquid crystal spatial light modulator can be deleted. Therefore, it is possible to reduce the size of the SR optical flip-flop element using the liquid crystal spatial light modulator,
The cost can be reduced.

Further, in the liquid crystal spatial light modulator of the present invention, a response speed which is two to three orders of magnitude faster than that of the liquid crystal spatial light modulator of the free type is obtained, and it becomes possible to execute higher speed optical information processing.

[Brief description of drawings]

1 (a), (b), FIG. 2 (a), and (b) are schematic views of the liquid crystal spatial light modulator of Embodiment 1 of the present invention, and FIG. 3 (a).
~ (D), 4 (a) to (d) are diagrams showing the driving method of the first embodiment of the present invention, and Figs. 5 (a) and 5 (b) are liquid crystal spatial light modulation of the second embodiment of the present invention. Schematic of the container, Fig. 6 (a),
FIG. 7B is a schematic diagram of a conventional liquid crystal spatial light modulator, and FIG. 7 is a schematic diagram of an SR optical flip-flop element using the conventional liquid crystal spatial light modulator. In the figure, 101 ... Pixel electrode, 102 ... Photoconductor layer A,
103 ... Conductive light-shielding film A, 104 ... Photoconductor layer B, 105 ...
Conductive light-shielding film B, 106 ... Glass substrate A, 107 ... Counter electrode, 108 ... Glass substrate B, 109 ... Ferroelectric liquid crystal, 11
0 …… DC power supply A, 111 …… DC power supply B, 113 …… Reset light signal, 114 …… Set light signal, 115 …… Read light,
116 …… Output light, 117 …… Polarizing plate A, 118 …… Polarizing plate B, 6
01 ... Transparent electrode A, 602 ... Photoconductor layer, 603 ... Shading film, 604 ... Reflective film, 605 ... Glass substrate A, 606 ... Transparent electrode B, 607 ... Glass substrate B, 608 ... ... nematic liquid crystal, 609 ... AC power supply, 610 ... input light, 611 ... output light, 614 ... polarizing plate A, 615 ... polarizing plate B, 701 ... liquid crystal spatial light modulator A, 702 ... liquid crystal Spatial light modulator B, 703 ...
Gran Thompson Prism, 704 ... Half mirror, 705
…… Mirror A, 706 …… Mirror B, 707 …… Mirror C, 70
8 ... Polarizing plate A, 709 ... Polarizing plate B, 710 ... Output light Q, 7
11 ... Output light Q.

Claims (2)

[Claims] 1. One or a plurality of pixel electrodes, first and second photoconductor layers respectively formed at different ends of the pixel electrodes, and the first and second photoconductor layers without contacting the pixel electrodes. A first transparent insulating substrate including first and second conductive light-shielding films formed so as to respectively cover the second photoconductor layer, and a second transparent insulating substrate having a counter electrode formed thereon. ,
A ferroelectric liquid crystal is sandwiched between the first and second direct current power sources so that the first and second conductive light-shielding films have reverse biases with respect to the counter electrode. Liquid crystal spatial light modulator. 2. One or a plurality of pixel electrodes, first and second photoconductor layers respectively formed at different ends of the pixel electrodes, and the first and second photoconductor layers without contacting the pixel electrodes. A first transparent insulating substrate including first and second conductive light-shielding films formed so as to respectively cover the second photoconductor layer, and a second transparent insulating substrate having a counter electrode formed thereon. ,
Is sandwiched between the first and the second electrodes with respect to the counter electrode.
In a method of driving a liquid crystal spatial light modulator in which first and second DC power supplies are connected so that the second conductive light-shielding film has a reverse bias, one of the first and second photoconductor layers is provided. , A set optical pulse signal is input from the second transparent insulating substrate side, and a reset optical pulse signal is input to the other of the first and second photoconductor layers from the second transparent insulating substrate side, A method for driving a liquid crystal spatial light modulator, characterized in that irradiation is performed from the side of the first transparent insulating substrate as readout light.