JPH0497135A - Liquid crystal light valve - Google Patents

Abstract

PURPOSE:To obtain specific performance without using any dielectric mirror by setting a transient rise and a fall in voltage applied to liquid crystal below the inverted threshold voltage of the liquid crystal. CONSTITUTION:A photoconductor or photodiode is formed by sequentially laminating a transparent electrode 103, a photoconductive film 104, and a metallic picture element electrode 105 which serves as a reflecting film, and the transient voltage rise and drop DELTAVLC in the voltage applied to the liquid crystal 106 which is shown by an equation I is set below the inverted threshold voltage of the liquid crystal 106. Here, Cpc is the capacity of the photoconductor or photodiode, CLC is the capacity of the liquid crystal on the metallic picture element electrode, and DELTAV is variation in the amplitude of applied driving pulses. The electric inversion of the liquid crystal is therefore eliminated. Namely, basic operation which controls the liquid crystal inversion according to whether or not there is write light is enabled. Consequently, the basic operation can be obtained by using a metallic reflecting film which is easily manufactured and provides high reflection over a wide wavelength range instead of a dielectric mirror.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical writing type liquid crystal light valve that converts an optical signal into another optical signal and is used in optical information processing, optical computing, and the like.

In particular, the present invention relates to a liquid crystal light valve that has a photoconductor or a photodiode on one substrate and that uses light to control the electric field applied to the liquid crystal.

(Prior art) Liquid crystal light valves are optical switching elements used in optical projection displays, optical information processing, optical computing, etc., and are optical writing devices using ferroelectric crystals with high-speed response. The one shown in Figure 3 is known. As shown in FIG. 3(a), the liquid crystal light valve consists of a glass substrate 308 on which an ITO electrode 302, a photoconductive film 301, a dielectric mirror 303 are laminated, and an ITO
Although an electrode 307 is provided, the structure is such that a ferroelectric liquid crystal 306 is sandwiched between it and a glass substrate 309. Amorphous silicon is used for the photoconductive film 301.

The operating principle will be explained. The equivalent circuit of the liquid crystal light valve is shown in FIG. 3(b). In Figure 3(b), Figure 3(a)
) includes the photoconductive film 301 and the ITO electrode 307 to form a photoconductor. A pulsed driving voltage 201 is applied to the light valve. When the photoconductor is not irradiated with write light 206, the photoconductor resistor 204 is in a high resistance state. Therefore, since the voltage applied to the liquid crystal is lower than its inversion threshold voltage, the alignment state of the liquid crystal molecules does not change. On the other hand, write light 20 on the photoconductor.
When 6 is irradiated, the resistance 204 of the portion of the photoconductor that is irradiated with light decreases significantly.

Therefore, most of the driving voltage is divided into the liquid crystal, inverting the liquid crystal molecules. In this way, since the orientation of the liquid crystal differs between the portions of the photoconductor that are hit by light and the portions that are not hit by light, readout light can be obtained as intensity modulation by using a polarizing plate.

(Problems to be Solved by the Invention) A problem with conventional liquid crystal light valves is that it is difficult to form a dielectric mirror that separates writing light and reading light. Usually, a dielectric mirror is made by alternately laminating a transparent dielectric material with a high refractive index such as TiOZnS2 and a dielectric material with a low refractive index such as MgF2 with a film thickness of λ/4. Laminated film thickness is 2
The film needs to have a thickness of about 4 microns, takes a lot of time to form, and is difficult to obtain a uniform film thickness over the entire surface. Furthermore, unlike a metal film, the reflection wavelength range is limited.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal light valve that solves the above-mentioned problems of the prior art and can achieve a predetermined performance without using a dielectric mirror.

(Means for Solving the Problems) The liquid crystal light valve of the present invention has a transparent insulating substrate on which a photoconductor or photodiode is formed in a pixel shape and a transparent insulating substrate with a transparent electrode facing each other. The photoconductor or photodiode is a liquid crystal light valve with a liquid crystal sandwiched between the photoconductor or the photodiode, and the photoconductor or photodiode is composed of a transparent electrode laminated in sequence, a photoconductive film, and a metal pixel electrode that also serves as a reflective film. When the capacitance of the photodiode is C1°, the capacitance of the liquid crystal on the metal pixel electrode is C5°, and the amplitude change of the applied driving pulse is ΔV, then ΔV. Transient voltage rise and drop △V applied to the liquid crystal expressed as = (C1° / (C1° 0 CLo)) × ΔV
It is characterized in that LC is less than or equal to the inversion threshold voltage of the liquid crystal.

(Function) In the liquid crystal light valve of the present invention, a divided metal pixel electrode is used to separate writing light and readout light and reflect the readout light. Therefore, a dielectric mirror, which is difficult to form, is unnecessary. Furthermore, since it is a metal film, high reflection can be obtained over a wide wavelength range.

In this way, the liquid crystal light valve of the present invention uses a metal reflective film instead of a dielectric mirror, but it is not possible to simply replace the dielectric mirror 303 in FIG. 3(a) with a pixel-shaped metal reflective film. Basic movements cannot be obtained. The reason for this will be explained using FIG. 2. FIG. 2 shows an equivalent circuit and driving voltage for one pixel of a liquid crystal light valve using a pixel-shaped metal reflective film instead of a dielectric mirror. Therefore, the capacitor 304 and resistor 305 of the dielectric mirror shown in FIG. 3(b) are not included. Since the drive voltage 201 is in the form of a pulse, a transient response occurs at its rise and fall. This transient response is the rise and fall of the voltage applied to the liquid crystal, Δy.

It is. Here, the amplitude change of the pulse is ΔV, the capacitance 202 of the photoconductor is C1°, and the capacitance 203 of the liquid crystal on the pixel electrode is CL.

Then, △V,. =(CPo/(CPo+CL6))×△V,,
, , , , , , (1). When the dielectric mirror 303 in FIG. 3(a) is replaced with a pixel-shaped metal reflective film,
The areas of the photoconductor and liquid crystal are the same. Therefore, assuming that the dielectric constant is approximately the same, the thickness of a normal photoconductor is about 1 micron, and the thickness of a liquid crystal layer is about 2 to 5 microns.
The capacity of the photoconductor becomes 2 to 5 times the capacity of the liquid crystal. According to equation (1), ΔV. = (2/3) Δ■ ~ (5/
6) ΔV, which exceeds the threshold voltage of the liquid crystal,
It is electrically reversed regardless of the presence or absence of writing light. That is, even if there is no writing light and the liquid crystal should not be inverted, the liquid crystal will be transiently inverted due to the rising edge of the drive pulse. In this way, basic operation cannot be obtained simply by replacing the dielectric mirror with a pixel-shaped metal reflective film.

In the liquid crystal light valve of the present invention, the transient voltage rise and processing Δ■ applied to the liquid crystal expressed by equation (1) are below the inversion threshold voltage of the liquid crystal.

to L Therefore, the liquid crystal will not be electrically inverted.

That is, the basic operation of controlling liquid crystal inversion can be obtained depending on the presence or absence of writing light.

As described above, according to the present invention, basic operation can be obtained by using a metal reflective film that is easy to manufacture and highly reflective over a wide wavelength range instead of a dielectric mirror.

(Example) An example of the liquid crystal light valve of the present invention will be described together with its manufacturing process. In order to make ΔV expressed by equation (1) smaller than the inversion threshold voltage of the liquid crystal, it is sufficient that the capacitance CPC of the photoconductor is sufficiently smaller than the capacitance CLC of the liquid crystal. Capacitance is determined by the material's inherent dielectric constant, film thickness, and electrode area, but the easiest way to adjust it is by adjusting the electrode area. Here, we will give an example in which the electrode area is adjusted. Note that reducing ΔV leads to a reduction in contrast and is not a fundamental solution.

FIG. 1 shows the structure of a liquid crystal light valve according to an embodiment of the present invention. (a) is a cross-sectional view, and (b) is a plan view.

First, on the transparent insulating substrate 101, for example, ITO (Ind.
A transparent conductive film such as iumuTin oxide) is formed and patterned into a strip shape, for example, as shown in FIG. 1(b) to form a transparent electrode 103. A photoconductive film 104 made of amorphous silicon or the like is formed thereon. Next, a metal such as chromium, which will become the pixel electrode 105, is formed on it,
Patterning is performed in a pixel shape as shown in FIG. 1(b). At this time, the width of the transparent electrode 1030 is set to, for example, about one-tenth of the width of the pixel electrode. Due to such patterning, the effective area of the photoconductor of one pixel becomes smaller than the area of the liquid crystal pixel portion, and the capacitance CPo202 of the photoconductor becomes sufficiently smaller than the capacitance C0°203 of the liquid crystal. Therefore, ΔV is expressed by equation (1). becomes smaller than the inversion threshold voltage of the liquid crystal, and basic operation is obtained.

Here, the pattern shapes of the transparent electrode and the pixel electrode are not particularly important, but it is important that the effective area of the photoconductor of one pixel is sufficiently smaller than the area of the pixel electrode. Note that whether the junction between the transparent electrode 103, the photoconductive film 104, and the metal pixel electrode 105 becomes a photoconductor or a Schottky photodiode depends on the state of the interface.

Next, the substrate explained above and the transparent electrode 1 which will be the counter substrate
Polyimide film B, which will become an alignment film, is attached to both transparent insulating substrates 102 marked with 07. In FIG. 1(a), the alignment film is omitted. Further, the two substrates are bonded together, and a liquid crystal 106 is packed between them to complete the liquid crystal light valve of the present invention. Ferroelectric liquid crystals with high-speed response are usually used as liquid crystals.

Although the photoconductive film was not patterned in this example, it may be patterned in the shape of a pixel electrode in order to prevent leakage from adjacent pixels. In addition, the alignment film is L
Instead of the B film, rubbing may be applied to a polyimide film coated with a spin cord.

In this example, the capacitance C1 of the photoconductor is increased by forming the transparent electrodes constituting the photoconductor into a band-like pattern.
Although the liquid crystal capacitance CLo was adjusted to prevent transient inversion of the liquid crystal, the same effect can be obtained by changing the film thickness, dielectric constant, etc.

(Effects of the Invention) In the liquid crystal light valve of the present invention, basic operation can be achieved by using a metal reflective film that is easy to manufacture and highly reflective over a wide wavelength range instead of a dielectric mirror. As described above, the liquid crystal light valve according to the present invention is industrially very useful.

[Brief explanation of drawings]

FIG. 1 (aXb) is a cross-sectional view and a plan view showing an example of the structure of the liquid crystal light valve of the present invention, FIG. 2 is a diagram showing an equivalent circuit of the liquid crystal light valve of the present invention, and FIG. 3 (aXb) is a conventional FIG. 2 is a diagram showing the structure and equivalent circuit of a liquid crystal light valve. 101, 102...Transparent insulating substrate, 103.107
...Transparent electrode, 104.301...Photoconductive film, 1
05...Metal pixel electrode, 10660. LCD, 201・
... Drive voltage, 202... Capacity C1° of photoconductor, 2
03...Liquid crystal capacitance C5°, 204...Resistance of photoconductor. ,

Claims (1)

[Scope of Claims] A liquid crystal light valve in which a transparent insulating substrate on which a photoconductor or photodiode is formed in the shape of a pixel and a transparent insulating substrate with a transparent electrode face each other, and a liquid crystal is sandwiched between the two substrates. The photoconductor or photodiode is composed of a transparent electrode, a photoconductive film, and a metal pixel electrode that also serves as a reflective film, which are laminated in sequence, and the capacitance of the photoconductor or photodiode is C_P_C, and the capacitance on the metal pixel electrode is The capacitance of the liquid crystal is C_L_C, and the amplitude change of the applied driving pulse is Δ.
When V, ΔV_L_C=(C_P_C/(C_P_C+C_L_
C)) A liquid crystal light valve characterized in that a transient voltage rise and fall ΔV_L_C applied to the liquid crystal, expressed as ΔV, is less than or equal to the inversion threshold voltage of the liquid crystal.