JPS58173713A - Polarizing element - Google Patents

Abstract

PURPOSE:To obtain a polarizing element which permits electrical exchange of the axis of plarization by impressing an electric field to a liquid crystal layer which sandwiches a smectic liquid crystal exhibiting ferroelectricity and a dichromatic dye between transparent electrodes thereby changing the orientation direction of the liquid crystal molecules. CONSTITUTION:A liquid crystal layer 6 mixed with a smectic liquid crystal expressed by the formula and a dichromatic dye is sandwiched between the transparent electrodes 4, 4' which are formed respectively on transparent substrates 5, 5'. Thin films of polyimide are provided on the electrodes 4, 4' and are rubbed in parallel so that the long axis of the liquid crystal molecules is paralleled with the substrate plane. The liquid crystal molecules have the spontaneous polarization in the direction perpendicular to the long axis of the molecules; therefore, when an electric field acts thereon, the long axis directs perpendicularly to the electric field direction. Thus, the axis of polarization of a liquid crystal element (polarizing element) 3 can be changed so as to intersect orthogonally like directions A, A' by changing the direction of the voltage to be impressed on said element 3. The element which allows the transmission of light at a higher rate than conventional polarizing elements using an electrooptic crystal and consumes electricity less is easily obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polarizing element, and more particularly to a polarizing element whose polarization axis direction can be electrically changed.

Recently, various attempts have been made to control polarized light and perform light modulation such as changing the intensity and hue of the light, and it is expected that it will be applied to new fields such as image processing, optical communications, and optical computers. There is. Various types of light modulation elements have been proposed, but what has not yet been realized is a so-called 1-light @Machi R polarization element, which is a single element and has a plurality of polarization axes for linearly polarized light.

Conventionally, in order to vary the polarization axis, as shown in Figure 1,
The crystal axis is changed by two one-photons l, 1' and the electricity inserted between the polarizer. A composite element composed of a so-called electro-optic crystal 2 or a nematic liquid crystal is used. This composite element determines whether direct polarized light with a vibration direction determined by the polarization axis direction of the first polarizer l enters the electro-optic crystal 2, and whether or not an electric field is applied to the electro-optic crystal or the intensity of the electric field is determined. Accordingly, the directly polarized light is modulated to become elliptically polarized light, and linearly polarized light having a desired vibration direction is obtained from the elliptically polarized light by the second polarizer l'. However, in such a composite element, there is a large loss in the amount of light at an intermediate stage.
In addition, after making circularly polarized light, the ninth step is to extract linearly polarized light.
There is a problem that the degree of modulation decreases.

The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide a polarizing element that causes less loss of light quantity and does not reduce the degree of modulation.

In order to achieve the above object, the present invention uses two transparent substrates each having transparent electrodes, arranges the transparent substrates so that the transparent electrodes face each other, and creates a smectic structure exhibiting ferroelectricity between the transparent electrodes. A liquid crystal layer consisting of a liquid crystal and a dichroic dye is sandwiched between the liquid crystal layer and a means for applying an electric field to the transparent electrode.

In this smectic liquid crystal exhibiting ferroelectricity, in an unexcited state, the long axes of molecules are substantially parallel to the substrate surface and aligned in a substantially constant direction, and an electric field is applied in a direction perpendicular to the long axes of the molecules.

Next, the present invention will be explained using the drawings. In the polarizing element of the present invention, as shown in FIG. A liquid crystal layer 6 consisting of a smectic liquid crystal exhibiting ferroelectricity and a dichroic dye is sandwiched between electrodes 4 and 4', and a DC power source 7 is connected to electrodes 4 and 4'.

The polarizing element 3 of the present invention responds ferroelectrically to a DC electric field and takes two liquid crystal molecule alignment states shown in FIG. 3(1), φ) by inverting the electric field 01m property.

In this case, the molecular long axes B are perpendicular to the direction of the electric field. Therefore, the dichroic dye contained in the liquid crystal layer also has two alignment directions and its absorption axis changes due to the guest-host effect.

The directions of this absorption axis are indicated by symbols A and A'.

When natural light is made incident on the soft line polarizing element shown in Figure 3 (1), linearly polarized light with a vibration direction perpendicular to the absorption axis is obtained, and when natural light is made incident on the polarizing element in the state shown in Figure 3 Φ). Based on the same principle, linearly polarized light with a different vibration direction from that described above can be obtained. Therefore, by applying an electric field that maintains the state shown in FIG. Different polarizations are obtained alternately.

The smectic liquid crystal exhibiting ferroelectricity used in the present invention includes a chiral smectic C phase and a chiral smectic H phase. This smectate liquid crystal has a layer structure common to smectate liquid crystals, but
It is said that the direction of the long axes of liquid crystal molecules changes from layer to layer, and the molecules exhibit a spiral-like molecular arrangement with the helical axis in the direction perpendicular to each layer. A material exhibiting zero ferroelectricity, whose structure is thought to exhibit ferroelectricity, responds to a direct current electric field as a ferroelectric substance, and reverses the direction of spontaneous polarization depending on the direction of the electric field. This is a common practice known from the example of ferroelectric crystals. In the case of a smectic liquid crystal, the helical axes mentioned above melt, and the long axes of the liquid crystal molecules are perpendicular to the electric field and inwardly tilted with respect to the helical axis before being excited, which corresponds to the angle # inherent to the material. and rearrange it. Note that the direction of the angle is reversed by the heating of the electric field.The smectic liquid crystal used in the present invention is mainly a Schiff base type liquid crystal as shown below.

p-h*xyloxyb@agyl ideas-pL
amino-2-methylbutyl-cinna
@ale(HOBAMBC) p-octyloxyb@tuylidene-p'-
amino-2-methylbutyl-cinna
rylate (COBAMBC) p-decyloxybanzyl 1dene-p'
-azino-2-methylbutyl-cin
namate (DOBAMBC) p-dodecyloxybenzyl 1dene-
p' -amino ten melkyloutyl-cin
namate (DDOBAMBC) H p-tetradecyloxytenxyl 1de
ato4-amlno-2-gethylbutyl-c
ionamate (TDOBAMBC) The smectate liquid crystal of the present invention is subjected to so-called single domain formation in which the long axes of molecules are aligned in a certain direction.

In this way, the ferroelectric rearrangement produces a large optical change, and an element with a large transformation degree can be obtained. As described above, single domain formation in which the long axes of molecules are aligned in a certain direction over a certain area is achieved by applying an alignment treatment to the surface of the substrate on which the liquid crystal simulates.According to experiments conducted by the present inventors, It has been confirmed that several methods used to control the alignment of conventional nematic liquid crystals and cholesteric liquid crystals can be applied to the single domain alignment parallel to the substrate surface of the present invention.

In the present invention, the surfaces of the substrates were subjected to a soft rubbing treatment, the two substrates were combined so that the rubbing direction was 1,000 rows, and the molecules were arranged parallel to the substrates by newly adding liquid crystal. In this case, by providing a polyimide thin film on the substrate surface in advance, the uniformity of orientation could be improved.

The liquid crystal materials exemplified above all have the long axis Kl of the liquid crystal molecules.
Since it has spontaneous polarization in the perpendicular direction, the direction of the long axis of the liquid crystal molecules when an electric field is applied is perpendicular to the direction of the electric field. Therefore, the displacement of liquid crystal molecules that often occurs when the helical axes are aligned parallel to the substrate and an electric field is applied across the liquid crystal can be avoided by simply changing the direction of the molecular axes within the same plane, so low voltage is sufficient. It works and can respond quickly.

As the dichroic dye used in the present invention, nine materials that have been conventionally used in nematic liquid crystals and cholesteric liquid crystals for electro-optic effects collectively called guest-host effects are used, such as anth-2-quinone conductors, azo derivatives, Diazo conductor, merosiani'/,! Il conductor, tetrazine conductor, etc., 1 type or 211 or more? Used in combination with i&.

As shown in FIG. 4, if the polarizing element of the present invention is arranged 2111 with the absorption axes perpendicular to each other, it becomes possible to perform optical switching that can control the transmission of two linearly polarized lights whose vibration directions are perpendicular to each other. . That is, in state (a), only linearly polarized light perpendicular to the absorption axis is transmitted, and linearly polarized light parallel to the absorption axis is not transmitted, while in state (b), the absorption axis is 90°
``The rotating 9th type and the 11th type of linearly polarized light that passes through it are reversed.This pattern can be switched relatively quickly, making it possible to transmit optical information in parallel and simultaneously using two types of polarized light. In particular, the device of the present invention controls only the amount of transmitted linearly polarized light, rather than the conventional method of converting it into elliptically polarized light and then extracting linearly polarized light, so coherent light can be transmitted as is. There is a characteristic that it is done.

Further, the polarizing element of the present invention can be used as a basic circuit element of an optical moat circuit. Figures 3 and 4 (1)
, φ) for linearly polarized light incident on an element whose absorption axes are perpendicular to each other, when the transmission intensity is l corresponds to the logic @l'', and the state of the transmission intensity O corresponds to the logic ``0''. A complex logic circuit can be constructed by combining such polarizing elements.

Since the above switching is performed at a low voltage of 5V or less, it can be said that the modulation element is operated by a very simple drive circuit.

As described above, according to the present invention, it is possible to provide a polarizing element having a plurality of polarization axes for linearly polarized light with a single configuration.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a conventional variable polarizing element, and Fig. 42 is a cross-sectional view of the polarizing element of the present invention. FIG. 3 is an explanatory diagram for explaining the operating mechanism of the polarizing element of the invention.

Claims (1)

[Claims] 1. Two transparent substrates equipped with transparent electrodes and arranged so that the transparent electrodes face each other, and in an unexcited state, the long axes of molecules are substantially parallel to the substrates and arranged in a substantially constant direction. A liquid crystal layer consisting of a smectic liquid crystal exhibiting a strong electric pole and a dichroic dye and sandwiched between the transparent electrodes, and means connected to the electrodes and applying an electric field in a direction perpendicular to the long axis of the molecules. A polarizing element including.