JPH04186228A - optical modulation element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical modulation element using a material having refractive index anisotropy, and particularly relates to an optical modulation element using a material having refractive index anisotropy.
ric Liquid Crystals, hereinafter referred to as FL
The present invention relates to an optical modulation element using a C. Such optical modulation elements are suitably used in display devices that display characters and images.

[Prior art] In an optical modulation element using ferroelectric liquid crystal, a liquid crystal layer is formed between two parallel plates having a thin gap (for example, 1 to 2 μm), and the surface effect of the two plates is A method to create a bistable state using
, Phys, Lett, 36 (1980) 899
) is expected to find a variety of applications due to its high-speed response and memory performance.

The above-mentioned bistable ferroelectric liquid crystal element has a liquid crystal molecule axis that is constant with respect to the axial direction (rubbing direction, etc.) of the alignment working surface formed by rubbing etc. on the liquid crystal layer side of the plates on both sides sandwiching the liquid crystal layer. It shows two stable states in angularly different directions. This angle is called the cone angle (hereinafter expressed as θ).

When a voltage is applied in a direction perpendicular to the liquid crystal layer surface of the element,
A ferroelectric liquid crystal moves from one stable state to another. This change causes the principal axis of the refractive index ellipsoid of the material with refractive index anisotropy to be at an angle of 2θ within the plane of the liquid crystal layer. It corresponds to high rotation. Although the liquid crystal molecule axis and the principal axis of the refractive index ellipsoid may not exactly match, here, for simplicity, they are assumed to be in the same direction. Therefore, when polarized light is incident on the ferroelectric liquid crystal element having a thickness corresponding to the effect of a 1/2 wavelength plate, the polarization rotation effect on the incident polarized light due to the two bistable states is 40 degrees from each other. Very different. Polarizing element C with crossed Nicols or parallel Nicols arrangement
When the ferroelectric liquid crystal element is sandwiched between two (FA light plates, etc.), when 4θ = 90 @ (θc = 22.5°), the on-off ratio (transmittance ratio, contrast ) will be the highest.

FIG. 3 shows an example of a ferroelectric liquid crystal element when the polarizing elements are arranged in a crossed Nicol arrangement. incident on the Here, the liquid crystal molecular axis 45 in one stable state of the liquid crystal layer 4 and the direction of incident polarization coincide. An analyzer (not shown) is arranged perpendicular to the polarizer. The liquid crystal molecular axis 46 corresponds to the other stable state, and the molecular axes 45 and 46 correspond to the alignment effect axis 44 due to rubbing etc.
are 100 each. and has a cone angle of −θ0. When the night crystal molecules are in the 45 state, the polarization direction of the incident polarized light does not change and is completely cut off by the analyzer, expressing black. On the other hand, when the liquid crystal molecules are in the 46 state, the polarization direction is 4
The ratio of light that rotates by θ0 and passes through the analyzer is 5 in 2 (4 θC), which represents a white state.

Note that when the polarizing element has a parallel Nicol arrangement, the white state is when the liquid crystal molecules are in the 45 state, and the white state is when the liquid crystal molecules are in the 46 state.
It expresses the black state when it is in the state of .

[Problems to be Solved by the Invention] Incidentally, the cone angle θ in a bistable ferroelectric liquid crystal is temperature dependent. For this reason, even if the structure shown in FIG. 3 is arranged at a certain temperature, the direction of incident polarization will deviate from the direction of one of the liquid crystal molecular axes 45 in a stable state at another temperature. Therefore, the incident light is subjected to a polarization rotation effect, and a portion of the light is transmitted through the analyzer. Therefore, in the crossed Nicol arrangement, a sufficiently dark state cannot be achieved, resulting in a decrease in contrast.

On the other hand, if the polarizer and analyzer are arranged in parallel Nicols, the transmittance in the white state will be lowered.

The present invention has been made in view of the problems in the conventional example described above, and an object of the present invention is to provide an optical modulation element that prevents a decrease in contrast due to temperature.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides: (1) an optical modulation element consisting of a polarizer, a bistable strong 8-electroconductor liquid crystal (FLC) that performs modulation, and an analyzer; A polarizer and an analyzer consist of a bistable guest-host strong-conductivity liquid crystal (hereinafter referred to as GH-FLC), and the GH-FLC which forms the polarizer and analyzer and the F which performs the above modulation.
The temperature dependence of the cone angle is the same as that of the LC, and the GH-FLC, which serves as a polarizer and analyzer, has two stable states of liquid crystal molecules during use; However, it is characterized by being kept in a stable state where it rotates in the same direction.

In a preferred embodiment of the present invention, the alignment axes of the GH-FLC of the polarizer and analyzer are perpendicular to each other, and the alignment axis of the modulating FLC is parallel to any of the alignment axes.

In another preferred embodiment of the present invention, the alignment operating axes of the GH-FLC of the polarizer and analyzer are parallel, and the alignment operating axis of the modulating FLC is parallel or perpendicular to the operating axis.

[Operation] According to the above configuration, the relative angle between the polarizer and the analyzer is kept constant even if a temperature change occurs. Further, regarding the modulating FLC, the direction of the liquid crystal molecule axis in one of the stable states is kept at a constant relative angle with respect to the direction of the liquid crystal molecule axes of the polarizer and analyzer. Therefore, these two
Due to these two effects, the display state of one of the modulating FLCs in the stable state is not affected by the temperature dependence of the FLC cone angle.

In addition, if the alignment axes of the GH-FLC of the polarizer and analyzer are orthogonal, and the modulation FLC alignment axis is parallel to the alignment axis of either the polarizer or the analyzer, regardless of temperature changes, It serves as a polarizer and analyzer with crossed Nicols arrangement. Furthermore, in one stable state of the modulating FLC, the direction of the life axis of the refractive index ellipsoid and the direction of the transmission axis of the polarizer coincide regardless of temperature changes, so the polarization direction of the incident light does not rotate. Due to the above two effects, in one stable state of the modulating FLC, a black state with low transmittance can be stably displayed regardless of temperature changes, and an image with high contrast can be displayed.

Furthermore, if the alignment action axes of the GH-FLC of the polarizer and analyzer are made parallel, and the alignment action axis of the modulation FLC is made parallel or perpendicular to the action axis, regardless of temperature changes,
The polarizer and analyzer have a parallel Nicol arrangement. Furthermore, in one stable state of the modulating FLC, the direction of the life axis of the refractive index ellipsoid and the direction of the transmission axis of the polarizer coincide regardless of temperature changes, so the polarization direction of the incident light does not rotate. Above 2
Due to these two effects, in one stable state of the modulating FLC, a white state with high transmittance can be stably displayed regardless of temperature changes.

[Example] 1 Upper and 2 Forks 1j FIG. 1 is a sectional view showing the layer structure of a ferroelectric liquid crystal element according to an example of the present invention.

In the figure, GH type bistable FLC layers 1 and 3 constitute a polarizer and analyzer, respectively, and bistable FLC layer 2 constitutes a modulator. The incident polarized light that has passed through the polarizer 1 is phase-modulated by a bistable FLC layer (modulator) 2 capable of modulation, and only the component in the non-absorption axis direction of the analyzer 3 is transmitted to become output light.

The modulator 2 consists of opposing transparent substrates 21,23 and a layer of FLC molecules 22 implanted therebetween. The FLC molecular layer 22 is aligned in a fixed direction by an alignment film (not shown) formed inside the substrate 21.23, and is controlled by an electric field applied to a transparent conductive film (also not shown) formed inside the substrate 21.23. Depending on the direction, it can be in one of two bistable states.

The GH type bistable FLC layer 1.3 also has the same layer structure as the FLC layer 2. The electric field applied to the GH-type bistable FLC layer 1.3 at all times or at any time is used to maintain uniform and stable molecular axis direction as a polarizer and analyzer 1.3.

FIG. 2 shows the orientation state of each layer and the state of light rays at the temperatures in the configuration of FIG. 1. Unpolarized incident light Ein is incident on the GH-FLC layer 1, and a polarized light component in the host liquid crystal molecule axis direction 15 forming a cone angle θ0 with respect to the alignment action axis 14 is transmitted to become output light E1. This emitted light E1 becomes incident light E1 to the FLC layer 2. Although the absorption axis of the guest molecule is set perpendicular to the guest molecule axis here, in the opposite case, the direction of the emitted light E1 may be rotated by 90 degrees.

The orientation axis direction 24 of the FLC layer 2 coincides with that of the first layer 1, and the cone angle θ. is also the same liquid crystal molecule 2 as the first layer 1
It consists of 5. When an electric field is applied in the direction in which the first layer and the liquid crystal molecular axis coincide, the incident light El becomes the output light E2 while maintaining its polarization direction.

The third GH-FLC layer 3 is formed in a direction in which the alignment action axis direction 34 is rotated by 90 degrees with respect to that of the first layer 1, and the cone angle θC is also made of the same liquid crystal molecules 35 as the first layer 1. There is. An electric field is constantly or occasionally applied so that the liquid crystal molecular axes 15, 35 of the first layer 1 and the third layer 3 are perpendicular to each other. '83 Since the incident light E2 to the layer 3 is perpendicular to the transmission axis 35 of the third layer 3 in the above state, the outgoing light E out
The component becomes zero, representing black.

In the above configuration, the polarizer 1 and the analyzer 3 have a crossed Nicol arrangement, and one stable state of the polarizer 2, which is the second FLC layer, is in the transmission axis direction of the polarizer 1, which is the first FLC layer. , it is possible to express a black state with high contrast.

Next, consider the orientation state when the temperature changes.

The three FLC layers 1, 2.3 consist of those whose cone angles have the same temperature change. If the temperature changes, the first
Since the direction of the molecular axis 15 of layer 1 changes, the direction of the emitted light E1 also changes, but the molecular axis 25 of the second layer 2 also changes in the same way, so the directions of the incident light E1 and the molecular axis 25 remain the same. It is. Furthermore, since the molecular axis 35 of the third layer 3 changes in the same way, it remains perpendicular to the molecular axis 15 of the first layer 1.

As described above, in this configuration, the relative relationships among the polarizer 1, modulator 2, and analyzer 3 do not change even when the temperature changes, so the device can display high-quality images with high contrast over a wide temperature range. I can provide it.

Figure 4 shows the structure of an optical modulation element according to another embodiment of the present invention. The alignment effect axis was made to coincide with the alignment effect axis of the first FLC layer 1, whereas the alignment effect axis of the second FLC layer 2 was made to coincide with the alignment effect axis of the third FLC layer 3. be.

According to the configuration shown in FIG. 4, since the direction of the molecular axis 25 of the second layer 2 is orthogonal to the polarization direction of the incident light E1, no polarization rotation occurs. Therefore, the operation is similar to that of the first embodiment.

The present invention is not limited to the embodiments described above, and can be implemented with appropriate modifications.

For example, the directions of the alignment axes of the first layer 1 and the third layer 3 are parallel, and the alignment axis of the second layer 2 is perpendicular or parallel to those of the first and third layers (parallel Nicol arrangement). In this case, the maximum transmittance can always be kept at a high value.

It is also possible to configure a reflective ferroelectric liquid crystal element consisting of a first GH-FLC polarizer (which also serves as an analyzer), a second FLC layer, and a reflector. With this reflective ferroelectric liquid crystal element, the number of layers can be reduced due to the reflective configuration. Moreover, it becomes a parallel Nicol arrangement, and has the same effect as the case of the above-mentioned parallel Nicol arrangement structure consisting of three layers.

[Effects of the Invention] It is possible to always achieve stable contrast or high transmittance even with temperature changes, and it is possible to display high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of an optical modulation element according to an embodiment of the present invention, FIG. 2 is a perspective view showing an example of the arrangement of each layer in the element of FIG. 1, and FIG. FIG. 4 is a perspective view showing the configuration of a conventional modulation element, and FIG. 4 is a perspective view showing another example of the arrangement of each layer in the element shown in FIG. 3. 1. Polarizer (GH type bistable FLC) 2.4: Modulator (bistable FLC) 3: Analyzer (GH type bistable FLC) 11.13, 21, 23, 31, 33: Transparent substrate (transparent conductive 12.32: GH type bistable FLC layer 14.24, 34.44: Alignment axis 15.25, 35, 45, 46: Liquid crystal molecular axis 22: Bistable FLC layer Patent application Person Canon Co., Ltd. Agent Patent Attorney Tetsuya Ito Agent Patent Attorney Tatsuo Ito Figure 1

Claims (3)

[Claims] (1) In an optical modulation element consisting of a polarizer, a modulator, and an analyzer, the modulator is made of bistable ferroelectric liquid crystal, and the polarizer and analyzer are made of bistable guest-host ferroelectric liquid crystal. In addition, the bistable guest-host ferroelectric liquid crystal forming the polarizer and analyzer has the same temperature dependence of cone angle as the bistable ferroelectric liquid crystal forming the modulator, and Of the two stable states of liquid crystal molecules, the optical modulation element is maintained in a stable state rotated in the same direction with respect to the direction of the action axis within the alignment action plane. (2) The alignment action axes of the bistable guest-host ferroelectric liquid crystal forming the polarizer and the bistable guest-host ferroelectric liquid crystal forming the analyzer are orthogonal to each other, and 2. The optical modulation element according to claim 1, wherein the alignment axis of the stable ferroelectric liquid crystal is parallel to the alignment axis of any of the bistable guest-host ferroelectric liquid crystals. (3) The alignment action axes of the bistable guest-host ferroelectric liquid crystal forming the polarizer and the bistable guest-host ferroelectric liquid crystal forming the analyzer are parallel to each other, and the bistable liquid crystal forming the modulator is parallel to each other. 2. The optical modulation element according to claim 1, wherein the alignment axis of the ferroelectric liquid crystal is parallel or perpendicular to the alignment axis of any of the bistable guest-host ferroelectric liquid crystals.