JPS62105120A - Reflection type liquid crystal electro-optical device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal light switching having a high efficiency and an extinction ratio by forming a reflecting surface on one substrate, and making a spiral axis direction of a ferrodielectric liquid crystal and an incident optical axis direction vertical to each other. CONSTITUTION:A thin film transistor 2 is formed as an active switching element on a transparent substrate, a reflecting surface 3 is formed on an opposed substrate, a high polymer thin film is formed on both the substrates and a rubbing processing is executed, and thereafter, a liquid crystal cell is inserted between a pair of substrates through a spacer and a ferrodielectric liquid crystal 4 is enclosed under a vacuum. Also, an incident light is made incident from a direction of an optical axis 6, so that a spiral axis 5 of the ferrodielectric liquid crystal layer 4 and an incident optical axis become vertical to each other. In this way, switching of light having a high utilization efficiency of light and a high extinction ratio can be executed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a reflective liquid crystal electro-optical device.

[Summary of the invention]

The present invention provides a liquid crystal electro-optical W I in which a ferroelectric liquid crystal is held between a pair of substrates, and means for controlling the light scattering effect of the ferroelectric liquid crystal is provided on at least one of the substrates. By forming a reflective surface on the ferroelectric liquid crystal and allowing the incident light to enter so that the incident optical axis and the helical axis of the ferroelectric liquid crystal are perpendicular to each other, optical switching with high efficiency and high extinction ratio was made possible. Furthermore, by controlling the above-mentioned light scattering effect using active switching elements arranged in a matrix, and by forming an image of the incident reflected light on a screen, it was possible to obtain a bright projected image with a high contrast ratio. .

[Conventional technology]

A liquid crystal electro-optical device using the light scattering effect of ferroelectric liquid crystal was published in Ferro Electrics Magazine No. 59 in 1984.
A transient scattering type (TSM type) is known as described on page 145 of Vol. This continuously causes light scattering that occurs when an alternating current electric field is applied to a ferroelectric liquid crystal layer oriented in the -axis direction to reorient it in the other uniaxial direction. This enables highly efficient and high-speed optical switching by switching between transmission and scattering.

[Problems and Objects to be Solved by the Invention] However, the above-mentioned prior art has the problem that a high contrast ratio cannot be obtained when non-coherent light such as a halogen lamp is used as the incident light source. One way to solve the above problems is to increase the light scattering effect and improve the extinction ratio by increasing the thickness of the ferroelectric liquid crystal layer, but this method conversely slows down the response measurement and also reduces the driving voltage. It gets expensive.

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and its purpose is to provide liquid crystal optical switching with high efficiency and high extinction ratio, and to provide bright, high-contrast images using the liquid crystal optical switching mode. It's there.

[Means for Solving the Problems] A reflective liquid crystal electro-optical device of the present invention holds a ferroelectric liquid crystal between a pair of substrates, and displays the light scattering effect of the ferroelectric liquid crystal on at least one of the substrates. 6. In the liquid crystal electro-optical device provided with a means for controlling the ferroelectric liquid crystal, a reflective surface is formed on one of the substrates, and the direction of the helical axis of the ferroelectric liquid crystal and the direction of the incident optical axis are perpendicular to each other. 6. The present invention is characterized in that active switching elements are formed in a matrix as means for controlling the light scattering effect, and means is provided for forming an image of the light emitted from the reflecting surface on a screen.

[Effect]

The operation of the present invention will be explained with reference to FIG. 3.4.

Generally, when the light scattering type switching mode is changed to a reflective type, the optical path length is doubled, so that the scattering efficiency is increased and the extinction ratio is improved. However, when a ferroelectric liquid crystal, particularly a chiral smectic C phase, is used as in the present invention, the scattering efficiency simply does not improve. As shown in FIG.
It has been experimentally confirmed that when the light is incident at an appropriate incident angle θ7, light scattering occurs with maximum efficiency and the extinction ratio becomes maximum. The output light intensities in the scattered state of the output light 2 and the output light 4 when the incident light is made incident from the directions of the optical axis 1 and the optical axis 3 are shown by 1 and 2 in FIG. 4, respectively. When the incident light is incident in a direction such that the output light angle is perpendicular to the helical axis of the ferroelectric liquid crystal at θ with respect to the normal line (
The intensity of the emitted light is smaller on the optical axis 1). Therefore, the extinction ratio is high. On the other hand, compared to the transmission type, the cell thickness does not need to be particularly thick, so the response speed and driving voltage are slow and do not become high. Therefore, as described above, the light scattering effect of the ferroelectric liquid crystal is switched in the reflection mode by making the incident light enter such that the optical axis of the incident light is perpendicular to the helical axis of the ferroelectric liquid crystal. By using active switching elements arranged in a liquid crystal optical switching pattern with high light utilization efficiency, high speed, and poor extinction ratio, the reflected light is projected onto a screen, resulting in a bright and high contrast ratio. You can get the image.

〔Example〕

FIG. 1 is a sectional view of the liquid crystal light valve of this embodiment. This embodiment will be described below using FIG. 1.

A thin film transistor 2 was formed on a transparent substrate as a typical example of an active switching element. A reflective surface 3 is formed on the counter substrate, a polymer thin film is formed as an oriented RM conductive layer on the substrate, and after a rubbing process, a liquid crystal cell is assembled between the pair of substrates with a spacer interposed therebetween, and the liquid crystal cell is placed in a vacuum. A ferroelectric liquid crystal was sealed at the bottom.

The ferroelectric liquid crystal used was a mixture of those shown below.

OCH.

-〇1lHt, l□ Cll H2□10@-N = CIf■-C~○CH
zCH.

H3 C1H2,,410■-C-co-C-0-C1(ZC
H.

CH.

The ferroelectric liquid crystal used in the present invention is not limited to those mentioned above, but any liquid crystal that exhibits ferroelectric liquid crystal may be used. However, in order to achieve higher speed, higher efficiency, and higher extinction ratio, liquid crystals with large spontaneous polarization and large invariant refraction are preferable.

A two-dimensional reflective liquid crystal light valve was obtained in which a prism was attached to the thin film transistor side of the liquid crystal cell.

The reflective liquid crystal light valve of this embodiment allows incident light to enter from the direction of the optical axis 6. The helical axis 5 of the ferroelectric liquid crystal layer 4 and the incident optical axis 6 are arranged to be at right angles. This liquid crystal light valve was operated with this configuration. By changing the polarity of the input signal for each frame, an alternating current signal was applied to the matrix to create a scattering state, and by keeping the polarity constant for each frame, a transparent state was created. As a result, the brightness is approximately 90% in the transmission state, and the extinction ratio is 1:15, making it possible to switch light with a high extinction ratio.

Moreover, the switching speed was about 1013. This is significantly faster than conventional liquid crystals.

[Example 2] In this example, a projection type liquid crystal display was manufactured using a reflective liquid crystal panel manufactured in the same manner as in Example 1. FIG. 2 is a configuration diagram of a projection type liquid crystal display according to this embodiment. A polysilicon thin film transistor was placed on a transparent substrate as an active switching element, and a ferroelectric liquid crystal cell was assembled using an opposing substrate with a reflective surface, and a prism was attached to the thin film transistor side to form a light valve. Here, the active switching element is not limited to the above-mentioned polysilicon thin film transistor, but may also include an amorphous silicon thin film transistor, MOS) run sister, M
An IM element 1 or the like may also be used. Furthermore, the active switching element may be formed on the reflective surface, for example, a silicon substrate, without requiring that the reflective surface and the active switching element or the like face each other.

A projection type display as shown in FIG. 2 was constructed using the above reflective liquid crystal light valve. Incident light from a light source 1 including an ellipsoidal mirror is made to enter a liquid crystal light valve 3 via a condenser lens 2, and the output light from the liquid crystal light valve passes through a projection lens 4 and forms an image on a screen 5. The contrast ratio of the projected image was approximately 1=13. Furthermore, the brightness was high and good image quality could be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the optical axis of the incident light is made perpendicular to the helical axis of the ferroelectric liquid crystal, and the light scattering effect of the ferroelectric liquid crystal is used in a reflective optical switch. This enables high-speed switching with high light utilization efficiency and a large extinction ratio. Furthermore, by controlling the above-mentioned light scattering effect using active switching elements arranged in a matrix and forming an image of the emitted light on a screen, a bright projected image with a high contrast ratio could be obtained.

[Brief explanation of drawings]

The first part is a cross-sectional view of a reflective liquid crystal panel. ! , prism 2, thin film transistor 3, reflective surface 4, /! The crystal layer 5, the helical axis 6, and the optical axis of the incident light (FIG. 2) are the configuration diagram of a reflective liquid crystal electro-optical device. Relationship between incident optical axis and helical axis Diagram 1.3. Incident optical axis 2.4. Output optical axis 5, panel normal 6, helical axis 7, incident angle Figure 4 shows the output light intensity distribution diagram 1, the output light intensity 2 when incident perpendicular to the helical axis, and the incident parallel to the helical axis. The output light intensity of

Claims (3)

[Claims] (1) In a liquid crystal electro-optical device in which a ferroelectric liquid crystal is held between a pair of substrates and a means for controlling the light scattering effect of the ferroelectric liquid crystal is provided on at least one of the substrates, a reflective surface is provided on one substrate. A reflective liquid crystal electro-optical device characterized in that the helical axis direction of the ferroelectric liquid crystal and the incident optical axis direction are perpendicular to each other. (2) A reflective liquid crystal electro-optical device according to claim 1, characterized in that active switching elements are formed in a matrix as means for controlling the light scattering effect. (3) The reflective electro-optical device according to claim 1, further comprising means for forming an image of the light emitted from the reflective surface onto a screen.