JPS62238525A - Liquid crystal optical switch device - Google Patents

Abstract

PURPOSE:To execute a response at a high speed without lowering a contrast, by turning on and off a voltage which is applied between both transparent electrodes, and changing a transmittivity of light by utilizing a specific torsion state of a liquid crystal molecule. CONSTITUTION:When a voltage is not applied between both transparent electrodes 2A, 2B, a liquid crystal 4 molecule takes a torsion state of about 90 deg.+180 deg. in a cell, and when the voltage is applied, the liquid crystal 4 molecule takes a vertically oriented state. Thereafter, when the voltage has been turned off, the liquid crystal 4 molecule takes successively a torsion state (m) of about 90 deg.+180 deg.Xm (m is an integer of 0<=m<n), which is a relaxed state to a torsion state at the time when no voltage is applied, extending from '0' to (n)-1. Also, a transmittivity of light is changed by utilizing two states of the vertically oriented state at the time when this voltage is applied, and the torsion state of about 90 deg.+180 deg.Xm of the liquid crystal molecule at the time when the voltage has been turned off. In such a way, switching can be executed much more quickly than a conventional liquid crystal display device of a TN mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal optical switch device that repeatedly turns on and off at high speed.

[Prior Art] As a conventional liquid crystal optical switch device that repeatedly turns on and off at high speed, a printer hand device using a dual-frequency drive method is known.

In this two-frequency drive method, a low frequency of up to several KHz and a high frequency of several 1.KH2 to several hundred KHz are used.

For this reason, in the high frequency range, unless the electrode resistance of the transparent electrode plate 2 is lowered, the effective voltage applied to the liquid crystal will be lowered, making it difficult to drive a large area.

Furthermore, liquid crystal materials suitable for dual-frequency driving have a much higher viscosity than normal nematic liquid crystals because the interaction in the lateral direction with respect to the molecular axes of liquid crystal molecules is strong. Therefore, in order to achieve high-speed response, a high voltage is required, which has the disadvantage of increasing power consumption.

Therefore, a drive system using low frequency medium signals of up to several KHz is desired. In this conventional driving method using a low frequency medium signal, in the normal twisted nematic (TN) mode, the response when voltage is applied (on) can be made faster by increasing the voltage. but,
That voltage! , lJ (off) response cannot be made faster by voltage, and the cell substrate gap IX
Although it can be made somewhat faster by increasing the viscosity of the liquid crystal or lowering the viscosity of the liquid crystal, this response speed is at most a few 1-m5e at 0°C.
It was only about c. Furthermore, due to the thinning of the gap between the substrates and the lowering of the viscosity of the liquid crystal, the contrast of the liquid crystal optical switching device itself may become low f, making it difficult to obtain a liquid crystal optical switching device that has good contrast and high-speed response. There wasn't.

[Problems to be solved by the invention] The purpose of the undeveloped (!rl) is to solve the above-mentioned problems that the prior art had, and to drive by low-frequency medium/signal with low power consumption. The object of the present invention is to obtain a liquid crystal optical switch device capable of high-speed response to RTF without low contrast.

[L stage for solving the problem] The present invention has been made to solve the problem, and includes: - A transparent J with a pair of transparent electrodes (arranged so that one electrode faces each other through a transparent plate) In a liquid crystal optical switch device formed by sealing the surrounding area with a sealing material, placing a nematic liquid crystal inside, and disposing a pair of polarizing films on the outside of the nematic liquid crystal layer; , (plate is water) i-oriented treated.

Between both transparent substrates, phase 1. − to that ice ^', Ii+l
- arranged so that the J-th i+1 is almost orthogonal to each other, and the polarization axis of each polarizing film is arranged to be about 1L row or almost perpendicular to the orientation direction of liquid crystal molecules - on the plate surface, Relationship d/ between pitch P of nematic liquid crystal and substrate gap d
p is greater than 0.5X n, and 0.5i, 5X n
By sequentially turning on and off the voltage applied between the two transparent electrodes, the liquid crystal molecules - are approximately 90° + 180' when the voltage is turned off.
Take the twisted shape yE of X n, and when the voltage is on, the liquid crystal molecules are vertically aligned! Taking E, when the voltage is turned off for a short time after the voltage is turned on, the liquid crystal molecules are in a relaxed state to the twisted state when the voltage is turned off, which is approximately 90° + 180° x m (m is O≦m<
When the voltage is on, the liquid crystal molecules are vertically aligned yE, and when the voltage is off, the liquid crystal molecules Y- are twisted at approximately 90° + 180' Xm. The present invention provides a liquid crystal optical switch device characterized in that the transmittance of light is changed using two states.

The present invention does not change the light transmission rate by using only the two stable states of voltage on and voltage off, which are used in ordinary liquid crystals, but completely turns off the liquid crystal by turning off the voltage for a long time. yITi, which is more twisted than a normal liquid crystal, and utilizes two states yE: a stable state yE when the voltage is on, and a metastable state of the relaxed state yE, which changes to a completely off state 51 when the voltage is turned off. It changes the transmittance of light, allowing for high-speed response and high contrast.

Since the present invention uses this metastable state, several m5
It is suitable for applications in which the light transmittance of liquid crystal is repeatedly changed at a certain high speed such as ec-asee.

The configuration of the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view showing the basic structure of a liquid crystal optical switch device of the present invention.

In Fig. 1, IA and IB are transparent plates made of glass, plastic, etc., and transparent electrodes 2A and 2B made of tin oxide, indium oxide-tin oxide, etc. are attached to the inner surface of the plate in a desired pattern as necessary. The surface of this transparent electrode is horizontally aligned by rubbing or vacuum deposition so that the liquid crystal molecules are oriented in the direction of the water layer. ) 1 (plates face each other perpendicularly to each other and are sealed at the periphery with a sealing material 3, and a nematic liquid crystal 4 is sealed inside to form a liquid crystal cell.On the outer surface of this liquid crystal cell,
The pair of polarizing films 5A and 5B are arranged so that the polarization axes of the respective polarizing films are substantially parallel to or substantially perpendicular to the orientation direction of the liquid crystal molecules on the respective J and L plate surfaces, so that the polarized light of the pair is The polarization axes of the films are arranged so as to be substantially parallel or perpendicular to each other.

Although omitted in this explanation, applications such as those used in general liquid crystal display devices, such as forming metal leads on transparent electrodes and using electroless Ni except for parts that change light transmittance, are possible. Forming an opaque mask with plating or Cr vapor deposition shade, forming a color filter, forming an overcoat for alignment films such as polyimide, polyamide, silica, alumina on transparent electrodes, and inside liquid crystal cells) (In order to accurately maintain the gap between the plates, spacers such as glass fibers, alumina particles, plastic particles, etc. may be scattered, or a sealing material containing such spacers may be dotted.)

FIG. 2 is a model III diagram showing the relationship between the orientation processing direction of the liquid crystal optical switch device of FIG. 1 and the polarizing film cut optical axis direction.

In FIG. 2, 11 is the polarization axis direction of the polarizing film 5A on the front side, 12 is the transparent front side), (the rubbing direction of the plate IA,
Reference numeral 13 indicates the polarization axis direction of the polarizing film 5B on the back side, and 14 indicates the direction of the rubbing treatment of the transparent plate IB on the front side.

In this example, the polarization axis direction of the polarizing film and the alignment treatment direction are parallel, but IT! The directions can be perpendicular to each other, and the polarization axes of both polarizing films can also be parallel to each other instead of being perpendicular to each other as in this example. However,
If the polarization axes are orthogonal to each other as in this example, it is possible to block the light only in the necessary areas when necessary.

Note that the intersection angle between the orientation direction and the polarization axis of the polarizing film, and the relationship between the orientation direction and the polarization axis are not limited to exactly 41 lines or orthogonal, but are, for example, 5°, 10", 2", etc.
It is also possible to shift it by about 0°.

[Function] Also in the present invention, as in the normal liquid crystal display device; 11!1, when the voltage is off, the liquid crystal molecules assume the first stable state flf, which is a twisted shape of approximately 90' + 180° x n, and when the voltage is on. A second stable state IE, which is a vertically oriented state ff, is sometimes formed, and up to this point it is the same as a conventional liquid crystal display device.

However, in the present invention, since the twist angle of the liquid crystal molecules is large,
In addition to these two stable states, there is a second stable state when the voltage is on, which is the vertical alignment state, and then when the voltage is turned off, the first stable state is when the voltage is completely off, albeit for a short time. Approximately 90'+180°× which is a relaxed state to a twisted state
At least one stable state of torsion yE with m (m represents an integer of 0≦m<n) is taken. In the present invention, the twisting force of the liquid crystal itself is strong, so this stable state of bevel is extremely fast.
, r4 physically reaches the state at a high speed of about 1 to fIrasec at room temperature, is maintained for a certain period of time, and reaches the next stable state Jg or the first stable state. The present invention is designed to drive between two states, the second stable state yE when the voltage is on, and at least one metastable state ff), and to turn on and off at high speed.

Since this metastable state 71 is not stable for a long time,
It shifts to the next horizontal stable state or the first stable state, but both of these are determined by the orientation direction, so
Between these, the twist increases by 180@. Therefore, there are relatively few changes in light transmittance between the metastable states and between the metastable states and the first stable state, especially at 80°. 270
Changes between the metastable IEs of a are small, and changes in state are hardly recognized.

In this case, the relationship between the pitch p of the nematic liquid crystal and the substrate gap d is 0.5X n < d/p < 0.5+0
．． 5×n (n is an integer greater than or equal to 1). As a result, when both No. 1 (horizontal alignment blade directions on the board are perpendicular to each other), when the voltage is off, the Y outside the liquid crystal is 90° +
Take a twisted state of 180°×n. This is the first stable state 1B.

Here, when a voltage is applied, the liquid crystal molecules stand up, become almost vertical, and become vertically oriented. This is the second stable state jm.

Next, check the voltage! , IJ, the liquid crystal molecules tend to form a twisted pattern, and the liquid crystal molecules tend to align in the orientation direction of the substrate. In this case, in the present invention, when the voltage is completely turned on, the liquid crystal molecules are in the first stable state, 80°-180"
c7) Twisted f1. Buried 270°.

450'', 830', etc., so even if the voltage is turned off, the liquid crystal molecules do not immediately return to this state; they first twist to 90'.
, followed by 270”, 450”, etc.
The torsion gradually expands in this way, and takes the metastable state 11 from 1 to 1.0 The present invention utilizes the tongue stable state, which is the torsion state in the intermediate stage. be.

In addition, in this case, the alignment state of liquid crystal molecules is approximately 90°+
By aligning the pretilt angle by the horizontal alignment process in the torsion state of 180" Metastable state!Tends to last much longer than E, sometimes lasting for several seconds.For this reason,
It is preferable to determine the direction of alignment treatment in consideration of the helical direction of the liquid crystal. In particular, than the steady state of :tSl 18
By aligning in a metastable state with less 0° twist, this metastable state can be easily stabilized.

This example will be explained with reference to FIGS. 3 and 4.

3 and 4 show examples in which only the pretilt direction of the liquid crystal molecules differs, where (A) shows a 270° twisted state and (B) shows a 450° twisted IE.

In the example shown in FIG. 3, in this state, the L side plate 21A,
At 218, the left ends 22A and 22B of the liquid crystal molecules are in contact with the substrate, and at the negative side substrates 23A and 23B, the back sides 24A and 24B of the liquid crystal molecules are in contact with the substrate. For this reason, the third
The 270° twist in figure (A) results in a consistent state yE,
The pitches shown by curves 25A and 28A in the figure are the same, resulting in a stable matching state. Conversely, 4 in Figure 3 (B)
A 50" twist results in a misaligned condition, resulting in curves 25B and 2 in the figure.
The pitch indicated by '8B' is different. For this reason, 4
Suitable for liquid crystal optical switch devices with 50” twist as the first stable state, and 90° of the first slip stable state.
The twist is short and the 270'' twist of the second metastable state 71 continues for a long time.

Further, in the example shown in FIG. 4, in this state, the L side substrates 31A, 3
18-r! (*Substrate Ni M Product Molecule' (7) Left end 32A
,32B,! +<contacting, on the C side), 1. , board 3
:lA, 33B, the front side 34A of liquid crystal molecules on the substrate,
34B is in contact. Therefore, 270° in Figure 4 (A)
Curves 35A and 3 in Figure 1 are in an inconsistent state due to twisting.
The pitch indicated by 6A is different. On the contrary, Figure 4 (B)
The 450° twist of
Therefore, the bina indicated by 5B and 38B are the same =.

Suitable for liquid crystal optical '1 swift device with 450° twist as the first stable state, and 8 of the first metastable state Jg.
Although the 0'' twist is relatively stable from the point of view of a coherent state, it is relatively short because the twisting force of liquid crystal molecules is strong, and the 270' twist in the second metastable state is a mismatched state I.
E, the 450° twist of the third metastable IE continues for a long time.

For example, when a rubbing method is used as the water 41 alignment treatment method, pretilting of liquid crystal molecules occurs in the rubbing direction. Here, suppose we use a liquid crystal whose first stable state is 450° in the left helix.

It is desirable to use the processing direction as shown in FIG.

That is, for the transparent substrate IA on the front side, the rubbing direction may be set from left to right when viewed from the outside (front side) of the cell, and for the transparent substrate IB on the 'A side, the rubbing direction may be set from lower right to left F.

Also, if a right-handed spiral liquid crystal is used and the rubbing direction of the front transparent substrate IA is the same as in the above example, then the rubbing direction of the back transparent substrate IB should be from left a to right do. Become.

In the present invention, the liquid crystal is adjusted so that the first stable state is 450°, that is, a liquid crystal with l<d/p<1.5 is used, and the metastable state is 270°, and this 270°
Preferably, the alignment condition is at .degree.

This is because the larger the d/p of the liquid crystal and the stronger the force that forces the liquid crystal molecules to twist, the faster the first metastable state where the velocity <90° is reached, and the first stable state is 270°. @
This is because a faster response is possible in the case of 450° than in the case of .

The difference between the first stable state being 270° and 450° is larger than the difference between 450° and 630°. This means that when the first stable state y8 is 270°, it is stable! This is because 8 is only 90",
This is considerably faster than a conventional liquid crystal display device in which the first stable state is 90', but one in which the first stable state is 450° is even faster. In addition, in the present invention, the on-off state is switched between two states: the second stable state when the voltage is turned on and the stable state immediately after the voltage is turned off, and the quasi-stable state yE
The longer the value, the greater the usability, and the first stable state is 450
” is preferable. In particular, the first stable state is 450°.
By making sure that the orientation of the liquid crystal molecules matches the pretilt in the metastable state of 270'', it is possible to use the device even if the switching is repeated for several seconds.

As the torsion angle becomes larger, the response speed for transition to the metastable state tends to slow down, but setting the torsion angle to 1-1 or more than 830'' is different from the case where the first stable state IE is 270°.
The difference from the case of 450° is not very large; on the contrary, the driving voltage becomes higher, the circular polarization increases, and the light transmission becomes lower.
Since the contrast becomes low, it is most preferable to set the angle to 450°. In addition, when the helix angle is increased, the retardation tends to increase to 11!
I-f colors may appear.

In this case, as explained in FIG.
The torsional metastable IE is relatively long, specifically lasting several seconds, and the time range in which it can be turned on and off between the second stable state when the voltage is on and the tongue stable state when the voltage is off is wide and fast. This is preferable because it has a wide usable range with high response speed and high contrast.

Further, the product Δnd of the refractive index anisotropy Δn of the liquid crystal used in the present invention and the substrate gap d is 0.5 to 0.7 or 0.9 to
It is preferable to set it to 1.2, whereby high contrast can be obtained.

In 13+1, the liquid crystal is turned on and off using two states IE: the second stable state fKj when the voltage is turned off and the slip stable state immediately after the voltage is turned off.

As a result, the power I [from the second stable state when off?] ll
; As mentioned above, the transition to a stable state is fast; conversely,
The transition from the flat stable state to the second stable state when the voltage is on is also the first stable state! This is because it is faster than the transition from the first stable state to the second stable state yE number.

Furthermore, in the first stable state, the twist of the liquid crystal increases, making circular polarization more likely, and the voltage is repeatedly turned on and off at high speed so that the voltage is turned on again before reaching the first stable state. This is preferable because it does not have this negative effect.

[Example] Polyimide was applied as an overcoat for an alignment film on the electrode surface side of each of the front and back substrates having transparent electrodes patterned on a glass substrate, and the film thickness after thermosetting was approximately 800 mm. . The surface of these polyimide films was rubbed using a rubbing method.

As shown in FIG. 2, two substrates were arranged so that their rubbing directions were perpendicular to each other, and the periphery of one was sealed with a glue material except for the injection 11 part to form a cell.

The cell gap of this cell before liquid crystal injection was 4.88 parts m.

In this cell, a liquid crystal rZLI-+5F15J manufactured by Merck Co., Ltd. with a refractive index anisotropy Δn of 0.13 was added with 5.5 wt% of cholesteryl nonanate as a chiral component so that the helical pitch' was 3.7 gm. Injected 11 injections and made 11 injections.

A liquid crystal optical switch device was manufactured by installing a pair of polarizing films on the front and back sides of this cell so that their polarization axes were parallel to the rubbing direction of the cell, as shown in FIG.

In the liquid crystal optical switch device manufactured in this way, when no voltage was applied, the liquid crystal molecules were in a state twisted by 450", which was the first stable state. In this state, light was not transmitted within the liquid crystal cell. The light propagated along the twist of the liquid crystal molecules and was twisted by 450 degrees, and the light incident on the liquid crystal optical switch device was transmitted because the polarization axes of the pair of polarizing films were perpendicular to each other.

Next, when a voltage is applied, the liquid crystal molecules become vertically aligned,
A second stable state has been reached. In this state, the liquid crystal cell became isotropic with respect to light, and the light incident on the liquid crystal optical switch device was blocked because the polarization axes of the pair of polarizing films were perpendicular to each other.

When the voltage is turned off from this IE, the liquid crystal molecules within the cell instantly turn into the first metastable IE twisted by 90@1.The incident light that passes through the front polarizing film travels inside the cell and becomes polarized according to the twisted structure of the liquid crystal. Components are twisted 90° and transmitted through the back polarizing film iT
It became 7-power, and light was transmitted through it.

Since this first semi-stable state jai is in a mismatched state and is not very stable, the liquid crystal component p further progresses in twisting in a relatively short period of time, resulting in a second meta-stable state with a 270° twisted structure7.
It becomes iT. Even in this state fE, incident light was transmitted as in the 90° heel structure, and the contrast change due to this change was slight. In this 270° twisting structure, the orientation state of the liquid crystal molecules matches the pretilt angle created by the horizontal alignment process, making it a consistent state! E, it was relatively stable and continued for several seconds at room temperature.

This situation! After passing through E, it transitions to a 450° twisted structure, and inside the cell, the polarization component of the incident light becomes elliptically polarized light.
The transmitted light H, +- decreased slightly.

When a voltage is applied between the 270° twisted structure, which is the second metastable state before the transition to the 450° twisted structure, it immediately shifts to the vertical orientation, which is the first stable state, and has a high speed and contrast. High switching was the key.

[Effect of the invention] The present invention has positive dielectric anisotropy, and the pitch p of the liquid crystal is
The relationship d/p between and plate gap d is 0.5X n <
A nematic liquid crystal with d/p < 0.5+0.5
, and when a voltage is applied, the liquid crystal molecules take a 1it alignment state, and after that, at 11ν when the voltage is turned off, the liquid crystal molecules are in a relaxed state to the twisted state when no voltage is applied, which is approximately 90" + 180' The twisted states of X m (m indicates %tv where O≦m<n) were sequentially taken from m O to n-1, and when this voltage was applied, the vertical orientation state y was !1, and the voltage was turned off. liquid crystal molecule - approximately 80°+180°×m
Transmission of light by using the two states of bending and bending - (
By changing the number of pixels, it has an excellent effect of being able to switch much faster than the conventional TN mode liquid crystal display device.

Furthermore, by not using a highly twisted IE, which is the twisted shape yE when no Ichikawa is applied, there is little decrease in contrast despite the large twist, and there is little adverse effect due to retardation.

In addition, the present invention can be used in various other applications without detracting from the effects of the present invention, including applications that require high-speed switching such as high-speed display devices, high-speed shutters for cameras, and optical printers. It can be applied to

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the final configuration of the liquid crystal optical switch device of the present invention. FIG. A cross-sectional view showing the relationship. Figures 3 and 4 are cross-sectional views explaining the relationship between the pretilt direction and alignment of liquid crystal molecules. Transparent substrate: 1A, 1B Transparent electrode J4i: 2A, 2B sealing material
:3 Nematic liquid crystal ・4

Claims (6)

[Claims] (1) A pair of transparent substrates with transparent electrodes are arranged so that the transparent electrodes face each other, the periphery is sealed with a sealant, nematic liquid crystal is sealed inside, and a pair of polarized light is placed outside the nematic liquid crystal layer. In a liquid crystal optical switch device formed by arranging films, each transparent substrate is horizontally aligned, and both transparent substrates are arranged so that their horizontal alignment directions are substantially orthogonal to each other, and the polarization axis of each polarizing film is The substrates are arranged substantially parallel to or substantially perpendicular to the alignment direction of liquid crystal molecules on each substrate surface, and the relationship d/p between the pitch p of the nematic liquid crystal and the substrate gap d is larger than 0.5×n, and 0. .5
Less than +0.5×n (n indicates an integer greater than or equal to 1)
By sequentially turning on and off the voltage applied between both transparent electrodes, the liquid crystal molecules are aligned at approximately 90°+1 when the voltage is off.
When the voltage is on, the liquid crystal molecules are in a vertically aligned state, and when the voltage is off for a short time after the voltage is on, the liquid crystal molecules are relaxed to the twisted state when the voltage is off, which is approximately 90°. +180°×m (m is an integer of 0≦m<n), and the vertical alignment state of the liquid crystal molecules when the voltage is on and the approximately 90° alignment state of the liquid crystal molecules when the voltage is off.
A liquid crystal optical switch device characterized in that the transmittance of light is changed using two states: a twisted state of +180°×m. (2) The alignment state of liquid crystal molecules is approximately 90° + 180° × m
2. The liquid crystal optical switch device according to claim 1, wherein the twisted state of the liquid crystal optical switch is made to match a pretilt angle obtained by horizontal alignment processing. (3) d/p is set to 1<d/p<1.5, so that the liquid crystal molecules are twisted by 450° in a completely relaxed state when no voltage is applied, and when the voltage is turned off for a short time, the liquid crystal molecules are twisted by approximately 270°.
Claim 1 or 2 made to be twisted
The liquid crystal optical switch device described in Section 1. (4) Product Δn of refractive index anisotropy Δn of liquid crystal and substrate gap d
4. The liquid crystal optical switch device according to claim 3, wherein d is 0.5 to 0.7. (5) Product Δn of refractive index anisotropy Δn of liquid crystal and substrate gap d
4. The liquid crystal optical switch device according to claim 3, wherein d is 0.9 to 1.2. (6) The liquid crystal optical switch device according to claim 1 or 2, wherein the pair of polarizing films are arranged so that their polarization axes are substantially perpendicular to each other.