JPS62287225A - Liquid crystal optical switch device - Google Patents

Abstract

PURPOSE:To perform much faster switching by using nematic liquid crystal which has positive dielectric anisotropy and has a specific relation between the pitch of liquid crystal and a substrate gap, and varying the transmissivity to light by utilizing a voltage. CONSTITUTION:When the relation between the pitch (p) of the nematic liquid crystal and substrate gap (d) is so set that 0.5Xn<d/p<0.5+0.5Xn (n: integer >=1), liquid crystal molecules are twisted by 90 deg.+180 deg.Xn in a voltage off state on condition that the horizontal orientation directions of both substrates cross each other at right angles. When a voltage is impressed here, the liquid crystal molecules raised and become nearly vertical to enter longitudinal orientation. Then when the voltage is disconnected the liquid crystal molecules are in a 90 deg.+180 deg.Xn twist state or the 1st stable i.e. twisted large by 270, 450, 630 deg.... in a complete voltage-off state, so the liquid crystal molecules are twisted by 90 deg. firstly and then 270 deg., 450 deg.... successively to increase in its twist angle, so that they are enters a semistable state of >=1. Then, this semistable state is utilized.

Description

Detailed Description of the Invention 3. 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 head device using a dual-frequency drive method is known.

In this two-frequency driving method, a low frequency of up to several KHz and a high frequency of several tens of Kl (z to several hundred K) Iz are used. For this reason, in a high frequency range, unless the electrode resistance of the transparent electrode substrate is lowered, the effective voltage applied to the liquid crystal will decrease, resulting in a drawback that it is difficult to drive a large screen display.

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 obtain high-speed response, high voltage is required.
This also has the disadvantage of increasing power consumption.

Therefore, a driving method using a low frequency single signal of up to several KHz is desired. In this conventional driving method using a single low frequency signal, in the normal twisted nematic (TN) mode, the responsiveness when voltage is applied (on) can be made faster by increasing the voltage. However, the response when the voltage is turned off (off) cannot be made faster by changing the voltage; it can be made somewhat faster by thinning the gap between the cell substrates or lowering the viscosity of the liquid crystal. The speed was at most several tens of m5ec at O'C. Furthermore, due to the thinning of the substrate gap and the lowering of the viscosity of the liquid crystal, the foot last of the liquid crystal optical switch device itself may be reduced, making it impossible to obtain a liquid crystal optical switch device that provides good contrast and high-speed response. There wasn't.

Furthermore, when a dichroic dye is added to adjust the amount of transmitted light, the viscosity of the liquid crystal increases, resulting in poor responsiveness.

[Problems to be Solved by the Invention] The purpose of the invention is to solve the above-mentioned problems that the prior art had, and to provide a driving method using a low-frequency single signal with low power consumption. An object of the present invention is to obtain a liquid crystal optical sinch device capable of high-speed response without deterioration of contrast.

[Means for Solving the Problems] The present invention has been made to solve these problems, and includes a pair of transparent substrates with transparent electrodes arranged so that the transparent electrodes face each other, and a sealing material surrounding one. In a liquid crystal optical switch device that is sealed, nematic liquid crystal to which a dichroic dye is added is enclosed, and a pair of polarizing films are arranged outside the nematic liquid crystal layer, each transparent substrate is horizontally aligned. The two transparent substrates are arranged so that their horizontal alignment directions are substantially orthogonal to each other, and the polarization axes of the respective polarizing films are arranged substantially parallel to or substantially perpendicular to the alignment direction of liquid crystal molecules on the respective substrate surfaces. The relationship d/p between the pitch p of the nematic liquid crystal and the substrate gap d is larger than 0.5X n and smaller than 0.5+Q, 5X n (n is an integer of 1 or more), and both transparent By sequentially turning on and off the voltage applied between the electrodes, the liquid crystal molecules assume a twisted state of approximately 90° + 180° × n when the voltage is turned off.
When the voltage is on, the liquid crystal molecules take a vertical alignment 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, approximately 30''', 18Q°.
It is in a twisted state of Almost 90' + 1 of liquid crystal molecules when state and voltage off
The present invention provides a liquid crystal optical switch device characterized in that the light transmittance is changed using two states: a twisted state of 80@Xm and a twisted state.

The present invention does not change the light transmittance of the liquid crystal using only the two stable states of voltage on and voltage off, which are used in ordinary liquid crystals, but it is possible to change the light transmittance by changing the light transmittance by using a completely off state by turning off the voltage for a long time. The light transmittance is changed by using two states: a stable state when the voltage is on, and a metastable state where the voltage is then turned off to completely relax and become completely off. Even when dichroic dyes are added, high-speed response and high contrast can be obtained.

Since the present invention uses this metastable state, several m5
It is suitable for applications in which the light transmittance of a liquid crystal is changed over and over again at a relatively high speed of about ec-several seconds.

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 substrates made of glass, plastic, etc., and transparent electrodes 2A, 2B made of tin oxide, indium oxide-tin oxide, etc. are formed on the inner surfaces of the substrates by patterning them into desired patterns as necessary. has been done. The surface of this transparent electrode is horizontally aligned by rubbing or diagonal vapor deposition so that the liquid crystal molecules are horizontally aligned in one direction. The cell is sealed with a sealing material 3, and a nematic liquid crystal 4 to which a dichroic dye is added is sealed inside to form a liquid crystal cell. A pair of polarizing films 5A and 5B are arranged on the outer surface of this liquid crystal cell so that the polarization axis of each polarizing film is substantially parallel to or substantially perpendicular to the alignment direction of liquid crystal molecules on each substrate surface. The polarizing films are arranged so that their polarization axes are substantially parallel or orthogonal 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 by plating, Cr vapor deposition, etc., forming a color filter, forming an overcoat for an alignment film such as polyimide, polyamide, silica, alumina, etc. on a transparent electrode, or forming a substrate inside a liquid crystal cell. Spacers such as glass fibers, alumina particles, plastic particles, etc. may be sprinkled or a sealing material containing such spacers may be dotted to maintain the gap accurately.

FIG. 2 is an explanatory plan view showing the relationship between the orientation processing direction of the liquid crystal optical switch device of FIG. 1 and the polarization axis direction of the polarizing film.

In FIG. 2, 11 is the polarization axis direction of the front polarizing film 5A, 12 is the rubbing direction of the front transparent substrate IA, and 13 is the direction of the rubbing process of the front transparent substrate IA.
indicates the polarization axis direction of the polarizing film 5B on the back side, and 14 indicates the rubbing direction of the transparent substrate IB on the back side.

In this example, the polarization axis direction of the polarizing film and the orientation treatment direction are parallel, but they can also be perpendicular, and the polarization axes of both polarizing films are not perpendicular as in this example. It can also be made parallel. However, if the polarization axes are orthogonal to each other as in this example, the light can be blocked only in the necessary areas and when necessary.

Note that the angle of intersection between the alignment direction and the polarization axis of the polarizing film, and the relationship between the alignment direction and the polarization axis are not limited to being exactly parallel or orthogonal, for example, 5', 10', 2', etc.
It is also possible to shift by about 0'.

[Function] Also in the present invention, like a normal liquid crystal display device, when the voltage is off, the liquid crystal molecules assume the first stable state, which is a twisted state of approximately 90° + 180' X n, and 1! When the pressure is turned on, the second stable state is a vertically aligned state, 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°X which is a relaxed state to a twisted state
At least one metastable state is a twisted state of m (m is an integer of O≦man). This metastable state is
In the present invention, since the liquid crystal itself has a strong twisting force,
Even if the dichroic dye is added and the viscosity has increased somewhat, it reaches the second stable state at a high speed of 1 to several rasec at room temperature, and reaches a certain level. The present invention drives between two states: a second stable state when the voltage is on, and at least one metastable state. , which turns on and off at high speed.

This metastable state is not stable for a long time, so it sequentially shifts to the next metastable state or the first stable state, but each of these is determined by the orientation direction, so the twist between them is 180" Therefore, the change in light transmittance between the metastable states and the change in light transmittance between the metastable state and the first stable state are relatively small. In particular, the change between the metastable states of 90° and 270° is small, and the change in state is 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 represents an integer of 1 or more),
This allows when the horizontal alignment directions on both substrates are orthogonal! When the pressure is off, the liquid crystal molecules are 80° + 180°
Take the twisted state of ×n. This is the first stable state.

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.

When the voltage is then turned off, the liquid crystal molecules tend to become twisted and align in the orientation direction of the substrate. At this time, the added dichroic dye molecules follow the movement of the liquid crystal molecules.

In this case, in the present invention, when the voltage is completely turned off, the liquid crystal molecules are in the first stable state, a twisted state of 90" + 180'
Because the liquid crystal molecules are twisted so much that even when the voltage is turned off, they do not immediately return to this state; they first become 90°, then 270°, and then 450°.
' , . . . and so on, the twist gradually expands, and a metastable state of 1 or more is achieved. The present invention utilizes this metastable state, which is a twisted state at this intermediate stage.

In addition, in this case, the poor orientation of the liquid crystal molecules is approximately 90' +
By aligning the pretilt angle created by the horizontal alignment process in the twisted state of 180@Xm (m is an integer of 0≦man), this particular metastable state is more stable than other metastable states. They tend to last much longer, sometimes lasting more than a few 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, it is preferable to match in a metastable state with less 180° twist than the first stable state because 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 CB) shows a 450° twisted state.

In the example shown in FIG. 3, in this state, the upper substrates 21A, 2
In the case 1B, the left ends 22A and 22B of the liquid crystal molecules are in contact with the substrate, and in the lower substrates 23^ and 23B, the back sides 24A and 24B of the liquid crystal molecules are in contact with the substrate. For this reason, Figure 3 (
The matching state is reached at 2706 twists in A), and the pitches shown by curves 25A and 28A in the figure are the same, resulting in a stable matching state. Conversely, 450° in Figure 3 (B)
The torsion is in a mismatched state, resulting in curves 25B and 213B in the figure.
The pitches indicated by and are different. Therefore, it is suitable for liquid crystal optical switching devices that have a 450° twist as the first stable state, where the 90° twist in the first metastable state is short and the 2700° twist in the second metastable state lasts for a long time. That will happen.

Further, in the example shown in FIG. 4, in this state, the upper substrates 31A, 3
In the case 1B, the left ends 32A and 32B of the liquid crystal molecules are in contact with the substrate, and in the lower substrates 33A and 33B, the front sides 34A and 34B of the liquid crystal molecules are in contact with the substrate. For this reason, the 270° twist in FIG. 4(A) results in a mismatched state, and the pitches shown by curves 35A and 313A in the figure are different.

Conversely, the 450° twist in FIG. 4B results in a matched condition, with the pitches shown by curves 35B and 36B in the figure being the same. For this reason, it is suitable for liquid crystal optical switch devices that have a 450° twist as the first stable state, and the 90° twist in the first metastable state is relatively stable from the point of view of matching state, but the liquid crystal molecules The 2700° twist in the second metastable state is short due to the strong twisting force, and the 450° twist in the third metastable state continues for a long time.

For example, when a rubbing method is used as a horizontal alignment processing method, pretilting of liquid crystal molecules occurs in the rubbing direction. If we use a liquid crystal whose first stable state is 450° in the left helix, it is preferable 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 the lower left to the upper right when viewed from the outside (front side) of the cell, and for the transparent substrate IB on the back side, the rubbing direction may be set from the lower right to the upper left.

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 the top left to the bottom right. .

In the present invention, the liquid crystal is adjusted so that the first stable state is 450', that is, l<d/p<1.5.
using a liquid crystal with a metastable state of 270°, and this 27°
Preferably, the alignment state is at 0°.

This is because the larger the d/p of the liquid crystal and the stronger the twisting force of the liquid crystal molecules, the faster the first metastable state at 90° will be reached, and the first stable state will be at 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 at 270° and 450° is larger than the difference between 450' and 630°. This means that the first stable state is 2706
This is because the metastable state is only at 90°, and although it is considerably faster than the conventional liquid crystal display device whose first stable state is 90°, it is In addition, in the present invention, the voltage is turned on and off between two states: the second stable state when the voltage is on and the metastable state immediately after the voltage is turned off, and the longer the metastable state is, the faster the It is preferable that the first stable state is 450° because of its high usability.In particular, the first stable state should be 450°, and the alignment state where the orientation of the liquid crystal molecules and the pretilt match in the metastable state of 270°. By setting it so that it is, it becomes possible to use the device even if the switching is repeated for several seconds.

Although there is a tendency for the response speed of the transition to the metastable state to improve as the torsion angle increases, a torsion angle of 630° or more is different from the case where the first stable state is 270'.
The difference from the case of 0° is not very large, and on the contrary, as the driving voltage increases, the circular polarization increases, the light transmittance decreases, and the contrast decreases, so it is most preferable to set it to 450@. . Furthermore, when the twist angle is increased, the turbulence color tends to become stronger in an element that does not contain a normal dichroic dye, but the hue can be adjusted by the added dichroic dye.

In this case, as explained in FIG. 3, it is preferable that the matched state be achieved with a 270° twist, and the metastable state of the 270° twist is relatively long, specifically lasting several seconds, and the voltage is turned on. This is preferable because the time range in which the device can be turned on and off between the second stable state when the voltage is turned off and the quasi-stable state when the voltage is turned off is widened, and the range in which it can be used with a fast response speed and high contrast is widened.

Further, it is preferable that the relationship between the refractive index anisotropy Δn of the liquid crystal used in the present invention and the substrate gap d is Δnd of 0.3 to 2.0, whereby high contrast can be obtained.

In the present invention, the liquid crystal is turned on and off using two states: a second stable state when the voltage is turned on and a metastable state immediately after the voltage is turned off.

As a result, the transition from the second stable state to the metastable state when the voltage is turned off is as fast as described above, and conversely, when the voltage is turned on, the transition from the metastable state to the second stable state is faster than the first one. This is because it is faster than the transition from the stable state to the second stable state.

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 since it does not have this negative effect.

[Example] Polyimide was applied as an overcoat for an alignment film on a front substrate having a patterned transparent electrode on a glass substrate and on each electrode surface side of the front substrate, and the film thickness after thermosetting was approximately 800 mm. . The surfaces of these polyimide films are horizontally aligned using a rubbing method, and as shown in Figure 2, two substrates are arranged so that the rubbing directions are orthogonal, and the periphery of one is sealed with a sealant except for the injection port. to form cells. The cell gap of this cell before liquid crystal injection was 4.6 lm.

In this cell, a black liquid crystal r LHA-040cl manufactured by Mitsubishi Kasei Co., Ltd. whose base liquid crystal is a liquid crystal manufactured by Merck Co., Ltd. r ZLI-IFd5J with a refractive index anisotropy △n of 0.13 was placed so that its helical pitch was 3.7 gm. A liquid crystal containing 5.5 wt % of cholesteryl nonanate as a chiral component was injected into the solution, and the injection port was sealed.

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, the liquid crystal molecules were in a state twisted by 450 degrees when no voltage was applied, and the device was in the first stable state. In this state, light travels within the liquid crystal cell while being absorbed by the added black dichroic dye along the twist of the liquid crystal molecules.
The light that entered the liquid crystal optical switch device was twisted by 450° and 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 becomes isotropic with respect to light, and although the light incident on the liquid crystal optical switching is not absorbed by the added dichroic dye, it is blocked because the polarization axes of the pair of polarizing films are perpendicular to each other. It was done.

When the voltage is turned off from this state, the liquid crystal molecules within the cell instantly enter the first metastable state twisted by 90 degrees, and the incident light that passes through the front polarizing film travels inside the cell according to the twisted structure of the liquid crystal. While being absorbed by the polarizing dye, the polarized component was twisted by 90 degrees and became able to pass through the back polarizing film, allowing light to pass through.

Since this first stable state is a mismatched state and is not very stable, the twisting of the liquid crystal molecules progresses further in a relatively short period of time, resulting in a second metastable state with a 270° twisted structure. Even in this state, the incident light was transmitted while being absorbed by the added dichroic dye, similar to the 90" twisted structure, and the contrast change due to this change was slight. This 270" twisted structure The alignment state matches the pretilt angle created by the horizontal alignment process, and because it is in a consistent state, it is relatively stable and lasts for a few seconds at room temperature!
! continued.

After passing through this state, the structure shifted to a 450° twisted structure, the polarization component of the incident light became elliptically polarized light within the cell, and the amount of transmitted light 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, the structure quickly shifts to the first stable state, the vertical orientation, and is fast and has a high contrast. Switching was possible6 [Effect of the invention] The present invention has positive tonal anisotropy and the pitch p of the liquid crystal.
d/p of the relationship between and the substrate gap d is 0.5X n <
A nematic liquid crystal with d/p < 0.5 + 0.5X n is used, and when no voltage is applied, the liquid crystal molecules in the cell are twisted at approximately 90° + 180' X n, and when a voltage is applied, the liquid crystal molecules are twisted. The molecules assume a vertically aligned state, and when the voltage is subsequently turned off, the liquid crystal molecules are relaxed to the twisted state when no voltage is applied, which is approximately 9.
The twisted state of 0°÷180°Xm (m is an integer of O≦man) is taken sequentially from O to n-1, and the vertical alignment state when this voltage is applied and the liquid crystal when the voltage is turned off. By changing the light transmittance by utilizing the two states of the molecule, the approximately 90" + 180' Xm twisted state,
It has an excellent effect of being able to switch much faster than conventional TN mode liquid crystal display devices.

Furthermore, by not using a highly twisted state that is the twisted state when no voltage is applied, there is little reduction in contrast despite the large twist, and there is little adverse effect due to retardation.

Furthermore, by adding a dichroic dye, it is possible to switch the transmittance according to the purpose of use.

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

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the basic structure of the optical switch head according to the present invention. FIG. 2 is a plan view showing the relationship between the alignment processing direction of the liquid crystal optical switching shown in FIG. 1 and the polarization axis of the polarizing film. FIGS. 3 and 4 are cross-sectional explanatory diagrams illustrating the relationship between the pretilt direction and alignment of liquid crystal molecules. Transparent substrate: 1A, 1B Transparent electrode: 2A, 2B Sealing material = 3 Nematic liquid crystal: 4 Polarizing film: 5A, 5 days 3 Closed

Claims (5)

[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, a nematic liquid crystal added with a dichroic dye is sealed inside, and the nematic liquid crystal layer In a liquid crystal optical switch device in which a pair of polarizing films is arranged on the outer side of The polarizing axis of the polarizing film is arranged so as to be 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 0.5. ×n and smaller than 0.5+0.5×n (n is an integer of 1 or more), and by sequentially turning on and off the voltage applied between both transparent electrodes, when the voltage is off, the liquid crystal molecules are almost Take a twisted state of 90° + 180° × n,
When the voltage is on, the liquid crystal molecules take 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, approximately 90° + 180° x m.
(m represents an integer of 0≦m<n),
At this time, the incident light is absorbed by the added dichroic dye, and the vertical alignment state of the liquid crystal molecules when the voltage is on and the approximately 90° + 180° x
A liquid crystal optical switch device characterized in that the transmittance of light is changed using two states: a twisted state and a twisted state of 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 △n of refractive index anisotropy △n of liquid crystal and substrate gap d
4. The liquid crystal optical switch device according to claim 3, wherein d is 0.3 to 2.0. (5) 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.