JPH10333130A - Optical device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change a device state only by an electric field without necessitating electric power for holding the device state by making liquid crystal particles as dual frequency smectic liquid crystal particles at an optical device having a structure where the liquid crystal particles are dispersed in a translucent substance. SOLUTION: The optical device has the structure where the dual frequency smectic liquid crystal particles 14 are dispersed in a resin 13 held between transparent plates 12, for instance, glass plates provided with an electrode 11, for instance, ITO. Incident light 15 is scattered by the liquid crystal particles 14 in a device because of a difference in the refractive index of the liquid crystal particles 14 and that of the resin 13 at the optical device, so that the device is made in a scattering state. When the voltage of a frequency to make the dielectric constant anisotropy of liquid crystal positive is applied between the electrodes 11 and 11 of the device by a power source, the liquid crystal is oriented in parallel with the electric field by the electric field, and a refractive index difference with high polymer resin 13 is eliminated, so that scattered light caused by each liquid crystal particle 14 vanishes and transmitted light 18 is obtained and the device state is made a transmission state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element for transmitting, reflecting and scattering incident light and a method for driving the same.

[0002]

FIG. 13 is a schematic view showing a holographic polymer-dispersed liquid crystal using a smectic liquid crystal according to the prior art disclosed in Japanese Patent Application No. 8-242823 previously proposed by the present inventors. is there. As shown in the figure, the element has a structure in which liquid crystal grains 04 are periodically distributed in a resin 03 sandwiched between a glass plate 02 on which a transparent electrode 01 is provided. The incident light 05 is scattered by the liquid crystal particles in the element because the liquid crystal particles and the resin have different refractive indexes. Since the liquid crystal particles are periodically distributed, only light of a specific wavelength is reflected by the interference effect to become reflected light 06, which enters the eyeball 07,
Light of other wavelengths is transmitted as it is to become transmitted light 08. When a voltage is applied between the electrodes of this element, the liquid crystal is oriented by the electric field and the difference in refractive index from the polymer resin disappears, so that the scattered light by each liquid crystal particle disappears and the reflected light disappears. Conventionally, the presence or absence of the reflected light is used as an element operation.

In the device according to the prior art, since a smectic liquid crystal is used, liquid crystal molecules form a layer structure in liquid crystal grains. When the liquid crystal molecules are aligned by the electric field, a layer structure in a direction orthogonal to the alignment direction is formed, and the layer structure is maintained even when the electric field is removed, so that the transparent state is maintained. When this element is heated, the liquid crystal transitions to a less viscous isotropic phase, and thus returns to the original reflection state.

[0004]

However, the element according to the prior art requires heating for erasing and cannot be operated only by an electric field. An object of the present invention is to provide an optical element that does not require power to maintain an element state and can change the element state only by an electric field, and a driving method thereof.

[0005]

According to a first aspect of the present invention, there is provided an optical element having a structure in which liquid crystal particles are dispersed in a light-transmitting substance, wherein the liquid crystal particles have a dual frequency smectic liquid crystal. It is characterized by consisting of.

A second optical element according to the present invention is characterized in that, in the first optical element, the liquid crystal particles are dispersed such that the light transmitting substance and the liquid crystal particles form a layered fine periodic structure.

[0007] The third optical element of the present invention comprises the first or second optical element.
Characterized in that the optical element is sandwiched between a pair of electrodes.

A fourth optical element according to the present invention is characterized in that, in the third optical element, the paired electrodes are matrix electrodes.

The first method for driving an optical element according to the present invention is a method for driving a third or fourth optical element, wherein the pair of electrodes is provided with a dielectric anisotropy of the two-frequency smectic liquid crystal. A first AC voltage mainly having a positive frequency and a second AC voltage mainly having a frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal becomes negative are sequentially applied,
The orientation direction of the liquid crystal grains is switched.

The driving method of the second optical element is a method of driving the third or fourth optical element, wherein the two-frequency smectic liquid crystal has a positive dielectric anisotropy at the pair of electrodes. Applying both a first AC voltage mainly at a frequency and a second AC voltage mainly at a frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal is negative, the first AC voltage and The orientation direction of the liquid crystal grains is controlled by changing the amplitude ratio of the second AC voltage.

A third method for driving the optical element is a method for driving the third or fourth optical element, wherein the dielectric anisotropy of the dual frequency smectic liquid crystal is positive at the pair of electrodes. Applying an AC voltage having a center frequency within a frequency band including both a first frequency region and a second frequency region in which the dielectric anisotropy of the two-frequency smectic liquid crystal is negative, the center of the AC voltage The orientation direction of the liquid crystal grains is controlled by changing a frequency to change a ratio between the first frequency region and the second frequency region in a frequency band of the AC voltage.

A fourth method of driving the optical element is a method of driving the third or fourth optical element, wherein the pair of electrodes has a positive dielectric anisotropy of the dual frequency smectic liquid crystal. Applying both a first AC voltage centered on a frequency and a second AC voltage centered on a frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal is negative, the first AC voltage and The orientation direction of the liquid crystal grains is controlled by changing the ratio of the bandwidth of the second AC voltage.

FIG. 1 is a schematic diagram showing an optical element capable of storing a state. As shown in FIG. 1, the optical element according to the present embodiment has a resin 13 sandwiched between two glass plates 12, 12 which are substrates on which a transparent electrode 11 is provided. Liquid crystal grains 14 composed of a two-frequency smectic liquid crystal are periodically (striped) distributed.

The dual frequency smectic liquid crystal used in the present invention is described in the first document (D. Coates, “Asmectic A phase of
positive and negative dielectric anisotropy ”, Mo
As shown in l. Cryst. Liq. Cryst, vol 49, pp. 83-87 (1978).), the dielectric constant in the major axis direction of liquid crystal molecules is ε _e , and the dielectric constant in the uniaxial direction is Assuming that ε ₀ and two kinds of frequencies for measuring the permittivity are f _a and f _b , ε _e (f _a ) <ε ₀ (f _a ) and ε ₀ (f _b ) <ε _e (f _b ) Means a smectic liquid crystal in which the magnitude relation of the dielectric constant is reversed by the frequency. Further, in the present element, the refractive index ε ₀ of the liquid crystal in the uniaxial direction is almost equal to the refractive index of the resin.

The element having the transparent electrode 11 has a structure in which particles 14 made of a two-frequency smectic liquid crystal are periodically distributed in a resin 13 sandwiched between glass plates 12. The specific dimensions of the device, such as the liquid crystal particle size and period, are as follows:
Second reference (Muneka Date, Keiji Tanaka, Kenya Kato, Shigenobu Sakai, "Reflective display device using holographic polymer dispersed liquid crystal (HPDLC)", IEICE Technical Report EID95-147, ED95-221, SDW
95-261, pp. 131-136 (1996-2)) and the third document (M. Date, N. Naito, K. Tanaka, K. Kato and S. Saka).
i, “Three primary-color holographic polymer disper
sed liquid crystal (HPDLC) devices for reflective
displays. ”, Proceedings of Asia Display95, pp.603-
606 (1995)), which is almost the same as a conventional device using a nematic liquid crystal for liquid crystal grains.

Here, the incident light 15 is scattered by the liquid crystal particles in the device, but since the liquid crystal particles are periodically distributed, only the light of a specific wavelength is reflected by the interference effect and the reflected light 16 is reflected. The light enters the eyeball 17, and the light of another wavelength is transmitted as it is to become the transmitted light 18. When a voltage having a frequency f _b such that the dielectric anisotropy becomes positive is applied between the electrodes of this element,
The liquid crystal is oriented in parallel with the electric field by the electric field, and the difference in the refractive index from the polymer resin is eliminated. In the device of the present invention, since the smectic liquid crystal is used as the liquid crystal, this transmission state is stored even when the electric field is cut off. Here, when _a voltage of a frequency f _a is applied between the electrodes of this element so that the dielectric anisotropy becomes negative, the liquid crystal is oriented perpendicular to the electric field by the electric field, and a difference in the refractive index from the polymer resin occurs again. And return to the reflection state. This reflection state is maintained even when the electric field is cut off because the smectic liquid crystal is used.

As described above, an element that does not require electric power to maintain the element state and can change the element state only by the electric field is obtained.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIGS. 2 and 3 are schematic views showing an optical element having a scattering / transmission function. In the present embodiment, the liquid crystal has a different refractive index in the long axis direction and in the single axis direction. Further, the refractive indices of the resin and the liquid crystal in the uniaxial direction are substantially equal.

As shown in FIG. 2, the element is, for example, ITO
It has a structure in which dual frequency smectic liquid crystal particles 14 are dispersed in a resin 13 sandwiched between transparent plates 12 such as a glass plate provided with electrodes 11 such as (indium tin oxide). In the figure, the arrow of the two-frequency smectic liquid crystal particles 14 indicates the orientation direction of the liquid crystal. In FIG. 2, the incident light 15 is scattered by the liquid crystal particles 14 in the device due to the difference in the refractive index between the liquid crystal particles 14 and the resin 13, so that the device is in a scattering state.

A power supply 20 is provided between the electrodes 11 of the device.
When a voltage having a frequency at which the dielectric anisotropy of the liquid crystal becomes positive is applied, the liquid crystal is oriented in parallel with the electric field by the electric field, and the refractive index difference from the polymer resin 13 disappears. The scattered light 19 due to the liquid crystal particles disappears and becomes the transmitted light 18 as shown in FIG. In the present invention, since the smectic liquid crystal is used, the transparent state is maintained even when the electric field is cut off.

Here, when a voltage having a frequency at which the dielectric anisotropy of the liquid crystal becomes negative is applied between the electrodes 11 of the device, the liquid crystal is oriented in a direction perpendicular to the electric field and refracted by the polymer resin. Since a rate difference occurs, a scattering state as shown in FIG. 2 results. In the present invention, since the smectic liquid crystal is used, the scattering state is maintained even when the electric field is turned off.

That is, an element capable of switching the scattering / transmission state only by the electric field and capable of holding both states without power can be realized.

The present device is, for example, 4-n-pentylphenyl 2'-
A solution obtained by dissolving a dual-frequency smectic liquid crystal such as chloro-4 '(6-n-hexy1-2-naphthoyloxy) benzoate in an ultraviolet curable resin (for example, “NOA-65 (brand name)” manufactured by Norland) is attached to the electrode. It can be produced by sandwiching between two glass plates and irradiating with ultraviolet rays.

In this embodiment, a glass plate is used as the plate, but a plate or film made of an organic material such as acrylic may be used. In addition, although ITO was used as the electrode, it is not limited to this.

By using a matrix-shaped electrode in this embodiment, it is possible to use the electrode intersection as a pixel and display almost arbitrary image information. here,
The matrix-shaped electrode is, for example, one in which a strip-shaped electrode 44 is provided on a substrate 43 as shown in FIG. 4A, but the present invention is not limited to this. At the time of use, as shown in FIG. 4B, the two substrates 43-1 and 43-2 may be used so that the electrodes 44-1 and 44-2 intersect each other. FIG. 4C is a cross-sectional view as viewed from the lateral direction.

[Second Embodiment] FIG. 5 is a schematic diagram showing an optical element capable of storing a state. The element has a structure in which two-frequency smectic liquid crystal particles 14 are periodically distributed in a polymer resin 13 sandwiched between transparent plates 12 such as glass plates provided with electrodes 11 such as ITO. The incident light 15 is scattered by the liquid crystal particles in the element, but since the liquid crystal particles are periodically distributed,
Due to the interference effect, only light of a specific wavelength is reflected and becomes reflected light 16 and enters the eyeball 17. Light of other wavelengths is transmitted as it is to become transmitted light 18.

When an AC voltage is applied between the electrodes of the device so that the dielectric anisotropy of the liquid crystal becomes positive, the liquid crystal is oriented by the electric field and the difference in the refractive index from the polymer resin disappears, so that the scattering by each liquid crystal particle occurs. The light disappears and there is no reflected light. In the device of the present invention, since the smectic liquid crystal is used as the liquid crystal, this transmission state is maintained even when the electric field is cut off.

FIG. 6 is a schematic view showing a method for manufacturing the optical element of the present invention. A raw material 23 in which a dual-frequency smectic liquid crystal is dissolved in a photo-curable resin is put between transparent plates 22 having electrodes 21 attached thereto. Here, an interference fringe 26 generated by causing two light beams to interfere with the output light 25 emitted from the laser light source 24 is irradiated. Polymerization of the resin occurs at the antinode portion of the interference fringes, and the remaining portion becomes a liquid crystal region precipitated by phase separation, whereby a desired structure as shown in FIG. 5 can be obtained.

In the present embodiment, a glass plate is used as the plate, but a plate or film made of an organic material such as acrylic may be used. In addition, although ITO was used as the electrode, it is not limited to this.

Further, as shown in FIG. 7, a transmission type diffraction grating structure 30 may be provided between the substrates 22 provided with the electrodes 21. Note that this structure can be manufactured by making two laser beams incident from one plate side and causing two-beam interference in the manufacturing method of FIG.

The structure may generally be a hologram. As shown in FIG. 8, a hologram is formed by irradiating an interference fringe composed of output light 25 of a laser light source 24 and any coherent light such as scattered light 42 from an object 41 as shown in the figure. Refers to the resulting structure.

Also in the present embodiment, by using the above-mentioned matrix-shaped electrodes, it is applicable to display and can display almost arbitrary image information.

According to the present embodiment, a monochromatic display element which holds displayed information without power can be realized.

The device according to the present embodiment can be multicolored by stacking a plurality of devices 91-1 to 91-3 having different reflection wavelengths as shown in FIG.

[Third Embodiment] FIG. 10 is a schematic view showing an optical element of the present invention. FIG. 2 or FIG.
And the like, and then the glass plate 12 with the electrode 11 is peeled off. By applying an electric field during the production, the orientation of the liquid crystal can be controlled to produce a film having a distribution in optical characteristics.

The film having the structure of the first embodiment is a film having a different degree of scattering depending on the location (FIG. 10).
(A)).

The one having the structure of the second embodiment is
A film hologram whose diffraction state differs depending on the location can be realized (FIGS. 10B and 10C).

Since the device of this embodiment uses a two-frequency smectic liquid crystal, the state of the portion corresponding to the shape of the electrode can be changed by sandwiching the film between the electrodes and applying an electric field. .

[Fourth Embodiment] In the first and second embodiments, by applying voltages of two different frequencies,
Although the element state is switched, the invention is not limited to the drive using two discrete frequencies. As shown in FIG. 11A, the applied voltage is
A first AC voltage having a width mainly at a frequency at which the dielectric constant of the smectic liquid crystal becomes positive, and a second AC voltage having a width at a frequency mainly at a frequency at which the dielectric constant of the smectic liquid crystal becomes negative. Two types of AC voltages may be used as the AC voltage. Also, as shown in FIG. 11B, the element state can be switched by superimposing the first and second AC voltages and changing the ratio of the respective amplitudes. It is also possible to obtain an intermediate state by continuously changing the amplitude ratio. This makes it possible to adjust the level of the switch to a desired state.

As shown in FIG. 12A, the first frequency component in which the dielectric anisotropy of the two-frequency smectic liquid crystal is positive and the dielectric anisotropy of the two-frequency smectic liquid crystal are negative. Applying an AC voltage having a center frequency within a frequency band including both of the second frequency components, changing the center frequency in the frequency spectrum of the AC voltage, the first frequency component having the AC voltage and the An intermediate state can be obtained by changing the ratio of the second frequency component.

Further, as shown in FIG. 12B, an AC voltage centered on the first frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal becomes positive, and a dielectric anisotropy of the two-frequency smectic liquid crystal. Applying an AC voltage centered on the second frequency at which the AC voltage is negative, changing the bandwidth in the frequency spectrum of the AC voltage, and an AC voltage centered on the first frequency having the AC voltage The intermediate state can also be obtained by changing the component ratio of the AC voltage centered on the second frequency.

In Embodiment 1-3 described above, the refractive index of the liquid crystal in the uniaxial direction is made to match the refractive index of the resin to create a transparent state. In this case, an element whose scattering degree or reflectance changes depending on the state is obtained.

Further, the light-transmitting substance according to Embodiment 1-3 described above may be isotropic or have birefringence.

[0044]

According to the present invention, it is possible to realize a display element which can change the display state and maintain the display state only by the electric field. Therefore, unlike the related art, there is no need to provide a heating unit for erasing, and the simplification can be achieved.

By using a polymer resin, the element can be made variable (flexible).

[Brief description of the drawings]

FIG. 1 is a schematic view showing an optical element of the present invention.

FIG. 2 is a schematic diagram of an optical element (scattered state) according to the first embodiment of the present invention.

FIG. 3 is a schematic view of an optical element (transparent state) according to the first embodiment of the present invention.

FIG. 4 is a schematic view of an optical element using a matrix electrode according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram of an optical element according to a second embodiment of the present invention.

FIG. 6 is a schematic view of an optical element according to a second embodiment of the present invention.

FIG. 7 is a schematic diagram of an optical element according to a second embodiment of the present invention.

FIG. 8 is a schematic diagram of a hologram of an optical element according to a second embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating a configuration of a display element of an optical element according to a second embodiment of the present invention.

FIG. 10 is a schematic view of an optical element according to a third embodiment of the present invention.

FIG. 11 is a diagram showing a relationship between frequency and amplitude of a voltage applied to an optical element according to a fourth embodiment of the present invention.

FIG. 12 is a diagram illustrating a relationship between frequency and amplitude of a voltage applied to an optical element according to a fourth embodiment of the present invention.

FIG. 13 is an explanatory diagram illustrating a conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 01 transparent electrode 02 glass plate 03 resin 04 liquid crystal particle 05 incident light 06 reflected light 07 eyeball 08 transmitted light 11 transparent electrode 12 glass plate 13 resin 14 liquid crystal particle composed of dual frequency smectic liquid crystal 20 power supply 21 electrode 22 transparent plate 23 dual frequency Raw material in which smectic liquid crystal is dissolved 24 Laser light source 25 Output light 26 Interference fringe 43 Substrate 43-1 Substrate 44-1 Electrode 91-1 to 3 Element

Claims (8)

[Claims] 1. An optical element having a structure in which liquid crystal particles are dispersed in a translucent substance, wherein the liquid crystal particles are formed of a two-frequency smectic liquid crystal. 2. The optical element according to claim 1, wherein the liquid crystal particles are dispersed such that the translucent substance and the liquid crystal particles form a layered fine periodic structure. 3. An optical element comprising the optical element according to claim 1 sandwiched between a pair of electrodes. 4. The optical element according to claim 3, wherein the pair of electrodes is a matrix electrode. 5. The method for driving an optical element according to claim 3, wherein the pair of electrodes mainly has a frequency at which the dielectric anisotropy of the dual-frequency smectic liquid crystal is positive. One AC voltage and a second AC voltage mainly having a frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal becomes negative are sequentially applied, and the orientation direction of the liquid crystal grains is switched. Driving method of optical element. 6. The method for driving an optical element according to claim 3, wherein the pair of electrodes mainly has a frequency at which the dielectric anisotropy of the dual-frequency smectic liquid crystal is positive. Applying both one AC voltage and a second AC voltage mainly having a frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal becomes negative, wherein the first AC voltage and the second AC voltage are applied. A method for controlling the orientation direction of the liquid crystal grains by changing an amplitude ratio of the optical element. 7. The method for driving an optical element according to claim 3, wherein the pair of electrodes includes a first frequency region in which the dielectric anisotropy of the dual frequency smectic liquid crystal is positive. Applying an AC voltage having a center frequency within a frequency band including both the second frequency region in which the dielectric anisotropy of the two-frequency smectic liquid crystal is negative, and changing the AC voltage by changing the center frequency of the AC voltage. A method for driving an optical element, comprising: controlling an orientation direction of liquid crystal grains by changing a ratio between the first frequency region and the second frequency region in a voltage frequency band. 8. The method for driving an optical element according to claim 3, wherein the paired electrodes are centered around a frequency at which the dielectric anisotropy of the dual frequency smectic liquid crystal is positive. Applying both one AC voltage and a second AC voltage centered on a frequency at which the dielectric anisotropy of the two-frequency smectic liquid crystal is negative, the first AC voltage and the second AC voltage Controlling the orientation direction of the liquid crystal grains by changing the ratio of the bandwidth of the optical element.