JPH0652348B2 - Light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a desired diffraction phenomenon of incident light by controlling a refractive index of a light modulation element, particularly a diffraction grating and a refractive index variable substance to control the refractive index variable substance. The present invention relates to a light modulation element that causes

[Prior art]

Conventionally well-known light modulators include a pair of polarizing plates arranged so that their polarization directions are orthogonal to each other, and a pair of transparent substrates disposed between the pair of polarizing plates are perpendicular to each other. And a so-called TN (two-way) which modulates the incident light by switching the orientation state of the liquid crystal between a twisted state and a state perpendicular to the substrate surface. There is an (istonematic) type liquid crystal display device. This type of display element is widely used because of its simple structure and easy driving.
Since the light flux is transmitted and blocked by using a single polarizing plate, the transmittance at the time of erasing, that is, at the time of light transmission is poor, and it cannot be said to be a preferable light modulator in terms of light flux utilization efficiency.

Further, as a display element of the same type using liquid crystal, there is a so-called guest-host mode liquid crystal display element in which a dye is mixed in a liquid crystal molecule. The transmittance was about 75% at best.

Meanwhile, Japanese Patent Publication No. 53-3928 and USP 4,25
No. 1,137, etc., a display element and a variable subtractive color filter element in which a reflection type or transmission type phase diffraction grating and a liquid crystal are combined are disclosed. Although the elements disclosed in these are certainly excellent in luminous flux utilization efficiency, the elements disclosed in Japanese Patent Publication No. 53-3928 show only a decorative effect and are display elements for displaying characters and images. It has not been satisfactory as a light modulation element for transmitting and blocking light beams. The variable subtractive color filter element disclosed in US Pat. No. 4,251,137 has a pair of facing substrate surfaces, each of which is formed of a isotropic material with a diffraction grating so that the array directions thereof are orthogonal to each other. Is used to change the refractive index by controlling the alignment state of liquid crystal molecules, and to change the spectral transmittance characteristics by changing the refractive index difference between the substance forming the diffraction grating and the liquid crystal. It is highly efficient and has high performance as a variable color filter. However, since the light modulation element using the conventional diffraction grating of this kind diffracts the incident light in a static state because the liquid crystal is homogeneously aligned, it is not actually used as a display element. In order to maintain the display state, that is, the state in which all the incident light flux is transmitted, it is necessary to constantly apply a voltage or the like (normally closed). Therefore, a lot of power is consumed. However, it has a problem that it is not preferable as a display device, such as a drastic decrease in reliability.

[Outline of Invention]

In view of the above-mentioned conventional problems, an object of the present invention is to provide a diffractive light modulation type light modulation element capable of maintaining a non-display state when no electric field is applied.

In order to achieve the above object, the light modulation element according to the present invention,
An element having a pair of substrates, a diffraction grating existing on at least one surface of the pair of substrates facing each other, a liquid crystal arranged in a groove portion of the diffraction grating, and a control means for controlling an alignment state of the liquid crystal, It is characterized in that almost all incident light is transmitted in a static state where the control means is not driven.

Further features of the present invention will be apparent from the examples shown below.

〔Example〕

FIG. 1 shows a basic configuration diagram of an optical modulator according to the present invention,
It also serves as a functional explanatory view of the present light modulation element. In the figure, 1 is a refractive index variable substance represented by a liquid crystal, 2 is a diffraction grating made of a substance transparent to a used wavelength, 3 is a transparent electrode, 4 is a transparent substrate made of a transparent optical member, and 5 is any polarized light. Incident light having characteristics, 6 and 6'are polarization components of the incident light 5 which are orthogonal to each other, 6 is a direction perpendicular to the paper surface, and 6'is a direction parallel to the paper surface.

In the present light modulation element, a transparent electrode 3 is formed on opposite surfaces of a pair of transparent substrates 4, and a rectangular diffraction grating 2 made of a transparent material is provided on one transparent electrode 3 of the pair of transparent substrates 4. The refractive index variable substance 1 is arranged in the groove (concave portion) of the diffraction grating 2, and the refractive index is variable by applying an electric field through the transparent electrode 3.

Hereinafter, the modulation principle of the present light modulation element will be described with reference to FIG. 1. For ease of explanation, the refractive index variable substance 1 will be referred to as liquid crystal 1 hereinafter, and the alignment state of the liquid crystal 1 is controlled by applying an electric field. This will cause a predetermined diffraction effect.

As shown in FIG. 1, in a static state in which no electric field is applied, the liquid crystal 1 is oriented in the direction perpendicular to the array surface of the diffraction grating 2, that is, in the vertical direction of the paper, and maintains the homeotropic alignment state. I shall. Therefore, the polarization components 6, 6 ′ of the incident light 5 having an arbitrary polarization component incident on the present light modulation element in the static state feel the ordinary refractive index no of the liquid crystal 1.

Here, if the diffraction rate of the substance forming the diffraction grating 2 is ng, the wavelength of the incident light 5 is λ, and the thickness of the diffraction grating 2 is T, in the case of a rectangular wave diffraction grating, the polarization component 6 of the incident light 5 is , 6 ', the diffraction efficiency ηo of the zero-order transmitted diffracted light can be roughly expressed by the following equation (1).

However, Δn represents the difference in the diffraction rate between the diffraction rate ng of the diffraction grating 2 and the diffraction rate ne or no of the liquid crystal 1.

Therefore, from the equation (1), when Δn = 0, the diffraction efficiency ηo of the zero-order transmitted diffracted light is ηo = 1, and When (m = 0,1,2,3, ...), the diffraction efficiency ηo is η
o = 0.

Next, when an electric field is applied to the liquid crystal 1 through the transparent electrode 3, the alignment direction (optical axis direction) of the liquid crystal 1 is gradually changed. The polarization component 6'in the incident light 5 always feels the ordinary refractive index no of the liquid crystal 1 irrespective of the application of the electric field, and the polarized component 6 shows the abnormal refractive index ne and the ordinary refractive index no of the liquid crystal 1 according to the applied electric field. Feel the synthetic diffractive index n _θ that is synthesized at a predetermined ratio. Needless to say, the synthetic refractive index n _θ changes as the alignment direction of the liquid crystal 1 changes. When the amount of applied electric field is further increased, the liquid crystal 1 is aligned parallel to the substrate 4 (transparent electrode 3) and the lattice groove direction, and is in a homogeneous alignment state.

At this time, among the polarization components 6 and 6 ′ of the incident light 5, the polarization component 6 ′, which is a component orthogonal to the alignment direction of the liquid crystal 1, feels the ordinary refractive index no of the liquid crystal 1, and also the alignment direction of the liquid crystal 1. The polarization component 6, which is a parallel component, feels the anomalous diffraction rate ne of the liquid crystal 1.

Even in this state, the incident light 5 is modulated according to the equation (1).

Here, if ng = no, from the equation (1), in the static state, the polarization components 6 and 6'of the incident light are in the non-diffraction state, that is, in the total transmission state.

On the other hand, of the polarization components 6 and 6'of the incident light, 6'is in the non-diffraction state, that is, the transmission state when the electric field is saturated. 6
Becomes a diffracted state.

From the above, a normally open is achieved in principle.

Hereinafter, a specific configuration example of the present light modulation element will be described and described.
Using a pair of ordinary glass substrates, a transparent electrode such as ITO is formed on one surface of each glass substrate, and octadecyltriethoxysilane 0.5 wt% ethanol solution is spun on each ITO surface as an aligning agent. After coating with a coat and treatment at 100 ° C. for 1 hour, rubbing treatment was performed. Next, a diffraction grating is formed on one of the substrates that has been subjected to rubbing treatment with an electron beam resist, and the two substrates are bonded so that the transparent electrodes face each other. A Nr liquid crystal was filled to prepare a light modulation element as shown in FIG.

In the light modulation element produced by the above-mentioned manufacturing method, the liquid crystal molecules are oriented in the thickness direction of the diffraction grating, that is, in the direction perpendicular to the substrate surface, and in the static state, so-called homeotropic alignment is exhibited.

Further, since it was Nr liquid crystal, incident light was modulated as the electric field was applied, and after the electric field was saturated, a predetermined 0th order diffraction color was exhibited.

The orientation agent and the degree of orientation treatment used in this example generally overcome the physical orientation control force due to the grooves of the diffraction grating,
It was selected so as to obtain a regulation force sufficient to force the liquid crystal existing in the diffraction grating groove portion from the homogeneous alignment to the homeotropic alignment.

FIG. 2 is a schematic view showing another embodiment of the optical modulator according to the present invention. In the figure, the same members as those in FIG. 1 are designated by the same reference numerals. Reference numerals 7 and 7'indicate the directions of the optical axes of the variable refractive index material 1 such as liquid crystal. Further, 2'is a diffraction grating (not shown),
3'denotes a transparent electrode and 4'denotes a transparent substrate.

In this embodiment, an element is shown in which the diffraction gratings 2 and 2'are superposed so that the arrangement directions thereof are orthogonal to each other, and is formed by using a pair of the light modulation elements shown in FIG. With such a configuration, it is possible to simultaneously modulate the polarization components 6 and 6'of the incident light 5 shown in FIG.

Further, the shape of the diffraction grating of the present light modulation element is not limited to the rectangular shape, and various shapes can be used. However, the equation of the diffraction efficiency shown in the above equation (1) differs depending on the shape of the diffraction grating.

As described above, in the light modulation element according to the present embodiment, when no electric field is applied, the "bright" state, that is, the total transmission state,
Since "dark", that is, a modulation state (display state) is obtained when an electric field is applied, current consumption in the normal state ("bright" state) is eliminated, and the degree of freedom in designing the drive circuit used to drive the element is increased. .

In addition, the contact speed of the transparent electrode is slowed down, and the reliability as an element is significantly improved. Therefore, the applicable range of the present light modulation element such as a display element, a color filter, an optical switch, etc. is greatly expanded.

Further, as a matter of course, unlike the display element using the conventional liquid crystal, the polarizing plate and the light absorbing substance (for example, dye) are not used, so that the luminous flux utilization efficiency is excellent.

As can be seen from FIG. 1, the diffraction grating which constitutes the light modulation element according to the present invention is a so-called phase type diffraction grating which is composed of an uneven relief pattern. As a method for forming this kind of relief pattern, for example, a photolithographic method is used. Various methods such as a method combining E and dry etching, a replica method using a thermosetting resin or an ultraviolet curable resin, a cutting method using a ruling engine, an embossing method and the like can be mentioned.

〔The invention's effect〕

As described above, the light modulation element according to the present invention is an element suitable for a display element, a color filter, or the like that can obtain a total transmission state in a static state and stabilize a non-display state.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration principle of an optical modulator according to the present invention. FIG. 2 is a diagram showing another embodiment of the light modulation element according to the present invention. 1 ... Variable refractive index material (liquid crystal) 2, 2 '... Diffraction grating 3, 3' ... Transparent electrode 4, 4 '... Transparent substrate 5 ... Incident light 6, 6' ... Component 7, 7 '... Optical axis of variable refractive index material

Claims (4)

[Claims] 1. An element having a pair of substrates, a diffraction grating existing on at least one surface of the pair of substrates facing each other, a liquid crystal arranged in a groove portion of the diffraction grating, and a control means for controlling an alignment state of the liquid crystal. A light modulation element that almost completely transmits incident light in a static state in which the control means is not driven. 2. A vertical alignment treatment is applied to at least one of the substrate and the groove of the diffraction grating.
An optical modulator according to the item. 3. The light modulation element according to claim 1, wherein the liquid crystal is a nematic liquid crystal having a negative dielectric property. 4. The light modulation element according to claim 3, wherein said control means is means for applying an electric field, and applies an electric field substantially perpendicular to the array surface of said diffraction grating.