JPS62238529A - Optical modulation element - Google Patents

Abstract

PURPOSE:To enable a stabilized non-display state and to obtain an optical modulation element suitable for use as a display element by using a control means having electrodes provided on the side face of a diffraction grating. CONSTITUTION:This optical modulation element is provided with the phase type diffraction grating 5 consisting of a prescribed member, a liquid crystal 4 existing in the groove parts of the diffraction grating 5 and the control means to change the orientation condition of the liquid crystal 4. The control means has the electrodes 2 provided on the side face of the diffraction grating 5. The transparent electrodes 2 of the adjacent projecting parts are connected via lead wires to a driving power source 8 and a switch 7 and further a transparent insulating film 3 is subjected to a vertical orientation treatment so that the molecules of the liquid crystal 4 are vertically oriented, i.e., homeotropically oriented. A full transmission state in a static state is thereby obtd. and the optical modulation element is made suitable for the display element, color filter, etc., which can stabilize the non-display state.

Description

[Detailed Description of the Invention] Technical Field> What has not yet been invented is a light modulation element, particularly a light modulation element that combines a diffraction grating and a liquid crystal to control the refractive index of the liquid crystal to produce a desired diffraction phenomenon in incident light. Regarding.

<Prior art> Conventionally well-known light modulation elements include , I
A pair of polarizing plates are arranged so that the directions of polarization are perpendicular to each other, and a pair of transparent substrates are arranged between the pair of polarizing plates.The opposing surfaces of the substrates are aligned to be orthogonal to each other, and liquid crystal is encapsulated. The so-called TN (twin nematic) type liquid crystal display element modulates the incident light by switching the alignment state of the liquid crystal between a twisted state and a state facing straight toward the substrate surface. be. This type of display element has a simple structure and is easy to drive, so it is used in a wide variety of ways.However, since it uses two polarizing plates to transmit and block the light flux, it is difficult to change the color when decoloring, that is, when light is transmitted. The light transmittance was poor, and it could not be said to be a desirable light modulation element from the viewpoint of luminous flux utilization efficiency.

Also, as a similar type of display element using liquid crystal.

There is a so-called guest-host mode liquid crystal element that uses a dye mixed into liquid crystal molecules, but since the dye is present in this display element, the transmittance when decoloring is at best about 70%. .

On the other hand, Japanese Patent Publication No. 53-3928 and USP 4.251
, 137, etc., disclose display elements and color filter elements in which a reflective or transmissive phase diffraction grating is combined with a liquid crystal. The elements disclosed in these documents are certainly excellent in luminous flux utilization efficiency, but the element disclosed in Japanese Patent Publication No. 53-3928 merely exhibits a decorative effect, and is not a display element for displaying characters or images. However, it has not been satisfactory as a light modulation element for transmitting and blocking light beams. In addition, the color filter element disclosed in US Pat. By controlling the state, the refractive index is changed and the difference in refractive index between the substance that makes up the diffraction grating and the liquid crystal is changed, thereby making the spectral transmittance characteristics variable.It has excellent luminous flux utilization efficiency and is highly effective as a variable color filter. Has performance. However, since this type of conventional light modulation element using a diffraction grating generally diffracts incident light even in a static state, when actually used as a display element, it is required to be in a non-display state, i.e. It was necessary to constantly apply a voltage or the like in order to maintain a state in which all the luminous flux was transmitted. Therefore, a large amount of power is consumed, and the transmission characteristics of the element in the non-display state are unstable because it depends on the alignment state of the liquid crystal.

It had problems that were undesirable as a display element.

<Summary of the invention> The object of the present invention is to solve the above-mentioned conventional problems.

The object of the present invention is to provide a light modulation element which can provide a stable non-display state and is suitable for use as a single display element.

In order to achieve the L-leg effect, the light modulation element according to the present invention is as follows:
An element comprising a phase type diffraction grating made of a predetermined material, a liquid crystal existing in the grooves of the diffraction grating, and a control means for changing the alignment state of the liquid crystal, the control means comprising an electrode provided on a side surface of the diffraction grating. It is characterized by having the following.

Further features of the present invention will become clear from the Examples shown below.

<Example> FIGS. 1(A) and 1(B) are schematic diagrams showing an example of the light modulation element according to the present invention, in which 1 is a transparent substrate, 2 is a transparent electrode, and 3
4 is a transparent insulating film, 4 is a liquid, 11□, 5 is a transparent insulator forming a diffraction grating, and 6 is a transparent protective film which also serves as an insulating film. 7 is a switch, 8 is a driving power source, 9 is incident light, 10 is zero-order diffracted light,
10' indicates higher-order diffraction light.

In FIG. 1(A), the switch 7 is in the OFF state ff4
In the state where no electric field is applied, Fig. 1 (B) shows that switch 7 is ON.
In this embodiment, it is assumed that a positive dielectric Nebchik liquid crystal is used as the liquid crystal 1.

The light modulation element in the wooden embodiment is formed by forming a transparent insulating film on one side of each of a pair of transparent plates 1,
NOSHI 1111 Mb 11 RI 31- NIZUKI 111 paid furlough 5
A rectangular diffraction grating made of
is provided, and the diffraction grating is transparently protected 1! The transparent substrate 1 covering the first diffraction grating and the other transparent substrate 1 are pasted together so that the transparent protective film 3 faces each other, and the liquid crystal 4 is placed in the gap.
It is composed of enclosed. Note that the transparent electrodes 2 of adjacent convex portions are connected to a drive power source 8 and a switch 7 via lead wires. Furthermore, the transparent insulating film 3 has been subjected to a vertical alignment treatment, so that the molecules of the liquid crystal 4 are vertically aligned, so-called homeotropic alignment.

The function of the single-wire optical modulation element will be described below.

In the state shown in FIG. 1(A), that is, in the state where the switch 7 is OFF and no voltage is applied between the transparent electrodes 2, the liquid crystal 4 is homeotropically aligned as described above, and the substrate 1
The long axis is oriented perpendicular to. At this time, the incident light 9 has the ordinary refractive index no of the liquid crystal 4 regardless of its polarization state.
If the film thickness of the transparent electrode 2 and the transparent protection n 6 is sufficiently smaller than the line width (width of the convex portion) of the diffraction grating, then the refractive index n of the transparent insulator 5 can be expressed as the ordinary refraction of the liquid crystal 4. By setting the ratio equal to no, the incident light 9 passes through the hydrogen atoms without being subjected to diffraction and is emitted as zero-order outgoing light IO.

On the other hand, the state shown in FIG. 1(B), that is, the switch 7 is ON.
When a predetermined voltage is applied between the transparent electrodes 2,
The long sleeves of the molecules of the liquid crystal 4 are aligned in the direction of the electric field, and are aligned in a direction parallel to the plane of the substrate l (homogeneous alignment) as shown.

At this time, among the polarized light components of the incident light 9, the polarized light components in the same direction as the alignment direction of the liquid crystal 4 sense the extraordinary refractive index ne of the liquid crystal 4.

Therefore, the difference in optical path length between the optical path length of this polarized component light when it passes through the liquid crystal 4 and the optical path length when it passes through the transparent insulator 5 is exactly 0/2 (where 0 is the wavelength of the incident light). LCD 4
By setting the extraordinary refractive index ne of the transparent insulator 5, the refractive index ng of the transparent insulator 5, and the height T of the diffraction grating, the incident light 9 does not become the zero-order output light 10, but all becomes the higher-order diffracted light 10'. Emits light. In addition, the diffraction angle (output angle) of the higher-order diffracted light 10'
depends on the wavelength and the pitch of the diffraction grating.

1! The diffraction efficiency η0 of the zero-order transmitted diffracted light (output light 10 in the figure) in a rectangular diffraction grating as shown in Figures 1 (A) and (B) is approximated by the following equation (1). Therefore, in order to set the diffraction efficiency η0 of light incident at a predetermined wavelength to η040, it is sufficient to satisfy the condition of equation (2).

Evening 1 ΔnT η0-T(1+cos(2π)) -1--(1) In Δn T = (m + 7) In (m=0.1, 2.--) --(2)
However, Δn=lne−ngl.

In FIG. 1(B), among the polarized light components of the incident light 9, the polarized light components polarized in the direction perpendicular to the alignment direction of the liquid crystal 4, that is, in the direction of the grooves of the diffraction grating, are affected by the electric field when the switch 7 is turned on. Even in the applied state, the ordinary refractive index no of the liquid crystal 4 is felt. Therefore,
This polarization component of the incident light 9 cannot be modulated by the light modulation element in this embodiment. Therefore, in order to modulate incident light with arbitrary polarization characteristics, it is sufficient to use two elements as shown in FIG. Each element can independently modulate mutually orthogonal polarization components.

As explained above, the light modulation element according to this embodiment is in the "bright" state, that is, in the fully transparent state when no electric field is applied.
When an electric field is applied, a "dark" modulation state (display state) can be obtained immediately, so there is no current consumption in the normal state (bright state), and there is freedom in designing the drive circuit used to drive the element. The frequency also increases.

Furthermore, the electrolytic corrosion rate of the transparent electrode is also increased to R, and the reliability of the device is significantly improved. Therefore, display elements and color filters
The scope of application of single optical modulation elements such as optical switches and the like is greatly expanding.

Furthermore, although it generates heat, it has excellent luminous flux utilization efficiency because it does not use polarizing plates or light-absorbing substances (such as dyes) unlike conventional display elements using liquid crystals.

As can be seen from FIG. 1, the diffraction grating constituting the optical modulation element according to the invention is a so-called phase-type diffraction grating consisting of a relief pattern of unevenness. Various methods include a method combining graphie and dry etching, a replica method using a thermosetting resin or an ultraviolet curable resin, a cutting method using a ruling engine, or an embossing method.

Further, although this embodiment shows an element having a rectangular diffraction grating, light modulation is possible regardless of the shape. For example, diffraction gratings of various shapes such as triangular wave, sinusoidal, and asymmetric shapes can be used, and the separation angle between the diffracted lights depends on the pitch of the diffraction grating and the wavelength of the incident light. The spectral transmittance characteristics mainly depend on the shape (waveform profile) and height T of the diffraction grating, and the refractive index difference Δn. In other words, the above equation (1), which expresses the diffraction efficiency η0 of the zero-order transmitted diffraction light in a rectangular diffraction grating, cannot be applied to the diffraction efficiency in a triangular or sinusoidal diffraction grating, and the design In this case, a formula corresponding to each diffraction grating shape is used.

Furthermore, although this embodiment shows a so-called transmission type light modulation element, it is also possible to use it as a reflection type light modulation element. In this case, one of the pair of transparent electrodes 3 in FIG. Do you give it?
A reflective film may be formed on the entire surface of the uneven relief pattern forming the diffraction grating.

Furthermore, in the device shown in FIG.
! It is also formed at the interface with +1!23.

It is not necessarily necessary to form the transparent electrode 2 at this interface, and it is sufficient if a transverse electric field (an electric field parallel to the surface of the substrate 1) can be applied to the so-called correct reading nematic liquid crystal as in the device shown in FIG. Therefore, it is sufficient that it is formed on the side wall of the transparent insulator that normally forms the five-diffraction grating. Furthermore, the means for controlling the alignment state of liquid crystals is not limited to electric fields;
Although it is possible to use a control means that generates heat, a magnetic field, etc., control using an electric field is most preferable in view of the element configuration, simplicity of the control method, response characteristics, etc.

<Effects of the Invention> As described above, the uninvented light modulation element is an element suitable for display elements, color filters, etc., which can obtain a fully transparent state in a static state and can stabilize a non-display state. be.

[Brief explanation of drawings]

FIGS. 1(A) and 1(B) are schematic diagrams showing one embodiment of the light modulation element according to the present invention, with FIG. 1(A) showing a static state and FIG. 1(B) showing a driving state. . 1--------- =-m-transparent substrate 2-------1-transparent electrode 3--1 transparent insulation 4------1-- --Liquid crystal 5-----Transparent insulator (diffraction grating) 6--
---1--------Transparent protective film 7------------Switch 8--1---------Drive power supply 9------1--Infrared light

Claims (3)

[Claims] (1) An element comprising a diffraction grating made of a predetermined member, a liquid crystal existing in the grooves of the diffraction grating, and a control means for changing the alignment state of the liquid crystal, the control means being provided on a side surface of the diffraction grating. A light modulation element with electrodes. (2) The light modulation element according to claim (1), wherein the liquid crystal is a nematic liquid crystal having positive dielectricity. (3) The control means is means for applying an electric field,
The light modulation element according to claim 2, further comprising an electrode on a side surface of a convex portion of the diffraction grating.