JPS62237427A - Light modulating element - Google Patents

Abstract

PURPOSE:To eliminate the need for a stage for forming an insulating film and to improve the adhesiveness to substrates by constituting a diffraction grating of a relief pattern of ruggedness and forming the recesses of the relief pattern of the same member as the member for the adjacent projecting parts so that the patterns are made continuous. CONSTITUTION:This light modulating element is so formed that the insulating film 3 does not exist on the substrate side having the diffraction grating 8. More specifically, the light modulating element is formed with transparent electrodes 2 on the opposed surfaces of a pair of the substrates 1 and is further formed with the diffraction grating 8 on one of the transparent electrodes 2. Said diffraction grating 8 consists of a prescribed optical member having an insulating characteristic and the relief patterns to constitute the diffraction grating 8 are formed continuously to cover the entire surface of the transparent electrode 2. One of the stages for forming the element is thereby omitted and since the adhesiveness of the diffraction grating to the substrate is high, the light modulating element having excellent durability and reliability is obtd.

Description

Detailed Description of the Invention [Technical Field] The present invention provides desired diffraction to incident light by controlling the refractive index of the variable refractive index material by combining a light modulation element, particularly a diffraction grating, and a variable refractive index material. The present invention relates to a light modulation element that causes development.

<Prior art> A conventionally well-known light modulation element consists of a pair of polarizing plates arranged so that the polarization directions are perpendicular to each other, and a pair of transparent substrates arranged between the pair of polarizing plates. It consists of an element in which a liquid crystal is sealed with its planes aligned perpendicularly to each other, and the alignment state of this liquid crystal is switched between a twisted state and a state perpendicular to the substrate surface to modulate incident light. There is a so-called TN (twisted nematic) type liquid crystal display element. This type of display element has a simple structure and is easy to drive, so it is used in a wide variety of ways.
Since two polarizing plates are used to transmit and block the light flux, the transmittance during decolorization, that is, the time when light is transmitted, is poor, and it cannot be said to be a desirable light modulation element from the viewpoint of luminous flux utilization efficiency.

In addition, as a similar type of display element that uses liquid crystal, there is a so-called guest-host mode liquid crystal display element that uses a dye mixed into the liquid crystal molecules, but since the dye is present in this display element as well, there is a problem when the color is erased. The transmittance was about 75% at best.

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 publications certainly have excellent luminous flux utilization efficiency, but the element disclosed in Japanese Patent Publication No. 53-3928 merely exhibits a decorative effect.
This has not been satisfactory as a display element for displaying characters or images, or a light modulation element for transmitting or blocking light beams.

In addition, the color filter element disclosed in USP 4.251.137 has a diffraction grating formed on the surfaces of a pair of opposing substrates so that the alignment directions are perpendicular to each other, and liquid crystal is filled between the substrates to align the liquid crystal molecules. By controlling the state, the refractive index is changed, and the difference in refractive index between the material forming one diffraction grating and the liquid crystal is changed, thereby making the spectral transmittance variable.

An example of the configuration of this type of light modulation element is shown in FIG.

1 is a substrate, 2 is a transparent electrode, 3 is an insulating film, 4 is a diffraction grating,
5 is a liquid crystal.

A glass plate is generally used as the substrate 1, on which a transparent electrode 2 is formed. The insulating film 3 is formed on the transparent electrode 2 by printing, spinner vapor deposition, etc., and the diffraction grating 4 is formed on the insulating film 3 by methods such as photolithography, etching, lift-off, replica, embossing, etc. Further, the liquid crystal 5 is filled between the pair of substrates 1.

Next, the principle of this light modulation element will be explained.

6 is a polarized component of the incident light in the same direction as the grooves of the diffraction grating 4;
7 is the emitted light. Note that the liquid crystal 5, which is a variable refractive index material,
The refractive index of is controlled by an electric field. Under static conditions with no electric field applied, the polarization component 6 of the incident light is
By sensing the homogeneous alignment, that is, the extraordinary refractive index ne of the liquid crystal 5 aligned in the groove direction of the diffraction grating 4, and applying an electric field, the homeotropic alignment, that is, the substrate 1
The ordinary refractive index n□ of the liquid crystal 5 aligned perpendicular to is felt. Here, the difference between the refractive index ng of the first diffraction grating 4 and the refractive index of the liquid crystal is Δ
If n is the wavelength of the incident light, and the height of the diffraction grating is T, then the diffraction index η0 of the zero-order transmitted diffracted light in the diffraction grating can be approximately expressed by the following equation (1).

That is, by controlling Δn using an electric field, the incident light becomes (1
) is modulated by the equation. However, equation (1) is an approximate equation that is effective only for a rectangular diffraction grating as shown in FIG.

When modulating light by controlling the refractive index of a variable refractive index material such as the liquid crystal 5 using energy such as an electric field as described above, to prevent conduction between the upper and lower substrates 1 and electrolytic corrosion of the transparent electrode 2, etc. In addition, as shown in FIG. 1, in the conventional element, it was necessary to form a protective film on the transparent electrode 2 at the interface with the insulating film 3 made of polyimide, Si02, etc. and the liquid crystal 5.

In addition, in conventional elements of this type, the relief pattern forming the diffraction grating 4 has convex portions made of the same material formed discontinuously at a predetermined pitch, and generally the adhesion between the upper and lower substrates is weak, so the element It lacked credibility.

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

In addition to being able to omit the insulating film formation process during device fabrication,
An object of the present invention is to provide a light modulation element having a diffraction grating that has high adhesion to a substrate.

In order to achieve the above object, the light modulation element according to the present invention includes:
A pair of substrates, a diffraction grating formed on at least one of opposing surfaces of the pair of substrates, a refractive index variable material existing between the opposing surfaces of the pair of substrates, and means for controlling the refractive index of the refractive index variable material. The element is characterized in that the diffraction grating consists of an uneven relief pattern, the concave portions of the relief pattern are formed of the same material as the adjacent convex portions, and the pattern is continuous.

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

Incidentally, the refractive index variable material is, for example, 5.

Liquid crystal, PLZT, LiNbO3, LiTaO3.

TiO2, PMMA, CC1a, KDP, ADP, Zn
O, BaTiO3, B112Si02p.

B a 2 N a N b' 5015, M n
B i , E u O.

CS2, Gd2 (MOO4)3, BaTiO01
2, CuC1, CaAs, ZnTe, As2Se3,
Se, AsGe5eS, DKDP.

Examples include MNA, mNA, UREA, and 7 otoresist. In particular, liquid crystals such as positive and negative neptic liquid crystals and ferroelectric liquid crystals have a large refractive index difference Δn (difference between extraordinary refractive index and ordinary refractive index) at low prices.

This is suitable because the control method is simple. or.

The method for producing the grating includes a method combining photolithography and dry etching, a replica method using a thermosetting resin or an ultraviolet curable resin, etc.
Various methods such as a cutting method using a ruling engine or an embossing method may be used.

Furthermore, in the present invention, there is no limitation to the shape of the diffraction grating, and in addition to the rectangular diffraction grating shown in the examples described later, diffraction gratings of various shapes such as triangular wave, sine wave, and asymmetric shapes are applicable. .

<Example> Fig. 7J42 is a schematic configuration diagram showing an example of a light modulation element according to the present invention, and the same members as in Fig. 1 are denoted by the same reference numerals. In FIG. 1, numeral 8 indicates a diffraction grating consisting of a continuous relief pattern.

The main difference between the optical modulation element of this embodiment and the optical modulation element shown in FIG. 1 is that the insulation II! shown in FIG. 3 does not exist. As shown in FIG. 2, this optical modulation element has transparent electrodes 2 formed on opposing surfaces of a pair of substrates 1.

Furthermore, a diffraction grating 8 is formed on one of the transparent electrodes 2, and this diffraction grating 8 is made of a predetermined optical member having insulating properties, and the relief pattern constituting one diffraction grating 8 is formed continuously. Covers all aspects of 2.

Here, as described above, there are various methods for forming the diffraction grating 8 of the light modulation element shown in FIG.
This will be explained using B) and (C).

Figures 3 (A), (B), and (C) are diagrams showing an example of the method of forming the diffraction grating of the present optical modulation element. In the figures, the same members as in Figure 2 are designated by the same numbers. 9 is photoresist, 10 is
indicates an exposure mask.

First, as shown in FIG. 2(A), a photoresist 9 is applied to a substrate 1 to a thickness of about fifiLm by spin cord, roll coating, dipping, or the like. Next, as shown in FIG. 3(B), by exposing and developing through a mask 10 having a diffraction grating pattern, as shown in FIG. 3(C).
A diffraction grating 8 as shown in is obtained. At this time, the diffraction grating shape according to the present invention can be obtained by adjusting the exposure conditions, development conditions, etc., and leaving resist residue in the concave portions between the convex portions of the first diffraction grating 8.

In addition, an oxide insulating film is deposited on the substrate by vapor deposition, sputtering, CV
A diffraction grating shape as described above can also be obtained by forming a film to a thickness of about several gm by a method such as D, and then adjusting the dry etching conditions.

In addition, the thickness of the recess is preferably 500 to 5000 mm, considering the occurrence of pinholes and the effective voltage.
Furthermore, it is preferable to have a zero thickness of about 2000, taking into consideration the aspects of manufacturing the element structure 1.

With the above-mentioned diffraction grating shape, the step of forming an insulating film on a substrate having at least one diffraction grating structure is omitted, and the manufacturing process is simplified. Also.

This is because the area where the diffraction grating separates from the substrate increases.

It is possible to prevent the diffraction grating from peeling off or being damaged during liquid crystal filling, that is, during vacuum injection.

That is, the adhesion between the first diffraction grating and the substrate is greatly improved, and the durability and stability of the element can be increased.

Further, although the above embodiment shows an element having a diffraction grating on only one side, the present invention can of course be applied to a case where a diffraction grating is formed on both opposing surfaces of the substrate.

In this embodiment, a transmission type light modulation element is shown, but it is also possible to form a reflection type element by applying a light reflection film to one of the substrates, for example.

However, in the case of a 1-reflection type, the behavior of diffracted light within the element becomes complicated, so in consideration of the design and application of actual display elements, it is preferable to use a transmission type light modulation element in the present invention. desirable.

In this case, as a matter of course, the diffraction grating, the refractive index variable material, the substrate, etc. are made of members that are transparent to the wavelength used.

<Effects of the Invention> The light modulation device according to the present invention can omit one step of device fabrication, and the adhesion of the diffraction grating to the substrate is high, making it a highly durable and reliable light modulation device. It has become.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional light modulation element having a diffraction grating. FIG. 2 is a schematic configuration diagram showing an example of a light modulation element according to the present invention. FIGS. 3A, 3B, and 3C are diagrams showing a manufacturing method for obtaining the diffraction grating and structure of the present invention. 1---------One board

Claims (5)

[Claims] (1) A pair of substrates, a diffraction grating formed on at least one of opposing surfaces of the pair of substrates, a refractive index variable material existing between the opposing surfaces of the pair of substrates, and controlling the refractive index of the refractive index variable material. said diffraction grating is comprised of an uneven relief pattern, said relief pattern depressions are formed of the same material as adjacent projections, and the pattern is continuous. (2) The light modulation element according to claim (1), wherein the refractive index variable material is a liquid crystal. (3) The thickness T_0 of the recess is 500 Å≦T_0≦50
00 Å. (4) The light modulation element according to claim (1), wherein the substrate and the variable refractive index material are transparent to the wavelength used. (5) The light modulation element according to claim (2), wherein the orientation direction of the liquid crystal is changed by an electric field.