JPS62237423A - Light modulating element - Google Patents

Abstract

PURPOSE:To prevent the generation of abnormal polarized light and to improve contrast by sticking substrates of plural elements having diffraction gratings and refractive index variable materials to each other. CONSTITUTION:The transparent substrates 3, 3' consist of glass plates having 0.3mm thickness and ITO electrodes having 400Angstrom film thickness are patterned on the opposed surfaces of the respective transparent substrates 3, 3'. The diffraction gratings 2 are formed by contact-exposing and using resist agent after forming the ITO electrodes on the transparent substrate 3'. A positive dielectric nematic liquid crystal is packed between the transparent substrates 3 and 3' and the transparent substrate 3' sides of the two elements are stuck to each other by using an optical adhesive agent 4 in a manner as to avoid the intrusion of foam. The contrast ratio is thereby made 1:10 and the element exhibits substantial performance even when used for a display element, etc.

Description

Detailed Description of the Invention [Technical Field] The present invention combines a light modulation element, particularly a diffraction grating, and a refractive index variable material to control the refractive index of the refractive index variable material, thereby imparting desired diffraction to incident light. The present invention relates to a light modulation element that causes a phenomenon.

<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. This 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 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 as well, when the color is erased, The transmittance was about 70% at best.

On the other hand, Japanese Patent Publication No. 53-3928 and USP 4.251
．． No. 137 and the like disclose display elements and color filter elements in which a reflection type or transmission type 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 a single character or image. 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 refractive index, the spectral transmittance characteristics can be varied by changing the refractive index difference between the material that makes up the diffraction grating and the liquid crystal, and it has excellent luminous flux utilization efficiency and is a high-performance variable color filter. has.

However, in the device configuration shown here, there is a large disturbance in the alignment state of liquid crystal molecules near the interface between opposing diffraction gratings, so that the light beam that has passed through one of the diffraction gratings has no polarization direction. It has the disadvantage that it is irregularly changed or diffused, which prevents good diffraction effect, that is, light modulation. Furthermore, it is extremely difficult to control the alignment of the liquid crystal at the above-mentioned interface, and the yield rate is particularly poor during mass production.

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

It is possible to provide a light modulation element that can be manufactured at a high yield and at low cost even when mass-produced, has excellent luminous flux utilization efficiency, and can produce a good diffraction effect.

In order to achieve the above object, the light modulation element according to the present invention includes:
a pair of transparent substrates, a diffraction grating on at least one opposing surface of the pair of transparent substrates, a refractive index variable material disposed between the pair of transparent substrates, and means for controlling the refractive index of the refractive index variable material; It is characterized in that it has two elements having the same structure, and the two elements are bonded to each other through transparent substrates so that the arrangement directions of the diffraction gratings of the two elements are substantially perpendicular to each other.

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

The variable refractive index material may include, for example, liquid crystal, PL
ZT, LiNbO3, LiTaO3゜TiO2, PMM
A, CCl4. KDP, ADP, ZnO, BaTiO3
, B112Si020°Ba2NaNb5015. Mn
B1, EuO.

C52, Gd2 (MOO4)3. Bi4Ti3O1
2, CuC1, CaAs, ZnTe, As2Se3
, Se, AsGe5eS, DKDP.

Examples include MNA, mNA, UREA, photoresist, and the like. In particular, liquid crystals such as positive and negative nematic liquid crystals and ferroelectric liquid crystals are suitable because they are inexpensive, have a large refractive index difference Δn (difference between extraordinary refractive index and ordinary refractive index), and are easy to control. Further, the method for creating the grating includes a method combining photolithography and dry etching,
Various methods include 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.

Further, in the present invention, the shape of the diffraction grating is not limited, and in addition to the rectangular diffraction grating shown in the embodiments described later, diffraction gratings having a triangular wave shape, a sine wave shape, an asymmetric shape, etc. are applicable.

<Example> FIG. 1 is a functional principle diagram of a light modulation element according to the present invention,
1 is a refractive index variable material, 2 is a diffraction grating made of a transparent material, and has a rectangular relief structure with a height T and a pitch Δ.

Further, 5 indicates the incident light, and 6 and 6' indicate mutually orthogonal polarization components of the incident light 5. Here, the refractive index of the variable diffraction index material 1 is changed by a control means (not shown) such as an electrode or a heater. Therefore, the refractive index difference Δn between the refractive index of the variable refractive index material 1 and the refractive index of the material forming the diffraction grating 2 becomes variable, and the diffraction effect on the incident light 5 can be controlled.

That is, assuming that the wavelength of the incident light 5 is input, the diffraction efficiency η0 of zero-order transmitted diffracted light by a rectangular diffraction grating as shown in FIG. 1 can be approximately expressed by the following equation (1).

η0=-L (1+COS (2π thousand)...(1)
For example, when the shape of the diffraction grating in FIG. 1 is a triangular wave shape and a sine wave shape, the diffraction efficiency η0 of the zero-order transmitted diffracted light is approximately as shown in (2) below.

It can be expressed by equation (3).

'70 = J O2 (πLXLK) ' -----
--(3) Input As can be seen from equations (1) to (3) above, by controlling the refractive index difference Δn, the transmittance, that is, the intensity, of the zero-order transmitted diffraction light can be varied, and the zero-order transmitted diffraction light and other higher-order diffracted light 1
For example, diffracted light of ±1st order, ±2nd order, etc. can be controlled using the same principle.

More specifically, unless the incident light 5 is a laser beam or enters the diffraction grating 2 via a polarizing plate, etc.
Normally the incident light 5 has various polarization components. for example,
Assuming that a positive magnetic liquid crystal or the like is used as the refractive index variable material 1, and that the liquid crystal 1 is oriented in the initial state in the direction of the grooves of the diffraction grating 2 in FIG.

That is, the polarized light component 6 of the incident light 5 perpendicular to the long direction of the liquid crystal molecules senses the ordinary refractive index no of the liquid crystal 1.

In addition, the polarized light component 6' in the direction that coincides with the long sleeve direction of the liquid crystal molecules
feels the extraordinary refractive index n9 of the liquid crystal 1.

Therefore, in relation to the refractive index ng of the substance forming the diffraction grating, the alignment of the liquid crystal 1 is perpendicular to the alignment plane of the diffraction grating 2 using, for example, an electric field.

Even when changing the apparent refractive index, the polarization component 6 of the incident light 5
Since the normal diffraction index n□ is always felt, Δn in the above equation (1) does not change and cannot be substantially modulated. On the other hand, the polarized light component 6' of the incident light 5 experiences a refractive index ranging from the extraordinary refractive index ne to the ordinary refractive index n□, and the diffraction efficiency η0 becomes variable as Δn in equation (1) changes. That is, if the incident light 5 has completely random polarization characteristics.

Light modulation is possible only for 50% of the light, and the other 50% of the light does not undergo any modulation. In order to solve this problem and increase the light utilization efficiency, it is disclosed in US Pat. No. 4.251,137.

The refractive index can be controlled by using a pair of diffraction gratings 2 and arranging them to face each other so that the alignment directions of the gratings intersect with each other, and disposing a refractive index variable material such as liquid crystal between the diffraction gratings. Preferably, the pair of diffraction gratings are orthogonally arranged, and in principle, a light utilization efficiency of 100% can be obtained.

However, this configuration has the drawbacks as described in the <Prior Art> section and causes a reduction in contrast.

FIG. 2 is a diagram showing an example of the basic configuration of the light modulation element according to the present invention, where l is a liquid crystal, 2 is a diffraction grating whose arrangement directions are orthogonal to each other, 3 and 3' are transparent substrates, and each diffraction grating 2 is It is formed on the transparent substrate 3' side. Also, 4 is two transparent substrates 3
This is the adhesive used to bond the . Here, to explain each member in more detail, the transparent substrate 3.3' has a plate thickness of 0.3
ITO electrodes (not shown) having a thickness of 400 mm are patterned on opposing surfaces of each transparent substrate 3.times.3'. or.

The diffraction grating 2 was formed using a resist agent by contact exposure after forming an ITO electrode on a transparent substrate 3'. Further, a positive dielectric nematic liquid crystal manufactured by Roche is filled between the transparent substrates 3 and 3'.

The two elements having the above structure on the transparent substrate 3' side are bonded together using a well-known optical adhesive 4.

1565 manufactured by Gain Co., Ltd. is used to bond the pieces together to prevent air bubbles from being mixed in.

When white light was incident on the light modulation element shown in FIG. 2 as described above and the diffraction index of the zero-order transmitted diffracted light was measured, the transmittance in the decolorized state, that is, in the completely transmitted state, was 85%, and the contrast ratio The ratio was 1:10, and it was confirmed that sufficient performance was exhibited even when used in display elements, etc.

In the above description, liquid crystal is used as the refractive index variable material, but it goes without saying that the present invention is applicable to other refractive index variable materials. However, liquid crystals, particularly nematic liquid crystals, can be said to be suitable materials for the present invention because they are easily available, easy to control, and whose orientation can be controlled using a diffraction grating. Further, it is preferable to use an electric field control method as a control method in view of response characteristics and ease of driving as a display element.

Further, the variable refractive index material is preferably one having a large refractive index difference between the extraordinary refractive index r19 and the ordinary refractive index n□, which increases the degree of freedom in element configuration and modulation function. Therefore, in this sense as well, liquid crystal is a preferable substance, and preferably a substance with a refractive index difference (ne - no) of 0.2 or more.

In addition, in the light modulation element shown in Fig. 2, the thickness of the substrates 3' on the side to be bonded together is generally the thinner one, especially 0.3 mm or less, considering the image shift that occurs between the upper and lower elements. is desirable. Further, it is preferable that the refractive index of an intermediate member such as the adhesive 4 used for bonding is equal to that of the substrate 3'.

Furthermore, the upper part of the first diffraction grating 2 and the facing surface of the substrate 3 are in close contact with each other, which is desirable in order to prevent the alignment state of the liquid crystal from being disturbed.

Although the above description shows a transparent light modulation element, it is also possible to form a reflective element by applying a light reflecting film or the like to one of the substrates, for example.

However, in the case of a reflective 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 transmissive type light modulation element in the present invention. 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> As described above, the light modulation element according to the present invention can be constructed by simply bonding the substrates of a plurality of elements each having one diffraction grating and a variable refractive index material, and can be manufactured at low cost.

In addition, by bonding the substrates forming the diffraction grating, there is no system between the two mutually orthogonal diffraction gratings that disturbs the polarization characteristics of the incident light, such as disturbances in the liquid crystal, and abnormal polarization can occur. can be prevented and the contrast can be improved. Furthermore, it is possible to produce a good diffraction effect while maintaining high luminous flux utilization efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the modulation principle of the light modulation element according to the present invention. FIG. 2 is a diagram showing an example of the basic configuration of a light modulation element according to the present invention. 1----------one refractive index variable material, 2---------- one diffraction grating, 3, 3'---- one transparent substrate. 4---------Adhesive. 5----------One person's light. 66'-----Polarized light components orthogonal to each other. A-11 ~--- Pitch of diffraction grating. T-----Height of diffraction grating

Claims (6)

[Claims] (1) A pair of substrates, a diffraction grating existing on at least one opposing surface of the pair of substrates, a refractive index variable material disposed between the pair of substrates, and means for controlling the refractive index of the refractive index variable material. 1. A light modulation element having two elements having the above, and the substrates of the two elements are bonded together so that the arrangement directions of the diffraction gratings of the two elements are substantially orthogonal. (2) The light modulation element according to claim (1), wherein the substrates of the two elements are the substrates on the side where the diffraction gratings of the respective elements exist. (3) The light modulation element according to claim (1), wherein the substrate and the variable refractive index medium are transparent to the wavelength used. (4) Among the substrates, the thickness of the substrate to be bonded is 0.
．． The light modulation element according to claim (1), which is 3 mm or less. (5) The light modulation element according to claim (1), wherein the refractive index of the adhesive for bonding the substrates is made substantially equal to the refractive index of the substrates to be bonded. (6) The light modulation element according to claim (1), wherein the refractive index variable material is a liquid crystal.