JPS62235925A - Optical modulation element - Google Patents

Abstract

PURPOSE:To attain full transmission state independently of the wavelength of light beams to be used by setting up a prescribed composite refractive index of a refractive index variable substance almost equally to the refractive index of a substance forming a diffraction grating. CONSTITUTION:Transparent electrodes 3, 3' are formed on respective opposed surfaces of two transparent bases 3, 3' and diffraction grating 2, 2' consisting of a transparent substance are formed on respective one surfaces of the electrodes 3, 3' so that respective array directions intersect with each other at right angles. The grooves parts of the gratings 2, 2' are filled with the refractive index variable substance 1 such as liquid crystal. The prescribed composite refractive index between the maximum refractive index and the minimum refractive index of the substance 1 is made almost equal to the refractive index of the substance forming the gratings 2, 2' over the whole wavelength area of incident light. Consequently, full transmission state can be obtained independently of the wave-length of the used light beams and multiplex driving with high contrast can be attained.

Description

Detailed Description of the Invention [Technical Field] The present invention provides a method for producing a desired diffraction phenomenon in incident light by controlling the refractive index of the variable refractive index material by combining a light modulating element, particularly a diffraction grating, and a variable refractive index material. The present invention relates to a light modulation element that generates.

<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 encapsulated with an orientation treatment perpendicular to the surface of the substrate, and the orientation state of this liquid crystal is switched between a twisted state and a state perpendicular to the substrate surface to modulate the 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 applications.
Since two polarizing plates are used to transmit and block the luminous flux, the transmittance is poor during decolorization, that is, when the light is transmitted, but is the light change favorable from the viewpoint of luminous flux utilization efficiency? I couldn't say it was JR Motoko.

In addition, as a similar type of display element using liquid crystal, there is a so-called guest-host mode liquid crystal display element that uses a dye mixed into 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 a display element and a variable subtractive color filter element 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 was not satisfactory as an optical modulation element for passing or blocking light beams. In addition, the variable subtractive color filter element disclosed in US Pat. Oriented! It has functions such as changing the refractive index by controlling 8 and changing the refractive index difference between the substance forming the diffraction grating and the liquid crystal, making the spectral transmittance characteristics variable.It has excellent luminous flux utilization efficiency and It has high performance as a variable color filter. However, this variable color reduction filter mainly uses the three desired primary colors R and G.
, B, or their complementary colors C1M, Y, etc., are transmitted and displayed. For example, when decoloring, that is, when completely transmitting the incident light, the wavelength dependence of the refractive index of the liquid crystal and the wave of the material forming the diffraction grating are Since scratch dependence was not taken into consideration at all, it was impossible to achieve color erasure, that is, a completely transparent state, which caused a decrease in contrast.

In addition, in an element configuration consisting of a combination of this type of diffraction grating and a variable refractive index material, when controlling the refractive index of the variable refractive index material, there is no clear threshold value for changing the refractive index, and the refractive index varies greatly. Because of the slow rate of change, it is difficult to completely transmit the incident light and erase the color, and multiplex driving cannot be performed when a display device is constructed using a plurality of elements of this type.

<Summary of the Invention> In view of the above-mentioned drawbacks of the conventional art, an object of the present invention is to provide an optical modulation device that enables total transmission of the used luminous flux, has high contrast when used as a display element, and enables multiplex driving. The purpose is to provide devices.

In order to achieve the above object, the light modulation element according to the present invention includes:
a plurality of transparent substrates, a diffraction grating existing on at least one opposing surface of an adjacent transparent substrate, a refractive index variable material disposed between the plurality of transparent substrates, and means for controlling the refractive index of the refractive index variable material; where nθ is a predetermined refractive index existing between the maximum refractive index nmax and the minimum refractive index nm1n of the variable refractive index material, and ng is the refractive index of the material forming the diffraction grating, It is characterized in that the refractive index no and the refractive index ng are approximately equal in the entire wavelength range of incident light.

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

In addition, as the refractive index variable substance, for example, liquid crystal, P
L Z T , L i N b O3, L i T
a O3.

TiO2, PMMA, CCl4. KDP, ADP, Zn
O, BaTiO2, B112Si020゜Ba2NaN
b5015. MnB1, EuO.

C32, Gd2 (MOO4) 3. Bi4Ti3O12
, CuC1, CaAs, ZnTe, As2Se3. Se
, AsGe5eS, DKDP.

Examples include MNA, mNA, UREA, and 7 otoresist. 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 Δn (the difference between the extraordinary refractive index and the ordinary refractive index), and are easy to control. In addition, the method for producing the grating includes various methods such as a method combining photolithography 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, etc. can be mentioned.

<Example> FIG. 1 shows a basic configuration diagram of a light modulation element according to the present invention,
In Figure 0, which also serves as a functional explanatory diagram of this light modulation element, l is a variable refractive index material represented by liquid crystal, 2 is a diffraction grating made of a material that is transparent to the wavelength used, 3 is a transparent electrode, and 4 is a A transparent substrate made of a transparent optical member, 5 is incident light having arbitrary polarization characteristics, 6 and 6' are mutually orthogonal polarization components of the incident light 5, 6 is a direction perpendicular to the plane of the paper, and 6' is a direction parallel to the plane of the paper. It shows.

This light modulation element has transparent electrodes 3 formed on opposing surfaces of a pair of transparent substrates 4, and a rectangular diffraction grating 2 made of a transparent material on one transparent pole 3 of the pair of transparent substrates 4. A refractive index variable material 1 is disposed in the groove (recess) of the diffraction grating 2, and its refractive index is made variable by applying an electric field through the transparent electrode 3.

Hereinafter, the modulation principle of the present optical modulation element will be explained using FIG. 1, but for ease of explanation, the refractive index variable object If! Hereinafter, il will be referred to as liquid crystal 1, and a predetermined diffraction effect will be produced by controlling the alignment state of liquid crystal 1 by applying an electric field.

As shown in FIG. 1, in a static state where no electric field is applied, the liquid crystal 1 is oriented in the direction of the grooves of the diffraction grating 2, that is, in the direction perpendicular to the plane of the paper, and maintains a homogeneous orientation state. Therefore, among the polarized light components 6.6' of the incident light 5 that enters the optical modulator in this static state, the polarized light component 6', which is a component orthogonal to the alignment direction of the liquid crystal 1, has the ordinary refractive index no. The polarized light component 6, which is a component parallel to the alignment direction of the liquid crystal I, senses the extraordinary refractive index ne of the liquid crystal I. Here, if the refractive index of the material forming the diffraction grating 2 is ng, the wavelength of the incident light 5 is input, and the thickness of the diffraction grating 2 is T, then in the case of a rectangular diffraction grating, the polarization component 6 of the incident light 5 The diffraction efficiency η0 of the zero-order transmitted diffracted light for each of .6′ can be approximately expressed by the following equation (1).

ηO~7 (1+t;, 65 (2wxQyu))・
, (1) ~ 1 However, Δn indicates the refractive index difference between the refraction −Kng of the diffraction grating 2 and the refractive index ne or no of the liquid crystal 1, and for the polarization component 6 of the incident light 5, Δn= I ne-ng I
, for the polarization component 6', Δn=lng-nol.

Therefore, from equation (1), Δn=o, that is, ne-ng or no
= r1g, the diffraction efficiency η0 of the zero-order transmitted diffracted light is ηQ=
1, and when ΔnT= (m=0.1.2.3.---), the diffraction efficiency η0 becomes η0=Q.

Next, when an electric field is applied to the liquid crystal l through the transparent electrode 3, the alignment direction (optical axis direction) of the liquid crystal l gradually changes, and the polarization component 6' of the incident light 5 is independent of the applied electric field. Normal refractive index n of liquid crystal l.

The polarized light component 6 senses a composite refractive index no, which is a combination of the extraordinary refractive index ne and the ordinary refractive index no of the liquid crystal 1 at a predetermined ratio, according to the amount of applied electric field.

Needless to say, the composite refractive index nQ changes as the alignment direction of the liquid crystal l changes. If the applied electric field is further strengthened,
The liquid crystal 1 is aligned perpendicularly to the substrate 4 (transparent electrode 3), and in order to be in a homeotropic alignment state, the polarized light component 6 of the incident light 5 is
, 6' both sense the ordinary refractive index no of the liquid crystal and become saturated.

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

FIG. 2 shows a light modulation element having the basic configuration as shown in FIG. 1, in which liquid crystal l is aligned by a diffraction grating 2.
FIG. 3 is a diagram showing the voltage dependence of the diffraction efficiency ηO expressed by the above equation (1) in the case of ng=n. However, when ng=no, the polarized light component 6' of the incident light 5 does not depend on the electric field and always feels the ordinary refractive index no of the liquid crystal l, so it is always in a completely transparent state, as shown in Figure 2. The diffraction efficiency ηO is the incident light 5
This is for polarization component 6 of . The graph in Figure 2 shows the refractive index control voltage (■) on the horizontal axis and the diffraction efficiency (ηO) on the vertical axis.
), and γ1 and γ2 represent the main slopes of the V-10 curve.

As can be seen from FIG. 2, the slope formed by the V-10 curve has two or more slope components 1. γ2, the curve changes slowly, and the V-10 curve does not have the slope required for normal multiplex driving, making it difficult to use this driving method. Furthermore, it is not easy to make the polarized light component 6 completely transparent at low voltage.

Furthermore, as can be seen from equation (1) above, the diffraction efficiency η0 is determined by the refractive index ng of the material forming the diffraction grating 2 and the refraction in the liquid crystal 1 (7).
refractive index difference Δn with e, no, (no) and refractive index n
It is greatly influenced by the wavelength dispersion characteristics of g, no, ne, and (no). Therefore, it is not possible to obtain a completely transparent state especially with an element configuration having poor wavelength dispersion characteristics.

However, in the light modulation element according to the present invention, in the configuration as shown in FIG. Second, the refractive index nθ (no<no=ng) of the liquid crystal 1 and the refractive index ng of the substance forming the diffraction grating 2 are made to match. By configuring the element in this way, it is possible to prevent the decrease in transmittance caused by the wavelength dispersion characteristics of the refractive index of each element that makes up the element (diffraction grating and variable refractive index material), and to achieve a completely transparent state. along with the second
By making the slope of the -η0 curve as shown in the figure steep, multiplex driving is essentially possible. That is, liquid crystal 1
A predetermined composite refractive index nO existing between the extraordinary refractive index ne and the ordinary refractive index no is explained using the configuration of FIG. 1 as follows.
This is the state before the liquid crystal 1 is completely aligned perpendicular to the substrate 4 due to the application of an electric field, and is the refractive index when the liquid crystal molecules are oriented at a predetermined angle. Therefore, this state I
The refractive index nQ at E and the refractive index ng of the material forming the diffraction grating 2
If they are made equal, it is possible to match the refractive index of the liquid crystal 1 and the diffraction grating 2 by applying a low electric field, and it is possible to obtain a completely transparent state with a low voltage, and the slope of the -η0 curve is also steep. become.

Hereinafter, a specific example of the configuration of the present optical modulation element will be described and explained.
Using a pair of regular glass substrates.

A transparent electrode such as ITO is formed on one surface of each glass substrate, and 5EL-N is further formed on the transparent electrode of one glass substrate.
(manufactured by Somar Industries, refractive index ng = 1.57) to form a diffraction grating, and bonded both substrates so that the transparent electrodes faced each other. .79, no=1.53),
A light modulation element as shown in FIG. 1 was prepared.

Figure 3 is a diagram showing the wavelength dispersion characteristics of the refractive index of SEL-N (ng) and RO-TN403 (ne, no) with respect to white light at room temperature.
), and is a graph plotting the refractive index of 5EL-L and RO-TN403 on the vertical axis. As can be seen from Fig. 3, (ne-no) is approximately equal in the entire wavelength range of the incident light, and ng
Although the absolute values of the wavelength dispersion characteristics of and no are different, they follow similar curves, and it is impossible to obtain a completely transparent state.

Further, FIG. 4 is a diagram showing the voltage dependence V-η0 curve of the diffraction efficiency η0 of the zero-order transmitted diffracted light of the light modulation element in this embodiment. As can be seen from the figure, the V-10 curve in this example shows a steep rise, and the slope component mainly consists of γ1, and compared to the V-10 curve in Figure 2, total transmission is achieved at a lower voltage. You can get the status. Furthermore, it showed characteristics that make multiplex drive possible.

Although this embodiment shows a transmissive light modulation element, it is also possible to form a reflective element by applying a light reflecting film 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. It is desirable that the diffraction grating, the refractive index variable material, the substrate, etc. be made of members that are transparent to the wavelength used.

5 to 7 are schematic diagrams showing other embodiments of the photovariable 3I element according to the present invention, in which the same members as in FIG. 1 are denoted by the same reference numerals. Further, 7 and 7' indicate the direction of the optical axis of the refractive index variable material 1 such as liquid crystal, and 7 indicates the direction perpendicular to the plane of the paper;
7' indicates a direction parallel to the plane of the paper and orthogonal to direction 7. Furthermore, 2' is a diffraction grating (not shown), 3' is a transparent electrode, and 4' is a transparent substrate.

FIG. 5 shows an element constructed by superimposing diffraction gratings 2 and 2' so that their arrangement directions are perpendicular to each other, and is formed using a pair of the light modulation elements shown in FIG. 1.

With such a configuration, it is possible to simultaneously modulate the polarization components 6 and 6' of the incident light 5 shown in FIG.

6 and 7 show an element in which the form of the diffraction grating 2 is changed in the light modulation element shown in FIG. 1, with FIG. 6 having a triangular wave-like diffraction grating and FIG. 7 having a sine wave-like diffraction grating. It is a light modulation element that In this way, the shape of the diffraction grating of the light modulation element is not limited to a rectangular shape, and various shapes can be used. However, the equation for diffraction efficiency as shown in equation (1) above differs depending on the shape of the diffraction grating.

In the following explanation, 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 crystal, especially nematic liquid crystal, can be easily used. This is because it is readily available, easy to control, and allows orientation regulation using a diffraction grating.

It can be said that this material is suitable for the present invention. In addition, 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.Furthermore, as a refractive index variable material, a refractive index between an extraordinary refractive index ne and an ordinary refractive index no is used. It is preferable to have a large rate difference, which increases the degree of freedom in element configuration and modulation function. Therefore, in this sense as well, liquid crystal is a preferable material, and desirably has a refractive index difference (ne-no).
A substance with a value of 0.2 or more is preferable.

<Effects of the Invention> As described above, the light modulation element according to the present invention can obtain a completely transparent state regardless of the wavelength of the used luminous flux, and can also achieve multiplex drive, so it is suitable for use as a variable subtractive color filter, a display element, etc. This is a light modulation element with excellent performance.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of a light modulation element according to the present invention. Figure 2 shows the voltage (V) and diffraction efficiency (η
0) is a diagram showing the relationship. FIG. 3 is a diagram showing the wavelength dispersion characteristics of the refractive index of the diffraction grating and liquid crystal of the light modulation element according to the present invention. FIG. 4 is a diagram showing the relationship between the voltage (V) and the diffraction efficiency (η0) of the optical modulator according to the present invention. Figures 5 to 57 are diagrams showing other embodiments of the optical modulation element according to the present invention. 1 ----1 refractive index variable material (liquid crystal) 2, 2'
-----1 Diffraction grating 3, 3' -----1 Transparent electrode 4, 4' -1 - Transparent substrate 5 -----1 Incident light

Claims (4)

[Claims] (1) A diffraction grating existing on at least one opposing surface of a plurality of substrates and an adjacent substrate, a refractive index variable material disposed between the plurality of substrates, and a means for controlling the refractive index of the refractive index variable material. When a predetermined refractive index existing between the maximum refractive index n_m_a_x and the minimum refractive index n_m_i_n of the variable refractive index material is n_θ, and the refractive index of the material forming the diffraction grating is n_g, the incident light A light modulation element in which the refractive index n_θ and the refractive index n_g are approximately equal in all wavelength regions. (2) The light modulation element according to claim (1), wherein the refractive index variable material is a liquid crystal. (3) The light modulation element according to claim (1), wherein the substrate and the refractive index variable material are transparent to the wavelength used. (4) The light modulation element according to claim (1), wherein the orientation direction of the liquid crystal is changed by an electric field.