JPS62238530A - Optical modulation element - Google Patents

Abstract

PURPOSE:To improve the function relating to liquid crystal orientation by a diffraction grating and to improve an electrooptic characteristic and the temp. dependency thereof by subjecting the groove bottom part of the diffraction grating or the opposed surfaces of substrates to an orientation treatment to define the inclination direction of the molecules of a liquid crystal. CONSTITUTION:This optical modulation element has the plural transparent substrates 4, the diffraction grating 2 existing on at least one of the surfaces, which face each other, of the adjacent transparent substrates 4, the liquid crystal 1 disposed between the plural transparent substrates 4 and means for controlling the orientation condition of the liquid crystal 1. The diffraction grating 2 has the function to orient the liquid crystal 1. The groove bottom part of the diffraction grating 2 or the opposed surfaces of the substrates 4 are subjected to the orientation treatment, by which the inclination direction of the liquid crystal 1 molecules is defined. The groove bottom part of the diffraction grating 2 or the opposed surfaces of the substrates 4 are subjected to the orientation treatment in the above-mentioned manner in addition to the orientation control power by the diffraction grating 2, by which the display contrast particularly in the case of using the optical modulation element as a display element is improved and the uneven response and uneven display, etc., are prevented. The high display grade and responsiveness are thus obtd.

Description

Detailed Description of the Invention Technical Field> The present invention combines a light modulation element, particularly a liquid crystal, and a diffraction grating to change the refractive index of the liquid crystal with respect to incident light, thereby imparting a desired diffraction effect to the incident light (1 The present invention relates to a light modulation element suitable for display elements, optical recording, optical communications, etc.

<Prior art> Conventionally, a liquid crystal and a diffraction grating are combined to produce a light quantity of 1 element-L, as disclosed in Japanese Patent Publication No. 53-3928 and USP 4,251.
, 137, etc., and TTT color changing filter elements. The light modulation elements disclosed in these publications utilize diffraction phenomena to obtain decorative effects and color filter effects, and the relief patterns formed on the I and Q plates function as diffraction gratings.

On the other hand, USP3.787,110 and USP4.256,
787 shows that liquid crystals are aligned by a fine regular relief pattern with a shape similar to a diffraction grating, and by giving a single diffraction grating a predetermined size and shape, both the diffraction function and the liquid crystal alignment function can be simultaneously satisfied. It is also possible to do so in view of the conventional technology.

However, USP 3,787,110 and USP 4.
256.787 etc., the orientation regulating force exerted only within the area surrounded by the side and bottom surfaces of the concave portion of the relief pattern,
Even if it is applied to the device disclosed in No. 3928 or USP 4,251,137, the tilt direction of the liquid crystal molecules with respect to the electric field is uneven, resulting in poor reliability, and this type of device cannot be used as a display device. When used.

It also has the disadvantage that display unevenness occurs in a static state, and response unevenness occurs in a dynamic state. That is, since there is no regulating force regarding the pretilt of liquid crystal molecules, there is a problem in that the orientation of liquid crystal molecules changes locally depending on the interface state due to thermal motion or electric field energy.

<Summary of the Invention> In view of the above-mentioned conventional problems, an object of the present invention is to provide a light modulation element that improves the function related to liquid crystal alignment using a diffraction grating and also improves the electro-optic characteristics and its temperature dependence. be.

In order to achieve the above object, the light modulation element according to the present invention includes:
comprising a plurality of transparent substrates, a diffraction grating existing on at least one opposing surface of an adjacent transparent substrate, a liquid crystal disposed between the plurality of transparent substrates, and means for controlling an alignment state of the liquid crystal,
The diffraction grating is an element having a liquid crystal alignment function.

The present invention is characterized in that the direction of inclination of the molecules of the liquid crystal is defined by applying alignment treatment to the bottom of the groove of the diffraction grating or to the opposing substrate surface.

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

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. 1 shows a basic configuration diagram of a light modulation element according to the present invention,
It also serves as a functional explanatory diagram of the present optical modulation element. In the figure, l is a liquid crystal, 2 is a diffraction grating made of a substance transparent to the wavelength used, 3 is a transparent electrode, 4 is a transparent substrate made of a transparent optical member,
5 is incident light having predetermined polarization characteristics, 6 and 6' are mutually orthogonal polarization components of incident light 5, 6 is in the direction perpendicular to the plane of the paper,
6' indicates a direction parallel to the plane of the paper.

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 is provided at the 11 poles 3, the refractive index variable material 1 is placed in the grooves (four parts) of the diffraction grating 2, and an electric field is applied through the transparent electrode 3. Its refractive index is variable.

Hereinafter, the modulation principle of the present optical modulation element will be explained using FIG.

Here, it is assumed that a predetermined diffraction effect is produced by controlling the alignment state of the liquid crystal I 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. Therefore, the incident light 5 that enters the optical modulation element in this static state
Of the polarized light components 6.6', the polarized light component 6', which is a component perpendicular to the orientation direction of the liquid crystal 1, senses the ordinary refractive index no of the liquid crystal 1, and the polarized light component, which is a component parallel to the orientation direction of the liquid crystal 1, is Ingredient 6
senses the extraordinary refractive index ne of the liquid crystal l. Here, if the refractive index of the material forming one diffraction grating 2 is ng, the wavelength of the incident light 5 is input, and the thickness of the first diffraction grating 2 is T, then in the case of a rectangular diffraction grating, the polarization component of the incident light 5 is 6. The diffraction efficiency η0 of the zero-order transmitted diffracted light for each of .6′ can be approximately expressed by the following equation (1).

η0:' (1+cos ('2△dan]))...
(1) Two people However, Δn indicates the refractive index difference between the refractive index ng of the diffraction grating 2 and the refractive index ne or no of the liquid crystal 1, and the incident light 5
For polarization component 6 of Δn=I ne-ng 1.
For polarization component 6', Δn=I ng-no I.

Therefore, from equation (1), Δn=o, that is, ne=ng or n(
, =ng, the diffraction efficiency η0 of the zero-order transmitted diffracted light is η0=
It becomes l, and again.

Δn T = (m + 2) input (m=o, 1, 2.3.---) When , the diffraction efficiency η0 becomes η0=Q.

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 gradually changes, and the polarization component 6' of the incident light 5 is independent of the electric field application. is the ordinary refractive index n of the liquid crystal 1.

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 1 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 equation (1) above.

FIG. 2 is a schematic perspective view showing one embodiment of the light modulation element according to the present invention, in which light is produced by superimposing elements having the basic configuration shown in FIG. It is a modulation element. In the figure, the same parts as in the ¥pJ1 figure are labeled with the same numbers.

Reference numeral 7 denotes a transparent substrate forming a spacer, and transparent electrodes 3 are formed on one surface of the transparent substrate.

As explained using FIG. 1, when optical modulation is performed using a single diffraction grating 2, for example, when the orientation state of the liquid crystal 1 is changed from homogeneous orientation to homeotropic orientation by an electric field, etc., the first In the figure, the polarization component 6 of the incident light 5 is modulated, but the polarization component 6' is not modulated because the perceived refractive index does not change, and when the incident light 5 has random polarization characteristics, it does not appear in the actual image. This means that only 50% of the light can be modulated. However, by adopting the superimposed configuration as shown in FIG. 2, each diffraction grating 2 independently exerts a diffraction effect on each polarization component 6,6' of the incident light 5,
This makes it possible to modulate light of all polarization components.

As shown in FIGS. 1 and 2, the liquid crystal 1 is oriented in the direction of the grooves of the diffraction grating 2. In the conventional system, the regulating force that orients the liquid crystal 1 is applied to the grooves (recesses) of the diffraction grating 2. ), and when actually driving the device, the orientation of liquid crystal molecules changes due to thermal interlocking, electric field energy, and interfacial conditions such as yF;.

When applied as a display element, uneven display and response occur, resulting in poor reliability.

However, in the present invention, the bottom of the diffraction grating 2 or the opposing substrate 4 (3) of the device as shown in FIGS.
, 7 is subjected to alignment treatment to define the tilt direction of the liquid crystal molecules, thereby keeping the tilt direction of each liquid crystal molecule constant. still.

Suitable examples of this orientation treatment include generally known rubbing treatment and oblique evaporation of 5i02.

Figures 3 (A), (B), and CC) are schematic diagrams for explaining the effect of the alignment treatment that defines the tilt of liquid crystal molecules in the present invention, and Figure 3 (A) is a schematic diagram for explaining the effect of the alignment treatment that defines the tilt of the liquid crystal molecules. Figure 3 (B) shows the state of liquid crystal molecules at the interface without alignment treatment, and Figure 3 (C) shows the state of liquid crystal molecules at the interface with alignment treatment. The behavior of molecules when an electric field is applied is shown.

As can be seen by comparing FIGS. 3(A) and 3(B), at the interface where no alignment treatment has been performed.

The tilt direction of the liquid crystal molecules is random, which not only causes the above-mentioned problems when driving the device by applying an electric field, but also causes problems due to the disorder of the liquid crystal molecules at the interface even in a static state. The incident light receives abnormal polarization and the display performance deteriorates. on the other hand,
At the interface that has been subjected to alignment treatment, the liquid crystal molecules are aligned at the interface with a uniform inclination, that is, a pret-2-reto angle of 0, mainly due to the chemical alignment regulating force.

Therefore, since the tilt and tilt directions are aligned, no abnormal polarization occurs even in a static state, and as shown in Figure 3 (C), the behavior of liquid crystal molecules when an electric field is applied is , each molecule coincides and changes the orientation direction. Therefore, compared to the conventional orientation using only a diffraction grating, the response is better and display unevenness does not occur.

A specific example of a single light modulation element will be described below along with a simple manufacturing method.

First, a diffraction grating having a thickness of 1.5 gm and a pitch of 1.5 gm was also formed in the shape of a display pattern on a transparent electrode patterned on a substrate in the shape of a display pattern.

On the other hand, after forming a transparent electrode on the substrate surface of the counter substrate to be bonded to the substrate having this diffraction grating, a polyimide alignment film is provided at the transparent Iπ pole so that the groove direction of one diffraction grating and the tilt direction of liquid crystal molecules are the same. Orientation treatment was performed by rubbing treatment so that the film was oriented in the same direction. and 2 produced by one or more methods.
A light modulation element as shown in FIG. 1 was fabricated by placing two transparent substrates tightly together and encapsulating a liquid crystal therein.

In the light modulation element of this embodiment, the liquid crystal has a pretilt in a predetermined direction and has a so-called homogeneous alignment with a director (alignment direction) in the groove direction of one diffraction grating.

Therefore, by turning on and off the application of an electric field, the liquid crystal molecules uniformly and rapidly change their orientation, making it possible to respond at high speed. In addition, the time required for rearrangement of liquid crystal molecules when the electric field is turned off at low temperatures is shortened, and the temperature dependence of the refractive index, which defines the displayed color of the present light modulation element, is also improved. Also, color variations due to temperature were reduced.

Furthermore, a gap exists between the opposing substrate and the upper part of the diffraction grating,
Even if liquid crystal molecules exist in this gap, the liquid crystal molecules will not be disturbed, and reliability against electric fields and temperatures can be obtained, as well as display unevenness and display delay can be reduced. 1 Display quality and reliability can be improved. It is possible.

In this embodiment, a rubbing method is used as the orientation treatment method for the substrate, but it is also possible to use anisotropic etching such as IonBee 11 Blaze F or diagonal etching of Si02. Needless to say, on the contrary, the orientation treatment may be performed on the substrate surface having the diffraction grating using the above-mentioned method.

Hereinafter, an example will be described in which an orientation regulating force different from that in the example described in -A is generated.

In this example, 0.00% of octadecyltriethoxysilane was applied as an alignment agent to the substrate opposite to the substrate on which the diffraction grating was to be formed.
A 5 wt% ethanol solution was applied using a spin cord, heat treated at 100''C for 1 hour, and then rubbed so that the groove direction of the diffraction grating and the tilt direction of the liquid crystal molecules matched, and the same procedure as in Example 5 was performed. A light modulation element was fabricated using the method described above. Through this alignment treatment, the liquid crystal molecules on the surface of the alignment substrate were aligned in the thickness direction of the diffraction grating, that is, in the direction perpendicular to the substrate surface, and in a static state. This shows a so-called hybrid orientation, in which the molecular alignment changes from a homeotropic state to a homogeneous state, and the tilt of the liquid crystal molecules at the interface can be defined.

In the above embodiments, a transmissive light modulation element is shown, but 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 is complicated, so when considering the design and application aspects of actual display elements, *In the invention, it is difficult to configure a transmissive type light modulation element. preferable. In this case, as a matter of course, the diffraction grating, liquid crystal, substrate, etc. are made of members that are transparent to the wavelength used.

<Effects of the Invention> (1) The light modulation element according to the present invention is particularly advantageous when used as a display element by performing alignment treatment on the groove bottom of the first diffraction grating or on the opposing substrate surface in addition to the alignment regulating force provided by the first diffraction grating. This is a light modulation element that can increase the display contrast of L: to prevent uneven response, display unevenness, etc., and obtain high display quality and responsiveness.

[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 schematic perspective view showing one embodiment of a light modulation element according to the present invention. FIGS. 3(A), 3(B), and 3(C) are explanatory diagrams showing the effects of the alignment treatment in the present invention. 1 -----1 Liquid crystal or liquid crystal molecules 2 -----1 Diffraction grating 3 -----1 Transparent electrode 4 -----1 Transparent substrate 5 -----1 Incident light

Claims (1)

[Scope of Claims] (1) A diffraction grating existing on at least one opposing surface of a plurality of substrates and an adjacent substrate, a liquid crystal disposed between the plurality of substrates, and means for controlling the alignment state of the liquid crystal. The light modulation element is an element in which the diffraction grating has a liquid crystal alignment function, and the direction of inclination of the liquid crystal molecules is defined by applying an alignment treatment to the bottom of the groove of the diffraction grating or the opposing substrate surface. (2) A patent in which the liquid crystal is oriented such that the liquid crystal molecules are tilted in the thickness direction of the diffraction grating, and the projection of the liquid crystal molecules onto the substrate surface of the director is approximately parallel to the groove direction of the diffraction grating. A light modulation element according to claim (1). (3) The light modulation element according to claim (1), wherein the substrate and the liquid crystal are transparent to the wavelength used. (4) The light modulation element according to claim (1), wherein the liquid crystal is oriented perpendicularly to the opposing substrate surfaces in a static state.