JPS63281131A - Optical modulator - Google Patents

Abstract

PURPOSE:To contrive the improvement of a normally open display and a multiplex characteristic of the title modulator by specifying the dimension of a recessed part of a diffraction grating, placing periodically a limited length grating unit of the diffraction grating, and also, providing an oriented film for controlling a spontaneous orientation state of a liquid crystal on at least one substrate surface side of the opposed substrate surface sides. CONSTITUTION:Length in the grating direction of a recessed part 2a of a diffraction grating 2 is set within a range of 1/5-100 times as long as a grating pitch, and plural pieces of limited length grating units 2c consisting of a grating part 2b and the recessed part 2a are placed periodically, for instance, in a checked pattern. Also, on at least one substrate surface side of the opposed substrate surface sides, oriented films 3, 3' for controlling a spontaneous orientation state of said liquid crystal 1 are provided. In such a way, the control of the spontaneous orientation state is facilitated, and the realization of a normally open type display and the improvement of a multiplex characteristic can be executed.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a light modulation device, and in particular to a light modulation device that modulates light such as passing light or blocking light by using a diffraction grating and a variable refractive index material such as a liquid crystal. The present invention relates to a light modulation device suitable for display, optical recording, optical coupling, optical communication, optical calculation, and other devices.

(Prior art) A display element that utilizes well-known light modulation consists of a pair of polarizing plates arranged so that the polarization directions are perpendicular to each other, and a pair of transparent polarizing plates arranged between the pair of polarizing plates. It consists of an element in which a liquid crystal is sealed by applying orthogonal alignment treatment to the facing surfaces of the substrates, and the alignment state of this liquid crystal is switched between a twisted state and a state perpendicular to the substrate surface to control the incidence of light. There is a so-called TN (twisted nematic) type liquid crystal display element that modulates light. This type of display element has a simple structure and is easy to drive, so it is used in a wide variety of applications.However, since it uses two polarizing plates to transmit and block the light flux, it is difficult to transmit light when it is extinguished. The display element had poor transmittance and could not be said to be a desirable display 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 display element that uses a dye mixed into liquid crystal molecules, but even in this display element, due to the presence of the dye, the The transmittance was about 70% 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. Although the elements disclosed in these documents are certainly excellent in luminous flux utilization efficiency, the element disclosed in Japanese Patent Publication No. 53-3928 merely exhibits a saturation effect, and is not suitable for displaying characters or images. Transmission of elements and luminous flux,
This was not satisfactory as a display element that performs blocking.

Further, the variable subtractive color filter element disclosed in US Pat. This is a display element that changes the refractive index of the liquid crystal by applying the same amount of light, and uses the diffraction effect of the diffraction grating to perform optical modulation such as transmitting light and blocking light.

In order to perform optical modulation control of incident light having an arbitrary polarization component using this display element, these display elements must be connected to each other,
The diffraction gratings may be stacked so that their directions are perpendicular to each other, or the diffraction gratings may be formed on a pair of opposing substrate surfaces so that their alignment directions are perpendicular to each other, and liquid crystal may be filled between the substrates. becomes necessary.

However, in devices with a structure in which the recesses of the diffraction grating are filled with liquid crystal, in many cases each liquid crystal molecule in the diffraction grating has a cylindrical or groove-like grating wall (usually the grating length s〉〉lattice pitch x 100). For this reason, it is constrained by a large shape alignment regulating force in the direction parallel to the lattice due to the lattice wall force, and no voltage can be applied due to the alignment films on the opposing upper and lower substrate surfaces, which is not possible with ordinary lattice-free liquid crystal display elements. It has become difficult to set the spontaneous alignment state of the liquid crystal at the time, resulting in functional and structural inconveniences.

(Problems to be Solved by the Invention) The present invention fills the recesses of a diffraction grating with liquid crystal, controls the alignment state of the liquid crystal, and performs light modulation such as light transmission or light blocking. By providing an alignment film with a predetermined function on at least one of the shape in the lattice direction and the opposing substrate surface side, and setting the alignment state of the liquid crystal filled in the recess to the desired state, it is possible to achieve normalization, which was previously difficult. The purpose of the present invention is to provide a light modulation device with improved functions for open display and multiplex characteristics.

(Means for solving the problem) A diffraction grating is provided on one of two substrates facing each other, a liquid crystal is filled between the diffraction grating and the substrate, and a liquid crystal is filled between the diffraction grating and the substrate. In the light modulation device, the length of the concave portion of the diffraction grating in the grating direction is set to 115 to 100 times the grating pitch, and the finite length grating units of the diffraction grating are periodically arranged. In addition, an alignment film for regulating the spontaneous alignment state of the liquid crystal is provided on at least one of the opposing substrate surfaces.

(Embodiment) FIG. 1 is an explanatory diagram showing the configuration and light modulation function of an embodiment of the present invention. In the figure, 5.5' is a transparent substrate, 4.4' is a transparent electrode, and 2 is a diffraction grating, which are made of optical members that are transparent to the wavelength used. In this embodiment, the length 1□ of the concave portion 2a of the diffraction grating 2 in the grating direction is 175~
A plurality of finite length lattice units 2C each having a shape of lattice portions 2b and recesses 2a are arranged periodically in a checkerboard pattern, for example.

1 is a liquid crystal, for example a nematic liquid crystal with negative dielectric anisotropy, and is filled in the recess 2a of the diffraction grating 2. In particular, in this embodiment, when no voltage is applied, the liquid crystal 1 is regulated by alignment films 3 and 3', which will be described later, and exhibits homeotropic alignment in the direction of the transparent substrate 5 and 5'. 3
, 3' are alignment films treated with a vertical alignment agent, which are provided on both substrate surfaces of the transparent substrate 5 and 5', and have a structure in which the length of the recess of the diffraction grating is limited. The orientation state of the liquid crystal molecules 1 filled in the recesses 2a of the checkered diffraction grating with a small shape orientation regulating force is controlled.

6 is incident light having arbitrary polarization characteristics, 7 and 7' are polarization components of the incident light 5 whose polarization directions are perpendicular to each other, polarization component 7 is a component in the grating direction of diffraction grating 2, and polarization component 7' is This is the component in the direction perpendicular to the lattice direction.

In this embodiment, the liquid crystal l is filled into the concave portion of the diffraction grating 2 via transparent electrodes 4 and 4' provided oppositely on both sides of the diffraction grating 2.
By applying an electric field to the liquid crystal 1, changing the tilt angle of the liquid crystal 1, and controlling the refractive index of the liquid crystal 1, a desired diffraction effect is produced in the incident light 6, and light modulation is performed.

Next, the light modulation principle of the light modulation device in this embodiment will be explained. In FIG. 1, in a spontaneous alignment state where no electric field is applied to the liquid crystal 1, that is, in a static state, the liquid crystal 1 is aligned in the direction of the transparent substrates 5 and 5' within the recess 2a of the diffraction grating 2, as shown in the same figure. It shows a homeotropic orientation. When the incident light 6 is incident on the light modulation device in a static state, the polarization components 7 and 7' of the incident light 6 are both polarized by the liquid crystal 1.
Feel the ordinary refractive index n0. Here, the grating part 2 of the diffraction grating 2
If the refractive index n6 of b is set in advance so that n, I=no, the incident light 6 will be completely transmitted without causing any diffraction.
The light modulator is in an erased or oven state.

Next, when an electric field is applied to the liquid crystal 1 through the transparent electrodes 4.4', the liquid crystal 1 becomes homogeneously aligned along the lattice direction. Then, among the polarized light components 7.7' of the incident light 6, the polarized light component 7' that is perpendicular to the orientation direction of the liquid crystal 1 will not change at all and will be transmitted as is because it will feel the ordinary refractive index n0 of the liquid crystal 1 as before the voltage application. do. On the other hand, the polarized light component 7 parallel to the alignment direction of the liquid crystal 1 senses the extraordinary refractive index ne of the liquid crystal 1.

Here, since n, = ne, the polarized light component 7 of the incident light 6
is diffracted by the diffraction grating 2. Therefore, the light modulation device is in a display state, that is, a closed state. As described above, the optical modulation device shown in FIG. 1 has a so-called normally open display function in which the display state is set by applying a voltage, and the erase state is set by applying no voltage.

Generally, in order to perform optical modulation of polarized light components in arbitrary directions, it is sufficient to stack the main parts of the optical modulation device shown in FIG. 1 so that the grating directions of the diffraction gratings are orthogonal to each other.

Here, as shown in FIG. 1, the grating pitch dimensions of the grating part 2b and the recessed part 2a of the diffraction grating 2 are P, , P2, the grating pitch is 2P (=P+ +P2), and the grating part 2b and the recessed part 2a.
The dimension in the lattice direction is l+, 12, the pitch in the lattice direction is 21 (=1.+12), and the line ratio of the lattice dimension is P+
/ (PI+p2), space ratio in lattice direction is 11
/ (II +12). Then, the refractive index n of the grating portion 2b during one period determined by these values,
The refractive index n6 for the polarized light component 7 in the lattice direction of the liquid crystal 1 due to the homogeneous orientation of the liquid crystal 1 filled in the recess 2a is as shown in FIG. In FIG. 2, the horizontal axis shows the grating pitch, and the vertical axis shows the pitch in the grating direction. Further, 20a indicates a region of the recessed portion 2a, and 20b indicates a region of the lattice portion 2b.

In addition, in this embodiment, the switch 21 in the lattice direction is set to 11≠1.
A finite length lattice unit may be constructed from two, four, or more regions and arranged periodically. Now, assuming that the height of the grating portion of the diffraction grating 2, that is, the concave portion 2a, is T, and the diffraction grating 2 is rectangular, the diffraction efficiency η of the zero-order transmitted diffracted light of the diffraction grating 2 with respect to the polarization component 7.7' is. is roughly expressed by the following equation.

ηo = P%・Py' + (1-PX)24y2
+PxJ]-Py)2+(+-Pj2・(+-py)2+2P,-P,"-(1-P,)・cos(2yrR
)+2P,2・P,−(1−P,)−cos(2yr
R)+ 4P, -P,・(1-PX)・(1-P,)+
2n-pX)-(+-py)(px+py-2pxp
y) cos(2πR)p, -7/ (PI+P2)
, p, -II / (it÷12)R-(ne
-n, )4 /λ-Δn-T /λ Note that the above equation (1) is an approximate equation assuming that the wavelength λ<<P, l, and if P, 1 is about several μm, there will be some deviation. occurs.

Next, in this embodiment, under the conditions in which the length of the concave portion of the diffraction grating 2 in the grating direction was specified as described above, the liquid crystal 1 of the alignment film 3.3' provided on both substrate surfaces of the transparent substrate 5.5'. The effect on this will be explained.

FIG. 3A is an explanatory diagram of the main parts of a conventional optical modulation element. In the light modulation element shown in the figure, the length in the grating direction is much larger than the grating pitch (grating and pitch X100<length in the grating direction), so the liquid crystal 1 is constrained by a strong shape orientation regulating force generated in the lattice direction, and is forced to have homogeneous orientation in the lattice direction. This shape orientation regulating force in the lattice direction is extremely large in a diffraction grating with a submicron-Lumicron lattice pitch, so when trying to obtain various orientation states, it is necessary to It becomes difficult to control the spontaneous alignment state by the alignment films provided on the upper and lower substrate surfaces.

For example, in the case of a vertical alignment film, the liquid crystal is not perfectly homeotropically aligned, but the shape regulating force in the lattice direction and the regulating force of the upper and lower vertical alignment films overlap, and as a result, only an inclined alignment in the lattice direction is achieved.

On the other hand, in this embodiment, as described above, the length of the diffraction grating in the grating direction is limited to 175 to 100 times the grating pitch, and finite length grating units are arranged periodically to improve the shape orientation in the grating direction. As a result of weakening the regulating force, the alignment state of the liquid crystal can be well controlled by the regulating force by the alignment films provided on the upper and lower substrate surfaces.

For example, as shown in FIG. 3(B), vertical alignment is achieved by alignment film treatment on the upper and lower substrate surfaces, as in a normal non-lattice liquid crystal cell;
Parallel orientation in the direction orthogonal to the lattice direction as shown in Figure (C),
Furthermore, it is possible to arbitrarily set a spontaneous alignment state such as a parallel twist alignment as shown in FIG. 3(D) to a good state.

Here, the principle of controlling the shape alignment regulating force of the diffraction grating 2 on the liquid crystal 1 in this embodiment will be briefly explained using a model of "wall force" based on the repulsion between rigid bodies as an example.

As shown in FIG. 4(A), the height of the concave portion of the diffraction grating 2 is T.
, a rigid wall box 30a consisting of a diffraction grating 2 with a width (half period of the grating pitch) of P and a length of L (grid center (0, 0, 0)
) at any position (Xo+Y0, Zo
) is the composite vector of each wall force due to the length of the recess (=shape orientation regulating force) among the rigid repulsive forces that the rigid rod of ) receives from the 8 walls.
Qualitatively explain the changes in

As shown in FIGS. 4(A) and 4(B), the state in which the wall surface and the liquid crystal molecules 31 exert the least repulsive force, that is, the state in which they are parallel to each other, is considered to be energetically stable. In the same figure, the point (x, y, T/2
) is the liquid crystal molecule 31
Force d F (x, y, T
/2) is e whose direction is parallel to the xy plane, (X component) e2 (
X component), and its size is proportional to the effective area of the micro wall surface taking into account the angles α (X component) and β (X component) formed between the liquid crystal molecules 31 and the micro wall surface, as shown in Figure 4 (C). , the function of the distance between the liquid crystal molecules and the minute wall exp(-(x-xo)2◆(y-yo)2+(T/2
-za)2/p) (where ρ is a constant indicating the effective distance of repulsive force transmission). Then xy wall surface z
= Force F that T/2 exerts on liquid crystal molecules (z-T/2)
becomes −−1−−(2). However, ' and p are constants.

Similarly, the resultant force of the 6 walls F=F, +F, +F2 is x
, y, and z (where k is a constant).

Liquid crystal pretilt angle θ. (The angle formed by the x, y plane and the liquid crystal molecules) is the parallel alignment regulating force FP=FX+F.

is determined by the vertical alignment regulating force Fv=FX, and θo=
jan-' (Fv / Fp) =・=・
”−=·(4).

For example, when the height T of the recess of the diffraction grating is 1.5 μm and the grating width P = 0.75 μm, the length of the recess will affect the liquid crystal (0,0,0) located at the center of the grating. When the changes in the vertical alignment regulating force FV and the parallel alignment regulating force FP are calculated according to equations (2) and (3), the results are shown in FIG.

As shown in the figure, the vertical alignment regulating force Fv is the length of the recess L#
On the other hand, the parallel alignment regulating force Fp continues to increase up to the length L of the recessed portion to approximately 50 μm, and is approximately saturated at around 50 μm, whereas it hardly changes at 1 μm or more.

In particular, the convexity ratio in the lattice direction based on finite length lattice units, that is, 1
．． If the +12 ratio is 1:1, Fraunhofer's (1)
As shown by the formula, while maintaining the zero-order diffraction efficiency equivalent to that of a normal diffraction grating (grating pitch x 100 × length of the recess), the length of the recess can be changed as described above without deteriorating the optical function. The feature is that it can be set as follows. If the length of the recess becomes too short, i.e. less than the grating pitch I75, the length of the recess will become larger than the length in the grating groove direction even if the ratio of the length of the recess to the convex part in one cycle is 1:4. Since it becomes difficult to align the liquid crystal in the direction of the grating grooves, the optical function is no longer fulfilled, and if the length is too long (more than 100 times the grating pitch), as shown in Figure 4, the horizontal alignment regulating force FP will be almost zero. This results in saturation, and the length in the groove direction becomes substantially equal to a normal lattice that does not limit the length.

For this reason, in this embodiment, the length of the concave portions of the diffraction grating 2 in the grating direction is set to a pitch of several tens of μm or less, that is, as described above, approximately 175 to 100 times the grating pitch, and the shape orientation regulating force F=
Fp+Fv is reduced to about a fraction of that of a normal grid cell. This creates a state in which the alignment state of the liquid crystal 1 can be well controlled by the alignment regulating force of the alignment films provided on the upper and lower substrate surfaces.

Next, an embodiment of the present invention shown in FIGS. 3(B), 3(G), and 3(o) will be described. In Fig. 3(B), the upper and lower substrate surfaces are subjected to vertical alignment treatment using, for example, a silanine-based surfactant with a relatively small critical surface energy, and the upper and lower arrows B1 of the diffraction grating indicate the upper and lower directions, respectively. The direction of the regulating force of the alignment film (not shown) is shown. The shape orientation regulating force is weakened by the diffraction grating, which has a structure in which finite length lattice units with limited length in the lattice direction are periodically arranged in a checkered pattern, thereby reducing the regulating force due to the alignment films provided on the upper and lower substrate surfaces. By improving the liquid crystal, which was dominant and tilted in conventional diffraction gratings, a good homeotropic alignment was created.

In Figure 3(C), the upper and lower substrate surfaces are subjected to parallel alignment treatment using polyimide, etc., and then rubbed in a direction perpendicular to the lattice direction to create a homogeneous alignment state in the direction perpendicular to the lattice direction. be.

By combining the lattice direction orthogonal alignment type element shown in the figure with the conventional lattice direction parallel alignment type element, it is possible to realize an optical modulation device that structurally does not require an intermediate plate. In a conventional configuration in which lattice-direction parallel alignment type elements are directly combined with the lattice directions perpendicular to each other without sandwiching an intermediate plate, the alignment may be disturbed in the boundary area of the liquid crystal whose alignment directions are orthogonal to each other, the occurrence of dispersion, and electrode problems may occur. There were problems such as an upper limit of the driving voltage due to the doubling of the distance between the two, which was not very desirable.

FIG. 6 shows two display elements having the basic configuration shown in FIG. The structure is such that the periodically shifted lattice portion and the recessed portion are combined so as to coincide with each other.

Then, the filled portions of liquid crystals are isolated from each other, and there is no boundary where liquid crystals 1.1' with different alignment directions come into contact with each other. Also, before the patterning and dry etching processes of the diffraction chair, a transparent electrode 4' and an alignment film 3 are placed on the upper part of the grating. ' By forming transparent electrodes 4.4', 4'' and alignment films 3', 3゜3'', 3'' on the upper and lower surfaces of each isolated liquid crystal filling part, that is, on the grid part and the bottom of the recess, respectively. The structure in which the structure exists is removed.

As a result, a direct combination type optical modulation device that does not require an intermediate plate is achieved, which solves the above-mentioned problems of the conventional type.

In FIG. 6, the rubbing direction of each alignment film is perpendicular to the rear of the grating for the alignment films 3, 3'', and the rubbing direction for the alignment films 3',
3"' is parallel alignment, and in order to ensure transparency above the grating part and conduction of the polar pattern 4', the corners of the concave parts of each diffraction grating unit are not connected by lines, but are curved surfaces with a certain curvature. , or a structure connected by a plane.

In FIG. 6, the polarized light component 7 of the incident light 6 is in the first layer (1
The polarized light component 7' that has been diffracted by the first layer (1, 2') and passed through the first layer is diffracted by the second layer (1, 2), thereby optically modulating any polarized light component as a whole.

Figure 3 (D) shows that after applying a parallel alignment agent such as polyimide to the upper substrate side, one side of each side is rubbed in a direction parallel to the lattice direction and in a direction perpendicular to the lattice direction. The twist mote is realized. Arrows D1 above and below the diffraction grating indicate the direction of the regulating force of the upper and lower alignment films, respectively.

A substance that rotates liquid crystal molecules in a helical shape, such as a chiral agent, is added to a nematic liquid crystal that has positive galvanicity as a liquid crystal, and the desired Rice 1-angle is obtained by aligning the spontaneous chiral pitch with the cell cap. There is.

For example, if the spontaneous chiral pitch is set to 4 times the cell cap, the twist angle will be 1/2π, and if it is set to 473 times, the twist angle will be 3/2π. In this way, by introducing the parallel twist mode into the diffraction grating, the threshold voltage of the applied voltage characteristic of the zero diffraction efficiency η0 increases, and the steepness of the rise increases. The aim is to improve multiplex performance, which was a problem with alignment elements.

In each of the above embodiments, the alignment film is provided on each of the two substrate surfaces, but the alignment film may be provided on only one substrate surface.

Note that the pattern in which the finite length lattice units are arranged in this example is not limited to a checkerboard pattern, but as long as the finite length lattice units are in the same direction in the lattice direction and the orientation direction of the liquid crystal to be filled is uniaxial. Any pattern is acceptable.

For example, as shown in FIG. 7, the length of the recess 82 of the diffraction grating may be limited by a partition wall 81 having a thickness of approximately 0.5 μm or less.

(Effects of the Invention) According to the present invention, when the concave portion of a diffraction grating is filled with liquid crystal and the orientation state of the liquid crystal is controlled to perform light modulation, the dimensions of the concave portion are specified as described above, and the shape and orientation regulating force is controlled. By weakening the regulating force and making the regulating force by the alignment films provided on the upper and lower substrate surfaces or on one substrate surface dominant, it is possible to solve the problem naturally, which is difficult in conventional display elements in which liquid crystal is filled in the recesses of the diffraction grating. It is easy to control the orientation state, for example, it is possible to realize a normally open display (display when the electric field is ON, disappear when the electric field is OFF) by vertical alignment, improve multiplex performance by parallel twist orientation, and achieve parallel orientation in the direction orthogonal to the lattice direction. By realizing a direct combination type element that does not require an intermediate plate, it is possible to achieve a low-cost optical modulation device.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of a finite length grating unit of a diffraction grating according to the present invention, and FIG. 3 (A)
, (B), (D), and (D) are explanatory diagrams showing a spontaneous alignment state of liquid crystal in a recessed portion due to a combination of a finite length lattice unit and an alignment film in a display element according to the present invention, FIG. 4(A) , (B) and (C) are explanatory diagrams of the rigid wall model of the shape regulating force, and FIG. 5 is the length of the recess of the height direction component F V s lattice direction component Fp of the shape regulating force according to the model shown in FIG. FIG. 6 is a schematic diagram of another embodiment of the present invention, and FIG. 7 is an explanatory diagram of another embodiment of the finite length lattice unit according to the present invention. In the figure, 1 is a liquid crystal, 2 is a diffraction grating, and 3.3'. 3 // and 311/ are alignment films, 4 and 4' are transparent electrodes, 5°5' is a transparent substrate, and 6 is incident light. Patent Applicant: Canon Co., Ltd. High School 1st Figure 2 Figure 0cL Lattice B, Tsuyo Figure 10 (A) 6 7

Claims (5)

[Claims] (1) A diffraction grating is provided on one of the opposing substrate surfaces between two substrates, a liquid crystal is filled between the diffraction grating and the substrate, and the alignment state of the liquid crystal is controlled. In the light modulation device, the length of the concave portion of the diffraction grating in the grating direction is set to 1/5 to 100 times the grating pitch, and the finite length grating units of the diffraction grating are arranged periodically, and A light modulation device characterized in that an alignment film for regulating the spontaneous alignment state of the liquid crystal is provided on at least one of the opposing substrate surfaces. (2) The light modulation device according to claim 1, wherein the alignment film is a vertical alignment agent. (3) The alignment films are provided on both sides of the opposing substrate surfaces, and are formed from a parallel alignment treatment agent that has been subjected to a rubbing treatment so that the alignment regulating directions of the two alignment films are perpendicular to each other. and the spontaneous alignment state of the liquid crystal filled in the concave portion of the diffraction grating is (n+1/2)π, (n=0,
2. The light modulation device according to claim 1, wherein the light modulation device has a parallel orientation twisted by an amount of 1, 2, . . . . (4) The alignment films are provided on both sides of the opposing substrate surfaces, and are subjected to a rubbing treatment so that the alignment regulating directions of the two alignment films are both perpendicular to the grating direction of the diffraction grating. the liquid crystal filled in the recesses of the diffraction grating is formed of a parallel alignment agent, and the spontaneous alignment state of the liquid crystal filled in the recessed portion of the diffraction grating is parallel alignment in a direction perpendicular to the grating direction of the diffraction grating. The light modulation device according to scope 1. (5) Claim 1, 2, 3, or 4, characterized in that the finite length lattice units are arranged in a checkered pattern.
The light modulation device described in .