JP2551025B2 - Liquid crystal light modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal optical modulator that performs optical modulation by controlling the alignment of liquid crystal molecules, and more particularly to a liquid crystal optical modulator suitable for transmissive optical modulation. It is a thing.

(Prior Art) Conventionally, a technology of combining a diffraction grating and a liquid crystal is known for several different purposes.

As one of them, a technique utilizing a phenomenon in which a groove having periodic regularity is formed on a substrate surface and a liquid crystal is arranged on the groove shows an alignment ability that liquid crystal molecules are aligned along the groove. There is.

Since the groove formation as the alignment treatment is not mainly intended to function as a diffraction grating, an extremely shallow groove may be formed. In particular, the difference in refractive index (Δn) between the material forming the groove and the liquid crystal and the thickness thereof. d, that is, the phase difference Δnd was not taken into consideration.

Further, a method is known in which a minute grating is formed of materials having different reflection characteristics, and a grating member utilizing the polarization function of the grating and a liquid crystal are combined. This method also forms a grating with a material having a large reflectance, such as a metal, as a configuration for constantly exhibiting polarization characteristics, and is not a technique that considers the difference in refractive index from the liquid crystal material, the thickness of the grating material, and the like.

On the other hand, there is known a phase diffraction grating in which a grating is formed by a transparent member and a liquid crystal is arranged in a groove between the gratings.

Further, the display element disclosed in Japanese Patent Publication No. 53-3928 is for merely displaying a decorative effect, and is used as a light modulation element for displaying characters and images, or for controlling transmission and blocking of light flux. It did not have the function of.

In addition, the variable subtractive filter element disclosed in USP 4,251,137 changes the director (direction of the long axis direction of liquid crystal molecules) of liquid crystal arranged between diffraction gratings by an electric field, and transmits light through the liquid crystal cell at a constant angle. Is used to change the refractive index difference between the grating and the liquid crystal, which changes the diffraction effect.

However, the variable subtractive color filter element has technical drawbacks regarding the production of the diffraction grating and the encapsulation of the liquid crystal, and has the drawback that the operating characteristics are insufficient. That is,
With a liquid crystal material that can be actually used, even if a relatively large refractive index difference (Δn) is used, in order to obtain a sufficient diffraction effect, it is necessary to form a grating having a large groove depth with respect to the grating pitch. I won't.

In particular, a grating having a depth equivalent to a pitch of 3 μm or less is optically effective, and the processing technology of such a size has to use the latest technology of semiconductor devices.

On the other hand, the problem of the operating characteristics is that the liquid crystal entered in such a deep groove is restrained by the upper and lower surfaces of the substrate and is restrained by the left and right wall surfaces of the lattice with an equal force or more.

Therefore, the long axes of the liquid crystal molecules are stably aligned in the groove direction, but on the contrary, a large resistance force is exerted when the liquid crystal molecules are changed into different alignment states by an external force.

This means that the initial orientation is not easily broken by the external force, that is, the electric field applied in the cell, and it is difficult to obtain the steep voltage transmittance characteristic (the threshold value characteristic) required for the time division characteristic. I mean.

As another technique, a DC voltage is conventionally applied to a liquid crystal cell to form a parallel optically anisotropic region having a uniform width with a voltage exceeding a threshold voltage, and the anisotropic region causes a diffraction phenomenon. It is known to show. This is'Optical computing with
variable grating motde liquid crytal devices'Proc.
It is shown in SPIE.1980.218 etc.

In the diffraction grating that causes the diffraction phenomenon, the grating pitch changes as the voltage changes, and the spectral characteristics of the diffracted light change accordingly.

This makes it difficult to maintain a constant diffraction condition, and at the same time, since it is an analog change, it is also disadvantageous to the threshold value characteristic described above.

(Problems to be Solved by the Invention) The present invention has high workability and productivity, has a large steepness of the alignment portion with respect to voltage application, and is suitable for time-division driving. It is an object of the present invention to provide a liquid crystal light modulator that can maintain the conditions, has an achromatic display color, and has less color unevenness.

(Means for Solving the Problems) At least two kinds of fine regions having different liquid crystal alignment ability are alternately arranged in a plurality of kinds of cycles on at least one of the two substrates holding the liquid crystal, and Is to form a diffraction grating and change the alignment state of the liquid crystal to change the diffraction state in which the incident light is diffracted to the transmission state in which the incident light is transmitted.

(Embodiment) FIG. 1 (A) shows different 2 which are arranged in a fine structure.
A plan view of the seed alignment region, here showing a conventional pattern.

FIG. 1 (B) is a sectional view showing a liquid crystal light modulator of one embodiment of the present invention, and shows a sectional structure taken along one-dot chain lines A1 and A2 in FIG. 1 (A).

In the figure (A), P0 represents the pitch of the alignment region, and
Reference numerals b and b indicate different alignment regions, for example, a is a homeotropic region and b is a homogeneous alignment region.

In FIG. 1B, 110 and 111 are transparent substrates made of glass or the like. 130 and 131 are transparent electrodes, 140 and 141 are treated surfaces showing a homogeneous alignment ability, 150 is a treated surface showing a homeotropic alignment ability, 160, 161, and 162 are liquid crystal molecules, and the direction of the director is a long ellipse, which is close to a circle (161). It shows the molecules in the direction perpendicular to the plane of the paper. 170 is a liquid crystal layer, 18
Is incident light and d is a cell gap.

A transparent substrate 110 having the alignment region shown in FIG.
As the upper substrate and the transparent substrate 111 as the lower substrate.
In this case, a homogeneous alignment treated surface 141 is provided on the entire surface on the liquid crystal layer 170 side.

When linearly polarized light (incident light 18) along the stripe direction of the upper substrate 110 is incident on the present liquid crystal light modulator, the extraordinary refractive index n _e is sensed in the homogeneous alignment region b and the ordinary refraction in the homeotropic alignment region. sensing the rate n _o. The heterologous incident light sensing ordinary refractive index n _e continues to sense the extraordinary refractive index n _e while rotating toward the lower substrate 111 in the thickness direction.

Meanwhile, light incident on the homeotropic region a proceeds toward the lower substrate 111 while sensing the ordinary refractive index n _o.

Therefore, there is a refractive index difference of n _e −n _o = Δn between the homogeneous and homeotropic regions and the respective alignment regions a and b, and a phase difference Δnd is produced by the product of the thickness d shown in FIG. Predetermined diffraction is obtained when the phase difference is held at the illustrated pitch P0.

FIGS. 2 (A), (B) and (C) are explanatory views showing pattern examples of the alignment region according to the present invention. The same figure (A),
In (B) and (C), a (and a with a subscript) and b
(And subscript b) respectively indicate different alignment regions. For example, a is homeotropic and b is homogeneous alignment region as shown in FIG.

FIG. 1A shows a conventional pattern example in which the alignment regions a and b are regularly arranged at the pitch P0. FIGS. 9B and 9C relate to the present invention and show an example in which a plurality of pattern pitches in the alignment region are provided.

In the same figure (B), the pitch is different between the alignment regions a and b and a1 and b1, and the combination of the alignment regions a and b and a1 and b1 is the same thereafter, and the repeating pitch is regularly arranged as Pc. are doing.

In the same figure (C), the pitch of the two alignment regions is P1, P2, P3, P4.
4 different species (increasing in order), each of which l1, l2,
In the example provided at intervals of l3 and l4, the orientation regions at that time are a and b, respectively.
And a1, b1 and a2, b2 and a3, b3.

FIGS. 3 (A), (B), and (C) are explanatory views showing the spectral transmission characteristics of the 0th-order light in the liquid crystal light modulator of the present invention.
The figures (A), (B), and (C) are obtained as a result of carrying out two numerical examples described later.

In FIGS. 9A, 9B and 9C, the vertical axis indicates the transmittance T.
And is shown on an arbitrary scale. The horizontal axis represents the wavelength, which is the visible region from 400 nm to 700 nm.

The solid line shows 0 when no voltage is applied between the transparent electrodes.
The spectral transmission characteristics of the next light are shown, and the dotted line shows the transmission state when a sufficient voltage is applied to a constant threshold voltage.

FIG. 2A shows the spectral transmission characteristics of the liquid crystal light modulator in which two different kinds of alignment regions shown in FIG. As is clear from the figure, the maximum diffraction occurs at a specific wavelength where the spectral transmittance becomes the lowest.

Therefore, in order to obtain sufficient diffraction, the light source used is limited to a light source near a specific wavelength, which is not preferable in a display application in which predetermined visibility is required for various lights.

FIGS. 9B and 9C show the spectral transmission characteristics of the liquid crystal optical modulator of the present invention. Unlike the case of FIG. 9A, the spectral transmission characteristics vary slightly depending on the operating wavelength of the light source. is there.

Therefore, the present liquid crystal light modulator has an advantage that a predetermined sufficient visibility can be obtained in various light environments (light sources).

The effective purpose of the present invention is to use the diffraction state when no voltage is applied and the transmission state when a voltage is applied as a display or an optical modulator.

Moreover, if the pitch of the diffraction grating and the width of the stripe pattern are always constant and can be manufactured with high precision, the display color exhibits a constant hue, but in reality, some errors occur, which are visually recognized as color unevenness.

However, in the present invention, since two different types of orientation regions are formed in stripes at a plurality of pitches instead of the diffraction grating, it suffices to perform surface patterning such as printing, resulting in high manufacturing accuracy and display color. Color unevenness can be minimized.

 Next, two numerical examples will be shown.

(Numerical Example 1) A transparent conductive film having a thickness of 300 Å to 500 Å, which has In ₂ O ₃ as a main component, is formed on a blue glass plate having a thickness of 1.1 mm and a size of 300 x 300 mm, and a thickness of 300 Å to 800 Å is formed on the transparent conductive film. Photoresist AZ-1350J (manufactured by Spree) on a substrate in which polyimide is sequentially laminated.
Alternatively, spin-coat a positive type resistor such as OFR-77 (manufactured by Tokyo Ohka Co., Ltd.) and heat at 80 ° C for 10 minutes.
In the pattern shown in, the pitch Pc is 4.5 μm, and four kinds of stripe widths are 0.3, 0.6, 1.2, and 2.4 μm, respectively.
Develop with a prescribed developer and dry, and then clean this surface with FS-116.
It was dip coated with a 0.5 wt% diflon solution and dried at 100 ° C. for 20 minutes. After that, the remaining photoresist portion is dissolved and removed together with FS-116 applied on the surface thereof using a stripping solution such as acetone or MEK, and is further heated and baked at 150 to 200 ° C. for 1 hour. The substrate thus obtained is rubbed in the stripe direction to form an upper substrate, the other surface is subjected to polyimide treatment, and the lower substrate rubbed in a direction orthogonal to the upper substrate is provided with a spacer so that the cell gap becomes 2.0 μm. Placed through the material. A nematic liquid crystal RO-TN403 (made by Roche) was filled between the upper and lower substrates, and the periphery was sealed to form a liquid crystal cell. The liquid crystal cell was diffracted without applying a voltage, and the diffraction was substantially extinguished at 2.6 V, and the liquid crystal cell was in a transmissive state. The spectral transmittance characteristic in the diffracted state at this time is shown in FIG.

(Numerical Example 2) The alignment region pattern shown in FIG. 2 (C) is formed with the same material configuration as that of Numerical Example 1. The pitches P1, P2, P3, P4 are 0.6 μm, 1.2 μm, 2.4 μm, and 4.8 μm, respectively, and each is formed with about 10 μm. A cell having a cell gap of 2 μm was prepared by giving orientation. The spectral transmittance characteristic of this cell when no voltage is applied is shown in FIG.

Next, for comparison, a conventional pattern shown in FIG. 2 (A) was formed with the same material configuration as in Numerical Example 1 with a pitch P0 of 2 μm, and the same liquid crystal cell was formed with a cell gap of 2 μm. The spectral transmittance characteristic of the 0th-order light at this time is shown in FIG.

Comparing the present configuration example with the two numerical embodiments of the present invention, the present liquid crystal cell having a pattern of equal pitch is the third one.
As is clear from FIG. 6A, at the wavelength that minimizes the spectral transmittance, the transmission characteristics are lower than those of the two numerical examples, but a strong blue color is exhibited. Further, the liquid crystal cell of the present invention showed purple color unevenness in the display color.

On the other hand, in the case of the liquid crystal cell of the present invention shown in FIGS. 3B and 3C, the minimum transmittance is slightly higher than that in the case of FIG. 3A, but it is achromatic as a whole, It had a slightly cloudy dark color. However, color unevenness was hardly visible.

(Effects of the Invention) According to the present invention, not the diffraction grating formed by the grating, but the alignment treatment regions are arranged in a finely arranged manner and a plurality of arrangement pitches are provided. Therefore, the processability, the productivity, and the reliability are high. Since the difference in the refractive index of the liquid crystal itself is used, even a small Δn value is effective, the prescribed optical characteristics can be obtained with a large cell gap, and steepness can be obtained at a low threshold voltage compared to the conventional method, so time-division driving It is suitable for large area processing and can be applied to multiple surfaces on a single substrate because it only requires surface patterning such as printing. In addition, an achromatic liquid crystal light modulator with less color unevenness is achieved. can do.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (A) and (B) are explanatory views showing an embodiment of the present invention, and FIGS. 2 (A), (B) and (C) are liquid crystal light modulations of the present invention. Explanatory drawing which shows the pattern example of the orientation area | region in a container, 3rd
(A), (B) and (C) are explanatory views showing the spectral transmission characteristics of the 0th order light in the liquid crystal light modulator of the present invention. In the figure, 110 and 111 are transparent substrates, 130 and 131 are transparent electrodes, and 140 and 14
1 is a homogeneous alignment treated surface, 150 is a homeotropic alignment treated surface, 160, 161, 162 are liquid crystal molecules, 170 is a liquid crystal layer,
18 is incident light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuro Takashi 770, Shimonoge, Takatsu-ku, Kawasaki City, Kanagawa Canon Inc. Tamagawa Plant (56) Reference JP-A-53-94955 (JP, A) JP-A-52- 21845 (JP, A) JP-A-56-38329 (JP, A)

Claims (1)

(57) [Claims] 1. A diffraction grating made of liquid crystal is formed by alternately arranging at least two kinds of fine regions having different liquid crystal aligning ability on at least one of the two substrates sandwiching the liquid crystal with a plurality of kinds of periods. Then, the liquid crystal light modulator is characterized in that by changing the alignment state of the liquid crystal, a diffractive state in which incident light is diffracted is changed to a transmissive state in which incident light is transmitted.