JPH06175098A - Spatial light modulation element and its driving method - Google Patents

Abstract

PURPOSE:To provide the spatial light modulation element which does not require photoconductive film, has a high resolution and is inexpensive and its driving method. CONSTITUTION:After liquid crystal oriented films 3 and 3' are formed on transparent substrates 1 and 1' consisting of glass, etc., having transparent electrodes 2 and 2' consisting of ITO, etc., a gap is formed via spacers and a discotic liquid crystal 4 contg. liquid crystal molecules having spiropyrane groups is packed into this gap. Information is written on the spatial light modulation element 5 by impressing of a voltage and irradiating with writing light 6 which is UV light and the information is read out by reading out light 7 which is visible light. The information is erased by erasing light 8 which is visible light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator capable of spatially modulating light in parallel and applicable to optical calculation and image recognition, and a driving method thereof.

[0002]

2. Description of the Related Art As information processing technology capable of high-speed and large-capacity processing, there is information processing using light, and an optical modulator plays a central role in optical calculation. In particular, a spatial light modulator is required to process two-dimensional information such as an image in parallel. Currently proposed spatial light modulators include acousto-optic modulators and electro-optic modulators, but the most actively studied are spatial light modulators using liquid crystals.

As a structure of a conventional spatial light modulator using a liquid crystal, the alignment state of the liquid crystal is twisted nematic (Ap
plied Optics, vol.26, p.241, 1987) or super twisted nematic (Technical report of IEICE, Vol.90, No.431, p.23, 1990), or has memory function Using a ferroelectric liquid crystal (Japanese Patent Application Laid-Open No. 2-
289827) is known.

As a conventional example, FIG. 3 shows the structure of a spatial light modulator using a ferroelectric liquid crystal. In FIG. 3, 11 and 11 'are transparent substrates, 12 and 12' are transparent electrodes, 13 and 13 'are liquid crystal alignment films, 14 is a ferroelectric liquid crystal, 19 is a photoconductive film, 20 is a dielectric mirror, and 16 is Writing light, 17
Is the reading light. In the structure of FIG. 3, hydrogenated amorphous silicon (a-Si: H) is used as the photoconductive film 19.
Is used for the ferroelectric liquid crystal 1 via the dielectric mirror 20.
4 is filled.

In the portion irradiated with the writing light 16, the specific resistance of the photoconductive film 19 is lowered and the voltage applied to the ferroelectric liquid crystal 14 is increased to exceed the threshold voltage of the liquid crystal. The array state of changes. Therefore, the plane of polarization of the linearly polarized read light 17 rotates. On the other hand, in the portion where the writing light 16 is not irradiated, the alignment state of the ferroelectric liquid crystal 14 does not change, so that the polarization plane of the reading light 17 does not rotate. Therefore, a pattern corresponding to the write pattern can be read by reading through a detector (not shown).

[0006]

However, in the above-mentioned conventional spatial light modulator using liquid crystal, it is necessary to interpose a photoconductive film in order to write light into the liquid crystal layer. That is, in the conventional spatial light modulator using the liquid crystal, the alignment state of the liquid crystal could not be changed by direct light. Therefore, the resolution of the read pattern after modulation is limited by the photoconductive film,
The high resolution that liquid crystals originally have has not been fully demonstrated. In addition, the necessity of the photoconductive film not only requires the film forming step in the device manufacturing process but also causes the cost to increase.

The present invention eliminates the need for the photoconductive film required for writing in the liquid crystal layer in the spatial light modulator,
An object of the present invention is to provide a spatial light modulator capable of increasing the resolution of a read-out pattern after modulation and reducing the manufacturing process of the element, and a driving method thereof.

[0008]

In order to solve the above-mentioned problems, in the present invention, liquid crystal alignment films are arranged on two transparent substrates having transparent electrodes and face each other, and a liquid crystal is filled in a gap between both liquid crystal alignment films. In the above spatial light modulator, the liquid crystal is a spatial light modulator which is a discotic liquid crystal containing liquid crystal molecules having a photochromic group.

Further, in the above spatial light modulator, the photochromic group is a spiropyran group.

In the above spatial light modulation element, a method of driving the spatial light modulation element in which the arrangement state of the discotic liquid crystal is changed by applying a voltage to the transparent electrode and irradiating with light.

[0011]

According to the present invention, since the discotic liquid crystal composed of liquid crystal molecules having a photochromic group is used in the spatial light modulator, when light is irradiated while applying a voltage to the spatial light modulator, the liquid crystal molecules are The structural change of the photochromic group of (2) triggers the change of the alignment state of the liquid crystal.

When a discotic liquid crystal composed of liquid crystal molecules having a spiropyran group as a photochromic group is used, when the spatial light modulator is irradiated with ultraviolet rays, the structure of the spiropyran group is changed, thereby changing the alignment state of the discotic liquid crystal. be able to. Then, in this state, if the light having a wavelength that does not affect the structural change of the spiropyran group is transmitted through the spatial light modulator, the modulated light can be obtained by utilizing the birefringence of the liquid crystal.

Therefore, according to the present invention, in writing to the liquid crystal layer by the writing light in the spatial light modulator, direct writing can be performed without passing through the photoconductive film, so that the read pattern after modulation can be made high. Resolution can be increased.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a spatial light modulator according to an embodiment of the present invention. After forming the liquid crystal alignment films 3 and 3 ′ on the transparent substrates 1 and 1 ′ having the transparent electrodes 2 and 2 ′, a gap is formed between them through a spacer (not shown), and liquid crystal molecules having a photochromic group are formed in the gaps. A spatial light modulator 5 was prepared by filling the discotic liquid crystal 4 containing the liquid crystal. In this example, a glass substrate was used as the transparent substrate and an ITO thin film was used as the transparent electrode.

As the discotic liquid crystal, liquid crystal molecules having the structure shown in the following molecular structure formula 1 were used.

[0017]

[Chemical 1]

In the above molecular structural formula, SP is a spiropyran group,

[0019]

[Chemical 2]

And LC is

[0021]

[Chemical 3]

Is shown.

That is, the discotic liquid crystal used in this example contains liquid crystal molecules having a spiropyran group as a photochromic group. Further, this liquid crystal compound can be synthesized by a hydrosilylation reaction with a combination of cyclic (pentamethylhydro) cycloxane, cyanobiphenyl- (allyloxy) benzoate, and nitrobenzospiropyran mesogen.

In the case of the liquid crystal molecule forming the above discotic liquid crystal, spiropyran groups were introduced at three positions, but the present invention is not limited to this.

Next, an operation experiment of the spatial light modulator of this embodiment will be described with reference to FIG. The measurement system irradiates the spatial light modulation element 5 produced as described above with the writing light 6 while applying a voltage to perform writing, irradiates the linearly polarized reading light 7 and transmits the spatial light modulation element 5, A detector (not shown) detects the optical rotation.
In this embodiment, the writing light 6 is the ultraviolet light of 366 nm obtained by passing the light from the mercury lamp through the filter.
A He—Ne laser with a wavelength of 633 nm that does not affect the structural change of the spiropyran group was used as the reading light 7.
Further, in order to restore the changed alignment state of the discotic liquid crystal, an Ar excitation dye laser having a wavelength of 580 nm that returns the structure of the spiropyran group to the initial state was used as the erasing light 8.

FIG. 2 shows the results obtained by alternately irradiating the spatial light modulator 5 with the writing light 6 and the erasing light 8 and measuring the optical rotation of the modulated reading light 7. In FIG. 2, ultraviolet light is light of 366 nm obtained from a mercury lamp, that is, writing light, and visible light is Ar excited dye laser light of erase light of 580 nm, that is, erase light. From this result, the value of the optical rotation of the read light after the modulation is high when the ultraviolet light is irradiated, and is low when the visible light is irradiated. This is because when ultraviolet rays are applied while applying a voltage to the spatial light modulator 5, structural change of the spiropyran group of the liquid crystal molecule is a trigger,
It is shown that the change of the alignment state of the discotic liquid crystal can be induced and the initial alignment state can be returned by the irradiation of visible light.

As described above, the spatial light modulator of the present embodiment can write information by applying a voltage and irradiating 366 nm light, reading information by 633 nm light and 580 nm light. Clearly, information can be erased.

In this embodiment, the spiropyran group was used as the photochromic group, but the photochromic group is not limited to this, and a photochromic group such as an azobenzene group or a diarylethene group may be used. Further, in the present embodiment, the liquid crystal molecule represented by the molecular structural formula 1 was used as the liquid crystal molecule having a photochromic group, but the liquid crystal molecule is not limited to this, and it has a photochromic group such as a spiropyran group, Any liquid crystal molecule that forms an array of liquid crystals may be used.

[0029]

As described above, according to the present invention, by using a discotic liquid crystal containing liquid crystal molecules having a photochromic group in a spatial light modulator, it is possible to write by light without using a photoconductive film. Therefore, it is possible to increase the resolution of the read pattern after modulation. In addition, not requiring a photoconductive film not only enables high-resolution reading, but also eliminates the photoconductive film manufacturing process in the device manufacturing process, which can reduce the manufacturing cost. Becomes

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a spatial light modulator according to an embodiment of the present invention.

FIG. 2 is a graph showing the results of measuring the optical rotation of the spatial light modulator according to the present invention.

FIG. 3 is a sectional view showing a structure of a conventional spatial light modulator.

[Explanation of symbols]

 1, 1 ', 11, 11' Transparent substrate 2, 2 ', 12, 12' Transparent electrode 3, 3 ', 13, 13' Liquid crystal alignment film 4 Discotic liquid crystal 5 Spatial light modulator 6, 16 Writing light 7, 17 Read light

Claims (3)

[Claims] 1. A spatial light modulator in which a liquid crystal alignment film is disposed on two transparent substrates having transparent electrodes, and the liquid crystal alignment films are opposed to each other and a liquid crystal is filled in a gap between both liquid crystal alignment films, wherein the liquid crystal has a photochromic group. A spatial light modulator which is a discotic liquid crystal containing molecules. 2. The spatial light modulation element according to claim 1, wherein the photochromic group is a spiropyran group. 3. The spatial light modulator according to claim 1 or 2, wherein the arrangement state of the discotic liquid crystal is changed by applying a voltage to the transparent electrode and irradiating light. Driving method of spatial light modulator.