JP2939072B2 - Spatial light modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, can modulate the light in parallel spatially, but about the applicable spatial light modulation element to the optical operation or an image recognition.

[0002]

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

As a structure of a conventional spatial light modulator using a liquid crystal, a twisted nematic (Ap.
plied Optics, vol.26, p.241, 1987) or Super Twisted Nematic (IEICE Technical Report, Vol.90, No.431, p.23, 1990), or has a memory function Using ferroelectric liquid crystal (Japanese Unexamined Patent Publication No.
No. 289827).

FIG. 3 shows a structure of a spatial light modulator using a ferroelectric liquid crystal as a conventional example. 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 a dielectric mirror. Writing light, 17
Is a reading light. In the structure of FIG. 3, hydrogenated amorphous silicon (a-Si: H) is used as the photoconductive film 19.
Is used, and the ferroelectric liquid crystal 1 is passed through the dielectric mirror 20.
4 are filled.

In the portion irradiated with the writing light 16, the specific resistance of the photoconductive film 19 decreases, the voltage applied to the ferroelectric liquid crystal 14 increases, and exceeds the threshold voltage of the liquid crystal. Changes the state of the array. For this reason, the plane of polarization of the linearly polarized readout light 17 rotates. On the other hand, in the portion where the writing light 16 has not been irradiated, the arrangement state of the ferroelectric liquid crystal 14 does not change, so that the polarization plane of the reading light 17 does not rotate. Therefore, by reading through a detector (not shown), a pattern corresponding to the write pattern can be read.

[0006]

However, in the spatial light modulator using a liquid crystal in the above-mentioned prior art, writing to the liquid crystal layer by light had to be performed through a photoconductive film. That is, in the conventional spatial light modulator using liquid crystal, the arrangement 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 inherent to liquid crystals has not been sufficiently exhibited. Further, the necessity of a photoconductive film not only requires a film forming step in a device manufacturing process, but also causes an increase in cost.

According to the present invention, in a spatial light modulator, a photoconductive film required for writing to a liquid crystal layer is not required, thereby enabling a high-resolution read pattern after modulation and a reduction in the process of manufacturing the device. and to provide a spatial light modulator element capable.

[0008]

In order to solve the above-mentioned problems, in the present invention, a liquid crystal alignment film is disposed on two transparent substrates having transparent electrodes so as to face each other , and a liquid crystal is filled in a gap between the two liquid crystal alignment films. In the filled spatial light modulator, the liquid crystal is :
Multiple photochromic groups and liquid crystal molecules on the side chain
The spatial light modulator is a discotic liquid crystal.

[0009]

[0010]

[0011]

According to the present invention, in the spatial light modulator, discotic liquid crystal composed of liquid crystal molecules having a photochromic group is employed. The change in the structure of the photochromic group serves as a trigger to induce a change in the alignment state of the liquid crystal.

When a discotic liquid crystal composed of liquid crystal molecules having a spiropyran group is used as a photochromic group, the structure of the spiropyran group changes when the spatial light modulator is irradiated with ultraviolet rays, thereby changing the arrangement state of the discotic liquid crystal. be able to. Then, in this state, if light having a wavelength that does not affect the structural change of the spiropyran group is transmitted through the spatial light modulator, 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, writing can be performed by direct light without passing through the photoconductive film, so that the height of the read pattern after modulation is high. It is possible to increase the resolution.

[0014]

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 the liquid crystal alignment films 3 and 3 'are formed on the transparent substrates 1 and 1' having the transparent electrodes 2 and 2 ', a gap is formed therebetween through a spacer (not shown), and liquid crystal molecules having a photochromic group are formed in the gap. The discotic liquid crystal 4 containing the liquid crystal was filled to produce a spatial light modulator 5. In this embodiment, a glass substrate was used as a transparent substrate, and an ITO thin film was used as a transparent electrode.

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

[0017]

Embedded image

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

[0019]

Embedded image

And LC is:

[0021]

Embedded image

Is shown.

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

In the case of the liquid crystal molecules forming the discotic liquid crystal, spiropyran groups are 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 manufactured as described above with the writing light 6 while applying a voltage, performs writing, irradiates the linearly polarized reading light 7 and transmits through the spatial light modulation element 5, The optical rotation is detected by a detector (not shown).
In this embodiment, the writing light 6 is ultraviolet light having a wavelength of 366 nm obtained by passing light from a mercury lamp through a filter.
As the reading light 7, a He-Ne laser having a wavelength of 633 nm, which does not affect the structural change of the spiropyran group, was used.
In addition, in order to restore the changed arrangement state of the discotic liquid crystal, an Ar-excited dye laser having a wavelength of 580 nm for returning the structure of the spiropyran group to the initial state was used as the erasing light 8.

FIG. 2 shows the results obtained by irradiating the spatial light modulator 5 with the writing light 6 and the erasing light 8 alternately and measuring the optical rotation of the read light 7 after modulation. In FIG. 2, ultraviolet light is light at 366 nm obtained from a mercury lamp, ie, writing light, and visible light is Ar excitation dye laser light at 580 nm of erasing light, ie, erasing light. From this result, the value of the optical rotation of the readout light after the modulation is higher when irradiating ultraviolet light, and lower when irradiating visible light. This is because when ultraviolet irradiation is performed while applying a voltage to the spatial light modulation element 5, a structural change of a spiropyran group of a liquid crystal molecule becomes a trigger,
This indicates that a change in the alignment state of the discotic liquid crystal can be induced, and the alignment state can be returned to the initial state by irradiation with visible light.

As described above, the spatial light modulator of this embodiment can write information by applying a voltage and irradiating it with 366 nm light, reading information with 633 nm light, and using 580 nm light. It is clear that information can be erased.

In this embodiment, a spiropyran group is used as a photochromic group. However, the present invention is not limited to this, and a photochromic group such as an azobenzene group and a diarylethene group may be used. In this example, the liquid crystal molecules having a photochromic group were the liquid crystal molecules represented by the molecular structural formula 1. However, the present invention is not limited to this, and the liquid crystal molecules having a photochromic group such as a spiropyran group may be used. Any liquid crystal molecules that form a liquid crystal array may be used.

[0029]

As described above, according to the present invention, in the spatial light modulator , a plurality of photochromic groups are provided on the side chain.
By using the discotic liquid crystal having liquid crystal molecules Rabbi, without passing through the photoconductive film, since it is writing with light, thereby enabling high resolution of the readout pattern after modulation. In addition, the fact that a photoconductive film is not required means that high-resolution reading can be performed, and also that a photoconductive film is not required in the element manufacturing process, thereby reducing manufacturing costs. Becomes Furthermore, multiple photochromic groups are linked to the side chain.
Because the combined discotic liquid crystal is used,
The sensitivity of the modulation element can be improved.

[Brief description of the drawings]

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

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

FIG. 3 is a sectional view showing the 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 modulation element 6, 16 Writing light 7, 17 Readout light

Claims (1)

(57) [Claims] 1. A liquid crystal alignment film is arranged opposite to each other with the two transparent substrates having transparent electrode, in the spatial light modulator filled with liquid crystal in the gap between the two liquid crystal alignment film, the liquid crystal is, the side chain A spatial light modulation device, which is a discotic liquid crystal having a plurality of photochromic groups and liquid crystal molecules.