JPH03209431A - Space optical modulating element - Google Patents

Abstract

PURPOSE:To reduce the size of an optical system by sticking a polarizing plate to the substrate surface on the side where a photoconductive layer and a multilayered dielectric film mirror are not formed. CONSTITUTION:A light shielding layer 16 is provided on films 13a, 13b to prevent the incidence of projected light onto the photoconductive layer 15 and further, the dielectric mirror 17 laminated with 15 layers is laminated and formed. The substrates 11a, 11b are disposed in such a manner that the oriented film layers 13a, 13b thereof face each other. The spacing therebetween is controlled and formed via a spacer 19 consisting of an adhesive agent. Further, the polarizing plate 10 is stuck to the surface of the substrates 11a, 11b on the side where the photoconductive layer is not formed. Ferroelectric liquid crystal molecules are, therefore, put into the stable state in which the molecules are arrayed uniaxially when viewed from the substrates 11a, 11b by impressing a DC electric field between the transparent electrodes of the two substrates 11a, 11b from the outside. The optical system is miniaturized in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a liquid crystal spatial light modulator used in optical information processing, optical computing, machine vision, display terminals, and the like.

[Summary of the Invention] The present invention relates to a liquid crystal spatial light modulator used in optical information processing, optical computing, machine vision, display terminals, etc. layer and a dielectric multilayer mirror,
As a film for aligning liquid crystal molecules on both substrates, silicon monoxide was obliquely deposited at an angle of 750 to 85 degrees to the normal direction of the substrates, and the film was controlled to have a constant gap. In a liquid crystal element using a ferroelectric liquid crystal composition as the liquid crystal composition sealed in the gap, monochromatic light with a wavelength λ is used as the readout light of the liquid height spatial light modulator, and the ferroelectric liquid crystal layer is The gap d is controlled so that it satisfies the relationship d=a・λ/4・Δn (Δn is the refractive index anisotropy of the ferroelectric liquid crystal composition, and a is an integer) or is within ±10% of the relationship. Then, on the surface of the substrate on the side where the photoconductive layer and the dielectric multilayer mirror are not formed, the change axis of the polarizing plate and the direction of incidence of oblique evaporation form an angle of 22.5'±2.5'. By attaching a polarizing plate, the optical system can be made smaller and used in optical information processing, optical computing, machine vision,
This allows for application to systems such as display terminals.

[Prior Art] Conventionally, a spatial light modulation device using ferroelectric liquid crystal has a polarizer, an analyzer, a half mirror, a cube beam splinter, etc. arranged outside the device, and readout light is irradiated through the polarizer. A modulated image was obtained by reading out the reflected light through an analyzer.

[Problems to be Solved by the Invention] However, in the conventional method, a polarizer, an analyzer, a half mirror, a cube beam splinter, etc. are arranged in the optical system, so there is a problem that a large space is required for the optical system. there were.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides optical information processing,
Monochromatic light with a wavelength λ is used as the readout light of a ferroelectric liquid crystal spatial light modulator used in optical computing, machine vision, display terminals, etc., and the gap d between the ferroelectric liquid crystal layers is set as d=a・λ/ The photoconductive layer and the dielectric are On the substrate surface on the side where the multilayer film mirror is not formed, the change axis of the polarizing plate and the incident direction of oblique evaporation are set at 22.5
A polarizing plate was attached so as to form an angle of @±2.5@.

[Effect]

The angle between the two stable states corresponds to the cone angle of the ferroelectric liquid crystal, and the optical axis is 2 degrees from the oblique deposition direction of silicon monoxide.
It has an angle of 2.5° (45' between optical axes), and by attaching the polarizing plate so that the change axis of the polarizing plate and the incident direction of the oblique evaporation form an angle of 22.5 @. In one of the two stable states, the optical axis of the ferroelectric liquid crystal molecules and the polarizing plate's polarizing axis coincide, and in the other, the optical axis of the ferroelectric liquid crystal molecules and the polarizing plate's polarizing axis form an angle of 45''. Therefore, in a stable state where the optical axis of the ferroelectric liquid crystal molecules and the change axis of the polarizing plate coincide, the incident light is reflected by the ferroelectric liquid crystal layer without any modulation, resulting in a bright state. In addition, in a stable state where the optical axis of the ferroelectric liquid crystal molecules and the changing axis of the polarizing plate make an angle of 456, the incident light is modulated within the ferroelectric liquid crystal layer, and the phase difference φ
It comes out as =2π・Δn・2d/λ. At this time, φ=a
If π (a is an integer), the reflected light becomes linearly polarized light whose plane of polarization is rotated by 90 degrees, and is blocked by the attached polarizing plate, resulting in a dark state. That is, d=aλ/4Δn (a is an integer)
The maximum contrast is obtained when the condition is satisfied, and a certain degree of contrast can be obtained in the vicinity thereof.

[Example] The contents of the present invention will be explained in detail below using the drawings.

FIG. 1 is a conceptual diagram of a liquid crystal spatial light modulator according to the present invention. Transparent glass substrates were used as substrates 11a and 11b for sandwiching liquid crystal molecules. ITO on the surface of both substrates
Transparent electrode layers 12a and 12b were provided. Here, the ITO electrodes 12a and 12b may be made of tin antimony oxide or the like without any problem. Furthermore, the surface of both substrates is 85 @ from the normal direction of the substrates.
Alignment film layers 13a and 13b were provided in which silicon monoxide was obliquely vapor-deposited so that the incident angle and the direction of incidence on the write side and read side substrates coincided in the combined state. -Alignment film layers 13a and 13b in which silicon oxide is obliquely deposited
The incident angle from the normal direction of the substrate may be selected in the range of 75° to 85° in consideration of the characteristics. The a-5i:1 layer with a thickness of 2 μm was formed by discharging a gas mainly consisting of . Here, the amorphous silicon photoconductive layer 15 may have a film composition to which P, N, etc. are added during discharge decomposition, or may be a semiconductor film of other composition such as n-type or p-type on the a-5i:8 layer. There is no problem even if the structure is a stacked structure.

Furthermore, a light shielding layer 16 was provided on the film to prevent projection light from entering the photoconductive layer 15, and a dielectric mirror 17 in which a total of 15 layers of SiO□ and Si were alternately laminated was formed. Furthermore, the substrates 11a and llb have their alignment film layers 13a.
, 13b side facing each other, SiO□ with a diameter of 0.85 μm
A gap was controlled and formed through a spacer 19 made of an adhesive to which balls were added, and the gap d that was formed to sandwich the ferroelectric liquid crystal layer 14 was about 0.9 μm. 5CE-6 (manufactured by BDH) was used as the encapsulated ferroelectric liquid crystal composition. Its refractive index anisotropy Δn was 0.18. Further, a polarizing plate was attached to the surface of the substrate on the side on which the photoconductive layer was not formed so that the change axis of the polarizing plate and the incident direction of oblique evaporation formed an angle of 22.5 @.

The above-described ferroelectric liquid crystal spatial light modulator is brought into a stable state in which the ferroelectric liquid crystal molecules are uniaxially aligned when viewed from the substrate surface by applying a direct current electric field between the transparent electrodes of both substrates from the outside. Furthermore, by reversing the polarity of the applied electric field, a stable state is achieved in which the other ferroelectric liquid crystal molecules are uniaxially aligned when viewed from the substrate surface. This reversal between the two states due to the electric field has nonlinearity and a clear threshold with respect to the electric field applied to the ferroelectric liquid crystal layer. The applied electric field may be one in which alternating current is superimposed on direct current.

The angle between the two stable states corresponds to the cone angle of the ferroelectric liquid crystal, and in this example, the optical axes are each at an angle of 22.5' (45° between the optical axes) from the oblique deposition direction of silicon monoxide. It had The change axis of the polarizing plate and the incident direction of oblique evaporation are 2.
By pasting the polarizing plates so as to form an angle of 2.5', one of the two stable states is where the optical axis of the ferroelectric liquid crystal molecules and the changing axis of the polarizing plate coincide, and the other is when the ferroelectric liquid crystal molecules are in a stable state. The optical axis of the liquid crystal molecules and the polarizing axis of the polarizer have an angle of 45''.

Therefore, in a stable state where the optical axis of the ferroelectric liquid crystal molecules and the change axis of the polarizing plate coincide, the incident light is reflected by the ferroelectric liquid crystal layer without any modulation, resulting in a bright state. In addition, in a stable state where the optical axis of the ferroelectric liquid crystal molecules and the changing axis of the polarizing plate make an angle of 456, the incident light is modulated within the ferroelectric liquid crystal layer, and the phase difference φ=2π・Δn・2d/λ Come out (ru).

At this time, if φ=aπ (a is an integer), the reflected light becomes linearly polarized light whose plane of polarization has been rotated by 90″, and is blocked by the attached polarizing plate, resulting in a dark state. That is, d=aλ/4Δ
The maximum contrast is obtained when n (a is an integer) is satisfied, and a certain degree of contrast can be obtained in the vicinity thereof. However, the gap d must be smaller than the inherent pitch of the ferroelectric liquid crystal material, and a value of a that satisfies this condition must be selected. In the ferroelectric liquid crystal composition used in this example, Δn=0°18, and the readout light was H
Since it is an e-Ne laser (λ-6328 people), a=
1 and set the gap d to 0.88 μm to make φ−π.
It was set nearby. The actual gap d was approximately 0.9 μm.

Note that the angle between the oblique deposition direction and the changing axis of the polarizing plate can be set in accordance with the cone angle of the ferroelectric liquid crystal so that the optical axis in one stable state and the changing axis coincide. The contrast decreases as the angle deviates from 45°. In this example, the cone angle was approximately 45°, so good contrast was exhibited.

According to the ferroelectric liquid crystal spatial light modulator as described above, due to the bistability of the ferroelectric liquid crystal element, after erasing by applying an erasing electric field, the voltage divided across the liquid crystal layer in the opposite direction to the erasing electric field is While applying an electric field that is below the threshold value when the photoconductive layer is dark and above the dark value when the photoconductive layer is dark, an optical image is irradiated with writing light 20 from the outer surface of the cell, or a polygon mirror or galvano mirror is modulated while a semiconductor laser is modulated. By performing scanning using the ferroelectric liquid crystal layer 14, the liquid crystal molecules are inverted only in the areas irradiated with light, and this is maintained stably, making it possible to write and form images on the ferroelectric liquid crystal layer 14. did it. Further, the image formed by writing can be read out by irradiation with the projection light 21.

The applied voltage may be a direct current with an alternating current waveform superimposed thereon. Further, while applying an electric field in a direction opposite to the direction of the electric field during writing, such that the voltage divided across the liquid crystal layer is below the threshold value when the photoconductive layer is dark and is above the dark value when the photoconductive layer is turned off, the semiconductor laser By scanning using a polygon mirror or galvano mirror while modulating the ferroelectric liquid crystal layer, the liquid crystal molecules are inverted only in the part of the ferroelectric liquid crystal layer that is irradiated with the laser beam, and this is maintained stably. , I was also able to erase parts of the image.

Figure 2 shows a readout optical system when using a conventional ferroelectric liquid crystal spatial light modulator, and Figure 3 shows a readout optical system when a ferroelectric spatial light modulator according to the present invention is used. show.

In FIG. 2, after the readout light 21 passes through the analyzer 22,
It is reflected by the half mirror 23 (or beam splinter), enters the ferroelectric liquid crystal element 24, is modulated by the element, is reflected, passes through the half mirror 23 and the analyzer 25, and is read out as an image. In FIG. 3, by using the ferroelectric liquid crystal spatial light modulator 26 according to the present invention,
It can be seen that there is no need to arrange an external polarizer, half mirror, or cube beam splitter-1 analyzer, making it possible to downsize the optical system.

[Effects of the Invention] As described above, by using the ferroelectric liquid crystal spatial light modulator according to the present invention, optical systems can be miniaturized, and systems such as optical information processing, optical computing, machine vision, and display terminals can be used. It can be easily applied to

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of a ferroelectric liquid crystal spatial light modulator according to the present invention, and FIG. 2 is a readout optical system when using a conventional ferroelectric liquid crystal spatial light modulator. The schematic diagram in FIG. 3 is a schematic diagram showing a readout optical system when using the ferroelectric liquid crystal spatial light modulator according to the present invention. 10...Polarizing plate 11a, llb...Transparent substrate 12a, 12b...Transparent electrode 13a, 13b...-Alignment film 14...Ferroelectric liquid crystal layer 15...Photoconductive film 16... Light shielding film 17 ・ ・ 19 ・ ・ 20 ・ ・ 21 ・ ・ 22 ・ ・ 23 ・ 24 ・ ・ 25 ・ ・ 26 ・ ・ ・Dielectric mirror・Spacer Writing light・Reading light polarizer・Half mirror ・Conventional ferroelectric Liquid crystal spatial light modulator, analyzer, ferroelectric liquid crystal spatial light modulator according to the present invention or more

Claims (2)

[Claims] (1) A photoconductive layer and a dielectric multilayer film mirror are provided on one electrode between a pair of substrates having electrodes, and the film serves as a film for orienting liquid crystal molecules on both substrates.
Silicon monoxide is obliquely deposited at an angle in the range of 5° to 85°, and these are controlled to have a certain gap and are faced to each other.
In a liquid crystal element using a ferroelectric liquid crystal composition as the liquid crystal composition sealed in the gap, a polarizing plate is attached to the outer surface of the substrate on the side on which the photoconductive layer and the dielectric multilayer mirror are not formed. Liquid crystal spatial light modulator. (2) Monochromatic light with a wavelength λ is used as the readout light of the liquid crystal spatial light modulator, and the gap d between the ferroelectric liquid crystal layers is d=a・λ/
4・Δn (Δn is the refractive index anisotropy of the ferroelectric liquid crystal composition,
a is an integer) or its vicinity ±10
%, and the change axis of the attached polarizing plate and the incident direction of the oblique vapor deposition are set to form an angle of 22.5°±2.5°. element.