JPH04178616A - Optical phase modulator - Google Patents

Abstract

PURPOSE:To obtain bright and fine reproduction by using a liquid crystal light valve which has a liquid crystal layer operating with a voltage control double refraction mode, a dielectric mirror and a photoconductor layer and provides a light source for projecting two-dimensional images for the purpose of recording phase distributions on the photoconductor layer side. CONSTITUTION:A laser beam is two-dimensionally scanned from a laser beam source 101 in accordance with the signal from a signal generator 100 and the phase patterns are recorded in the liquid crystal light valve 102. On the other hand, the beam emitted from a laser light source 107 for reproduction is collimated by a collimating lens 106 to collimated beams of light which are made incident on a half mirror 103. The beam reflected by the half mirror is made incident perpendicularly on the liquid crystal light valve 102 and is subjected to phase modulation by the previously recorded phase patterns. The beam reflected there is again made incident on the half mirror and the beam transmitted therethrough is emitted by a Fourier transform lens 104 to output desired patterns onto an output surface 105.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information processing device using a liquid crystal light valve.

[Prior Art] Conventionally, there has been an optical phase modulation device using a liquid crystal light valve, such as APPLIED 0PTIC3/Vo1.
28 N.

, 22 (1989) 4845. The conventional optical phase modulator, whose configuration is shown in FIG. 6, uses a transmissive liquid crystal light valve and is driven by simple matrix electrodes or active elements. The operating mode of liquid crystal is voltage-controlled birefringence (
Electrically controlled B
(hereinafter referred to as ECE) is used. However, in the conventional technology, the number of samples of the recorded phase pattern is limited by the size of the pixels of the drive electrode, and the reproduced image is not clear. Furthermore, in a simple matrix, the quantization number of samples can only take two values,
Since the aperture ratio of the active element is low, it has not been possible to effectively utilize the liquid crystal light valve, which is the recording surface.

To solve these problems, APPLIED OP
TIC3/Vo1.26 No. 5 (1987) 929
(As shown in D, a method has been proposed in which the liquid crystal light valve is of an optical writing type and the phase distribution is recorded using a laser or the like.

[Problems to be Solved by the Invention] However, the conventional optical phase modulation device using an optically written liquid crystal light valve is
d Nematic) mode, apply iif
The phase change with respect to pressure was less than π. In addition, the phase change could only take two values due to 0N10FF of the writing light, and only an unclear reproduced image was obtained due to the roughness of the sample approximation.

The present invention is intended to solve these problems, and its purpose is to realize an optical phase modulation device that can obtain a clear and precise reproduced image by using an ECB mode optical writing type liquid crystal light valve. It is something.

[Means for Solving the Problems] The optical phase modulation device of the present invention has the following features: (1) In the optical phase modulation device using a liquid crystal light valve, the liquid crystal light valve is a liquid crystal that operates in a voltage-controlled birefringence mode. layer, a dielectric mirror, and a photoconductor layer, on the photoconductor layer side of the liquid crystal light valve;
It is characterized by being equipped with a two-dimensional image projection light source for recording phase distribution.

(2) The II crystal prite valve is characterized in that a phase plate is disposed between the liquid crystal layer and the dielectric mirror.

[Example 1] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a configuration diagram in which an optical phase modulation device of the present invention is added with an optical system for reproduction.

Laser light source 10 based on the signal from signal generator 100
A laser beam is two-dimensionally scanned from 1, and a phase pattern is recorded on the liquid crystal light valve 102. On the other hand, the beam emitted from the laser light source 107 for reproduction is turned into parallel light by the collimating lens unit 06, and the beam is turned into parallel light by the half mirror 1.
03. At this time, the beam is linearly polarized. The beam reflected by the half mirror enters the liquid crystal light valve 102 perpendicularly and is phase modulated by the previously recorded phase pattern. The beam reflected here enters the half mirror again, and the transmitted beam is outputted onto the output surface 105 by the Fourier transform lens 104 in a desired pattern.

FIG. 5 shows the relationship between the phase change obtained from the liquid crystal light valve 102 in ECB mode and the applied voltage.

This liquid crystal light valve has a liquid crystal layer with homocyanous alignment. That is, the orientation of liquid crystal molecules is horizontal to the substrate. Since the phase change Δnd of the liquid crystal can be set arbitrarily, a phase change of 2π or more can be continuously obtained depending on the applied voltage.

The optical phase modulation device obtained as described above was able to perform predetermined phase modulation on a laser beam by using the phase modulation effect of the ECB mode liquid crystal light valve. The reproduced image was clear and precise because the number of quantized samples was increased due to a phase change of 2π or more, and the samples were arranged in a high density.

Example 2 In this example, a CRT was used as a two-dimensional image projection light source used to record a phase pattern. FIG. 4 shows a configuration diagram of the optical phase modulation device of the present invention and the optical system for reproduction.

Light emitted from the CRT 400 based on the signal from the signal generator 100 passes through a lens 401 and is projected onto the liquid crystal light valve 102, where a phase pattern is recorded. on the other hand,
A beam emitted from a laser light source 107 for reproduction is turned into parallel light by a collimating lens 106 and enters a half mirror 103. At this time, the beam is linearly polarized. The beam reflected by the half mirror enters the liquid crystal light valve 102 perpendicularly and is phase modulated by the previously recorded phase pattern. The beam reflected here enters the half mirror again, and the transmitted beam is outputted onto the output surface 105 by the Fourier transform lens 104 in a desired pattern.

The relationship between the phase change obtained in the liquid crystal light valve and the applied voltage is the same as in Example 1, and a phase change of 2π or more can be continuously obtained depending on the LFj force and zero voltage.

The optical phase modulation device obtained as described above can perform a predetermined phase modulation on the laser beam by using the phase modulation effect of the ECB mode liquid crystal light valve, and as in Example 1, The reproduced image is clear and M M
It was i.

<Embodiment 3> FIG. 2 is a block diagram of an optical phase modulation device of the present invention.

Laser light source 10 based on the signal from signal generator 100
A laser beam is scanned from 1 to 20, and the liquid crystal light valve 20
A phase pattern is recorded at 0.

On the other hand, the beam emitted from the laser light source 07 for reproduction becomes parallel light by the collimating lens 106 and enters the polarizing beam splitter 201. At this time, the beam is linearly polarized light perpendicular to the plane of the paper, and the planes of polarization are aligned so that it is reflected by the polarizing beam splitter. The beam enters the liquid crystal light valve perpendicularly and is phase modulated by the previously recorded phase pattern. When the modulated beam is reflected by the liquid crystal light valve, it passes through a phase plate, and the plane of polarization is rotated by 90 degrees to become polarized light parallel to the plane of the paper, which then enters the polarizing beam splitter. This beam passes through the polarizing beam splitter as it is, and outputs a desired pattern onto the output surface 105 by the Fourier transform lens 104.

FIG. 3 is a sectional view of a liquid crystal light valve in the optical phase modulation device of the present invention. In the figure, 1 is a glass substrate, 2
3 is a transparent electrode, 3 is a photoconductor layer, and 4 is a dielectric mirror. Further, 5 is a phase plate, 6 is a liquid crystal alignment film, and 7 is a liquid crystal layer.

The phase plate of this example is obtained by diagonally depositing Ta205 on a dielectric mirror using Method I described in Optics Vol. 19, p. 93. This phase plate utilizes the polarization characteristics of a diffraction grating, and the obliquely deposited film has the function of a phase type diffraction grating.

Explain that the plane of polarization rotates in a liquid crystal light valve. When a laser beam with the alignment direction of the liquid crystal and the polarization direction aligned is incident on the liquid crystal light valve obtained as above,
After the laser beam is phase-modulated in the liquid crystal layer, it becomes circularly polarized light by the action of the phase plate and is reflected by the dielectric and body mirrors. From here, the beam passes through the phase plate again and becomes linearly polarized light rotated by 90° with respect to the polarization direction at the time of incidence. This beam passes through the liquid crystal layer as it is.6 In this example, a Ta205 layer was used as a phase plate, but a diffraction grating with a polarizing function can be used in the same way. In that case, the pitch of the grating must be less than or equal to the wavelength of the laser beam.

Furthermore, although Ta2's is used in this embodiment, any material may be used as long as it is substantially transparent in the wavelength range of the laser beam used and functions as a phase plate.

Furthermore, the obliquely deposited film can be used as a liquid crystal alignment film, and in that case, there is no need to provide a liquid crystal alignment film.

The relationship between the phase change and the applied voltage is as shown in FIG. 5, and as in the first embodiment, a continuous phase change of 2π or more can be obtained.

The optical phase modulator r obtained as follows is the ECB
A predetermined phase modulation of the laser beam could be performed using the phase modulation effect of the mode liquid crystal light valve, and as in Example 1, the reproduced image was clear and precise. Further, unlike Examples 1 and 2, a polarizing beam splitter was used to prevent loss of the laser beam, so a good reproduced image was obtained at the output.

[Effects of the Invention] As described above, according to the present invention, the phase pattern recorded on the liquid crystal light valve is not limited by an electrode mask or the like, so sampling can be made close to the recording beam diameter. , can be arranged in high density. Furthermore, since the ECB mode is used, a phase change of 2π or more can be continuously obtained depending on the applied voltage. This has the effect of increasing the quantization number of the sample and obtaining a high contrast ratio and sufficient gradation. These effects are further enhanced by the fact that the liquid crystal light valve is of a reflective type for optical writing, which doubles the optical path length and provides high contrast. Therefore, clear and high-definition reproduction can be performed.

Further, according to the present invention, the optical system can be made compact by using a half mirror or a polarizing beam splitter.

According to the liquid crystal light valve of the present invention, an optical system without light loss can be configured using a polarizing heam splitter. This can be applied not only to recording the phase pattern according to the present invention but also to processing general image information, etc., and can realize a reflective optical system that is compact and easy to design.

In this embodiment, a laser beam and a CRT are used as light sources for recording the phase pattern, but real-time processing is also possible by recording on these liquid crystal light valves at high speed. Therefore, it can be applied to optical correlators, optical computers, optical interconnections, etc.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical phase modulation device in Example 1 of the present invention. FIG. 2 is a configuration diagram of an optical phase modulation device according to a third embodiment of the present invention. FIG. 3 is a sectional view of a liquid crystal light valve of an optical phase modulation device according to a third embodiment of the present invention. The fourth example is a configuration diagram of an optical phase modulation device according to a second embodiment of the present invention. FIG. 5 is a diagram for explaining the phase modulation characteristics of the liquid crystal light valve of the optical phase modulation device of the present invention. FIG. 6 is a block diagram of a conventional optical phase modulation device. 100... Signal generator 101... Laser light source <i5 record) 102...
Optical writing type liquid crystal light valve 103... Half mirror 104... Collimating lens 105... Output surface 106... Fourier transform lens 107... Laser light source (reproduction) 108... Optical phase modulation device 109 ... Optical phase modulator 200 ... Optical writing type liquid crystal light valve 201 having a phase plate ... Polarizing beam splitter 300 ...
- Transmissive liquid crystal light valve 301 ... Polarizing plate 400 ... CRT 401 ... Lens 500 ... Substrate 501 ... Transparent electrode 502 ... Photoconductor layer 503 ... Dielectric mirror 504 - ... Phase plate 505 ... Liquid crystal alignment film 506 ... Liquid crystal layer and above Applied voltage (V) Fig. 5

Claims (2)

[Claims] (1) In an optical phase modulation device using a liquid crystal light valve, the liquid crystal light valve has a liquid crystal layer that operates in a voltage-controlled birefringence mode, a dielectric mirror, and a photoconductor layer; On the photoconductor layer side,
An optical phase modulation device comprising a two-dimensional image projection light source for recording phase distribution. (2) The optical phase modulation device according to claim 1, wherein in the liquid crystal light valve, a phase plate is installed between the liquid crystal layer and the dielectric mirror.