JPH0233126A - Holographic electro-optical device - Google Patents

Abstract

PURPOSE:To activate an optical function of a holographic element by controlling a refractive index of an electro-optical medium by providing the holographic element for coming into contact with the electro-optical medium between electrodes for applying a control electric field, on the electrode or in the vicinity of the electrode. CONSTITUTION:Between electrodes 101 for applying a control electric field, a nematic liquid crystal 102 being an electro-optical medium is held, and a grating 103 being a holographic element is installed so as to come into contact with the nematic liquid crystal 102. Also, its outside surface is supported by a transparent substrate 104, and an external power source 105 is connected to the electrode 101. When an electric field is applied, a liquid crystal 106 is reoriented in the electric field direction, and an incident laser light 107 is brought to linear polarization in the direction for receiving a variation of a refractive index anisotropy of the liquid crystal. The incident laser light 107 is diffracted by the grating and a diffracted light transmits through in order from zero-th order, but by controlling an electric field applied to the liquid crystal layer 106, an angle of diffraction of the grating 103 is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electro-optical device having a holographic element.

[Prior Art] An electro-optical device having a conventional holographic element is
As disclosed in Japanese Patent Application Laid-Open No. 153936/1983, it was used as a color filter that functioned by scattering smectic liquid crystal, and was passive and single-functional.

[Problem to be solved by the invention] However, the conventional electro-optical device having a holographic element only performs spectroscopy of incident light, and there is a problem in that the optical function of the holographic element is not fully utilized. . Therefore, an object of the present invention is to activate a holographic element by controlling the refractive index of an electro-optic medium.

[Means for Solving the Problems] An electro-optical device of the present invention is characterized in that it is in contact with an electro-optic medium between electrodes for applying a control electric field, and has a holographic element. , or placed close to the electrode.

Further, the holographic element is characterized in that it is a grating element.

Further, the electrode is characterized in that it is driven by an active element.

Hereinafter, the details of the present invention will be shown by examples.

[Example] Example 1 FIG. 1 is a sectional view of the simplest cell of the present invention.

A nematic liquid crystal +02, which is an electro-optic medium, is held between electrodes 101 for applying a control electric field, and a grating 103, which is a holographic element, is placed in contact with the nematic liquid crystal. 104 is a support transparent substrate, 105
is an external power supply.

The liquid crystal is aligned parallel to the substrate.

The liquid crystal molecules 106 are parallel when no electric field is applied, and when an electric field is applied, they are reoriented in the direction of the electric field due to the dielectric anisotropy of the liquid crystal.

The incident laser beam 107 has a refractive index anisotropy (hereinafter, Δ
It is linearly polarized in the direction in which it undergoes a change in the amount of light (referred to as n).

The grating has grooves in the direction parallel to the electric field vibration of polarized light, and is installed on the electrode.

This is to increase the diffraction efficiency of the grating. The incident laser beam is diffracted by the grating, and the diffracted beams are transmitted in order from the 0th order. By applying a voltage to the liquid crystal layer, the refractive index of the incident laser beam changes by a maximum of Δn. This change in Δn changes the refractive index of the incident medium and changes the diffraction angle of the grating. Next, the mechanism by which the diffraction angle changes will be explained.

The diffraction conditions are given by the following two equations.

+ k, I = l k k s = k + f m K where k is the wave vector of the ray, K is the grating vector of the grating, and m is the order of diffraction.

i and S indicate an incident wave and a diffracted wave, respectively.

Furthermore, by adding the incident angle θI and the diffraction angle θ, and rewriting the matching condition, lk, 1 sin θ++ l ksl sin θ, = ±m
It becomes 1Kl. If θ1,m,K,1 is fixed at 1, θ can be changed by 1. Furthermore, since I k+l =n+(Elka), θS becomes a function of the electric field E.

In this example, a glued near grating with a pitch of 2 μm was made of photoresist. The medium on the incident side is biphenyl-based nematic liquid crystal E-7 (manufactured by BDH), and the medium on the output side is Pyrex glass. The transparent electrode ITO is 1000
It's about 8 times thinner than a human, so it can be ignored.

Here, a 633 am S-polarized He-Ne laser was irradiated at an incident angle of 20°. The first order diffraction angle at this time is 7.5
°, and when an external voltage of 5 V or more was applied, the first-order diffraction angle changed to about 8.8 °.

Although an example has been shown in which the refractive index of the incident medium is controlled, the diffraction angle can be similarly controlled by changing the position of the grating and changing the refractive index of the exit side medium.

Embodiment 2 FIG. 2 is a perspective sectional view of an electro-optical device using a metal thin film layer 201 exposed with a hologram pattern as a hologram element. 202 is a support substrate, 203 is a power source, a metal layer 201 is coated on an electrode 204, and a nematic liquid crystal 205 is sandwiched between the metal layer 201 and the other electrode. The alignment of the liquid crystal is parallel to the substrate as in Example 1. 206 is a laser light source.

The movement of the liquid crystal with respect to the electric field is the same as in the first embodiment. The manner of diffraction changes because the refractive index of the surrounding medium of the hologram element changes. An example in which a zone plate is used as a hologram pattern will be explained.

The zone plate acts as a lens for laser light,
As shown in Figure 2, it has a light-concentrating effect. If the focal point in the absence of an electric field is fl, then when an electric field is applied, the refractive index experienced by the light beam becomes smaller, and the focal point f2 at this time becomes shorter than fl.

This made it possible to create a varifocal lens that can be controlled by an electric field.

Embodiment 3 FIG. 3 is a sectional view of a matrix type electro-optical device in which a grating is installed in each pixel. Each pixel is an active element T P T 301 (Thin Film
Transistor). The grating 302 of each pixel has a primary diffraction angle determined in a specific direction.

This direction can be changed by the applied voltage as in the first embodiment. Therefore, the emission direction of the laser light 309 irradiated onto the pixel is controlled by the applied voltage. A detector array 303 is installed in advance in the direction of the first-order diffracted light 31G. The black circle shown at 307 is a detector that corresponds to when the voltage is 0, and 30g is a detector that detects the displacement component of the first-order diffracted light. When a matrix type electro-optical device is two-dimensionally modulated according to image information, a displacement signal corresponding to the amplitude of the image information can be detected. Correlation of image information can be determined from this signal.

Also, if the diffraction direction of the pixel grating is aligned to one position as a whole, and the entire pixel has a lens effect,
The focal position of the lens can be changed depending on the display information of the pixel. In this way, a functionalized lens can be realized.

Furthermore, in combination with a Schlieren optical system, it is possible to detect the modulation component of the diffraction angle and apply intensity modulation to the image. This can be applied as a display.

Embodiment 4 FIG. 4 is a configuration diagram of an optical interconnection device in which a grating is installed in each optical switch element and the direction of emitted light is controlled by a voltage applied to the element. 401 is an optical switch matrix. A light-shielding mask 402 is placed close to each switch element so that the first-order diffracted light 408 hits a specific detector in the absence of an electric field. As described in Example 1, the refractive index of the medium in the grating of each element changes, and the direction of the first-order diffracted light changes. These are stacked in two directions, X and Y, to control the two-dimensional emission direction. 404 is a detector matrix. On the opposite side of the detector matrix, laser diodes, which are emission light sources, are arranged in an array to form a light source matrix 403.

This modulates and emits light according to input information 405.

This input laser light is collimated and enters the switch element. The switch elements receiving this are given connection information 406, and a voltage is applied to each switch element according to this signal. As described in Example 1, the diffraction angle of the transmitted light beam can be changed according to the voltage, but in this case, the two switch elements are molded and the direction of the grating is shifted by 90'', so that the diffraction angle can be changed in the two directions of X-Y. The photodiodes arranged in each boat on the receiving side form a detector array 404.Then, the diffracted light selected by the two switch elements enters the boat.The detector signal is finally converted into the signal of each boat. 407 is output.

Although a transmission type switch matrix has been described in this embodiment, it is also effective to use a reflection type switch element configuration in which a detector array and a laser diode array are disposed on the same substrate.

Although nematic liquid crystal having large electrically induced birefringence was used as the electro-optic medium, other electro-optic media such as ferroelectric liquid crystal or PLZT capable of high-speed response can also be used.

In this way, conventionally only voltage-induced intensity modulation was used, but
The present invention allows angle modulation.

For this reason, it is not limited to displays, but also active lenses,
Optical interconnection has become possible. Although the embodiments have been described above, the present invention can be widely applied not only to the above embodiments but also to functional optical elements of optical neural networks.

[Effects of the Invention] As described above, the present invention has the revolutionary effect of activating the optical function of the holographic element.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a simple cell of the present invention. FIG. 2 is a perspective sectional view of an electro-optical device using a hologram element in which a hologram pattern is exposed on a metal thin film layer. FIG. 3 is a sectional view of a matrix type electro-optical device in which a grating is installed in each pixel. FIG. 4 is a configuration diagram of the optical interconnection device. 101... Electrodes 102, 205 for applying an electric field... Graining which is a nematic liquid crystal holographic element which is an electro-optic medium... Metal thin film... TPT which is an active element... Detector array... Light switch matrix... Light source matrix... Detector matrix and above Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. An electro-optical device in which an electro-optic medium is installed between electrodes for applying a control electric field, characterized by having a holographic element in contact with the electro-optic medium. . 2. The holographic electro-optical device according to claim 1, wherein the holographic element is placed on or in close proximity to the electrode. 3. The holographic electro-optical device according to claim 1, wherein the holographic element is a grating element. 4. The holographic electro-optical device according to claim 1, wherein the electrode is driven by an active element.