JPH09274168A - Multiple reflection element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a conversion efficiency and to attain the high speed of the conversion by providing mirrors while opposing them to both side faces of a liquid crystal cell and passing the light beam of a laser beam or the like through the liquid crystal cell and reflecting it in between respective mirrors in multiple while impressing a voltage on the liquid crystal cell. SOLUTION: Transparent electrodes 1a, 1a are provided in both side faces confronted with each others of a liquid crystal cell 1 by being polymerized directly and mirrors 2, 2 are provided while being opposed to respective electrodes and the light beam of the laser beam or the like is passed through the cell 1 and is reflected in between the two opposed mirrors 2, 2 in multiple while impressing a variable voltage V on the respective transparent electrodes 1a, 1a of the cell 1. In this case, the phase and the polarization of the light beam are largely changed by varrying the voltage V. Then, in using of a multiple reflection liquid crystal cell, the phase and the retardation (relative phase difference between orthogonal polarized components) of the light beam are increased according to reflection times without changing the main axis or polarization of the light beam by arranging the cell so that the main axial plane of the liquid crystal coincide with the incident plane of the light beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiple reflection element used for an optical interferometer, a voltage sensor, a liquid crystal switch, a display element and the like.

[0002]

2. Description of the Related Art Conventionally, as a phase shifter, a method utilizing an electro-optic crystal such as lithium niobate or KDP or a liquid crystal has been known as an electrically driven one, and a reflection mirror as a mechanically driven one. There is known a method of moving the.

[0003]

However, the one using the electro-optical crystal or the liquid crystal has a small changeable phase change, while the one using the reflecting mirror has a very high response speed because it involves mechanical movement. It had the drawback of being slow.
Therefore, there is no phase converter that can achieve a large phase change at high speed, which has been a major obstacle in optical application technology.

Therefore, the present invention provides a multiple reflection element in which the conversion amount is increased due to a change in phase, a change in polarization, and a change in intensity due to the change, the conversion efficiency is good, and the speed can be increased.

[0005]

First, the invention according to claim 1 is to provide mirrors on both side surfaces of a liquid crystal cell so as to face each other,
A multi-reflection element having a structure in which light such as laser light is multiply reflected between these mirrors through the liquid crystal cell by applying an appropriate voltage to the liquid crystal cell is provided.

According to the second aspect of the invention, mirrors are directly provided on both side surfaces of the liquid crystal cell by superimposing them, an antireflection film is provided on a part of these mirrors, and transparent electrodes are superposed on the outside of these mirrors. And a suitable voltage is applied to these transparent electrodes to allow light such as laser light to pass through the liquid crystal cell through the antireflection film and undergo multiple reflection between the mirrors. .

According to a third aspect of the present invention, in the multiple reflection element according to the first or second aspect, an appropriate voltage is applied to the liquid crystal cell so that light such as laser light is provided on both sides through the liquid crystal cell. A multi-reflection element having a structure in which multiple reflections are made between the mirrors, and light rays that have passed through these mirrors are made to go backwards to the incident light rays by a reflection mirror provided separately.

According to a fourth aspect of the present invention, in the multiple reflection element according to the first or second aspect, an appropriate voltage is applied to the liquid crystal cell so that light such as laser light is provided on both sides through the liquid crystal cell. A multi-reflection element having a structure in which multiple reflections are made between the mirrors, and light rays that have passed through these mirrors are made to go backwards to the incident light rays by a separately provided phase conjugate mirror.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of a multiple reflection element, and shows two types of transmissive multiple reflection elements shown in FIGS. Transparent electrodes 1a and 1a are directly provided on opposite sides of the liquid crystal cell 1 by superposition, and mirrors 2 and 2 are provided to face them, and a variable voltage V is applied to each transparent electrode 1a of the liquid crystal cell 1. Thus, as shown in FIG. 1, light such as laser light is passed through the liquid crystal cell 1 and is reflected multiple times between two opposing mirrors 2, 2. Then, by changing the voltage V, the phase, polarization, etc. change significantly.

In the use of the multi-reflection liquid crystal cell, by arranging the principal axis plane of the liquid crystal so as to coincide with the incident plane of the ray, the phase and retardation (orthogonal polarization component) of the ray can be changed without changing the principal axis of polarization of the ray. Relative phase difference)
Can be increased corresponding to the number of reflections. FIG. 2 is a graph showing phase change or retardation characteristics of a liquid crystal having 20 reflections and a liquid crystal having one transmission as an example of this multiple reflection. It can be seen that the number of reflections increases in this way.

FIGS. 3 and 4 show a second embodiment and a third embodiment in which the multiple reflection element of the first embodiment is a reflection type. In FIG. 3, FIG.
A light beam that has passed through a multiple reflection element similar to the above is reflected by a reflection mirror 6 provided separately, and is made to travel backward from the incident light beam. This doubles the number of reflections, and thus doubles the phase change. Further, in FIG. 4, a phase conjugate mirror 7 is provided instead of the reflection mirror 6. The phase conjugate mirror 7 is a photorefractive nonlinear optical crystal such as barium titanate, and pump laser beams 7a and 7b are applied from opposite sides thereof.

The light beam may be disturbed due to fluctuations of air in the middle of the beam, spread of the beam due to propagation, and the like, resulting in deterioration of practical performance. However, due to the photorefractive effect of the crystal, the light ray incident on the phase conjugate mirror 7 is reflected by the wavefront conjugate with the incident light ray, and goes backward with respect to the incident light ray. As a result, the turbulence of the beam due to the fluctuations and propagation of air in the middle is canceled, the undisturbed beam similar to the original incident light is reproduced, and the size of the phase conversion by the liquid crystal is double that of the transmission type. The reflected light can be achieved. The above operation is possible even when there is no pump laser light from the phase conjugate mirror.

FIG. 5 shows a fourth embodiment in which the multiple reflection element of the first embodiment is made more compact. The liquid crystal cell 1 is housed in a glass box 1a, and the reflection films 3 and 3 are attached to both upper and lower surfaces of the glass box 1a.
Further, the transparent electrodes 5 and 5 are provided outside the upper and lower reflective films 3 and 3. Then, a variable voltage V is applied to these transparent electrodes 5 and 5 to allow light such as laser light to pass through the inside of the liquid crystal cell 1 through one of the antireflection films 4 as shown in FIG. 3 is reflected multiple times and led out from the other antireflection film 4.

This compact multiple reflection element may also be of a reflection type as shown in FIG. That is, in FIG. 6A, the reflection mirror 6 is provided, and the reflection mirror 6 is configured to reflect the light at the six points and reverse the incident light beam. Further, in FIG. 6B, a phase conjugate mirror 7 is provided instead of this reflection mirror, and since the number of reflections increases twice as in the above embodiment, the phase change also occurs. Doubles.

These multiple reflection elements are used, for example, as a phase modulator to stabilize an interferometer. FIG. 7 shows an example of this embodiment. A part of the light from the light source 8 such as laser light passes through the semitransparent mirror BS1, is reflected by the mirror M2 through the object 9 to be inspected, and is reflected by the semitransparent mirror BS1 to reach the plate 11 having the pinhole 10. Part of the light from the light source 8 is reflected by the semitransparent mirror BS1, passes through the phase modulator 12 using the multiple reflection element, is reflected by the mirror M1, passes through the semitransparent mirror BS1, and is a pinhole. Board 11 with 10
Leading to. The light causes interference fringes to appear on the plate 11.

In this embodiment, the light source 8 and the phase modulator 12 are provided with the polarizer P having the same polarization direction to eliminate the error caused by the polarized light.
Is not an essential requirement of this device. If a polarized light source is used and the direction of rotation of the principal axis of the liquid crystal is aligned with that direction, or if the polarization does not change due to the operation in the optical fiber, then the above polarizer P should not be used. Good.

When there is a disturbance such as vibration in these optical paths, the intensity of light passing through the pinhole 10 varies. This is detected by a photodetector 13 provided at the rear of the pinhole 10, converted into a voltage by a differential amplifier 14 according to the intensity of light, and fed back to the phase modulator 12. Therefore, the phase is always changed by the phase modulator 12 according to the drool of the light to stabilize the signal light and the reference light. Also, a plate 1 having a semitransparent mirror BS1 and a pinhole 10
A semi-transparent mirror BS2 is provided in the optical path between the optical path 1 and the optical path 1, and these lights are reflected to display interference fringes on the monitor 15.

Further, conventionally, when it is desired to measure the unevenness of the surface of the object 16 to be inspected as shown in FIG. 8 by the interferometer, the semitransparent mirror 17 is irradiated with the laser light from the light source 18 and the passed light is passed through the surface of the object 16 to be inspected. Then, the light from the light source 18 is reflected by the semitransparent mirror 17, the light is reflected by the mirror 19 and passed through the semitransparent mirror 17, and the interference fringes of these lights are reflected. Is automatically read.
This principle is expressed by the following equation.

I ₁ = A + B cos φ Δφ = 0 I ₂ = A-B sin φ Δφ = π / 2 I ₃ = A-B cos φ Δφ = π I ₄ = A + B sin φ Δφ = 3π / 2 tan φ = (I ₄ −I ₂ ) ÷ ( I ₁ -I ₃ ) The above Δφ is shifted by 90 °, the phase is changed, each I is measured, these are substituted into the above equation to finally obtain Δφ, and the above A and B are constants. .

Conventionally, the mirror 19 has been moved to shift the phase by 90 °. However, it is difficult to move the mirror 19 in this way because of a complicated mechanism and a highly accurate structure. Therefore, in the present invention, liquid crystal is used, and the phase is changed every 90 ° very easily by changing the voltage applied to the liquid crystal.

FIG. 9 shows an automatic reading device for interference fringes in this interferometer. Multiple reflection liquid crystal element 2 for laser light
0, irradiate the object 21 to be inspected, and the CCD camera 23 reads the interference fringes through the interferometer 22, and the microcomputer 24 applies this to the surface shape of the object to be inspected on a display device 25 such as a television screen or a printer. The refractive index distribution is displayed three-dimensionally.

Further, in the shearing interferometer, the interferometer itself is highly stable because the signal light and the reference light spatially pass through substantially the same place. Therefore, by using the variable phase function of the liquid crystal, it became possible to automatically read the interference fringes, which was impossible with the conventional shearing interferometer. FIG. 10 shows the shearing interferometer provided with a multiple reflection liquid crystal element 20.

The shearing interferometer shown in FIG. 10 utilizes a lateral shift caused by a birefringent crystal plate Qd such as calcite to give a shear to the wavefront. Polarization is performed in a direction of 45 ° with respect to the crystal to form an interference image. A polarizer P having an axis and an analyzer A are arranged so that light passing through the multiple reflection liquid crystal element 20 is transmitted to the object O.
Then, the image of the object O is projected by the lens L, and a shearing interference image between the wavefront Wo by the ordinary ray and the wavefront We by the extraordinary ray is formed on the image plane, which is captured by the CCD camera 23, In the same manner as in the above embodiment, a microcomputer is used to three-dimensionally display the surface shape and the refractive index distribution of the object to be inspected by a display device such as a television screen or a printer. Wp is an incident plane wave and is a coherent wavefront, and W is a wavefront after passing through the object O.

Further, it is possible to read the interference fringes, which was not possible with the conventional Nomarski differential interference microscope. FIG. 11 shows a Nomarski differential interferometer, in which the illumination light transmitted through the polarizer P and the multiple reflection liquid crystal element 20 is reflected by the semitransparent mirror BS, and the Nomarski prism P
n, the sample S is illuminated through the objective lens Ob. The Nomarski prism Pn is a prism whose optical axis is formed by laminating prisms as illustrated. The prism Pn is actually in a direction rotated by 45 ° around the optical axis. Therefore, the incident ray is decomposed into an ordinary ray and an extraordinary ray having the same amplitude.
The ordinary ray and the extraordinary ray travel in different directions on the bonding surface as shown in the figure, but after traveling through the prism Pn, they intersect at the focal point F of the objective lens Ob. After passing through the objective lens Pn, it becomes parallel and enters the sample S, is reflected here, and follows the same optical path to reach the Nomarski prism Pn again. After passing through the prism, the light travels on the same optical path, passes through the analyzer A, and reaches the eyepiece lens Oc. On the image plane IP, a shearing interference image in which the image of the sample is laterally displaced by the magnification of the objective lens Ob can be seen. CC this through the eyepiece Oc
It is captured by the D camera 23.

FIG. 12 shows an example in which a multiple reflection element is used for a voltage sensor or an optical switch. Light from the light source is applied to the polarizer P
Through a multi-reflection liquid crystal element similar to that shown in FIG. 1 (A), multiple reflection is performed by this liquid crystal, and it is detected as a change in light quantity by the photodetector D through the analyzer A (actually, current output). . Although this serves as a voltage sensor or an optical switch, as shown in FIG. 13, it can be seen that the slope becomes steeper with respect to the change in voltage and the sensitivity is higher than that of the conventional single-transmission liquid crystal. In addition, it can be operated at low voltage with a low voltage, which saves power and speeds up.

In the above embodiments, the multiple reflection element of the invention of the child is used for an interferometer, a voltage sensor, or an optical switch, but the invention is not limited to these and can be used for an appropriate element such as a display element. Further, the multiple reflection liquid crystal element of the present invention may be either a reflection type or a transmission type.

[0027]

According to the multiple reflection element of the first aspect of the invention, when it is used for an optical interferometer, a voltage sensor, a liquid crystal switch, a display element, etc., the phase change, the polarization change and the intensity change due to the change are caused. The amount of conversion increases, and the conversion efficiency is extremely good. In addition, these conversions are speeded up. Therefore, the responsiveness and accuracy when used in the above-mentioned ones becomes extremely high, and further, these constitutions are extremely simple and the manufacturing cost can be kept low.

The multiple reflection element according to the invention of claim 2 is
In addition to the effect of the invention according to claim 1, it is extremely compact, and even when incorporated in a device, it does not interfere with other configurations and has a wide range of application.

Further, according to the invention of claim 3, the light ray which has passed through the multiple reflection element is configured to be reflected by a reflection mirror provided separately and to go in the opposite direction to the incident light ray. Since the number of reflections is doubled as compared with the element No. 3, the phase change is also effectively doubled.

According to the fourth aspect of the present invention, the light ray incident on the phase conjugate mirror 7 is reflected by the wavefront conjugate with the incident light ray by the photorefractive effect of the crystal, and goes backward with respect to the incident light ray. This cancels the turbulence of the beam due to air fluctuations and propagation in the middle, and reproduces the same undisturbed beam as the original incident light.In this state, the magnitude of the phase conversion by the liquid crystal is larger than that of the transmissive type. And twice the reflected light can be achieved. Therefore, its application range is extremely wide.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of the present invention.

FIG. 2 is a graph showing phase change or retardation characteristics of the multiple reflection element of the present invention.

FIG. 3 is a schematic configuration diagram of a second embodiment example of the present invention.

FIG. 4 is a schematic configuration diagram of a third embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a fourth embodiment example of the present invention.

FIG. 6 is a schematic configuration diagram of fifth and sixth embodiments of the present invention.

FIG. 7 is a schematic configuration diagram in which the multiple reflection element of the present invention is used for stabilizing an interferometer.

FIG. 8 is an explanatory diagram showing the principle of reading interference fringes in an interferometer.

FIG. 9 is a schematic configuration diagram in which the multiple reflection element of the present invention is used for automatic reading of interference fringes of an interferometer.

FIG. 10 is a schematic configuration diagram in which the multiple reflection element of the present invention is used for automatic reading of interference fringes of a shearing interferometer.

FIG. 11 is a schematic configuration diagram in which the multiple reflection element of the present invention is used for automatic reading of interference fringes of a Nomarski differential interference microscope.

FIG. 12 is a schematic configuration diagram in which the multiple reflection element of the present invention is used in a voltage sensor or an optical switch.

FIG. 13 is a graph showing the characteristics of optical output change rate when the multiple reflection element of the present invention is used in a voltage sensor or an optical switch.

[Explanation of symbols]

1 Liquid crystal cell 2 Mirror 3 Reflective film 4 Antireflection film 5 Transparent electrode 6 Reflective mirror 7 Phase conjugate mirror 8 Light source 9 Object to be inspected 10 Pinhole M Mirror BS Semi-transparent mirror 11 Plate 12 Phase modulator 13 Photodetector 14 Differential Amplifier 15 Monitor 16 Object to be inspected 17 Semi-transparent mirror 18 Light source 19 Mirror 20 Multiple reflection liquid crystal element 21 Object to be inspected 22 Interferometer 23 CCD camera 24 Microcomputer 25 Display device O Object to be inspected Qd Birefringent crystal plate L Lens P Polarizer A Analyzer Pn Nomarski prism Ob Objective lens Oc Eyepiece S Sample IP Image plane

Claims (4)

[Claims] 1. A structure in which mirrors are provided on opposite sides of a liquid crystal cell so as to face each other, and an appropriate voltage is applied to the liquid crystal cell so that light such as laser light is multiply reflected between these mirrors through the liquid crystal cell. The multiple reflection element characterized by the above. 2. A mirror is directly provided on both side surfaces of the liquid crystal cell, an antireflection film is provided on a part of these mirrors, and a transparent electrode is provided on the outside of these mirrors by superposition.
A multiple reflection element, characterized in that a suitable voltage is applied to these transparent electrodes to allow light such as laser light to pass through the liquid crystal cell through the antireflection film to cause multiple reflection between the mirrors. 3. An appropriate voltage is applied to the liquid crystal cell to allow light such as laser light to pass through the liquid crystal cell, to undergo multiple reflection between mirrors provided on both sides, and a light beam passing through these is provided separately. The multiple reflection element according to claim 1 or 2, wherein the multiple reflection element has a structure in which a reflection mirror is configured to reverse the incident light beam. 4. An appropriate voltage is applied to the liquid crystal cell to allow light such as laser light to pass through the liquid crystal cell, to undergo multiple reflection between mirrors provided on both sides, and a light beam that has passed through these is provided separately. The multiple reflection element according to claim 1 or 2, wherein the multi-reflection element has a structure in which the phase conjugation mirror is configured to cause the incident light beam to travel backward.