JP2964467B2 - Multiple reflection element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 converter, a system using an electro-optical crystal such as lithium niobate or KDP or a liquid crystal has been known as an electrically driven one, and a reflection mirror has been used as a mechanically driven one. Is known.

[0003]

However, those using an electro-optic crystal or liquid crystal have a small changeable phase change, while those using a reflection mirror have a very high response speed because of mechanical movement. There was the disadvantage of being slow.
For this reason, there is no phase converter that can achieve a large phase change at high speed, which has been a major obstacle in applied technology of light.

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

[0005]

According to the first aspect of the present invention, mirrors are provided on both sides of a liquid crystal cell so as to face each other.
An appropriate voltage is applied to the liquid crystal cell, and light such as laser light is multiply reflected between these mirrors through the liquid crystal cell to be led out, thereby obtaining a multi-reflection element configured to increase phase modulation.

According to a second aspect of the present invention, mirrors are provided on both side surfaces of the liquid crystal cell by directly superimposing them, and a part of these mirrors is cut out, and an anti-reflection film is formed at the positions substantially flush with the mirrors. The transparent electrodes are superposed and provided outside these mirrors, and an appropriate voltage is applied to these transparent electrodes to pass light such as laser light through the liquid crystal cell through the anti-reflection film, thereby forming a space between the mirrors. And a multiple reflection element having a configuration for multiple reflection.

According to a third aspect of the present invention, in the multiple reflection element according to the first or second aspect, light such as laser light is provided on both sides through the liquid crystal cell by applying an appropriate voltage to the liquid crystal cell. The multi-reflection element has a configuration in which the light is multiply reflected between mirrors, and the light passing therethrough is made to travel in a direction opposite to the incident light by a separately provided reflection mirror.

According to a fourth aspect of the present invention, in the multiple reflection element of the first or second aspect, light such as laser light is provided on both sides through the liquid crystal cell by applying an appropriate voltage to the liquid crystal cell. The multi-reflection element has a configuration in which the light is multiply reflected between the mirrors, and the light passing therethrough is returned in a direction opposite to the incident light 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 transmission type multiple reflection elements shown in FIGS. Transparent electrodes 1a, 1a are provided by directly superimposing on opposite side surfaces of the liquid crystal cell 1, and mirrors 2, 2 are provided opposite thereto, respectively, and a variable voltage V is applied to each transparent electrode 1a of the liquid crystal cell 1. As shown in FIG. 1, light such as a laser beam is passed through a liquid crystal cell 1 and reflected between two opposing mirrors 2 and 2 in a multiplex manner. By changing the voltage V, the phase, polarization, and the like change greatly.

In the use of a multi-reflection liquid crystal cell, by arranging the liquid crystal so that the principal axis plane of the liquid crystal coincides with the plane of incidence of the light beam, the phase and retardation of the light beam (orthogonal polarization component) can be maintained without changing the principal axis of the light beam. Relative phase difference)
Can be increased corresponding to the number of reflections. FIG. 2 is a graph showing a phase change or retardation characteristic of a liquid crystal having 20 reflections and a liquid crystal having transmitted once as an example of the multiple reflection. Thus, it can be seen that the number increases in accordance with the number of reflections.

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.
In this configuration, a light beam that has passed through a multiple reflection element similar to that described above is reflected by a separately provided reflecting mirror 6, and travels in a direction opposite to the incident light beam. As a result, the number of reflections doubles, so that the phase change also doubles. 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 irradiates pump laser beams 7a and 7b from opposite sides.

The light beam may be disturbed by the fluctuation of air on the way, the spread of the beam due to propagation, and the like, resulting in a reduction in practical performance. However, the light beam incident on the phase conjugate mirror 7 is reflected by the photorefractive effect of the crystal with a wavefront conjugate with the incident light beam, and goes backward with respect to the incident light beam. As a result, beam disturbance due to air fluctuations and propagation in the middle is canceled out, a beam without disturbance similar to the original incident light is reproduced, and the phase conversion by the liquid crystal is twice as large as that of the transmission type. Reflected light can be achieved. The above operation is possible even when there is no pump laser beam 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 reflective films 3, 3 are adhered to both upper and lower side surfaces of the glass box 1a.
Further, transparent electrodes 5, 5 are provided outside the upper and lower reflective films 3, 3. Then, a variable voltage V is applied to these transparent electrodes 5, 5, and light such as laser light is passed through the liquid crystal cell 1 through one anti-reflection film 4 as shown in FIG. 3 is multiple-reflected, and is derived from the other anti-reflection film 4.

The compact multiple reflection element may be of a reflection type as shown in FIG. That is, FIG. 6A shows a configuration in which a reflecting mirror 6 is provided, reflected at the six reflecting mirrors, and made to travel in a direction opposite to the incident light beam. FIG. 6B shows a case in which a phase conjugate mirror 7 is provided in place of this reflection mirror. Since the number of reflections is doubled by this in the same manner as in the above-described embodiment, the phase change also occurs. Double.

These multiple reflection elements are used, for example, as a phase modulator for stabilizing an interferometer. FIG. 7 shows this embodiment. Part of the light from the light source 8 such as a laser beam passes through the translucent mirror BS1, is reflected by the mirror M2 through the test object 9, is reflected by the translucent mirror BS1, and reaches the plate 11 having the pinhole 10. Part of the light from the light source 8 is reflected by the translucent mirror BS1, passes through the phase modulator 12 using the multiple reflection element, is reflected by the mirror M1, passes through the translucent mirror BS1, and becomes a pinhole. Plate 11 with 10
Leads to. These lights cause interference fringes to appear on the plate 11.

In this embodiment, polarizers P having the same polarization direction are provided at the positions of the light source 8 and the phase modulator 12 to eliminate errors caused by polarized light.
Is not an indispensable requirement of this device, and if a polarized light source is used and the rotation plane of the main axis of the liquid crystal is aligned in that direction or the polarization does not change by operation in the optical fiber, the above polarizer P is not used. Is also good.

If there is disturbance such as vibration in these optical paths, the intensity of light passing through the pinhole 10 fluctuates. This is detected by a photodetector 13 provided behind 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 modulator 12 always changes the phase in accordance with the light and stabilizes the signal light and the reference light. A plate 1 having a translucent mirror BS1 and a pinhole 10
A semi-transparent mirror BS2 is provided in the optical path between the light source 1 and the light source 1 to reflect the light and display interference fringes on the monitor 15.

When it is desired to measure unevenness of the surface of the test object 16 as shown in FIG. 8 by the conventional interferometer, the light transmitted from the light source 18 to the semi-transparent mirror 17 is applied to the surface of the test object 16. The light from the light source 18 is reflected by the translucent mirror 17, and the light from the light source 18 is reflected by the mirror 19 to pass through the translucent mirror 17, and the interference fringes of these lights are reflected. Is reading automatically.
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 ° and the phase is changed, I is measured, and these are substituted into the above equation to finally obtain Δφ, and A and B are constants. .

Conventionally, the mirror 19 has been moved to shift the phase by 90 °. However, moving the mirror 19 in this manner requires a complicated mechanism and is difficult to achieve a highly accurate configuration. Accordingly, in the present invention, a liquid crystal is used, and the phase applied to the liquid crystal is changed very easily by 90 ° by changing the voltage applied to the liquid crystal.

FIG. 9 shows an apparatus for automatically reading interference fringes in this interferometer. Multiple reflection liquid crystal element 2
0, further passes through a test object 21, reads interference fringes with a CCD camera 23 via an interferometer 22, reads the interference fringes through a microcomputer 24, and displays the surface shape of the test object on a display device 25 such as a television screen or a printer. This is a three-dimensional display of the refractive index distribution.

In the shearing interferometer, the signal light and the reference light spatially pass through substantially the same place, so that the interferometer itself is highly stable. Therefore, the use of the variable phase function of the liquid crystal makes it possible to automatically read interference fringes, which was impossible with a conventional shearing interferometer. FIG. 10 shows a multi-reflection liquid crystal element 20 provided in this shearing interferometer.

The shearing interferometer shown in FIG. 10 imparts shear to the wavefront by utilizing the lateral shift caused by a birefringent crystal plate Qd such as calcite, and is polarized at 45 ° to the crystal to form an interference image. A polarizer P having an axis and an analyzer A are arranged, and light passing through the multi-reflection liquid crystal element 20 is reflected by an object O.
, An image of the object O is projected by the lens L, and a shearing interference image between the wavefront Wo due to the ordinary ray and the wavefront We due to the extraordinary ray is formed on the image plane. A three-dimensional display of a surface shape and a refractive index distribution of a test object is performed by a display device such as a television screen or a printer through a microcomputer as in the embodiment. Note that Wp is an incident plane wave, which is a coherent wavefront, and W is a wavefront after passing through the object O.

In addition, it is possible to read an interference fringe which has been impossible 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 multi-reflection liquid crystal element 20 is reflected by the semi-transparent mirror BS, and the Nomarski prism P
n, illuminate the sample S via the objective lens Ob. The Nomarski prism Pn is a prism having an optical axis bonded to a prism as shown in the figure. This prism Pn is actually in an azimuth rotated by 45 ° around the optical axis. Accordingly, the incident light beam is decomposed into an ordinary light beam and an extraordinary light beam having the same amplitude.
The ordinary ray and the extraordinary ray travel in different directions on the bonding surface as shown in the drawing, and travel so as to intersect at the focal point F of the objective lens Ob after passing through the prism Pn. After passing through the objective lens Pn, it becomes parallel and enters the sample S, where it is reflected, follows the same optical path in reverse, and reaches the Nomarski prism Pn again. After passing through the prism, the light travels along the same optical path and reaches the eyepiece Oc via the analyzer A. On the image plane IP, a shearing interference image in which the image of the sample is laterally shifted by the magnification of the objective lens Ob can be seen. This is CC through the eyepiece Oc
This 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. The light from the light source is
The light passes through a multiple reflection liquid crystal element similar to that shown in FIG. 1A, is multiply reflected by the liquid crystal, and is captured as a change in the amount of light by a photodetector D through an analyzer A (actually a current output). As a result, it becomes 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 voltage change and the sensitivity is higher than that of the conventional single-transmission liquid crystal. In addition, the switch can be used at a low voltage and save power, thereby increasing the speed.

In the above embodiment, the multi-reflection element of the present invention is used for an interferometer, a voltage sensor or an optical switch. The multiple reflection liquid crystal element of the present invention may be of a reflection type or a transmission type.

[0027]

According to the multiple reflection element of the present invention, when used in an optical interferometer or the like, the amount of conversion increases in a change in phase, a change in polarization, and a change in intensity due to the change.
Very good conversion efficiency. Also, these conversions are speeded up. Therefore, the responsiveness and accuracy when used in the above-mentioned interferometer and the like become extremely high, and furthermore, these configurations are extremely simple and the production cost can be kept low.

The multiple reflection element according to the second aspect of the present invention comprises:
In addition to the effects of the first aspect of the present invention, the present invention is extremely compact and does not hinder other structures even when incorporated into the apparatus, so that the applicable range is large.

According to a third aspect of the present invention, a light beam that has passed through the multiple reflection element is reflected by a separately provided reflecting mirror and is made to travel in a direction opposite to the incident light beam. Since the number of reflections is twice as large as that of the element, the phase change is also efficiently doubled.

According to a fourth aspect of the present invention, the light beam incident on the phase conjugate mirror is reflected with a conjugate wavefront with the incident light beam due to the photorefractive effect of the crystal, and travels counter to the incident light beam. As a result, beam disturbance due to air fluctuations and propagation in the middle is canceled out, and a beam without disturbance similar to the original incident light is reproduced.In this state, the magnitude of phase conversion by the liquid crystal is larger than that of the transmission type. Thus, twice as much reflected light can be achieved. Therefore, the range of application is extremely wide.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic configuration diagram of a second embodiment 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 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 diagram showing a configuration in which the multiple reflection element of the present invention is used for automatic reading of interference fringes by an interferometer.

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

FIG. 11 is a schematic diagram showing a configuration in which the multiple reflection element of the present invention is used for automatically reading 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 for a voltage sensor or an optical switch.

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

[Explanation of symbols]

Reference Signs List 1 liquid crystal cell 2 mirror 3 reflection film 4 antireflection film 5 transparent electrode 6 reflection mirror 7 phase conjugate mirror 8 light source 9 test object 10 pinhole M mirror BS translucent mirror 11 plate 12 phase modulator 13 photodetector 14 differential Amplifier 15 Monitor 16 Test object 17 Translucent mirror 18 Light source 19 Mirror 20 Multiple reflection liquid crystal element 21 Test object 22 Interferometer 23 CCD camera 24 Microcomputer 25 Display device O Test object Qd Birefringent crystal plate L Lens P Polarizer A analyzer Pn Nomarski prism Ob objective lens Oc eyepiece S sample IP image plane

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/13 505 G02F 1/1335 520 G01B 9/02 G01B 11/00

Claims (4)

(57) [Claims] 1. A mirror is provided on both 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 reflected multiple times between these mirrors through the liquid crystal cell. A multiple reflection element, which is derived and configured to increase phase modulation. 2. A mirror is provided on both sides of the liquid crystal cell by direct polymerization, and a part of these mirrors is cut out, and an anti-reflection film is provided on that part on substantially the same plane as the mirrors. A transparent electrode is provided on the outside by polymerization, and an appropriate voltage is applied to these transparent electrodes so that light such as laser light passes through the liquid crystal cell through the antireflection film and is multiply reflected between the mirrors. A multiple reflection element, characterized in that: 3. An appropriate voltage is applied to the liquid crystal cell to pass light such as a laser beam through the liquid crystal cell, multiple-reflect the light between mirrors provided on both sides, and separately provide a light beam passing therethrough. The multi-reflection element according to claim 1, wherein the reflection mirror is configured to reverse the incident light beam. 4. An appropriate voltage is applied to a liquid crystal cell to pass a light such as a laser beam through the liquid crystal cell and multiple-reflect it between mirrors provided on both sides, and light beams passing through these are separately provided. The multi-reflection element according to claim 1, wherein the multi-reflection element is configured to reverse the incident light by a phase conjugate mirror.