JPH04294322A - Optical device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device using a liquid crystal element.

0002

2. Description of the Related Art Conventionally, in order to compensate for phase errors in optical wavefronts, the mainstream method has been to deform the shape of a series of mirrors from behind using an actuator. Piezo elements are widely used as actuators for deformation, and one with a stroke of several μm and around 500 pieces has been prototyped (for example, Proc. SPIE, Vol. 1114,
p134 (1989)).

0003

[Problems to be Solved by the Invention] However, piezo elements have problems such as the need for control of heat generation and hysteresis, the limited number of elements, and the high driving voltage.

The present invention is intended to solve these problems, and its object is to provide an optical device that can compensate for phase errors in optical wavefronts with high precision and high speed using simple means.

[0005]

[Means for Solving the Problems] A first optical device of the present invention includes at least a phase modulating liquid crystal element, a signal generator for the liquid crystal element, and a polarizing element that converts random polarized light into linearly polarized light in one direction. , comprising an optical wavefront measuring device and a circuit for feeding back the output of the optical wavefront measuring device to the signal generator.

A second optical device of the present invention includes at least a phase modulating liquid crystal element, a signal generator for the liquid crystal element, a polarizing element for separating random polarized light into two linearly polarized lights, and an optical wavefront measuring device. , comprising a circuit for feeding back the output of the optical wavefront measuring device to the signal generator.

A third optical device of the present invention is that in the first or second optical device, the phase modulation liquid crystal element is an EC
It is characterized by being a B (field-controlled birefringence) mode liquid crystal element.

[0008]

[Examples] The contents of the present invention will be explained in detail below based on Examples. (Embodiment 1) FIG. 1 shows the configuration of an optical device of this embodiment. Randomly polarized light a containing a phase error is passed through the polarizing element 101
Due to this action, the light becomes linearly polarized in one direction. After receiving phase modulation in the phase modulation liquid crystal element 102, a portion is guided to the optical wavefront measuring device 104 by the mirror 103.
The remainder exits the device as light b whose wavefront phase error has been compensated.

The phase modulation liquid crystal element 102 used in the present invention is a matrix drive type liquid crystal element having a TFT (thin film transistor) in each pixel, and can be used at a voltage of 5 volts or less. The number of effective pixels is 320×220, and the pixel spacing is 80 μm in the horizontal direction and 90 μm in the vertical direction. By adopting the ECB mode in which the initial orientation of liquid crystal molecules is homogeneous, the phase of light can be continuously modulated (
Proceedings of the 51st Academic Conference of the Japan Society of Applied Physics 26a-H-1
0).

[0010] The optical wavefront measuring device 104 measures the phase error included in the optical wavefront from time to time. Then, based on the measurement results, the voltage value to be applied to each pixel of the phase modulation liquid crystal element 102 is calculated, and this is used as a compensation command to the signal generator 1.
Return to 05. The signal generator 105 controls the phase of the passing light on a pixel-by-pixel basis according to the received compensation command. As a method for measuring the phase error of an optical wavefront, the Jack Hartmann method (Publ. Nat. Astron. Ob
s. , Vol. 1, p. 49 (1989)) and the Roger method (Proc. SPIE, Vol. 1114. p. 92 (
1989)) is used.

Next, the structure and operation of the polarizing element 101 used in this embodiment will be explained.

FIG. 4 shows the structure of the polarizing element 101. This polarizing element has a periodic structure consisting of alternating repetitions of birefringent material layers 401 and 402. However, the length of one unit of this repetition is sufficiently short compared to the wavelength of the incident light.

Here, the refractive index of the birefringent material layer 401 for ordinary rays is no1, and the refractive index for extraordinary rays is ne1.
, the refractive index of the birefringent material layer 402 for ordinary rays is no2
, the refractive index for the extraordinary ray is ne2. However, n
Let o1=ne2, ne1≠no2. The optical axis 403 of the birefringent material layer 401 is oriented at 45° with respect to the periodicity direction 405. On the other hand, the optical axis 404 of the birefringent material layer 402
It is oriented at 90° with respect to the optical axis 403 of.

The behavior of the polarization components of the incident light when the light is perpendicularly incident on the upper surface 406 of the polarizing element having such a structure will be described below.

FIG. 5 shows the polarizing element of FIG. 4 viewed from above. The behavior of the polarization component of the incident light may be considered separately into the extraordinary light component 505 and the ordinary light component 506 of the birefringent material layer 502. Since the repetition period of the birefringent material layer is sufficiently short relative to the wavelength, each polarized light component senses the average refractive index of the birefringent material layer 501 and the birefringent material layer 502. First, the extraordinary light component 505 is no.
Since 1=ne2, the polarized light component is maintained as it is and is transmitted. On the other hand, for the ordinary light component, since ne1≠no2, the refractive index is different between the component perpendicular to the periodic repeating direction 509 and the component 508 parallel to 507, resulting in structural birefringence. In other words, the ordinary light component 506 propagates through the polarizing element 101 while changing its polarization state. Therefore, if the element is designed so that the optical path difference is half a wavelength, the ordinary light component 506 will all become the extraordinary light component 505 and will be emitted from the polarizing element, allowing linearly polarized light with the same direction to be produced without energy loss. Obtainable.

According to this embodiment, it is possible to compensate for the phase error of the light wavefront with one phase modulation liquid crystal element. Liquid crystal elements are characterized by low voltage drive, low power consumption, and high pixel density, and can control the phase of a light wavefront with much higher precision than conventional piezo elements.

Note that if the degree of linear polarization of the target light wavefront is sufficiently high, it is also possible to exclude the polarizing element used in this embodiment from the constituent elements. (Embodiment 2) FIG. 2 shows the configuration of an optical device of this embodiment. Randomly polarized light a containing a phase error is passed through the polarizing element 201
Due to this action, the light becomes linearly polarized in one direction. The light is then reflected by the polarizing beam splitter 202 and enters the phase modulation liquid crystal element 203. Here, the light undergoes phase modulation and at the same time its polarization plane is rotated by 90 degrees and output. After that, the light passes through the polarizing beam splitter 202, and part of the light is guided by the mirror 204 to the optical wavefront measuring device 205, and the rest goes out of the device as light b whose wavefront phase error has been compensated. .

The optical wavefront measuring device 205 measures the phase error included in the optical wavefront every moment. Then, based on the measurement results, a voltage value to be applied to each pixel of the phase modulation liquid crystal element 201 is calculated, and this is fed back to the signal generator 206 as a compensation command.

Phase modulation liquid crystal element 20 used in this example
Reference numeral 1 denotes an optical writing type liquid crystal element that includes a quarter-wave plate between a liquid crystal layer whose initial orientation is homogeneous and a light reflection layer. This liquid crystal element performs continuous phase modulation and simultaneously rotates the orientation of incident linearly polarized light by 90 degrees. A signal generator 206 writes signals to the liquid crystal element 201 . The signal generator 206 includes a laser scanning mechanism and writes a two-dimensional image generated in accordance with the compensation command onto the liquid crystal element 201. Note that the two-dimensional image is displayed on the liquid crystal element 20.
1, a CRT display or a liquid crystal display can also be used.

According to this embodiment, by using an optical writing type liquid crystal element with high light utilization efficiency and high resolution, distortion of the optical wavefront can be compensated with extremely high precision. (Embodiment 3) FIG. 3 shows the configuration of an optical device of this embodiment. Randomly polarized light a containing a phase error is split by a polarization beam splitter 301 into a component perpendicular to the plane of the paper (S polarization) and a component parallel to the plane of the paper (P polarization). After each component undergoes phase modulation in phase modulation liquid crystal elements 302 and 303,
A part of the optical wavefront measuring device 306 is formed by mirrors 304 and 305.
, 307, and the rest is polarized beam splitter 310.
incident on the Here, the two components are combined and exit from the device as light b whose wavefront phase error has been compensated.

Phase modulation liquid crystal element 302 used in the present invention,
Reference numeral 303 is a matrix drive type liquid crystal element having a TFT (thin film transistor) in each pixel, and can be used at a voltage of 5 volts or less. Effective number of pixels is 320 x 2
20. Pixel spacing is 80 μm in the horizontal direction and 90 μm in the vertical direction.
It is. By adopting the ECB mode in which the initial orientation of liquid crystal molecules is homogeneous, the phase of light can be continuously modulated (Proceedings of the 51st Japan Society of Applied Physics Conference 26a-H-10).

The optical wavefront measuring devices 306 and 307 measure the phase error included in the optical wavefront every moment. Based on the measurement results, the voltage value to be applied to each pixel of the phase modulation liquid crystal elements 302 and 303 is calculated, and this is fed back to the signal generators 308 and 309 as a compensation command. Signal generator 308,3
09 controls the phase of the passing light on a pixel-by-pixel basis in accordance with the received compensation command. Note that the method for measuring the phase error of the optical wavefront is the same as in the first embodiment.

According to this embodiment, by combining two liquid crystal elements and a polarization separation element, it is possible to compensate for phase errors in optical wavefronts with high precision and high speed.

[0024]

According to the present invention, phase errors in optical wavefronts can be compensated with high precision. The optical device of the present invention can be applied to a wide range of fields of adaptive optics, including astronomical observation, by taking advantage of its real-time properties.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of Example 1 of the present invention.

FIG. 2 is a plan view showing the configuration of Example 2 of the present invention.

FIG. 3 is a plan view showing the configuration of Example 3 of the present invention.

FIG. 4 is a perspective view showing the structure of a polarizing element used in Example 1 of the present invention.

FIG. 5 is a diagram illustrating the action of a polarizing element used in Example 1 of the present invention.

[Explanation of symbols]

101 Polarizing element 102 Matrix-driven ECB mode liquid crystal element 1
03 Mirror 104 Optical wavefront measuring instrument 105 Signal generator 201 Polarizing element 202 Polarizing beam splitter 203 Optical writing type ECB mode liquid crystal element 204
Mirror 205 Optical wavefront measuring device 206 Signal generator 301 Polarizing beam splitter 302 Matrix-driven ECB mode liquid crystal element 3
03 Matrix drive type ECB mode liquid crystal element 30
4 Mirror 305 Mirror 306 Optical wavefront measuring device 307 Optical wavefront measuring device 308 Signal generator 309 Signal generator 401 Birefringent material layer 402 Birefringent material layer 403 Optical axis 404 Optical axis 405 Periodic repeating direction 406 Upper surface 501 Birefringent material 502 Birefringent material layer 403 Refractive material 503 Optical axis 504 Optical axis 505 Extraordinary light component 506 of birefringent material layer 502
Ordinary light component 507 of birefringent material layer 502 Component 508 perpendicular to the periodic repeating direction Component 509 parallel to the periodic repeating direction Periodic repeating direction

Claims (3)

[Claims] 1. A phase compensation technique for a light wavefront, comprising at least a liquid crystal element for phase modulation, a signal generator for the liquid crystal element, a polarizing element for converting random polarized light into linearly polarized light in one direction, and an optical wavefront measuring device. , an optical device comprising: a circuit for feeding back the output of the optical wavefront measuring device to the signal generator. 2. A phase compensation technique for a light wavefront, comprising at least a phase modulating liquid crystal element, a signal generator for the liquid crystal element, a polarizing element for separating random polarized light into two linearly polarized lights, and an optical wavefront measuring device. , an optical device comprising: a circuit for feeding back the output of the optical wavefront measuring device to the signal generator. 3. The optical device according to claim 1, wherein the phase modulation liquid crystal element is an ECB (Electric Field Controlled Birefringence) mode liquid crystal element.