Optical apparatus including a liquid crystal modulator

What is claimed is:

1. An optical apparatus for controlling the wave front of a coherent light by using phase distributions recorded in a spatial light modulator, comprising:

at least one electrically addressed liquid crystal spatial light modulator, said liquid crystal spatial light modulator including a liquid crystal panel having a liquid crystal layer sandwiched between a pair of substrates, a plurality of discrete electrodes formed on at least one of said substrates, active elements connected to the respective electrodes, said electrodes and active elements defining an array of pixels and at least one director for orienting the molecules of said liquid crystal layer so that the liquid crystal molecules are oriented uniformly parallel to the panel substrates at the initial stage of operation;

means for driving said liquid crystal spatial light modulator;

means for polarizing the coherent light into a linearly polarized light before application to said at least one liquid crystal spatial light modulator, said polarized light having a direction parallel to a plane defined by a line normal to said substrates and by said director of the liquid crystal molecules.

2. An optical apparatus, comprising:

a coherent light source for producing light;

at least one electrically addressed liquid crystal spatial light modulator means for receiving said coherent light from said coherent light source and having a light emitting side;

means for recording complex amplitude distributions in said liquid crystal spatial light modulator means so that said coherent light applied to said liquid crystal spatial light modulator means is modulated in response to said complex amplitude distributions;

liquid photo-setting material responsive to light from said coherent light source;

container means for carrying said photo-setting material and positioning said material in the path of light from the light emitting side of said liquid crystal spatial light modulator means;

whereby said photo-setting material, when illuminated by said coherent light as modulated by the liquid crystal spatial light modulator means is set in accordance with an amplitude distribution from said recording means to create an image.

3. An optical apparatus according to claim 2, wherein said container means is transparent.

4. An optical apparatus according to claim 2, wherein light from the light emitting side of said liquid crystal spatial light modulator means defines an image in a plane, said image having a two-dimensional intensity distribution in accordance with an amplitude distribution from said recording means, and including means for moving said container means in a direction which is not parallel to said plane of said image, whereby said photo-setting material is set in accordance with said two-dimensional intensity distribution.

5. An optical apparatus according to claim 2, wherein said recording means sequentially records a series of amplitude distributions; and means for sequentially displacing the set portion of photo-setting material out of a setting position in coordination with said sequential recording of said series of amplitude distributions to produce a three-dimensional object.

6. An optical apparatus according to claim 2, wherein the light from the light emitting side of said liquid crystal spatial light modulator means defines an image in a plane, said image having a two-dimensional intensity distribution in accordance with an amplitude distribution from said recording means, said apparatus further comprising means for moving said plane defined by said image having a two-dimensional intensity distribution in a direction which is not parallel to the plane of said image, whereby said photo-setting material is set in accordance with said two-dimensional intensity distribution as said two-dimensional intensity distribution is moved in said direction which is not parallel to the plane of said two-dimensional intensity distribution.

7. An optical apparatus according to claim 2, wherein said liquid crystal spatial light modulator means produces an image having a three dimensional intensity distribution in accordance with amplitude distributions from said recording means, said photo-setting material being set in accordance with said three-dimensional intensity distribution.

8. An optical apparatus according to claim 2, wherein said recording means sequentially records a series of amplitude distributions, wherein light from the light emitting side of said liquid crystal spatial light modulator means defines an image in a plane, said image having a two dimensional intensity distribution in accordance with said amplitude distribution;

and wherein said plane is moved within said container means in coordination with said sequential recording of said series of amplitude distributions to produce a three-dimensional object.

9. An optical apparatus according to claim 8 and including at least two of said liquid crystal spatial light modulator means each producing an image on a plane, one of said means for moving the image plane being associated with each of said at least two liquid crystal spatial light modulator means, said recording means sequentially recording a series of amplitude distributions on each of said at least two liquid crystal spatial light modulator means, so that each of said planes is moveable in said container means in coordination with said sequential recording of said series of amplitude distributions to produce a three-dimensional image.

10. An optical apparatus, comprising:

an electrically addressed liquid crystal spatial light modulator of a phase modulation type;

an electrically addressed liquid crystal spatial light modulator of an amplitude and phase modulation type;

means for driving said liquid crystal spatial light modulators independently of each other;

a coherent light source;

means for splitting the coherent light from said coherent light source into a first path and a second path;

said liquid crystal spatial light modulator of a phase modulation type being disposed on said first path of split light, said liquid crystal spatial light modulator of an amplitude and phase modulation type being disposed on said second path of split light;

means for causing the first and second light paths after passing through the respective liquid crystal spatial light modulators to interfere with each other;

an optical recording medium responsive to the light from said coherent light source at the location where the first and second light paths interfere with each other; and

recording means including said driving means for encoding the light wave front of said first path by use of a phase distribution of said liquid crystal spatial light modulator of the phase modulation type and for applying two-dimensional complex amplitude distributions representative of image information to the light wave front of said second path by use of said liquid crystal spatial light modulator of the amplitude and phase modulation type, thereby encoding the light wavefront of said first path for each two-dimensional complex amplitude distribution, and performing the multiplex recording of a plurality of the images of said two-dimensional complex amplitude distributions in said optical recording medium by interference exposure.

11. An optical apparatus according to claim 10, wherein said liquid crystal spatial light modulator of the amplitude and phase modulation type includes:

an electrically addressed liquid crystal spatial light modulator of amplitude modulation type;

and a further electrically addressed liquid crystal spatial light modulator of the phase modulation type;

each of said liquid crystal spatial light modulator of the amplitude modulation type and said further liquid crystal spatial light modulator of the phase modulation type including a liquid crystal panel having a nematic liquid crystal layer sandwiched between a pair of substrates, a plurality of discrete electrodes formed on at least one of said substrates and active elements connected to the respective electrodes, said electrodes and active elements defining an array of pixels in each of said liquid crystal spatial light modulator means of the amplitude modulation type and said further liquid crystal spatial light modulator means of the phase modulation type;

each of said liquid crystal spatial light modulator of the amplitude modulation type and said further liquid crystal spatial light modulator of the phase modulation type being disposed on an optical axis one behind the other with their pixels in alignment, a pair of polarizing plates positioned so that at least said liquid crystal spacial light modulator of the amplitude modulation type is sandwiched by said pair of polarizing plates; and

said liquid crystal spatial light modulator of the amplitude modulation type including a liquid crystal panel of TN (twisted nematic) mode having a twisted nematic liquid crystal layer; said further liquid crystal spatial light modulator of the phase modulation type including a liquid crystal panel of an ECB (electrically controlled birefringence) mode having a liquid crystal layer sandwiched between a pair of substrates and wherein the liquid crystal molecules are oriented uniformly parallel to the panel substrate at the initial stage of operation.

12. An optical apparatus according to claim 11, wherein said recording medium is made of an electro-optical material.

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BACKGROUND OF THE INVENTION

The present invention relates to an optical apparatus which uses a liquid crystal device.

Holography has commonly been used as means for controlling the wave front of coherent light. Various types of information apparatus which use a holographic device have been developed and some of them have been put into practical use as a laser scanner or optical disk head.

Since holographic devices are manufactured using a recording material, such as a silver halide photosensitive emulsion or a photo-resist, such devices must be reconstructed each time the requirements for the holographic device change. The man-hours and equipment investment required for reconstruction are a great burden to the manufacturer.

By providing a programmable function for controlling the light wave front by use of a liquid crystal device exhibiting the desired light wave modulation characteristics, the foregoing problem is solved.

SUMMARY OF THE INVENTION

Generally speaking in accordance with the present invention, an optical apparatus is provided.

The optical apparatus behaves as follows. Complex amplitude distribution data (e.g. Fourier transform data) is input to a liquid crystal device. As light is transmitted through the liquid crystal device, its phase and/or amplitude is modulated. The degree of modulation can be changed instantaneously by changing the complex amplitude data displayed on the liquid crystal device (also called a liquid crystal spatial light modulator).

Accordingly, it is an object of the present invention to provide an improved optical apparatus for controlling the wave front of coherent light.

Another object of the present invention is to provide an optical apparatus which can be applied to programmable optical interconnections, large-capacity optical storage devices and three-dimensional display devices.

A further object of the present invention is to provide a optical device which forms three-dimensional models formed from an optical resin.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For more complete understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of a first embodiment of an optical apparatus in accordance with the present invention;

FIGS. 2(a) and 2(b) are schematic views showing modifications of the first embodiment in accordance with the present invention;

FIG. 3(a) is a top plan view showing the external view of an electrically addressed transmission type liquid crystal device;

FIG. 3(b) is a top plan view showing an example of the pixel arrangement of the electrically addressed transmission type liquid crystal device;

FIG. 3(c) is an exploded schematic prospective view of the polarizing plates and the liquid crystal material showing the respective polarization directions;

FIG. 4 is a graph showing the phase modulation characteristics of a twisted nematic (TN) mode liquid crystal device;

FIG. 5 is a graph showing the amplitude modulation characteristics of a TN mode liquid crystal device;

FIG. 6 is a graph showing the phase modulation characteristics of an ECB mode liquid crystal device;

FIG. 7 is a graph showing the amplitude modulation characteristics of an ECB mode liquid crystal device;

FIG. 8 is a cross-sectional view of an electrically addressed reflection type liquid crystal device;

FIG. 9 is a cross-sectional view illustrating a first method of manufacturing an optically addressed liquid crystal display member using an electrically addressed transmission type liquid crystal device;

FIG. 10 is a cross-sectional view illustrating a second method of manufacturing an optically addressed liquid crystal display member using an electrically addressed transmission type liquid crystal device;

FIG. 11 is a schematic perspective view illustrating reduction projection of two-dimensional images recorded on electrically addressed transmission type liquid crystal devices;

FIG. 12 is a cross-sectional view illustrating a third method of manufacturing an optically addressed liquid crystal display member using an electrically addressed transmission type liquid crystal device;

FIG. 13 is a top plan view of an example of pixel orientation illustrating the concept of the positional relation between the pixels of an active device;

FIG. 14 is a schematic view of a seventh embodiment in accordance with the present invention;

FIGS. 15(a) and 15(b) show the amplitude distribution of a kinoform;

FIG. 16 is a schematic view of an eighth embodiment in accordance with the present invention;

FIGS. 17(a) and 17(b) are schematic views of a ninth embodiment in accordance with the present invention;

FIG. 18(a) is a top plan view of a lens recorded on a liquid crystal device, showing a tenth embodiment in accordance with the present invention;

FIG. 18(b) is a side elevational schematic view of a lens recorded on the liquid crystal device having a lens recorded thereon and converging light in the tenth embodiment of the present invention;

FIGS. 19(a) and 19(b) are top plan views of two embodiments of a plurality of lenses recorded on the liquid crystal device in an eleventh embodiment of the present invention;

FIG. 20(a) is a top plan view of a plurality of lenses recorded on the liquid crystal device in a twelfth embodiment of the present invention;

FIG. 20(b) side elevational schematic view of the twelfth embodiment of the present invention;

FIG. 20(c) is a partially enlarged cross-sectional view of the twelfth embodiment of the present invention;

FIG. 21 is a schematic view of the thirteenth embodiment of the present invention;

FIGS. 22(a), 22(b), 22(c), and 22(d) are perspective view of various wiring patterns;

FIG. 23 is a schematic view of the fourteenth embodiment in accordance with the present invention;

FIG. 24 is a schematic view of the fifteenth embodiment of the present invention;

FIG. 25 is a schematic view of the sixteenth embodiment of the present invention;

FIG. 26 is a schematic view of the eighteenth embodiment of the present invention;

FIG. 27(a) is a perspective view of a three-dimensional formed model;

FIG. 27(b) is a cross-sectional view of a three-dimensional formed article;

FIG. 28 is a schematic view of the nineteenth embodiment of the present invention;

FIG. 29 is a schematic view of the twentieth embodiment of the present invention;

FIG. 30 is a schematic view of the twenty-first embodiment of the present invention;

FIG. 31 is a schematic view of the twenty-second embodiment of the present invention;

FIG. 32 illustrates an aberration of a liquid crystal panel; and

FIG. 33 is a schematic view of the twenty-third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will now be described with reference to the accompanying drawings.

First Embodiment

FIG. 1 shows the configuration of a first embodiment of an optical apparatus according to the present invention. A laser beam 109 emanating from a laser beam source 104 is converted into parallel rays of light by means of a collimator lens 105. A computer generated hologram recorded on liquid crystal device 106 modulates the wave front of the incident light. The modulated light passes through a lens 107 and then forms a laser beam spot or a spot row 110 on a predetermined output screen 108.

A video signal for recording the computer-generated hologram on liquid crystal device 106 is created by a personal computer (PC) 101. PC 101 includes a processing unit and memory 102. The signal is input to liquid crystal device 106 through an interface circuit 103. The birefringence of each pixel of liquid crystal device 106 changes in accordance with the level of the input signal, by which amplitude modulation of the wave front of the laser beam is performed. The computer-generated hologram recorded on liquid crystal device 106 can be rewritten at high speed by reading out the pattern data previously stored in memory 102 of PC 101.

FIGS. 2(a) and 2(b) show two further configurations of the optical apparatus according to the present invention, like reference numbers being used for like elements in FIG. 1. In FIG. 2(a), the optical path is bent using two mirrors 201 and 202. In FIG. 2(b), the laser beam propagates between two light guiding plates 211 and 212.

By employing the configurations shown in FIGS. 2(a) and 2(b), it is possible to reduce the size of the optical apparatus.

FIG. 3(a) shows the external view of a liquid crystal device 301 which is the major component of the optical apparatus in accordance with the first embodiment of the present invention. Liquid crystal device 301 is driven by signals applied through a lead array 303. This liquid crystal device has the following features:

(1) There is no cross talk between the pixels because a poly-Si thin-film transistor (TFT) on each pixel acts as an active element.

(2) The size is small because of a built-in driver.

(3) In one example, a display area 302 measuring 19 mm.times.14 mm having a rectangular pixel matrix 320 pixels in the horizontal direction and 220 pixels in the vertical direction is provided, although the display area dimensions, pixel counts and pixel orientations can be provided.

FIG. 3(b) is a fragmentary enlarged top plan view of the display area 302 of liquid crystal device 301. The pixels 311 are regularly arranged in the form of a lattice or matrix in which they are equally spaced from each other in both the horizontal and vertical directions.

The thin film transistor (TFT) and other circuit elements of active matrix type liquid crystal device 301 are disposed below a light blocking mask 312 in order to avoid malfunctions caused by potential irradiation.

The use of a liquid crystal device having the aforementioned features enable the laser beam spot arrangement having a desired intensity distribution to be freely generated.

In the optical apparatus in accordance with a first embodiment of the present invention, the computer-generated hologram comprises a Fourier transform type amplitude hologram which is characterized in that each segment of Fourier data is expressed using the amplitude distribution of nine of pixels 311. The Fourier data has nine components each of which is expressed using one of pixels 311. This is described further in Appl. Opt. 9 (1970) p. 1949.

The liquid crystal device used in the optical apparatus in accordance with a first embodiment includes a twisted nematic (TN) mode liquid crystal panel 310 and two polarizing plates 315 and 316 disposed on each side of panel 310. In this invention, the directions of axes of these elements have the following relationship.

(1) The directions of the axes of polarizing plates 315 and 316 are orthogonal to each other.

(2) The direction of transmission of front polarizing plate 315 is perpendicular to the director of the liquid crystal molecules 311 on the incident surface.

The above-described arrangement of the components of liquid crystal device 301 is necessary for the following reasons.

The computer-generated hologram is recorded on liquid crystal device 301 using two-dimensional amplitude distribution. Unfortunately, phase shifts also occur (Opt. Lett. 13, 251-53 (1988)). Hence, the directional relation between liquid crystal panel 310 and polarizing plates 315 and 316, which assures the smallest possible phase shifts must be obtained.

FIG. 4 shows the relationship between the phase shift and the voltage applied to the liquid crystal panel, obtained in the four fundamental conditions under which a TN mode liquid crystal panel is used. In FIG. 4, curve 1 denotes the case where the directions of the two polarizing plates are parallel to each other while the direction of the front polarizing plate is parallel to the director of the liquid crystal molecules on the incident surface. Curve 2 denotes the case where the directions of the polarizing plates are parallel to each other while the front polarizing plate is orthogonal to the director of the liquid crystal molecules on the incident surface. Curve 3 denotes the case where the directions of the two polarizing plates are orthogonal to each other while the direction of the front polarizing plate is parallel to the director. Curve 4 denotes the case where the directions of the polarizing plates are orthogonal to each other while the direction of the front polarizing plate is orthogonal to the director.

As is clear from FIG. 4, the phase shifts are the smallest when the directions of the polarizing plates are orthogonal to each other while the direction of the front polarizing plate is orthogonal to the director (case 4).

FIG. 5 shows the relationship between the applied voltage and the amplitude shifts, obtained when the liquid crystal panel and the polarizing plates are arranged in the above-described manner. It is possible to obtain large contrast and sufficient gradient.

In this way, a high performance amplitude type computer-generated hologram can be recorded on the liquid crystal device.

As will be understood from the foregoing description of the optical apparatus according to the present invention, it is possible to perform highly accurate position control of a laser beam and generation of irregular spot arrangements on a real-time basis by using wave front reconstruction of the amplitude type computer-generated hologram recorded on a TN mode liquid crystal device.

In this embodiment, two-dimensional position control of the laser beam has been described. However, control of the laser beam in three-dimensional space is made possible by sequentially changing the pattern of the computer-generated hologram.

Second Embodiment

In a second embodiment in accordance with the invention, an electrically controlled birefringence (ECB) mode liquid crystal device is used in place of the TN mode liquid crystal device used in the first embodiment.

The liquid crystal device in this optical apparatus according to the present invention includes an ECB mode liquid crystal panel and a single polarizing plate disposed on the side of the panel on which a laser beam is incident. The liquid crystal molecules in the liquid crystal panel are oriented uniformly parallel to the panel substrate at the initial stage of the operation. The direction of transmission of the polarizing plate is parallel to the plane made by the panel substrate and the director of the liquid crystal molecules.

The above-described structure of the liquid crystal device enables changes in birefringence of the liquid crystal layer, caused by applied voltage, to be effectively utilized. It is therefore possible to attain excellent phase modulation of the laser beam.

FIG. 6 shows the relationship between the phase shift and the applied voltage obtained from the ECB mode liquid crystal device. Linear phase shift can be obtained in the applied voltage range from 1.2-2.5 volts. That relationship must be maintained in order to achieve phase control of the wave front of the light at each pixel and hence control of the laser beam. It is clear from FIG. 6 that a phase shift of 2.pi., required for recording a phase type hologram, can be obtained when the amplitude of the video signal is 2.1 volts.

FIG. 7 shows the relationship between the transmission of light and the applied voltage obtained from the liquid crystal device used in FIG. 6. In FIG. 7, another polarizing plate was disposed on the light emitting side of the liquid crystal device for measurements. The directions of transmission of the two polarizing plates were parallel to each other. It is apparent from FIG. 7 that the transmission, i.e., the square of the amplitude, is substantially constant regardless of the applied voltage. This relationship must be maintained in order to have control of the laser beam which is free from disturbance caused by amplitude modulation.

It is possible to record high-performance phase type computer-generated hologram on the liquid crystal device by utilizing the characteristics shown in FIG. 6 and 7.

The computer-generated hologram used in the optical apparatus of this embodiment is of the Fourier transform type in which pixels and Fourier transform data has a one-to-one correspondence. The amplitude and phase of each Fourier data (complex number) corresponds to the phase value of the light wave of each pixel. This is described further in Opt. Eng. 19 (1980) p. 297.

In this way, a limited number of pixels can be effectively utilized when a computer-generated hologram is recorded on an ECB mode liquid crystal device.

As will be understood from the foregoing description, in the optical apparatus according to the present invention, highly accurate position control of a laser beam and generation of an irregular laser beam spot arrangement can be performed on a real-time basis utilizing the wave front reproduction function of a phase type computer-generated hologram recorded on an ECB mode liquid crystal device.

In this embodiment, position control of the laser beam in a two-dimensional space has been described. However, control in a three-dimensional space is made possible by exchanging the pattern of the computer-generated hologram.

Third Embodiment

This embodiment differs from the first embodiment in that a liquid crystal device having a configuration shown in FIG. 8 is used in place of the TN mode liquid crystal device.

First, a method of manufacturing this liquid crystal device 800 will be described.

After a transistor-type active element 811 and a matrix electrode 808 are formed on a silicon substrate 810, they are sealed with an insulating material 809. Second insulator 812 (e.g. SiO) is disposed between active elements 811. The surface is then etched to obtain a flat surface. Next, a dielectric mirror 807 is formed by evaporation. Oblique evaporation of the surface of the dielectric mirror 807 is then performed to form an oriented surface 806 for alignment of the liquid crystal molecules. A liquid crystal 805 (e.g. TN mode) is charged in the gap between dielectric mirror 807 having the oriented surface 806 for alignment and a glass substrate 802 on which a transparent opposed electrode 803 is formed. In addition, an orientation layer 804 is disposed on glass substrate 802. A polarizing plate 801 is disposed on the outside of glass substrate 802.

Light incident on the liquid crystal device 800 through glass substrate 802 is reflected by dielectric mirror 807. It then passes back through liquid crystal 805 and then leaves liquid crystal device 800 through glass substrate 802. During that time, the polarization of the light is changed by liquid crystal 805 whose orientation is controlled by an applied voltage. An electric field is generated between matrix electrode 808 and opposed electrode 803 when a voltage is applied to matrix electrode 808. The electric field changes the orientation of the liquid crystal molecules and, hence, the polarization of the light emitted from the liquid crystal device.

In this embodiment, matrix electrode 808 is comprised of aluminum. Normally, when aluminum is utilized a protective film is required in order to prevent an electrochemical reaction. However, in this embodiment, a protective film is not necessary due to the presence of dielectric mirror 807.

Furthermore, since dielectric mirror 807 is seamless, a uniform display state can be obtained when no voltage is applied to matrix electrode 808. Even when a voltage is applied, a high-definition display, having less seams than a conventional liquid crystal device, can be obtained.

Matrix electrode 808 can also be made of chromium. Such an electrode which cannot be conventionally used due to low reflectance, is electrochemically stable and therefore appropriate for this embodiment.

Dielectric mirror 807 is formed by alternately laminating thin films of SiO.sub.2 and amorphous silicon by electron beam evaporation. Dielectric mirror 807 has at least 90% reflectance for the central wavelength thereof.

The oblique evaporation used for orientation of liquid crystal 805 is an alignment technique in which liquid crystal molecules are oriented using the crystals grown obliquely relative to the normal of the substrate. In this embodiment, SiO.sub.2 is evaporated on the substrate inclined at 85 degrees relative to the normal of the substrate.

Alignment of liquid crystal molecules 805 by the film formed on dielectric mirror 807 may also be performed by a rubbing method. In that case, dielectric mirror 807 must be designed with the thickness or reflectance of the oriented film taken into consideration in order to prevent a reduction in the index of refraction.

This embodiment has the following advantages.

(1) Since the dielectric mirror formed on the liquid crystal driving electrode is used as a reflecting plate, it is not necessary for the reflectance of the liquid crystal driving electrode to be taken into consideration. Therefore, a wide variety of materials can be used.

(2) Since the dielectric mirror acts as a protective film for the electrode, materials having low electrochemical stability can be used increasing the degree of freedom in designing the device.

(3) Presence of a seamless dielectric mirror ensures uniform display when no voltage is applied to the electrode and ensures high-definition display having less seams than the conventional display device when voltage is applied.

(4) Since the reflecting film is above the liquid crystal driving electrode, spec