Reflective matrix mirror visible to infrared converter light valve

• US 4,973,136 A
• Filed: 01/10/1990
• Issued: 11/27/1990
• Est. Priority Date: 07/25/1985
• Status: Expired due to Term

• Current Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Braatz, Paul O.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Lerner, Martin
• Application Number:
  US07/463,904
• Time in Patent Office: 321 Days
• Field of Search: 250/213 R, 250/330, 250/331, 350/338, 350/342, 350/354, 350/355, 350/356, 357/19, 427/88
• US Class Current: 349/25
• CPC Class Codes: G02F 1/133553 Reflecting elements associated to illuminating devices G02F1/133605
• CPC Class Codes: G02F 1/135 Liquid crystal cells structurally associated with a photoconducting or a ferro-electric layer, the properties of which can be optically or electrically varied G02F1/133348 takes precedence
• CPC Class Codes: G02F 1/1352 Light-reflecting layers

Abstract

A reflective matrix mirror visible to infrared converter light valve (5) includes a liquid crystal medium (60) for spatially modulating an incident infrared beam by polarization rotation, a photosubstrate (30) for receiving an incident visible wavelength image (115) and for controlling the polarization rotation of the liquid crystal medium (60) responsively to the visible image (115), and a reflective matrix mirror (40). The reflective matrix mirror (40) is positioned between the liquid crystal medium (60) and the photosubstrate (30) and reflects the incident infrared beam (125) back through the liquid crystal medium (60) such that the infrared beam (125) passes through the liquid crystal medium twice and is polarization rotated responsively to the visible wavelength image (115). A polarizer (90) positioned exteriorly of the liquid crystal medium (60) converts the polarization rotation of the infrared beam (125) into output intensity modulation to produce an infrared image (130). The reflective matrix mirror (40) comprises an M×N array of infrared reflective islands comprising metallic or semiconductor/metallic compounds. The reflective matrix mirror (40) can be formed by depositing reflective material on a layer of silicon dioxide in a grid pattern using a masking technique. Alternatively, the silicon dioxide may be etched to provide an M×N array of depressions which are then used as deposition sites for the reflective material. In this later embodiment, the reflective material may be in contact with photosubstrate (30) so as to form Schottky Barrier contacts.

Claims

1. A visible to infrared image converter light valve which is operable by alternating current comprising:

(a) liquid crystal means for spatially modulating input infrared radiation by polarization rotation to produce a modulated infrared beam;

(b) a photosensitive semiconductor substrate for receiving an incident visible wavelength image and for controlling said polarization rotation of said input infrared radiation responsively to said image;

(c) insulating means in contact with said semiconductor substrate and positioned between said liquid crystal means and said semiconductor substrate, said insulating means including a continuous layer of material suitable for blocking DC current, said insulating means preventing direct contact between said liquid crystal means and said semiconductor substrate; and

(d) reflective matrix mirror means, disposed on said insulating means between said liquid crystal means and said insulating means, for reflecting said modulated infrared beam back through said liquid crystal means, said reflective matrix mirror means including a plurality of isolated reflective islands.

2. The light valve of claim 1 wherein the material of said reflective islands comprises metal.

3. The light valve of claim 2 wherein said reflective islands are arranged as an array, the spacing between adjacent said reflective islands being related to the wavelength of said input infrared radiation so that said array acts as an optically continuous reflective surface for said input infrared radiation while maintaining electrical isolation between said reflective islands in a direction parallel to said semiconductor substrate.

4. The light valve of claim 3 wherein the spacing between said reflective islands is on the order of 0.1 μ

m to 10 μ

m.

5. A reflective matrix mirror for use in liquid crystal light valves operable in an A.C. reflective mode with incident radiation having wavelengths in the infrared wavelength ranges comprising:

an array of infrared reflective elements positioned on a supporting insulating substrate and spaced apart by a distance smaller than the wavelength of incident radiation to be reflected, with each said element having dimensions on the order of the resolution element dimensions for the liquid crystal light valve used and thickness sufficient to provide desired reflectivity such that reflection of incident infrared radiation is achieved with improved spatial resolution;

said insulating substrate comprising a continuous layer suitable for blocking DC current.

6. A reflective matrix mirror for use in alternating-current driven liquid crystal light valves operable in reflective mode, comprising an M×

N array of infrared reflective elements positioned on a supporting substrate where M and N are integers and each element is spaced apart from adjacent elements by a distance smaller than the wavelength of incident radiation to be reflected, so that said array acts as an optically continuous reflective layer for the incident radiation, wherein said reflective elements are spaced apart on the order of 0.1 μ

m to 2 μ

m, with each element having dimensions on the order of the resolution element dimensions for the liquid crystal light valve used and comprising infrared reflective material having a thickness at least of a magnitude sufficient to provide reflectivity of incident radiation.

7. A reflective matrix mirror for use in alternating-current driven liquid crystal light valves operable in reflective mode, comprising an M×

N array of infrared reflective elements positioned on a supporting substrate, where M and N are integers, and each reflective element is spaced apart from adjacent elements by a distance smaller than the wavelength of incident radiation to be reflected, so that said array acts as an optically continuous reflective layer for the incident radiation, and wherein each element comprises either metallic or metallic/semiconductor compounds, and has a thickness greater than 0.05 μ

m and comprising either gold or aluminum, and dimensions on the order of the resolution element dimensions for the liquid crystal light valve used and comprises infrared reflective material having a thickness at least of a magnitude sufficient to provide desired reflectivity of incident radiation.

8. A reflective matrix mirror for use in alternating-current driven liquid crystal light valves operable in reflective mode, comprising an M×

N array of infrared reflective elements positioned on a supporting substrate, where M and N are integers, wherein said reflective elements comprise platinum-silicide on the order of 0.01 μ

m or greater in thickness and are spaced apart by a distance smaller than the wavelength of incident radiation to be reflected so that said array acts as an optically continuous reflective layer for the incident radiation, and comprise either metallic or metallic/semicondcutor compounds, with each element having dimensions on the order of the resolution element dimensions for the liquid crystal light valve used and comprising infrared reflective material having a thickness at least of a magnitude sufficient to provide desired reflectivity of incident radiation.

9. An alternating-current driven visible to infrared converter light valve comprising:

liquid crystal means for spatially modulating an input infrared beam by polarization rotation to produce a modulated infrared beam;

photoconductor means for receiving an incident visible wavelength image and for controlling said polarization rotation responsively to said image;

reflective matrix mirror means, disposed between said liquid crystal means and said photoconductor means, for reflecting said modulated infrared beam back through said liquid crystal means, whereby said modulated infrared beam passes through said liquid crystal means twice and is polarization rotated in proportion to said visible wavelength image, said reflective matrix mirror means including an N by M array of electrically isolated reflective islands disposed on a substrate, where N and M are integer quantities and are determined by the size and shape of the desired light valve divided by the number of resolution elements available, and said islands are spaced apart by a small distance as compared to the wavelength of said infrared beam so as to appear as an optically continuous reflective layer to said infrared beam, wherein said reflective islands comprise a material reflective of infrared wavelengths and wherein the distance between said reflective islands is less than the wavelength of said infrared beam and wherein the spacing between said reflective islands is on the order of 0.5 μ

m to 2.5 μ

m, and

polarization means, positioned exteriorly of and disposed adjacent said liquid crystal means, for converting said polarization rotation of said modulation infrared beam into intensity modulation to produce an infrared image.

10. An alternating current driven visible to infrared converter light valve comprising:

liquid crystal means for spatially modulating an input infrared beam by polarization rotation to produce a modulated infrared beam;

photoconductor means for receiving an incident visible wavelength image and for controlling said polarization rotation respectively to said image;

reflective matrix mirror means, disposed between said liquid crystal means and said photoconductor means, for reflecting the modulated infrared beam back through said liquid crystal means, whereby said modulated infrared beam passes through said liquid crystal means twice and is polarization rotated in proportion to said visible wavelength image, said reflective matrix mirror means including an N by M array of electrically isolated reflective islands disposed on a substrate, where N and M are integer quantities and are determined by the size and shape of the desired light valve divided by the number of resolution elements available and being spaced apart by a small distance as compared to the wavelength of said input infrared beam radiation so as to appear as an optically continuous reflective layer to said input infrared beam of radiation, wherein said reflective islands comprise a material reflective of infrared wavelengths of input infrared radiation, wherein said substrate comprises an isolated array of doped regions and said islands are positioned at each doped site so as to form Schottky Barrier diodes, and

polarization means, positioned exteriorly of and disposed adjacent said liquid crystal means, for converting said polarization rotation of said modulation infrared beam into intensity modulation to produce an infrared image.

11. A visible to infrared converter light valve comprising:

liquid crystal means for spatially modulating an input infrared beam by polarization rotation to produce a modulated infrared beam;

photoconductor means for receiving an incident visible wavelength image and for controlling said polarization rotation responsively to said image;

reflective matrix mirror means, disposed between said liquid crystal means and said photoconductor means, for reflecting the modulated infrared beam back through said liquid crystal means, whereby said modulated infrared beam passes through said liquid crystal means twice and is polarization rotated in proportion to said visible wavelength image, said reflective matrix mirror means including an N by M array of electrically isolated reflective islands, where N and M are integer quantities, and are determined by the size and shape of the desired light valve divided by the number of resolution elements available and being spaced apart by a small distance as compared to the wavelength of said input infrared beam radiation so as to appear as a uniform reflective layer to an input infrared beam of radiation, wherein each reflective island corresponds to one pixel in said infrared image, and

polarization means, positioned exteriorly of and disposed adjacent said liquid crystal means, for converting said polarization rotation of said modulated infrared beam into intensity modulation to produce an infrared image.

12. A visible to infrared converter light valve, comprising:

liquid crystal means for spatially modulating an input infrared beam by polarization rotation to produce a modulated infrared beam;

photoconductor means for receiving an incident visible wavelength image and for controlling said polarization rotation responsively to said image, wherein said photoconductor means comprises a metal oxide semiconductor substrate;

reflective matrix mirror means, disposed between said liquid crystal means and said photoconductor means, for reflecting said modulated infrared beam back through said liquid crystal means, whereby said modulated infrared beam passes through said liquid crystal means twice and is polarization rotated in proportion to said visible wavelength image, said reflective matrix mirror means including a plurality of isolated reflective islands spaced apart so as to provide an optically continuous reflective surface to infrared radiation; and

polarization means, positioned exteriorly of and disposed adjacent said liquid crystal means, for converting said polarization rotation of said modulated infrared beam into intensity modulation to produce an infrared image.

13. A visible to infrared converter light valve comprising:

liquid crystal means for spatially modulating an input infrared beam by polarization rotation to produce a modulated infrared beam;

photoconductor means for receiving an incident visible wavelength image and for controlling said polarization rotation responsively to said image;

reflective matrix mirror means, disposed between said liquid crystal means and said photoconductor means, for reflecting the modulated infrared beam back through said liquid crystal means, whereby said modulated infrared beam passes through said liquid crystal means twice and is polarization rotated in proportion to said visible wavelength image, said reflective matrix mirror means including a plurality of isolated reflective islands spaced apart so as to provide an optically continuous reflective surface to infrared radiation, and

polarization means, positioned exteriorly of sand disposed adjacent said liquid crystal means, for converting said polarization rotation of said modulated infrared beam into intensity modulation to produce an infrared image,

wherein said light valve further comprises second faceplate means, disposed exteriorly of said liquid crystal means and transparent to infrared radiation, for receiving said input infrared beam, wherein said faceplate means comprises potassium chloride or germanium.