Hughes Aircraft Company

United States of America As Represented by the Secretary of the Air Force

The United States of America As Represented by the Secretary of

Paul O Braatz

Jan Grinberg

Uzi Efron

Alexander D Jacobson

Michael Waldner

Chiung-Sheng Wu

Murray S Welkowsky

William P Bleha

Yuri Owechko

Michael J Little

Prahalad K Vasudev

Lewis M Fraas

Kuen Chow

William P Bleha, Jr

J Gregory Nash

Glenn D Robertson, Jr

Robert N Schwartz

Raymond Balcerak

A liquid crystal light valve is provided with an array of photoconductive pedestals surrounded by a dielectric matrix material. Metal mirror pads are formed on top of each pedestal to form a high resolution metal matrix mirror, with each pedestal/mirror combination servicing one image pixel. The dielectric matrix forms a potential barrier between the individual photoconductive pedestals which prevents lateral charge migration between pedestals. The metal matrix mirror also shields the underlying photoconductive pedestal from photoactivation by the readout beam. The dielectric matrix material has a lower dielectric constant than the photoconductive pedestals, allowing the impedance of the photoconductive pedestals to match the impedance of the liquid crystal layer with a much thinner layer of photoconductive material than in prior LCLVs using a continuous photoconductive layer. The thinner photoconductive layer results in higher electric fields which improve the LCLV's response time, photodegradation rate, spatial resolution and spectral response.

LCLV having photoconductive pedestals each having a cross-sectional area

An infrared (IR) radiation transducer integrates an IR detector array with a liquid crystal (LC) readout. The IR detector is preferably a pixelized bolometer array, but other detectors such as pyroelectric materials are possible. To modulate the LC in response to detected IR radiation, a modulating section is provided that includes a charge injection structure which injects electrical charge in response to the detected IR radiation, and a charge transfer structure that transfers the injected charge to the LC readout section. During its active phase the charge transfer layer is depleted of majority charge carriers, and the charge injection and transfer mechanism operates in a manner analogous to a bipolar transistor. A visible readout is obtained by directing readout light through the LC, where it is modulated in accordance with the detected IR image. The transducers are small and light weight enough to be incorporated into a pair of goggles, for which no separate cooling is required.

Infrared transducer and goggles incorporating the same

An infrared (IR) simulator is disclosed in which an array of pixels is defined on an insulative substrate by resistor bridges which contact the substrate at spaced locations and are separated from the substrate, and thereby thermally insulated therefrom, between the contact locations. Semiconductor drive circuits on the substrate enable desired current flows through the resistor bridges in response to input control signals, thereby establishing the appropriate IR radiation from each of the pixels. The drive circuits and also at least some of the electrical lead lines are preferably located under the resistor bridges. A thermal reflector below each bridge shields the drive circuit and reflects radiation to enhance the IR output. The drive circuits employ sample and hold circuits which produce a substantially flicker-free operation, with the resistor bridges being impedance matched with their respective drive circuits. The resistor bridges may be formed by coating insulative base bridges with a resistive layer having the desired properties, and overcoating the resistive layers with a thermally emissive material. The array is preferably formed on a silicon-on-sapphire (SOS) wafer. Arrays of electromagnetic radiation bridge detectors may also be formed, with the bridges having either resistor, thermocouple or Schottky junction constructions.

Radiation detector array using radiation sensitive bridges

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.times.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.times.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.

Reflective matrix mirror visible to infrared converter light valve

A single-Schottky liquid crystal is disclosed in which a series of Schottky contacts are made on one side of a photoconductor substrate by a metal matrix mirror, with a doped semiconductor back contact electrode on the other side of the substrate. The light valve offers several operational advantages over MOS devices, and is easier to fabricate than double-Schottky light valves. It can be operated either in an AC mode or, by doping the liquid crystal ions, in a DC mode.

Single-Schottky diode liquid crystal light valve and method

A double Schottky diode light valve (5) includes a liquid crystal (80) for locally modulating a beam (120) by polarization rotation to produce a modulated beam (121), and a photoconductor (40) located adjacent the liquid crystal (80) for receiving and absorbing a second beam (110). The photoconductor (40) controls the polarization responsively to the optical content of the second beam (110). The photoconductor (46) includes a semiconductor substrate and a pair of Schottky diodes (60/40, 30/40) disposed on opposing sides of the substrate. The absorption of the second beam (110) by the substrate (40) produces photogenerated carriers. The pair of Schottky diodes (60/40, 30/40) maintain the substrate (40) substantially depleted of such carriers and also reflects the modulated beam back through the liquid crystal.

Double-Schottky diode liquid crystal light valve

A double Schottky diode light valve (5) includes a liquid crystal (80) for locally modulating a beam (120) by polarization rotation to produce a modulated beam (121), and a photoconductor (40) located adjacent the liquid crystal (80) for receiving and absorbing a second beam (110). The photoconductor (40) controls the polarization responsively to the optical content of the second beam (110). The photoconductor (46) includes a semiconductor substrate and a pair of Schottky diodes (60/40, 30/40) disposed on opposing sides of the substrate. The absorption of the second beam (110) by the substrate (40) produces photogenerated majority carriers. The pair of Schottky diodes (60/40, 30/40) maintain the substrate (40) substantially depleted of such carriers and also reflects the modulated beam back through the liquid crystal.

Double-schottky diode liquid crystal light valve

An LCLV is formed with a sapphire substrate base, a highly doped, thin silicon epitaxial layer forming an ohmic back contact on a smooth surface of the sapphire substrate, and a lightly doped, high resistivity silicon epitaxial layer in the range of about 20-60 microns thick on the back contact. The use of a sapphire substrate provides a better surface quality and higher resolution than previously available with the semiconductor substrates. Lattice defects in the thin back contact are reduced by the formation of a buried amorphous layer adjacent the sapphire substrate, and subsequent recrystallization thereof using the unamorphized portions of the back contact as recrystallization seeds. The application of the invention to both MOS and Schottky diode LCLVs is discussed.

Silicon-on-sapphire liquid crystal light valve and method

A pulsed readout technique is described for liquid crystal light valves which eliminates the problem of readout beam leakage through the light valve mirror. The readout beam is pulsed on only when the light valve's semiconductor layer is out of a depletion state. This can occur during an accumulation state or, in certain applications, during a specially inserted quiescent period in the light valve voltage cycle. The invention is applicable to light valves with various types of modulating inputs, and can be used with either dielectric or metal matrix mirrors.

Light valve system and method with pulsed readout

There is disclosed a single crystal silicon charge storage apparatus suitable for use in an alternating current driven liquid crystal light valve having therein a moderately doped microchannel stop grid. The charge storage medium is made of a high resistivity substrate on which an MOS capacitor is formed having fast photoelectric transient response and capable of operating over a wide frequency range. A doped microgrid structure is formed in one side of the substrate to prevent charge carrier spreading at the silicon-silicon dioxide interface and to provide a focusing electric field for the charge carriers. The signal from the substrate is electrically coupled through high-reflectivity mirrors and light blocking layers to the liquid crystal.

High resolution AC silicon MOS-light-valve substrate

A liquid crystal light valve having an improved counterelectrode structure. The light valve includes a layer of liquid crystal material which lies intermediate a photosensitive substrate of intrinsic semiconductive material and the counterelectrode. The upper surface of the substrate is characterized by a highly doped peripheral channel stop. The counterelectrode comprises electrically insulated inner and outer regions, the inner region substantially overlying only the intrinsic material interior said highly doped peripheral channel stop so that an electrical bias may be selectively applied, greatly enhancing the dark current breakdown voltage of the device.

Semiconductor light valve having improved counterelectrode structure

There is herein described a device useful to store a frame of low-intensity optical information over a wide spectral range or useful as a real-time light valve in visible to infrared conveter application. The device basically includes either a storage mode liquid crystal or a dynamic scattering or a field-effect liquid crystal, and a semiconductor diode array substrate wherein an insulating film with an array of conducting windows separates the liquid crystal from an active region in the substrate. A separate diffused junction is disposed in the active region adjacent each of the windows, the latter being adapted to both reflect incident light energy and conduct electrical current.

Semiconductor diode array liquid crystal device

This invention is directed to a semiconductor structure that includes at least one wafer that is fully depleted of all mobile carriers and is used as a medium for the movement of spatially modulated signal represented by charge carriers through the wafer with a spatial resolution that is smaller than the thickness of the wafer. This may be used in the form of a continuous high resolution silicon photodiode substrate to serve as an image input means for an electro-optical display medium, such as a liquid crystal. Next to the photoactivated substrate is a liquid crystal and next to the crystal is a transparent electrode. The photodiode is reverse biased and both of its sides are depleted of all mobile charges throughout its entire thickness. Thus, charges generated in the substrate move to the display not by diffusion as in prior art devices (e.g. the solid state silicon vidicon) but by the influence of the electric field which tends to minimize their lateral spread and thereby achieves a high spatial resolution in spite of the continuous character of this silicon diode device.

High resolution continuously distributed silicon photodiode substrate

There is disclosed a single crystal silicon charge storage apparatus suitable for use in an alternating current driven liquid crystal light valve having therein a PIN photodiode structure. The charge storage medium is made of a high resistivity substrate on which an MOS capacitor is formed having fast photoelectric transient response an capable of operating over a wide frequency range. A PIN photodiode structure is provided on one side of the substrate next to the MOS capacitor to deplete the substrate of its mobile charge carriers during a portion of the AC cycle and to collect the electric field-guided signal representing charge carriers that are generated or introduced into the substrate by an input mechanism. The signal from the substrate is electrically coupled through high-reflectivity mirrors and light blocking layers to the liquid crystal.

AC silicon PN junction photodiode light-valve substrate

There is disclosed a single crystal silicon charge storage apparatus suitable for use in an alternating current driven liquid crystal light valve. The charge storage medium is made of a high resistivity and photosensitive under AC excitation substrate on which an MOS capacitor is formed having fast photoelectric transient response and capable of operating over a wide frequency range. The AC activation provides to a liquid crystal light valve a greatly improved electrochemical stability. Electrically coupled high-reflectivity mirrors and light blocking layers can be used to couple the liquid crystal to the MOS capacitor.

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Canoga Park, CA, United States of America

Paul O Braatz