Trex Communications Corporation

Thermotrex Corporation

Michael D Rivers

Victor Hokkiu Chan

Scott Harris Bloom

James H Menders

Eric John Korevaar

Richard G Trissel

Irene Chen

Amy Low

A liquid crystal variable retarder (LCVR) with automatic gain control for use with an imager-based target tracking application such as a free-space laser communication system. An LCVR is made of two optical windows separated by a gap, typically of a few microns. The gap is filled with nematic liquid crystal material. Electrodes are situated to enable an electric field to be applied between the optical windows and thus across the liquid crystal material. With no voltage applied to the electrodes the liquid crystals lie parallel to the optical windows. In this state of operation, the LCVR exhibits maximum retardation. As voltage is applied to the electrodes the liquid crystal molecules rotate away from the optical windows, becoming perpendicular to the optical windows. In this state of operation, the LCVR exhibits minimum retardation. A preferred embodiment of the invention includes an optical train having a first polarizer, a filter, a second polarizer orthogonal to the first polarizer, a liquid crystal variable retarder, and a third polarizer orthogonal to the second polarizer. The light then passes through focusing optics that image the light onto an imaging array, such as a CCD device, or a photodetector. A feedback circuit controls the liquid crystal variable retarder to provide variable attenuation of an incoming light beam.

Liquid crystal variable retarder for free-space laser communication system

A method and apparatus for setting the wavelength of a laser beacon in a free-space laser communication system. The invention uses the absorption and transmission attributes of a material, such as cesium, to generate a physical environment at the transmitting transceiver that essentially exactly replicates the environment that governs the physics of an atomic line filter at a receiving transceiver that is based on the absorption and transmission attributes of the same material. In general, the invention includes an apparatus for setting the wavelength of a laser beacon in a free-space laser communication system, comprising: a wavelength-tunable laser beacon having an output beam; optical means for directing at least part of the output beam through an absorption cell having at least one absorption peak; a photodetector positioned relative to the absorption cell for detecting wavelengths output from the absorption cell corresponding to a selected range of wavelengths for the output beam; a circuit, coupled to the wavelength-tunable laser beacon and the photodetector, for determining laser beacon tuning parameters corresponding to at least one absorption peak from the detected wavelengths and for setting a wavelength for the output beam corresponding to the determined tuning parameters.

Method and apparatus for locking the wavelength of beacon beam in a

A laser communication device for transmitting and receiving information imposed on laser beams. A transmitting unit and a receiving unit are implemented based on atomic line filters. The transmitting unit includes a compact tunable laser locked to a selected atomic transition line. Information may be imposed on a laser beam by modulating the frequency thereof while maintaining its output power substantially unchanged.

Laser communication device

A portable laser communication transceiver for transmitting and receiving information imposed on laser beams. A communication signal is imposed on a laser beam having a divergence of between 1 degree and 4 degrees. The beam is directed by an operator, sighting through a telescopic viewing device, at a distant transceiver which collects light in the laser beam with a. In preferred embodiments, the transceivers are handheld and each comprises a microphone and earphones allowing operators to talk with each other. Digital information can also be transmitted from personal computers and other electronic information equipment at the location of each operator. In a preferred embodiment useful for military and surveying applications, a GPS, a compass and a laser ranging system is provided. This enables the operator to sight through a binocular to a target and determine its position in longitude, latitude and elevation. Target position information can then be transmitted to a distant transceiver which in this case could be a base transceiver.

For transmitting information via laser beams to and from other similar laser communication transceivers. Each transceiver comprises a wavelength locked beacon laser providing a beacon beam. The transceivers determine the precise location of other transceivers by detecting these beacon beams with beacon receive units comprising atomic line filters matched to the beacon wavelength. Signals are transmitted by imposing an electronic signal on laser beams produced by one or more signal laser devices. These signals are directed with precision at other transceivers, and the signal beams are detected with very narrow field of view signal receive units. In a preferred embodiment, these transceivers are installed on 66 satellites in low earth orbit and on selected mountain tops on earth to provide a global communication system.

Point-to-point laser communication device

A laser communication transceiver for transmitting information via laser beams to and from other similar laser communication transceivers. Each transceiver comprises a wavelength locked beacon laser providing a beacon beam. The transceivers determine the precise location of other transceivers by detecting these beacon beams with beacon receive units comprising atomic line filters matched to the beacon wavelength. Signals are transmitted by imposing an electronic signal on laser beams produced by one or more signal laser devices. These signals are directed with precision at other transceivers, and the signal beams are detected with very narrow field of view signal receive units. In a preferred embodiment, these transceivers are installed on 66 satellites in low earth orbit and on selected mountain tops on earth to provide a global communication system.

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Santee, CA, United States of America

Michael D Rivers