Abstract: 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.

Abstract: A free-space laser communication system having six axes of movement. The system includes a fine tracking and acquisition system comprising a low inertia steering mirror having two axes of movement which points the communication laser transmission optical apertures separately from the optical apertures for the beacon laser, a coarse tracker, and a communication receiver. A fine tracking centroider and the communication lasers have the steerable mirror in common, and thus do not experience any alignment error that might arise from use of a separate deflecting element for each. The fine tracking and acquisition system is preferably mounted on a gimbal having two axes of movement, and the gimbal in turn is preferably mounted in a housing having two axes of movement.

Abstract: A free-space atmospheric laser communications error control circuit. The invention includes a control circuit that circumvents the problems of scintillation and other atmospheric degradation of signal propagation in a free-space atmospheric laser communication system by transmitting a “signal strength” data stream between each pair of communicating laser transceivers. The signal strength data stream indicates the signal strength of the sending transceiver as actually received by the remote receiving transceiver. If the sending transceiver receives data from the remote receiving transceiver indicating that the signal strength of the sending transceiver has fallen to or below a selected threshold, or if the sending transceiver cannot detect the signal strength data stream, then the sending transceiver suspends transmission of information packets. The sending transceiver resumes transmission of information packets when the indicated signal strength level returns to an acceptable level.

Abstract: 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.

Abstract: 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.

Abstract: 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.