Alignment acquiring, optical beam communication link

Abstract

A pair of remote non-cooperating, optical beam transceivers are disposed so that optical alignment between them is possible. A controller selectively causes one of the transceivers, while acquiring a communication link, to operate in a search mode, and the other to operate in a stare mode. Each transceiver has an optical axis and retro-reflects all incident beams which are not substantially aligned with the axis but does not reflect incident beams aligned with the axis. Each transceiver includes an axis-aligned beam transmitting source, a detector of incoming axis-aligned beams, a pointer for aiming the axis anywhere within a hemispherical range while searching for the other transceiver, a component which distinguishes between a retro-reflection of a transmitted beam and an incoming beam from another such transceiver, a sensor for quantitatively measuring the power of retro-reflected beam, a controller for moving the axis in an abbreviated search for a direction in which the power of a retro-reflected beam is maximum, and a beam tracker for maintaining boresight alignment once the transceivers' optical axes are aligned. Preferably, each transceiver includes a matched pair of reflecting telescopes rigidly mounted with their optical axes precisely aligned, one each for transmitting and one for receiving optical beams. Each telescope should include a primary reflector, a subreflector with a Cassegrainian focus behind the primary reflector, and a retro-reflector behind a vertex aperture in the primary reflector.