US 5,142,400 A · Method and apparatus for automatic acquisition and alignment of an optical beam communication link

Abstract

A method and a preferred apparatus for the searching, acquisition and locking into boresight alignment of two remote optical beam transceivers suitable for use in satellite communications. A first transceiver operates in a search mode while acquiring a communications link with a second transceiver operating in a stare mode. Each transceiver has an optical axis and a retro-reflector that reflects incident beams that are not substantially aligned with the local optical axis while not reflecting all incident beams substantially aligned with the local optical axis. Each transceiver includes an axis-aligned beam transmitting source, a axis-aligned optical detector for incoming beams, a pointing system for aiming the local optical axis in any direction over a hemispherical range, and a beam tracker for maintaining boresight alignment following acquisition. The decision processor includes means for distinguishing between optical beams reflected from the second transceiver and optical beams transmitted by the second transceiver. In operation, the reflected beam increases in intensity as the two transceivers approach alignment but drops to zero as the transceivers attain boreslight alignment. The preferred apparatus includes a matched pair of reflecting telescopes rigidly mounted on a gimballed platform with the transmitting and receiving telescope axes precisely aligned and parallel. Each telescope includes a primary reflector, a secondary reflector with a Cassegrainian focus behind the primary reflector and a tertiary retro-reflector behind an aperture at the vertex of the primary reflector.

Claims8

Dependent claims

An optical transceiver communications system comprising at least two transceivers, each having an optical axis and each comprising:

optical transmitter means for projecting a first outgoing optical beam aligned with said optical axis, said beam having at least one modulation characteristic;
optical receiver means for collecting an incoming optical beam;
receiver demodulator means for detecting the modulation characteristics of said incoming optical beam and for generating at least one modulation detection signal;
mode selector means, responsive to said modulation detection signals, for generating a mode control signal specifying one of a plurality of preselected searching and tracking modes;
search controller means, responsive to said mode control signal, for generating a search control signal;
decision processor means, responsive to said modulation detection signals and said search control signal, for generating a pointing signal;
and
pointing controller means, responsive to said pointing signal, for steering said optical axis to a desired direction.

5 more elements

A method for acquiring boresight alignment between the optical axes of at least two transceivers in a communications system comprising at least two remote optical transceivers disposed such that optical alignment between them is possible, at least one transceiver having a stare mode in which an optical beam modulated by a first baseband signal is transmitted along the transceiver optical axis and another transceiver having a search mode in which it points in a direction within a hemisphere while transmitting an optical beam modulated by a second baseband signal, said transceiver in stare mode having means for retro-reflecting all incident optical beams not substantially aligned with the optical axis of said staring transceiver while not reflecting incident optical beams that are substantially aligned with said staring transceiver optical axis, each transceiver having means for detecting an incident beam substantially aligned with its optical axis, comprising the steps of:

causing a first transceiver to operate in said stare mode while continuously transmitting an optical beam modulated by said first baseband signal;
pointing a second transceiver in a search pattern over a hemisphere while transmitting an optical beam modulated by said second baseband signal;
reducing the angular search pattern region of said second transceiver upon detection of a second baseband modulated incoming optical beam;
adjusting the pointing direction of said second transceiver as necessary to increase the intensity of said second baseband modulated incoming optical beam;
switching said second transceiver detection means to detect an incoming optical beam modulated by said first baseband signal upon detection of a significant and relatively abrupt reduction in said second baseband modulated incoming optical beam;
and
tracking said first baseband incoming optical beam from said first transceiver with said second transceiver to maintain boresight alignment between said first and second transceiver optical axes.

4 more elements

Dependencies are inferred from the claim text.

Method and apparatus for automatic acquisition and alignment of an optical beam communication link

Life of this patent

Method and apparatus for automatic acquisition and alignment of an optical beam communication link

Life of this patent

Abstract

Claims8