Process and apparatus for controlling alignment of a transmit laser beam of a coherent detection optical communications transmitter/receiver terminal

摘要

A process and apparatus are provided for controlling the alignment of a transmit laser beam (1a) of a first coherent detection optical communications transmitter/receiver terminal with a further coherent detection optical communications transmitter/receiver terminal relative to a receive laser beam (8). The first terminal incorporates a transmit laser beam generator (1) operable to form and pass the transmit beam (1a) through a point ahead mechanism (2) to a telescope assembly (6) operable to receive the receive laser beam (8). The apparatus includes a detector/receiver unit, means (3) for taking a component (1b) of the transmit laser beam (1a) from the transmit laser beam (1a) for receiving the receive laser beam (8) from the telescope assembly (6) and for feeding the transmit laser beam (8) to the detector/receiver unit (10), and means (16, 17, 18, 19, 20, 21, 22, 23, 24) for detecting, separating and processing the received transmit laser beam component (1b) and received receive beam (8) at the detector/receiver unit (10) to provide signals indicative of the actual alignment of the transmit and receive beams (1a, 8), means (25) for comparing the actual alignment signals with desired alignment values to generate difference signals and means for operating the point ahead mechanism (2) in dependence upon the generated difference signals variably to control the alignment of the transmit beam (1a) relative to the receive beam (8).