Method and apparatus for tracking an optical communications system

Abstract

A tracking system and method in an optical communications system utilizing an optical communications beam. In one embodiment, the disclosed optical communications system includes a communications receiver circuit and a tracking circuit. The optical communications system generates a communications signal. The tracking system includes a tracking detector having a plurality of regions coupled to a corresponding plurality of tracking channel circuits. Each of the tracking channel circuits includes an optical detector coupled to receive the optical communications beam. The peak-to-peak amplitude modulation in the optical communications beam is measured by substantially reducing or removing a direct current (DC) offset present in the optical communications beam. In one embodiment, after the DC offset is substantially reduced or removed, the signal is then amplified, mixed with the communications signal and then filtered. The filtered signal is one of a plurality of tracking signal outputs, which are input to an alignment circuit. The alignment circuit is used to help maintain the alignment of the optical communications beam between the optical transmitter and receiver of the optical communications system. In one embodiment, each of the plurality of tracking signal outputs are also input into a gain control circuit. The gain control circuit is coupled to generate a gain control signal, which used to control the gain of variable gain amplifiers in the tracking channel circuits.