Simulation study of an adaptive phase alignment system for optical heterodyne communications under misalignment conditions

A postphotodetection adaptive phase alignment system using an aperture arra y of photodetectors is presented to reduce the signal loss in an optical (f ree-space) heterodyne receiver resulting from wavefront misalignment (tilt) on a satellite platform. This paper compares two kinds of rectangular aper ture configurations-full aperture and array aperture configurations-via a s oftware simulation study of the error performance after DPSK demodulation f or different angles of arrival (tilt) of the received signal wavefront. For the array configuration, an adaptive phase alignment system is used that p hase aligns the signals from the different photodetector array elements, an d constructively adds them to yield a higher signal magnitude as compared t o that of signal of a single-element photodetector of the same total area. The optimum aperture length for a given wavefront misalignment is derived, and is verified via simulation.