Heterodyne optical detection/spatial tracking system using spatial field pattern matching between signal and local lights

Abstract

The spatial tracking system controlling the directivity of the optical antenna determines the quality of communication in the ultradistance intersatellite optical communication system. The spatial tracking system using optical heterodyne detection has a high receiver sensitivity, being less susceptible to background light. This is the dominating factor for noise in cosmic space. In recent years, intensive studies have been made on this system hoping for the tracking performance with a higher accuracy than that obtained by the direct detection system. This paper presents a principle of angular error detection which is different from the conventional system and proposes a new optical heterodyne/spatial tracking system based on that principle. The principle on which the proposed system is based is that the incoming angle of the signal light is tracked by utilizing the variation of the spatial matching to the local light due to the variation of the incoming angle of the signal light. Its feature is that the angle error can be detected using a single ordinary optical detector, not the quadrant optical detector.A theoretical analysis of the noise equivalent angle (NEA) is presented. The optimal local light diffraction pattern is shown for the rectangular antenna apenure.The performance of the system is analyzed from the viewpoint of NEA, and the result is compared to the performance of the optical heterodyne detection/spatial tracking system using the quadrant optical detector.

Optical Communication in Space: Challenges and Mitigation Techniques

“…Doppler shift frequency compensator for coherent homodyne receiver with optical phase lock loop is investigated in [187]. [188], [189]. Gimbal tracking is generally used where large beam divergences are available as the gimbal jitter is large enough to support narrow beams.…”

“…Various tracking techniques such as dc tracking, pulse tracking, square law tracking, coherent tracking, tone tracking, feed-forward tracking and gimbal tracking are implemented for inter-satellite FSO links. Coherent tracking uses high front end LO gain to compensate for large background noises that limit the receiver sensitivity [188], [189]. Gimbal tracking is generally used where large beam divergences are available as the gimbal jitter is large enough to support narrow beams.…”