Effects on performance of a 90° optical hybrid due to rotation of a 45° reflector scanner in a free space optical communication terminal

The effects on the performance of a 90° optical hybrid due to rotation of a 45° reflector scanner in a free space optical communication terminal were analyzed. A geometrical model of the 45° reflector was first established. Its polarization transmission characteristics were analyzed by three-dimensional polarization calculus, and the effect on the response of the 90° optical hybrid was analyzed. The relationship between the scanning angle in the pitching and azimuth directions and the effects on the beam ratio and phase shift were simulated for both a polarization-maintaining film and Ag. The results showed that the performance of the 90° optical hybrid was hardly affected during scanning of 45 ± 12° in the pitching direction for both the polarization-maintaining film and Ag, but the phase shift of the 90° optical hybrid changed markedly during scanning from −12° to 12° in the azimuth direction, especially for Ag. These results may be useful in the design of coherent laser communication systems.