System and method for heterodyne detection of an optical signal

摘要

An optical heterodyne detection system includes an input signal (302) and a local oscillator signal (306) that are combined in an optical coupler (310) and output as a first beam and a second beam. A polarizing beam splitter (324) is optically connected to the optical coupler in order to receive the first beam and the second beam. The polarizing beam splitter includes four outputs for outputting four beams to four photodetectors (544, 546, 548, and 550) including two polarized portions of the first beam and two polarized portions of the second beam. The four photodetectors generate four electrical signals in response to respective ones of the four beams. The four electrical signals are transmitted to a processor (316) and processed to provide an output response that is independent of the polarization state of the original input signal and in which the intensity noise has been suppressed. Processing of the electrical signals to suppress the intensity noise involves canceling the intensity noise component of similarly polarized beams by subtracting (902) the similarly polarized beams. Processing of the electrical signals to provide polarization independence involves squaring (904) the values generated from the two subtraction operations, low pass filtering (906) the values generated from the two squaring operations, and then adding (908) the values generated from the two filtering operations. <IMAGE>