ASYNCHRONOUS POLARIZATION DIVERSITY RECEIVERS FOR COHERENT OPTICAL COMMUNICATIONS - A PERFORMANCE REVIEW

The performance of coherent receivers in optical communication systems is impaired by polarization mismatchings between the received optical signal and the local laser field. One of the most effective technique s to cope with such a phenomenon is the use of polarization-diversity receivers which, at the cost of a higher complexity in the optical fro nt-end and a small performance degradation, guarantee insensitivity to changes in the state of polarization of the received signal. The goal of this paper is twofold: firstly, we present here an exact theoretic al analysis of balanced polarization-diversity receivers for ASK, FSK or DPSK modulation schemes in the shot-noise-limited regime, deriving closed-form expressions for the receiver Bit Error Rate (BER) of each of the cited modulations. Secondly, we assess the sensitivity of the s ame receivers to a slowly-varying frequency detuning of the heterodyne laser, in order to allow for a well-aimed design of the Automatic Fre quency Control (AFC) circuit of the local laser. This work was perform ed in the Framework of the ''Telecommunications'' project funded by th e Italian National Research Council (CNR).