Polarization state and phase noise insensitive POLSK phase-diversity homodyne system in coherent optical communications

The authors propose a polarization shift keying (POLSK) phase-diversity homodyne system insensitive both to the polarization state and phase noise in coherent optical communications. The proposed system can reduce the influence of state-of-polarization (SOP) fluctuations on the receiver sensitivity by using multiplying detection with in-phase and quadrature optical signal components of two orthogonal polarizations. The proposed system is insensitive to phase noise and is attractive for high speed transmission since the receiver is of the homodyne type. The most attractive features of the proposed system are that neither a polarization controller nor an electronic feedback loop for matching the SOPs is needed and that two problems, polarization state and phase noise, are solved. The authors theoretically analyze the receiver sensitivity considering the influence due to the elliptical SOP of received optical signals and the power penalty of the proposed system in the case of the unbalanced optical 90° hybrid