Phase-noise and polarization state insensitive coherent optical receivers

Different schemes that make it possible to compensate both phase-noise and polarization fluctuations due to single mode fibers are presented. The first two systems, double-frequency phase shift keying (DFPSK) and Jones matrix inversion PSK (JMPSK) rely on the principle of transmitting a reference carrier to compensate for the phase noise effect at the receiver. The polarization independence is attained in DFPSK by polarization diversity detection and in JMPSK by the electronic feedforward technique. The second pair of systems, antipodal Stokes parameters shift keying (ASPSK) and differential Stokes parameters shift keying (DSPSK), is based on polarization modulation and Stokes parameter detection. Because the Stokes parameters are independent of the phase terms common to both polarization components, the systems are widely tolerant with respect to the phase noise. The polarization fluctuation insensitivity is realized in ASPSK by means of a feedforward electronic control circuit, while in DSPSK the adopted decision criterion allows instantaneous polarization fluctuation compensation. The first class of systems is suitable for long-haul applications, the second class for local and metropolitan area networks