Optical monitoring of PMD accumulation on a Pol-MUX phase-modulated signal using degree-of-polarization measurements

We experimentally demonstrate a chromatic dispersion insensitive monitoring technique for monitoring of polarization mode dispersion and time misalignment in a 80 Gbit/s polarization-multiplexed return-to-zero differential phase-shift-keying (Pol-MUX RZ-DPSK) signal using a polarimeter and degree-of polarization (DOP) measurements. This technique is modulation format independent (i.e., applicable to both the phase- and amplitude-modulated data) and capable of measuring the fast change of polarization effects caused by vibration or other fast disturbances in the fiber link. We show that the monitored DOP of this signal decreases by 10.8% with differential group delay of 0-12 ps and decreases by 20% with a maximum misalignment of 12.5 ps between two orthogonally polarized RZ-DPSK channels. These measurements are less sensitive to chromatic dispersion of 0-400 ps/nm.