Differential group delay monitoring used as feedforward information for polarization mode dispersion compensation

A novel differential-group-delay (DGD) monitoring scheme that can provide feedforward information to facilitate the compensation of polarization mode dispersion (PMD) is demonstrated. Using a polarization scrambler at the beginning of the link, the instantaneous DGD can be monitored at the end of the link by using a second polarization scrambler followed by a fixed 0.8-dB polarization dependent loss (PDL) element or a polarizer. As the PMD value along the link increases, the instantaneous degree-of-polarization will decrease, thereby resulting in a decrease in the measured RMS power fluctuation value through the PDL element. The authors show instantaneous DGD monitoring of up to /spl sim/70 ps for both nonreturn-to-zero (NRZ) and return-to-zero data formats, and they demonstrate PMD compensation of a 10-Gb/s NRZ channel using the monitor output as part of the control feedforward signal.