An adaptive first-order polarization-mode dispersion compensation system aided by polarization scrambling: Theory and demonstration

An adaptive polarization-mode dispersion (PMD) compensation system has been developed to cancel the effects of first-order PMD by producing a compleme ntary PMD vector in the receiver. Control parameters for the PMD compensati on system comprised of a polarization controller and a PMD emulator are der ived from the nonreturn-to-zero (NRZ) signal in the channel to be compensat ed. Estimates of the link's differential group delay (DGD) and principal st ates of polarization (PSP's) based on this signal are reliable when the sig nal power is equally split between the link's two PSP's; however this condi tion cannot be assumed, To meet this requirement, we scramble the state of polarization (SOP) of the input signal at a rate much greater than the resp onse time of the PMD monitor signal so that each sample represents many dif ferent SOP alignments. This approach allows the effective cancellation of t he first-order PMD effects within an optical fiber channel.