a method and a system for dynamic compensating polarization mode dispersion in an optical communication system . an optical input signal passes through a compensating element first . a splitting device taps a fraction of the optical input signal and sends it to a monitoring element with birefringence properties . the monitoring element separates the fraction into two split signals with orthogonal principal states of polarization . the split signals are detected at photodetectors . an optimised coefficient is obtained from the detected split signals , and used to calculate an angle between a fast axis of the monitoring element and the fast axis of the optical fiber . the compensating element is set according to the determined angle to compensate the pmd . one or both of the monitoring element and the compensating element may be liquid crystal .