The information explosion ignited by the Internet has created an insatiable appetite for bandwidth. To appease the bandwidth hunger, most telecommunications operators are pushed to increase the per-channel data rate of wavelength division multiplexing (WDM) systems. Systems based on the 10-Gb/s channel rate are being deployed, and 40-Gb/s systems are on the horizon. Unfortunately, as the bit rate increases, communications networks become increasingly sensitive to polarization-related impairments such as polarization mode dispersion in optical fibers, polarization-dependent loss in passive optical components, polarization-dependent modulation in electro-optic modulators and polarization-dependent gain in optical amplifiers...