Abstract:In 40 Gb/s systems with low polarization-mode dispersion (PMD) fibers, first-order PMD is the dominate factor with quite small value. An adaptive PMD compensator consisting of an electrical polarization controller (PC), a section of polarization maintaining fiber (PMF), a degree of polarization (DOP) detector and a feedback control module is employed in 40 Gb/s NSFCNet. This compensator has a simple structure and high speed, which can compensate up to 20 ps first-order PMD adaptively and the average searching time is 2 ms.