Optical Polarization-Mode-Dispersion Compensators for High- Speed Optical Communication Systems

We first discuss some general issues of an optical polarization- mode-dispersion compensator (PMDC), including its operating principle, practical implementation considerations, and its performance evaluation methods. We then describe an optical PMDC with fast tracking speed for an 40-Gb/s non-return-to- zero differential phase-shift keying (NRZ-DPSK) system. The performance of the PMDC is tested in both back-to-back operation and in an 1100-km transmission system. Back-to-back measurements show that the PMDC can increase the polarization-mode dispersion tolerance of a 40-Gb/s NRZ-DPSK system to about 8 ps mean differential group delay at an optical signal-to-noise ratio margin of less than 1.5 dB. It is able to track principle state of polarization changes as fast as 45 o/ms. Fiber nonlinear effects on the PMDC are investigated in the 1100-km transmission system with neighboring 10-Gb/s on-off-keying (OOK) channels with 50-GHz channel spacing. Applications of the optical PMDC to other modulation formats such as differential quadrature phase-shift keying are also discussed