Polarization mode dispersion monitoring

Polarization mode dispersion (PMD) is an important impairment in high-speed reconfigurable optical networks, affects system performance, and might be monitored. By its inherent nature, deleterious PMD effects are stochastic, time-varying, vibration-dependent, and temperature-dependent. In addition, reconfigurable optical networking will change the signal path and thus the accumulated PMD. Therefore, real-time PMD monitoring is required in order to dynamically tune a compensator or for network control and management. In order to enable robust and cost-effective automated operation of high-speed reconfigurable optical networks, it is desirable to intelligently monitor the state of the network as well as the quality of propagating data signals, isolate specific impairments including PMD, and automatically diagnose and repair the network. The value of monitoring increases with increasing intelligence and bit rates. In addition, one should seek to maintain the right balance among monitoring coverage, sensitivity, and cost. Single-mode fibers actually support two perpendicular polarizations of the original transmitted signal (fundamental mode). In an ideal fiber (perfect), these two modes are indistinguishable and have the same propagation constants owing to the cylindrical symmetry of the wave guide. However, practical fibers are not perfect and, as a result, the two perpendicular polarization components (along the two PSPs) of the signal light may travel at different speeds and consequently arrive at the end of the fiber at different times.