Research On Alternative Approaches To Polarization Mode Dispersion Compensation For High-speed Optical Communication Systems

Polarization Mode Dispersion (PMD) has become one of dominate limiting factors in 40 Gbps or higher speed fiber-optics communication systems. The research on the techniques of PMD compensation in installed fiber cable links will enable a full use of underground fiber link resources, improving the performance of signal transmission capacity and quality in optical communication networks at a reduced cost.The design principle of PMD emulator is based on the model of stochastic-rotated concatenation of multi-segments of birefringence crystals. Analysis of two types of PMD emulator shows that rotatable crystal type has a good probability distribution of differential group delay (DGD), while polarization controller type has a favorable probability distribution of second-order PMD (SOPMD).PMD compensation schemes were similarly divided into two types according to the ways how they are used, one of them is adaptive compensation scheme and the other is partial compensation scheme, the latter is used to compensate the time-independent portion of PMD. It is found that optical communication system design software can be a great help to evaluate various PMD compensation schemes. Simulation experiments show that pre-compensation scheme is not suitable for practical engineering because of its occupancy of a channel while single stage post-compensation scheme is able to compensate a small portion of PMD, whereby two-staged post-compensation scheme can reduce PMD significantly and thereby improve the performance of signal transmission quality, it is also cost-effective and easy to adjust. A one-stage PMD compensator model based on silica planar lightwave circuit was also discussed.A PMD partial compensator based on two-stage fixed delay structure was designed, fabricated and tested in practical underground fiber links. Compensation experiment for four 60 km-long installed fiber cable links was in a good agreement with the simulated result, with a 15～20% of PMD compensation achieved.