The influence of polarization mode dispersion on high bit-rate optical transmission systems

Polarization mode dispersion (PMD) occurs in the optical fibers due to circular asymmetries of the fiber core. PMD can be described locally as fiber birefringence and globally, the birefringence is combined with random polarization mode coupling. As PMD varies randomly with time and wavelength, it is rather difficult to describe theoretically and must involve the statistical approach. At 10 Gbit/s PMD is no more negligible and at higher bit-rates (40 Gbit/s and more) it represents the major limitation in optical transmission systems. In the paper we have given an overview of the mathematical description of PMD. We have demonstrated the deleterious effect of PMD on high bit-rates in various simulations preformed by the computer program FiberProp we developed. The special attention is given to the impact of PMD on solitons, which had been introduced as a solution to compensate the group velocity dispersion problem. It is shown that they can be used also for mitigation of PMD. The solution to the PMD problem is either to install new fibers with low PMD, or to try to compensate PMD on already installed fibers. Some principles of PMD compensation for various applications are discussed in the paper.