Dense wavelength division multiplexing (DWDM) system is the tendency of optical fiber communication systems because of its high speeds and capacities. DWDM systems with channel data rates of 40 Gbit/s bring us both advantages and challenges. With broader spectrum, the signal suffers more from chromatic dispersion, optical fiber nonlinear effects and polarization mode dispersion (PMD). Simultaneously, the combination of PMD and nonlinear effects results in more complexity. In this paper, amended nonlinear Schrodinger equations, which include group velocity dispersion (GVD), third order dispersion (TOD), self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and PMD synthetically, are derived, then the system degradation induced by PMD and nonlinear effects is investigated via numerical simulation. The results show that when the power of input signal is low, PMD has more affection on system comparing with nonlinear effects, and nonlinear effects become dominating with power increasing, but mild PMD may mitigate their impact to some extent. The results in this paper are valid for design and analysis of long haul DWDM systems with high bit rate.
In this paper, a novel method to reproduce the maximum DGD is proposed. In the model different PMD states are obtained by randomly varying the polarization coupling angle between sections. By confining the coupling angles' distribution to a shrinking range, the statistics of DGD will be distorted and the low probability events will be efficiently produced. The relationship between the mean DGD of changed DGD distribution and the angle range is given to make it convenient to choose a suitable angle range at a given maximum DGD and simulating sections.