高速率、大容量的密集波分复用系统是光纤通信系统的最终发展方向,单信道速率达到40 Gbit/s时,光纤的非线性效应、偏振模色散现象对系统的影响更加突出。在综合考虑群速度色散、自相位调制、交叉相位调制、四波混合、偏振模色散等因素的基础上,推导了密集波分复用系统中任意信道的耦合非线性薛定谔方程组。利用扩展的分步傅里叶方法对该方程进行了数值计算,通过对8×40 Gbit/s密集波分复用系统的仿真,分别研究了非线性效应和偏振模色散对密集波分复用系统的影响。发现由于交叉相位调制和四波混合作用,多波长的密集波分复用系统比单波系统受非线性效应影响严重;系统受偏振模色散与非线性效应的影响程度与输入信号功率有关,在入射光单信道平均功率较低0.1 mW时,偏振模色散是影响系统性能的主要因素;当入射光单信道平均功率较高1 mW时,系统受非线性效应影响严重。而偏振模色散在使信号脉冲展宽的同时,类似于非零色散位移光纤中的微小色散,对非线性效应又有一定的抑制作用。

Dense wavelength division multiplexing system is a final selection as an optical communication system because of its high speed and big capacities, but the fiber nonlinear effects and polarization mode dispersion limit severely the performance of the system when signal propagates at 40 Gbit/s in a single channel. The coupled nonlinear Schrodinger equations of a single channel in dense wavelength division multiplexing system are derived, considering all factors of group velocity dispersion, self-phase modulation, cross phase modulation, four wave mixing and polarization mode dispersion, and their number results are obtained with extended Split-step Fourier Method. To analyze the impacts of the fiber nonlinear effects and polarization mode dispersion on the optical communication system, the simulated results of a 8×40 Gbit/s dense wavelength division multiplexing system are discussed under different conditions respectively at last. It is found that nonlinear effects influence dense wavelength division multiplexing system more severely than single wave-length system because of the effects of cross phase modulation and four wave mixing. The degree of impacts of polarization mode dispersion and nonlinear effects on system is related to the power of the input signal. When the average power of the input signal is below 0.1 mW, the influence of polarization mode dispersion is dominating; while it is 1 mW, the impact of nonlinear effects is worse than polarization mode dispersion. But polarization mode dispersion, which can widen pulse and is similar to the small chromatic dispersion in G.655 fiber, can mitigate the impact of nonlinear effects.