Modeling Of Four Wave Mixing Noise In Large Capacity DWDM Systems

With an increase in the capacity of dense wavelength division multiplexing(DWDM)systems,the four wave mixing(FWM)effect has become one of the main factors for such systems.In order to optimize the performance of this kind of DWDM systems,evaluating the impact of FWM effect is more and more important.In this paper,the effect of FWM noise on large capacity DWDM systems is studied theoretically and numerically.Many important propagation effects,such as the randomness of bit sequence,the pulse walk-off effects between channels and other factors are taken into account,semi-analytic models are deduced in detailed to calculate the variance of FWM noises for dispersion-managed DWDM systems with the D8 PSK and the 8APSK channels.And examples are analyzed using the formula,the numerical results show that although FWM tolerance of a center channel in 8APSK is worse than that with D8 PSK,a central channel with 8APSK is still superior to that with D8 PSK when some linear noises and FWM noises are considered simultaneously for given system conditions,which is mainly attributed to a relatively large Euclidean distance for the 8APSK constellation than the D8 PSK one.With co-simulation method based on Opti System and Matlab softwares,a nonlinear separation model is also presented to calculate the standard deviation of FWM noises for coherent quadrature amplitude modulation(QAM)DWDM systems.With the model,the relationship among bit error rate(BER),error vector magnitude(EVM)and FWM noises is numerically analyzed.For different bit rates,channel numbers and channel spacing,the overall nonlinear tolerance of the systems is also shown.The semi-analytic models derived for 8APSK\D8PSK DWDM systems and the nonlinear separation model for coherent QAM DWDM systems with co-simulation method provide a new way to understand deeply the influence of the FWM effects on the performance of large capacity DWDM systems.