Study On Dispersion Management And Nonlinear Effects In WDM Optical Transmission Systems

With the growth of transmission capacity and transmission distance in optical transmission system, group velocity dispersion(GVD),nonlinear optical effect become the major obstacles in these systems. By optimizing dispersion map to avoid effects of chromatic dispersion and to reduce the impairment of nonlinearity in optical transmission systems, dispersion management which is an effective way to improve the performance of optical transmission system.The thesis introduces the classical dispersion management technology and the effect of nonlinearity in WDM system. Some key techniques of dispersion management were discussed. Then some kinds of dispersion management schemes were focused by simulation and analyses in WDM transmission system. On the other hand, the effect of nonlinearity was simulated in WDM system and then some methods of suppressing nonlinearity effects were proposed. The main research work and results are as follow:1. Starting from the nonlinear Schrodinger equation, by numerical simulation, we have compared four kinds of typical dispersion managed methods in optical fiber transmission link, and concluded that the post-dispersion compensation schematic is better than other. Furthermore we also optimized a series of parameters of the transmission system, such as dispesion value and length of fiber.2. At analyzing the dispersion map, we mainly study dispersion management scheme within a dispersion compensaton period, and pre-compensation and post-compensation two kinds of schemes are also investigated out of the dispersion compensatin period. By optimizing dispersion scheme, we found that positive dispersion cumulation is beneficial to improve the performance of optical fiber transmission system. 3. The influence of nonlinear effects (such as SPM, XPM, and FWM) in WDM system is investigated. Based on the coupled nonlinear Schrodinger equation, after analyzing and comparing the above kinds of nonlinear effects, we find that the effect of SPM is larger than others in WDM optical transmission system.4. Under different launching power and different channel interval, we analyze nonlinear effect of WDM system respectively and obtain some effective methods of restraining nonlinear effect. We analyse the effect of FWM in WDM system which have different channel frequency intervals and find that the system performance can be improved greatly when channels have equal frequency spacing in partly.5. Based on a new dispersion map proposed in [64], we optimize some parameters futher, and make the performance of the system improve greatly.