Investigation On The Nonlinear Impairments And Mitigation Method In Coherent Optical Ofdm System

With the rapid increase of information capacity requirements, future communication system should be able to provide more communication traffic, higher date rate and better communication quality by using limited spectrum resources. In order to meet these requirements, current lOGbit/s single-channel transmission rate in backbone networks should be update to40Gbit/s, or even100Gbit/s. Coherent optical orthogonal frequency division multiplexed (CO-OFDM) technology, which combines the coherent optical communication techonlology and OFDM technology together, has high spectrum efficiency and high-speed transmission data rate. It is also possible to utilize the chromatic dispersion and nonlinear impairement compesation algorithm in the electrial domain. In recent years, CO-OFDM technology has become one of the candidate technologies in the next generation optical transmission network.In this paper, we establish a simulation platform of CO-OFDM system by utilizing MATLAb softwares. Typtical transmission link impairements and correspoding equalization algorithm in CO-OFDM system are invesitgated, such as chromatic dispersion and fiber nonlinearity. For chromatic dispersion equlizaiton, we utilize the LS (Linear Least Squares Estimate) and LMSSE (Linear Minimum Mean Square Estimate) estiamtion algorithms. Signal constellations before and after equlization show that chromatic dispersion can be equlized well by these algorithms. For fiber nonlinearity, we mainly discuss how to decrease high peek-to-average power ratio and mitigate four-wave-mixing effect in transmission link. Clipping algorithm, selected mapping algorithm and partial sequence transmission algorithm are introduced to decrease the high peek-to-avergae power ratio. Simulation results show that peak-to-average power ratio is significantly decreased by these algorithm, and the minimum and maximum CCDF (Complementary Cumulative Distribution Function) value decrements are2.7dB and4.8dB respectively. PCF-PTS and selected mapping method combined with the clipping algorithm are employed to decrease the serial correlation for supressing the FWM in transmission link.1000km transmission simulation results indicate that BER value of10-3is able to be obtained by using the PCF-PTS algorithm, and3.4dB sensitivity improvement is acheived by utilizing selected mapping method combined with the clipping algorithm.