Nonlinear Compensation With Digital Backward Propagation In Phase-estimated Optical Coherent Transmission

With the rapid development of broadband services and data services, the traditional IM/DDoptical communication systems will be unable to meet the demand for greater capacity of datatransmission in the future,so the improvement of the capacity has become the urgent problems inthe development of optical communication. For this purpose,coherent optical communications areconcerned again. Optical signals in optical fiber transmission is inevitable in the penalty ofdispersion and nonlinear, so the digital backward propagation is used to compensate them.First, this paper introduces the structure of optical coherent communication system and thedevelopment and actual state of this system. Based on the development and actual state of thedispersion and nonlinear penalties in optical coherent communication system, the digital backwardpropagation has broad prospects,then the topic of the thesis is determined and the significance of theresearch is proposed.Secondly, the article introduces two kinds of the key technologies, one is the carrier phaseestimation technology and the other is the digital backward propagation technology. This paperalso indicates the theoretical basis of two technologies and analyzes the characteristics of thisscheme on conditions of step size in backward propagation. The simulation shows that there is astep making the bit error rate minimum. Meanwhile,it is proposed that the backward propagation isbased on the optimal backward length, which is given to prove the feasibility.Finally, this paper designs the optical coherent communications system, and compares theperformance of five kinds of schemes that are the digital backward propagation, the simplifieddigital backward propagation, the carrier phase estimation and a mixture of them. The simulationshows that the first has very good results,but there is less amount of calculation in the second one.Then this paper proposes the backward propagation based on the optimal backward length which isapplied to the optical coherent communications system,the simulation shows that this scheme canget the minimum bit error rate on condition that signal-to-noise ratio is the same.