The Study Of Optical Signal-to-Noise Monitoring Method In Coherent Optical Communication System Under The Effects Of Fiber Nonlinearity

With the rise of the Internet technology,the demand for data traffic in human society is rapidly increasing.As the main medium of information transmission,optical fiber communication system will develop in the direction of high rate,large capacity and dynamic reconfiguration in order to meet the needs of mass information,which is also the development goal of the new generation optical fiber communication system.In order to ensure the reliability of information transmissioned in the communication system,it is necessary to achieve optical performance monitoring.OSNR is one of the most critical optical performance monitoring parameters,which is directly related to the bit error rate of the system receiver.As we all know,the research on OSNR monitoring has achieved initial results.The traditional OSNR monitoring adopted the method of out of band linear interpolation,which estimates the level of in-band noise through the level of out-of-band noise.With the development of optical fiber communication system,the efficiency of optical spectrum is gradually improved,and the channel spacing becomes narrower and narrower,which leads to the failure of the linear interpolation,thus the OSNR monitoring has to be towards in-band development.With the advent of coherent receivers and digital signal processing techniques,OSNR monitoring based on high-order statistical moments is proposed,greatly reducing monitoring costs and errors.However,with the international application of the optical fiber communication system,the long distance transmission across the ocean requires the larger power to compensate for the loss caused by the optical fiber transmission link,but the corresponding cost is the obvious improvement of the nonlinear effect in the optical fiber.The nonlinear effect of optical fiber will lead to the nonlinear distortion of optical signal,and the nonlinear noise will be introduced into the whole system,which will affect the reliable and stable transmission of the system.Under the condition of optical fiber nonlinearity,the traditional OSNR monitoring technology is no longer applicable.Therefore,it is urgent to solve the problem of OSNR monitoring under the condition of nonlinearity in the optical communication system.In this paper,the development of OSNR monitoring technology is introduced and analyzed,and the corresponding OSNR monitoring method under the condition of nonlinearity is studied.Eventually,a method based on the correlation function of signal amplitude is proposed.We carried out the simulation verification of the proposed method and designed a reasonable experimental scheme.In general,the major accomplishments and innovations are as follows:(1)We studied the common OSNR monitoring technologies in optical communication systems,such as polarization-based method,delay-tap sampling technology,filter-based technology,high order statistical moments-based method,differential pilot-based scheme,correlation function-based method and so on.Futhermore,the performance of these technologies was analyzed.(2)We studied the mechanism of fiber nonlinear effect on OSNR,as well as the principle of OSNR monitoring using nonlinear GN model.Finally,the disadvantages of this method were analyzed.(3)This paper studied the OSNR monitoring of PM-QPSK-Nyquist-WDM system under the condition of nonlinearity and proposed a signal amplitude correlation function-based method,then made a comparison with traditional statistical moments-based method.The proposed method greatly reduced the OSNR monitoring error,and the error is below 1.28dB.