The Study Of Optical Signal-to-Noise Monitoring Method In Coherent Optical Communication System

With the rapid development of Internet technique, global communication service shows a dramatically increase. As the foundation of information transmission, optical communication technology holds up the era of massive amounts of information. In order to ensure the transmission reliability of the optical fiber communication system, it is very important to monitor and evaluate the system performance. Optical signal-to-noise(OSNR) is one of the key parameters to be monitored which directly reflects the amplifier spontaneousemission noise(ASE) noise influence introduced by optical amplifiers in transmission system and has the direct relationship with the bit error rate(BER) at the receiver.Therefore, the investigation of an effective OSNR monitoring scheme become a significant research direction.Traditional OSNR monitoring technique is the out-of-band linear interpolation but it is not applicable because of the reduction of channel spacing in order to rationally use the spectrum bandwidth and improve the spectral efficiency, thus leading to the development of in-band monitoring technique, such as methods based on polarization analysis, delay interference and high order statistical moments. However, these methods are only suitable for the optical communication system with weak fiber nonlinearity. With the increase of optical launch power for longer transmission distance, nonlinear effects cannot be ignored anymore since the amplitude and phase of signal has been distorted and the OSNR of communication system will be influenced by nonlinear amplitude noise.Thus, the study of the OSNR monitoring method applicable to systems which is subject to nonlinear damage is urgent and significant.This paper studied the OSNR monitoring technique in coherent optical communication system with the influence of nonlinearity, mainly analyzed the OSNR monitoring for PM-QPSK and Nyquist-WDM system,additionally made a comparison with the traditional monitoring method.The main work and innovation are as follows:(1) This paper studied the OSNR monitoring method for 112Gb/s coherent optical communication system with fiber nonlinearity and proposed a new monitoring method based on cross-correlation function of signal, the estimation error is below 1dB.(2) This paper proposed a OSNR monitoring method based on correlation function for the Nyquist-WDM system in nonlinear case and made a comparison with traditional statistical moments-based method. Our proposed method greatly reduced the monitoring error with a wider monitoring range.