| With the continued explosive growth of the new applications such as mobile internet,big data,and Internets of Things,as one of the mainstream technologies of the modern communication technology,the optical fiber communication system is facing the challenges of high-capacity and long-haul.Coherent optical communication systems have strong receiving sensitivity and high spectrum utilization.The received signal can be recovered by digital signal processing(DSP)algorithms in electrical domain in coherent optical systems,which have attracted widespread attention and research.In optical coherent systems,the system performance impairment mainly comes from linear impairments represented by chromatic dispersion and linewidth,and nonlinear impairments represented by intra-channel nonlinear effect and inter-channel nonlinear effect.Linear impairments and intra-channel nonlinear effect have been extensively studied and amount of mature DSP algorithms are available.Therefore,inter-channel nonlinear effect becomes the main factor limiting the performance of wavelength division multiplexing(WDM)systems.The monitoring,suppression and equalization of inter-channel nonlinear noise are important in the research of optical fiber communication systems.The method of inter-channel nonlinear noise power monitoring by using differential pilot(DP)signal has good accuracy and low complexity.With the single-frequency-nature of DP signal,different power components can be distinguished in the frequency domain,and the power of inter-channel nonlinear noise power can be obtained.This thesis investigates the monitoring technology of inter-channel nonlinear noise power by using DP signal.The specific research contents are as follows:1.Experimental research on monitoring inter-channel nonlinear noise power by using DP.Based on the method of monitoring inter-channel nonlinear noise power with DP,an experimental scheme to verify its practicability is presented on the basis of previous simulation research.This thesis further investigates the distribution of each power component in the frequency domain after transmitted over the link in the experiment.The experimental platform of 25-GBaud quadrature phase shift keying(QPSK)WDM system is established to verify the feasibility of the inter-channel nonlinear noise power monitoring method.The experiment results show that the inter-channel nonlinear noise power monitoring error is less than 1.5 dB when launch power is larger than 4 dBm per channel.And the monitoring error will become larger if the launch power is lower than 4 dBm per channel.In view of this phenomenon,a simulation system with the same conditions as the experiment system is set up to discuss the critical launch power that the main factor of system performance degradation changes from amplifier spontaneous emission(ASE)noise to nonlinear noise.2.An improved method of inter-channel nonlinear noise power monitoring based on DP signal.In this thesis,an important measurement steps(measurement of ASE noise power)in the traditional inter-channel nonlinear noise power monitoring method with DP signal is optimized.According to the equality between the ratio of the signal power transmitted on each polarization in the dual polarization system and the ratio of the inter-channel nonlinear noise power on each polarization,the ASE noise power on the signal sampling bandwidth can be directly obtained.The simulation platform of 28-GBaud dual-polarization 16-quadrature amplitude modulation(DP-16QAM)WDM coherent transmission system with 800-1400 km standard single-mode fiber(SSMF)for inter-channel nonlinear noise power monitoring is established and the channel number is 5.The inter-channel nonlinear noise power monitoring error is less than 1 dB when launch power is 0?6 dBm per channel,which proves the good accuracy of this method.The monitoring steps are further simplified,the computational complexity is reduced,and the operability of the measurement process is improved. |
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