Research On Dispersion Monitoring Technology Of Low Complexity Coherent Optical Communication System Based On Radio Frequency Pilot

With the rapid development of Internet services and mobile communication services,people have higher requirements for data transmission rate and transmission quality.Optical fiber communication is constantly developing in the direction of high transmission rate,long distance and large capacity.In order to ensure the quality of optical signal transmission,it is necessary to monitor the dispersion of the optical signal.This thesis proposes and implements a dispersion monitoring method for polarization multiplexing coherent optical communication system based on RF pilot.The main research content and innovative results are as follows:(1)Aiming at the chromatic dispersion monitoring problem of coherent optical communication systems,the basic principles and structure of coherent optical transmitters are studied,as well as the principle and effect of chromatic dispersion on the power of RF pilot signals.In this way,the influence of the RF pilot frequency on the dispersion monitoring range is analyzed.(2)Based on the above research content,an RF pilot dispersion monitoring algorithm suitable for polarization multiplexed coherent optical communication systems is proposed,which uses the power ratio of two RF signals of different frequencies modulated in two polarization states at the receiving end to achieve dispersion monitoring.Taking the polarization multiplexing quadrature phase shift keying(PM-QPSK)signal as an example,simulation analysis verifies the dispersion monitoring range and monitoring accuracy of the monitoring system under different OSNR and RF pilot power.Monitoring range under the the dispersion monitoring in the range of 0～1380 ps/nm is realized,and the accuracy reaches10.6 ps/nm.At the same time,it is confirmed that the monitoring method is not sensitive to the modulation format and has strong robustness to OSNR.(3)In order to meet the long-distance transmission needs of coherent optical communication systems,the dispersion monitoring system and algorithm is further optimized.By changing the extreme point position of the monitoring curve and increasing the number of RF pilots,the monitorable distance is significantly extended and the dispersion monitoring is expanded.Simulation analysis verified the dispersion monitoring range and monitoring accuracy of the optimized monitoring system under different OSNR and PMD conditions,and achieved dispersion monitoring in the range of 0～15000 ps/nm,with an accuracy of 43.5 ps/nm,and proved that the monitoring method is robust to OSNR and PMD,and has strong anti-interference ability.Compared with other dispersion monitoring systems,this method has lower computational complexity.The dispersion monitoring range can be flexibly adjusted by changing the RF pilot frequency,and it can be flexibly applied to various polarization multiplexing coherent optical communication systems.Also it has a simple structure and uses coherent reception’s built-in photodiode(PD)can complete the dispersion monitoring.