Research On Optical Fiber Transmission Of The Nyquist Signal Based On Coherent Detection

In recent years,with the rapid increase demands in transmission rate and bandwidth,cost-effective and large-capacity optical transmission systems are desired for the future optical network.Improving the spectrum efficiency(SE)is an effective method to meet the bandwidth demands.There are two proposals show the promise of reaching higher SE so far,coherent optical orthogonal frequency division multiplexing(CO-OFDM)and Nyquist wavelength division multiplexing(Nyquist WDM)technologies.CO-OFDM can resist chromatic dispersion well,but it has high peak to average power ratio(PAPR)and is sensitive to frequency offset and phase noise at the same time.Nyquist-WDM can match the Nyquist first rule with Nyquist pulse shaping technique.And it can reach higher spectrum efficiency.In single carrier system,Nyquist signal is more suitable to optical long haul transmission because of its lower PAPR.In this paper,the generation and transmission performance of Nyquist signal with high spectrum efficiency over coherent optical communication system are studied.The innovations of the work in this paper are as follows:1.The generation of optical polarization division multiplexed(PDM)16QAM Nyquist signal is proposed.Then research has been done on the optical transmission performance of PDM-16QAM Nyquist signal over PDM coherent optical communication system.The PDM-16QAM Nyquist signal based on Nyquist pulse-shaping technology brings a double spectrum efficiency compared with the PDM-16QAM signal.Meanwhile,PDM-16QAM Nyquist coherent optical communication system is demonstrated by simulation in order to study the bit error rate(BER)performance of PDM-16QAM Nyquist signal and PDM-16QAM signal under different transmission distances.The results show that 224-Gbit/s 16QAM-Nyquist and 16QAM signal can transmit over 720km and 800km standard single mode fiber(SSMF)respectively at the FEC threshold of 3.8×10-3.Morever,the influence on optical transmission performance is analysised respectively based on data-aided frequency domain equalization(FDE)algorithm and overlap frequency domain equalization(OFDE)algorithm.The simulation results show that the performance with OFDE algorithm has an obvious promotion of 4.2dB gains compared with FDE algorithm after 480km SSMF transmission.2.The generation of Nyquist optical frequency combs based on dual parallel MachZehnder modulator(DPMZM)is proposed.And it is used to build Nyquist wavelength division multiplexing(WDM)optical communication system based on coherent detection.The BER performance of 16QAM-OFDM signal over Nyquist-WDM optical communication system has been analysised compares with conventional WDM optical communication system.16QAM-OFDM signal has greatly influenced by nonlinear damage during the transmission over WDM system.Thus the simulation results show that 60Gbit/s 16QAM-OFDM signal can only transmitted over Nyquist WDM system and conventional WDM system for 40-km and 60-km at the FEC threshold of 3.8×10-3,respectively.