Research On Time-Frequency Packing Modulation And Receiver Processing Techniques Of Super-Nyquist Optical Transmission

With the high integration and collaborative development of the global economy,communication has become the basic demand of human society,which brings about the continuous growth of communication capacity,and constantly puts forward higher requirements and challenges for optical fiber transmission.With the application of Erbium-doped fiber amplifier(EDFA),digital coherent receiver and wavelength division multiplexing(WDM)technology in commercial communication systems,the spectrum resources of single-mode optical fiber communication window are increasingly scarce,and further improving the communication capacity of single-mode optical fiber encounters bottlenecks.Using advanced high spectral efficiency(SE)modulation formats to make fine use of spectrum resources has become an important direction of optical communication development.Among them,high-order modulation formats can rapidly increase transmission capacity,but the rapid increase of signal-to-noise ratio(SNR)requirements restricts its development in long-distance optical fiber transmission.In addition,Nyquist-WDM as a representative of high SE transmission technology has received widespread attention in the industry,but the orthogonal transmission criteria limit the further improvement of transmission capacity.By breaking the limitation of orthogonal transmission,super-Nyquist rate transmission technology compensates inter-symbol interference(ISI)by using the computational power of digital signal processing(DSP)in exchange for the continuous growth of transmission capacity.However,the current super-Nyquist rate optical transmission technology is still in the exploratory stage.The compression modulation technology is few.The time-packing technology and the time-frequency joint packing technology are lack of exploration and research.The compression efficiency is low,and the SE improvement is limited.At the same time,the ISI compensation algorithm has high complexity and low tolerance.The serious ISI also reduces the compensation of other channel effects.Aiming at the above problems,this dissertation explores a variety of new super-Nyquist modulation technologies and low-complexity ISI compensation mechanism,realizes the highest 11.2bit/s/Hz SE using QPSK signal,and achieves some leading innovative research results.The main innovations and work of this dissertation include the following aspects:In order to meet the rapid growth of transmission capacity in optical networks and the increasing shortage of optical spectrum resources,super-Nyquist time-packing modulation is realized for the first time in optical communications.A super-Nyquist time-division multiplexing(TDM)scheme based on single carrier and a linear time-domain multiple-input-multiple-output(MIMO)receiving scheme are proposed.Experiments verify that the two-channel 20Gbit/s RZ-QPSK super-Nyquist TDM system achieves twice the transmission capacity at the cost of ldB Q factor.In addition,a super Nyquist WDM scheme based on DFTS-OFDM is proposed.The SE of OFDM is further improved by using DFT Spread technology.The simulation results show that the OSNR cost of 128Gbit/s QPSK-OFDM with 20GHz channel spacing is reduced by 1.5dB with Duobinary filter at BER threshold of 1 × 10-2,and the SE of 6.4bit/s/Hz is realized.Aiming at the bottleneck of improving the SE of super-Nyquist single-dimensional multiplexing system,a simpler and more efficient super-Nyquist time-domain overlapping multiplexing system is proposed,which is combined with frequency-packing to form a super-Nyquist time-frequency two-dimensional multiplexing system,and the SE is doubled.The simulation results show that the 224Gbit/s PDM-QPSK super-Nyquist time-frequency two-dimensional multiplexing system can achieve a SE of 11.2bit/s/Hz.Compared with the same rate PDM-16QAM super-Nyquist WDM system,the system has an OSNR advantage of 5.5dB at 26GHz channel spacing.Aiming at the contradiction between the large-capacity transmission demand of short-distance optical interconnect and the narrow bandwidth and low sampling rate of low-cost optoelectronic devices,a frequency-domain segmented compensation mechanism based on S21 curve is proposed.Combining with Duobinary coding technology,the anti-narrowband filtering ability of IM/DD system is improved,and the bandwidth requirement of optoelectronic devices is reduced.In the experiment,the 1 km single mode optical fiber transmission of 112 Gbit/s PAM4 signal is realized by using 18GHz DML,and the sensitivity is optimized to-10 dBm.In addition,it is proposed to reduce the ADC sampling rate to below Nyquist sampling rate by using super-Nyquist technology on the basis of improving SE.The simulation and experimental results show that in the super Nyquist WDM system,the sampling rate requirement of ADC is reduced by 75%compared with Nyquist sampling rate.