Research On Signal Processing Techniques For Ultra-high Speed Optical Transmission

To release the increasing demand for communication traffic,ultra-high speed and large capacity is the inevitable trend of optical communication technology development.In order to further improve the speed of optical communication and meet the practical needs,this dissertation focuses on the theoretical and experimental research on ultra-high speed optical transmission system and its key enabling techniques:1.During the in-depth study process of ultra-high speed Nyquist time-division multiplexing(Nyquist OTDM)system,the effectiveness of optical Nyquist shaped pulse as signal carrier in time division multiplexing system is demonstrated,and 160 Gbaud QPSK transmission system is experimentally completed,including pulse source generation,realization of high quality QPSK signal modulation,construction of time-division multiplexer,coherent receiver debugging,etc.Coherent matching sampling and Gaussian sampling for Nyquist OTDM signal demultiplexing are both demonstrated,and the demultiplexing performance of both schemes are also detailedly compared.The influence of relevant parameters in coherent matched sampling scheme on system demultiplexing performance is well studied,also the mechanism is explained in detail through simulation.2.Demutiplexing of Nyquist OTDM signal based on temporal magnification aided optical sampling is proposed and experimentally demonstrated,combining with space-time duality,a complete construction theory of temporal magnifier is conducted.The feasibility of the proposed scheme is qualitatively studied through simulation,then the proposed temporal magnifier is successfully applied to the 160 Gbaud Nyquist OTDM demultiplexing experiment.Experimental results show that the proposed scheme can effectively reduce the sampling pulse-width requirement as well as achieving better demultiplexing performance compared with traditional scheme.Gaussian sampling pulse-width requirement could be released to 10.4 ps with temporal magnification.The demultiplexing operation of Nyquist OTDM system can be even realized utilizing a baseband rate(pulse-width=12.4 ps)optical Nyquist pulse through the proposed scheme.3.Demutiplexing of Nyquist OTDM signal utilizing a single IQ modulator is proposed and demonstrated,Compared with Gaussian sampling,we achieve better experimental demultiplexing performance through quasi-Nyquist pulse sampling generated from the receiver-side single IQ modulator without any other spectral manipulations.The proposed scheme exhibits about 6.8 dB required-OSNR improvement(@BER=10-4)compared with Gaussian sampling with the same pulse-width(4.5 ps).At the same time,the performance analysis and optimization of some relevant parameters in this scheme are explicitly studied through simulation.Experiment and simulation results will provide an effective reference for the future application of Nyquist OTDM system.4.The Kramers-Kronig(KK)receiver system is deeply studied,the influence mechanism of the CSPR,prefilter setup,up-sampling rate and other related parameters on the performance in KK receiver system is investigated in detail,and related key problems toward practical KK receiver application are discussed.A low CSPR KK receiver scheme based on probabilistically constellation shaping is proposed.Simulation and experimental results both show that the proposed scheme can effectively reduce the CSPR in KK receiver system.112 Gbit/s,240 km single-mode optical fiber transmission experiment results further show the advantages of the scheme in fighting against the nonlinear effect of optical fiber.5.An all-optical signal encryption/decryption scheme based on time-domain Talbot effect is proposed,and the detailed theoretical framework of time-domain Talbot effect is given.The feasibility of the scheme is successfully verified through qualitative optical PAM 4 signal encryption/decryption simulation,and the reliability of the scheme for optical signal encryption is also evaluated.