Studies On Key Technologies Of Signal Processing In Medium-short-distance Optical Network

With the rapid development of new types of services such as cloud computing,the internet of things,and virtual reality,the demand of users for bandwidth is increasing.To cope with this demand,as an important foundation for supporting the information society,optical communication networks are developing toward higher speeds and greater capacity.Typical medium-short-distance optical network such as data center optical interconnection,optical access network and metropolitan optical network is an important component of optical networks.Its transmission distance varies from a few meters to several hundred kilometers.Unlike long-distance data transmission,it is more sensitive to the cost and energy consumption of the system.The research of medium-short-distance optical network,especially the signal processing technology of optical access and optical interconnection,is of great significance to the future innovation and development of optical network technology,and is also a hot and difficult point in current optical communication research.At present,there are still some key issues to be solved of signal processing technologies in optical access and optical interconnect.For example,optical access and optical interconnect nodes lack flexible and reconfigurable optical signal processing subsystems,resulting in poor network adaptability and flexibility;lack of parallel multi-channel,multi-function,mixed modulation format processing functions;the optical power of system is limited resulting the actual capacity is less than the theoretical value and so on.This paper focuses on the key issues facing signal processing technology in medium-short-distance optical network.The main innovations are as follows:Firstly,aiming at the problems of complex structure,small bandwidth and low resource utilization of traditional electrical domain multicast schemes in wavelength division multiplexing(WDM)optical access networks,a reconfigurable downlink WDM multicast scheme based on four-wave mixing(FWM)in semiconductor optical amplifier(SOA)is proposed.Experimental results show that this scheme can provide a convenient and reliable multicast service by installing a multicast module on an optical line terminal(OLT)or a remote node(RN)without changing the structure of the WDM optical access network.This scheme can implement 10 Gbps differential phase shift keying(DPSK)signal from 1 to 6 reconfigurable WDM multicasts.The bit error rate(BER)performance of each multicast signal is better than the threshold forward error correction(FEC).Secondly,aiming at the problem of inelastic bandwidth and non-reconfigurable system of optical interconnect nodes resulting poor adaptability and flexibility,two software-defined reconfigurable optical signal processing schemes in metropolitan optical interconnects are proposed:a)a software-defined reconfigurable filtering scheme was proposed using a programmable bandwidth-based wavelength selective switch(TB-WSS)based on liquid crystal silicon(LCoS)independently developed by a domestic cooperation unit;b)a software-defined reconfigurable multi-wavelength multicast solution for metropolitan area optical interconnects is proposed to solve the problem of wavelength conflicts and multicast requirements between the data source and the first-hop network nodes and the optical interconnect nodes,achieving reconfigurable Multi-wavelength multicast function.Thirdly,in order to solve the problem that optical signal processing in traditional optical interconnect nodes is limited to single function processing and lack of mixed modulation format processing functions,a multi-wavelength and multi-function signal processing scheme of optical signal XOR with multicast and wavelength conversion based on FWM effect in highly nonlinear fiber(HNLF)of three-channel binary phase shift keying(BPSK),BPSK,quadrature phase shift keying(QPSK)is proposed.The simulation results show that inputting two 10 Gbps BPSK signals and one 10 Gbaud/s QPSK signal,through the FWM effect of HNLF,simultaneously generates a five mixed modulation format XOR gate signal,two wavelength conversion signals,and two channels Wavelength multicast signal.The BER performance of the generated signal is better than the FEC threshold,and the optical signal-to-noise ratio(OSNR)cost does not exceed 0.7 dB(@BER=10-3)Fourthly,in order to improve the security of the optical signal in optical interconnection,a three-channel BPSK,BPSK,QPSK optical signal encryption/decryption scheme based on FWM effect in HNLF is proposed.The simulation results show that this scheme does not require special pump light,and inputs two 10 Gbps BPSK signals and one 10 Gbaud/s QPSK signal to realize the encryption/decryption of two BPSK signal optical domains.The BER performance of the decrypted signal is better than the FEC threshold,and the OSNR cost is less than 0.8 dB(@BER=10-3).This scheme ensures the security of the optical signal service and also improves the signal processing efficiency of the optical interconnection node.Fifthly,the actual optical interconnection system cannot reach a very high OSNR due to optical power limitation,and thus the actual capacity is less than the theoretical value.To solve this problem,an optical interconnection scheme combining probability shaping algorithm and 4-level pulse amplitude modulation(PS-PAM4)is proposed.The paper simulates and analyzes the transmission performance of PS-PAM4 signals and evenly distributed PAM4 signals in optical fibers under different received optical powers,transmission distances,and speeds.The simulation results show that when the optical fiber interconnection system has limited optical power and low signal-to-noise ratio(SNR),the scheme can effectively improve system performance and improve system capacity.In addition,the paper experimentally verifies the transmission performance of two PS-PAM4 signals and evenly distributed PAM4 signals in visible light communication(VLC)channels.Experimental results show that the scheme can reduce the SER and increase the system capacity of VLC system.Compared with the even distribution of PAM4 signal,these two PS-PAM4 signals respectively increase the transmission rate of VLC system by 18.6%and 22.6%(@SER=10-3).