Research On The Key Techniques For The Single Sideband Modulation Direct Detection Opticalfiber Communication System

The traditional intensity modulation direct detection system is restricted by the power fading effect which aggravated by the high bandwidth and long distance fiber transmission.Compared with the traditional intensity modulation,the single sideband modulation technology can not only effectively resist the power fading effect,but also improve the spectral efficiency of optical fiber communication system.Single sideband modulation with direct detection technology has been widely applied in many areas,such as data center,optical access network and so on.The core and key issues of single sideband modulation with direct detection technology are the reduction for the cost of the system,the eliminatation for the signal signal beat interference(SSBI),the improvement for the transmission capacity and so on.Focuses on these issues,theoretical analyses combine with experimental and simulation verifications are carried out in this dissertation.The main innovations are as follows:(1)A low-cost single side band vector signal modulation scheme is proposed.The scheme is realized by appling a single dual-drive Mach-Zehnder modulator(DDMZM)and frequency shifting algorithm.The feasibility of the scheme is proved by theoretical analysis.Based on the study of 16 QAM single-sideband signal after 75 km standard single mode fiber(SSMF)transmission,a comparison is made between the proposed scheme and the traditional optical In-Quadrature modulator(IQM)based virtual carrier single side band modulation scheme.The differences between these schemes in the structure,principle of parameters optimization and the transmission performance are analyzed.The results show that the two schemes have similar transmission performance under their optimal parameters configuration.Compared with the traditional scheme,the proposed DDMZM based frequency-shift single sideband vector signal modulation scheme is less costly and easier to implement.(2)For the issue that SSBI will appear after the square law detection,the principle of the Kramers-Kronig(KK)algorithm based single sideband signal recovery is studied.The effect of the phase modulation to amplitude modulation noise caused by the laser linewidth and transmission distance is analyzed by experiment and simulation.The feasibility of combining the DDMZM based frequency-shift single sideband vector signal modulation scheme and KK algorithm,is validated through the experiment 42.5 Gbps 16 QAM signal over 75 km fiber transmission.(3)A novel passive optical network(PON)downstream transmission scheme based on Multi-Twin-SSB modulation and KK algorithm is proposed.By combining the advantages of the multiband carrierless amplitude phase(Multi-CAP)and twin single sideband(Twin-SSB)modulation techniques,the application of the Multi-Twin-SSB modulation technique can not only meet the needs of multi-user access in PON systems,but also solve the problem of power fading caused by dispersion and square-law detection.The proposed system has been validated with 4 sub-bands using 50 Gbps 16 QAM modulation for each sub-band by numerical simulations.The results show that the proposed scheme can improve the bandwidth utilization and spectral efficiency.In addation,the SSBI impact can also be reduced by the KK algorithm.(4)A zero guard band(ZGB)Multi-Twin-SSB bidirectional PON scheme is proposed.The downstream single sideband signal is coupled with a local oscillator that split from the uplink light source before detection,which eliminates the guard band between the left sideband and right sideband signals,and further improves the transmitter-side DACs bandwidth utilization and the spectral efficiency.On the other hand,the upstream and downstream signals are at different sides of the optical carrier,so the Rayleigh backscattering noise is easy to be eliminated.The proposed scheme can also improve the optical noise tolerance of the system and the sensitivity of the receiver.(5)In order to compensate the linear and nonlinear crosstalks in the degenerate mode division multiplexing(MDM)system with single sideband modulation and direct detection techniques,an equalization scheme,which combines the Hilbert superposition cancellation(HSC)algorithm and Volterra nonlinear multi-input multi-output(MIMO)equalizer is proposed.The source of channel crosstalk and the principle of the compensation for the HSC algorithm with equalizers are analyzed theoretically.The feasibility of the scheme is verified by the degenerate MDM transmission system with single sideband PAM 4 modulation and direct detection techniques through experiment and simulation.The simulation and experimental results are in good agreement with the theoretical analysis.The results confirm the superior performance of HSC algorithm and Volterra nonlinear MIMO equalizer in the degenerate MDM system with single sideband modulation and direct detection techniques.