Study On Key Technologies And Fiber Nonlinearity Impairments Of CO-OFDM Systems

In recent years, as society continues to raise the level of information, particularly the growth of IP-based data services was explosive, for the basis for information transmission—fiber optic backbone transmission network, it has become an inevitable trend that the single-channel transmission rate improve from the current 10Gbit/s to 40Gbit/s or even 100Gbit/s. OFDM technology does not require any compensation and management for chromatic dispersion of optical links, and can be very effectively to compensate CD and PMD only using the electric field compensation algorithm. Especially coherent optical OFDM (CO-OFDM) combining the benefits of coherent optical communications and OFDM technology has inherent advantages, such as high transfer rate, high resistance to dispersion capacity, high spectrum efficiency and other advantages. The studies show that, CO-OFDM system can built on a high-speed, low-cost, long-distance optical transmission network based on existing optical transmission system and is the very competitive technology one for the next generation ultra-high speed long distance optical transmission.This dissertation researches on single-channel high-speed CO-OFDM systems, focusing on key technologies and fiber nonlinear impairments, and has made some valuable research results. The main work and innovations are:1. Depth studied on BER and Q factor estimation algorithms based on Eb/No for CO-OFDM systems. This method can accurately assess the system performance and does not require a tremendous amount of simulation or experimental data. The simulation study shows that, even if there are dispersion, nonlinearity, phase noise and other link damages, the estimates results based on Eb/No is same as Monte-Carlo. But in the same number of simulation data conditions, the measured scope of BER by Eb/No is much greater than the Monte-Carlo method.2. A detailed analysis on the injury mechanisms of the dispersion, polarization mode dispersion, laser linewidth, frequency offset in CO-OFDM, and proposed electric field corresponding to the solution:electrical dispersion compensation algorithm (EDC), the minimum squared channel estimation and compensation algorithm (LSCEC), the pilot supporting phase compensation algorithm (PC) and Synchronization algorithm. By numerical simulation, when the accumulated dispersion in link is less than the tolerance of the cyclic prefix, EDC can completely compensate for the phase shift due to dispersion; LSCEC can full compensate for PMD within DGD tolerance; PC algorithm can control the damage within 1dB when the laser linewidth is smaller than 160kHz value.3. Studied on CO-OFDM channel nonlinear effects from different points:synthesis signal and single carrier, and analyzed the effects of link parameters to the nonlinear impairments. The study shows that, the number OFDM subcarriers influence power threshold, the smaller the number the more thresholds. Link dispersion offset benefits to mitigate the damage of nonlinear. Finally, also studied the combined effect of EDFA noise and nonlinear effects, nonlinear phase noise (GM noise).4. First proposed the joint dispersion and nonlinear phase electrical domain compensation (JCNPC) algorithm for the CO-OFDM system with high residual dispersion link. The simulation shows that JCNPC is less affected by the dispersion walkoff and is more suitable for the residual dispersion link.5. First proposed midlink OPC to compensate the Kerr nonlinear damages and Gordon-Mollenauer nonlinear phase noises in CO-OFDM system, which OPC is based on the realization of SOA-FWM effect. Simulation results show that, whether or not the link has the inline dispersion compensation, the algorithm can effectively compensate for nonlinear damages, and greatly improve transmission performance. For Single channel the maximum Q factor can be increased by more than 3dB, the threshold power can be increased by above 4dB. For WDM systems, the increase of the maximum Q factor is 1.1dB, the increase of nonlinear threshold power is 1dB.6. First proposed pre-and post-compensation algorithm (Pre-OPC, Post-OPC) combining high-nonlinear fiber (HNLF) with OPC. Those OPC algorithms just need to place after the transmitter or in the front receiver, and do not disconnect the link, with high practicality. Numerical simulations show that Pre-OPC (or Post-OPC) can greatly compensate for nonlinear damages, especially suiting for the low residual dispersion link. The series algorithm can increase the maximum Q factor of about 2dB, and the nonlinear threshold value above 3dB.