Researches On Mitigation And Compensation For Signal Impairments In High-Speed Optical Fiber Communication Systems

By virtue of its huge bandwidth, ultralow loss and low cost, fiber proved to be a preferred medium for long-haul and large-capacity communications. In pursuit of larger capacity and further reach, mitigation and compensation for signal impairment in the fiber link is the key to system upgrade.In40G optical fiber transmission systems, PMD became one of the main factors limiting system upgrade, which was previously ignored. In the earlier laid fiber with large PMD, PMD compensation is required. In systems employing direct detection, to compensate signal impairment in electrical domain means higher cost. Optical PMD compensator should be a preferred solution to overcome PMD in a40G direct detection system. Duo to the random characteristics of PMD, feedback control structure was mainly applied for OPMDC. Researchers have to meet challenges including how to find out a batter feedback control signal, how to manipulate the compensation unit in accordance with the feedback signal and how to minimize the duration of the feedback control loop.Step into the100G era, polarization multiplexing, various of advanced modulation formats and coherent detection have been widely used. The degradation of system performance has been caused by the chromatic dispersion, polarization crosstalk, PMD, phase noise of laser and optical fiber nonlinearity in the optical link. It was possible for signal compensation in electrical domain due to the adoption of coherent receiver. How to design efficient DSP algorithms to compensate the signal impairment became the new challenge now.This paper concentrates on the mitigation and compensation technologies of signal impairment in high-speed optical fiber communication system. It has carried on a thorough research on these technologies used in40G,100G and beyond100G systems. Highlighted work includes: (1) An experiment was performed in a40G optical communication system, using a combination of advanced modulation formats and OPMDC. The first domestic prototype of adaptive OPMDC has been developed. The tracking speed was45.4μs; The experiment proved that in a43Gb/s RZ-DQPSK system, the OSNR introduced by the prototype was less than0.8dB; Given1dB OSNR margin, the tolerance of first-order PMD for the system increased from17ps to45ps; It could work through10hours error free at present of DGD change, as well as rapid SOP and PSP change at a speed of85rad/s; In an experiment of1200km transmission, it could work error free through12hours(2) A study of the technologies of high-order QAM modulation and coherent detection was made in beyond100G optical communication systems. A scheme to generate16-QAM signals only using dual-drive I-Q modulator driven by2-level signals was proposed, which could avoid the use of special structured modulator or expensive four-level scheme; A low complexity DSP algorithm for16-QAM format was put forward to compensate CD, PMD, polarization crosstalk, laser phase noise and frequency offset; Simulations was done to test the performance of the proposed solution in31different testing cases, which proved the feasibility of the solution.(3) Hexagonal-16-QAM generating technology and the corresponding DSP algorithms in coherent receiver. A new way to generate Hexagonal-16-QAM signal was proposed. Compared to conventional square16-QAM format, hexagonal16-QAM format which have the triangular lattice leads to hexagonal closest packing on plane allows for higher energy efficiency; Training-based DSP algorithm for hexagonal-16-QAM signal was proposed; Experimental realization of a100-Gb/s Hexagonal-16-QAM signal generation and reception.