Simulation And Research Of Digital Signal Processing For Coherent Optical Communication System

In the field of optical communications, with constant pursuit for larger bandwidth, longer transmission distance and higher receiver sensitivity, coherent optical communications technology came into being. Coherent detection can not only improve the receiver sensitivity but also acquire all the light field information can be obtained, thus giving coherent optical communications unparallel advantages over traditional Intensity Modulation/Direct Detection (IM/DD) system. Thanks to high-speed development in advanced modulation format and digital signal processor (DSP), digital coherent optical communication technology is developing rapidly. Advanced modulation formats provide flexible methods of information encoding in coherent optical communication system and improve the spectrum efficiency. On the other hand, with the improved digital signal processor computation speed, digital coherent optical communication systems has become a promised candidate for next-generation optical networks.Thesis investigated the digital compensation algorithms in coherent communication receivers with the focus on carrier frequency offset estimation and carrier phase estimation. Firstly we investigate various noise and distortion effects in the transmission via a systematic simulation using VPItransmissionMakerTM and Matlab. Then, the received signal is off-line processed and the performance is analyzed. Also, some of the algorithms have been tested experimentally. By using the simulation platform and digital compensation algorithms mentioned above, we have achieved polarization diversity detection system with no dispersion compensation fiber and phase-lock-loop. Meanwhile, we proposed a carrier phase recovery algorithm with weighting coefficients, which can improve the sensitivity penalty by 0.2dB; a feedforward carrier phase recovery algorithm based on QPSK partitioning and maximum likelihood detection, the complexity is less than half of reported algorithms in other literatures, The proposed new carrier recovery algorithm either improves system performance or reduces computation complexity, which will relief hardware burden in future high-speed real-time coherent optical communication systems. Finally, system performance is analyzed. The paper sets up a simulation platform incorporated with digital signal processing algorithms and achieved PDM-QPSK and PDM-16QAM coherent transmission system with bit error rate lower than 10-3, the results agrees with experimental outcomes and will provide back ground and theoretical guidance for future high-speed digital coherent optical communication systems.