Research On Key Techniques In DP-QPSK Optical Coherent Communication Systems

In recent years, with the rapid development of high-speed Internet, big data processing, Internet of things (IoT) and HD network TV and other new technology and businesses, the rapid growth of network traffic makes people more and more demand for bandwidth. How to further improve the transmission capacity and spectral efficiency of optical communication system has become a hot research topic again in optical communication field. Optical coherent communication systems, based on advanced modulation format and digital signal processing, has been considered as a promising technology for next generation high-speed optical communication systems due to its high sensitivity of optical receiver, long-distance relay, large communication capacity and compensation for impairments in electric field. In this thesis, we conduct a deep simulation and experimental investigation on the high-speed optical coherent communication systems based on dual polarization quadrature phase shift keying (DP-QPSK) modulation format, coherent detection and digital signal processing. The main work and research results of this thesis are as follows:Simulation study is taken on the performance of single carrier, DWDM and OTDM optical coherent communication systems. Result shows that in the absence of nonlinear damage compensation, the most far transmission distance of the BER of the three systems below the FEC threshold is 5200km,1500km and 1800km, respectively.For the first time, the influence of carrier phase noise caused by the linewidth of light source on the OTDM optical coherent communication system is studied. Comparative study on the effects of different laser linewidth on the bit error rate of single carrier, DWDM and OTDM optical coherent communication systems, the results show that the single carrier and DWDM optical coherent communication systems require laser linewidth less than 0.1 MHz, and OTDM optical coherent communication systems require laser linewidth less than 0.01 MHz.Take a research on the DSP algorithm for the signal transmission damage compensation in the electric field, including frequency domain filter scheme to compensate chromatic dispersion, dynamic equalizer based on the constant modulus algorithm to compensate polarization mode dispersion and Viterbi & Viterbi algorithm to compensate the frequency offset and phase offset. Then, through the Optisystem platform and Matlab joint simulation to achieve the algorithm function, compensate the signal transmission damage in real time in a way that is more close to hardware DSP, and get a good compensation effect.Experimental study is taken in DP-QPSK optical coherent communication systems. Based on the experimental results, analyzed the importance of the DQPSK modulator operating at the optimum bias point and the effect of phase noise on the optical coherent communication systems.