Research On Polarization Demultiplexing And Carrier Phase Recovery For Coherent Optical Communication Based On NPCA

Polarization multiplexing(PDM)coherent optical communication system has become an inevitable choice for high-speed optical communication due to its high spectral efficiency and high optical received sensitivity.In the PDM coherent optical communication system,the received signal needs to be compensated for damage by a series of digital signal processing(DSP)algorithms.Rotation of state of polarization(RSOP)is a typical damage to PDM coherent optical communication system.The conventional polarization demultiplexing algorithm,constant modulus algorithm(CMA),has poor dynamic tracking ability,and it is difficult to be used in communication transmission scenarios with high-speed RSOP.Phase noise is another typical damage to the coherent optical communication system.The conventional carrier phase recovery algorithm,the blind phase search(BPS)algorithm has very high computational complexity,and it is difficult to be applied to low-cost coherent optical communication scenarios.To solve the problem of high-speed RSOP in coherent optical communication system and explore a low-complexity carrier phase recovery algorithm for various modulation formats.Based on the nonlinear principal component analysis(NPCA)algorithm,the polarization demultiplexing technology and carrier phase recovery technology is studied in this paper.The main research contents of this paper are as follows:(1)A polarization demultiplexing algorithm based on NPCA is proposed.NPCA is a modulation-transparent polarization demultiplexing algorithm,can avoid the singularity problem that occur in traditional CMA,and has fast polarization tracking capability.For QPSK and 16 QAM signals,NPCA can track the RSOP angular velocity of more than10Mrad/s and 2Mrad/s,respectively.(2)A low-complexity joint compensation scheme with adaptive channel equalization,RSOP tracking,and phase recovery is proposed for PDM-QPSK signal coherent optical transmission system.The experimental results show that compared to the conventional CMA and VVPE schemes,the proposed joint compensation schemes have better transmission performance at RSOP speed of more than 1Mrad/s,can achieve a computational complexity reduction of more than 40%.(3)A low complexity carrier phase recovery algorithm based on the cascade of NPCA and decision-directed least mean square(DD-LMS)algorithm(NPCA+DD-LMS)is proposed.The experimental results show that the proposed algorithm is suitable for various modulation formats,like QPSK,16 QAM and 64 QAM.And compared to the conventional BPS scheme,the proposed algorithm shows similar transmission performance and very low computational complexity.