Study On Carrier Phase Recovery Methods Of High-Order Modulation Formats In High-Speed Optical Coherent Transmission Systems

With the explosive growth in the demand of network traffic since the21st century, the transmission rate and distance of optical fiber communication systems are facing a new round of great challenge. As a result, the traditional intensity modulation and direct detection technology is replaced by the coherent optical communication technology due to the higher receiver sensitivity, the longer transmission distance, the larger capacity and the adaption to a variety of modulation formats.In such high-speed optical transmission systems, the receiver is particularly sensitive to the phase and polarization information of the signal. Therefore, the phase noise induced by the linewidth of lasers in transmitter and receiver, and the birefringence effect and polarization mode dispersion of the fiber have become two important factors which affect the transmission quality. Based on the two effects above, we focus on the study of algorithms aiming at carrier phase estimation, polarization demultiplexing and PMD compensation in this paper after introducing the principle and state of development of coherent optical communication systems. The main work includes:(1)Comprehensive and detailed analysis of optical communication system. The basic principles of optical fiber communication, the condition of single-mode fiber transmission are introduced. In addition, the mechanisms how the effects such as birefringence, chromatic dispersion, polarization mode dispersion, loss and nonlinear effects in the fiber do damage to the optical signal are studied;(2)Theoretical and experimental study of coherent optical transmission system. Firstly, the function and applied algorithms of each module in the transmitter and receiver of coherent optical transmission systems are analyzed. Secondly, an experimental224Gb/s PDM-16QAM coherent transmission platform is set up;(3)Deep research of carrier phase estimation module in coherent receiver. Firstly, the principle and necessity of carrier phase estimation are analyzed in detail. Secondly, carrier phase estimation algorithms and their improvements for PDM-QPSK and PDM-16QAM formats are studied, such as4th power algorithm, pre-decision algorithm, blind phase search algorithm and so on. Thirdly, experimental verification based on the platform in2is done, coming to the result that the cascade algorithm of QPSK Partitioning and Maximum Likelihood is the most suitable algorithm. Finally, a improved algorithm is proposed based on the trade-off between performance and computational complexity. Results show that, the improved algorithm reduced the computational complexity in a factor of2while the bit-error rate and error vector magnitude performance remain nearly unchanged.(4)Simulation study of polarization demultiplexing and PMD compensation. Firstly, the principle and necessity are introduced. Secondly, a112Gb/s PDM-16QAM simulation platform is set up based on matlab. Thirdly, the performance of algorithms like standard CMA, modified CMA, CMA with variable step size, CMA with adaptive step size and decision directed least mean square are compared in the simulation platform, resulting that the adaptive CMA is the algorithm which plays best in singular resistance, bit-error rate and signal recovery.As a whole, the work done in this paper focused on the modules of carrier phase estimation, polarization demultiplexing and PMD compensation based on the high-speed coherent optical transmission system. In addition, verification and improvements of the algorithms applied in the modules above are done in experimental and simulation platforms.