Research On New Modulationg Formates And Mode Division Multiplexing Technology In Coherent Optical Communication System

With large emergency of new terminal equipment, as well as the widely application of cloud computing and three dimensional video applications, the demand for bandwidth is growing rapidly. The high-speed, large-capacity and high-spectral-efficiency optical communication networks have become the next-generation mainstream communications networks. Currently,100G optical transmission networks are in full swing all over the world, and400G optical networks are becoming increasingly approaching. To further improve the spectrum efficiency, increase system capacity and reduce transport costs, a lot of technologies have been introduced to make significant breakthroughs, including coherent reception, digital signal processing, advanced modulation formats, and multidimensional multiplex. All these promote the continuous development of optical communication systems.However, the phase noise introduced by coherent optical communication systems lead to serious errors, which greatly limits the transmission efficiency of the system. What’s more, the new modulation format is particularly sensitive to phase noise, so the research of carrier phase estimation algorithm suitable for new modulation formats is very necessary. On the other hand, as a special mode multiplexing mode, the orbital angular momentum (OAM) multiplexing adds a new dimension, and exponentially increases the transmission capacity of the system. However, in space coherent optical communication systems, many issues are much needed to overcome, including the turbulence effects, crosstalk, multiplexing and demultiplexing of OAM modes.In this paper, we focus on the new modulation formats and mode multiplexing in coherent optical communication systems. Some depth research and analysis about carrier phase estimation with new modulation formats and OAM mode transmission have been done, and the main innovations are as follows:(1) We have built a coherent optical communication system to load and transport new modulation format signals. We explore the performance of carrier phase recovery algorithms with new modulation, and obtain detailed analysis and comparison results about BER, EVM, OSNR Penalty, the complexity of variety algorithms.(2) For64-QAM signal, we propose a two-phase carrier phase estimation algorithm. Compared with the traditional BPS algorithm, the complexity of our proposed algorithm can reduce by a factor about3, when obtaining the same noise estimation performance.(3) We propose a kind of three-stage carrier phase estimation algorithm, which is transparent to modulation format. Digital analysis results show that for32-,64-, and128-QAM, the linewidth tolerance of the three-stage algorithm can reached1.4M,1.1M, and224K, and compared with BPS algorithm, the complexity can reduce by a factor about3,5and7.(4) Based on Kolmogorov spectrum model, we analysis the influence on phase and intensity of OAM mode, as well as crosstalk between multi OAM modes in turbulence by simulation. The simulation results show that when introducing weak and moderate atmospheric turbulence, in order to ensure the signal performance at receiver, the multiplex interval of OAM modes is at least equal to1and3, respectively.