Research On High Spectral Efficiency Modulation And Signal Impairments Recovery Algorithms Of High-Speed Cpherent Optical Communication Systems

To provide reliable support for the rapidly increasing traffic demands of communication network, recently, coherent optical communication system is developing towards higher speed, larger capacity, and better spectral efficiency (SE). Achieving flexible-grid terabit and ultra-terabit transmission system has become the inevitable development trend of next generation optical network. During this process, how to maximize system SE, reduce the hardware complexity and energy loss, and at the same time overcome electrical bandwidth bottleneck is one of the critical challenges faced by researchers. Coherent optical orthogonal frequency division multiplexing (OFDM), Nyquist Wavelength Division Multiplexing (Nyquist-WDM) joined with high order modulation formats are foreseen to be the preferred solution of future Terabit transmission system.During the transmission optical signals will acquire a variety of impairments, which will affect the quality of communication seriously. Coherent detection enables us to off-line compensate using a DSP treatment. As for the future terabit and ultra-terabit transmission system, it has narrower signal spectrum, more compact arrangement of the channel, and the modulation format constellation point distributed more closely, which may result in damage of impairments tolerance of the system. Thus it will raise more strict requirements of signal impairments recovery algorithms.This work concentrates on the high spectral efficiency modulation techniques and signal impairments recovery algorithms of high-speed coherent optical communication systems. It has carried out a thorough research on pilot-aid (PA) DSP algorithms in Nyquist-WDM and CO-OFDM system. The main work and innovations as follows: (1) Study CO-OFDM and Nyquist-WDM these two high SE modulation techniques. The Nyquist-WDM has been analyzed in depth, including the basic principles of system. Technique solution of Nyquist spectral shaping implementations based on optical filter, electric filter and DSP filter are discussed. In addiation, deep discussion about the Nyquist pulse shaped scheme using DSP technology has been carried on.(2) Study the DSP algorithms in high-speed coherent optical communication system. Briefly discuss the theory of transmission impairments and the corresponding recovery algorithms. Focus on the pilot-aided algorithms and conduct thorough research on this theme. The application of PA algorithm has been studied in CO-OFDM and Nyquist-WDM systems. Several implementation schemes to add pilot in system have been described in detail. As a comparison, we have introduced traditional carrier phase recovery (CPR) algorithms.(3) Propose a set of new optical domain pilot-aided CPR schemes in single-carrier (SC), dual-carrier (DC) Nyquist system and Nyquist-WDM system. Simulations have been carried out to prove the feasibility of the proposed scheme. Besides that, the theoretical analysis and optimization results of the key parameters in these schemes have been studied. Not that, the proposed schemes use one pilot signal to compensate the phase noise of two channels simultaneously, which make the system spectral redundancy fall by half improving the SE. In addition, introduce a new pilot-aided Nyquist-WDM system scheme and analyze the application prospects of PA algorithm in this scheme.(4) Furthermore, we propose two-stage PA-CPR algorithm combinations, which use traditional Maximum Likelyhood (ML) or Constellation Comformed (CT) algorithm as the second stage just after the pilot phase compensation. We also make evaluation and comparison of the performances among those CPR methods in Nyquist PDM-mQAM SC and DC system. It turns out that our proposed PA+ML/CT CPR algorithms have better laser linewidth tolerance and lower complexity.