Research On Key Technologies Of CO-OFDM Systems

With the development of broadband video, multimedia services and other emerging data-based services, the rapid growth of bandwidth demand driving the continuous development of optical transport networks. Large capacity and high-speed optical communication systems have become the vital infrastructure of the next generation communication networks. Optical orthogonal frequency division multiplexing system has high spectral efficiency, and excellent robustness against chromatic dispersion (CD) and polarization mode dispersion (PMD). Combined with coherent detection technology can also improve the receiver sensitivity, and be more flexible and simple to achieve the high-order modulation format and channel equalization. Many studies show that the coherent optical orthogonal frequency division multiplexing (CO-OFDM) is a very competitive solution for beyond100Gbit/s optical transmission systems.However, the OFDM signal is more sensitive to synchronization error and phase noise, and has higher peak to average power ratio (PAPR) which will cause serious nonlinear impairment. The study of the paper is based on the compensation of these injuries. The synchronization technologies and PAPR reduction technologies are researched. And we focused on the study and improvement of timing synchronization and phase estimation technologies. The main work and innovation as follows(1) The basic principles of CO-OFDM system are analyzed, including the mathematical description of OFDM, the signal modulation/demodulation and the cyclic prefix. The basic principles and structure of the coherent reception systems are reviewed, and two common receiver schemes are introduced. (2)Based on the implementation schemes of CO-OFDM system, build a112Gb/s polarization-division-multiplexing CO-OFDM simulation system.(3) Analysis of the signal processing of CO-OFDM system, and achieved the frequency synchronization and channel estimation. Based on the PAPR characteristic of OFDM systems, compared several PAPR reduction techniques.(4) Proposed two modified algorithms of timing synchronization. Then compared with the traditional algorithms in PDM-CO-OFDM simulation system, proved that the modified algorithms can achieve higher timing accuracy, and improved the tolerance to CD and PMD.(5) Based on the analysis of the CO-OFDM system phase noise theory and several traditional phase estimation algorithms, proposed novel blind phase estimation algorithms based on decision-direction and decision-feedback. The proposed algorithms are demonstrated in a112Gb/s PDM-CO-OFDM system, and compared with traditional algorithms by the estimation performance, pilot overhead and the laser linewidth tolerance.The results verified the superiority of the proposed algorithm.