Research On Code Modulation Formats And Transmission Performance Of High-Speed Optical Communication System

As they developing towards high speed, large capacity and long distance, the high-speed optical communication systems are badly infected by transmission impairments such as fiber dispersion and nonlinear effect hence goes down the transmission performance. The code modulation formats, as one of the key technologies studied in high-speed optical fiber communication systems, can effectively reduce the transmission impairments, enhance the anti-dispersion and anti-nonlinear-effect capability and improve the transmission performance and spectrum efficiency. Therefore, it is significant to study the code modulation formats.Aiming at the code modulation formats and its performance (including dispersion tolerance and nonlinear effect tolerance), this thesis implemented deeply theoretical analysis, system model simulation and comparison. The main work included:1. Studied the generation and demodulation of various modulation formats. By launching intensity modulation and phase modulation generators in optic communication simulation software, we got spectra of kinds of modulation formats.2. Adopted the method of combining the theoretical analysis and software simulation, successfully built the high-speed single-channel optic communication system models by using OptiSystem, studied and analyzed the anti-dispersion and anti-nonlinear-effect capability of intensity modulation format in the systems and compared the advantages and shortages on dispersion tolerance and nonlinear effect tolerance of five kinds of intensity modulation formats. The results showed: the dispersion tolerance of RZ was worst, NRZ had better dispersion tolerance than RZ, but NRZ was more vulnerable to nonlinear effect than RZ, the anti-nonlinear-effect capability of CSRZ and all kinds of RZ exceeded NRZ, DRZ and MD-RZ had fine anti-nonlinear-effect capability. CSRZ, DRZ and MD-RZ were fit for high-speed long-distance transmission.3. Built high-speed single-channel optical transmission system models, studied, analyzed and compared the anti-dispersion and anti-nonlinear-effect capability of phase modulation format in the systems. The results showed: the anti-dispersion capability of DQPSK modulation format was better than others, in which NRZ-DQPSK had the strongest anti-dispersion capability; DPSK's anti-nonlinear-effect capability was better than others, especially, RZ-DPSK's nonlinear effect tolerance was the strongest. And discussed the compensation effects of three different kinds of dispersion compensation of SMF+DCF scheme for phase modulation format system, the results turned out that DPSK and DQPSK had the optimal compensation effects and system transmission performance in symmetric compensation scheme. In the end we studied the impact of optical amplifiers'spontaneous emission to transmission performance of phase modulation systems, it turned out that the main factor to limit transmission distance of DPSK system was ASE noise.