| With the development of social informatization and increasing demand ofcommunicaition traffic, optical fiber communication systems are evolving to high inspeed, lager in capacity and long in distance. As the transmission rate of a singlechannel increases, the performance of optical fiber communication systems would bemore and more affected by the dispersion, non-linear and so on. While the novelmodulation formats become one of the key techniques which could mitigate thetransmission impairments effectively. With the decreases of channel spacing, theinfluence of four-wave-mixing (FWM) has been the main factor which limits thecapacity of wavelength division multiplexing (WDM) system. Therefore, the researchon FWM is significant for improving the performance of optical communicationsystems.Firstly, the modulation and demodulation principles of the novel modulationformats used in current high-speed optical fiber communication systems aresummarized in this thesis. Secondly, the performance evaluation metrics of optical fibertransmission systems are presented. A simulation model with40Gb/s in a single channelis built. We studied with simulation for the dispersion tolerance, non-linear toleranceand transmission distance limit of several novel modulation formats. The results showthat the modulation formats with narrow spectrum have higher performance indispersion tolerance and the phase modulation formats outperform the intensitymodulation formats in non-linear tolerance. In addition, the mechanism resulted fromFWM, the effects of FWM on WDM system performance and the methods ofsuppressing FWM effects are studied. We also investigate the relationship betweenFWM and channel spacing. The results show that small channel spacing result in anincrease in FWM cross-talk and the channels located at the middle have the worst biterror rate (BER). Using unequal channel spacings would reduce the overall BER of thesystem. Finally, the thesis summarization is given. |
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