Study On Modulation Transparent Dispersion Monitoring Method

In order to satisfy the increasing demands of data traffic, optical fiber communication systems are now rapidly evolving toward the direction of high speed, long distance and dynamic reconfiguration. In addition to support different data transport services, optical signals with different modulation formats and data rates may be transmited in the same optical fiber communication system simultaneously. With increasing data rate, dispersion tolerance is decreased rapidly. Furthermore the reconfiguration of optical links and the environmental temperature drift can also cause the dynamic change of the accumulated dispersion of the signal, so the online real-time dispersion monitoring for optical signals with different modulation formats and data rates is needed to realize optical performance monitoring, as well as adaptive dispersion distorions compensation. Thus, the modulation transparent dispersion monitoring technology has become one of the key technologies for next generation optical fiber communication networks.This thesis is articulated around the theoretical and experimental study of the modulation transparent dispersion monitoring technology. First, an all-optical chromatic dispersion monitoring device based on Four Wave Mixing(FWM) is designed. Base on the systematical analysis of the influence of the phase matching condition on the FWM gain, an effective method is given to obtain high order Nonliner Power Transfer Function(NPTF). Furthermore, an optimization method is proposed to improve the output contrast 3dB for advanced modulation format signals. On this basis, by using the proposed sysmmetry center recognition algorithm, the dispersion monitoring range is expanded and the modulation transparent all-optical dispersion monitoring technology is realized, which is insensitive to spontaneous radiation noise and polarization mode dispersion. Then we experimentally deomonstated the high order NPTF using FWM, and the experimental results agree well with the simulation results. Secondly, a dispersion monitoring technology based on the Auto-Correlation Function(ACF) of signal power waveform is studied. A method is proposed to improve the monitoring accuracy for signals with different pluse duty cycles and Nyquist pulse shapes by introducing a difference filter. The tolerance of the method to different distoritons have been studied by simulation and experiment. Finally, according to the change of signal's peak to average power ratio versus the dispersion, this thesis proposes a dispersion monitoring method based on Width to Area Ratio(WAR) of the signal waveform histogram, which is suitable for asychrounous amplitude histogram(AAH) based Modulation Format Identification(MFI) system. By this method, the dispersion tolerance of MFI system is expanded and the recognition of the polarization multiplexing signal and the non-polarization multiplexing signal is realized.