The Study Of Modulation Instability In Optical Fiber Communication

Modulation instability (MI) is an universal and very important physical phenomenon in optical communication system, it results from the interplay between the dispersion (or diffraction) and nonlinear effects. MI manifests itself as the occurrence of the spectral side bands and breakup of cw or quasi-cw light radiation into a train of ultra short pulses in spectral and temporal domain, respectively. The research on MI can be very helpful in improving the performance of optical communication system. It can facilitate the researches in the field of ultra short pulse and soliton communication. However, MI is also an important limiting factor for optical fiber communication. It may lead to the signal amplitude modulation, then limit the output power and increase the cost of the system. Thus, the research on MI is necessary.Firstly, the research situation and significance of MI have been simply introduced; Then adopting the method of the traditional linear-steady analysis, the fundamental gain spectrum of MI induced by SPM and XPM in optical fiber is investigated from the nonlinear Schr(o|¨)dinger equation, respectively; Further, taking into account the second- to the fourth-order dispersion and the quintic nonlinearlity, the modulation instability in optical fiber is studied, and the numerical simulation is done; Finally, MI in dispersion-managed system is analysed and investigated, some results are obtained, which are useful for analysis and design of long distance and high capacity dispersion management(DM) communication system.The results show: the third-order dispersion does not influence the gain spectra of MI; Because of fourth-order dispersion, MI can occurs at two spectrum regions under certain conditions; The positive quintic nonlinear refractive index intensifies the MI, making the width of the power gain spectrum of modulation instability become wider and the peak gain higher, otherwise, suppresses the MI; The effects of quintic nonlinearity on MI is few, and it is reasonable that quintic nonlinearity can be ignored when input power is small, the effects of quintic nonlinearity on MI are more and more evident when input power increases, The dispreading distance will make the width of the power gain spectrum of MI become narrower and the peak gain smaller. In dispersion management system, the much stronger the dispersion-map strength, the control to the gain duo to the MI is more evident, the much greater the path-average dispersion, the control to the process of MI is more evident.