The Interaction And Suppress Of Femtosecond Solitons In Fiber Communication

In fiber communication, propagation of picosecond(ps) solitons in monomode fibers is well described by the nonlinear Schr?dinger equation(NLSE). However, for sub-picosecond and femosecond(fs) pulses, effects of the nonlinear dispersion is so significant that it can no longer be treated as a perturbation. The equation including the nonlinear dispersion, the modified high-order nonlinear Schr?dinger equation(HNLSE), is a better model. In this thesis, we take HNLSE solitons as a model for fs solitons, adopt Split-step Fast Fourier Transform Method, numerical studied the transmission characteristics and the interaction of fs optical pulses under high-order effects in fiber, the effective suppress methods of interaction were gave. Some new results were obtained. The numerical studied results show that the propagation characteristics of fs pulses were different from that of ps pulses. When the width of initial pulse was fixed, the propagation characteristics were mainly control by the initial pulse intensity, and the fs pulse can transmit steadily when its intensity satisfied certain value. With the increase of intensity, the fs pulse begin to fission, but it was completely different from that of ps pulses repulsive and attractive periodically, the new pulse of fission fast separate nonlinear. The third order dispersion(TOD) and four order dispersion(FOD) affect the communication quality, the pulse width is expanded and the pulse is drift backwards and ahead by the positive and negative TOD respectively, the pulse width is expanded and the side spectra on caused by FOD, and the TOD was a mainly effect factor when the TOD and FOD were considered at the same time. The pulse become steep, its width was compressed and its peak value power was increased by self-steepening effect. The pulse was drift backwards nonlinear by the self-frequency shift effect. For the interaction of fs pulses, which was completely different from that of ps pulses too, the latter is repulsive and attractive periodically, but the former keeps repulsive after the first collision, which was not periodical, and the high order effect affect it seriously. At the same time, the numerical results also indicated that the interaction of pulses with Raman self-frequency shift effect can be effectively suppressed by the control of synchronous amplitude modulation and the control of nonlinear gain with filters. Those provided the theoretical and experimentation basis for increasing the capacity and transmission distance of optical fiber soliton communication system, improving communication quality and raising the bit rate.