Research Of Optical Soliton Dynamics And Methods

The great achievement of nonlinear science lead people to study complex phenomena. Nowadays, the main research directions of nonlinear science in-clude soliton, fractal and chaos. Since 1970, soliton phenomena attract numer-ous attentions of researchers in different fields. Soliton had been observe in a number of systems, such as Bose-Einstein condensation, optical fiber, nan-otube, liquid crystal and plasma. Due to the advantage of long-distance soliton communication without shape and velocity change, the research of optical soli-tons has obvious academic significance and great practical significance.The research contents of this thesis include the soliton interactions in nonuniform optical fibers, the existence prove of like-dromion structure and single soliton solution in fiber laser. The stability of these phenomena have been analyzed. Moreover, the effect of modified parameter in modified bilin-ear method has been studied, and the generalized method has been established through conventional bilinear structures. The detailed frame of this thesis is as following:(1) The relation between nonlinear science and soliton research history will be described. The next part is research background of optical soliton. It in-cludes that concepts of opticals soliton renewed by the view of energy and balance. Finally, the research methods will be discussed detaily;(2) The paper will study optical soliton interactions in the nonuniform op-tical fibers. The study of soliton interactions is of significance for improv-ing pulse qualities in optical communications. The model equation is higher-order nonlinear Schrodinger equation. This model includes third-order dis-persion, self-steeping effect and intrapulses Raman scattering. When the co-efficients of self-steeping effect and intrapulses Raman scattering equal, this equation reduces to Hirota equation. Through the split-step Fourier method,the strong relation between frequency separation and soliton interactions will be obsearved. However, the frequencies of two-soliton solution obtained by bilinear method is non-synchronous. When modulating system into Gauss dis-persion management, two non-synchronous soliton orbits interact and generate a new phenemenon as two-periodic oscillation. Moreover, if third-order disper-sion is modulated as cosine profile, multi-periodic oscillation will be observed.Through controlling the shift of third-order dispersion, the emitting anlge will be changed, which can be realized to modulate the velocities of optical solitons;(3) The paper will discuss the nonlinear phenomena in fiber laser. The mod-el equation is the standard Ginzburg-Landau equation. Through modified bilin-ear method, a dromion-like structure will be obtained. Moreover, the symmetry of dromion-like structure can be devided into two parts: space-time distribution symmetry and leading-trailing edge symmetry. These symmetrys stem from the nonuniform distribution of dispersion and nonlinearity in the propagation direc-tion. In addition, the stability against perturbation on dispersion losses will be studied. When the perturbation makes the losses into gains, the dromion-like structure will appeared as oscillation. Through enhancing the outer modified effect, one dromion-like structure will evolve into two dromion-like structures.Hence, under the condition of translation between losses and gains, the role of modified parameter is to control the coherence degree of two dromion-like structures;(4) The paper will study ultrashort pulse transmission in fiber laser. In ul-trafast optics, optical pulses are generated to be of shorter pulse duration, which has enormous significance to industrial applications and scientific research. The model equation is higher-order Ginzburg-Landau equation. The single-soliton solution will be firstly obtained through the assymmetric preseantion based on the bilinear method. Through split-step Fourier method, the realistic transmis-sion of single soliton will be simulated successfully. In addition, if adding 10%amplitude perturbation, the soliton will be stable always.