The Femtosecond Optical Solitons In Monomode Fibers

Hasegawa et al. showed theoretically that an optical pulse in a dielectric fiber could form a solitary wave due to the balance between the nonlinear effects and the group dispersion effects in 1973, but it was not until 1980 that Mollenauer observed the optical soliton in the experiment at the famous Bell Laboratories. Since then, the study of optical solitons has been remaining active, great progress has been made in both theoretical research and experiments. However, in recent years, to increase the capacity of the communication system, the researchers put more and more emphases on the transmission of ultrashort pulse (femtosecond solitons), in this case, some higher order effects (such as higher order dispersion, self-steepening and self-frequency shift) that are always neglected should be included.In this paper, we study the evolution of optical solitons that obey the cubic nonlinear Schrodinger equation numerically and we solve the modified nonlinear Schrodinger equation analytically, some important results are presented.The thesis consists of six chapters: In chapter 1, we introduce the basic theoretical concept of solitons, particular attention is paid to the summary of fundaments of optical solitons and their application to transmission system. Moreover, several numerical methods, such as the Split-Step Fouriermethod, the fourth-order Runge-Kutta method, are also introduced. Chapter 2 is devoted to demonstrating the setup and principle of optical soliton communication system, and presenting varieties of factors that affect the transmission of optical solitons. In chapter 3, we simulate the evolution of an optical soliton and the interaction of two solitons under the different initial conditions in the monomode fibers. In chapter 4, we present the derivation of the extended nonlinear Schrodinger equation and the study situation on it, and then, we solve the extended nonlinear Schrodinger equation by means of amplitude-phase transformation and obtain bright and dark solitons solutions. We solve the higher order nonlinear Schrodinger equation by means of the small amplitude approximate method and present the bright and dark solitons solutions in chapter 5. In the final chapter, we summarize the present paper and give an outlook of the future study in this field.