Spectral Of Chirped Solitons And Transmission Of Similaritons In Saturable Inhomogeneous Fibers

As one of the optimal information carriers for large capacity and long distance optical transmission systems,optical solitons occupy a crucial position in optical communication.With the development of nonlinear material science,similaritons with strong stability and high pulse power have also become one of the hot research topics in academic circles.Moreover,for the ultrashort pulses,saturated nonlinear effects and some higher-order effects such as third-order dispersion,Raman effect,and self-steepening also need to be taken into account in addition to group velocity dispersion and cubic nonlinear effects as the pulse intensity increases.Considering the nonuniformity of optical fibers in practice,the theoretical model describing solitons and similaritons propagation in optical fiber is modified to the cubic-quintic higher-order nonlinear Schr(?)dinger equation with variable coefficients.Usually the higher-order effects lead to the distortion of the pulse,which results in the generation of new spectral components of the pulse.Therefore,it is of great significance to investigate the spectra of solitons.In addition,seeking for exact similaritons solutions for different theoretical models is a significant direction for studying similaritons.The research of exact similaritons solutions can help to find out the new characteristics of similaritons in different systems,and it can provide a certain theoretical basis for the transmission and control of similaritons in experiments.In this paper,based on the higher-order nonlinear Schr(?)dinger equation with cubic-quintic variable coefficients including Raman effect and external potential,the spectral evolution characteristics of chirped solitons in saturable inhomogeneous fiber systems are investigated.Furthermore,two novel bright and one kink similaritons solutions are presented by the hidden symmetry reductions method and the propagation characteristics of similaritons in dispersion-decreasing inhomogeneous fibers are investigated.The main research contents are as follows:1.The research background and status of optical solitons,the research status of optical solitons and similaritons in saturable inhomogeneous fibers are briefly introduced.2.Based on the chirped soliton solutions of the cubic-quintic variable coefficient nonlinear Schr(?)dinger equation with Raman effect,the spectral evolution characteristics of chirped one-soliton and two-soliton in saturable inhomogeneous fiber systems with periodic dispersion distribution are studied.The results show that in the homogeneous fiber,the higher-order effects make the spectra of the unchirped one-soliton red shift and accompany sidelobe at high frequency.Compared with the one-soliton,the spectra of two-soliton with both parallel transmission and colliding evolution will appear split,and the higher-order effects will enhance the spilt of the spectra of two-soliton.In the periodic dispersion-distributed fiber,the periodical chirp parameter causes that the pulse width and spectra of one-soliton are compressed and expanded periodically.For the two-soliton,its spectra are greatly broadened in collision,and the chirp makes the spectra of two-soliton blue shift when they approach each other for both quasi-parallel transmission and the colliding evolution cases,while the higher-order effects make the spectra red shift.The presented results are of great significance to study the spectral characteristics of high power signals in ultrafast optical communication systems.3.Based on the cubic-quintic variable coefficient nonlinear Schr(?)dinger equation with external potential in saturable inhomogeneous fiber,two novel bright and one kink similaritons solutions of the equation are presented by the hidden symmetry reductions method.Based on these similaritons solutions,the propagation characteristics of bright and kink similaritons in the exponentially decreasing system are investigated.It is found that the pulse width,amplitude,trajectory and velocity of similaritons can be controlled by selecting appropriate system parameters and similaritons parameters.The research results are expected to provide a theoretical basis for the study of the transmission of high power pulses and the compression of optical pulses in ultra-high speed optical communication systems over long distances.4.The full thesis is summarized and the next work is look forward.