Theoretical And Experimental Investigation On Collision And Pulsation Dynamics Of Dissipative Soliton In Passive Mode-locked Fiber Laser

Passive mode-locked fiber laser（PMLFL）is widely used in laser processing,high-speed optical fiber communication,ultrafast spectral imaging,biomedicine and other fields because of its high stability,compact structure,very short pulse duration and low mode-locked threshold.The existence of attractors in dissipative systems will lead to the formation of various self-organizing structures,including soliton molecules（SMs）and pulsating solitons（PSs）.Based on PMLFL and high-speed detection technology such as time stretched dispersion Fourier transform（TS-DFT）,the transient dynamic process of the interaction between these self-organized states can be characterized in real time for in-depth research.Studying the interaction between self-organizing structures in dissipative systems theoretically and experimentally is not only helpful to improve the output characteristics of lasers and the quality of pulse,but also of great significance to explore the general law of soliton interaction in dissipative systems,expand the analogy between dissipative solitons（DSs）and matter particles,and enrich the theory of dissipative nonlinear systems.Based on the cubic-quintic Ginzburg-Landau equation（CQGLE）,combined with nonlinear Fourier transform（NFT）,moment method and variational method,this thesis carries out numerical simulation and analysis of the interaction between single solitons（SSs）and SMs,also the interaction among（PSs）in dissipative system.In Experimence,the dynamics of the interaction between SSs and SMs with different configurations and the interaction between PSs is characterized in real time by using TS-DFT.The main research contents and innovative achievements of this thesis are as follows:1.Based on the generalized CQGLE,the collision dynamics between SSs and SMs is studied.We find that under the gain fast response dynamics,SSs and SMs will obtain different drift velocity responses,and the elastic and inelastic collision processes between SSs and SMs are observed.With the analysis of the collision dynamics based on NFT,we find that the SSs and SMs have different momentum in the gain fast response dynamics.The elastic collision and inelastic collision correspond to the recovery and change of the momentum structure of SMs,respectively.The drift of centroid of SSs and SMs in gain fast response is analyzed by moment method.We point out that the velocity difference between them due to the gain depletion caused by the coherent overlap between SMs and the asymmetry of gain distribution in pulse duration caused by gain fast response dynamics.Based on the extended semi analytical model of three soliton interaction,we find out that inelastic collision and elastic collision essentially correspond to whether SMs have potential well transition under perturbation of SSs.Further more,The transient collison dynamics between SSs and SMs are found in experiment,both the elastic collision and inelastic collision.We find out that the soliton molecular structure determines the drift velocity difference between SMs and SSs.The loose soliton molecule in the excited state will transition to the compact soliton molecule in the ground state under the perturbation of SSs collision.In the process of SMs dissociation,the interval has higher stability than the relative phase.The difference of interaction force caused by the different soliton separation distribution is the key factor of soliton molecular reconstruction2.The interaction between PSs is studied based on CQGLE.We find that the asynchronous PSs are assembled into pulsating soliton molecule（PSM）with drift velocity.The interaction within the PSM is related to the coherent overlap between dispersion wave（DW）and solitons.It is proved that the asymmetric DW radiation of strong PSs leads to the drift of PSM.The collision dynamics between PSs are analyzed,both the elastic collision and inelastic collision.We find that the DW plays a key role in soliton state exchange and new soliton generation,the elastic and inelastic collisions are determined by the asymmetric dispersive wave radiation.3.The dynamics of PSs interaction is observed in the anomalous dispersion region,including oscillatory PSM,pulsating soliton state transition and chaotic pulsation.we find out that the interaction of PSs is synchronous with the pulsating behavior of solitons.And the DW plays a guiding role in the recovery of PSs from chaotic pulsation to synchronous pulsation.Two self energy regulation paths of laser are found:In the path of soliton pulsation,the chaotic pulsation soliton changes from asynchronous weak pulsation to synchronous weak pulsation,and finally returns to synchronous strong pulsation;In the path of soliton collision,multiple solitons split due to collision,which leads to the readjustment of soliton spacing.Finally,the energy level is restored by soliton annihilation.4.In L-band PMLFL,the dynamics of PSs collision in positive dispersion region is detected in real time.The coexistence of heteromorphic solitons caused by PSs collision is observed,and the collision of heteromorphic solitons will lead to the regeneration of PSs.We find out that the depletion of gain and the absorption characteristics in the band of Er³⁺ions are the reasons for the generation of heteromorphic solitons.We find that the annihilation and regeneration of solitons are the common process of soliton collision in the positive dispersion region.