Study On Multiple Soliton Pulse Based On Passive Mode-locked Fiber Laser

The passively mode-locked fiber laser is actually a dissipative system for observing various soliton dynamics and nonlinear phenomena,and it has advantages of small size,good anti-interference performance and high power,etc.Therefore,it has attracted a great of research attention in recent years.Up to now,various passively mode-locked techniques have been utilized to generate multi-solitons,such as:nonlinear polarization rotation technology(NPR),figure-eight fiber laser,two-dimensional material SAs mode-locked technology,multimode fiber hybrid structure,and so on.In this paper,the dissertation focuses on study of multi-solitons output in the passive mode-locked erbium-doped and ytterbium-doped fiber lasers based on nonlinear multimode interference effect and the mode-locked erbium-doped fiber lasers based on nonlinear polarization rotation effect.In this paper,the saturable absorber based on a combination of three different kinds of multi-mode fibers is used to study the generation of multi-solitons in passively mode-locked erbium-doped fiber lasers.Multi-soliton mode-locking phenomena such as:single-pulse bound state solitons,twin-pulse bound-state solitons,soliton clusters with different pulse numbers and intervals,and noise-like pulses are obtained.Moreover,the second-order soliton to eleventh-order soliton with order continuously adjustable were obtained by adjusting the pump power and PC,which enriches the output characteristics of multi-soliton mode locking.In order to study the generation of multiple soliton pulses in passively mode-locked fiber lasers at different bands,the ytterbium-doped fiber was used as the gain medium to study the generation of multiple solitons near the 1 micron.By continuously optimizing the length of various multi-mode fibers in the saturable absorber and the intra-cavity parameters,such as: dispersion,loss and other parameters,the single-dissipative soliton,double-dissipative soliton with unequal pulse interval,and triple-loss with unequal pulse interval are obtained.At the same time,we study the the influence of pump power on the mode-locking of the dissipative soliton by adjusting the pump current at the single-dissipative soliton mode-locking state.In order to study the multiple soliton pulses in passively mode-locked fiber lasers based on different mode-locking principles,we established a passively mode-locked erbium-doped fiber laser based on nonlinear polarization rotation effect(NPR).The mode locking phenomena such as: bound state soliton,noise-like pulse,soliton cluster and harmonic mode locking are observed by optimizing the cavity length,intra-cavity dispersion parameters,and adjusting the polarization states of the two polarization controllers(PC)in the cavity.The research work in this paper can be served as a guideline to investigate the generation multi-soliton pulse output in passive mode-locked fiber lasers at different wavelengths and different structures,and it also can provide an important reference significance for the application of multi-soliton mode-locking technology at different working wavelengths.