Mechanism Of Soliton Evolution In Mode-locked Fiber Laser Cavity

Mode-locked fiber laser has the advantages of compact structure,low cost,good beam quality and easy maintenance.It has important applications in the fields of biological imaging,industrial processing and manufacturing,high-speed optical communications,national defense and military security.In addition,the modelocked fiber laser has became an ideal platform for studying the evolution of optical soliton in the laser cavity because of its rich gain effect,loss effect,dispersion effect and nonlinearity effect.Mode-locked fiber laser can output not only stable single soliton but also abundant multi pulse state,especially stable soliton molecular structure,which is of great significance to promote the development of optical communication technology.The abundant soliton states of fiber laser show complex nonlinear dynamic evolution process in the cavity.The study of these transient dynamic processes is conducive to the effective control of the output state of the laser,and is of great significance to the basic research and application of fiber laser.This paper mainly studies the evolution mechanism of intracavity soliton state in mode-locked fiber laser,and reveals the influence of spectral filtering effect on the evolution process of intracavity soliton state in mode-locked fiber laser.The paper explored the soliton in mode-locked fiber laser and soliton dynamics in the cavity.First,this article built up mode-locked fiber laser systems based on different nano material saturable absorbers,and observed the laser output under different net cavity dispersion conditions and fiber birefringence.Then,the influence of the spectral filtering effect on the evolution of soliton and soliton molecules in the cavity of the mode-locked fiber laser was researched by using the dispersive Fourier transform real-time spectroscopy measurement technology.The complete dynamic process of the transition of different soliton states in the cavity of the mode-locked fiber laser under the spectrum filtering effect is revealed.The main work and research results of this paper are as follows:1.The paper studied theoretical simulation of the mode-locked fiber laser model,and simulated the dispersion-managed mode-locked fiber laser by the transmission model with segmented expression(pulse transmission in single-mode fiber,pulse transmission in gain fiber,saturable absorption model)based on the split-step Fourier algorithm.The conventional solitons,dispersion-managed solitons and dissipative solitons are output under anormalous,near-zero and normal dispersion net cavity dispersion conditions,respectively.The simulation results and the experimental results of the dispersion management mode-locked fiber laser are in good consistency.2.Build a mode-locked fiber laser system based on different mode-locking mechanisms(including nonlinear polarization rotation,carbon nanotubes and molybdenum disulfide/graphene heterojunction saturable absorber),focusing on:(1)erbium-doped fiber mode-locked laser based on carbon nanotube saturable absorber realizes the output of L-band vector soliton;(2)manage the net dispersion of erbium-doped fiber mode-locked laser based on the molybdenum disulfide/graphene heterojunction saturable absorber.When the dispersion changes from anomalous dispersion to near-zero dispersion to normal dispersion,the laser can stably realize the mode-locked pulse output.3.Adding a wavelength tunable band-pass filter element to an erbium-doped fiber mode-locked laser based on a carbon nanotube saturable absorber,and a realtime spectrum measurement method based on dispersive Fourier transform technology is used to study the evolution process of soliton in mode-locked fiber laser cavity under the effect of spectral filtering.The results show that the spectrum filtering effect can make the laser output different types of soliton molecules,and can control the switching between different soliton molecular states,revealing the complete dynamic process of switching between different soliton molecular states in the cavity of the mode-locked fiber laser under the spectrum filtering effect.