Research On The Soliton Dynamics Characteristics Of The Passively Mode-locked Fiber Laser

Ultrafast lasers(ultrashort pulses)are irreplaceable in industrial processing,national defense,biomedicine,and scientific research.Passively mode-locked fiber lasers are considered as the ideal laser source for generating ultrashort soliton pulse because of their simple structure,and easy collimation.Since passively mode-locked fiber lasers are dissipative systems,the soliton pulses generated by them will exhibit complex dynamic characteristics under certain conditions.Such dynamics has been one of the hotspots for researchers in the laser field.This paper mainly focuses on the numerical simulation and experimental research on the soliton dynamic of passively mode-locked fiber lasers.The main contents are as follows:(1)Research background and theoretical basis of passively mode-locked fiber lasers.This section introduces the classification,system structure,and basic theory of passively mode-locked fibers,and reviews the research progress of the stationary soliton and transient soliton dynamics of passively mode-locked fiber lasers.Describe the establishment of the nonlinear Schr(?)dinger equation and the Ginzberg-landau equation to understand the establishment of the simulation model of such fiber lasers,analyze the calculation method of the soliton evolution in the above equations,and introduce the transmission functions of different saturable absorbers.(2)Numerical simulation of the two-soliton molecule and three-soliton molecule dynamics in the passively mode-locked fiber laser.Build up a simulation model of the passively mode-locked ytterbium-doped fiber laser.By changing the length of the single-mode fiber,the fiber laser works in the normal dispersion and abnormalous dispersion regions,respectively.Investigate the effects of the small signal gain and gain saturation energy on the properties of the two-soliton molecule and three-soliton molecule dynamics under the above two dispersion conditions.With the increase of small signal gain or gain saturation energy,a single soliton will split into multi-soliton.The transition between the two-soliton molecule and three-soliton molecule is not direct,they appear in intervals.And the pluse peak power,pulse duration,and pulse energy will change accordingly.The change of small signal gain and gain saturation energy corresponds to the variation of the pump power in the experiment,which proves that pump power has an important influence on the state and characteristics of multi-soliton molecules.(3)Numerical simulation on soliton pulsation in the passively mode-locked fiber laser.This section studied the effects of the small signal gain and the coupler's splitting ratio on soliton pulsation dynamics characteristic in the model of the carbon nanotube passively mode-locked fiber laser.At the fixed splitting ratio,with the increase of small signal gain,there are various soliton pulsations: typical soliton pulsation,soliton pulsation with obvious Kelly sideband,soliton pulsation with soliton splitting,explosion-like soliton pulsation,and creeping vibration soliton molecule.(4)Numerical simulation and experimental research on the breathing behavior of soliton pulsation in passively mode-locked fiber lasers.This section has constructed the model of the anomalous dispersion nonlinear polarization rotation passively modelocked fiber laser.And studied the influence of the angle of the polarization controller on the breathing characteristics of soliton pulsation,including different fluctuations in the time domain evolution,changes in the breathing period,and the shape of the spectrum.Subsequently,a measurement experimental system capable of observing the real-time shot-to-shot spectrum evolution of the soliton pulsation breathing behavior was constructed based on the dispersive Fourier transform technique,which experimentally proved the breathing behavior of the soliton pulsation.