Dynamic Study Of Bidirectional Mode-locked Fiber Lasers Based On DFT

Fiber lasers have a wide range of applications in the fields of optical communications,optical sensing,laser processing and health care because of its compact structure,better heat dissipation and controllable performance.In the field of conventional optics,an ideal Fraunhofer diffraction system can be used to restore the frequency spectrum of the original image on the image surface,which shows that the Fraunhofer diffraction system can be used to complete the Fourier transformation between the time and frequency domains,and this Fourier transformation is introduced into the optical system to form Fourier optics.The dispersive Fourier transformation is a new measuring method based on the optical Fourier transformation,which uses group-velocity dispersion(GVD)to stretch and map the optical signal from the optical system into the time domain,therefore breaking the measurement limitations of traditional optical measuring instruments.This thesis mainly uses passively mode-locked Er-doped fiber laser to generate mode-locked pulses output,and then uses the dispersive Fourier transformation(DFT)method to experimentally analyze the soliton evolution dynamics in the passively mode-locked Er-doped fiber laser.The influence of gain distribution on the internal dynamics of bidirectional passively mode-locked Erdoped fiber laser and the influence on the evolution characteristics of soliton are studied.The main research contents of this thesis are as follows:1?Theoretical analysis of the process of dispersive Fourier transformation.Deduced the process of mapping the input spectral signal to the time domain waveform under the influence of the secondorder GVD and high-order GVD.And based on these results,the DFT process is simulated numerically,and the influence of DCF length and high-order GVD coefficients on DFT is studied.2?Dynamic analysis of negative dispersion passively mode-locked Er-doped fiber laser based on nonlinear polarization rotation effect.Experiments show that within a certain range,by adjusting the pump power and the rotation angle of the four wave plates,it can generate up to fourth-order harmonic mode-locked pulses.And through the DFT method,the influence of gain distribution on the working state of passively mode-locked Er-doped fiber laser is studied.It is proved that by controlling the pumping conditions and polarization state,the purpose of selecting the evolution characteristics of the output solitons can be achieved,and it lays the foundation for the subsequent research on bidirectional mode-locked fiber lasers.3?Dynamic analysis of a bidirectional mode-locked Er-doped fiber laser with a ring cavity structure based on the saturable absorption effect of carbon nanotubes.Experiments have been conducted on the breathing dynamics and acyclic pulsation dynamics of the bidirectional solitons(CP solitons)in the dual-pumped bidirectional mode-locked fiber laser,as well as the different soliton dynamics of CP solitons under symmetrical and asymmetrical pumping conditions.In addition,the discovery of the different pulsating dynamics of CP solitons in bidirectional mode-locked Er-doped fiber lasers at the same time also proves that the performance of bidirectional mode-locked Er-doped fiber lasers can be improved by controlling the pumping conditions.These results also open a new way for the construction of high-performance bidirectional mode-locked fiber lasers for various applications in metrology and dual-comb spectroscopy.