The Study Of Yb³⁺-doped All Polarization Maintaining Ultrashort Pulse Fiber Laser

Passive mode-locked fiber lasers with narrow pulse width and high peak power have attracted a great deal of interest recently Because of the wide application in basic scientific research,biomedical treatment,material micromachining and terahertz scanning imaging.All-fiber ultrafast fiber laser can be designed and mode-locked with semiconductor saturable absorbers,graphene,single-walled carbon nanotubes,topological insulators（Sb₂Te₃,Bi₂Se₃）and some sulfides such as molybdenum disulfide,even artificial saturable absorbers such as nonlinear polarization rotating,and nonlinear optical loop mirrors can be used for this purpose.However,for traditional glass clad fibers of 1μm band,the main difficulty is how to compensate for the normal material dispersion caused by the fiber.Conventional methods are to introduce a negative dispersion element such as a fiber Bragg grating,a spatial prism or a grating pair.The negative dispersion is introduced by the experimental chirped fiber Bragg grating to adjust intracavity dispersion.In this latter,all Yb³⁺-doped all polarization-maintaining mode-locked fiber laser in theoretical and experimental research was studied.The main research contents and specific methods are as follows:Firstly,the characteristics of polarization-maintaining fiber and the properties of Yb³⁺-doped fiber were studied as well as the laser generation mechanism.By numerical simulating the passive mode-locked laser system,we finally confirm the experimental scheme and component parameters.Secondly,based on the physical model of ultrashort pulse fiber laser,all polarization-maintaining Yb³⁺-doped mode-locked fiber laser based on chirped fiber Bragg grating was built.When pump power is up to 52 mW the stable mode-locking operation can be achieved.The maximum output power of laser was 9.8 mW by the pump power of 52mW.The fundamental repetition rate was 15.7 MHz.The center wavelength and the spectral bandwidth were 1030 nm and 7.2 nm,respectively.The pulse width was measured to be 4.26 ps,corresponding ideal Fourier transform limit pulse width is about 150 fs.The pulse energy is 0.76 nJ and the pulse peak power is 178 W.Finally,based on the study of the causes and properties of the dispersion management soliton,the stable output of the single pulse and dispersion management molecules is realized in the negative dispersion region by continuously changing the cavity length of the laser.In the single-pulse state,the pulse width was measured to be 4.8 ps,which can be compressed to 278 fs by an external grating pair.The center wavelength and the spectral bandwidth were 1029.8 nm and4.3 nm,respectively.In the dispersion management molecular state,the spectral modulation range is about 0.222 nm corresponding to the pulse interval of 15.9 ps.The simulation results were in accordance with experimental results.In addition,the resulting light-to-light conversion efficiency of the laser was 39%,which was relatively higher in similar experiments.