Mechanism And Experimental Study On The Ultrafast Passively Mode-locking Based On Transition Metal Tellurides

Ultrafast passive mode-locked fiber lasers have the advantages of high beam quality,high conversion efficiency,compact structure,etc.,which have important applications in the fields of communications,material processing,national defense,and biomedicine.With the application requirements of stable,high-efficiency,and cost-effective passive mode-locked fiber lasers,researchers continue to optimize the performance of ultrafast fiber lasers in terms of saturable absorber and cavity design.Saturable absorber is a key optical component in passively mode-locked fiber lasers.When the material interacts with light,the saturable absorber exhibits a nonlinear optical absorption effect with the increasing intensity of the incident light,with which the fiber laser can be modulated to generate ultrafast lasers.At present,the existing saturable absorbers such as semiconductor saturable absorber mirrors have controllable parameters such as modulation depth,but the preparation process is complicated and the cost is high.Low-dimensional materials such as carbon nanotubes,graphene and graphene-like materials have wide-band nonlinear absorption characteristics,and have been successfully used to produce ultrafast fiber lasers with different operating bands,but they have small modulation depths and limited damage thresholds.With the requirements of stable,economical,and efficient ultrafast fiber lasers,it is urgent to continuously improve the performance of passive mode-locked fiber lasers in terms of saturable absorber and resonant cavity optimization.In this thesis,focusing on the application requirements of ultrafast fiber lasers with stability,high efficiency and cost-effectiveness,the nonlinear optical response characteristics of transition metal pentatellurides(Zr Te₅and Hf Te₅)are studied,and transition metal pentatellurides based on evanescent field coupling are prepared.The stable ultrafast mode-locked fiber lasers have been delivered successfully based on the saturable absorption effect of the transition metal pentatelluride and the polarization-dependent nonlinear absorption characteristics introduced by it.The main research content includes:(1)Based on the saturable absorption effect of the transition metal telluride Zr Te₅,the mode-locked fiber laser with a center wavelength of 1568 nm and a pulse width of 810 fs has been obtained,which proves that the transition metal telluride has a good nonlinear optical modulation effect.(2)Based on the saturable absorption effect of the transition metal telluride Zr Te₅(Hf Te₅)and the nonlinear polarization rotation effect in the cavity,a mode-locked fiber laser with a center wavelength of 1562(1563)nm and a pulse width of 892(878)fs was obtained.