Research Of Passively Mode-locked Fiber Laser Based On Novel Saturable Absorber SnSe₂

Passively mode-locked fiber laser is a kind of pretty important laser with narrow pulse width,compact structure and good beam quality,which makes it have good application prospects in optical communication,biomedicine,material processing and scientific research.Passively mode-locked fiber laser based on tin diselenide(SnSe₂)saturable absorber(SA)is a new type of mode-locked fiber laser that has appeared in recent years.SnSe₂as a mode-locked device is a new two-dimensional material with excellent nonlinear saturable absorption characteristics.By introducing this material into the resonant cavity in combination with the optical fiber device,a stable mode-locked pulse can be generated.This structure is simple and compact,and can realize the full fiber of the system.In this thesis,passively mode-locked thulium-doped and erbium-doped fiber lasers based on SnSe₂-SA are constructed and studied theoretically and experimentally,the main content includes the following three parts:1?Firstly,the characteristics of fiber lasers and mode-locked fiber lasers are reviewed,as well as the research progress of passively mode-locked fiber lasers based on two-dimensional materials.Then,the mode-locked principle of the passively mode-locked fiber laser and the principle of pulse transmission in the fiber are analyzed in detail,and the saturable absorption characteristics of SnSe₂are studied by the balanced two-arm detection method.The results show that the modulation depth is 18.53%,the saturation flux is 1.15?J/cm²,and the unsaturated loss is 25.22%.2?Based on SnSe₂-SA,a passively mode-locked thulium-doped fiber laser was constructed.By adjusting the polarization state in the cavity,a single-soliton mode-locked pulse with center wavelength of 1922.4 nm,3 d B bandwidth of 2.45nm,and pulse width of 1.77 ps was obtained at a pump power of 105 m W.Then,the pump power was increased to 140 m W,and double-soliton mode-locked pulses with wavelengths of 1918.5 nm and 1934.8 nm were realized.After testing,these two states can continue to stably output,which provides reference value for the realization of multi-wavelength output of passively mode-locked fiber lasers based on SnSe₂-SA in the future.3?Based on SnSe₂-SA,a passively mode-locked erbium-doped fiber laser was constructed.By adding 30 m single-mode fiber to adjust the dispersion in the cavity,a soliton mode-locked pulse with center wavelength of 1566.7 nm,pulse width of1.36 ps,and repetition frequency of 5.96 MHz was obtained.At the same time,we tested the stability of the system for up to 24 hours,and finally found that the system can still maintain good stability under continuous operating conditions.The experimental results show that SnSe₂,as a new type of SA,has a stable and good mode-locked effect.