Research On The Mode-locked Pulse Characteristic Of All-anomalous Dispersion Tm-doped Fiber Laser

Due to the rich energy level structure and spectral characteristics of Tm³⁺,Thulium（Tm）-doped fiber lasers have important applications,such as laser medicine、atmospheric communication、military defense、laser radar and laser ranging etc.Now,the net-anomalous dispersion of Tm-doped fiber laser in most experimental reports is small.In order to know the soliton evolution and mechanism of Tm-doped fiber laser with large net-anomalous dispersion,the theoretical analysis and experimental research on Tm-doped fiber laser with long cavity and all-anomalous dispersion are carried out in this thesis.The“pulse tracing”method is used to simulate the nonlinear polarization rotation（NPR）mode-locked Tm-doped fiber laser,then a stable soliton pulse with pulse duration of 3.16 ps,spectral width of 1.4 nm and the time-bandwidth product of 0.315 is obtained.When the gain saturation energy is enhanced,the pulse splits,so two solitons are obtained.Different from the bound solitary pulses,where the pulse separation of neighboring solitons is fixed or almost fixed,the separation of two solitons is variational.The pulse separation of two solitons increases in the beginning of the round trips and then it gradually approaches to a fixed value.In this case,the pulse separation is several tens or even hundreds times as large as the pulse duration,even reaches the nanosecond order of magnitude.During the simulation,it’s found that the mechanism of pulse splitting determines the multisoliton generation when the Tm-doped fiber laser with large net-anomalous dispersion.Besides that,the stable multisoliton can be obtained when the angle between the polarizer and the fiber fast axis or the angle between the analyzer and the fiber fast axis approaches to 0.An experimental system of NPR mode-locked Tm-doped fiber laser with cavity length of110 m is built.A mode-locked pulse is obtained with the central wavelength of 2040 nm when the pump power is 8 W,which’s repetition rate is 1.9 MHz and the average output power is2.6 mW.Continue to increase the pump power,we obtain two solitons with a fixed separation of³0 ns.Besides that,the stable multisoliton with a maximum number of 17 is obtained.