Theoretical And Experimental Study Of High Power Tunable Thulium-doped Fiber Laser

2?m laser produced by high-power tunable thulium-doped fiber laser has many advantages,including strong absorption of water molecules,macromolecule materials and high penetration of silicon materials,etc.The laser has important applications in the fields of laser medical system,material processing,space communication,electro-optical countermeasure and material manufacturing,etc.Besides,2?m laser could be used as the ideal pump source of 3?5?m OPO.Thus,tunable thulium-doped fiber laser at 2?m has the important research value.The major work of this paper is summarized as follows:Firstly,we used the steady-state rate equations of thulium-doped fiber laser.Then,Via Matlab software,we do numerical simulation for the output characteristics of thulium-doped fiber laser.The output indexes of laser mainly include laser output power,threshold pump power,peak wavelength,laser slope efficiency,etc.Secondly,based on the multimode optical fiber bending loss theory,we simulated the relationship between the bending loss of each mode which transmitted in the fiber core of large core polarization-maintaining Tm-doped fiber and the bending radius of the fiber.Then,we obtained the critical bending radius corresponding to the LP11 mode is 66.8mm.Thirdly,we mainly studied the output characteristics of CW thulium-doped fiber laser at 2?m by using three kinds of lengths of large core polarization-maintaining Tm-doped fiber in the experiments.The fiber lengths are 3m,2.5m and 1.2m,respectively.In the case of pump power of 54W,we obtain the maximum output powers are 10.7W,9.02W and 5.35W,respectively.The threshold pump powers are 20W,16W and 8W,respectively.The slope efficiencies are 34%,24%and 11%,respectively.Then,the peak wavelengths are 1999nm,1996nm,and 1982nm,respectively.Fourthly,the designed low-cost combining LiNbO3 birefringent filter is proposed.It consists of three slices of LiNbO3 crystal plates,whose thicknesses are 1mm,2mm and 4mm,respectively.When the LiNbO3 birefringent filter is inserted into the cavity at the Brewster angle 65.17°,the free spectrum width of combining filter may be 60nm and the corresponding FWHM of combining filter may be 6nm.And when the tuning angle increases from 35°to 42°,the maximum transmittance wavelength will increase from 1.961 ?m to 2.002?m.In other words,its smooth wavelength tuning range is about 41nm.