Research On Ultrashort Pulse Tm³⁺-doped Fiber Laser

A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements, thulium-doped fiber laser can launch laser at the wavelength of2μm, which is in the range of eye-safe wavelength. As a result, the thulium-doped fiber laser has very great application value in the air communication、biological photonics、healthcare, laser radar, remote sensing.and now is being the research focus in the world. In this paper, through theoretical calculation and numerical simulation method, the relationship between the performance and various parameters of thulium-doped fiber laser and ultrashort pulsed thulium-doped fiber laser were discussed. The major and innovational work is as follows:1. Introduces the energy level structure of thulium and analyse the pump scheme of the thulium doped fiber laser:3H6�'3H4.Based on the velocity equation,the math-ematical model of the thulium doped fiber laser has been built.Simulation of ring cavity fiber laser characteristics,and analyse the relationship between some parameters and the laser output power or slope efficiency, such as the fiber length,the thulium ion doping concentration, and the coupler coupling ration.These parameters have an optimal value that can greatly improve the slope efficiency and the output power of thulium doped fiber laser. So by choosing appropriate structure parameters can optimise the performance of fiber laser.2. Introduces the principle, structure and related technology of the mode-locked laser. A ultrashort pulse fiber laser with graphene as saturated absorber has been presented. With ABCD matrix, the influence of some parameters, such as the fiber dispersion, nonlinearity, amplitude modulation coefficient of saturable absorber, the gain medium bandwidth, to the pulse width, chirp of ultrashort pulse thulium-doped fiber laser output effect. The studies show that the normal dispersion of the laser cavity makes the mode-locked laser output pulse chirp increase, pulse width wider.In order to get a ultrashort pulse, the normal dispersion in the laser cavity must be minimized.3. Starting from the nonlinear Schrodinger equation, a numerical simulation about the pulse evolution of passive mode-locking thulium-doped fiber laser was presented Discussed the role played by some of the parameters in the evolution of pulse.for exam-ple:fiber dispersion, nonlinearity, saturable absorber and polarization mode dispersion in the evolution of the mode-locked laser pulse.