Theoretical Research On Thulium-doped Fiber Lasers

Tm³⁺ ion has rich energy levels.The Tm-doped fiber lasers is able to produce broadband lasers of which the wavelengths are range from 1.8μm to 2.1μm through controlling the proper pump power and pump method.Tm-doped fiber lasers can be applied in many fields including industry,agriculture,military and healthcare. Particularly,the manufacture of the lasers which produces the wavelength of 2μm with high power and high efficiency is now a hot research topic.It is a key component of LIDAR,and it can be used as a scalpel with high precision and some advantages such as making less blood and smaller wound in the surgery,it also can be a pump source producing the laser of which wavelength is from 4μm to 5um through pumping other kind of material,it plays an important role in the air communication. At present,the problem of improving the lasers' power of output,efficiency and the quality of beam has been focused on in some domestic research institutions.In this thesis,the main task includes:(1)analyze the energy levels of Tm³⁺-ion and the characteristic of spectra absorption from the glass matrix of Tm³⁺ -ion theoretically based on the principle of thulium-doped fiber laser,after knowing the procedure of manufacturing the thulium-doped fiber and the model of thulium-doped fiber laser presented in some papers at abroad,some key parameters and conditions which can influence the characteristic of the laser such as the concentration of Tm³⁺,length of fiber and pump method is discussed in detail.(2)On this basis,the model of rate equations and simulations are set up for the three kinds of pumping methods in this paper,the simulations focus the impaction from the cross-relaxation to the absorption of pumping light in the fiber laser of which length is lmeter long,the impaction from different Tm³⁺ concentrations to the distribution of pump light and laser,the impaction from different Tm³⁺ concentrations to the best length of fiber and the ratio between the growth of Tm³⁺ concentrations and the cross-relaxation.(3)Two beam paths of thulium-doped fiber laser are structured under the condition of laboratory,double fiber bragg gratings are used in the resonant cavity.On the first path,the 800nm pump source is cooled by the nitrogen which has been cooled by liquid nitrogen so as to make the wavelength of pump source changed to 793nm.The spot of pumping light and the spot of pumping light which is coupled into the glass matrix are observed through the relative instrument;On the other path,980nm pump source is used to pump the thulium-doped fiber.At last,the outputs of the two fiber lasers are observed through the wavelength analyzer.The corresponding data,images and analysis of experimental results are written at the end of the paper.