Research On 2?m Gain-switched Tm-doped Fiber Laser

The 2?m nanoseconds thulium-doped fiber lasers have been widely used in military and industrial processing fields.The all-fiber-structured thulium-doped fiber lasers have become the current research hotspot because of the compact structure and good maintainability.Experimental researches at home and abroad have shown that a pulsed fiber laser,which wavelength is around 1.55?m,is the best way to achieve all-fiber-structured thulium-doped pulsed fiber lasers.In this thesis,the erbium-doped fiber amplifier and pumped gain-switched thulium-doped fiber laser have been studied.Theoretically,the basic principle of fiber gratings and the coupled-mode theory were introduced firstly,and the expressions of the homogeneous Bragg grating reflectivity and reflection spectrum bandwidth were derived.And then the principle of erbium-doped fiber amplifiers were expounded,and theoretical model of erbium-doped fiber amplifiers were discussed.the formula of the amplifier gain was deduced based on the approximation of a two-level system,and further discusses of the pump power amplifier threshold and the optimum erbium-doped fiber length were proceeded.Finally this thesis introduced the principle of gain switch and thulium-doped fiber laser rate equation theory,and derived the expressions of the laser energy threshold,pulse built-up time and pulse width.Experimentally,the optical sensitivity of the fibers were improved by the hydrogen-loading experiment,and the fiber gratings with various parameters were fabricated by phase mask method.The 2?m fiber gratings required for the thulium-doped experiment were included.Then,a pulse modulation 1551nm semiconductor laser was used as the seed source to conduct experiments on three-stage Erbium-doped Fiber Amplifier.The seed source output power was 20?W,the repeat frequency was 100kHz,and the pulse width was 104ns.The first-stage amplification used 1.3m erbium-doped fiber(EDF),and the maximum output power was 32.5mW.The second-stage amplification used 4.6m erbium-ytterbium co-doped optical fiber(EYDF),and the maximum output power was 1.218W at the pump power of 5W.The third-stage amplification used 4m erbium-ytterbium co-doped optical fiber(EYDF),and the maximum output power is 3.306W when the pump power was 11.83W.Finally,the gain switched experiment was carried out by pumping thulium-doped fiber with the output laser of the three-stage pulsed EDFA.The pulse output was obtained at a wavelength of 1954nm with a repetition rate of 100 kHz,a pulse width of 25.85ns and the maximum average power of 835mW.