The Theoretical And Experimental Research On The Actively Mode-locked Pulsed Yb³⁺-doped Fiber Laser

With the rapid development of laser technology, pulsed laser has been widely appliedin varies fields, including medical treatment, industrial processing, laser weapon,laser controlled nuclear fusion. Comparing with traditional solid-state laser, fiber laser havethe advantage of excellent gain characteristic, outstanding conversion efficiency, easy tocouple with fiber. Hence, mode-locked fiber laser have become a popular research subjectof ultrafast optics. This paper focuses on research of actively mode-locked ytterbium-dopedfiber laser both theoretically and experimentally. The main research contents and results arestated as follows:1. Literature research have been done on domestic and foreign development ofmode-locked ytterbium-doped fiber laser, the advantages and disadvantages of variesdesign have been analyzed. The individual design scheme has been proposed based on theresearch.2. Neglecting the ASE, according to the rate equation, the gain, the threshold power,the output power and the slope efficiency of both ring and linear cavity ytterbium-dopedfiber laser have been deduced. In addition, the relationship between key parameters ofresonant cavity (the pumping power, the length of gain fiber, the coupling rate) and theoutput parameters (the output power, the slope efficiency) have been discussed. From thenumerical simulation results, the optimal parameters have been obtained.3. Focused on the unstable problem of output pulse, resulting from using the phasemodulator, according to the nonlinear Schrodinger equation (NLSE), the numerical modelof actively mode-locked ytterbium-doped fiber laser has been established and simulatedthrough Matlab. The unstable problem has been solved by changing the average dispersionof the cavity gradually. What`s more, the effect of key parameters (the dispersion, thenonlinear coefficient, the small signal gain coefficient, the mode-locking orders, themodulation depth) on the characteristics of output pulses (the repetition rate, the pulsewidth) have been studied. The simulation results show that the laser could produce stablepicoseconds pulses with high beam quality. The repetition rate is4.9GHz and the pulse width is2.6ps, which demonstrate thefeasibility of the design scheme in this papertheoretically. The optimization of the structure and the coefficient of the laser is done. Thesimulation work plays a guiding role in the following experiment.4. The devices have been purchased and the experiment system of the activelymode-locked ytterbium-doped fiber laser is established.The characteristics of this paper is that a photonic crystalfiber (PCF) is applied to thering cavity to solve the unstable problem and compress the pulse width through dispersioncompasation.