Reseach On The Characteristics Of Mode-locked Oscillator And Amplifier Based On The Large-mode-area Photonic Crystal Fiber

Femtosecond lasers based on large-mode-area photonic crystal fibers, overcoming the limitations to average power and pulse energy imposed by the small mode area of single-mode fibers, can achieve output parameters comparable to those based on bulk crystals but with the advantages of fiber laser, such as compactness, low cost, high stability and high average power. In this dissertation, the amplifier similariton oscillator and the coupling optimization of the nonlinear amplification system are investigated using both numerical and experimental methods.The main work and innovations of the dissertation can be summarized as follows:1. The characteristics and development of femtosecond lasers are introduced. Different mode-locked regimes for oscillator and different fiber amplification technologies are discussed and compared.2. The nonlinear Schrodinger equation with gain solved by the symmetric split-step Fourier method is adopted to model the mode-locked fiber laser. In this model, the gain distribution along the fiber is determined by the intensity change of fluorescence leaked from the fiber side. Based on this numerical model,the impact of gain, dispersion, filter bandwidth and fiber length on intracavity self-similar evolution is discussed.3. A dispersion-mapped amplifier similariton oscillator based on a piece of 10 m large-mode-area photonic crystal fiber is demonstrated. The zeroth-order reflection of the first grating adopted as the output, the amplifier similariton is achieved in the linear cavity for the first time, and a pulse energy of 95 nJ at a repetition rate of 8.6 MHz is obtained. As far as we know, 95 nJ is the best result from similariton oscillator so far.4. A nonlinear amplifier system without stretcher is demonstrated. The highest average power of 34 W is obtained with a dechirped pulse duration of 50 fs and repetition rate of 42 MHz, corresponding to a pulse energy of 0.8 μJ and peak power of 16.2 MW.5. The impact of the intracavity dispersion on the output parameters of both the oscillator and the amplifier is discussed. Base on the simulation results, a dispersion-management soliton oscillator is chosen as the seed source. The output pulse quality of amplifier is optimized by modulating the intrcavity dispersion and the pump power of the oscillator, and the pedestal-free pulses are obtained with an average power of 28 W and a dechirped pulse duration of 45.7 fs.