The Research on the Optimization of the Dynamics in Photonic Crystal Fiber Mode-locking Lasers
|Keywords||photonic crystal fiber large-mode-area fiber fiber laser mode locking|
Mode-locking fiber lasers have been the subject of intense research and development due to significant advantages such as low cost, compact structure, and environmental stability. However, the scaling of power generation from a mode-locking fiber laser based on conventional fibers is limited by excess nonlinearity. The performance of mode-locked conventional fiber oscillators still lags behind that of their solid-state counterparts. Many facts of the mode-locking large-mode-area photonic crystal fiber (LMA PCF) laser have surpassed solid-state lasers since it appeared about two years ago, such as pulse energy and peak power, which will push forward the extensive applications of the femtosecond laser. This thesis focuses on the research of the dynamics in the mode-locking fiber laser. The main points include:1. A prototype laser was designed and set up based on Yb-doped single polarization LMA PCF. The power of the pulses with a duration of 480fs can be scaled up to 800mW at a repetition rate of 46.21MHz, corresponding to a pulse energy of 17nJ.2. A new hybrid mode-locking mechanism to enhance the pulse quality is demonstrated, in which spectral filtering is introduced to a stretched LMA PCF laser. The dynamics of this mode locking mechanism is studied by numerical simulation, which shows that pulse shaping is dominated by both pulse breathing and spectral filtering. High quality pulses of 376fs without edges with an energy of 8nJ are obtained experimentally.3. Bound states in a stretched-pulse LMA PCF laser operating in the vicinity of zero dispersion regime are demonstrated. The characteristics of bound states are investigated by numerical simulation, showing that the laser can operate in different bounds states depending on the semiconductor saturable absorber mirror (SESAM), which selects signal randomly from noise. The results indicate that the highest pulse energy of 19.6nJ can be obtained with a compressed pulse duration of 76fs and a reduced pulse energy of 11.8nJ due to about 40% compression loss. The numerical simulations agree well with the experiment and can be used to enhance the single pulse energy. 4. A dissipative-soliton laser based on Yb-doped single polarization LMA PCF is demonstrated. The dissipative soliton dynamics is explored by numerical simulation, showing that spectral filtering plays a dominated role in mode-locking, which shapes the pulses in both frequency domain and time domain and keeps the pulse duration below 1ps in the cavity. For the first time, sub-1ps pulse is directly generated in a dispersion compensation free cavity. The fiber laser directly generates 777fs pulse at 1W of average power and at a repetition rate of 51.4MHz, corresponding to a pulse energy of 20nJ.