Research Of Mode-locking In Fiber Lasers Based On Nonlinear Polarization Rotation And Waveguide Array

Due to their superior performance, low cost, compact and flexibility, ultra-short laser sources have important applications in fiber communication, fiber sensors, precision machining, biomedical and related areas. The mode-locking device serves as the key factor in generating ultra-short pulses. In this dissertation, we mainly focused on two mode-locking mechanisms, nonlinear polarization rotation and by waveguide arrays. Theoretical analysis, numerical simulation, as well as experimental investigation have been carried out. This dissertation includes:1. We briefly reviewed the history of fiber lasers and introduced active and passive mode-locking mechanisms. We emphasized on the present research of passively mode-locked fiber lasers.2. The operation mechanism of fiber lasers was analyzed. Then we built up a mode-locked fiber laser based on nonlinear polarization rotation. Stable continuous mode-locked pulses were generated, which had a 21.47MHz repetition rate, a 670 fs pulse width and a 6nm -3dB spectrum width centered at 1560nm. The soliton spectrum sideband was studied. We have also observed the phenomenon such as Q-switching, Q-switched mode-locking and different times of harmonic mode-locking in this fiber laser.3. We introduced the equations that determine the phenomenon in waveguide arrays. Two effects in waveguide arrays, discrete diffraction and discrete self-focusing, were studied and proved by numerical simulations respectively. Further we have investigated the influence of waveguide arrays'parameter on ultra-short pulse reshaping.4. We designed the blue print of waveguide arrays and have them manufactured. Then we built up an experimental device for measuring the ultra-short pulse reshaping in waveguide arrays. We measured the width before and after the pulse through the waveguide arrays. The loss in the experiment is analyzed. 5. Summarized the whole dissertation. The decoupling between waveguide arrays and fibers was the key issues for their applications in mode-locked fiber lasers. Some suggestions to lower the loss were proposed for future research reference.