Research On High-performance Mode-locked Fiber Laser

The generation of ultrashort pulses is not only one of the key technologies to realize OTDM/WDM but also the front edge research about nonlinear optics and ultrafast optics. Comparing with semiconductor lasers, the fiber lasers with rare-earth-element fiber as gain medium possess good gain features, high conversion efficiency, low threshold, high beam quality, and compatibility with fiber-optic communication system. Comparing with traditional solid lasers, fiber lasers offer a number of advantages including small volume, light weight, compact structure, and high stability. Now it has become one of the hottest topics in the field of the ultrashort pulse lasers. On the base of our laboratory environments, this dissertation is focused on mode-locked Er3+-doped fiber lasers which include(1) The physical mechanism of mode-locking in the fiber laser is investigated and the advantages of different mode-locking technologies have been analyzed. According to process of mode-locked pulses propagating in the different cavities, six models have been summarized and the mode-locked master equations for them have been discussed.(2) A novel numerical algorithm SSFD (split-step finite difference) has been presented for solving nonlinear pulse propagation equation. The numerical results show that this method can improve effectively the computation speed and accuracy in comparison with SSFT (split-step Fourier transform) and traditional FD (finite difference), especially for analyzing the problems with strong nonlinearity.(3) From the time-domain mode-locked master equation, the physical mechanism of nonlinear polarization evolution (NPE) mode-locking is analyzed in theory and the affects from cavity losses, dispersion, self-phase-modulation, and NPE saturation absorber have been discussed. With the average nonlinear Schrodinger equation, the self-starting and stability of the mode-locked fiber laser have been analyzed. We have investigated the influences of cavity parameters on the characteristics of self-starting and obtained the conditions to initiate the fiber laser to mode-lock automatically. With Er3+-doped fiber as gain medium and NPE mode-locking mechanism, we have presented an all-fiber mode-locked laser with self-starting and low pump threshold. Stable mode-locked pulses with an average output power of 0.36mW, 10nm spectral width and 258fs transform-limited duration at a repetition of 14.6MHz are obtained...