Research On Ultra-low Jitter Mode-Locked Fiber Laser And Its Pumping Mechanism For Supercontinuum Broadening

Low noise passively mode-locked fiber lasers, as a special kind of pulsed lasers, provide ultra low intensity fluctuation and timing jitter and therefore have significant applications in optical sampling, frequency metrology, etc. Furthermore, such a kind of laser is the ideal pump source for the low jitter supercontinuum (SC) generation, which is an important research direction of fast lasers’application. Since the characteristics of SC (such as extreme bandwith and high coherence), it has been used in optical communication, spectroscopy, biophotonics, etc. In this thesis, we design and build a high repetition frequency low timing jitter mode-locked fiber laser. Through optimizing the structure of laser cavity, the noise of output pulses can be reduced. Additionally, using this laser as the pump source, we further research SC broadening mechanism in the long pulse region. The main aspects of this thesis are listed as follows.(1) We design a high repetition frequency low timing jitter mode-locked fiber laser. In order to investigate the influence of intra-cavity pump coating on the output pulse noise properties, two lasers with similar design are made for comparison with one having a pump reflection coating whereas the other one has not. The noise conversion from pump relative intensity noise (RIN) to the RIN and phase noise of two lasers is evaluated experimentally. It is found that although the laser with pump reflection coating has much lower self-starting pump power and higher slope pumping efficiency, the pump-RIN-to-laser-RIN conversion scales as the square of the slope efficiency at low frequency region. The pump-RIN-to-laser-phase-noise conversion is also increased due to the existence of the slow saturable absorber effect.(2) We report that spectral phase coherence of supercontinuum in the long pulse regime can be measured simply and effectively by using interference technique with the help of Mach-Zehnder interferometer. We also demonstrate both in simulation and experiment a direct relation between the free fringe visibility of the averaged interference spectra of two delayed subsequent pulses and the degree of spectral phase coherence.(3) Using our home-made laser as the pump source, we further investigate the reasons for Rogue Waves (RWs) generation experimentally, which is related to the modulation instability (MI) effect. The RWs will occur when the quantum noise of pump laser is happens at or near the maximum of MI gain. Then we interpret physically the dynamics of resonant seed modulation instability of quasicontinuous picosecond pulse in terms of cascaded four-wave mixing and Bragg scattering in fiber frequency combs. Finally, we report a critical condition to excite the resonant seeding effect.(4) We propose and theoretically investigate As2Se3chalcogenide planar waveguide as a potential compact platform for SC generation. It is found that, because of the high nonlinear refractive index n2, the size of As2Se3waveguide can be greatly shortened. Moreover, the high nonlinearity of chalcogenide planar waveguide is helpful to decrease the initial peak power of input laser, indicating that it is a more energy efficient platform to generate SC. Meanwhile, dispersion engineering is performed by optimizing As2Se3waveguide structure parameters. The result shows that only a24W peak power of pump source and a10mm long waveguide can achieve SC generation with good coherence.