Femtosecond Noise-Like-Pulse Yb-Doped Fiber Amplification System

Passive mode-locked fiber lasers are widely used in the fields of military countermeasure,industrial processing,medical research and treatment due to their high quality,such as compact structure,low cost and easy adjustment.At the same time,with the continuous maturity of ytterbium doped fiber,its unique band advantages and application prospects have attracted the interest of the majority of researchers.In order to meet various needs,it is particularly important to study the output characteristics of passively mode-locked fiber lasers.In this thesis,the mode-locked ytterbium-doped fiber laser and its amplifier are studied.Mainly to "9" cavity fiber laser and nonlinear polarization rotation(NPR)mode-locked fiber laser has carried on the theoretical and experimental research,and by using optical fiber master oscillation power amplification(MOPA)system research on characteristics of its output amplifier,and aimed at to NPR mode-locked fiber laser as a seed source MOPA system output class noise-like pulse compression features analyzed.The main content of the paper is as follows:1.Explains the research background and significance of this topic,the research progress of three mode-locking mechanisms of passive mode-locked fiber lasers(saturable absorber,nonlinear loop mirror,nonlinear polarization rotation)and high-power ultrashort pulse fiber amplifiers is summarized.2.The mode-locking principles of three mode-locking mechanisms of passive mode-locked fiber lasers are briefly described.Based on Maxwell's equations,the nonlinear Schrodinger equation for pulse propagation in fiber is derived theoretically.By modifying the equation,a passive mode-locked fiber laser based on NPR is numerically simulated,and the effects of cavity length,filtering bandwidth and gain on the output characteristics of the laser are studied.3.The ytterbium doped "Figure-9" cavity mode-locked fiber laser is constructed,and the dark soliton,bright-dark soliton pair and bright soliton pulse output are obtained.At the same time,the polarization controller is placed at different positions in the resonator,and the first-order Raman peak appears in the output spectrum of the laser.In order to obtain high-energy output power,the optical fiber MOPA system was used to amplify its output in the experiment.4.High-power noise-like pulses' generation based on fiber MOPA system is investigated.In experiment,a free-space NPR mode locked fiber laser is built,whose output characteristics of the laser with different cavity lengths and simplified cavity conditions are studied.Furthermore,a fiber amplifier is setup with large-mode area Yb-doped fiber as gain medium,which compose the fiber MOPA system combined with the fiber laser.Appropriate seed source is selected and after amplification by the MOPA system,noise-like pulses with an average power up to 5.08 W are obtained.5.Using fiber and grating pair as the compression medium,the characteristics of noise-like pulse compression are experimentally analyzed.The optical fiber equilibrium dispersion and nonlinearity were introduced between the oscillating stage and the amplifying stage.By changing the relative position of the diffraction light incident grating 2 and combining with the grating pair distance,the influence of the grating on the noise-like pulse compression was studied.Finally,by adjusting the grating alignment to the optimal position,a noise-like pulse with a pedestal of 690-fs and a peak width of 59.6 fs is obtained,which is the narrowest noise-like pulse in pedestal width near 1 ?m to date.