Research On Mode-Locked Fiber Lasers Based On Figure-9 Cavity And Dumbbell-Shaped Cavity

Passively mode-locked fiber lasers have attracted much attention due to their advantages of compact structure,exceptional stability and high beam quality,and have broad application prospects in optical sensing,material processing,ultrafast spectroscopy and medicine.Nonlinear loop mirror is one of the effective ways to achieve passive modelocking in fiber lasers.Figure-9 and dumbbell-shaped mode-locked fiber lasers based on nonlinear loop mirrors have high structural flexibility and strong anti-interference ability.Particularly,they also show great potential in improving the optical pulse performance and soliton dynamics research.In this thesis,through theoretical and experimental means,mode-locked fiber lasers with different configurations of figure-9 cavity and dumbbellshaped cavity are studied,and the relevant performance characteristics are analyzed.The main research contents are as follows:1.A figure-9 erbium-doped fiber laser is designed in the experiment.By setting a nonreciprocal phase shifter in the cavity,the laser can generate mode-locked pulses more easily.The cavity of the laser is a fully anomalous dispersion cavity,which realizes the conventional soliton pulse.The pulse center wavelength is 1564.1 nm,the repetition rate is 6.44 MHz,and the pulse width is 930 fs.The output pulse characteristics at different positions in the cavity are investigated.The polarization-locked vector solitons are obtained by adjusting the polarization controller.By adjusting the pump power and polarization controller,bound-state solitons and soliton bunches are achieved.In addition,the numerical simulation of the figure-9 fiber laser is carried out,and the results obtained by the simulation are consistent with the experimental results.2.The structure of the figure-9 erbium-doped fiber laser is adjusted,and the nonreciprocal phase shifter is no longer set in the cavity.By increasing the length of the ring cavity and the pump power,sufficient nonlinear phase differences can be generated to achieve mode-locking of the laser.The rectangular noise-like pulses(NLP)are obtained experimentally.The maximum pulse packet duration and pulse energy are 128 ns and 98.8 nJ,respectively.In addition,by utilizing the high-speed real-time oscilloscope,a bunch of ultrashort subpulses with varying peak intensities are directly identified inside the rectangular NLP.3.Numerical simulation of sub-100 fs figure-9 ytterbium-doped fiber laser is presented.The chirped fiber Bragg grating acts as the intracavity dispersion compensation element,and the oscillator generates 188 fs ultrashort pulses.Then,the pulses could be compressed to 86 fs by a grating pair compressor.The evolution of the pulse in the cavity is numerically simulated,and the influence of several cavity design parameters and device parameters on the characteristics of the mode-locked pulse is discussed.4.A dumbbell-shaped erbium-doped fiber laser based on two nonlinear loop mirrors is designed and constructed.The cavity of the laser is a net normal dispersion cavity.The dissipative soliton resonance(DSR)pulses are achieved in the experiment,and the period doubling bifurcation of DSR pulses is observed.The simulation model of the dumbbellshaped fiber laser is established,and the influence of the length of the loop mirror on the output DSR pulse is mainly discussed.