| Nonlinear optical fiber-loop mirror(NOLM)is an all-fiber artificial saturable absorber.Passively mode-locked fiber lasers based on NOLM have the advantages of allpolarization-maintained(PM)design,all-fiber structure,cost efficiency,compactness and environmental immunity.The thesis mainly focuses on NOLM-based,all-normaldispersion(ANDi),Ytterbium-doped,mode-locked fibers.Numerical analysis was performed to understand the mode-locking mechanism and the pulse properties of this kind of lasers.A series of experimental works about figure-eight lasers and dumbbellshaped lasers were conducted.The main purpose of this thesis is to pursue higher pulse properties,namely the pulse energy,peak power and averaged power,without losing the advantageous all-fiber structure.The thesis achieved the following research results.A discrete modeling of NOLM-based,ANDi,Yb-doped,mode-locked fibers was proposed.Distributions of manifold pulse states,including dissipative soliton,dissipative soliton resonance(DSR)and unstable mode-locking,in two-dimensional parameter spaces were analyzed.In the parameter spaces,we systematically researched the localization pulse states and analyzed the properties of diversified pulse states and the impact of laser structural parameters.It is revealed that optimizing the bandpass filter bandwidth would increase the multi-pulsing threshold.A systematics analysis about the linear compression properties of dissipative soliton pulses was conducted for the first time.A transition state between traditional dissipative soliton and dissipative soliton resonance regime,is revealed to have compression properties than its vicinity.The dynamics of the transition state was also analyzed.Based on the figure-eight laser structure,by parameter optimization,DSR pulses with peak power of kW-level were proposes for the first time.The pulse width could be tuned from 48 ps to 146 ps with peak power almost fixed at 1.1 kW(1.6 times as high as the similar fore-reported results).The maximum average output power of the laser is 1.66 W,the maximum pulse energy is 161 nJ.The pulse spectrum centers at 1035 nm with a 3-dB spectrum width of ~10 nm.In the experiments of all-PM,dumbbell-shaped,mode-locked lasers,the improvement of output pulse properties was also realized.Under specified setting of laser parameters,various pulses with high performance were generated directly from all-PM,dumbbell-shaped,mode-locked fiber oscillators.The results include DSR pulses with pulse energy of 512 nJ(4 times of the fore-reported results in dumbbell-shaped lasers)and averaged power of 2W,DSR pulses with peak power of 600 W(first high-peak power DSR in all-PM mode-locked lasers)and average power of 4 W(highest in all-PM modelocked lasers).The thesis investigated the mode-locking mechanism of ANDi mode-locked fiber lasers in depth.The analysis on the pulse state distribution advanced the research of the localization of dissipative solitons,which could benefit the experiment and laser design.The experimental results of the thesis improve the currently achievable performance of mode-locked pulses,which could be integrated as high-power seeds for power amplification to simplify the MOPA system and improve the reliability. |
