High Performance Pulsed Fiber Lasers And Their Dynamics

High-performance pulsed fiber laser sources have greatly contributed to the significant progress of traditional laser industries in recent years owing to their excellent advantages,such as good beam quality,high efficiency,excellent reliability as well as compactness.Particularly,high-performance fiber lasers like mid-infrared（mid-IR）high-power fiber lasers,widely tunable fiber lasers,ultrashort pulsed fiber lasers,and other excellent fiber laser devices as well as related technologies have made significant progress,and have been applied in economy society,national defense and other fields.Accompanying with the requirements of laser wavelength extension and output power scaling for many applications,it is of great significance to deeply understand the output dynamics characteristics of pulsed fiber laser and explore new opto-electronic materials and devices.With the significant development of new material technology,two-dimensional atomic crystal nano-materials（such as graphene,topological insulator,molybdenum disulfide,black phosphorus,etc.）can provide more solutions for high-performance fiber lasers due to their unique and excellent opto-electronic and nonlinear optical properties.In this thesis,we focus on the theoretical and experimental research of high performance high-power and high-efficiency pulsed fiber lasers,mainly focusing on the new type passively Q-switched and mode-locked ultrashort pulse fiber lasers and its nonlinear optical soliton dynamics.Primary research results have been achieved and summarized as follows:（1）We built up a concrete model of the all normal dispersion（ANDi）passively mode-locked fiber laser,based on which systematic numerical simulation of the dissipative soliton explosions and multi-pulsing instability and their transition dynamics under different small signal gains were implemented.The evolution mechanism of the soliton explosion,noise-like pulse and the collision of the dissipative soliton pair as well as the exploding soliton pair were also analyzed.We illustrated the impact of the pump strength and the bandwidth of the spectral filter on the evolution of the various dissipative solitons and obtained the exact variation range of the corresponding parameters for each soliton pattern.The systematic theoretical analysis provides profound basis for the design and experimental research on the ultrafast high energy pulsed fiber laser（2）We built up the corresponding relation of the concrete model of the passive mode-locked laser and the distributed model based on complex cubic-quintic Ginzburg-Landau equation.We analyzed the impact of the high-order effects on the modes of soliton explosion to control the dissipative solitons and disclosed the bandwidth of the spectral filtering effect on the collisions of the exploding soliton pair and multi-solitons,which provides important practical guide for the stable and controllable pulsed fiber laser.We applied the concept of optical reflection and refraction,for the first time,to the spectral domain.The optical reflection and refraction phenomena are addressed in the spectral domain across a dispersion discontinuity boundary,where a weak probe pulse is co-propagating with a strong perpendicularly polarized parabolic pulse.The total internal reflection behavior in the spectral domain is analytically determined.Our results can complete the theory of the optical wave confinement in the spatial,temporal and spectral domains,which can be a guide for spectrum engineering and characterization.（3）Through optimizing the parameters of BP-SA and laser cavity design,we demonstrated the sub-hundred nanosecond Q-switched and sub-300 femto-second mode-locked pulse generation from an Er-doped all-fiber laser.By adjusting the optical deposition process,we deliberately increased the modulation depth of the BP-SA for the stable Q-switching operation.In an all-negative-dispersion mode-locked Er-doped fiber laser we also obtained stable conventional soliton mode-locking with pulse duration reduced to 280 fs.The experimental results can provide a highly effective solution in achieving sub-hundred nanosecond pulses and sub-300 fs soliton mode-locking pulses from all-fiber lasers.（4）We experimentally constructed a～3.5μm mid-IR Er³⁺-doped fluoride fiber laser and realized high power,high efficiency continuous-wave and Q-switched operation.We investigated the impact of gain fibers with different lengths and doping concentrations as well as other cavity parameters（such as transmission of the output coupler）on the output lasing characteristics in the dual-end dual-wavelength pumping regime.A passively Q-switched 3.5μm Er³⁺:ZBLAN fiber laser based on a SESAM was investigated for the first time.Stable pulse train can be obtained with a repetition rate between 26.83 k Hz and 58.71 k Hz.The pulse duration varied between 3.6μs and2.4μs when the pump power of 1973 nm increased from 0.83 W to 1.13 W.The relatively long pulse duration can be attributed to the low gain and significant loss in the resonator.Since the SESAM is not an optimal design for the operating wavelength around 3.5μm,the performance of the laser owns a large potential for improvement.