Research On 2 Μm Ultrafast Fiber Laser Based On Optical Micro Nano Devices

The 2μm ultrafast fiber laser has important application value in basic scientific research,industrial processing,environmental monitoring,specific medical and other fields.Micro-nano optical devices with high quality factor（Q value）and small mode volume are used for nonlinearity and dispersion control,which is a hot research trend of2μm ultrafast fiber lasers in recent years.Based on two micro-nano optical devices of whispering gallery microsphere cavity and tapered micro-nano fiber,this thesis systematically studies the optical control of 2μm fiber laser,especially ultrafast fiber laser.The main contents of the thesis are as follows:Based on the coupled Ginzburg-Landau equation and the dynamic equation of the saturable absorber,the second chapter of the thesis carried out theoretical simulation and experimental research on the dynamics of the 2μm ultrafast fiber laser system.Theoretically,the four states of high nonlinearity,soliton,dissipative soliton and large negative dispersion are simulated and analyzed by matlab program algorithm.In the experiment,through research and analysis of the parameter output evolution under different experimental conditions,a 2μm noise stable light source with tunable wavelength（1966nm-2010nm）and tunable pulse repetition frequency（496k Hz-18.4MHz）was obtained.A new type of h-shaped pulse with femtosecond pulse substructure was obtained under short cavity and long cavity.This kind of pulse presents a nanosecond pulse profile in the shape of the letter"h"on the oscilloscope,but it is detected by autocorrelation.To the femtosecond substructure pulse.The h-shaped pulse we obtained is the first report to prove that it is a kind of noise-like pulseThe third chapter prepared and characterized the optical micro-nano devices that can be used in the 2μm wave band.Several samples of whispering wall microspheres with diameters of 200～520μm were prepared by CO₂ laser fusion method and silica fiber.Through characterization and comparative analysis of their Q value,loss,coupling efficiency and other important parameters,the final diameter of 300 microns was selected,and the Q value of microspheres was as high as 1.13?10⁸ are used as the micro-nano device of this system.Several tapered micro-nano fiber samples with diameters of0.8～2.8μm were prepared by using a hydrogen-oxygen flame tapering platform and silica fiber.A tapered micro-nano fiber with a diameter of 0.7μm that exhibits a sub-wavelength structure in the 2μm band is specially prepared.Through characterization and comparative analysis of its loss,transmittance,dispersion distribution and other important parameters,a tapered micro-nano fiber with a diameter of 1μm was finally selected as the optical control device to be applied to this system.The fourth chapter mainly carried out the experimental verification of the optical control to 2μm continuous laser and 2μm noise-like pulsed laser by micro-nano optical devices.Experiments prove that the tapered micro-nano fiber produces modulation effects such as wavelength tuning and spectral base narrowing on the 2μm laser.In the modulation experiment of the microsphere cavity-tapered fiber coupling system on the 2μm laser,not only the modulation effects such as wavelength tuning and narrowing of the spectral base were observed;a single-frequency spectrum with a line width of about 0.44pm was also selected;generate regular comb-like stripes with modulation spacing multiples of the free spectral range,etc.In the end,the feasibility of using thulium-doped active fiber to fabricate a microsphere cavity to generate a 2μm laser was also experimentally explored.This article explores the application of fiber micro-nano devices as optical modulation devices to ultrafast fiber laser systems in the 2μm waveband,and provides a reference for subsequent research on the optical control of 2μm ultrafast lasers.