Supercontinuum Generation In Soft-Glass Fiber Based On 2 μm Mode-Locked Pulses

Mid-infrared super-continuum(SC) sources have been studied intensively because of its potential applications in many fields such as military defense, gas detection, spectroscopy, biomedical and environmental monitoring. In recently years, Mid-IR SC with high power and broad band spectrum has attracted focus attention. SC generation in single mode ZBLAN and As2S3 fiber was numerically and experimentally investigated based on 2 μm mode-locked ultra-short pulses. The main point can be concluded as the following three parts:(1) Theoretical model of pulse propagation in nonlinear fibers based on general Nonlinear Schrodinger Equation(GNLSE) was established. Based on the split-step Fourier method, GNLSE was numerically solved. The process of pulse propagation and spectral evolution was numerical simulated in both normal and anomalous dispersion regime of single-mode ZBLAN fiber. Influences of SPM, SRS and soliton fission on SC generation were discussed. Impacts of peak power, pulse width and fiber length on SC power distribution and flatness were quantitatively analyzed.(2) Theory of passively mode-locked fiber lasers based on NPR and Single-walled Carbon Nanotube(SWCNT) was established. Then mixed mode-locking fiber laser based on NPR and SWCNT was innovatively investigated. Fiber lasers with 1979 nm central wavelength, 2 ps and 1969.9 nm central wavelengths, 15.14 ps pulse width were successfully achieved. For the 2 ps pulses, the repetition rate was 15.37 MHz; output average power was 13.696 m W; and threshold pump power was 3.93 W. For the 15.84 ps fiber laser; output average power was 8.56 m W; repetition rate was 9.07 MHz and threshold pump power was 3.76 W. The mixed mode-locked fiber laser as the seed laser in the Master Oscillator Power-Amplifier(MOPA) system, spectrum of pulses was stretched after amplification. Spectral width for 2 ps pulses exceeded 250 nm and average power reaches 613.3 m W. Energy of single pulse was amplified by 65 times. For the case of 15.84 ps pulses, spectrum width was 175 nm and output average power reached 308.3 m W. Single pulse energy was amplified by 37.3 times.(3) Based on the former experiments, spectrum covering from 1950 nm to 2400 nm with 149 m W output average power was obtained in ZBLAN fiber when pumped by amplified 2 ps pulses; spectrum covering from 1940 nm to 2400 nm with 104.2 m W average power was achieved when pumped by amplified 15.84 ps pulses. In single mode As2S3 fibers, the spectrum covers from 1950 nm to 2300 nm and the output average power is 182.8 m W when pumped with amplified 2 ps pulses. For the case of amplified 15.41 ps pulses, the output spectrum only covers about 50 nm because of low peak power and normal dispersion regime pumping, the average is 67.9 m W.