Research Of 2 ?m Mode-locked Fiber Lasers And Wavelength Conversion Technology

2 ?m ultrashort pulsed laser sources have been widely used in applications such as gas detection,remote sensing,material processing and medical sciences.Ultrafast fiber lasers own the advantages of compactness,low cost and high reliability.They are very suitable for scientific research and industrial applications.This paper focuses on generation of ultrashort pulses in fiber lasers,and we have investigated 2?m mode-locked fiber lasers and wavelength conversion technology in optical fibers.The main contents of this thesis are as follows:1.We have studied the optical properties of a large-area,high-quality Weyl semimetal film WTe2 which was grown by a pulsed laser deposition technology.It was found that WTe2 thin film exhibits strong nonlinear absorption at a wavelength of 2 ?m.We further demonstrated a passively mode-locked Thulium-Holmium co-doped fiber laser using a WTe2 absorber.Our work reveals the potential of Weyl semimetals in ultrafast photonic applications.2.We have demonstrated mid-infrared supercontinuum generation in chalcogenide fiber.The pump laser was from a wide-band tunable 2 ?m ultrafast fiber laser mode-locked by single-wall carbon nanotubes.A two-stage Thulium doped fiber amplifier was used to boost the pump laser power to 500 mW.Finally,by pumping a segment of chalcogenide fiber,a tunable supercontinuum source was obtained.3.A wavelength tunable ultrashort pulsed laser source was realized based on Raman-induced soliton self-frequency shift.We first built a SESAM mode-locked fiber laser at 1550 nm.Then,power amplification and high-order soliton pulse width compression of the seed were simultaneously achieved in an erbium-doped fiber amplifier.Finally,we injected the amplified source into a highly-non-linear fiber.Raman soliton with wavelength continuously tuned from 1550 nm to 2050 nm was obtained.This is proved to be a simple,reliable and cost-effective way to realize wavelength conversion of ultrashort pulses.