Experimental Investigation On Ultrafast Ytterbium Doped Fiber Amplifier And Supercontinuum Generation

Passive mode-locked fiber laser is widely used in many important fields such as optical communication,military defense,aerospace and so on because of its good output beam quality,simple structure,low cost and easy adjustment.Passive modelocked lasers obtain ultrashort pulses with high peak power and high energy,and pumping nonlinear media can produce a supercontinuous spectrum that combines the advantages of a laser source with an ultra-wide spectrum.In this thesis,the modelocked ytterbium-doped fiber laser,amplifier and its application in supercontinuum generation are investigated both in theory and experiment.The research contents of this thesis are as follows:1.The research background and significance of this topic are recommended,and the current status of research on passive mode-locked fiber lasers and supercontinuous spectrum light sources is investigated and summarized in the literature.2.The principles of three modes of mode locking in passive mode-locked fiber lasers: saturable absorber,nonlinear polarization rotation and nonlinear loop reflector are briefly described,and the principles of several nonlinear effects affecting the generation of supercontinuum spectrum are introduced and the corresponding equations are derived.3.A figure-9 Yb-doped fiber laser has been studied.By changing the pump power,the angle and position of the polarization controller,the figure-9 Yb-doped fiber laser can output different types of mode-locked pulses,the transition of bright and dark solitons is observed,and the output spectra of the first-order Raman Peaks is obtained.4.The nonlinear polarization rotation(NPR)mode-locked fiber ytterbium-doped laser and amplifier are studied.A spatially separated NPR mode-locked fiber laser is experimentally constructed.By adjusting the wave plate and pump power,the modelocked output of fundamental to third-harmonic dissipative solitons and noise-like pulses are achieved,and the central wavelength of the latter is tunable from 1022 nm to 1044 nm.In addition,ytterbium-doped fiber amplifier system is built to amplify the output noise-like pulse.The maximum power of the amplified noise-like pulse is 4.6W,and the single pulse energy is 239 n J.5.Two ultrashort pulsed laser sources were used as pump sources to compare the characteristics of photonic crystal fiber-based supercontinuum spectrum generation.One is a noise-like pulse pump source and the other is a dissipative soliton pulse pump source,the effects of central wavelength,pump power and polarization state of the pump pulse on the output characteristics of the supercontinuum are researched experimentally.When noise-like pulse is used as the pump source,the supercontinuum output with 20 d B bandwidth of 1141 nm is obtained.The supercontinuum output with20 d B bandwidth of 873 nm is obtained by using a dissipative soliton pulse as the pump source.And when using the dissipative soliton pulse as the pump source,the flatness is best when the pump light is vertically polarized,and the spectrum width is best when the circular polarized light is input.