Ytterbium-doped Mode-locked Fiber Laser And Fiber Amplification System

Mode-locked fiber lasers have the advantages of high peak power,compact structure,and low cost.In recent years,they have been widely used in non-invasive detection,biomedicine,national defense,and terahertz generation.However,due to the limitation of the saturation power of the fiber and the damage threshold of each device in the laser,the average output power of the mode-locked fiber laser still cannot meet some requirements.In order to obtain higher power pulse output or special wavelength,we can build the fiber optic master oscillation power amplification(MOPA)system,use mode-locked laser as seed source,and inject its output into a fiber amplifier based on a large mode field gain fiber to increase amplify output power or broaden the spectrum.This thesis focus on theoretical and experimental researches of ytterbium-doped fiber lasers and fiber amplifiers,including the following main contents:1.We discript the principle of several commonly used passive mode-locking mechanisms and briefly introduce the research status of mode-locked fiber laser.The research status of MOPA system are also investigated.2.The nonlinear coupled mode equation of fiber and the model of each device in the laser are used to build a numerical simulation model of the nonlinear polarization rotating(NPR,nonlinear polarization rotation)fiber laser.The effects of various parameters of the laser on the output result are studied,and the multi-pulse,pulsating solitons and noise-like pulse results are obtained.3.Research on Yb-doped fiber laser and polarization-maintaining fiber laser based on NPR technique.These experiments include two groups.short ring cavity laser which generate dissipative solitons with spectrum width of 13.6 nm,pulse width of 6.05 nm,and repetition rate of 35.7 MHz;long ring cavity laser which output single-wavelength mode-locked pulses and dual-wavelength mode-locked pulses in three different wavelength ranges.4.Research on linear cavity NPR laser and polarization maintaining linear cavity NPR laser.The polarization-maintaining linear cavity NPR laser uses three different cavity lengths for testing,self-started,long-term stable mode locking are achieved.Mode-locked pulses with repetition frequency of 2.75 MHz,spectral width of 5.7 nm,and maximum single pulse energy of 26.9 n J was obtained.Theoretical analysis of the principle of polarization-maintaining linear cavity mode-locking is carried out,which is well consistent with the experimental results.5.The numerical simulation and experiments of the fiber MOPA system are carried out.The effects of the pumping method,the length of gain fiber,and the frequency,power and pulse width of the seed light on the output characteristics of the fiber amplifier are discussed.The influence of external interference light on continuous wave amplifier and pulses amplifier is discussed.Dissipative soliton pulse with a center wavelength around 1030 nm is injected into Yb-doped fiber amplifier,and a broadband spectrum output is obtained.The spectrum is range from 1050 nm to 1570 nm,and the pulse width is 2.9 ps,obtained by compressing the pulse through the grating pair.