Research On All-Fiber 2?m Pulsed Fiber Lasers And Amplification Technology

Compared with traditional solid-state lasers,optical fiber lasers have the advantages of high efficiency,low threshold,easy to dissipate heat and compact structure.The pulsed thulium-doped fiber laser works around the 2 ?m wavelength inside the human eye safety band,and has excellent heat dissipation and good beam quality.It has broad application prospects in environmental monitoring,material processing,laser radar,biomedical and mid-infrared super-continuum generation.In this thesis,the principle of optical pulse generation in fiber laser is studied firstly,and a theoretical model is built to simulate the 2 ?m mode-locked fiber laser.Then,the Q-switched and mode-locked pulsed fiber lasers were experimentally studied by designing different schemes,and the advantages and disadvantages of each scheme were compared and analyzed.Finally,using the chirped pulse amplification(CPA)technology and the main oscillation power amplification(MOPA)technology,the optical pulse of the mode-locked fiber laser is used as seed light to be amplified,so as to obtain higher average output power and peak pulse power,and the experimental results of optical pulse amplification are discussed and analyzed.The structure of this thesis is as follows:In the first chapter,the advantages of 2-micron pulsed fiber lasers over conventional lasers are expounded,and the research background and significance of 2-micron pulsed fiber lasers are explained as well.Then,the pulsed fiber lasers are classified in detail according to the mechanism and mode of optical pulse generation.Finally,the research status of 2-micron pulsed fiber laser is introduced,and the main research contents of the thesis are also illustrated.The influence of loss,dispersion and non-linearity on optical signal in the process of optical fiber transmission are firstly introduced in the second chapter.The generation mechanism of Q-switched pulse and mode-locked pulse is also provided in detail,and the characteristics of Q-switched and mode-locked lasers are clarified,respectively.Furthermore,the theoretical model of 2-micron mode-locked fiber laser is established,and the simulation is carried out by MATLAB.The simulation results clearly demonstrate the evolution process of spectrum and pulse during the mode-locking process in the laser.Chapter 3 describes the experimental results of 2 ?m pulsed fiber lasers with four different structure:(1)passively Q-switched thulium-doped fiber laser based on semiconductor saturable absorber mirror(SESAM);(2)passively mode-locked thulium-doped fiber laser based on nonlinear polarization rotation(NPR);(3)passively mode-locked thulium-doped fiber laser based on SESAM;(4)narrow line-width passively mode-locked thulium-doped fiber laser based on SESAM.In the fourth chapter,two different pulse amplification systems,CPA and MOPA,are established.According to the different output characteristics of mode-locked fiber lasers,appropriate amplification methods are selected to carry out the experiment of optical pulse amplification for mode-locked fiber lasers,which further improves the peak power and average output power of the lasers.Finally,Chapter 5 summarizes the research results of this thesis,and point out some shortcomings that should be improved in this work.