Research On Single-frequency Ytterbium-doped Fiber Laser Based On Ring Structure

This dissertation comprises two major parts,the construction of loop mirror filter(LMF)and ring cavity.These two parts are briefly summarized as follows.In the first part,theoretical modeling of the fiber laser is established with a group of rate equations.The Yb-doped fibers used in our fiber laser system is theoretically simulated.Based on the theoretical analysis of single frequency fiber laser,the 3dB bandwidth of the dynamic filter induced by the LMF is estimated.A configuration of a linear cavity with LMF is utilized in the Yb-doped fiber laser.We obtain a seed source with a central wavelength at 1063.9nm and 21.5mW maximum output power.The length of the unpumped fiber has been optimized to be 8m.The slope efficiency of multiple longitudinal modes and single longitudinal mode has been measured to be 7.7%and 5.1%respectively.After observing the SNR of the fiber laser for 3 hours,the fluctuation of the SNR is found to be less than 0.5dB.The mathematical modeling of FBG thermal response is established based on the coupling theory of FBG.The emitting wavelength of the SF fiber laser was shifted by temperature tuning of the FBG in the cavity,ranging from room temperature up to 200 ℃.The wavelength tuning range was 1.3 nm with a drifting coefficient of 0.077nm/10℃.Then the FBG was maintained at room temperature,LMF is undergoing a thermal treatment from-10 ℃ to 170℃.While the emitting wavelength maintains at 1064.18nm and the SNR decreases drastically.Then the power spectrum density with different delay time is simulated.Delayed Self-heterodyne Interferometer(DSHI)with 25km delay-fiber and 100MHz AOM is utilized to measure the linewidth of emission light.The experiment indicates the linewidth is less than the resolution of DSHI.In the second part,single frequency fiber laser with multiple ring cavity and M-Z interferometer cavity are studied.For the multiple-ring-cavity-based fiber laser,single frequency operation emitted at 1064.48nm is obtained,whose slope efficiency and maximum output power are 6.2%and 26.7mW respectively,as well as linewidth to be less than 10kHz.Contrast experiment is conducted to prove the excellent longitudinal-mode-selecting ability of MRC.For the M-Z interferometer cavity,we first verify the comb response spectrum experimentally,then it is inserted into fiber laser configuration.The maximum output power reaches 32.6mW under 500mW pump,resulting in a slope efficiency of 7.5%.In the comparison experiment,the mode-selection function of M-Z interferometer cavity is confirmed.Stability test shows the fluctuation of output power is less than 0.2mW and linewidth of the signal light is measured to be less than 10kHz with DSHI.