Research On Tunable Femtosecond Ytterbium-doped Fiber Laser With All Polarization-maintaining Wavelength

In recent years,ultra-short laser pulses generated by mode-locked fiber lasers have been widely used in fields such as microprocessing,ophthalmology,precision metrology,and medical imaging,due to their narrow pulse width,high peak power,and wide spectral range.These characteristics provide ultra-high temporal and spatial resolution,as well as high single-pulse energy.Compared to saturable absorber mode-locking and nonlinear polarization rotation mode-locking,nonlinear amplifying loop mirror mode-locking technology has advantages such as strong resistance to device damage and the ability to adopt all-polarization-maintaining fiber structures,which has recently attracted widespread attention.However,most reported all-polarization-maintaining mode-locked fiber lasers currently operate at a single fixed wavelength,while optical measurement,medical treatment,and biometric fields urgently require tunable ultra-short pulse sources.This paper uses an all-polarization-maintaining fiber design for the laser structure to achieve mode-locked pulse output with a tunable central wavelength and verifies the feasibility of a tunable erbium-doped fiber laser based on a nonlinear amplifying loop mirror through theoretical simulation and experiments.The main work of this paper is as follows:Firstly,through theoretical analysis and modeling simulation of the laser resonator,the feasibility of implementing a tunable mode-locked fiber laser near 1030nm is verified,and the effects of tunable filters and coupler coupling ratios on pulse shaping are analyzed.In the experimental part,an 8-shaped cavity nonlinear amplifying loop mirror mode-locking structure is adopted,using erbium-doped fiber as the gain medium,and a tunable filter as the filtering and wavelength selection structure to build a stable output all-polarization-maintaining erbium-doped fiber tunable mode-locked fiber laser.The output pulse repetition frequency can reach 10.84 MHz,and the tunable central wavelength range of the laser is 1017-1029 nm,reaching 12 nm.The output pulse width before compression is 9.4 ps,and after compression,it is 770 fs.The mode-locked pulse power reaches 11.16 mw,and the output pulse energy is 1.029 nJ.The mode-locked fiber laser presented in this paper has self-starting,tunable wavelength,and good stability features.It has potential important application value in fields such as solid-state regenerative laser amplifiers,optical measurement,medical treatment,and biometrics.