The Study Of Dispersion-Managed Passively Mode Locked Ytterbium Doped Fiber Lasers

Passive mode-locking technology is currently an important means to obtain ultrashort pulse output.The ultrashort pulse laser based on passive mode locking technology has the characteristics of extremely short duration and ultrafast interaction with matter.It is an ideal tool for studying microscopic ultrafast phenomena in various disciplines.It also plays an irreplaceable role in military defence and other fields.The ultra-short pulse ytterbium-doped fiber laser not only has the above characteristics,but also absorbs the advantages of trivalent ytterbium ions and optical fibers,and has become a special laser with short output pulse duration,high output power,compact structure,excellent heat dissipation and low use cost.It is of extremely high value in both theoretical research and actual practice.However,because the conventional fiber exhibits positive group delay dispersion in the 1 μm band where the ytterbium-doped fiber laser works,the dispersion of a single symbol will cause the output pulse of the laser to broaden,which is very unfavorable to obtain ultrashort pulse output.Therefore,the method of dispersion management is generally adopted,that is,a dispersion device with an opposite sign to the primary dispersion is introduced into the laser to cancel the adverse effects brought by the dispersion of a single sign.Based on the above background,this dissertation conducts research on dispersion management for passively mode-locked Ytterbium-doped fiber lasers.First,a chirped fiber Bragg grating(CFBG)is used for intracavity dispersion management in a ytterbium-doped fiber laser,and a sub-ps pulse output is obtained,and the stress-sensitive characteristic of CFBG is used in this femtosecond fiber laser to realize the output pulse wavelength tunable;then,G-T mirrors(Gires–Tournois interferometers)were used to manage the dispersion of the ytterbium-doped fiber laser,and by adjusting the number of reflections of the intra-cavity laser between the G-T mirrors,a sub-100 fs ultrashort pulse was obtained.The research work of this paper has important research significance and reference value for obtaining ultrashort pulse output based on ytterbium-doped fiber laser.The main research contents of the paper are as follows:First,using CFBG as a dispersion management device to introduce negative group delay dispersion in an all polarization-maintaining fiber laser,a pulse with a shortest duration of 575 fs was obtained with reference to theoretical simulations.The laser adopts the semiconductor saturable absorber mirror mode-locking method,and can output laser pulses with a repetition frequency of 24.3 MHz.The total output power of the three ports is up to 13.9 mW,and the signal-to-noise ratio reaches or exceeds 68 dB.Further,utilizing the stress-sensitive property of CFBG,a tunable pulse output is realized in the femtosecond fiber laser by applying stress to the CFBG gate region using an optical translation stage.This work has important reference value for studying dispersion-managed lasers with tunable output wavelength in all-fiber structure.Second,under the guidance of theoretical simulations,GT mirrors are introduced into Ytterbium-doped fiber lasers as dispersion management devices,and the net dispersion in the cavity is controlled by changing the number of reflections of the intracavity laser between the GT mirrors.A series of studies have been carried out on lasers under dispersive conditions.Among them,when the intracavity laser performs three round trips between the G-T mirrors,the laser works in the near-zero dispersion region.Under this condition,an ultrashort pulse output with a duration of 78 fs was obtained,and the pulse width was close to the Fourier transform limit,which is the shortest pulse obtained by G-T mirrors dispersion management in fiber lasers.This work demonstrates the excellent dispersion management performance of the G-T mirrors,which is of great significance for the study of extreme ultrashort pulses.