Research On Ultrashort Pulse Fiber Laser Technology Based On Two-dimensional Topological Materials

With the advantages of excellent beam quality,temperature stability,and compact structure,fiber lasers have been widely used in the fields of micro-nano processing,optical fiber communications,and laser medical treatment in recent years.Among them,ultrashort pulse fiber lasers have irreplaceable value in the actual application process.At present,the main method to realize ultrashort pulse laser output is passive mode-locking technology.Among them,SESAM has received a lot of research and application due to its high stability.Two-dimensional materials are expected to replace SESAM with wide-band absorption.Common new two-dimensional materials include graphene,carbon nanotubes,topological insulators,and transition metal chalcogenides.Among them,topological insulators have been extensively studied by virtue of high nonlinearity,full-wavelength absorption and high modulation depth independent of wavelength.However,the tuning of the modulation depth is still subject to the inherent limitations of the material at this stage,the tunable range is small,and the unsaturated absorption loss is large.In addition,in the field of laser processing,how to achieve high repetition rate ultrashort pulse output is also an urgent problem to be solved.The above issues have aroused the interest and concern of researchers.The research content of this thesis mainly includes:1.The optical properties of topological insulator materials are introduced theoretically,and further,the common methods of nonlinear measurement in experiments are introduced.Two commonly used measurement methods are introduced:Z-scan and pump-probe technology.The actual meaning of the measurement results is analyzed in principle;2.First,the significance of the high modulation depth saturable absorber is analyzed.Furthermore,five Bi₂Te₃-based topological insulators were prepared as saturable absorbing materials based on the doping effect.Through a series of quantitative and qualitative characterizations,it was proved that the prepared materials have the function of modulation depth with tunable.In order to analyze the microscopic mechanism of tunable modulation depth,the energy bands and projected density of states of five materials are calculated and analyzed based on first principles,and the answer is given based on it.Finally,five materials were applied to a 1.5?m fiber laser to achieve the shortest pulse output of 366 fs.The laser has the characteristics of low gain,no polarization adjustment,and self-starting;3.The asymmetric one-dimensional photonic crystal structure with defect layer is designed.The photonic crystal is composed of Si O₂ Ta₂O₅ and Bi_1.6Sb_0.4Te₃ prepared in the previous section.Among them,the application of Bi_1.6Sb_0.4Te₃ is based on the low-cost self-assembly technology.The nonlinear performance of the photonic crystal was tested through open-aperture z-scan and pump probe technology.The photonic crystal was applied in a fiber laser,and the 99th-order harmonic ultrashort pulse output with a repetition frequency of 3820 MHz was realized when the pump power was 317 mW.