Research On Mode-locked Fiber Laser Based On Novel Two-dimensional Materials

High-power pulsed fiber lasers have received extensive attention due to their potential applications in the fields of optical communications,biomedicine,industrial manufacturing,defense military,and nonlinear optics.Passive mode-locked technique is one of the effective means to obtain high-power pulses.As the core device of passive mode-locked fiber laser,saturable absorber?SA?has become a research hotspot in the world.In the past few decades,the semiconductor saturable absorption mirror?SESAM?has been widely used in mode-locked fiber lasers as the most mature commercial saturable absorption device.However,SESAM has the drawbacks of narrow absorption bandwidth,complicated preparation process,and expensive price,which also limits its further application and development.In recent years,with the emergence of graphene,various new two-dimensional materials such as transition metal dichalcogenides?TMDs?,topological insulators?TIs?,and black phosphorus?BP?have emerged.They are widely used in the research of passive mode-locked fiber lasersdue to their excellent saturable absorption characteristics.The damage threshold of two-dimensional material saturable absorber is one of the important parameters that determine whether it can obtain high-power pulse.Therefore,increasing the damage threshold of saturable absorber is the key to achieving the high-power output of the mode-locked fiber laser.This dissertation mainly proposes corresponding solutions for how to increase the damage threshold of two-dimensional material saturable absorbers.In this dissertation,the preparation and characterization of saturable absorbers based on bismuth selenide?Bi₂Se₃?and indium selenide?In₂Se₃?and their applications in high power mode-locked fiber lasers are introduced in detail.The main research contents of this dissertation are as follows:1.Bi₂Se₃ nanosheets with large size and high crystal quality were prepared by chemicalvapor deposition?CVD?method.The material characteristics and saturable absorption characteristics were characterized.Then the ytterbium doped linear-cavity mode-locked fiber laser based on Bi₂Se₃ saturable absorber was designed and constructed.The dark pulse with single pulse energy of 61.8 nJ was obtained.The experimental results show that the chemical vapor deposition method can effectively increase the damage threshold of the prepared two-dimensional material.Meanwhile,it is conducive to the realization of large-energy mode-locked pulse output.2.The physical vapor deposition?PVD?method was used to synthesize high-quality In₂Se₃ nanosheets on fluorophlogopite mica?FM?substrate.Moreover,the material characteristics of In₂Se₃ nanosheets were characterized.PVD-In₂Se₃-FM saturable absorber not only exhibits excellent saturable absorption characteristics,but also has a damage threshold of up to 50 mJ/cm².The stable mode-locked pulses were obtained with a maximum average output power of 172.4 mW by inserting the PVD-In₂Se₃-FM saturable absorber into the double-end pumped erbium-doped mode-locked fiber laser.Additionally,a dark-bright pulse pair generation was obtained.The experimental results indicate that the proposed PVD-In₂Se₃ could operate as a promising nonlinear optical material for high-power fiber laser.