Study On Medium-infrared Supercontinuum Source Seed Laser And Heterogeneous Fiber Fusion

In recent years,mid-infrared supercontinuum light sources have been used in many fields such as defense technology,biomedical and environmental monitoring.Among them,mid-infrared supercontinuum light sources based on all-fiber structure have no discrete components,compact structure,good beam quality and easy maintenance is one of the hotspots in the research of supercontinuum source in the world.From these theoretical and experimental studies,it is not difficult to find that the seed light source with high output power and good environment stability,and the efficient coupling of quartz optical fiber and special optical fiber for infrared transmission are the fundamentals to achieve the output of all-fiberized supercontinuum.At present,with the development of fiber lasers,the use of pulsed lasers in the 2?m band as the seed source of the mid-infrared supercontinuum source is a trend.In addition,among many special infrared optical fibers,fluoride fiber has perfect manufacturing process and good mid-infrared transmittance.Using it as a medium to obtain mid-infrared supercontinuum is the first choice.Based on this,this thesis mainly studies 2?m passive mode-locked fiber laser,fluoride fiber and single-mode quartz fiber fusion and supercontinuum output.The content of the paper mainly includes the following chapters:The first chapter introduces the generation and development of supercontinuum,the development status of 2?m short pulse fiber laser,and the characteristics of fluoride fiber,and explains the purpose and significance of this paper.The second chapter introduces the theoretical basis of the mode-locked fiber laser.Firstly,the dispersion and nonlinear effects of optical fiber are introduced.Then the basic principle of mode-locking is expounded.Finally,the working principle and development of active mode-locking and several types of passive mode-locking are analyzed in detail.The third chapter introduces a 2?m all-fiber laser based on Mo Se₂ saturable absorber.Firstly,the research background based on the new type of saturable absorber clamping is introduced.Then the Mo Se₂ saturable absorber is prepared by liquid phase separation method,and its nonlinear optical properties are measured by standard double-arm experiments.Finally,the experimental device of mode-locked fiber laser based on saturable absorber Mo Se2-PVA film is introduced in detail,and stable mode-locking is achieved,with pulse repetition frequency of 23.53 MHz and center wavelength of 1943.35nm.The fourth chapter introduces a 2?m all-fiber laser based on nonlinear polarization rotary mode-locking.The research background of nonlinear polarization rotary mode-locking is introduced.Then,an all-fiber laser based on nonlinear polarization rotary mode-locking is built and the mode-locking is successful.The center wavelength of the spectrum is 1969.56 nm and the 3 d B bandwidth is 4.42.nm,with a pulse interval of 75 ns,corresponds to a fiber laser repetition rate of 13.3 MHz and a signal-to-noise ratio of 60d B.The fifth Chapter:Firstly,the principle and welding parameters of the heating wire fusion method are introduced.The two major factors affecting the fusion point of the fiber are theoretically analyzed.Then,the welding power,the head offset and the mechanical strength are discussed in turn,the welding parameters of fluoride fiber and single-mode quartz fiber were optimized and the welding was successful.The minimum loss of the fusion splice is 0.30 d B,and the mechanical strength of the fusion splice can exceed 85 g,which fully meets the experimental requirements.Finally,a 2?m fiber laser was used to pump a section of fluoride fiber to obtain a supercontinuum.The sixth chapter:analyzes and summarizes the main contents of this thesis,and looks forward to the next work.