The Research And Test Of Ytterbium-Doped Double-clad All-Fiber Laser

In recent years, fiber laser with its remarkable advantages arouse widespread attention, and become a research hotspot in the field of laser .Even working in the case of high power ,as wave guide laser, the energy of fiber laser almost entirely focus on fundamental transverse mode, and the output beam is superior in quality . However, if used dielectric film as cavity mirrors, the output laser linewidth would be wide, moreover the longitudinal mode frequency and output power are not stable enough because of the lack of effective mechanisms for frequency selection .Using fiber grating as laser resonator mirrors, we can acquire stable, narrow linewidth laser output, at the same time the fiber grating can make cavity more stable, compact, reliable, and can easily match the fiber optic system follow-up, which will be propitious to realize the industrialization of fiber lasers. Due to the simple level structure of ytterbium and without problems like excited state absorption and concentration quenching , Yb3+-doped double-clad fiber has broad application prospects in the Industry, biotechnology,optical communications, medical and other fields.The contents of this paper include:Introduce the characteristics of double-clad fiber laser and the current research situation, At the same time , the basic characteristics of Yb³⁺- doped double-clad fiber,pumping scheme and structure of fiber laser cavity are analyzed theoretically.Through the analysis of fiber-optic Bragg grating formation mechanism, the frequency selection principle of Bragg gratings and dual Bragg fiber grating linear cavity theory, characteristics and advantages of the fiber grating resonator are illustrated. Taking into account the phenomenon that thermal effect can result in fiber Bragg grating center wavelength drift, we propose two measures including refrigeration and temperature compensation, further more a laboratory refrigeration system designed is introduced simply.Based on the rate equations theory of double-clad fiber laser with Fabry-Perot Cavity and take into account the specific requirements of experiments, the effects of fiber length,mirror reflectivity, pump power and signal loss coefficients on performances of fiber laser are theoretically researched and numerically simulated with Matlab software.According to comprehensive analysis of the simulated results ,we obtain the best fiber length in the experiment,and using fiber grating as laser resonator mirrors,the output characteristics of Yb3+-doped double-clad fiber laser is studied experimentally.