Study On Temparature Characteristic Of Yb-Doped Double-Clad High Power Fiber Lasers

High power fiber laser is a novel laser technology that combines LD fiber modules and its pump techniques, double-clad fiber fabrication technology and fiber grating techniques. Fiber laser has an important application foreground in many fields such as communications, industrial process, military affairs, laser printing, medical treatment, etc. Double-clad fiber laser has become a research focus in international laser domain recently.The history, recent research status and developmental direction are summarized in this paper. Integrated the absorption and emission characteristics of rare-earth-ions, the steady-state rate equations model of high power ytterbium doped double-clad fiber laser (DCFL) is established, and the influences of pump absorption coefficient, pump method, the reflectivity of pump power and signal loss on output characteristic are numerically simulated as well. The results indicate that the slope efficiency can be enhanced by increasing the reflectivity of pump power;pump absorption coefficient has great influence on output power and optimum fiber length;pump method decides power density and gain distribution in the cavity, moreover, adopting many-position pump can smooth pump power distribution and magnify signal power uniformly, suitable for super high power fiber laser apparatus.Aiming at thermal effect produced by the deposit of pump power in high power lasers, Numerical and analytical solutions of interior temperature in DCFL are obtained by the conductive equations, and the influences of pump absorption coefficient, pump method, fiber attenuation coefficient, convective coefficient and fiber radius are also analyzed. It is indicated that the temperature variation in radius can be neglected compared to axial direction;decreasing pump absorption coefficient can improve temperature effect obviously, but will also cause output power drop to some extent;along with the increase of backward pump in two-side end pump, the minimum value of maximum temperature in cavity will be obtained;increasing inner clad radius and adopting different cooling measures such as air and water cooling also can lower operating temperature in DCFL.Based on the research and analysis of two important factors that must be takeninto account for high power laser systems: output power and operating temperature, through the optimization of segment numbers, lengths and pump absorption coefficients in each segment, an approach under distributed pump and with nonuniform pump absorption coefficients is proposed to reach the best match of temperature distribution and output power, which provides the theoretical reference for optimization design in high power DCFL.