Study On High Power Yb-Doped Double Clad 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. Because of the special double-clad structure, much more pump power can be coupled into the fiber and get much higher output power. At present, the thermal effect and nonlinear effect are the main constraints to get higher output power.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 pwer ytterbium doped double-clad fiber laser(DCFL) is established, and the influences of pump absorption coefficient, fiber length, the reflectivity of pump power and signal loss on output, threshold, gain characteristic, the useful results which provide theoretical basis are obtained.Aiming at thermal effect produced by the deposit of pump power in high power ytterbium doped DCFL, considering the outter clad structure, the temperature distribution and thermal stress distribution in DCFL are obtained by the conductive equations and the expressions of plane strain. The influences of pump absorption coefficient, core radius, clad radius, convective coefficient, fiber length, pump wavelength and pump method on temperature field and thermal stress field are simulated.Aiming at the nonlinear effect in high power ytterbium doped DCFL, the stimulated raman scattering(SRS) is deeply studied. The mechanism of SRS is discussed. The SRS’s expression of threshold characteristic and gain characteristic are theoretical derived. Basing on the original rate equations model, stokes rate equation is introduced. The mathematical model including the SRS is established. Using the shooting method, the influences of fiber radius, fiber length, pump wavelength and the reflectivity of pump power on SRS are simulated. With different pump method(single-ended pump and double-ended pump), the distribution of signal power and stokes power are discussed in DCFL with SRS effects. The theoretical model is compared and confirmed by the existing experimental results. The conclusion obtained provides theoretical basis for optimizing the structure of DCFL and decreasing the effects of SRS.