Numerical simulation of Nd-fluoride and tellurite solar-pumped fiber lasers

Abstract

Numerical simulation of Nd-doped fluoride and tellurite fiber lasers pumped directly by sunlight have been performed. Calculations have been done for double clad fibers to achieve both efficient coupling sunlight with a fiber and spatial power condensation. The pumping source was assumed to be initially AM1.5 sunlight and was focused onto a fiber end. The both ends of the fiber were assumed to be transparent for at the pump wavelength and highly reflective at laser wavelength. It was assumed that the launched sunlight propagate in one longitudinal direction in the inner but the laser light propagate in both longitudinal directions in the core. Propagation equations were solved under boundary conditions determined by the reflectivity of the fiber ends by a boundary value problem solver in MATLAB. The calculated sunlight concentration ratio at lasing threshold was about 300 suns for solar pumped fiber lasers with optimized structure. This sunlight concentration can be achieved by conventional optics such as lenses and ellipsoidal mirrors. The slope efficiency was about 0.78 % for a fluoride fiber and 1.32 % for a tellurite fiber. These efficiencies are can be improved by farther optimization of fiber parameters and pumping scheme. Solar pumped fiber lasers will be able to provide alternative means to utilize solar power.