Design of an Er3+: InF3 fiber laser pumped with red light

Abstract

A novel fiber laser based on a fluoroindate glass doped with erbium ions and cladding pumped with red light is designed. In the simulation, the pump beam at 635 nm wavelength is injected in a commercially available double D-shaped, fewmode, optical fiber fabricated by Le Verre Fluoré in order to excite the 4F9/2 energy level. A strong population inversion between ⁴F_9/2 and ⁴I_9/2 energy levels is obtained, thus allowing emission in the 3400-3600 nm band. The electromagnetic analysis of the fiber, performed by the finite element method, shows that up to six signal modes at 3500 nm are supported. An exhaustive mathematical model based on five rate equations for the erbium ion populations, coupled with the power propagation equations for the pump and all the signal modes, is developed. Both cases of forward and bidirectional pumping are considered. All the spectroscopic parameters employed in the model, including the absorption/emission cross sections, the lifetimes and the branching ratios, are taken from the literature. The numerical code allows for evaluating the output signal power, the threshold pump power, and the slope efficiency. The behavior of the laser is studied by varying several parameters, such as the cavity length, the erbium concentration and the output mirror reflectivity. Preliminary simulations show that, with pump powers of a few hundred mW, lasing can be obtained. These results will be improved by using an evolutionary optimization technique, like the particle swarm optimization approach, and promise interesting low-cost applications.