Investigation of the few-mode ytterbium-erbium doped fiber amplifier including effects of ion clustering and secondary energy transfer

The complete computational model of a low-mode ytterbium-erbium doped fiber amplifier, based on the numerical analysis of rate equations, was developed. In contrast to existing models, we considered the effects of the secondary energy transfer and the upconversion as well as the presence of isolated ytterbium ions and clustered erbium ions in the aggregate. In addition, the presence of several transverse modes and the effect of transverse spatial hole burning were took into account, too. Necessary parameters of the active medium were determined experimentally by measuring the luminescence decay of active ions and the output power and optical spectrum of a fiber amplifier. The proposed model allows one to calculate both the power and spectral characteristics of ytterbium-erbium doped fiber amplifiers, and the nonstationary dynamics of the population inversion and the luminescence of active ions. This can help one to select the required concentrations of active ions, the geometry and the length of active fibers for each specific task.