Accurate modeling of cladding pumped, star-shaped, Yb-doped fiber amplifiers

Based on an iterative numerical approach, we model continuous wave (CW), high power, cladding-pumped Yb-doped fiber amplifiers with bi-directional pumping of the star-shaped cladding. Accurate prediction of over 1 kW output power is demonstrated, and the calculation results are in good agreement with experiments. Absorption and emission cross sections for the used doped fiber are determined experimentally in advance. Using the model at such high powers, it is shown that the Giles model parameter of the effective overlap integral in the star-shaped cladding may vary coupling the light from diodes with different numerical apertures, which is believed caused by the increasing amount of pump light launched into higher order modes.