Authors: Bertrand Morasse, Carl Hovington, Stéphane Chatigny, Michel Piché
We developed a model that accurately predicts the performances of high power double cladding erbium ytterbium fibre amplifiers. We experimentally validate the model in co- and counter-propagation configuration for different pump wavelengths and fibre lengths. By adjusting the ytterbium to erbium cross-relaxation rate with a simple amplifier experiment, we obtained a complete agreement between the model predictions and the experimental data regarding the output signal. We measured that the McCumber relationship considerably overestimates the ytterbium emission crosssection; with a correction of this parameter, we obtained an excellent prediction of the ytterbium spontaneous emission at 1.0 µm. The model is valid for high power singlemode amplifiers as we obtained a full agreement for a 4 W output power amplifier from a seed signal of 8 mW at 1556 nm. The output was diffraction limited with a measured M2 parameter of 1.03 without doing any mode selection from a slightly multimode fibre with a core diameter of 10 µm and a numerical aperture of 0.18.