Modelling of high-power diode-pumped erbium 3-µm fibre lasers

We present theoretical calculations that relate to the cw operation of a high-power Er3+,Pr3+:ZBLAN double-clad fibre laser. Using the measured energy-transfer, energy-transfer-upconversion and cross-relaxation parameters relevant to Er3+-doped and Er3+,Pr3+-codoped ZBLAN, we compare the theoretical calculations from the model with recent experimental measurements. The model is then used to analyse the important pump and interionic processes occurring in Er3+,Pr3+:ZBLAN fibre lasers. The theoretical results indicate that energy transfer from Er3+ to Pr3+ leads to a fast depletion of the lower laser level and, due to the cw threshold condition, to low population densities in both laser levels. Thus, ground-state bleaching, pump excited-state absorption and energy-transfer upconversion amongst the Er3+ ions are avoided.