Comparison of 970- and 790-nm pumping for a 2.8 μm, Er³⁺-doped ZBLAN fiber laser

This study investigated the pump wavelength dependence of the 2.8-μm lasing performance in a Fabry-Pérot laser based on a commercially available, Er³⁺-doped ZBLAN fiber with an Er³⁺ doping concentration of 6 mol.%. First, an experimental comparison between 790- and 970-nm pumping was conducted, and 970-nm pumping exhibited a better experimental slope efficiency than 790-nm pumping. Next, theoretical performance comparisons were conducted with three different models such as strong interaction (SI), weak interaction (WI), and ion clustering model. Both SI and WI models were found to provide the calculation results completely different from the experimentally measured ones. However, the calculation results from the ion clustering model were in good agreement with the experimentally observed ones. Further calculation results based on the ion clustering model showed that 790-nm pumping was the superior to 970-nm pumping at low cluster levels in terms of slope efficiency, whereas 970-nm pumping was better at higher levels. It was theoretically found that ion clustering reduced 790-nm excited state absorption (ESA) significantly at ⁴ I_13/2 for isolated ions and resulted in a significant decrease in population inversion; however, the impact of ion clustering on 970-nm ESA at ⁴ I_11/2 was not as much as that on 790-nm ESA at ⁴ I_13/2.