High-power-flatness wavelength-tunable Er-doped fluoride fiber laser pumped at 1650 nm.

A broadly wavelength-tunable Er-doped fluoride fiber laser with high power flatness was demonstrated in this work based on a 1650 nm pump scheme. Cascaded transitions of ground- and excited-state absorption processes at 1650 nm were used to motivate the population recycling among energy levels and suppress the reabsorption-induced wavelength tunability range shrinkage, as well as a red-shifted and steeper high-gain band. A wavelength-tunable range up to 157 nm from 2702 nm to 2859 nm was achieved at the watt level for the first time, to the best of our knowledge. High power flatness with a power difference less than 5% was realized in a wavelength-tunable range of 117 nm.