Resonantly (in-band) cladding-pumped Yb-free Er-doped fibre laser with record efficiency

Power scaling potential with record high efficiency for a resonantly (in-band) cladding-pumped Yb-free Er-doped eye-safe fibre laser utilising the fibre with non-clustering composition and increased cladding pump absorption is domonstrated. While pumping at 1532.5 nm by power-combined fibre-coupled spectrally-narrowed InGaAsP/InP diode laser modules, ~47 W of continuous-wave multimode output power at ~1590 nm with optical-to-optical efficiency over 77% were achieved. To the best of the authors?? knowledge, this is the highest efficiency ever obtained from a cladding-pumped Yb-free Er-doped fibre laser.