977-nm all-fiber DFB laser

Three-level operation of a fiber distributed feedback (DFB) laser operating around 980 nm is demonstrated for the first time. The ytterbium-doped DFB laser shows a maximum slope efficiency of 61% and output power of 38.2 mW under a launched single-mode pump power of 150 mW at 910 nm. The efficiency of lasers with different coupling strengths and at different pump wavelengths is also investigated.