An Er/Yb-doped double-clad fiber with a single-mode core composition designed for high conversion efficiency in high-power amplifiers pumped at 915 to 960 nm has been announced by Nufern. The SM-EYDF-6/125-HE operates over the C- and L-bands with a mode field diameter of 7 ±0.75 μm at 1550 nm and second mode cutoff at 1460 ±60 nm. Cladding ytterbium absorption at 915 nm is 0.60 ±0.15 dB/m, and peak core erbium absorption at near 1535 nm is 12 ±3 dB/m. Nominal core and cladding numerical apertures are 0.17 and 0.46, respectively. Core-cladding concentricity is ≤1 μm, and clad and coating diameters are 125 ±3 μm and 245 ±15 μm, respectively. The outer cladding material is low-index polymer.