100W linear-polarized single-mode CW emission is demonstrated in an all-fiber format at 1566 nm. The Yb3+/Er3+ doped fiber laser has an extinction ratio >20 dB and M2<1.1. Using an Yb-Er doped multi-mode fiber, the laser provides > 13% overall electrical efficiency and less than 4 nm linewidth without the onset of Yb ions generation at wavelength range of 1060-1080 nm. There are no saturation effects due to pump or nonlinear phenomena. Parasitic lasing is suppressed with fiber laser cavity design and specialty filters.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.