OFS Specialty Photonics has unveiled four optical fibers double-clad with erbium and ytterbium for high-power amplifiers and lasers. Single-mode fibers with a 6-μm core and medium-mode fibers with a 12-μm core are available. Both are sold with or without polarization-maintaining construction. The fibers provide high pump-to-signal power conversion efficiency at reduced required pump powers, and they manage heat well. Improved suppression of parasitic lasing increases stability and reliability of the fiber laser module.