Rare-Earth Doped Fiber is frequently used in fiber lasers, optical amplifiers, and ASE sources. Thorlabs offers fibers doped with Ytterbium (Yb) for emission at 1000 - 1100 nm and Erbium (Er) for emission in the C & L telecom bands (1530 - 1610 nm). Er and Yb single mode (SM) and large mode area (LMA) fiber is available as well as polarization-maintaining (PM) Yb-doped and Er-doped fiber.