Highly Doped Erbium Fiber Overview Thorlabs offers a wide range of highly doped erbium fibers suitable for fiber lasers and amplifiers operating in the 1.53-1.61 µm wavelength region. These fibers cover broad application field ranging from telecommunication amplifiers (EDFAs) to high power PON/CATV boosters and ultra-short pulse amplifiers used in instrumentation, industrial and medical applications. Large-Mode-Area (LMA) Double Cladding Erbium fibers are also available on request. These highly doped fibers have a core size from 20 to 30 microns with a 125 micron cladding.