Abstract

In recent years, gain characteristics of erbium-doped fibers (EDF's) have been much improved by reducing the erbium concentration^1,2 and by adoption of a structure confining the erbium-doped region to the central part of the mode field³ However, these techniques elongated the optimum lengths of the EDF's tens or severa1 hundreds of meters. To mount such long EDF's in compact amplifier modules, they must be coiled up to a small diameter, potentially reducing the mechanical reliability of the EDF's. In this paper we demonstrate a compact and efficient EDF coil with a hermetic carbon coating to prevent mechanical fatigue under the strained conditions.

© 1991 Optical Society of America