Multimode Er-doped fiber for single-transverse-mode amplification

Abstract
We demonstrate that spatial distribution and doping level of the active ions can be designed to provide efficient fundamental mode selection in multimode erbium-doped fiber at high output power. As a result an improvement in scaling fiber devices with single-transverse-mode output to higher power levels is achieved through an increase in mode–field area. It was found that pump-induced guiding contribute the light propagation in a multimode fiber amplifier.