Single-mode operation of a pedestal-free 25µm core double-clad Tm-doped fiber with >50% efficiency for 2μm applications

We present a novel pedestal-free large-mode area (LMA) thulium-doped fiber (TDF) for 2μm fiber lasers and amplifiers. Unlike pedestal-based LMA-TDFs, which require custom cleaving and splicing, this new design supports conventional processing while achieving >50% slope efficiency and diffraction-limited beam quality. Traditional LMA-TDFs rely on a pedestal to reduce core NA, enabling high-power (>1 kW) operation but increasing integration complexity. This new pedestal-free LMA-TDF maintains high efficiency, single-mode operation while offering improved scalability, repeatability, and lower manufacturing costs—paving the way for industrial-scale 2μm fiber laser systems.