Controllable structural tailoring for enhanced ∼2 µm emission in heavily Tm-doped germanate glasses.

Heavily -doped glass fibers are urgently desired for ∼2µ single-frequency fiber lasers and high-repetition-rate mode-locked fiber lasers. Here the structure of glass networks was tuned through controlling the numbers of non-bridging oxygens and bridging oxygens by adjusting the composition of the glasses, hence increasing the doping concentration of germanate glasses. The increased flexibility of the glass networks favors the distribution of ions to decrease fluorescence quenching, which was confirmed by the experimental and theoretical results. A heavily (9.8×10/)-doped germanate glass was successfully fabricated without quenching by tuning the components of the glass. To the best of our knowledge, the ion doping concentration is the highest reported level in -doped glasses and fibers. The results suggest that the heavily -doped germanate glass is highly promising for fabricating ∼2µ glass fibers with high gain per unit length.