LAUSR

Heavily Tm3+-doped glass fibers are urgently desired for ∼2µm 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 Tm3+ doping concentration of germanate glasses. The increased flexibility of the glass networks favors the distribution of Tm3+ ions to decrease fluorescence quenching, which was confirmed by the experimental and theoretical results. A heavily Tm3+ (9.8×1020ions/cm3)-doped germanate glass was successfully fabricated without quenching by tuning the components of the glass. To the best of our knowledge, the Tm3+ ion doping concentration is the highest reported level in Tm3+-doped glasses and fibers. The results suggest that the heavily Tm3+-doped germanate glass is highly promising for fabricating ∼2µm glass fibers with high gain per unit length.