Low-Loss Optical Channel Waveguides in ZnF₂-AlF₃ Based Fluoride Glass for Integrated Photonics

We report the fabrication of low-loss channel-type optical waveguides in a novel ZnF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>-AlF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> based fluoride glass using femtosecond laser direct writing. The induced refractive index contrast ranges from -2 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to +3 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> relative to the bulk glass, enabling effective light confinement. By optimizing the laser processing parameters, a minimum propagation loss of 0.93 dB/cm was achieved. Additionally, active waveguides doped with varying concentrations of Tm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions were inscribed, demonstrating strong emission centered at 1810 nm when pumped at 1570 nm. These results highlight the potential of ZnF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>–AlF<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fluoride glass as a promising platform for mid-infrared integrated photonic circuits and next-generation optical communication devices.