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 $\text{ZnF}_{\mathbf {2}}$ - $\text{AlF}_{\mathbf {3}}$ based fluoride glass using femtosecond laser direct writing. The induced refractive index contrast range from $- 2\times 10^{\mathbf {-3}}$ to $+ 3\times 10^{\mathbf {-3}}$ 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 $\text{Tm}^{\mathbf {3+}}$ ions were inscribed, demonstrating strong emission centered at 1810 nm when pumped at 1570 nm. These results highlight the potential of $\text{ZnF}_{\mathbf {2}}$ – $\text{AlF}_{\mathbf {3}}$ fluoride glass as a promising platform for mid-infrared integrated photonic circuits and next-generation optical communication devices.