Femtosecond laser-written mid-infrared waveguides in a heavy oxide germanate glass

We report on the fabrication and characterization of mid-infrared waveguides in Corning 9754 germanate glass using a femtosecond laser multi-scan technique. This approach enables good control over mode shape through additional tunable writing parameters. Smooth and positive transverse refractive index changes were achieved, with a relatively high peak refractive index contrast ((1.2±0.07)⋅10^-2 measured at 600 nm) and low propagation loss (0.5±0.1 dB/cm at a wavelength of 3.2 µm). Circular mid-infrared guided modes were obtained by fine-tuning the multi-scan parameters. A Finite Difference Time Domain (FDTD) simulation model based on experimentally measured refractive index profiles confirmed the modal characteristics, validating the approach for mid-infrared photonics integration.