Refractive index and attenuation characteristics of SiO_2–Ta_2O_5 optical waveguide film

The refractive index and optical attenuation of sputtered SiO2–Ta2O5 waveguide film were measured in the 0.633–1.32-μm wavelength region. The waveguide film had a large refractive-index range of 1.46–2.08, which can be adjusted by suitable selection of the composition ratio of the SiO2–Ta2O5 target. Substrate heating, up to 270°C, during the sputtering process was effective for obtaining low attenuation. The waveguide films showed low attenuations, <0.41 dB/cm for the TE0 mode. The best fits of the form λγ to the measured attenuation have γ between 0 and −1, where λ is the wavelength. This wavelength dependence of the attenuation can be interpreted based on mode conversions due to the film surface roughness.