A low-scattering graded-index SiO2 planar optical waveguide thermally grown on silicon

Planar graded-index SiO2 optical waveguides characterized by very low scattering have been fabricated on silicon substrates by thermal oxidation. Three samples having thicknesses on the order of 15 μm are characterized by waveguide losses less than 1 dB/cm. The appearance of the waveguide streak and out-of-plane scattering measurements using photon counting indicate extremely low scattering. The low scattering along with the weak field confinement present in the graded-index waveguides is consistent with the dominant waveguide loss being due to coupling to the silicon substrate.