Fabrication of ultralow-loss Si/SiO2 waveguides by roughness reduction

We demonstrate 0.8-dB/cm transmission loss for a single-mode, strip Si/SiO2 waveguide with submicrometer cross-sectional dimensions. We compare the co nventional waveguide-fabrication method with two smoothing technologies tha t we have developed, oxidation smoothing and anisotropic etching. We observ e significant reduction of sidewall roughness with our smoothing technologi es, which directly results in reduced scattering losses. The rapid increase in the scattering losses as the waveguide dimension is miniaturized, as se en in conventionally fabricated waveguides, is effectively suppressed in th e waveguides made with our smoothing technologies. In the oxidation smoothi ng case, the loss is reduced from 32 dB/cm for the conventional fabrication method to 0.8 dB/cm for the single-mode waveguide width of 0.5 mum. This i s to our knowledge the smallest reported loss for a high-index-difference s ystem such as a Si/SiO2 strip waveguide. (C) 2001 Optical Society of Americ a.