Fabrication and demonstration of a pure silica-core waveguide utilizing a density-based index contrast

We report a novel approach for creating a dopant-free pure silica-core waveguide (PSCW) for chip-scale waveguides with the goal of reaching fiber-like losses on-chip. Stoichiometric silica films were used as both the cladding and core material for buried channel waveguides, with the required index contrast generated by a difference in physical density. The bulk densities of the thin-films were measured with X-Ray Reflectometry, and these density values were compared with the expected change in refractive index using the Lorentz-Lorenz (Clausius-Mosotti) relation. We found the difference in density of 5.29% to correspond with the difference in refractive index of 1.17%, and measured propagation losses of 2.119 to 2.660 dB/cm.