Low-loss planar optical waveguides based on plasma deposited silicon oxycarbide

Silicon oxycarbide deposited by plasma enhanced chemical vapor deposition is investigated regarding its application as a material for optical waveguides. The dependence of the infrared absorption, the refractive index, and the surface roughness on the precursor gas flow ratios is studied by Fourier transform infrared spectroscopy, ellipsometry, and atomic force microscopy, respectively. Results show that the refractive index can be tuned over a significant wider range compared to silicon oxynitride. Fabricated waveguides with a refractive index contrast of 0.05 show waveguide attenuation from about 0.3 dB/cm to 0.4 dB/cm for wavelengths between 1480 nm and 1570 nm. These low values were achieved without using a high temperature annealing process.