High-Quality Ring Resonators in High Refractive Index Contrast SiON Waveguides

We present the results of loss measurements on silicon-oxynitride waveguides with a relatively large refractive index contrast between core and cladding layers (0.05). The losses in these waveguides were determined from the finesse of small ring resonators consisting of a waveguide loop and two directional couplers for in- and outcoupling. For a 25-mm-long racetrack using 2-mm bending radii, we measured a finesse of 135, which corresponds to a waveguide loss of 0.08 dB/cm. This method allows us to determine low losses accurately, using measurements of a single device. Furthermore, the results do not depend on fiber-to-waveguide coupling efficiencies.