We report on the fabrication and characterization of silicon oxynitride (SiON) layers for applications as planar optical waveguides in the 1550 nm wavelength region. The optically guiding SiON waveguide core layer has a relatively high refractive index of 1500 and is sandwiched between two silicon oxide cladding layers with a lower refractive index of 1450. The SiON layer is deposited by plasma-enhanced chemical vapor deposition using silane, nitrous oxide, and ammonia as gaseous precursors. Waveguide bends with a radius of curvature as small as 1.5 nun can be realized because of the high refractive index difference achievable between core and cladding layers. This allows the fabrication of compact, relatively complex integrated optical waveguide devices. The deposition process and the characterization of the SiON films are discussed. The strengths of this high refractive index contrast planar waveguide technology are illustrated using the trample of an optical add/drop filter for wavelength division multiplexing applications in the field of optical communication systems.