Low loss Bragg reflectors on SiO(2)-Si(3)N(4)-SiO(2) rib waveguides

The added waveguide attenuation loss associated with Bragg reflector formation is measured. The added scattering loss due to the roughness of the Bragg grating is found to be only 0.2 +/- 0.1 dB/cm for a Bragg reflector with a 15-A stop band. In addition to this background loss, attenuation resonances on the high energy side of the Bragg resonance are found. These are due to the contradirectional coupling of the fundamental waveguide mode into continuum modes of the Si(3)N(4) core layer and into the modes associated with the thick SiO(2) cladding layer. The coupling wavelengths of these resonances are in good agreement with theory.