Scattering in ZnO-Sapphire Optical Waveguides.

Optical waveguide loss due to scattering in epitaxial ZnO-sapphire films was studied by measuring the dependence of attenuation on mode number and on optical wavelength. Analysis of the results in terms of wave-optical scattering theory enabled the bulk and surface scattering contributions to be determined. The bulk scattering showed the lambda(-4) dependence characteristic of Rayleigh scattering. A white noise spectrum of surface roughness was found to be in good agreement with surface scattering observed in most of the waveguides studied. The attenuation coefficients derived from the data were related to specific aspects of the waveguide fabrication process and allowed rational improvements resulting in a decrease in loss from 20 dB/cm to 1 dB/cm.