Optical and structural properties of proton-exchanged waveguides in Y-Cut ZnO:LiNbO3

Abstract

Fabrication and characterisation of proton exchanged planar optical waveguides in Y-cut ZnO:LiNbO3 crystal using adipic acid as proton source are reported in this paper. These waveguides have a linear-step index profile with a surface index increase of 0.138 at the wavelength of 0.633 μm. The activation energy Q and diffusion constant D0 for the proton exchange process are characterised optically to be 95.32 KJ/mol and 9.61 × 109 μm2/h. A critical thickness of about 2 μm for proton exchanged y-cut ZnO:LiNbO3 waveguides is optically determined in our experiments. Surface damage is observed for those waveguides with layer thickness larger than this critical value. The strains in y-cut waveguides are measured by using double-crystal X-ray symmetric and asymmetric diffraction method. Based on the measured data, an explanation is given for the surface damage occurred on y-cut samples.