Optical characterization of vapor Zn-diffused waveguides in lithium niobate

Optical waveguides in LiNbO3 crystals produced by Zn diffusion from the vapor phase have been characterized. Dark mode measurements have been used to determine the refractive-index profiles of the planar waveguides. The influence of the diffusion temperature and diffusion time on the waveguide depth and on the ordinary and extraordinary index changes has been investigated. The effect of the buffer pressure on the waveguide parameters has also been studied. Waveguide formation has been observed at temperatures as low as 550 degrees C, far from the Curie point and the Li out-diffusion temperature. Changes in refractive index higher than 2.5% have been obtained. The activation energy for the process was similar to that for diffusion of Zn from a ZnO source at a higher temperature. The results of the optical characterization are compared with those for the conventional Ti diffusion method, and some aspects of the diffusion process are discussed. (C) 1997 Optical Society of America [S0740-3232(97)01102-2]