We characterize the refractive-index profiles of <i>Z</i>-cut and <i>X</i>-cut Zn-diffused LiNbO<sub>3</sub> substrates from the vapor phase. We obtained these profiles by reflectivity measurements of the samples, using the prism coupling technique at each step of a systematic polishing, and then fitting the data with a program that models a multilayer optical structure. For diffusions performed at 800 °C, four different layers were clearly distinguished in the LiNbO<sub>3</sub>:Zn diffused samples, the first one being a very thin layer of polycrystalline ZnO. Two step-index layers were also detected: One was isotropic, and the other showed birefringence depending on the crystal cut. These two layers were correlated with Zn-rich phases previously detected in Zn-diffused LiNbO<sub>3</sub> by x-ray techniques. The fourth layer detected presents a graded-index profile and corresponds to the formation of a Zn-containing solid solution with a LiNbO<sub>3</sub>-likestructure. These results are discussed and compared with the phases reported for Ti-diffused LiNbO<sub>3</sub>.
© 1999 Optical Society of America
(130.3130) Integrated optics : Integrated optics materials
(130.3730) Integrated optics : Lithium niobate
(160.6990) Materials : Transition-metal-doped materials
(230.7390) Optical devices : Waveguides, planar
Rubén Nevado and Ginés Lifante, "Characterization of index profiles of Zn-diffused LiNbO3 waveguides," J. Opt. Soc. Am. A 16, 2574-2580 (1999)