Evaluation of crystals of LiNbo3 doped with MgO or TiO2 for electrooptic devices

Abstract

The applicability of LiNbO3 as a substrate for fabrication of Ti-indiffused waveguide electro-optic devices is limited. Ti diffuses comparatively slowly in congruently melting LiNbO3; the Curie temperature of this material is too low to permit diffusion temperatures much above 1100°C without the necessity of re-poling the crystal. Both of these difficulties could be eliminated by incorporating certain dopants in LiNbO3.Crystals of LiNbO doped with Ti and Mg were grown and evaluated. The electropic coefficients and birefringence of doped crystals were measured at \ = .6328 and 1.32μm. Curie temperatures were measured. The Curie temperature of both undoped and Ti-doped LiNb03 was 1130° C; tat for Mg-doped LiNb03 was 30° higher. From these data, a composition for the crystals was estimated. Thermogravimetric data confirmed this estimate and showed that the composition of Mg:LiNbo3 was 49.3 ± 0.2 mole % Li20; the composition of the undoped and Ti:LiNb03 samples was 48.6 ± 0.2 mole %. Diffusion of Ti into both Mg-doped and Ti-doped LiNb03 crystals was studied as a function of Li/Nb ratio and temperature.