Optical waveguides in LiTaO_3 formed by proton exchange

Abstract

We describe the fabrication of optical waveguides in LiTaO₃ using proton exchange in hot benzoic acid. All specimens analyzed were X cut. An increase in surface extraordinary index of ~0.14 has been observed for samples exchanged for 3 h at a melt temperature of 249°C. No change was observed in the ordinary index. Waveguide fabrication was facilitated by further baking the samples for an extended period of time at a temperature hotter than the acid melt. The latter technique also served to minimize the surface damage that is characteristic of acid baths exceeding roughly 4 h. The depth of proton exchange in X-cut LiTaO₃ appears to be considerably less than would be the case for X-cut LiNbO₃ under the same conditions.