Proton-exchanged optical waveguides in LiTaO3: phase composition and stress

Abstract

Planar optical waveguide layers were obtained in Z-cut LiTaO3 crystal substrates via proton exchange. Two different media were used as proton sources: benzoic acid melt and lithium hydrogensulphate vapors, controlling the thickness of the waveguides by duration and temperature of the proton exchange process and also by post-exchange annealing. The intrinsic stress caused by the penetration of the hydrogen ions into the crystal lattice was estimated by the optical integral method. The phase composition of proton-exchanged layers was analyzed based on the mode and IR-absorption spectra. An attempt to relate the level of stress to the level of proton doping has been made.