EFFECT OF CRYSTAL PHASES ON REFRACTIVE-INDEX PROFILES OF ANNEALED PROTON-EXCHANGED WAVE-GUIDES IN X-CUT LITAO3

A complete structural phase diagram of annealed proton-exchanged X-cut LiTaO3 is presented, to relate refractive index change to proton-indu ced lattice deformation. From this diagram, explanations for the previ ously observed phenomena of index increase upon annealing and index de crease with increasing proton concentration (above a certain value) ar e derived. We have analyzed the evolution of index profiles during pos texchange annealing, describing how the presence of multiple phases wi thin a waveguide can lead to large index variations and buried index p rofiles. Finally, we identify at least two high-concentration phases t hat exhibit large temporal instabilities. (C) 1998 American Institute of Physics.