Proton-outdiffusion effects on the domain inversion during the heat treatment of a proton-exchanged lithium tantalate

We report proton outdiffusion effects on domain inversion during the heat treatment of a proton-exchanged lithium tantalate substrate. The effects are the formation of a non-inverted layer at the surface and the reduction of the inversion depth. This layer is undesirable since it sometimes causes needle-shape micro-domains in the domain-inverted region at post-annealing. We show that by using an outdiffusion-protection mask, the amount of the initial proton exchange can be reduced so as to improve SHG waveguide device performance