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We show that proton exchanged LiNbO3 waveguides exhibit very complex structural chemistry. Seven HxLi1-xNbO3 crystallographic phases have been identified in PE LiNbO3 waveguides. A correlation is done between the electroptical, nonlinear and photorefractive properties, the processing conditions and the refractive index changes of the waveguides.

A new method to form optical waveguides in lithium tantalate crystals, the nonisovalent ion exchange in the salt melts, is proposed. We found that the waveguides can be formed by ion exchange reactions Zn2 → 2Li+, Ni2+ → 2Li+, Mn2+ → 2Li+, Fe2+ → 2Li+, Co2+ → 2Li+, Ca2+ → 2Li+, Mg2+ → 2Li+ in the melts of mixtures K2SO4—Na2SO4—Li2SO4—MeSO4 (Me:Zn, Ni, Mn, Fe, Co, Ca, Mg) at the temperatures below the Curie point of lithium tantalate. Refractive index profiles of extraordinary and ordinary rays are determined. We have calculated also the concentration of the doping ions, the appearing mechanical stresses and the contribution of the photoelastic effect to the changes of the refractive indices.