Calculation of extraordinary refractive index change in proton-exchanged LiTaO₃ waveguides

A theoretical index model for the extraordinary refractive index increase in proton-exchanged LiTaO₃ is presented. The index change is caused by two factors: the change in spontaneous polarisation and the change due to the photoelastic effect caused by the lattice volume expansion. Close agreement is obtained between quantitative calculation based on the proposed model and experiment data.