Temperature effects in proton exchanged LiNbO3 waveguides

Temperature effects on single, homogeneous phases of proton exchanged LiNbO₃ waveguides have been studied. The refractive index of -phase guides on z-cut and x-cut congruent substrates monotonically increases with temperature, the thermo-optical coefficient being similar to that of the substrate. In ₂-phases on z-cut congruent substrates and in ₁-phases on z-cut and x-cut congruent and quasi-stoichiometric substrates, the thermo-optical coefficient is smaller than that of the substrate below 60 °C and higher above this temperature. A rather similar effect has been observed in ₁-phases on z-cut and x-cut congruent substrates in the linear expansion coefficient. The microscopic origin of the phase transition is not known for the moment. PACS Provide PACS codes please.