Electro-optic properties of indium/erbium-codoped lithium niobate crystal for integrated optics

Clamped and unclamped electro-optic coefficients γ₁₃ and γ₃₃ of In³⁺/Er³⁺-codoped LiNbO₃ crystals, which were grown by Czochralski method from the melts containing 0.5 mol% Er₂O₃ while varied In₂O₃ contents of 0.0, 0.5, 1.0 and 1.5 mol%, were measured by Mach-Zehnder interferometry. The results show that In³⁺/Er³⁺ codoping does not cause change of γ₁₃ and γ₃₃, and both γ₁₃ and γ₃₃ can be regarded as unchanged in the studied In³⁺ concentration range of 0–2.6 mol% (in crystal) within the experimental error of 3%. The small doping effect is desired in light of the electro-optic application of the crystal. A qualitative, comprehensible explanation for the small effect is given on the basis of the EO coefficient model of LiNbO₃ and doping effect on the defect structure of LiNbO₃.