Zr⁴⁺ diffusion-doping effect on refractive index of LiNbO₃: A comparison with bulk-doping case

Zr⁴⁺-doped LiNbO₃ plates were prepared by diffusion of ZrO₂ films coated onto congruent LiNbO₃ substrates in wet O₂. After diffusion, Zr⁴⁺-doping effect on refractive index of LiNbO₃ and Li₂O out diffusion were studied by prism coupling technique. The results show that the Li₂O out diffusion is ignorable and Zr⁴⁺ doping has little effect on both the ordinary and extraordinary indices. The little effect of diffusion-doping is clearly different from the bulk doping case reported previously, in which both ordinary and extraordinary indices show definite Zr⁴⁺ doping concentration effect. The difference is attributed to the different ion arrangements from crystal growth to in-diffusion.