Contribution of Diffused Er3+ Ions to Refractive Index of LiNbO3 Crystal and Relation of Li Out-Diffusion to Er3+-Diffusion Condition.

Contribution of diffused Er3+ ions to refractive index of LiNbO3 crystal and relation of Li out-diffusion to Er3+-diffusion condition have been studied. Three X-cut and three Z-cut congruent LiNbO3 plates locally coated with 10, 15, or 20 nm thick Er metal films were annealed at 1100°C or 1130°C for 60 or 100 h under different atmospheres of surrounding air, wet O2 or wet Ar. After the anneal, the ordinary and extraordinary refractive indices at Er3+-doped and Er-free parts of crystal surface were characterized at the 633, 1311, and 1553 nm wavelengths by measurement of critical angle. The difference of surface index values at the Er3+-doped and Er-free parts enables to identify the Er3+-doping effect on substrate index. From the known birefringence, the surface Li2 O contents at the Er3+-doped and Er-free parts were evaluated. A comparison with the Li2 O content data before the anneal treatment allows to obtain the anneal-induced Li2 O loss and hence identify the anneal condition effect on the Li out-diffusion. The results show that the contribution of Er3+-doping to the ordinary index is within the measurement error of 1 × 10−3 and that to the extraordinary index is within ± 1.7 × 10−3, which is just slightly out of the measurement error. The diffusion temperature is while the diffusion environment is not the key factor responsible for the Li2 O out-diffusion. [ABSTRACT FROM AUTHOR]