Electro-Optic Property of Er 3+ -Doped LiNbO 3 Single Crystal for Integrated Optics

Er 3+ -doping effect on electro-optic property of LiNbO 3 crystal has been studied. A series of congruent LiNbO 3 crystals homogenously doped with different Er 3+ concentrations up to 2 mol% in melt were grown. Unclamped electro-optic coefficients ${r} _{13}$ and ${r} _{33}$ of these crystals were measured by Mach–Zehnder interferometry. The results show that both ${r} _{13}$ and ${r} _{33}$ reveal little dependence on Er 3+ doping level. $r_{13}$ hardly changes in the studied Er 3+ doping level range 0–2 mol% within the experimental error of 3%. $r_{33}$ reveals a degradation tendency with a rise in the Er 3+ doping level, but the degradation is no more than 5% in the Er 3+ doping level range studied. The small effect is consistent with previous result that the performance of an electro-optic device based on Ti 4+ -diffused Er 3+ -doped LiNbO 3 waveguide is not influenced noticeably by Er 3+ -doping. A qualitative, comprehensible explanation is given for the small effect.