Judd-Ofelt spectroscopic study of Er:In:LiNbO₃ crystals for integrated optics

Er:In:LiNbO₃ crystals were grown by Czochralski method from congruent melts containing 0.5/0.5, 0.5/1.0, and 0.5/1.5 mol%/mol% Er ₂O₃/In₂O₃. The Er and In concentrations in the crystals were determined by neutron activation analysis. The refractive indices at the 473, 633, and 1536 nm wavelengths were measured by prism coupling technique. The unpolarized Er³⁺ and OH^- absorption spectra of the crystals were measured at room temperature. The Er³⁺ absorption cross-section spectra were determined, and the Er³⁺ spectroscopic properties were analyzed by Judd-Ofelt (J-O) theory. The In segregation coefficient is 1.20±0.06, 0.95±0.05, and 0.89±0.05, respectively, and the Er concentrations in all of the three crystals studied have a nearly same value of 1 mol%. The ordinary index decreases while the extraordinary index increases with the increased In doping level. The 0.5 and 1.0 mol% In₂O₃-doped two crystals are below while the 1.5 mol% In₂O₃-doped crystal is above the photorefractive threshold concentration. The Er³⁺ absorption cross sections of some transitions change definitely due to In codoping, but reveal a weak dependence on the In₂O₃ doping level. The J-O-predicted spectroscopic parameters show similar In codoping effects. The In codoping hardly affects the Er³⁺ 1.5 μm radiative lifetime.