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Abstract: Noncongruent nearly stoichiometric/lithium‐deficient LiTaO3 crystal was grown by lithium‐rich/lithium‐deficient chemical vapor‐phase‐equilibration (VPE) technique, and low‐cost two‐phase powder LiNbO3‐Li3NbO4 or LiNbO3‐LiNb3O8 instead of expensive LiTaO3‐Li3TaO4 or LiTaO3‐LiTa3O8 was used in the VPE experiments. The LiTaO3 crystalline phase in the lithium‐rich/lithium‐deficient crystal was confirmed by X‐ray analysis. The lithium‐rich/lithium‐deficient VPE‐induced lithium‐oxide (Li2O) molar content increase/reduction was measured as a function of VPE duration using gravimetric method, and empirical relations between them are presented for both cases. We show that both the lithium‐rich and lithium‐deficient VPE techniques based on the two‐phase powder LiNbO3‐Li3NbO4 or LiNbO3‐LiNb3O8 can be successfully used to adjust the lithium‐oxide content in a LiTaO3 crystal and produce a noncongruent nearly stoichiometric or lithium‐deficient crystal plate with desired lithium‐oxide content. [ABSTRACT FROM AUTHOR]

A series of Mg2+/Er3+-codoped congruent LiNbO3 crystals were grown by Czochralski method from the growth melts containing 0.5 mol% Er2O3 while varied MgO content from 0.0 to 7.0 mol%. The unclamped electro-optic coefficients γ13 and γ33 of these crystals were measured by Mach-Zehnder interferometry. Two different voltage-applying schemes were adopted: one is the DC voltage applied to the crystal via Al films coated onto crystal surfaces and another is via a pair of external Cu slab electrodes. The coefficients measured by the two schemes show similar strong dependence on Mg2+ concentration. The dependence is non-monotonous, dramatic, and unusual, and reveals the features of two Mg2+ concentration thresholds of optical damage: one in the Mg2+ concentration range of 1.2-2.0 mol% (in crystal) and another in 4.5-5.0 mol%. Around the threshold the electro-optic coefficient decreases abruptly at first and then recovers quickly, and the coefficient drops by >20% (12%) at the first (second) threshold, which exceeds the error 3% considerably. The dramatic behavior is qualitatively explained on the basis of the EO coefficient model of LiNbO3 and the defect structure model for Mg2+-doped LiNbO3. [ABSTRACT FROM AUTHOR]

Zr4+/Ti4+-codoped LiNbO3 plates were prepared by local codiffusion of stacked ZrO2 and Ti metal films coated onto Z-cut congruent LiNbO3 substrates in wet O2 at 1060°C. The metal and oxide films have different thicknesses and coating sequences. After diffusion, the Zr4+ doping effect on the refractive index of LiNbO3 and the Li2O out-diffusion issue were studied by the prism coupling technique. The codiffusion characteristics of Zr4+ and Ti4+ were studied by secondary ion mass spectrometry. The results show that the Zr4+ doping has little contribution to the refractive index of the crystal. Li2O out-diffusion is not measurable. In the Zr4+-only diffusion case, the diffusivity of Zr4+ is four times smaller than that of Ti4+. In the Zr4+/Ti4+ codiffusion case, the Ti4+ codiffusion assists the Zr4+ diffusion. The Zr4+ diffusivity increases linearly by two more times with the increase in initial Ti film thickness from 0 to 200 nm. On the other hand, the Zr4+ affects the Ti4+ diffusion little. Neither the ZrO2 film thickness nor the coating sequence of Ti metal and ZrO2 oxide films influences the diffusivity of the two ions. All the codiffusion characteristics are explained. A Zr4+/Ti4+ codiffusion model is suggested that consists of two independent diffusion equations with a Zr4+ diffusivity dependent of Ti4+ concentration and a constant Ti4+ diffusivity. In addition, the existence of a waveguide in the Zr4+/Ti4+-codoped layer is verified experimentally, and the optical-damage-resistant feature of the waveguide is verified by two-beam hologram recording experimental results. [ABSTRACT FROM AUTHOR]

Diffusion properties of Sc3+ in LiNbO3 crystal were studied, together with other two related issues: Sc3+-doping effect on LiNbO3 refractive index and Li2 O out-diffusion arising from Sc3+ in-diffusion. To reach the goal, some Sc3+-doped LiNbO3 crystal plates were prepared by in-diffusion of Sc2 O3 film coated onto Z-cut congruent substrates in air at different temperatures ranging from 1030°C to 1130°C. After diffusion, the refractive indices at the doped and undoped parts of surface were measured by prism coupling technique and the surface composition was evaluated from the measured index. The results show that the Sc3+ doping has little contribution to the substrate index and the Li2 O out-diffusion is not measurable. The Sc3+ profile was analyzed by secondary ion mass spectrometry. Some characteristic parameters such as temperature-dependent diffusivity, diffusion constant, activation energy, and surface concentration are obtained. The Sc3+/ Ti4+ co-diffusion characteristics were also studied. Comparison shows that in the single-diffusion case, the Sc3+ diffusivity is considerably smaller than the Ti4+ diffusivity. In the Sc3+/ Ti4+ co-diffusion case, the Ti4+ co-diffusion results in substantial increase in Sc3+ diffusivity while the Ti4+ diffusivity changing little. The diffusion characteristics are qualitatively explained. The Ti4+-assisted Sc3+ diffusion would be utilizable in shortening the fabrication period of an optical-damage-resistant Ti-diffused LiNbO3 waveguide doped with Sc3+, and some considerations for the fabrication are given. [ABSTRACT FROM AUTHOR]

Co-diffusion characteristics of Er3+ and Tm3+ ions in LiNbO3 crystal have been studied, together with two other properties: doping effect on refractive index of substrate, and Li out-diffusion. Er3+/ Tm3+-codoped LiNbO3 single-crystals were prepared by co-diffusion of stacked Er- and Tm-metal thin films, coated onto parts of the surfaces of X- and Z-cut congruent LiNbO3 crystal plates, at different temperatures and different durations in air. After diffusion, the surface refractive indices of the doped and undoped parts were measured by prism coupling technique, and the surface composition was evaluated from the measured indices. The results show that the dopings have negligible effect on the substrate index and the Li out-diffusion depends mainly on the diffusion temperature. The Er3+ and Tm3+ profiles were studied using secondary ion mass spectrometry, and a co-diffusion dynamical model is proposed and verified experimentally. From the measured profiles, the temperature-dependent Er3+/ Tm3+ diffusivity and solubility were obtained together with other relevant parameters, such as diffusion constant, activation energy, solubility constant and heat of solution. The Er3+ and Tm3+ co-diffusion exhibits similar temperature dependent diffusivity, and the dependence is similar to that of single-diffusion. In the co-diffusion case, the total solubility consists of two parts: Er3+ and Tm3+ parts, there is no anisotropy, and the value is equal to that of single-diffusion case, in which both ions have the similar solubility. The Er3+ and Tm3+ parts of solubility change relatively with the initial metal film thicknesses and hence have different temperature dependences. Nevertheless, their sum, i.e., the co-diffusion solubility, remains a constant at a given temperature. [ABSTRACT FROM AUTHOR]

Diffusivity at 1130°C of Li+ in LiNbO3 crystal in off-congruent, Li-deficient regime has been studied as a function of Li2O-content. A diffusion-limited Li2O-content reduction depth profile in an X- or Z-cut plate, ranging from 47.2 to 48.5 mol%, was produced by carrying out Li-poor vapor transport equilibration ( VTE) treatment on 1-mm-thick, initially congruent plates at 1130°C for 150 h. The profile was obtained by alternatively doing the optical polish to one crystal surface and the Li2O-content characterization on the polished surface through the measurement on birefringence. The Boltzmann-Matano mathematical analysis was applied to the profile to obtain the Li2O-content dependence of Li+ diffusivity. The results show that the diffusivity decreases with the decreased Li2O-content and the decrease is by at least one order of magnitude as the Li2O-content decreases by 1 mol% from 48.5 mol%. The diffusion shows slight anisotropy and is faster along the optical axis direction of crystal. In combination with previously reported result in the near-stoichiometric regime, the diffusivity over the Li2O-content range from 47 to 50 mol% is presented. [ABSTRACT FROM AUTHOR]