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Er 3+ /Ti 4+ -co-doped LiNbO 3 plates were prepared by annealing congruent substrates coated with stacked Er- and Ti-metal films having different thicknesses and coating sequences. The crystalline phase, OH − absorption, Er 3+ -doping effect on LiNbO 3 refractive index and Li + -composition in the Er 3+ /Ti 4+ -co-doped layer were studied. The results show that the LiNbO 3 phase dominates in the co-doped layer, the Er 3+ -doping affects little the LiNbO 3 refractive index, slight Li 2 O out-diffusion occurred in the diffusion procedure, and the annealing procedure does not affect the OH − absorption band noticeably. The Er 3+ /Ti 4+ -co-diffusion characteristics were studied by secondary ion mass spectrometry. The study shows that Ti 4+ diffuses much faster than Er 3+ . The Ti 4+ co-diffusion assists and controls the Er 3+ -diffusion and Er 3+ diffusivity increases linearly with initial Ti-metal thickness. In contrast, neither Er-metal thickness nor coating sequence of Ti- and Er-metal films influences the Ti 4+ or Er 3+ diffusivity. The co-diffusion features are explained. A co-diffusion model is proposed. [ABSTRACT FROM AUTHOR]

Abstract: We report that potassium meta-phosphate (KPO3) is an adequate solvent for high-temperature fluxing salt of LiNbO3 crystal. As the KPO3 is used as the solvent, the solubility of LiNbO3 is as high as 3 g g−1 at 1050 °C. The dissolving is fast. Neither solute nor solvent evaporates from the melt during the dissolving procedure. A clear solution is obtained and verified valid for crystal composition analysis using chemical method of inductively coupled plasma atomic emission spectroscopy. To help for understanding the dissolving mechanism, the obtained fluxing melt product was further characterized using X-ray diffraction, nuclear magnetic resonance and Raman scattering spectroscopy. The results show that the melt is amorphous. The P ion in the melt is in the form of low condensation and the Nb ion is likely in the form of Lindqvist ion. Finally, the dissolving mechanism is discussed. [Copyright &y& Elsevier]

Abstract: A thermodynamic study on Li-poor vapor transport equilibration (VTE) in MgO-doped LiNbO3 crystal was carried out. A thorough thermodynamic VTE model is established that considers all of possible factors including the depth relative to crystal surface, VTE temperature and time. To solve the model, the composition on crystal surface was studied as a function of VTE temperature and time. To achieve that, a number of Li-deficient MgO(5 mol% in melt):LiNbO3 crystals were produced by the VTE under different temperatures from 1010 to 1130 °C for different durations up to 395 h, the crystalline phase contained was determined by X-ray powder diffraction and their surface compositions were determined from the measured birefringence. The results show that the Li-deficient crystal keeps the LiNbO3 phase. The surface Li2O-content has an Arrhenius relationship to the VTE temperature and a square-root dependence on the VTE duration. Based upon the VTE temperature and time dependences of surface Li2O-content, the solution to the thermodynamic VTE is obtained and verified experimentally. The solution is crucial to design and produce a Li-deficient MgO:LiNbO3 crystal with desired Li2O-content profile. By using the solution, one can predict the Li2O-content depth profile after a certain VTE time for a given VTE temperature. [Copyright &y& Elsevier]

Abstract: Rare-earth-doping and various post-growth heat treatments effects on OH− absorption in singly Er- and Yb-doped, doubly Er/Mg- and Er/Yb-doped LiNbO3 crystals have been investigated. The OH− absorption in the rare-earth-doped crystals shows definite anisotropy and is stronger in a Z-cut plate. Rare-earth-doping causes considerable OH− absorption reduction. MgO-codoping induces additional reduction. Slight/heavy rare-earth-doping causes slight/considerable spectral shape change. Thermal reduction treatment causes OH− absorption vanishing whether the crystal is originally congruent or near-stoichiometric. Further oxidation treatment renders the absorption reemerged. Li-rich vapor transport equilibration (VTE) treatment causes significant absorption decrease. For a slightly rare-earth-doped Li-rich VTE-treated crystal, its spectral feature is similar to that of the undoped near-stoichiometric crystal; for a heavily rare-earth-doped VTE-treated crystal, its spectral shape preserves the feature of the heavily rare-earth-doped as-grown crystal. For the Er/Mg-codoped crystal studied, the Li-rich VTE also induces an abrupt conversion of peaking position from 3483 cm−1 to 3535 cm−1. The absorption in the Li-rich VTE-treated crystals also reveals aging effects in spectral shape, peaking position and absorption intensity. Li-poor VTE induces significant absorption increase. In addition, the effect of OH− presence on lifetime of Er3+ emission at 1.5 μm was also studied. The results show that the effect is small for the as-grown congruent crystals and slight for Li-rich VTE-treated ones. [Copyright &y& Elsevier]

Abstract: X-, Y- and Z-cut congruently grown bulk Er(1.6, 2.0mol%):LiNbO3 crystals have been thermally treated using the vapor transport equilibration (VTE) technique. Optical absorption and X-ray powder diffraction measurements have been carried out to verify the existence of ErNbO4 precipitates induced by the VTE procedure in these crystals. Scanning electron microscope (SEM) has been used for the direct observation of crystallographic morphology of the ErNbO4 precipitates. The results show that the precipitates lie mainly in the (0001) crystallographic plane of the substrate and preferably grow with a crystallographic morphology of flat polyhedrons with rough dimensions of submicron×micron×micron. The precipitates on the surfaces of Z-cut substrates have only three orientations mutually aligned at approximately 60° or 120° angles being nearly parallel to the crystallographic axes of the host matrix. The SEM results show that VTE conditions and the type of crystallographic cut of the substrate remarkably affect the size and density of the precipitates. [Copyright &y& Elsevier]

The formation of ErNbO4 powder, prepared by calcining an Er2O3 (50 mol%) and Nb2O5 (50 mol%) powder mixture at 1100 and 1600 °C for different durations, was investigated by using X-ray diffraction. The experimental results have displayed that although the solid-state reaction had started to some extent when the mixture was pre-calcined at 1100 °C for a duration of 13 h, the two original phases Er2O3 and Nb2O5 still dominated the mixture. When the duration of the calcination reaction was increased to 120 h at the same temperature, the resultant mixture experienced a nearly complete phase transformation. Accordingly, the ErNbO4 phase was dominant phase in the mixture. Nevertheless, a small portion of the raw powder still existed in the mixture. When the calcining temperature was elevated to 1600 °C, ErNbO4 powder with higher purity could be obtained for a relatively much shorter duration (only up to several tens of hours). A simple formation mechanism of ErNbO4, an elevated-temperature-assisted solid-state chemical reaction: Er2O3+Nb2O5⇌2ErNbO4, is suggested. In addition, the present experimental results offer important evidence for the formation of the additional phase ErNbO4 induced in Er:LiNbO3 crystals by vapour transport equilibration (VTE) treatment. [Copyright &y& Elsevier]

Refractive index of optical material of powder is measured not as easily as a bulk material. Here, the prism coupling technique in combination with the immersion method is proposed to measure the refractive index of an optical material of powder. First, the powder material to be measured was dispersed in α-bromonaphthalene (C10H7Br) liquid to form a suspension mixture. The refractive index of the mixture, together with that of pure C10H7Br, was then measured at the wavelengths of 632.8, 1311, and 1553 nm using a commercial prism coupler. From the measured index values of pure C10H7Br and powder-dispersed mixture, the refractive index of the powder material was obtained on the basis of the Maxwell-Garnett model. Microcrystal powder from a LiNbO3 single-crystal, which has the known refractive index values, has been exemplified to demonstrate the method. The results show that the method is feasible with an accuracy of ±0.05. [ABSTRACT FROM AUTHOR]

Ti-diffused LiTaO 3 strip waveguide was fabricated by in-diffusion of 8-μm-wide, 100-nm-thick Ti-strip at 1300 °C for 6 h in wet O 2 atmosphere. Its composition, surface morphology, lattice parameter, optical properties and Ti profile characteristics were fully characterized. It is shown that the waveguide is in the congruent composition environment. The waveguide surface caves in ∼70 nm below the crystal surface due to Ti-induced lattice contraction, which is verified by X-ray single-crystal diffraction. Optical characterizations show that the waveguide well supports both TE and TM single-mode propagation at the 1.5 μm wavelength, is polarization-insensitive, and has a loss of 0.4 (0.3) dB/cm for the TM (TE) mode. Secondary ion mass spectrometry analysis shows that the Ti profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of the waveguide. [ABSTRACT FROM AUTHOR]

Effects of finite hole depth and non-cylindrical hole shape on stop-band characteristics of photonic crystal formed by air-hole square lattice in Ti-diffused LiNbO 3 strip waveguide were studied theoretically. The study shows that hole depth determines the contrast of stop-band, and the hole radius and conical angle determine the bandgap and location. Cylindrical holes must be sufficiently deep so as to overlap most of waveguide mode and hence obtain a stop-band with high contrast, sharp edge and broad bandgap. Non-cylindrical holes seriously affect the stop-band features. Conical holes cause low contrast and narrow bandgap, and the stop-band shifts with the conical angle. For the cylindrical-conical hybrid holes, the cylindrical portion determines the desired features. Given the difficulty in fabricating high aspect-ratio cylindrical holes, we propose to fabricate the holes at the bottom of a shallow trench, which is introduced into waveguide surface prior to the hole milling. [ABSTRACT FROM AUTHOR]