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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]

Multi-mode Ti:LiNbO 3 planar waveguide was fabricated by in-diffusion of 100-nm-thick Ti-metal film coated onto a near-stoichiometric LiNbO 3 substrate prepared by vapor transport equilibration. The crystalline phase and composition in the waveguide were characterized. The guided modes in the planar waveguide were characterized by prism coupling technique. The refractive index profile is constructed from the measured mode indices using the inverse Wentzel–Krames–Brillouin method, and correlated with the Ti 4+ - concentration profile, which was obtained from secondary-ion-mass-spectroscopy analysis. The results show that the waveguide still retains the LiNbO 3 phase, its composition is near-stoichiometric. The index change and Ti 4+ -concentration follow an exponential relationship with a power index 0.4 for an ordinary ray and 1.07 for an extraordinary ray. A comparison of various congruent and near-stoichiometric bulk materials or waveguides allows to conclude that the relationship is different from congruent to near-stoichiometric composition, from one fabrication method to another, and from bulk material to waveguide configuration. The difference is explained qualitatively. [ABSTRACT FROM AUTHOR]

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: Secondary ion mass spectrometry (SIMS) was used to study the diffusion properties of Mg2+ and Ti4+ ions in a peculiar optical-damage-resistant near-stoichiometric (NS) Ti:Mg:LiNbO3 waveguide structure that a number of strip waveguides are embedded in a planar waveguide. The structure was fabricated on an initially congruent, undoped Z-cut substrate with a technological process in sequence of planar waveguide, strip waveguide, MgO diffusion and post Li-rich vapor transport equilibration (VTE) treatment. The results show that the Mg2+-profiles in both strip and planar waveguide layers are desirably homogeneous with a concentration 1.7±0.3mol% above the optical damage concentration threshold. The Ti4+-profile in the strip waveguide follows a sum of two error functions along the lateral direction with a width 13±1.0μm and a sum of two Gaussian functions in the depth direction with a 1/e depth of ∼11μm all. The Ti4+ ions in the planar waveguide obey a Gaussian profile. From the measured profiles, characteristic diffusion parameters such as mean Mg2+ and Ti4+ diffusivities and surface Ti4+-concentration are evaluated. The diffusivity is discussed in comparison with the previously reported results on single Mg2+, Ti4+ diffusion and Mg2+/Ti4+ co-diffusion in pure (or bulk MgO-doped), congruent (or NS) LiNbO3 crystal. Finally, the keys to the succeeding in fabrication are highlighted. [Copyright &y& Elsevier]

Abstract Gallium-diffused lithium niobate (LiNbO 3) channel optical thin-film was fabricated by diffusion of photolithographically patterned gallium-oxide stripes on a Z-cut congruent LiNbO 3 substrate. Composition, optical properties of the channel thin-film and gallium diffusion profiles were characterized. The results show that the thin-film is in congruent composition environment, confines single-mode ordinary and extraordinary waves with a loss <0.5 dB/cm at 1.5 μm wavelength. The confined mode field follows Gaussian/Hermite-Gaussian profile in the width/depth direction of the channel thin-film, and shows definite anisotropy. The diffused gallium ions follow a sum of two error functions in the width and a Gaussian function in the depth direction of the channel optical thin-film. Two-dimensional gallium concentration and refractive index profiles in the channel thin-film are modeled. [ABSTRACT FROM AUTHOR]

Ga 3+ -diffused lithium tantalate (LiTaO 3 ) strip optical waveguide was fabricated by diffusion (at 950 °C for 1.5 h) of 8-μm wide, 112-nm thick Ga 2 O 3 -strips photolithographically patterned onto a Z-cut congruent LiTaO 3 substrate. Crystalline phase, composition, optical properties and profile characteristics of Ga 3+ ions in the waveguide were investigated. We show that the waveguide retains LiTaO 3 crystalline phase and is in congruent composition environment. Optical studies show that the waveguide supports single-mode propagation (at the 1.5 μm wavelength) of not only the extraordinary wave but also the ordinary wave, shows considerable polarization dependence in mode field distribution, and has a loss of 0.2/0.4 dB/cm for the ordinary/extraordinary wave. Secondary ion mass spectrometry analysis shows that the Ga 3+ profile follows a sum of two error functions (a Gaussian function) in the width (depth) direction of the waveguide. [ABSTRACT FROM AUTHOR]

Ti-diffused near-stoichiometric(NS) LiTaO 3 multimode planar waveguide was fabricated by diffusion of Ti-film coated onto a congruent LiTaO 3 substrate and post Li-rich vapor transport equilibration process. The crystalline phase in the Ti-diffused layer was analyzed by powder x-ray diffraction and the Li 2 O-content was evaluated from the measured birefringence. The Ti-concentration profile was analyzed by secondary ion mass spectrometry. The modes guided in the planar waveguide were characterized by prism-coupling technique. The refractive index profile was constructed from the measured mode indices, and correlated with the Ti-concentration profile. The results show that the waveguide retains the LiTaO 3 phase and is in an NS composition environment. Both the refractive index and Ti-concentration follow Gaussian profile. The extraordinary and ordinary index change profiles are almost same, implying that the electric field profile of the mode guided in the NS Ti:LiTaO 3 waveguide would be polarization-insensitive. The ordinary and extraordinary index changes and the Ti-concentration follow a similar exponential relationship with a power index ∼1.3. Comparison shows that the Ti:LiTaO 3 waveguide shows considerable differences from the Ti:LiNbO 3 in Ti diffusivity, index change profile and its relation to Ti-concentration, and polarization dependence of guided mode. [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]

Abstract: Diffusivity of Li+ in 5mol% (in growth melt) MgO-doped LiNbO3 crystal has been studied as a function of Li2O-content ranging from 43.4 to 44.4mol% under different temperatures. First, diffusion-limited Li2O-content depth profiles were produced by carrying out Li-poor vapour transport equilibration (VTE) treatments on two 0.5-mm-thick MgO-doped LiNbO3 plates at 1100 and 1130°C for 40h. Second, the profiles were obtained by alternatively doing the optical polish to one crystal surface and the Li2O-content characterization on the polished surface through the measurement of birefringence. Third, Boltzmann–Matano method was applied to the profile to derive the Li+ diffusivity as a function of Li2O-content. The results show that the diffusivity decreases with the reduced Li2O-content by at least two orders of magnitude as the Li2O-content reduces by 1mol% from the as-grown state. In the Li2O-content range studied, the diffusivity at 1130°C is at least two times larger than that at 1100°C. In addition, we also studied the time dependence of the Li-poor-VTE-induced reduction of Li2O-content on surface of the same MgO-doped crystal. The results show that the surface Li2O-content reduction induced has a square-root dependence on the VTE duration. Based upon this dependence, the mathematical solution to the Li+ diffusion equation, an integral of error function complement, is obtained and verified by the experimental result. It is concluded that the MgO doping has less effect on both the Li+ diffusivity and the dependence of surface Li2O-content reduction on the VTE duration. [Copyright &y& Elsevier]