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Diffusivity of Er3+ into LiNbO3 crystal has been studied as a function of Li2O content and crystal orientation. The Li2O content in single-crystal LiNbO3 plates was adjusted by Li-rich vapor transport equilibration (VTE) technique. Five X-cut and five Z-cut congruent substrates were VTE treated at first at 1100 °C for different durations ranging from 6 to 74 h, and then were subjected to a special post-VTE anneal procedure at the same temperature for 60 h to obtain homogeneous Li2O content. The Li2O content was determined from the measured fundamental optical absorption edge. Its homogeneity is verified by measuring the optical absorption edge as a function of the crystal thickness. After the composition characterization, the substrates were coated with 45 nm thick Er film and annealed at 1130 °C for 40 h in argon atmosphere. The Er3+ profile was analyzed by secondary ion mass spectrometry. The results show that the Er3+ diffusivity decreases monoexponentially with the increase in the Li2O content in both cases of X- and Z-cut. As the Li2O content is increased from the congruent point (48.4 mol %) to the near-stoichiometric composition (∼49.9 mol %), the diffusivity decreases from 0.107 (0.072) to 0.017 (0.018) μm2/h for the Z (X)-cut substrate. The diffusion shows considerable anisotropy for the lower Li2O content and the diffusivity in a Z-cut substrate is larger. The anisotropy weakens gradually with the increase in the Li2O content, and the diffusivities in the X- and Z-cut substrates ultimately tend to a same value (∼0.02 μm2/h) at the Li-rich phase boundary. After the Er diffusion procedure, endface coupling experiment was carried out to check if a planar waveguide layer was formed near the Er-diffused surface due to the Li outdiffusion. The results show that the Li outdiffusion did not accompany the Er diffusion procedure. [ABSTRACT FROM AUTHOR]

Diffusion properties of Tm3+ in congruent LiNbO3 crystal have been investigated, together with other two related issues, i.e., Tm3+-doping contribution to refractive index of LiNbO3 substrate and Li out-diffusion. Four X-cut and four Z-cut congruent LiNbO3 substrates locally coated with 15-31 nm-thick Tm-metal films were annealed in surrounding air under different temperatures of 1030°C-1130°C for different durations of 20-70 h. After anneal, refractive index at Tm3+-doped and Tm3+-free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li2 O contents were evaluated from measured refractive index. The results show that Tm3+ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti4+- or Zn2+ doping. The Li2 O content at the Tm3+-doped surface equals that at the Tm3+-free surface. The Li out-diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out-diffusion is not measurable. At 1130°C, a 30-h diffusion procedure may cause 0.2-0.3 mol% slight loss of Li2 O content. Secondary ion mass spectrometry was used to study the Tm3+ diffusion properties. The results show that the diffused Tm3+ ions in all samples follow a complementary error function profile. From measured Tm3+ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er3+ diffusion. In comparison with Er3+ diffusion, the Tm3+ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm3+ has a lower diffusivity than the Er3+, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C. [ABSTRACT FROM AUTHOR]

Locally Er3+-doped noncongruent, Li-deficient Ti:Er:LiNbO3 strip waveguide was fabricated with a technological process in sequence of preparation of Li-deficient LiNbO3 substrate using Li-poor vapor transport equilibration (VTE), Er3+, and Ti4+ diffusion in wet O2. The Li2O content change was evaluated from the measured birefringence. The Ti4+ and Er3+ profile characteristics in the waveguide were studied by secondary ion mass spectrometry. The results show that the VTE and subsequent Er3+ diffusion procedures resulted in totally ∼0.8 mol% Li2O content reduction. The Ti4+ profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of waveguide. The Er3+ profile follows also a Gaussian function. At 1130 °C, the Ti4+ surface/depth diffusivity and surface concentration are 8.5 ± 1.3/1.98 ± 0.06 μm2/h and ∼7 mol%, respectively, and the Er3+ diffusivity and surface concentration are (12.8 ± 0.3) × 10−2 μm2/h and ∼0.6 mol%, respectively. [ABSTRACT FROM PUBLISHER]

We have measured the polarized visible and near-infrared, and unpolarized mid-infrared (2.7 \mum) emission spectra of photorefractive-damage-resistant locally Er-Mg-doped near-stoichiometric (NS) Ti:Mg:Er:LiNbO3 strip waveguide, fabricated on an X-cut initially congruent LiNbO3 substrate in sequence by local Er doping in air, Mg-Ti pre-diffusion in wet O2 and post Li-rich vapor transport equilibration treatment. From the measured emission spectra, the emission and absorption cross section spectra were calculated based upon McCumber theory. The spectroscopic features are discussed in comparison with the spectra recorded from the area outside the waveguide, and with the previously reported results of bulk-doped NS Er:Mg:LiNbO3 crystals and congruent Er:LiNbO3 bulk material or Ti:Er:LiNbO3 waveguide structure. The results show that the spectra of the NS waveguide are traditional and reveal small differences from those spectra outside the waveguide in spectral shape, polarization dependence, as well as cross section values. In contrast, the cross section values of the NS waveguide show considerable differences from those of bulk-doped NS material and congruent bulk material or waveguide structure. The 552, 673, 996, and 1531 nm emission lifetimes of the Er^3+ ions outside the waveguide were also measured, and found to be comparable to the results of the bulk-doped NS crystal and the congruent bulk material or waveguide structure. [ABSTRACT FROM PUBLISHER]

Abstract: Starting with evolution equation of signal optical power in an Er-doped channel waveguide, rigorous theoretical expressions used for correct determination of net gain from signal enhancement measured by using pump-on/off method are derived. These expressions allow to clarify the argument on relationships between net gain, internal gain and signal enhancement in some earlier literatures. Physical implications of net gain, internal gain and signal enhancement expressions are analyzed. Standardized definitions for the three physical quantities are proposed. The definition for net gain is proposed on the basis of practical application of an EDWA in optical fiber communication and the definitions for the latter two are suggested based on the physical implication analysis of their expressions. [Copyright &y& Elsevier]

Diffusion characteristics of Zr4+ in LiNbO3 single-crystal were studied. Zr4+-doped LiNbO3 crystal plates were prepared by in-diffusion of 100 nm thick ZrO2 film coated onto Z-cut congruent substrates in wet O2 at different temperatures. Zr4+-diffused profile was analyzed by secondary ion mass spectrometry. The results show that the Zr4+ diffusion follows the traditional diffusion theory. From the measured profiles, important diffusion parameters are obtained, such as diffusivity and its temperature dependence, diffusion constant, activation energy, surface concentration, and solubility. The Zr4+ has a diffusivity similar to that of Ti4+, implying that the Zr4+ doping and the Ti4+ diffusion can be performed simultaneously to simplify the fabrication process of a photorefractive-damage-resistant Zr4+-doped Ti-diffused LiNbO3 waveguide. [ABSTRACT FROM AUTHOR]