Dynamic Simulation For Li-Ti Indiffusion Simultaneous: Fabrication Of Near-stoichiometric Ti: LiNbO₃ Optical Waveguide

This dissertation presents a detailed dynamic simulation study firstly to the best of our knowledge, on the physical process of simultaneous work of vapor transport equilibration (VTE) and Ti indiffusion on surface of a congruent LiNbO₃ substrate, to fabricate a near-stoichiometric Ti:LiNbO₃ strip waveguide.In the first part of this dissertation, a single VTE procedure without co-diffusion of Ti-metal was dynamically simulated. At first, the Li diffusion model was proposed on the basis of Fick's law, then the established diffusion equation and boundary condition were discreted by using the implicit finite difference method and relative difference equations were given. To solve the difference equations, the relationship between Li diffusivity in LiNbO₃ crystals with different cuts and Li₂O concentration inside the crystal was determined according to the following two steps: (1) fitting the previously reported experimental data of Li₂O concentration; (2) processing the fitted data of Li₂O concentration with Boltzman-Matano method. Afterwards, a series of VTE procedures on LiNbO₃ crystals that possess different thicknesses and cuts were dynamically simulated. Dependences of [Li]/[Nb] ratios inside the crystals on the VTE duration were presented from the simulation results. To varify the reliability of the numerical method adopted, the numerical result under the VTE condition of 1100℃/24h was compared with the reported experimental data. As a result our numerical result is in well agreement with the experimental data. Typically, the thickness of a diffused-type optical waveguide is less than 20μm, so the averaged [Li]/[Nb] ratios were colleted, discussed and analyzed especially. The effect of crystal thickness on Li₂O concentration inside the crystal was clarified. In addition, the error sources in the numerical simulations were analyzed.On the basis of above work, further dynamic simulations were carried out on single Ti diffusion procedure as well as on the procedures of simultaneous work of Li- and Ti-indiffusion. The numerically simulated results about the single Ti-indiffusion were consistent with the results alreadly reported in the earlier literatures, showing the validity of our numerical approach. To simulate the Li-Ti codiffusion procedure, we processed the secondary ion mass spectrum (SIMS) experimental data at first, from which the Ti concentration curves along depth and lateral directions of the Z-cut LiNbO₃ crystal were obtained. The data processing results show that Ti concentration profile along the depth direction follows complementary error function, while along lateral direction it can be fitted by a sum of two error funcions. Qualitative analysis...