Near-stoichiometric Ti: LiNbO₃ strip waveguides fabricated by standard Ti diffusion and post-VTE

We report near-stoichiometric (NS) Ti: LiNbO₃ waveguides fabricated by indiffusion of 4-, 5-, 6-, 7-μm-wide 120-nm-thick Ti-strips at 1060 °C for 10 h into a congruent LiNbO₃ (i.e., standard Ti diffusion procedure) and post-vapour-transport-equilibration (VTE) treatment at 1100 °C for 5 h. These waveguides are NS and single-mode at 1.5 μm, and have a loss of 1.0/0.8 dB/cm for the TM/TE mode. In the width/depth direction of the waveguide, the mode field follows a Gauss/Hermite-Gauss profile, and the Ti profile follows a sum of two error functions/a Gauss function. The post-VTE resulted in increase of diffusion width/depth by 2.0/1.0 μm. A two-dimensional refractive index profile in the guiding layer is suggested.