Refractive index profile in photorefractive-damage-resistant near-stoichiometric Ti:Mg:Er: LiNbO ₃ strip waveguide

Refractive index profile in photorefractive-damage-resistant near-stoichiometric (NS) single-mode Ti:Mg:Er: LiNbO ₃ strip waveguide is constructed from the measured mode field distribution. Like the conventional congruent Ti:LiNbO ₃ waveguide, the Ti-induced refractive index increase in the NS waveguide studied here follows a sum of two error functions in the width direction and a Gaussian function in the depth direction. Based upon the established index profile model, the mode sizes were calculated using the variational method and compared with the experimental results. The Ti-induced index increment at the NS waveguide surface was also evaluated according to the empirical relation previously reported for the conventional congruent Ti: LiNbO ₃ waveguide and compared with the data deduced from the mode field distribution. All comparisons show good agreement, showing that the index model proposed is close to the practical scenario.