Two-dimensional distribution of refractive-index changes in Ti-diffused LiNbO3 strip waveguides

Abstract

A method is reported for determining the two‐dimensional distribution of refractive‐index changes in Ti‐diffused LiNbO₃ strip waveguides. The measurement process was as follows. Distributions of diffused Ti concentration in LiNbO₃ were measured using an x‐ray microanalyzer. Using calibration curves the Ti concentrations were then converted into refractive‐index changes. To obtain high spatial resolution in the two‐dimensional XMA measurement the electron beam position was fixed and the sample was moved at a constant velocity. Lateral sliding of the sample perpendicular to the scanning direction was peformed mechanically, and the measured XMA data were corrected for edge effects. The results obtained for the Y‐cut LiNbO₃ waveguide diffused at 1000 °C for 10 h with a 10‐μm‐wide 500‐Å‐thick Ti strip showed that lateral diffusion of Ti was marked. The contour with a refractive‐index change of 1×10⁻³ is of approximate depth 3.5 μm and width 40 μm. The maximum values of Δn_e and Δn₀ were 1×10⁻² and 8×10⁻³, respectively.