2-DIMENSIONAL DISTRIBUTION OF REFRACTIVE-INDEX CHANGES IN TI-DIFFUSED LINBO3 STRIP WAVEGUIDES

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 Δne and Δn0 were 1×10-2 and 8×10-3, respectively.