Comparison of photorefractive index change in proton-exchanged and Ti-diffused LiNbO3 waveguides

A quantitative comparison of the photorefractive effect in proton-exchanged (PE), annealed-proton-exchanged (APE), and Ti-diffused LiNbO3 waveguides in the visible region is reported. In the low-intensity region, the optically induced index change in PE/APE waveguides is almost 3 orders of magnitude smaller than that of Ti-diffused waveguides for a given intensity, primarily as a result of the increased dark conductivity owing to proton exchange. However, the photorefractive index change at higher intensities is almost the same for all the waveguides. Our results indicate that the optically induced space-charge field is relatively independent of the concentration or the valence state of iron impurities and the waveguide fabrication process.