Characterization of LiNbO3 waveguides fabricated by proton exchange in water

Proton exchange of LiNbO3 substrates has been achieved by immersing the samples in distilled water in sealed ampoules at temperatures between 190 degrees C and 300 degrees C. The samples have been studied by infrared spectra analysis, dark mode reflectivity and X-ray rocking curve diffraction. The results obtained show that exchange rates as high as with common acids (similar to 85%) are easily reached. The structure of the exchanged waveguides varies from the low index alpha-phase to the high index beta-phases depending on the temperature and time length of the exchange process, as well as on the distilled water amount used. Optical waveguides made up of phases of high, sharp index jump (Delta n(e) similar to 0.12) as well as of low index jump and very low propagation losses (0.5 dB/cm) have been obtained and characterized.