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 °C and 300 °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 (85%) are easily reached. The structure of the exchanged waveguides varies from the low index -phase to the high index -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 (n_e0.12) as well as of low index jump and very low propagation losses (0.5 dB/cm) have been obtained and characterized. PACS 42.82.Et; 42.70.Mp