GUIDED MODES WITH ORDINARY REFRACTIVE-INDEX IN PROTON-EXCHANGED LINBO3 WAVE-GUIDES

A method is proposed and demonstrated to fabricate guiding layers on ordinary refractive index in proton exchanged LiNbO3 waveguides. The process consists of performing a reverse exchange in a melt very rich in lithium on a substrate previously exchanged in normal benzoic acid. Layers supporting several modes with ordinary polarization are easily obtained. Losses for these modes have been found to be below 0.7 dB/cm. Together with the increase of ordinary index, a decrease of the extraordinary one is obtained so that buried modes can be guided with this polarization. The influence on the reverse process of the exchange temperature, the substrate cut, and the melt composition is studied.