MODIFICATION OF PROTON-EXCHANGED LINBO3 LAYERS FOR GUIDING MODES WITHORDINARY POLARIZATION

To complete preliminary data recently published a detailed description is given for the fabrication procedure of guiding layers with ordinar y polarization on proton exchanged LiNbO3 waveguides. The process of ' 'reverse exchange'' of a substrate previously exchanged in benzoic aci d is carried out in a melt very rich in lithium. The influence of seve ral parameters on the process is studied. Melts with different concent rations of LiNO3 produce the same ordinary index profiles: they are pa rabolic-like for X- and Y-cut substrates and gaussian-like for Z-cut s ubstrates. On the other hand, 10% lithium benzoate melts produce sharp er, steplike profiles on Y-cut substrates and gaussianlike on Z-CUL On increasing the treatment temperature from 300-degrees-C to 375-degree s-C, the process speeds up and ordinary profiles appear smoothed. By c hoosing appropriated treatment parameters, losses for ordinary modes h ave been found to be below 0.7 dB/cm. The occurrence of buried extraor dinary modes induced by the reverse exchange treatment has been confir med here. Also, protons introduced during normal exchange in benzoic a cid partially go out of the guide during reverse exchange, as monitore d by the OH- infrared absorption band.