Proton-exchange influence on the polar phonons of LiTaO3 optical waveguides

Refractive index change and Raman scattering of Z-cut proton-exchanged LiTa O3 optical waveguides with different composition have been studied. Probing of the waveguide depth was carried out by using micro-Raman spectroscopy i n order to distinguish layers with different phase states. Varying the prot on-exchange and post-exchange annealing regimes, two phases - alpha and bet a - in addition to the pure LiTaO3, were clearly observed. The behaviour of the A(1) vibrations of the TaO6 groups was found to be very sensitive to t he phase changes. Using data from waveguide Raman spectra, normal and obliq ue E(TO, LO) phonons were sorted and their properties were followed in the alpha and beta phases. The OH-stretchings are considered to correspond to d ipoles turned out of the oxygen planes.