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

Refractive index change and Raman scattering of Z-cut proton-exchanged LiTaO3 optical waveguides with different composition have been studied. Probing of the waveguide depth was carried out by using micro-Raman spectroscopy in order to distinguish layers with different phase states. Varying the proton-exchange and post-exchange annealing regimes, two phases --*a and *b-- 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 the phase changes. Using data from waveguide Raman spectra, normal and oblique E(TO, LO) phonons were sorted and their properties were followed in the *a and *b phases. The OH-stretchings are considered to correspond to dipoles turned out of the oxygen planes.