Silica-titania planar waveguides, produced by radio frequency sputtering have been investigated by waveguided Brillouin spectroscopy. The laser beam was coupled by a prism to different transverse electric modes of the waveguide. Brillouin spectra are mode dependent because the light propagates in the waveguide at different angles for different modes. In waveguides with a single-step profile of the refractive index, two Brillouin peaks for longitudinal phonons, and two for transverse phonons, were observed. Brillouin spectra of waveguides with a graded index profiles show a rich phenomenology of lineshapes, with additional peaks between the two main longitudinal peaks. The experimental data are reproduced by a model which considers the electric field profile in the waveguides, by using the sound velocity of the film as a parameter .
展开▼
