Low cost sol gel derived silica-titania waveguide films – Characterization

Abstract

This work reports a study on low-loss waveguide layers for planar evanescent wave sensor applications. Crack-free SiOx:TiOy composite layers with refractive indices of ∼1.65, in the visible spectra range, were fabricated using a sol-gel method and a dip-coating technique. Layers of thickness in the 220–360 nm range were produced in a single coating process. By multiple coatings, SiOx:TiOy composite layers of thickness up to 1000 nm were produced. Fabricated layers demonstrated good waveguide properties in the Vis spectral range. The dispersion characteristics of the developed layers refractive index were determined using the spectroscopic ellipsometry method. Spectrophotometric tests validated their optical homogeneity. Using the Tauc method, the widths of optical band gaps were determined, and their high values (Eg > 3.7 eV) attest to the amorphous nature of the layer material. The FT-IR studies testified to Si-O-Ti bonds, an attribute of amorphous SiOx:TiOy composites. The tests of surface morphology of the SiOx:TiOy layers, using atomic force microscopy, scanning electron microscopy, and optical profilometry, confirmed their high smoothness. Using the m-line method, waveguide properties and optical losses were examined. To facilitate the interpretation of the experimental results, the mode characteristics and the calculated impact of surface morphology of the waveguide layer.