Microstructural and optical properties of sol-gel silica-titania waveguides

Two micron silica-titania coatings made by single step sol-gel dip-coating were prepared as planar waveguides. Acid catalyzed solutions of methyltriethoxysilane (MTES) mixed with tetraethoxysilane (TEOS) and tetrabutoxytitanate were used as precursors. Purely inorganic and crackfree silica-titania coatings were obtained after annealing at 500 degrees C. The waveguides had propagation losses, 0.3 dB/cm, of the same order as thin silica-titania films prepared without MTES, Films were studied by infrared spectroscopy, Rutherford backscattering spectrometry, nuclear reactions analysis and elastic recoil detection analysis. The waveguide structural composition after annealing at 500 degrees C was found to be similar to MTES and TEOS derived silica-titania coatings. The waveguides were characterized by measuring refractive index, porosity and shrinkage, with thermal treatment. The MTES derived films showed a higher shrinkage during annealing but the same refractive index and porosity as the TEOS derived waveguides. (C) 1997 Elsevier Science B.V.