Microstructural and spectroscopic studies of sol-gel derived silica-titania waveguides

Silica-titania planar waveguides were prepared via the sol-gel method from acid-catalyzed solutions of firstly, y-Glycidoxypropyltrimethoxysilane mixe d with tetrapropylorthotitanate (labeled as GT), and secondly, y-Glycidoxyp ropyltrimethoxysilane mixed with both tetrapropylorthotitanate and tetraeth oxysilane (labeled as GTT). Atomic force microscopy, thermal gravimetric an alysis, differential thermal analysis, UV-visible spectroscopy, Fourier tra nsform infrared spectroscopy, and Raman spectroscopy were used to study the structural and optical properties of the waveguide films prepared from the two types of sols. The obtained results showed that in both cases, crack-f ree and highly transparent silica-titania films with a thickness of more th an 0.5 mu m could be obtained by a single spin-coating process after a heat treatment at 500 degrees C. The GT derived films showed more shrinkage and a higher refractive index after annealing as compared to the GTT derived f ilms. When such films were deposited on a silica-on-silicon substrate to ac t as a surface planar waveguide, the light propagation loss was measured to be about 0.9 dB/cm and 1.3 dB/cm respectively. Raman spectroscopy results indicated that the GTT derived waveguide films with 0.5 molar titanium cont ent contained amorphous carbon phase after being heated at above 500 degree s C in air directly.