Optical and surface properties of inorganic and hybrid organic-inorganic silica-titania sol-gel planar waveguides

Inorganic and hybrid organic-inorganic silica (SiO2)-titania (TiO2) planar waveguides, with a relative molar composition 70-30, have been fabricated by sol-gel dip-coating. The composition and the density of the film samples have been measured by Rutherford backscattering spectrometry, nuclear reaction analysis and elastic recoil detection analysis. The measured compositions have been found to agree with the nominal composition of the sols. The film density of the inorganic samples increased with the firing temperature in the range 1.80-2.58. A root mean square roughness (rms) <1 nm was measured on the surface of the samples by atomic force microscopy. A refractive index in the range 1.61-1.54 was measured (λ = 632.8 nm). The inorganic waveguides had smaller losses (approximately 0.3 dB cm-1) compared to the hybrid waveguides (approximately 1 dB cm-1).