FABRICATION AND CHARACTERIZATION OF LOW-LOSS, SOL-GEL PLANAR WAVE-GUIDES

Applications of planar integrated optical waveguide (IOW) technology t o problems in surface spectroscopy and optical chemical sensing have b een partly limited by the difficulty of producing high-quality glass I OWs. The fabrication of IOWs by the sol-gel method from methyltriethox ysilane and titanium tetrabutoxide precursors is described here. The p hysical, chemical, and optical properties of the films during and afte r high-temperature annealing were studied using a variety of analytica l techniques. The results show that the catalyst used to accelerate th e sol-gel reaction strongly influenced the optical quality of the IOW. HCl catalysis produced waveguides with propagation losses of similar to 1 dB/cm, whereas in the case of SiCl4 catalysis, propagation losses were <0.2 dB/cm, a value significantly less than any previously repor ted for sol-gel-derived IOWs. An examination of film surface structure and morphology by scanning electron microscopy and atomic force micro scopy showed that the SiCl4-catalyzed IOWs were significantly smoother and more homogeneous on a submicrometer scale than the HCl-catalyzed IOWs. The use of SiCl4 is thought to retard formation of a microhetero geneous network containing Si-rich and Ti-rich domains, which is favor ed with HCl catalysis and contributes to the higher observed losses.