Fabrication and Characterization of Low-Loss, Sol-Gel Planar Waveguides

Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high-quality glass IOWs. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors is described here. The physical, chemical, and optical properties of the films during and after high-temperature annealing were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. HCl catalysis produced waveguides with propagation losses of ∼ 1 dB/cm, whereas in the case of SiCl₄ catalysis, propagation losses were <0.2 dB/cm, a value significantly less than any previously reported for sol-gel- derived IOWs. An examination of film surface structure and morphology by scanning electron microscopy and atomic force microscopy 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 microheterogeneous network containing Si-rich and Ti-rich domains, which is favored with HCl catalysis and contributes to the higher observed losses.