A new optical waveguide (OWG) with a composite structure was designed and fabricated for chemical and biological sensing applications. The composite OWG consists of a uniform TiO2 film and a pair of tapered SiO2 films coated together on the surface of a single-mode potassium ion-exchanged (PIE) planar waveguide. By use of the TiO2 film-covered SiO2 tapers as optical directional couplers,the TiO2 film becomes a single-mode waveguiding layer with an enhanced evanescent field and an increased surface-scattering loss. Such composite structure can be used to make a polarimetric OWG interferometer and to make the polarization-insensitive PIE waveguide a TM polarizer. The composite OWG was characterized theoretically and experimentally.
Zhi-Mei Qi, Naoki Matsuda, Kiminori Itoh, and De-Kui Qing, "Characterization of an Optical Waveguide With a Composite Structure," J. Lightwave Technol. 20, 1598- (2002)