Characterization of an optical waveguide with a composite structure

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 a 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.