title: Tin-diffused glass slab waveguides locally covered with tapered thin TiO2 films for application as a polarimetric interference sensor with an improved performance.
abstract: Common soda lime slide glass substrates made by floating molten glass on the surface of molten tin contain a tin-diffused layer that is demonstrated to be a low-loss polarization-insensitive slab optical waveguide. In this study, such a tin-diffused waveguide was locally covered with a tapered thin TiO2 film to form a composite structure in which the zeroth-order transverse electric (TE0) and magnetic (TM0) modes are spatially separated from each other. This feature enables the composite structure to serve as a highly sensitive polarimetric interferometer. Moreover, a negligible modal birefringence of tin-diffused waveguides offers the polarimetric interferometer an improved performance relative to those fabricated earlier using single-mode potassium ion-exchanged glass waveguides. In situ detection of both the protein adsorption and a small change in refractive index of liquid was accomplished using the tin-diffused waveguide-based polarimetric interferometer. With horse heart myoglobin, adsorption from aqueous solution less than 0.125 monolayer coverage can cause the interferometer to yield a phase-difference change of delta phi = 2pi.
authors.affiliation: Light and Control Research Group, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan.
authors.forename: Zhi-mei
authors.initials: ZM
authors.lastname: Qi
authors.forename: Itaru
authors.initials: I
authors.lastname: Honma
authors.forename: Haoshen
authors.initials: H
authors.lastname: Zhou
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D001718:Birefringence; D007368:Interferometry / Q000379:methods*; D009211:Myoglobin / Q000737:chemistry; D014001:Tin; D014025:Titanium
chemical_list: D009211:Myoglobin; C009495:titanium dioxide; D014001:Tin; D014025:Titanium