title: Asymmetric Mach-Zehnder interferometers without an interaction window in polymer foils for refractive index sensing.
abstract: We report on the fabrication and characterization of integrated Mach-Zehnder interferometers in polymer foil without an interaction window. The interferometers are based on inverted rib waveguides, which allow single mode behavior even for waveguide widths larger than a few micrometers. The phase change between the two interferometer arms upon a refractive index change of the analyte that serves as the upper cladding is generated by the asymmetricity of the two interferometer arms. A difference of the waveguide width in the straight part of the interferometer leads to different effective refractive indices and thus to a change in the interference signal. We show in small scale the process chain, which is compatible with a cost-effective roll-to-roll fabrication process. For a proof of principle we apply deionized water and a glucose solution as analytes to the sensor foils and detect the transmitted intensity as a measure of the induced phase change. A detection limit of 3·10⁻³ refractive index units is reached for homogeneous sensing at a total system length of 9.3 mm and a total waveguide core thickness of 3 μm.
authors.forename: Meike
authors.initials: M
authors.lastname: Hofmann
authors.forename: Yanfen
authors.initials: Y
authors.lastname: Xiao
authors.forename: Stanislav
authors.initials: S
authors.lastname: Sherman
authors.forename: Uwe
authors.initials: U
authors.lastname: Gleissner
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmidt
authors.forename: Hans
authors.initials: H
authors.lastname: Zappe