Fabrication of planar polymer waveguides for evanescent-wave sensing in aqueous environments

We present a detailed account of processing issues related to fabrication of optical waveguide sensors intended for evanescent-wave sensing in aqueous solutions or surface-bound fluorescence excitation in biological samples. The waveguides consist of a polymer layer on top of a fluoropolymer (Cytop^™) cladding. The fluoropolymer is closely index-matched to water, providing a symmetric cladding environment which simplifies optical excitation and provides tunability in penetration depth not available with other evanescent-wave techniques. We present methods of controlling the wettability of the fluoropolymer surface and improving adhesion to the core waveguide layer. Furthermore, we demonstrate the application of the waveguide structure to fluorescence imaging of cultured cells.