A WAVE-GUIDE-COUPLED SURFACE-PLASMON SENSOR FOR AN AQUEOUS ENVIRONMENT

Planar optical waveguides integrated with thin-film dielectric and metallic overlayers may be configured as transducers to probe the optical properties of a broad range of sensing films. We present a simple sensor consisting of a potassium ion-exchanged glass waveguide coated with a dielectric buffer layer and a thin silver film to demonstrate optical waveguide-coupled surface-plasmon resonance in an aqueous environment. For a given operating wavelength, the use of an intermediate buffer layer allows tuning of the coupling to a surface plasma wave in water. Theoretical and experimental results confirm that a magnesium fluoride buffer layer may be used to allow operation in an aqueous environment at visible wavelengths. In conjunction with thin sensing films, this waveguide probe is expected to find application in immunosensors for monitoring water pollution.