Step-etched prism coupling for optical waveguide biosensors

We report a light input coupling method into a buried planar waveguide that is very promising for applications in disposable optical waveguide biosensors. The superstrate of the waveguide is step-etched and a prism made from polystyrene is permanently bonded onto the etched step using optical glue. The plastic prism and the waveguide form a `plug-in' assembly of the disposable part of a biosensor system. For light input coupling, no other pressure sensitive contact of optical components is required and a laser beam simply needs to be directed at the right position. Our experimental results show that the coupling has a highly reproducible efficiency of more than 20% and the coupling efficiency is reasonably tolerant of misalignment. Since the waveguide is fabricated using the ion-exchange process and the prism can be made using injection molding, we believe that our method is very suitable for planar-waveguide-based disposable biosensors.