ABSTRACT
Sensitive surface and guided modes offer opportunities in optical waveguide design for biosensing applications. Scattering induced changes in thin films may convert light from Total Internal Reflection (TIR) to lost transmission from a prism. Temporal light scattering increases due to chemical species present is demonstrated with volatile vapours. Creation of a ‘leaky’ waveguide structure with scattering sites near a waveguide surface allows observation of ‘sharp’ reflection features below critical angle. Scattering effects are replicated in a planar geometry and enhanced further by design of a novel Coupled Optical Waveguide sensor (COWG), composed of a low-loss passive channel guide overlaid with a thin high index film. COWG has high sensitivity to scattering induced loss comparing favourably with existing sensors and is used here to detect alcohol vapour and monitor TE-TM mode interference for alcohol injected into water.
