A large penetration depth of an evanescent wave is the key to success for developing an ultra high-resolution fiber-based evanescent wave biosensor. Tapering the fiber and launching light at an angle has the potential of increasing the penetration depth of evanescent wave manifolds. The effects of tapering, launch angle and taper length of the fiber have been explored in detail using a ray-tracing model to calculate the highest possible penetration depth of the evanescent field. Evanescent wave penetration depths of the order of the size of living cells have been achieved by optimizing the parameters relating geometry of tapered fibers.
Department of Materials, Royal School of Mines, South Kensington Campus, Imperial College of Science, Technology and Medicine, London SW7 2BP, UK. mohammad.ahmad@imperial.ac.uk
