Surface plasmon resonance is possible in an optical fiber tapered to a point

Abstract

Surface plasmon resonance sensing using a flat surface or weakly narrowed fiber has been shown to be a sensitive indicator of probe environment. We report that surface plasmon sensing is possible at the tip of a sharpened optical fiber, tapered to a nanosized point, via a proof-of-principle study and modeling. The size of the region of interaction of the light in the tapered fiber with the outer environment is limited by the last ∼10 μm of the taper, so sampling is accomplished in an ultrasmall volume of liquid. Changes of light retroreflected through the fiber were measured as the chemical environment of the thin-metal coated, etched fiber optic tip was changed. We present a model for the sensor that shows how surface plasmon sensing, usually an angle-sensitive measurement, can work when implemented in backreflection from a tapered fiber.