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\u2009 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.