Numerical and Experimental Investigation of Surface Plasmon Resonance Excitation Using Whispering Gallery Modes in Bent Metal-Clad Single-Mode Optical Fiber

Abstract

We present a numerical and experimental study of surface plasmon resonance (SPR) excitation in a bent single-mode optical fiber with metalized cladding. It is shown that with a suitable combination of bend radius and metal film thickness surface plasmon waves can be excited in the film as a result of coupling between fundamental and surface plasmon modes via whispering gallery modes supported by the bent fiber cladding. The coupling brings about a dip in the transmission spectrum at the resonant wavelength which is strongly dependent on the ambient refractive index. This enables one to build a fiber optic SPR-refractometer with a standard single-mode fiber without breaking integrity of the fiber or using any additional elements. Refractometric sensitivity of ~5 μm per refractive index unit and resolution of ~4·10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> are experimentally demonstrated for the measured refractive index around 1.43. The reported results may find wide application in bio- and chemosensing.