High-resolution refractive index sensing by means of a multiple-peak surface plasmon resonance optical fiber sensor

When a thin metal layer is deposited on a single-mode tapered optical fiber the layer takes a semi-cylindrical shape. The fundamental fiber mode can excite the different hybrid surface plasmon modes supported by the semi-cylindrical metallic shell. As a consequence, the transmission spectrum of the device exhibits multiple resonance peaks with either TE- or TM-polarized light. The positions of those peaks are remarkably shifted when the refractive index of the medium adjacent to the metal layer changes. Experimentally, we have found that by monitoring the first three resonance peaks a refractive index resolution of about 7 × 10−7 can be achieved. Our devices can be used for high-resolution biosensing.