Calculation of Dispersion Relation and Single Mode Operation in Surface Plasmon Resonance Based Fiber Optic Refractive Index Sensors

The dispersion relations of two lowest-order surface plasmon (SP) modes are derived for a structure consisting of a thin silver layer around a reduced cladding fiber. Mode splitting is formed by reducing metal thickness. Fulfillment of phase matching condition is investigated by inspection of the SPs' and fiber modes' dispersion diagrams. Propagation lengths, field patterns, and resonance wavelengths are determined with high accuracy. The sensitivity of 7.13 × 10
^-6
RIU is obtained for ambient refractive index range of 1.333-1.375. Short-range SP modes cannot be excited in this structure even in IR region. Dependence of SP cutoff conditions on the core radii, metal thickness, ambient refractive index, and operating wavelength are explored. It is proved that the proposed method is going to be useful for proper structural design of single plasmonic mode operation in SP resonance based fiber optic refractive index sensors.