Modal analysis of thin long-range plasmonic waveguides

In this work, we present a comprehensive modal analysis, by means of numerical simulations, of a long-range surface plasmon polariton waveguide consisting of a metal stripe sandwiched between two dielectric claddings. Our results complement those from previous reports where similar structures have been studied and optimized for attenuation-based measurements. Specifically, we found conditions where a significant phase change can be induced while the losses of the structure vary minimally. Around these regions, an attenuation-based measurement would be insensitive for sensing, however, a high-sensitivity interferometric measurement could be performed without a significant penalty on the contrast of the interference signal. Our structure is designed specifically for biologically relevant situations and it can be fabricated with commercial-grade materials that are commonly available in clean room facilities.