Tailoring the coupling between localized and propagating surface plasmons: realizing Fano-like interference and high-performance sensor.

Surface plasmon modes originated from various metallic nanostructures possess unique features of strong nanoscale light confinement and enhancement with tunable energy, which make them attractive and promising for a variety of applications such as sensing, solar cell, and lasing. Here, we have investigated the interaction between localized and propagating surface plasmons in a structure consisting of a gold nanobar array and a thick gold film, separated by a silica dielectric spacer layer. It is found that the reflection spectrum of the designed plasmonic structure can be readily tailored by changing the gold nanobar size, array period and the spacer layer thickness. Moreover, the strong coupling between the localized and propagating modes can result in an anticrossing behavior and even induce a Fano-like asymmetric lineshape. Importantly, the sensitivity and the figure of merit (FoM) of this plasmonic system can reach as high as 936 nm/RIU and 112, respectively. Our study offers a new, simple, efficient and controllable way to design the plasmonic systems with desired modes coupling and spectral lineshapes for different applications.