High displacement sensitivity in asymmetric plasmonic nanostructures.
The strong couplings between two asymmetric plasmonic nanostructures can lead to ultra-sensitive optical responses when their separation changes. We employ electromagnetic numerical simulations to study the displacement sensitivity of two kinds of plasmonic systems: (1) a split-ring resonator and a metal rod; (2) two metal rods of asymmetric lengths. Structural asymmetry makes antiparallel current interactions possible and greatly enhances the sensitivity to 5%/nm for normalized frequency changes and 29%/nm for normalized transmittance changes. These are the highest displacement sensitivity among all physical systems investigated so far. In addition, we also find that these systems display a universal scaling curve independent of their shapes or dimensions. These asymmetric plasmonic nanostructures will open widespread applications from strain mapping, surface wave or heat wave imaging, optomechanical sensing, to environmental detections.