Plasmonic Fano interference produced by gold nano-disks on a dielectric Bragg stack

Abstract

Fano interference is predicted in a structure consisting of a periodic array of uncoupled gold nano-disks (AuNDs) supported by a Bragg stack. The phenomenon occurs due to resonant interference between the reflection spectrum of the Bragg stack and localized surface plasmon resonances (LSPRs) on the AuNDs. Fitting the computational results to the Fano lineshape formula yields the Fano parameters of the resonances including their linewidth. One of the most important advantages of the structure is that the linewidth of the Fano resonances (∼9 nm) is much narrower than the bandwidth of the LSPR nano-disks (∼80 nm) and the reflection bandwidth of the Bragg stack on which the disks are supported (∼100 nm). The narrow Fano linewidth and the ease with which they can be interrogated using perpendicularly incident light makes the structure attractive for biosensing applications. The bulk sensitivities and figure of merit of Fano resonances in a proposed design are 44 nm/RIU (redshift) and −52 nm/RIU (blueshift), and ∼4 RIU−1, respectively.