Controlling Fano resonances using the geometrical phase of light in spatially tailored waveguided plasmonic crystals

Abstract

Fano resonance exhibiting an asymmetric spectral line shape is a universal phenomenon observed in diverse physical systems. Here we experimentally establish a direct link between the spectral asymmetry parameter q and a physically realizable phase factor of interference between a continuum and a discrete mode that leads to Fano resonance. We demonstrate control on the spectral asymmetry of the Fano resonance through changes in the geometric phase of polarized light using a specially designed metasurface, namely waveguided plasmonic crystal with a spatially varying orientation axis of the plasmonic grating. In this scenario, the changes in the geometric phase for input left and right circular polarized light arise due to varying orientation angle of the grating axis. The systematic changes in the geometric phase and the resulting q parameter of Fano resonance are interpreted by an appropriate theoretical model connecting the two physical entities. The demonstrated control over the spectral line shape of Fano resonance achieved by tailoring geometric phase may open up routes for polarization-based photonic applications.