Plasmonic Multibowtie Aperture Antenna with Fano Resonance for Nanoscale Spectral Sorting

In this work we report a new type of nanostructure, the plasmonic multibowtie aperture antenna with Fano resonance for spectral sorting at the nanoscale. Redistribution of surface current in our device plays a critical role in mode coupling to generate Fano resonance, which has never been carefully discussed before. Numerical analyses show that interactions of the electric field, the surface current, and the resulting magnetic field are all important for achieving the desired spectral sorting. Depending on the constructive or destructive interference between the broadband dipole mode and the narrow band multipole mode, electric near-field amplitude and phase distributions switch dramatically across the Fano resonance, which are observed in real space using transmission-type s-SNOM. Based on the Fano interference, photons ranging, from visible to infrared spectrum can be sorted through different channels at the nanoscale according to their wavelengths, which shows apparent advantages over other existing nanoscale spectral sorters. Moreover, the narrow gap plasmonic bowtie aperture provides enhanced field of the sorted photons, thus, offers a new approach for multicolor photodetection, optical filtering, and advanced biosensing.