Demultiplexing surface waves with silicon nanoantennas

One of the crucial building blocks for optical devices operating in 2D is a spectral demultiplexer, which allow simultaneous operation at multiple wavelengths, thus dramatically accelerating the performance of the integrated... [ view full abstract ]

One of the crucial building blocks for optical devices operating in 2D is a spectral demultiplexer, which allow simultaneous operation at multiple wavelengths, thus dramatically accelerating the performance of the integrated photonic circuit. Usually, excitation of surface waves as well as their demultiplexing is performed using 1D and 2D structures like gratings, structured nanoslits, or arrays of nanoholes. However, severely limited amount of space available on a modern integrated optical circuit calls for using more compact structures for surface waves excitation and routing.

In this work, we reveal that a very basic dielectric nanoantenna (silicon nanosphere) provides unmatched performance serving as a highly efficient source and spectral demultiplexer for surface plasmon polaritons (SPPs). The unique opportunities for manipulation of directivity pattern of SPP are delivered by mutual interference of inherently strong electric and magnetic dipole resonances of the dielectric nanoparticle. Using analytical approach based on Green function and measurements with leakage radiation microscopy integrated with Fourier plane imaging optics, we predict and demonstrate experimentally the rapid switching between directional forward and backward excitation of SPP by silicon nanosphere on gold substrate within extremely narrow (<50 nm) spectral band. Importantly, inherently strong magnetic dipole response of the silicon particle provides extremely efficient excitation of a SPP wave, whereas mutual interference of the electric and magnetic dipole resonances of the nanoantenna provides high front-to-back ratio contrast and directivity values for the excited surface waves.

The theoretical framework that we formulate to describe the physics behind the observed phenomena can be easily extended to more complex interfaces supporting other types of surface waves. Furhermore, the combination of tunability of the nanoantenna radiation pattern that we demonstrate here and dispersion engineering of states supported by a 2D interface would be an important step forward to efficient routing of surface waves.