Tuning the scattering response of optical nanoantennas with nanocircuit loads

Abstract

Optical nanodipoles made of plasmonic elongated nanoparticles have been theoretically and experimentally characterized by various groups in recent studies1,2,3,4,5,6,7,8,9,10. However, compared with their radiofrequency counterparts, less attention has so far been paid to systematic design methodology for these nanoantennas, and in particular to the possibility of optimizing their radiation and scattering properties and tuning their frequency response by using proper ‘loading’ techniques. By interpreting nanoparticles' interaction with light as lumped nanocircuit elements11,12, we show how the concepts of antenna loading may be fully introduced in plasmonic nanoantenna design. In particular, we show how nanocircuit elements, and in general more complex nanofilters, designed within the framework of nanocircuit theory11 and used as nanoloads, may allow tuning of the frequency response of scattering from these nanoantennas at will. Series and parallel combinations of these nanoloads are also considered to add further degrees of freedom in the design. Optical-frequency antennas efficiently couple light into very small volumes. Introducing an important concept from radiofrequency antenna design, that of loading with so-called lumped circuit elements, may provide a way of tuning the frequency response of optical nanoantennas.