General considerations for the miniaturization of radiative antennae

The small size of plasmonic nanostructures compared to the wavelength of light is one of their most distinct and defining characteristics. It results in the strong compression of an incident wave to intense hot spots which have been used most remarkably for molecular sensing and nanoscale lasers. But another important direction for research is to use this ability to design miniaturized interconnects and modulators between fast, loss-less photonic components. Here we show that despite their high absorption, conductors are still the best materials to reach the sub-wavelength regime for efficient antennae when compared to polar crystals and high-index dielectrics, two classes of material which have shown a lot of potential recently in nanophotonic applications. By identifying the relevant dimensionless properties for the three materials considered, we present an unified understanding of the behaviour of sub-wavelength components which are at the heart of current photonic research and cast the upper achievable limits for radiative antennae crucial to the development of real-life implementation.