Miniaturizing nanoantennas with hybrid photonic-plasmonic modes for improved metasurfaces.

The increasing interest in manipulating light on scales much smaller than its wavelength has driven intensive research on designing high efficiency optical antennas for near and far field applications. In particular, such nanoantennas serve as the main building block of metasurfaces, which were identified as an emerging technology for their capability in constructing versatile optical and electromagnetic devices. Hence, reducing the antennas' dimensions without compromising on their scattering efficiency is of utmost importance. In this Letter, we show that nanoantennas carved from hybrid plasmonic-dielectric waveguides preserve the unique properties of the hybrid modes, showing stronger confinement and better tunability at a relatively low loss, emanating from the coupling between the dielectric and plasmonic modes. This enables a design of high performance ultrasmall antennas that outperform dielectric and plasmonic nanoantennas at similar dimensions. We demonstrate this capability by simulating the performance of metasurfaces made of ultrasmall hybrid nanoantennas, proven to be superior over their dielectric and plasmonic counterparts. Using such hybrid nanoantennas as unit-cells in metasurfaces holds a great promise for designing new tunable, multifunctional, and low-loss nano-optical materials and applications.