Hybrid optical antennas with photonic resistors.

Hybrid optical antennas, comprising active materials placed in the gaps of plasmonic split-ring-resonators and nano-dimers, have been the subject of numerous recent investigations. Engineered coupling between the two plasmonic resonators is achieved by modulating the active material, enabling control over the near- and far-field electromagnetic properties. Here, using electromagnetics calculations, we study the evolving optical response of a hybrid metal-semiconductor-metal nanorod antenna as the semiconductor free charge carrier density is continuously varied. In particular, we demonstrate qualitatively new behavior arising from epsilon-near-zero properties in intermediately doped semiconductors. In agreement with optical nano-circuit theory, we show that in the epsilon-near-zero regime such a load acts as an ideal optical resistor with an optimized damping response and strongly suppressed electromagnetic scattering. In periodic arrays, or metasurfaces, we then show how to use these effects to construct high-efficiency nanophotonic intensity modulators for dynamically shaping light.