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 in this work, using numerical simulations and semi-analytical calculations, I studied the evolving optical response of a hybrid metal-semiconductor-metal nanorod antenna as the semiconductor free charge carrier density was continuously varied. In particular, I demonstrated qualitatively new behavior arising from epsilon-near-zero properties in intermediately doped semiconductors.
In agreement with optical nano-circuit theory, I showed 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.
Finally, in periodic arrays, or metasurfaces, I showed how to use these effects to construct high-efficiency nanophotonic intensity modulators for dynamically shaping light.