Ambient-dependent reversal of unidirectional light scattering by metal–dielectric hybrid plasmonic nanoantenna

Unidirectional light scattering of plasmonic nanoantennas extends toward various nanophotonic applications, such as optical routers, molecular sensors, and light-driven actuators. The controllability of the direction of scattered light is crucial for those applications. So far, the large controllability enabling the reversal of the scattering direction has been achieved by tuning the wavelength and polarization of the incident light. Asymmetric dielectric nanostructures can also induce either unidirectional or bidirectional light scattering. However, such control methods relying on the incident light parameters and previous architecture limit the practical applicability of unidirectional light scattering, especially in sensing applications. Here, we propose and demonstrate a new hybrid architecture to control and reverse the unidirectional light scattering with respect to the ambient conditions through the integration of paired gold plasmonic nanorods and asymmetric dielectric shield. The dielectric shields selectively make certain nanorod less influential to the surrounding refractive index change, which results in the substantial controllability of direction of the scattered light with respect to the surrounding medium. Fourier imaging of the scattered light experimentally reveals the reversal of the scattering direction over a broad wavelength range. Numerical simulations reproduce the spectral response and directional scattering for various surrounding media, demonstrating a wide dynamic range and high sensitivity for the ambient refractive indices. These findings suggest that the nanoantenna can detect local molecular adsorption, leading to a compact and tunable platform for ambient-dependent optical devices with potential applications in nanophotonic sensing, reconfigurable photonics, and environment-adaptive light-driven nanomotors.