Steerable plasmonic nanoantennas: active steering of radiation patterns using phase change materials.

In this article, we describe active steering of radiation patterns by complex nanoantenna structures - called steerable nanoantennas (SNs) - formed by combining multiple Yagi-Uda nanoantennas and thin films of a phase change material (VO). The radiation patterns of these nanoantennas can be actively steered by tunably changing the phase of the VO thin films from the semiconductor phase to the metallic phase. Moreover, the nanoantennas enable steering of the radiation patterns 'in the plane' of the nanoantennas. We demonstrate that the radiation pattern's maximum achievable steering is 90° for a two-element steerable nanoantenna when the phase of the VO thin film is changed from the semiconductor phase to the metallic phase. Moreover, it was observed that the radiation pattern of the steerable nanoantennas being proposed in our paper can be designed to be much more directed than previously reported steerable nanoantennas. By employing a four element steerable nanoantenna, we also demonstrate a full 360° active steering of the radiation pattern. This steerable nanoantenna consists of four coplanar Yagi-Uda nanoantennas, with each Yagi-Uda nanoantenna being present inside a VO thin film but each individually addressable VO thin film being separated from the other VO films by an air gap. We demonstrate that the radiation pattern can be tunably steered in 12 different directions using this four element steerable nanoantenna depending on the states of the four VO thin films. The steerable nanoantennas can find applications in areas such as tunable on chip plasmonic interconnects, networks on chip, or for selective excitation of fluorophores on a sensor chip.