The highly engineerable scattering properties of resonant optical antennas underpin the operation of metasurface-based flat optics. Thus far, the choice of antenna has been limited to shaped metallic and high-index semiconductor nanostructures that support geometrical plasmonic or Mie resonances. Whereas these resonant elements offer strong light–matter interaction and excellent control over the scattering phase and amplitude, their electrical tunability has proven to be quite limited. Here, we demonstrate how excitonic resonances in atomically thin semiconductors can be harnessed as a different, third type of resonance to create mutable, flat optics. These strong materials-based resonances are unmatched in their tunability with various external stimuli. To illustrate the concept, we first demonstrate how excitons can enhance the focusing efficiency of a millimetre-scale, patterned WS₂ zone plate lens. We also show how electrical gating can completely turn on and off the exciton resonance and thereby modulate the focusing efficiency by 33%.

谐振光学天线的高度可工程散射特性为基于超表面的平面光学器件的运行提供了基础。到目前为止，天线的选择仅限于支持几何等离激元或Mie共振的成形金属和高折射率半导体纳米结构。尽管这些谐振元件具有很强的光-物质相互作用，并且可以很好地控制散射相位和幅度，但事实证明，它们的电可调性非常有限。在这里，我们演示了如何利用原子薄半导体中的激子共振作为另一种第三种共振来创建可变的平面光学器件。这些强大的基于材料的共振在各种外部刺激下的可调谐性是无与伦比的。为了说明这个概念，₂区平板镜头。我们还展示了电子门控如何完全打开和关闭激子共振，从而将聚焦效率调节33％。