Full 2π phase modulation using exciton-polaritons in a two-dimensional superlattice

Active metamaterials promise to enable active control over the propagation of wavefronts of light for applications such as beam steering, optical communication modulators, and holograms. Current commercial devices use active layers that are several wavelengths thick to modulate the phase of light, which limits their compactness and energy efficiency. In atomically thin optics, the phase has been modulated using a resonant mode such as a plasmon or high-Q cavity mode that enable light to accumulate a large amount of phase over a short distance and coupling it to an active material. Here, we report that electrostatic doping can modulate the light-matter interaction strength of a two-dimensional WS2-based multi-quantum-well (MQW) structure going from strongly coupled, phase-accumulating exciton-polaritons to weakly coupled exciton-trion-polaritons. This transition leads to 2.02π radians of phase modulation being observed. This result demonstrates the potential of the MQW structure as a compact, lightweight electro-optical modulators for light detection and ranging (LiDAR) and optical communications in the visible range.