Loss-Assisted Metasurface at an Exceptional Point

Loss in photonic devices is intentionally minimized, as it limits the efficiency and potential functionalities. Here, we report a loss-assisted non-Hermitian electromagnetic metasurface operating at an exceptional point (EP), showing extraordinary angular asymmetry at EP condition. Spatially engineered losses are essential for the exotic scattering response of this metasurface. As a proof of concept, a functional EP metasurface, composed of a judiciously tailored tri-meta-atom supercell, is shown to exhibit unidirectional retro-reflection: totally suppressed reflection when light illuminates from the left, but highly efficient reflection from the right. Our results open promising possibilities for developing new mechanisms and designing functional photonic devices for wave manipulation and fuse exceptional-point physics with flatland optics.