Photonic Heterostructures for Spin-Flipped Beam Splitting

Understanding and controlling chirality are important because of its ubiquity in nature. In recent years, we have witnessed the rapid development of chiral metamaterials with exceptional light-manipulating capabilities. Here, we present a design for photonic heterostructures in chiral photonics, demonstrating that photonic heterostructures stacked from achiral metasurfaces can create distinctive chiroptical functionalities. Analyses based on the symmetry group and microscopic dipolar interactions at two-dimensional boundaries reveal the implicit mechanism of the interlayer coupling in photonic heterostructures. By flip stacking, the photonic heterostructure gives rise to an asymmetric chiral phase from achiral composites, and hence, provides the full spin-flipped scattering of incident photons. Incident electromagnetic waves with arbitrary polarization orientations can be efficiently separated into two orthogonal circularly polarized ones with orthogonal trajectories, leading to an ideal circular beam splitter. This effect is experimentally demonstrated at microwave frequencies via the measurement of a scattering matrix. Due to its generality and scalability, we expect the methodology of photonic heterostructure might open up an alternative pathway for exploring intriguing and advanced metamaterials over a broad wavelength range.