Observation of Type I Photonic Weyl Points in Optical Frequencies

Manipulation of momentum space in photonic structures has enabled a range of physical phenomena including negative refraction, slow light, enhanced nonlinearity and three‐dimensional complete bandgaps. Recently, Topology, a property related to the global structure of the frequency dispersion of a photonic system, emerged as a new tool for the control of momentum space and an additional degree of freedom for the discovery of fundamentally new states of light. The Weyl point systems considered in this work are an excellent platform to investigate topological bosonic states. Weyl points act as monopoles or anti‐monopoles Berry flux in momentum space, and carry chirality defined by quantised topological charges. In this work, the experimental realisation of photonic type I Weyl points at optical frequencies is demonstrated in a bio‐inspired three‐dimensional photonic crystal coated uniquely with layered‐composite nanometric materials. More importantly, the chiral nature of the photonic Weyl points is discovered by coupling with spin‐angular momentum carried by circularly polarised light. This Weyl‐point induced mechanism leads to reversed circular dichroism along the directions that intersect the oppositely charged topological photonic states. This discovery provides an entirely new platform for developing topologically protected super‐robust photonic devices in angular‐momentum‐based information processing, circular‐dichroism‐enabled protein sensing, spintronics and quantum optoelectronics.