Nanowerk  January 28, 2022 Negative refraction has not been observed in nature but was theorized to occur in artificially periodic materials. Researchers at Caltech designed, fabricated 3D photonic crystals (PhCs) capable of negative refraction in the mid-infrared. Band structure and equifrequency contours were calculated to inform the design of 3D polymer–germanium core–shell PhCs. They successfully characterized a polymer–Ge core–shell lattice and mapped its band structure, which were used to calculate the PhC refraction behavior. An analysis of wave propagation revealed that this 3D core–shell PhC refracts light negatively and possesses an effective negative index of refraction in the experimentally observed […]