文摘
A Luneburg lens is a fascinating gradient refractive index lens that can focus parallel light on a perfect point without aberration in geometrical optics. A three-dimensional (3D) Luneburg lens operating at optical frequencies is proposed by Zhao et al. as a first experimental demonstration. This gradient refractive index lens is realized by laser direct writing, and the refractive profile of simple cubic metamaterials is tailored by the fill factor. Experimentally, 3D ideal focus performance has been observed via near-field optical microscopy, which is a direct experimental evidence for 3D Luneburg lens to achieve the ideal focus of mid-IR light.