Metamaterial Broadband Angular Selectivity
  We demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each effective anisotropic layer is constructed from a multilayered metamaterial. We show that by simply changing the structure of the metamaterials, the selective angle can be tuned to a broad range of angles; and, by increasing the number of stacks, the angular transmission window can be made as narrow as desired. As a proof of principle, we realize the idea experimentally in the microwave regime. The angular selectivity and tunability we report here can have various applications such as in directional control of electromagnetic emitters and detectors. 
Yichen Shen, Dexin Ye, Zhiyu Wang, Li Wang, Ivan Celanovic, Lixin Ran,   John D Joannopoulos, Marin Soljacic
physics.optics