Epsilon-near-zero three-dimensional metamaterial for manipulation of terahertz beams

Metamaterials offer the potential of unprecedented refractive indices and evolution into metadevices for the manipulation of electromagnetic waves. However, the potential of the epsilon-near-zero (ENZ) concept has not been fully demonstrated in the terahertz waveband. Most conventional ENZ lenses have a uniform distribution of refractive indices in spite of their three-dimensional structure. Here, inspired by the ENZ concept, we demonstrate the two-dimensional distribution of a three-dimensional ENZ lens realized by circular openings of varying diameters on metal plates and apply it to a metal-slit array lens with gradient indices of 0<n eff <1. The measurements of a fabricated metal-slit array lens with circular openings observe the focusing effect of a terahertz wave. We also apply the ENZ concept to the design of microlens arrays. The control of the gradient of the ENZ potentially offers a wide range of applications.