Abstract

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 $0<n_{\mathrm{eff}}<1$. 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.

© 2019 Optical Society of America

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