Dielectric Metamaterial-Based Gradient Index Lens in the Terahertz Frequency Range

We have tailored the effective refractive index of dielectric metamaterials to design a flat lens operating at terahertz frequencies. The studied dielectric metamaterials consist of high permittivity resonators, whose first Mie resonance gives rise to resonant effective permeability. The resonance frequency is fixed by the size of the resonators. By varying this size, we could adjust the value of the resonance of the effective permittivity and, thereby, of the effective refractive index. Then, we fitted this one to the profile of refractive index of a graded index flat lens, of which we show that it focuses an incident plane wave at terahertz frequencies and that the spot in the focal plane is diffraction limited. It is less than one and a half wavelength thick, its focal length is only a few wavelengths. Thus, we show that dielectric metamaterials are suitable for the design of metadevices, that is, photonic components for applications at terahertz frequencies.