Terahertz epsilon-near-zero graded-index lens

Abstract

An epsilon-near-zero graded-index converging lens with planar faces is proposed and analyzed. Each perfectly-electric conducting (PEC) waveguide comprising the lens operates slightly above its cut-off frequency and has the same length but different cross-sectional dimensions. This allows controlling individually the propagation constant and the normalized characteristic impedance of each waveguide for the desired phase front at the lens output while Fresnel reflection losses are minimized. A complete theoretical analysis based on the waveguide theory and Fermat's principle is provided. This is complemented with numerical simulation results of two-dimensional and three-dimensional lenses, made of PEC and aluminum, respectively, and working in the terahertz regime, which show good agreement with the analytical work.

Ultra-compact planoconcave zoned metallic lens based on the fishnet metamaterial

“…[1][2][3][4] Recently, several researchers have revisited this approach for artificial material lenses within the framework of metamaterials. [3][4][5][6][7][8][9][10][11] Metamaterials have attracted the attention of scientific community in the last years because they make it possible to create arbitrarily tailored electromagnetic parameters such as less than unity or even negative values of permittivity (e) and permeability (l). 12,13 This freedom allows realizing the Veselago's negative refractive index (NRI) medium investigated theoretically in 1960s.…”

[INVITED] Epsilon-near-zero metalenses operating in the visible

“…In this technique, both (input and output) faces of the metalens are planar and the required phase distribution to focus the incoming plane-wave should be introduced by each waveguide in the array. 15,16,33 As it has been explained in section 2, by correctly engineering h x , different values of propagation constant and phase will be obtained. The phase that each waveguide should introduce for optical focusing can be calculated as follows: 15,34 …”

“…[8][9][10] The field has matured significantly over the last years and several applications of ENZ-media have been proposed such as dielectric sensing, 11 nanocircuits, 12 Fourier transformation 13 and beamshaping. [14][15][16][17][18] In this work, the dispersion of metal-dielectric-metal plasmonic waveguides is exploited to artificially mimic an ENZ medium at optical wavelengths by working near the cut-off of the transverse electric TE 1 mode. This mode is intrinsically dispersive and can be modeled with a Drude function.…”

Low-index-metamaterial for gain enhancement of planar terahertz antenna

“…The refractive index of a metamaterial can be tailored to be negative, 13 close to zero, [14][15][16][17][18][19] 12,21,22 Among various metamaterials, zero-index-metamaterial (ZIM, n = 0), was first presented by Enoch et al 23 in 2002, and has received consistent attention in the microwave, 24,25 THz, 26,27 optics, 14,28 and even acoustics. 29 According to Snell's Law of refraction between two media (n 1 sin θ 1 = n 2 sin θ 2 ), if one medium is a ZIM with n 1 = 0 and the other one has n 2 = 0, then whatever the incident angle θ 1 is, the refraction angle θ 2 will trend to zero.…”