Negative refraction of a single-layer metamaterial inserted with dual-coaxial waveguides array

Single-layer metamaterials consisting of a hexagonal close-packed array of Ag/GaP/Ag/GaP/Ag dual coaxial waveguides are investigated by simulation, focusing on both the negative-index property and transmission performance at visible frequencies. Numerical simulations indicate that the negative index mode, the same as the one identified in the Ag/GaP/Ag coaxial waveguides arrays (Nat. Mater. 9, 407, 2010) perfectly conserves and exhibits two negative index bands centered at 400 and 800 THz, respectively. The transmission peaks of the Fabry-Perot resonance at 400 THz and the transmission intensity of the resonance at 800 THz are closely related to the thickness of the silver film. Moreover, the coupling of the two coaxial waveguides can dominate the negative refraction and optical transmission of the constructed metamaterial, only by changing the distance of the two annular apertures. The present configuration can provide more approaches to tune its properties than the single coaxial waveguide array.