Dual-band optical negative index metamaterial based on hexagonal arrays of triangular nanoholes in metal–dielectric films

Metal–dielectric–metal films perforated with triangular nanoholes arranged in a hexagonal array are theoretically analyzed as metamaterial slabs. Effective constitutive parameters are calculated using three-dimensional (3D) finite-difference time domain (FDTD) simulations and S-parameter retrieval method. Nanoholes side length and dielectric spacer thickness determine the magnitude and frequency of the hybridized plasmon modes resonances leading to negative effective permeability and plasmon modes inversion. Fundamental and second order asymmetric modes resonances lead to a double negative refractive index in the near infrared and a single negative refractive index in the visible range of the spectrum.