Simultaneously opening transmission channels with negative and positive phase velocities for the stacked subwavelength apertures in fishnet metamaterials with hybrid unit lattices

Hybridization of the unit lattice along the propagation direction was demonstrated to produce a negative-phase-velocity transmission band in the absence of the contributions from the higher diffraction orders for a stacked metallic fishnet grid with subwavelength apertures. This extraordinary transmission band is governed by the stacked resonators. The hybridized unit lattice configurations are not just slight modifications of the configurations with homogenous unit lattices. The volumetric proportions of different dielectric media are a key factor in the partitioned unit lattice for the estimation of the stacking and coupling effects between the resonators. The contribution of the coupling mechanisms enhances the transmission results almost by the same factor for the investigated lattice separations along the propagation direction in hybrid unit cells while the densely stacked resonators yield much higher transmission results, both around the regarding extraordinary transmission band that is associated with the negative phase velocity. A positive-phase-velocity transmission band was also exhibited by the hybridized unit lattice configuration when combined with a cavity resonator. Experimental transmission results of the hybrid configuration supported the theoretical predictions. The hybrid configurations are scalable to the near-infrared regime.