Enlarging the negative-index bandwidth of optical metamaterials by hybridized plasmon resonances

By exploiting the concept of internal surface plasmon polariton (I-SPP) resonances, which appear at nonsingle metallic film stacks, we have designed a metamaterial showing a negative effective index within a large frequency bandwidth. The designed structure consists of an arrangement of several fishnet layers. By properly adjusting the lattice and the thickness of the dielectric slab of the fishnet, an I-SPP mode can be excited at a certain frequency, giving rise to a negative permeability. Thus, when combining several fishnet layers, each one configured to excite an I-SPP at a slightly different frequency, the coupling among the fishnet layers will cause a plasmon hybridization effect that enables us to extend the negative-index bandwidth.