Enlarged negative effective index bandwidth from fishnet metamaterials

Abstract

Exploiting the concept of internal surface plasmon polariton (I-SPP) resonances, which appear at non-single metallic film stacks, we have designed a metamaterial showing a negative effective refractive index within a large bandwidth. The designed structure consists of an arrangement of several fishnet layers. By properly adjusting the lattice constant 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 effective refractive index. Thus, the combination of several fishnet layers, each one of them configured to excite an I-SPP at a different frequency, enables us to extend the bandwidth at which a negative effective refractive index is achieved, as long as the selected resonances are close enough. Specifically, from a subwavelength chain of two fishnet layers, the retrieved effective parameters show a negative index behavior in a frequency span of about 44THz centered at 210THz, owing to the fact that an I-SPP is excited in each fishnet layer at slightly different frequencies.