J. Opt. Soc. Am. B 29, 2839–2847 (2012)

The past decade has seen several impressive demonstrations of metamaterials that exhibit negative refractive indices. Such studies were originally performed in the microwave region, and there have been relatively few demonstrations in the important visible region of the electromagnetic spectrum. Scientists from the USA and Pakistan have now proposed a metamaterial that simultaneously exhibits a negative refractive index in two different regions of the visible spectrum. Their design — a modified version of the established fishnet structure — involves adding a metal layer to form a four-functional-layer structure. The additional layer extends the plasma frequency deep into the visible range, slightly above the second-order magnetic resonance. This leads to two negative refractive index bands: one in the green, at around 550 THz, and the second one in the red, at around 450 THz. Moreover, the operation is independent of the polarization of the incident light. The researchers report that by incorporating additional metal layers and higher-order magnetic resonances, it may be possible to develop a metamaterial that exhibits an even greater number of multiple negative-index bands.