We present the first dual-band negative index metamaterial that operates inthe visible spectrum. The optimized four-functional-layer metamaterialstructure exhibits the first double-negative (i.e., simultaneously negativepermittivity and permeability) band in the red region of the visible spectrumwith a figure of merit of 1.7 and the second double-negative band in the greenregion of the visible spectrum with a figure of merit of 3.2. The opticalbehavior of the proposed structure is independent of the polarization of theincident field. This low-loss metamaterial structure can be treated as amodified version of a fishnet metamaterial structure with an additional metallayer of different thickness in a single functional layer. The additional metallayer extends the diluted plasma frequency deep into the visible spectrum abovethe second order magnetic resonance of the structure, hence provides a dualband operation with simultaneously negative effective permittivity andpermeability. Broadband metamaterials with multiple negative index bands may bepossible with the same technique by employing higher order magnetic resonances.The structure can be fabricated with standard microfabrication techniques thathave been used to fabricate fishnet metamaterial structures.
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