Multiband negative index metamaterials at optical frequencies

Based on the fishnet negative index metamaterials (NIMs) of circular-shaped holes operating at optical frequencies, the influence of modifying the hole shape is studied using the commercial software package CST Microwave studio. Numerical simulations show that, even a tiny modification may lead to broadening of the negative refractive band. So we designed two fishnet NIMs of the gradient holes and half-global holes. Compared with the fishnet NIMs of circular-shaped holes, these two structures can realize negative refraction at multi-frequency bands, and the resonance frequencies exhibit an obvious red-shift. We present a chemical technique for preparing the fishnet NIMs of half-global holes, which is a simple and feasible way to realize multiband negative index metamaterials at optical frequencies.