New design of multi-band negative-index metamaterial and absorber at visible frequencies

A new negative-index metamaterial (NIM) structure is proposed by designing the metallic holes of traditional double-fishnet (DF) structures from uniform sizes to several different sizes. Numerical results demonstrate that the new metamaterial, as an improved variant of the DF structure, achieved a multi-band negative refractive index across a wide range of visible frequencies from 470 THz to 540 THz, which covers the red, orange, yellow, and green regions of the visible spectra. Meanwhile, a low-profile nanostrctured absorber was obtained when one side of the perforated metal layer of this multi-band NIM was substituted with a continuous metal film with the same thickness. The absorber showed the high absorption of more than 95% at multiple frequencies of 511, 520, 523, 525, and 527 THz. The behavior of multi-frequency response effectively broadened the working bandwidth. Finally, the physical mechanism of the multi-band operating characteristics of NIM and absorber was analyzed with the distributions of current intensity at different resonant frequencies.