Broadband Mid-infrared Dual-Band Double-Negative Metamaterial: Realized Using a Simple Geometry

We design and numerically demonstrate a novel metamaterial structure consisting of a dielectric layer sandwiched between two silver films and is perforated with two kinds of square-shaped holes at different angles, which is a dual-band double-negative (each band possesses simultaneously negative permittivity and permeability) metamaterial with broad NRI bands in mid-infrared region(3-30 mu m). The broadband of NRI contributed to the strong magnetic resonance caused by the excitation of surface plasmon polaritons. The influence of the number of square-shaped holes on the properties of the designed structures are also investigated by analyzing and comparing the transmission, permeability, permittivity, refractive index, and figure of merit. Then, by optimizing the structural parameters, the proposed structure exhibits a negative band with a figure of merit of 3.3, which is to our knowledge larger than previously reported plasmonic metamaterial in mid-infrared region(M-IR). The value of negative refractive index(NRI) reaches -6 and the bandwidth of NRI can reach up to 4.2 THz in the low-frequency band of M-IR region, which is the widest NRI band in M-IR spectrum at present as far as we know. Moreover, the metamaterial structure is simple and easy to be manufactured with standard fabrication techniques. This work will be very meaningful in designing dual-band negative-index material with broad NRI band and low loss. Finally, the proposed metamaterial has huge potential applications in multiband or broadband devices.