Nanostructures with near-zero refractive index in mid-infrared region

The near-zero-index metamaterials (NZIMs) have been extensively studied in recent years. In this letter, we show that a NZIM can be achieved in metallic nanostructures in Mid-IR region. The structure is composed of parallel metal stripes arrays, so it can be easily fabricated. By scaling the dimensions of the structure, the effect can be tuned over a large bandwidth. Analysis is carried out to study the influence of the NZIM on infrared transmission in 28.3THz (10.6μm). The multilayer homogeneous medium model is employed based on the effective medium theory. Additionally, the theoretical analysis also provides a new method of determining the effective thickness of metamaterials, which is usually complicated. The results suggest that the ratio of the amplitude after the light beam propagates through the NZIM to that before it is about 80%, and there is a negative variation in the phase of the light transmitted through the NZIM, which is in agreement with numerical simulation. Simulation also indicates that there is a strong enhancement of the electric field between the metal stripes arrays, which plays an important role in the phase delay. This metamaterial has the potential to be used in some devices such as in waveguides.