Abstract-Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies

Eric Akmansoy, Simon Marcellin,

Schematic layout of the 2D ADM (cross-sectional view). The ADM consists of one infinite layer along the xdirection and is made up of two interleaved sets of high permittivity square cross-section dielectric cylinders, which resonate in the first two modes of Mie resonances: the small set resonates in the magneticmode and the second one in the electric mode. The equidistant cylinders are infinite along the y direction and their side lengths are am = 60 μm and ae = 90 μm, respectively. Their relative permittivity is er = 94. The unit cell actually consists of two subwavelength distinct building blocks. The lattice period is lp = 260 μm and p2is half the lattice period. The incident wave is transverse electric (TE).

https://www.edp-open.org/articles/epjam/full_html/2018/01/epjam180003/epjam180003.html#abs

We elucidate the role of the mode coupling of the Mie resonances in all-dielectric metamaterials to ensure a negative effective index at terahertz frequencies. We perform a study as a function of the lattice period and of the frequency overlapping of the modes of resonance. We show that negative effective refractive index requires sufficiently strong mode coupling and that for even more strong mode coupling, the first two modes of Mie resonances are degenerate; the effective refractive index is then undetermined. We also show that it is possible to obtain near-zero, or even null, effective index with a judicious adjustment of the mode coupling. Further, we discuss the mode coupling effect with hybridization in metamaterials.