Symmetry breaking and optical negative index of closed nanorings

Abstract

Metamaterials have extraordinary abilities, such as imaging beyond the diffraction limit and invisibility. Many metamaterials are based on split-ring structures, however, like atomic orbital currents, it has long been believed that closed rings cannot produce negative refractive index. Here we report a low-loss and polarization-independent negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite 'chess metamaterial'. The formation of an ultra-broad Fano-resonance-induced optical negativeindex band, spanning wavelengths from 1.3 to 2.3 mm, is experimentally observed in this structure. This discrete and mono-particle negative-index approach opens exciting avenues towards symmetry-controlled topological nanophotonics with on-demand linear and nonlinear responses.

Anisotropy Modeling of Terahertz Metamaterials: Polarization Dependent Resonance Manipulation by Meta-Atom Cluster

“…With respect to the meta-atom structure, unlike the structures of polarization independent metamaterials, such as the cross and ring-shaped structures313233, Split-ring resonators (SRRs), cut-wires (CWs)34, or their complementary structures35 are the most well-known metamaterial structures that exhibit anisotropic properties depending on the polarization property of the incident waves. Particularly, in the optical and terahertz regimes, planar SRR structures have a fundamental LC resonance, as well as a half wave resonance, (or plasmonic oscillation) along the side length of the SRR unit cell836.…”

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

“…The mode coupling effect we report on is different from hybridization [46] which is observed with plasmonic metameterial [12,47], split-ring resonators metametarials [48], inductor-capacitor resonators [49], cut wires [50], nanowires [51], nano-rings [52], nanoparticle dimers [53] or silicon nanoparticles [54]. In the latter cases, the coupling between the two identical meta-atoms which constitute the dimer leads from a trapped mode to the formation of new hybridized modes because it lifts the degeneracy of the mode of the individual meta-atoms.…”

A meta-substrate to enhance the bandwidth of metamaterials

“…Reversely, if the closed rings locate inside of the SRRs, the bandwidth will decrease. The concept of the meta-substrate can be readily extended to THz and optical frequencies as S-strings and metallic closed and split rings have been realized using micro- and nano-fabrication techniques142021. It should also be noted that the closed rings also exhibit electrical responses.…”