Realization of an all-dielectric zero-index optical metamaterial

Metamaterials offer unprecedented flexibility for manipulating the optical properties of matter, including the ability to access negative index 1 , 2 , 3 , 4 , ultrahigh index 5 and chiral optical properties 6 , 7 , 8 . Recently, metamaterials with near-zero refractive index have attracted much attention 9 , 10 , 11 , 12 , 13 . Light inside such materials experiences no spatial phase change and extremely large phase velocity, properties that can be applied for realizing directional emission 14 , 15 , 16 , tunnelling waveguides 17 , large-area single-mode devices 18 and electromagnetic cloaks 19 . However, at optical frequencies, the previously demonstrated zero- or negative-refractive-index metamaterials have required the use of metallic inclusions, leading to large ohmic loss, a serious impediment to device applications 20 , 21 . Here, we experimentally demonstrate an impedance-matched zero-index metamaterial at optical frequencies based on purely dielectric constituents. Formed from stacked silicon-rod unit cells, the metamaterial has a nearly isotropic low-index response for transverse-magnetic polarized light, leading to angular selectivity of transmission and directive emission from quantum dots placed within the material. Previously demonstrated zero- or negative-refractive-index metamaterials at optical frequencies suffer from large ohmic losses because of the need to use metals. Metamaterials formed by stacked silicon rod unit cells allow the realization of all-dielectric impedance-matched zero-index metamaterials operating at optical frequencies, potentially benefiting the development of angular-selective optical devices.