Metamaterials offer unprecedented flexibility for manipulating the opticalproperties of matter, including the ability to access negative index,ultra-high index and chiral optical properties. Recently, metamaterials withnear-zero refractive index have drawn much attention. Light inside suchmaterials experiences no spatial phase change and extremely large phasevelocity, properties that can be applied for realizing directional emission,tunneling waveguides, large area single mode devices, and electromagneticcloaks. However, at optical frequencies previously demonstrated zero- ornegative-refractive index metamaterials require the use of metallic inclusions,leading to large ohmic loss, a serious impediment to device applications. Here,we experimentally demonstrate an impedance matched zero-index metamaterial atoptical frequencies based on purely dielectric constituents. Formed fromstacked silicon rod unit cells, the metamaterial possesses a nearly isotropiclow-index response leading to angular selectivity of transmission and directiveemission from quantum dots placed within the material.
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