Experimental realization of an epsilon-near-zero metamaterial at visible wavelengths

Optical materials with a dielectric constant near zero have the unique property that light advances with almost no phase advance. Although such materials have been made artificially in the microwave and far-infrared spectral range, bulk three-dimensional epsilon-near-zero (ENZ) engineered materials in the visible spectral range have been elusive. Here, we present an optical metamaterial composed of a carefully sculpted parallel array of subwavelength silver and silicon nitride nanolamellae that shows a vanishing effective permittivity, as demonstrated by interferometry. Good impedance matching and high optical transmission are demonstrated. The ENZ condition can be tuned over the entire visible spectral range by varying the geometry, and may enable novel micro/nanooptical components, for example, transmission enhancement, wavefront shaping, controlled spontaneous emission and superradiance. Silver and silicon nitride metamaterial structures with dielectric permittivities close to zero are demonstrated at visible wavelengths. In such materials, the optical phase advance during propagation can be very small.