LETTERS Three-dimensional photonic metamaterials at optical frequencies

Metamaterials are artificially structured media with unit cells much smaller than the wavelength of light. They have proved to possess novel electromagnetic properties, such as negative magnetic permeability and negative refractive index1–3. This enables applications such as negative refraction4, superlensing5 and invisibility cloaking6. Although the physical properties can already be demonstrated in two-dimensional (2D) metamaterials, the practical applications require 3D bulk-like structures4–6. This prerequisite has been achieved in the gigahertz range formicrowave applications owing to the ease of fabrication by simply stacking printed circuit boards4,6. In the optical domain, such an elegant method has been the missing building block towards the realization of 3D metamaterials. Here, we present a general method to manufacture 3D optical (infrared) metamaterials using a layer-by-layer technique7–9. Specifically, w