Challenges in fabrication towards realization of practical metamaterials

Metamaterials, artificially structured materials consisted of sub-wavelength unit cells, have attracted tremendous attentions in physics, material science, and engineering over the past decade. Many exotic and extraordinary electromagnetic phenomena such as negative refractive index, invisibility cloaking and super-resolution imaging have been realized through metamaterials. Now, metamaterials need to be focused on nanoscale optical metamaterials, operating at ultra-violet (UV), visible and near-infrared (NIR) frequencies for practical applications of them. Here, we review the fundamentals, recent progress, main challenges, and future direction of optical metamaterials and related fabrication processes. The fundamentals and recent progress of the optical metamaterials are discussed with representative examples such as negative index metamaterials and invisible cloaks. Main challenges in fabrication for practical metamaterials, three-dimensional and large-scale metamaterials, and brief discussion about the outlook for the next generation scalable nanofabrication methodologies are followed.