Invited Paper
Uniaxial-Isotropic Metamaterials

Uniaxial-isotropic metamaterial consisting of three-dimensional (3D) metallic nanostructures is experimentally created by metal-stress driven self-folding method. Metamaterials is man-made materials using sub-wavelength resonant structures and have introduced a new paradigm to create unprecedented optical properties. Since the resonant element of metamaterial is an analog of antenna that asymmetrically interacts with light, the optical responses of metamaterials are inevitably anisotropic. Isotropic responses of metamaterials have been achieved at microwave frequencies by employing 3D symmetric alignment of meta-atoms, but their optical versions are still challenge due to the limitation of 3D nanofabrication. To this end, we present the first experimental realization of a uniaxial-isotropic metamaterial using fourfold-symmetric 3D configuration of metallic nanostructures as shown in Figure. Mass-productive formation of the assembled 3D stereo-structures was achieved by a metal-stress driven self-folding method. Transmission spectrum of this metamaterial shows unambiguous isotropic characteristics for any lateral rotation, polarization, and incident angle up to 40º. The corresponding numerical simulations well re-produced the experimental results, revealing that the interplay of electric and magnetic interactions of the 3D meta-atom plays a crucial role for the bi-anisotropic responses. We anticipate our technique to be a breakthrough for introducing the concepts of metamaterials to real-components.

t-tanaka@riken.jp