Fabrication of polarization-dependent reflective metamaterial by focused ion beam milling.

By focused ion beam milling, we fabricated near-IR reflective metamaterials consisting of nano-aperture arrays. Optimum parameters of ion beam current and accelerating voltage in the fabrication process are obtained. Nano-apertures constituting reflective metamaterial are successfully milled, and possess a reflective resonance in the near-IR spectral range. With a double-split-ring resonator structure for the nano-aperture, the intensity reflection at resonance is rendered polarization dependent. It is found that the point group symmetry of the nano-aperture array determines the amount of anisotropy in the intensity reflection. Finite-difference time-domain simulation was adopted to identify details of nano-aperture metastructures transferred from nano-aperture patterns by the focused ion beam milling.