Figure 3: (a) Microroll with six alternating layers of metal and semiconductor with a fishnet pattern obtained by focused ion beam milling. As visible, the end of the tube exhibits noncompact layer stacking. Nevertheless, in the area of the fishnet pattern the layer stacking is compact. The sketch shows the unit cell of the fishnet pattern. The electromagnetic wave is incident in direction. (b) Calculated reflection and transmission through the structure in (a). (c) The permeability and refractive index , calculated by a parameter retrieval method, reveal that becomes negative at certain frequencies. (d) A wave impinging from the left (  THz) gets negatively refracted by a prism that is cut into the fishnet structure. The prism is depicted by the white, dashed lines, with the structure infinitely extended in the direction perpendicular to the image plane. Figure reprinted from [29] with slight modifications.