Figure 4: (a) Sketch of the setup for measurements of the transmission through an active rolled-up metamaterial. The setup allows to optically excite active layers, for example, InGaAs quantum wells, inside the metamaterial to enhance the light transmission. (b) The transmission enhancement of an active rolled-up metamaterial is plotted against the photon energy showing a pronounced maximum of at a photon energy of eV. Images taken from [30].