Independent Control of Multiple Channels in Metasurface Devices

By analogy with electromagnetic networks that connect multiple input-output ports, metasurfaces can be considered as multiport devices capable of providing different functionalities for waves of different polarizations illuminating the surface from different directions. The main challenge in the design of such multichannel metasurfaces is to realize independent and full control of the electromagnetic response for each channel incidence, ensuring the fulfilment of the boundary condition at the metasurface. In this work, we demonstrate that by properly engineering the evanescent fields excited at each port (that is, for all possible illumination directions), it is possible to independently control the reflection or transmission for all different illuminations. Using the mode-matching method, we analyze the scattering properties of generic space-modulated impedance metasurfaces. This method, combined with mathematical optimiza-tion, allows us to find a surface-impedance profile that simultaneously ensures the desired electromagnetic responses at each port. We validate the technique via the design of phase-controlled multichannel retrore-flectors and multichannel perfect absorbers. In addition, we demonstrate that the method is rather powerful in the design of other functional metasurfaces, such as multifunctional reflectors.