Full Complex‐Amplitude Engineering by Orientation‐Assisted Bilayer Metasurfaces

Abstract Optical complex‐amplitude determines the propagation behavior of light in free space to the maximum extent. Precise control of complex‐amplitude is the key to generating user‐defined light fields. Current attempts to control optical complex‐amplitude using metasurface, however, either have limited amplitude/phase step numbers or lost high lateral resolution since amplitude and phase are usually manipulated with size‐varied nanostructures or several nanostructures integrated into a unit‐pixel. Here, it is shown that bilayer metasurface can readily decouple optical amplitude and phase, thus achieving arbitrary complex‐amplitude modulation only by arranging the orientation angles of nanostructures. In this design, each unit‐pixel in one layer has only one nanostructure with the same size, thus significantly increasing the lateral resolution of complex‐amplitude modulation. More importantly, the approach of controlling optical complex‐amplitude merely by changing nanostructure orientation can significantly simplify the metasurface design and aggrandize the fabrication tolerance, thus enhancing the robustness of metasurfaces toward practical applications.