Controlling angular dispersions in optical metasurfaces

Although metasurfaces have shown great potential for manipulating light, most previously realized meta-devices suffer from uncontrolled angular dispersions, making them unfavorable for many applications. Here, we propose a general strategy to realize optical metasurfaces with desired angular dispersions based on carefully controlling both the near-field couplings between meta-atoms and the radiation pattern of a single meta-atom. Utilizing such a strategy, we experimentally demonstrate a series of optical meta-devices with predesigned angular dispersions, including two incident-angle-insensitive absorbers, one incident-angle-selective absorber, and one multifunctional meta-polarizer whose functionality changes from a perfect mirror to a half-waveplate as the excitation angle varies. Finally, we design a gradient meta-device using meta-atom arrays with purposely controlled angular dispersions and numerically demonstrate that it can exhibit distinct wavefront-control functionalities when illuminated at different incident angles. Our findings establish a new platform for achieving angle-multiplexed functional meta-devices, significantly expanding the wave-manipulation capabilities of optical metasurfaces. Scientists can control how optical meta-surfaces interact with different angles of incident light by making changes to their individual building blocks. The finding, by Lei Zhou and colleagues at China’s Fudan University, could lead to the realization of angle-multiplexed meta-devices. The researchers measured how light was reflected by a typical optical meta-surface depending on its incident angle. Their observations led them to theorize that reflected light was controlled by the interactions between meta-atoms and by radiation from individual ones. Changes to the meta-atom arrays allowed them to fabricate devices that altered light’s polarization, selectively absorbed light based on the incident angle, or absorbed light regardless of it. Finally, they were able to simulate a device with specific meta-atom arrangements that could both focus light or act as a mirror depending on the incident angle.