Periodic Dielectric Metasurfaces with High‐Efficiency, Multiwavelength Functionalities

Abstract Metasurfaces are thin‐film optical devices for tailoring the phase fronts of light. The extension of metasurfaces to multiple wavelengths has remained a major challenge, and existing design techniques do not yield devices with high efficiency. This study reports a new design method, based on inverse freeform optimization, that enables high‐efficiency, multiwavelength metasurfaces. Using an iterative optimization solver, this study incorporates multiple wavelength responses into wavelength‐scale design domains in a straightforward and automated manner. In principle, this method can readily scale to a very large number of wavelengths. As a proof of concept, this study designs and characterizes periodic transmissive metasurfaces, made from silicon, that deflect N different incident near‐infrared wavelengths to N unique diffraction orders. The theoretical and experimental efficiencies of these devices scale as 1/N^0.5, which is significantly better than current state‐of‐the‐art devices. The implementation of large‐angle, broadband blazed grating devices is also demonstrated. This study envisions that this inverse design method can generalize to high‐performance, multiwavelength, aperiodic devices, and that it serves as a potential route to broadband metasurfaces.