Broadband Functional Metasurfaces: Achieving Nonlinear Phase Generation toward Achromatic Surface Cloaking and Lensing

Generalized law of refraction and reflection has enabled a tremendous amount of degrees of freedom for full vectorial electromagnetic manipulation with metasurfaces. However, owing to the fundamental limitations of bandwidth and efficiency, the implementation of such principle is still far from perfect as truly achromatic efficient wavefront manipulation has not been realized. Here, a design principle based on the generalized Gires–Tournois interference model and catenary electromagnetics theory is proposed that can achieve desired broadband dispersion engineering regardless of the incident polarizations. As a proof of concept, a surface cloak is fabricated and demonstrated with a large fractional bandwidth of more than 40%. An achromatic lens antenna is also designed with focal shift deviation ratio less than 2% across X band to Ku band. Both of the devices show great advances versus traditional approaches by at least one order of magnitude. Besides, this conceptually new design is also applicable to other scenarios, such as beam splitters, vortex beam generators, or metasurface holograms. Considering their compact profiles and simple topologies, it is believed that such functional metasurfaces are promising in practical applications such as beam control, camouflage, and space communications.