Achromatic Multibeam Diffraction Based on Phase Gradient Metasurfaces

Abstract

Metasurfaces have attracted extensive attention due to their excellent capabilities in wavefront manipulation. However, chromatic aberration, which is widely present in phase-modulated tuning metadevices, limits their applications in modern communication systems. Far-field achromatism has been explored but only considered for single-order diffraction. With increasing demands and studies on multibeam diffraction, including, but not limited to, phase-modulated metasurfaces and metagratings, most of them are not suitable for dispersion manipulation. In this article, we analyze the achromatic mechanism of the diffraction field and propose a feasible solution to coherently control the dispersion on multiorder diffractions simultaneously. The chiral phase is introduced in the meta-atom to engineer the dispersion characteristics. In addition, an achromatic dispersion metasurface is designed for dual-beam generation as proof of concept. The two beams with propagation direction −35° and +35° show good angle stability at the targeted frequencies of 7, 10, and 13 GHz. Moreover, the limitations on beam direction accuracy and metasurface aperture are also discussed. An improvement method that can greatly enhance the accuracy of diffraction angle is further proposed, where the deviation between actual beam angles and expected ones is reduced to below 0.8°, with a 73% enhancement. The proposed work builds up a major advance for diffraction management and shows great potential in wireless communications and radar detection.