Achromatic Multibeam Diffraction Based on Phase Gradient Metasurfaces

Metasurfaces have attracted extensive attention due to their excellent capabilities in wavefront manipulation. However, chromatic aberration,whichis widely present in phase-modulatedtuning meta-devices, limits their applications in modern communication systems.Far-field achromatismhas been explored but only consideredfor single order diffraction. With increasing demands and studies on multi-beam diffraction, including but not limited to, phase-modulated metasurfaces and metagratings, most of them are not suitable for dispersion manipulation. In this paper, we analyze the achromaticmechanism of diffraction field and propose a feasible solution to coherently control the dispersion on multi-order diffractions simultaneously. 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 propagationdirection -35° and +35° show good angle stability at the targeted frequencies of 7 GHz, 10 GHz and 13 GHz. Moreover, the limitations on beamdirection 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.