Broadband Amplitude–Phase Metasurface for Generating Crosstalk-Free Amplitude-Modulated Vortex Beams

Multimode vortex beams, especially if carrying modes are tailorable without crosstalk, possess ubiquitous applications from optical to radio fields. However, most of the metasurfaces demonstrated so far, for example, phase-only ones, only provide phase manipulation to generate multimode vortex waves, leading to unexpected crosstalk modes. In this article, we propose a reflection-type broadband amplitude-phase metasurface to generate broadband and crosstalk-free multimode vortex beams, which have also been theoretically verified. Specifically, the dipole-loaded quasi-I-shaped meta-atoms are applied to achieve broadband-independent controls of reflection amplitudes within a range of [0, 0.95] and a 360° phase coverage from 8.6 to 17.8 GHz. Inspired by the amplitude-modulated (AM) technology in the time domain, we mainly investigate the AM vortex beams in the space domain, which belong to multimode vortex beams that have spatially varying amplitude along the azimuth. Finally, two broadband amplitude-phase metasurfaces are devised to generate crosstalk-free AM vortex beams in both simulation and experiment. Those AM vortex beams have spatially tailored amplitude and phase patterns, which can promote the development of multimode communication and other beam-control applications.