Orbital angular momentum generator with multiple retroreflection channels enabled by an angle-selective metasurface.

Abstract

Vortex beams carrying orbital angular momentum (OAM) have aroused great attention on account of the remarkable potential in the field of communication. It has the characteristics of higher spectrum efficiency, greater channel capacity and stronger anti-interference, which will revolutionize the wireless communications in the future. However, target tracking on a vortex generator in practical applications is becoming a challenge because the backscattering of electromagnetic (EM) waves under oblique incidence is too small for detection. Currently, the main way to solve this problem is to load an extra retroreflector such as Luneburg lens, which in turn leads to increased weights and bulky volumes. In this paper, we propose a vortex generator simultaneously with retroreflective characteristics utilizing an angle-selective metasurface. The meta-atom can achieve broadband polarization conversion under normal incidence and efficient retroreflection under oblique incidence. Without the need for an additional retroreflection phase arrangement, an OAM generator composed of such meta-atoms can be achieved in 15.0-21.0GHz under both x- and y-polarized normal incidence. Meanwhile, four retroreflection channels are opened under oblique illumination of both transverse electric (TE) and transverse magnetic (TM) waves at 20.0GHz. Both the simulated and measured results show excellent performances. The integration of an OAM generator and retroreflector will greatly reduce the weight and volume and save in the cost of production, which will promote the development of miniaturized, multi-role, and even intelligent functional devices.