Abstract
Vortex beam generators, particularly those operating in transmission mode, are extremely important in modern communication systems because they are believed to be an effective way to extend the capacity of a communication channel. However, current approaches have suffered from complex configurations, fixed operation modes, and low efficiency, particularly in a transmissive case. In this study, we propose a new strategy for improving the transmissive amplitude and bandwidth of metasurfaces by optimizing microstructures with a non-uniform thickness based on the transfer matrix method (TMM). As a result, our designed meta-atom can achieve a high transmission of greater than 0.9 within a wide frequency interval of 12.6-16.2 GHz. As a proof of concept, we designed a vortex beam generator with topological charge l = 1 using the designed meta-atom. We conducted near- and far-field experiments to characterize its performance, indicating that our meta-device can realize a pure vortex beam with an efficiency of higher than 82.1% at a central frequency of 15 GHz. Our findings will lay a theoretical foundation for studies on metasurfaces with a non-uniform thickness and provide a way to design high-performance meta-devices with broad bandwidths.
Highlights
Orbital angular momentum (OAM) vortex beams have been extensively realized using different approaches owing to their strictly orthogonal channel with different modes and excellent transmission capability [1]–[4]
Numerous efforts have been devoted to generating vortex beams, such as spiral phase plates (SPPs) [13], [14], holographic diffraction gratings [15], [16], spiral reflectors [3], [17], [18], antenna arrays [19]–[22], and reflective metasurfaces [23]–[31]
We proposed an ultra-broadband reflective Pancharatnam–Berry metasurface for generating vortex beams within 12–18 GHz [27]
Summary
Orbital angular momentum (OAM) vortex beams have been extensively realized using different approaches owing to their strictly orthogonal channel with different modes and excellent transmission capability [1]–[4]. Because the different working modes of vortex beams are orthogonal to each other, each mode can be used for signal loading in an independent and convenient manner [5], [6]. Numerous efforts have been devoted to generating vortex beams, such as spiral phase plates (SPPs) [13], [14], holographic diffraction gratings [15], [16], spiral reflectors [3], [17], [18], antenna arrays [19]–[22], and reflective metasurfaces [23]–[31]. Some methods have been proposed to enhance the transmission amplitude and realize a high efficiency of the designed meta-device [32]–[37] These meta-atoms are seriously restricted to narrow bandwidths
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