Power modulation of vortex beams using phase/amplitude adjustable transmissive coding metasurfaces

Independent control of amplitude and phase using a single aperture is challenging but highly desirable due to its great potential applications in high-quality holograms, modern wireless communications, and other modern devices. In this paper, based on the generalized superposition principle of metasurfaces (MSs), a transmissive coding MS is proposed to manipulate the power transmitted toward specific angular directions. To this end, a cascaded coding meta-atom is presented to control both transmission amplitude and phase responses. These particles with 2-bit-phase and 1-bit-amplitude discretizations are designed by printing a metallic bar, square loops and split-ring resonators on dielectrics placed in a cascaded geometry. As an application, vortex beams carrying orbital angular momentum (OAM-VB) with controllable transmitted power levels are realized by suitably distributing the phase/amplitude adjustable coding particles. Three illustrative examples are demonstrated to realize high-power OAM-VB (h-OAM-VB), low-power OAM-VB (l-OAM-VB), and medium-power OAM-VB (m-OAM-VB), respectively. Some OAM-VBs with flexible features are also generated using the convolution operations of digital coding patterns. The presented models are experimentally validated in which m-OAM-VB and h-OAM-VB patterns are successfully generated at Ku band. The proposed MS-based architecture would enable flexible power allocations in the next generation of multi-input-multi-output communication platforms. (paper)