Mirror-symmetric multi-OAM vortex beam generation with 1-bit interleaved terahertz metasurfaces

Abstract

Recently, vortex beams carrying various orbital angular momentum (OAM) have become a research boom in terahertz wireless communications due to their infinite modes. However, existing metasurfaces difficultly generate multi-OAM vortex beams with different topological charges simultaneously, which severely limits their practical applications due to low channel capacity and number. To address the above issues, here, a 1-bit interleaved terahertz metasurface is proposed to implement the polarization multiplexing and generate mirror-symmetric multi-OAM vortex beams with opposite topological charges. The supercell of interleaved terahertz metasurface consisting of two pairs of cross-metal subunit. The irrotational cross-metal subunit can implement line polarization (LP) multiplexing by using the independent propagation phase, while the rotational cross-metal subunit can realize circular polarization (CP) multiplexing by combining the geometric phase and the propagation phase, thereby enhancing the channel number. By 1-bit quantization phase strategy, furthermore, each channel can generated mirror-symmetric vortex beam with opposite topological charge simultaneously, increasing the channel capacity. As a conceptual demonstration, a 1-bit interleaved terahertz metasurfaces is constructed by the above interleaved supercell. By adjusting the polarization states of the incident waves, three or four pairs of mirror-symmetrical vortex beams with opposite topological charges can be generated simultaneously. Moreover, the generated vortex beams have a good agreement with the theoretical design. Therefore, the proposed scheme shows the significant advantages of large channel number, high channel capacity, and simple construction of metasurfaces, which offers the promising applications in terahertz multifunctional integrated-devices and high-speed and large-capacity 6G communications.