Simultaneous and independent regulation of circularly polarized terahertz wave based on metasurface

Active multi-focus vortex beam terahertz encoding metasurface based on Dirac semimetals

An electromagnetic wavefront can be flexibly manipulated by discrete phase coding on the coding unit. In this paper, we designed two coding metasurfaces with 1-bit and 3-bit based on active tuning of Dirac semimetals by controlling the Fermi level (E F) with an external polarization voltage. The size and structure of the metasurface remain unchanged with this strategy. Both designs were found to be dynamically tunable. The 1-bit coding metasurface enables beam conversion, single-focus switching, and switching between single-focus and multi-focus. On the other hand, the 3-bit coding metasurface enables the switching between vortex beams and single-beam mirror reflections. These proposed structures have potential applications in terahertz (THz) communications and terahertz-focused imaging, opening up new possibilities for the dynamic modulation of THz waves.

Wideband reflective metasurface for independent control of mode and circular polarization of orbital angular momentum

Pancharatnam-Berry (PB) phase, usually utilized for phase manipulation of circularly polarized (CP) waves, has inherent symmetrical response on left-handed polarized (LCP) and right-handed polarized (RCP) for orbital angular momentum (OAM), which severely hinders its application. By modulating both propagation and PB phase allows independent control of LCP and RCP of OAM, but increases the design difficulty. Here, we propose a phase compensation scheme to independent control the CP states of OAM only utilizing PB phase, where arbitrary topological charges and deflection directions of LCP and RCP beams can be realized. Two wideband metasurfaces are designed to independent control the mode, circular polarization and beam directions of OAM at the frequency range of 10-20 GHz. This work significantly motivates the development of polarization division multiplexing in wireless communication system.

Dual-band metasurface generating multiple OAM beams independently in full polarizations

In this paper, a dual-band metasurface (MS) generating multiple orbital angular momentum (OAM) beams independently in full polarizations is proposed. First, the design principle of controlling full polarizations independently is analyzed. Second, the frequency selective surface is introduced to the meta-atom design that ensures the meta-atom operates at Ku- and Ka-band independently, while, at each band, sixteen optimized meta-atoms realize the high reflection amplitude and enough phase coverage. Next, the optimized dual-band meta-atom controlling full polarizations independently is utilized to design the MS, which could generate eight independent OAM beams including the x-polarized, y-polarized, left hand circularly polarized, and right hand circularly polarized OAM beams at dual-band. Finally, the MS is designed, fabricated, and measured. Both simulated and measured results verify that the proposed MS could generate multiple OAM beams in full polarizations at dual-band, showing the perspective in the OAM-based area, such as the wireless communication, target detection, and security encryption.