Three kinds of multifunctional graphene metasurfaces based on Pancharatnam–Berry (PB) phase cells are proposed and numerically demonstrated to control a reflected wave’s spin angular momentum (SAM) and orbital angular momentum (OAM) in the terahertz (THz) regime. Each proposed metasurface structure is composed of an array of graphene strips with different deviation angles and a back-grounded quartz substrate. In order to further help readers have a deeper insight into the graphene-based metasurfaces, a detailed design strategy is also provided. With the aid of the designed graphene elements, the proposed metasurfaces can achieve the full 360° range of phase coverage and provide manipulation of SAM and OAM of a circularly polarized (CP) wave at will. More importantly, simultaneous control of these two momentums can also be realized, and in order to demonstrate this function, a THz spin-controlled OAM beam generator with diverse topological charges is created, which can provide one more degree of freedom to improve the channel capability without increasing the bandwidth compared to a linearly polarized (LP) OAM beam. Numerical results verify the proposed graphene metasurfaces, which pave the way for generating spin OAM vortex waves for THz communication systems.
Driven by the continuous demand for system integration and device miniaturization, integrating multiple diversified functions into a single metasurface hybridized with the tunable metaparticle is highly demanding at terahertz (THz) range. However, up to now, because of the limitation of the tunable metaparticle at terahertz range, most of the metasurfaces feature a single function only or process similar functionalities at a single frequency. A reconfigurable multifunctional metasurface which can realize the switch of transmission and reflection and manipulate the linearized polarization state of electromagnetic waves simultaneously over a controllable terahertz frequency range based on the vanadium dioxide was designed for the first time in the paper. The numerical result demonstrates the validity of the appropriately designed metasurface. Simulation results show that the reconfigurable and multifunctional performance of this metasurface can be acquired over 1.59 THz to 1.74 THz without re-optimizing or re-fabricating structures, which effectively extends the operating frequencies. The proposed metasurface holds potential for electromagnetic wave manipulation and this study can motivate the realization of the wideband multifunctional metasurface and the software-driven reconfigurable metasurface at terahertz frequencies.
Orbital angular momentum (OAM) generation based on metasurfaces has attracted tremendous interest due to its potential in capacity enhancement of high-speed wireless communication systems. Reconfigurability is one of the key desired characteristics for the design of future metasurfaces. In this paper, a metasurface taking advantage of vanadium dioxide (VO 2) is proposed. The proposed design can generate a non-diffractive OAM beam and achieve the multiple reconfigurability of the topological charge, beam radius, beam deflection angle. The operation frequency can be adjusted by controlling the state of VO 2 at terahertz (THz) region. Simulation results demonstrate that the designed metasurface can generate a non-diffractive OAM beam with tunable topological charge and beam radius, propagating along ±x or ±y directions with the controllable deflection angle between 6.74°and 44.77°, ranging from 0.69 THz to 0.79 THz.
Multi-dimensional multiplexing based on the broadband metasurface is a promising candidate for the next generation terahertz (THz) communication system, which has become a research focus for data transmission rate and channel capacity enhancement. This paper proposes a THz frequency-reconfigurable metasurface hybridized with vanadium dioxide (VO2) for communication multiplexing on both dimensions of orbital angular momentum and frequency. Theoretically, 4 × n channel (n can be any positive integer) orthogonal coaxial beams carrying different data flow can be simultaneously generated based on the proposed metasurface in the tunable operating frequency band. The simulation results verify that the THz incident waves can be converted into orthogonal coaxial beams with different topological charges or frequencies, propagating perpendicular to the metasurface, when eight-channel oblique incident plane waves with varying angles or at various frequencies are reflected by the metasurface. The multi-dimensional multiplexing can be achieved in the frequency range of 0.29–0.39 THz and 0.24–0.34 THz with the VO2 switching between its fully insulating and metallic state. The proposed metasurface is expected to enable multi-band and broadband applications and has significant potential in high-speed and high-capacity THz communication.
We propose a novel method superposed two linearly polarized components to generate a right-handed circularly polarized (RCP) wave by using a holographic waveguide-fed metasurface. Combining with the holography principle and the polarizable particles based method, the expected RCP wave can be steered flexibly only by changing the slot state of each unit cell. A prototype generating a RCP wave at boresight direction is simulated, fabricated and measured, respectively. Both simulation and experiment results verify the good capability of the proposed metasurface. Applying this method, the resultant metasurface does not need a complex feeding network and can be easily extended to a reconfigurable CP metasurface. Therefore, the proposal has a huge potential in reconfigurable multifunctional CP devices.
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