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Terahertz (THz) communication is an up‐and‐coming technology for the sixth‐generation wireless network. The realization of ultra‐high‐speed THz communication requires the combination of multi‐dimensional multiplexing schemes, including polarization division multiplexing (PDM), mode division multiplexing (MDM), and wavelength division multiplexing, to increase channel capacity. However, most existing devices for MDM in the THz regime are single‐purpose and incapable of multi‐dimensional modulation. Here, all‐dielectric metasurfaces are designed for 2D multiplexing/demultiplexing, which takes the lead in combining orbital angular momentum (OAM) MDM and PDM in the THz regime. The multi‐functional wavefront phase modulations and interleaved meta‐atom arrangements are used to realize polarization‐selective multichannel OAM mode (de)multiplexing, in which the linear‐polarized 4‐channel and circular‐polarized 6‐channel demultiplexing are experimentally demonstrated. Between different linear‐polarized channels, the measured maximum crosstalk is −16.88 dB, and the isolation of each channel can be greater than 10 dB in a range wider than 0.1 THz. This study paves the way for multi‐dimensional multiplexing in the THz regime, which may benefit extremely high‐capacity and integrated THz communication systems. The proposed design strategy is readily applied to multi‐functional metasurfaces for microwaves and far infrared light, facilitating the development of multiplexing technology and OAM‐related applications. [ABSTRACT FROM AUTHOR]

Abstract: Weyl points, three‐dimensional linear bulk bands crossings possessing intrinsic helicities, are counterparts of magnetic monopoles in the momentum space. One of the most important features of Weyl semimetals is the presence of topologically protected non‐trivial surface states at the boundary that connect between Weyl points of opposite charges. In condensed matter physics, these surface states are called Fermi arcs whose length measures the topological strength of the system. Here we theoretically show that photonic ‘Fermi arcs’ can exist at the interface between two magnetized plasma under static bias magnetic fields of different orientations, i.e. a twisted configuration, whereas the length of the ‘Fermi arcs’ can be arbitrarily stretched by varying the relative orientation and intensities of two static bias magnetic fields. Interestingly, the ‘Fermi arcs’ join two Weyl points of the same sign but residing on different side of the interface. Our work gives insight to the connectivity of ‘Fermi arcs’ between two topological semimetals and could open gateway towards tunable photonic topological systems. [ABSTRACT FROM AUTHOR]

Terahertz (THz) metasurfaces have emerged as a powerful tool for manipulating THz wavefronts, typically achieved by adjusting various geometric parameters. In this study, an approach is introduced by incorporating interlayer coupling into twisted stacking metasurface design to completely control the amplitude and phase of circularly polarized THz waves. By leveraging the interlayer coupling effect and the Pancharatnam–Berry phase, the study achieves efficient control over transmission phase and amplitude by simply adjusting the relative twist angle between paired C‐shaped split‐ring resonators. To validate the concept, a holographic metasurface is fabricated and characterized, providing experimental evidence of its THz wavefront manipulation capabilities. This design strategy presents a versatile and tunable solution for THz wave control, promising applications in a wide range of functional devices. [ABSTRACT FROM AUTHOR]