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Abstract 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 Over the past decade, orbital angular momentum has garnered considerable interest in the field of plasmonics owing to the emergence of surface-confined vortices, known as plasmonic vortices. Significant progress has been made in the generation and manipulation of plasmonic vortices, which broadly unveil the natures of plasmonic spin–orbit coupling and provide accessible means for light–matter interactions. However, traditional characterizations in the frequency domain miss some detailed information on the plasmonic vortex evolution process. Herein, an exotic spin–orbit coupling phenomenon is demonstrated. More specifically, we theoretically investigated and experimentally verified a temporally deuterogenic vortex mode, which can be observed only in the time domain and interferes destructively in the intensity field. The spatiotemporal evolution of this concomitant vortex can be tailored with different designs and incident beams. This work extends the fundamental understanding of plasmonic spin–orbit coupling and provides a unique optical force manipulation strategy, which may fuel plasmonic research and applications in the near future. 

Abstract Geometric phase metasurfaces, as one of the main branches of meta‐optics, have attracted enormous interest in the last two decades. Recently, through rotating a set of subwavelength dipole sources, geometric phase concept has been extended to near‐field regime for the control of surface plasmons (SPs). Despite this progress, puzzles and shortcomings still exist: it is curious that geometric phases equal to once and twice the rotation angle of dipole source are both reported for SP controls, and the control strategies examined thus far only work for a single wavelength. Hereby, a rigorous derivation of the SP excitation of dipole sources upon circularly polarized illumination is performed, and the rotation dependence and in‐plane coordinate correlation of geometric phase control of SPs is clarified. Moreover, a holographic approach is proposed to implement multiplexed geometric phase control, experimentally demonstrating several metalenses that can couple and steer the incident circular polarizations of four wavelengths and two spin directions to different SP focusing beams. This work will pave an avenue toward the development of integrated and multiplexed SP devices. 

The terahertz regime is widely recognized as a fundamental domain with significant potential to address the demands of next-generation wireless communications. In parallel, mode division multiplexing based on orbital angular momentum (OAM) shows promise in enhancing bandwidth utilization, thereby expanding the overall communication channel capacity. In this study, we present both theoretical and experimental demonstrations of an on-chip terahertz OAM demultiplexer. This device effectively couples and steers seven incident terahertz vortex beams into distinct high-quality focusing surface plasmonic beams, and the focusing directions can be arbitrarily designated. The proposed design strategy integrates space-to-chip mode conversion, OAM recognition, and on-chip routing in a compact space with subwavelength thickness, exhibiting versatility and superior performance. 

Metasurfaces have been continuously garnering attention in both scientific and industrial fields owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures. Terahertz vortex beams have become a focus of research in recent years due to their prominent role in many cutting-edge applications. However, traditional terahertz vortex beam plates are often faced with challenges including large size, low efficiency, and limited working bandwidth. Here, we propose and experimentally demonstrate highly efficient and broadband vortex beam plates based on metasurface in the terahertz region. The experimental results well verify that the designed metasurfaces can efficiently generate terahertz vortex beams with different orbital angular momentum topological charges in the range of 0.5–1 THz. Notably, the maximum efficiency can reach about 65% at 0.5 THz. The proposed devices may play a vital role in developing vortex beams-related terahertz applications. 

Artificially designed modulators that enable a wealth of freedom in manipulating the terahertz (THz) waves at will are an essential component in THz sources and their widespread applications. Dynamically controlled metasurfaces, being multifunctional, ultrafast, integrable, broadband, high contrasting, and scalable on the operating wavelength, are critical in developing state-of-the-art THz modulators. Recently, external stimuli-triggered THz metasurfaces integrated with functional media have been extensively explored. The vanadium dioxide (VO2)-based hybrid metasurfaces, as a unique path toward active meta-devices, feature an insulator–metal phase transition under the excitation of heat, electricity, and light, etc. During the phase transition, the optical and electrical properties of the VO2 film undergo a massive modification with either a boosted or dropped conductivity by more than four orders of magnitude. Being benefited from the phase transition effect, the electromagnetic response of the VO2-based metasufaces can be actively controlled by applying external excitation. In this review, we present recent advances in dynamically controlled THz metasurfaces exploiting the VO2 phase transition categorized according to the external stimuli. THz time-domain spectroscopy is introduced as an indispensable platform in the studies of functional VO2 films. In each type of external excitation, four design strategies are employed to realize external stimuli-triggered VO2-based THz metasurfaces, including switching the transreflective operation mode, controlling the dielectric environment of metallic microstructures, tailoring the equivalent resonant microstructures, and modifying the electromagnetic properties of the VO2 unit cells. The microstructures’ design and electromagnetic responses of the resulting active metasurfaces have been systematically demonstrated, with a particular focus on the critical role of the VO2 films in the dynamic modulation processes.