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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. 

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. 

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.