All-dielectric metasurface enabling spin–orbital angular momentum demultiplexing in the terahertz regime

Résumé fourni par la source

Spin angular momentum (SAM) and orbital angular momentum (OAM), as two key degrees of freedom of light in the angular momentum dimension, show significant potential for high-capacity communications in the terahertz (THz) regime. However, conventional SAM or OAM multiplexing/demultiplexing systems based on bulky optical components suffer from complex configurations and large footprints, hindering on-chip integration and limiting their application in integrated THz optical communications. Here, we propose an all-dielectric metasurface scheme for spin–orbital angular momentum demultiplexing for the THz regime. By combining propagation phase and geometric phase in a single-layer architecture, the metasurface independently manipulates phase profiles under orthogonal circular polarizations, enabling simultaneous discrimination and spatial separation of SAM and OAM states. Through the incorporation of helical and off-axis phase designs, channels with different SAM and OAM are accurately focused into predefined positions and transformed into Gaussian spots, significantly improving coupling efficiency for THz detection. As a proof of concept, a 20-channel demultiplexing system (2SAM×10OAM states) is demonstrated, with inter-channel isolation better than −7.27dB and an overall transmittance of 68.2%–75.3% (insertion loss of approximately 1.25–1.65 dB). This work provides what we believe to be a novel and efficient technological pathway toward high-capacity, low-loss, and integrated angular momentum multiplexing communications in the THz regime.

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