Metasurface-enabled cylindrical vector beam multiplexing for compact, high-channel-count, and bidirectional optical fiber communication

Cylindrical vector beam (CVB) multiplexing has emerged as a promising strategy for high-performance optical backbone networks in sixth-generation communication systems, effectively addressing escalating bandwidth requirements. However, conventional CVB multiplexing systems typically scale by incorporating additional discrete optical components, presenting challenges in system integration, footprint, and bidirectional operability. In this study, we propose and demonstrate a compact, high-channel-count, bidirectional CVB multiplexing system employing all-dielectric metasurfaces (MSs) integrated onto the end facets of a few-mode fiber (FMF). The system employs identical MSs on the FMF end facets to enable nine off-axis vector mode conversions between CVBs propagating within the FMF core and fundamental Gaussian beams in free space. The FMF features an optimized core radius to ensure efficient, low-loss CVB transmission, enabling nine-channel bidirectional optical interconnection. The theoretical validation of the multiplexing and demultiplexing functions demonstrated the high mode selectivity of the system, compatibility with wavelength-division multiplexing, and significant scalability. This design forms a solid basis for scalable, low-latency, high-capacity bidirectional optical links with broad applicability in emerging domains such as smart cities, intelligent transportation systems, and quantum communication networks.