Multi-dimensional cylindrical vector beam multiplexing communication over few-mode fiber with dielectric metasurfaces

Cylindrical vector beams (CVBs) have garnered significant interest in mode-division multiplexing communication due to their ability to support orthogonal vector modes. As CVB modes represent the eigen-solutions of few-mode fibers, they are particularly well-suited for long-distance transmission. However, the current CVB mode modulation scheme, which relies on optical phase modulation devices, faces limitation because of the intrinsic uniform polarization response and structure dispersion feature. This leads to polarization insensitivity and fixed working wavelengths, thereby impeding multi-dimensional CVB mode multiplexing compatible with wavelength and polarization dimensions over few-mode fiber. To address these challenges, we leverage the powerful mode field modulation capabilities of the Pancharatnam-Berry phase based dielectric metasurfaces (PBMs). Through its spin conjugation property, we achieve polarization-sensitive mode conversion by independently loading opposite helical phases for the left and right spin components of CVBs. Additionally, its dispersion-free feature endows a wide operating bandwidth, enabling the CVB mode multiplexing compatible with wavelength division and polarization division multiplexing. As a proof of concept, we fabricate PBMs exhibiting CVB mode purity higher than 86.9 % with various polarization distributions in the C-L band. Experimentally results demonstrate the successful transmission of an 800-channel multi-dimensional CVB multiplexing communication, including 5 CVB modes, 2 polarizations, and 80 wavelengths, transmitting 18.75 Tbit/s QPSK-OFDM signals over a 5 km few-mode fiber with bit error rates below the FEC threshold (3.8 × 10⁻³). Furthermore, the mutually orthogonal polarization distribution of the same order CVB mode of the PBM modulation offers natural diversity gain, ensuring the effectiveness and reliability of communication.