Compact multimode vortex-wave radiator enabled by quasi-1D spoof plasmons

We demonstrate a compact multimode vortex-wave radiator based on quasi-one-dimensional spoof surface plasmon polaritons (quasi-1D SSPP). The structure supports simultaneous generation of four distinct orbital angular momentum modes l=1, -2, 3, -4 at a single frequency. Enabled by the high propagation constant and strong field confinement of the dispersion-engineered spoof surface plasmon polaritons (SSPP) waveguide, the device achieves a footprint of only 0.9\lambda while maintaining high mode purity and low intermodal crosstalk. Although implemented in the microwave regime for experimental accessibility, the subwavelength corrugated geometry and slow-wave phase control mechanism are directly scalable to terahertz and infrared frequencies. This work provides a practical platform for integrated orbital angular momentum (OAM) multiplexing using planar-compatible plasmonic architectures, with potential applications in structured light generation and high-capacity photonic systems.