Tuning Spoof Plasmons in GHz and THz Using Liquid Crystals

Spoof surface plasmon polaritons (SSPPs) offer a powerful way to confine and guide light at terahertz and gigahertz frequencies, but their functionality is typically locked by their static geometries. This study demonstrates the active tuning of SSPP resonances using nematic liquid crystals (LCs) integrated into metallic grating structures. Through full-wave numerical simulations, we show that both reorienting the LC director and inducing the nematic–isotropic phase transition enable the efficient modulation of the SSPP resonance frequency. In the terahertz regime, tuning ranges exceeding 150 GHz are achieved while preserving strong resonant absorption. For GHz-scale structures, we identify optimal configurations—such as partially dielectric-filled grooves topped with an LC layer—that overcome field confinement challenges and provide practical frequency shifts of several gigahertz. These results establish LCs as an effective tuning medium for reconfigurable SSPP devices for future applications in emerging THz and GHz photonics.