Extending the propagation distance of the sodium nanowire plasmonic waveguide with a LiNbO₃ slot on the dielectric substrate

The diffraction limit hinders the further miniaturization and integration of photonic devices, and the in-depth research of surface plasmon polaritons (SPPs) has brought a turning point to realize subwavelength photonic devices. However, the noble metal-based plasmons suffer from high loss with propagation distance on the order of 100[Formula: see text][Formula: see text]m. Here, we design and study a plasmon waveguide consisting of a vertical slot LiNbO 3 waveguide with an embedded Na nanowire and a thin Si layer. The results show that the proposed waveguide can support both the plasmon mode (PM) and the dielectric-based plasmon mode (DPM). The DPM exhibits ultra-low losses with propagation distances in the millimeter scale (even centimeter scale). Meanwhile, the DPM exhibits subwavelength characteristics. Finally, the low-loss property combined with the subwavelength modal field leads to an extremely high figure of merit (FoM) above 10 4 (even 10 5 ). Compared with the single Na nanowire, the proposed waveguide results in 2–3 orders of magnitude improvement in propagation distance and FoM. The results of this study will provide guidance for the design of novel low-loss plasmonic devices, and promote their applications in the field of nanophotonics.