Long-range spoof surface plasmons(LRSSP) on the asymmetric double metal gratings

Spoof surface plasmons (SSP) on the corrugated metal surfaces have been widely studied over the past decade in both microwave and Terahertz (THz) band. Previous studies show that SSP mode on the metal grating suffers from high dissipative losses in high THz band especially near asymptotic frequency which may limit its real applications. The issue can be addressed by utilizing long-range SSP mode (LRSSP). LRSSP is a special low-loss symmetric propagating surface wave mode along double-layer corrugated metallic waveguides. In this paper, the asymmetric double metal gratings are proposed to support LRSSP which can significantly reduce the damping losses of the other short-range SSP mode (SRSSP) on the conventional doubly-corrugated metallic surfaces, thus enabling new possibilities to utilizing this SRSSP mode within long-range manner. According to our dispersion theory and the numerical calculations, the propagation loss of LRSSP is still lower than that of SRSSP within asymmetric regime, which demonstrates good tolerance to the asymmetry of the double-layer corrugated structure. However, its long-range propagation superiority of LRSSP vanishes gradually as the degree of asymmetry is enlarged. This work provides an alternative approach to increase the propagation length of SRSSP mode on the doubly-corrugated metallic surfaces and can open up new avenues to develop some novel LRSSP-based plasmonic devices such as waveguides, filters, sensors and active powerful radiation sources induced by energy beam below optical spectrum.