Lateral dimension tuned ultra-low loss effective surface plasmonic waveguide

Recent theoretical and experimental works demonstrate that effective surface plasmon polaritons (ESPPs) induced by structural dispersion in bounded waveguide are perfect low-frequency counterpart of optical SPPs both for the double-layered and multi-layered systems. In all these efforts, the lateral dimension of each layer was assumed to be the same and the dispersion of the ESPPs was only tuned by the dielectric permittivity in each layer. Inevitably, the dielectric loss will deteriorate the transmission performance of ESPPs due to the huge field confinement and enhancement. In this work, we propose a simple but robust scheme to dramatically enhance the transmission efficiency of ESPPs by introducing a double-layered air-filled plasmonic waveguide with different lateral dimensions. Simulation and experimental results demonstrate that an ultra-low loss plasmonic waveguide with tunable bandwidth can be easily built by changing the lateral dimension of the upper air layer. This work provides valuable guidance for flexible design of low-loss plasmonic devices and systems at microwave and terahertz frequencies.