Coated Drop-Shaped Nanowires for Guiding THz Surface Plasmon Polaritons with Nanoscale Confinement and Ultra-Long Propagation Distances

Focusing far beyond the diffraction limit is very important for terahertz (THz) wave applications due to its much longer wavelength compared with optical wave. Surface plasmon polaritons (SPPs) on metal wires are frequently used to attain this focusing. However, when the mode width is reduced down to the nanometer scale, the mode loss is very high. Here, a coated drop-shaped nanowire (CDSN) is proposed for guiding THz SPPs with both ultra-strong mode confinement (10 nm) and extreme-long propagation length (1 similar to 15 mm), which result from the distinctive mode fields around the top and bottom arcs, respectively, of the metal wire. The fantastic mode properties make the waveguide very useful in nanophotonics, bio-photonics, and highly integrated photonic circuits.