Propagation loss of terahertz surface plasmon polaritons on a periodically structured Ag surface

We analyze the propagation of terahertz surface plasmon polaritons on a periodically structured Ag surface by using a full-vectorial finite-difference time-domain method. The impact of some structural parameters on the dispersion relation and the propagation loss is analyzed. As the groove width increases, the dispersion curves asymptotically reach lower frequency values at the Brillouin zone edge, while the relation between the propagation loss and the groove width is somewhat complicated. For a fixed air filling factor, the period of the structure has little influence on the asymptotic frequency but has a relatively large influence on the propagation loss. The effects of the groove depth and the shape of the groove corners are also studied. It is found that the propagation loss is mainly determined by the total area of the sidewalls of the grooves in a unit length. For a typical structure with a groove width of 2 mu m, a groove depth of 10 mu m, and a period of 10 mu m, the propagation loss is less than 0.2 dB/10 mu m below 5.67 THz, while it increases dramatically beyond this frequency.