| Propagating two-dimensional surface plasmon waveguide modes supported by silver nanoridges with flat-top, triangular, and elliptical cross sections are investigated. Mode profiles, dispersion relations, propagation distances, mode sizes, and figures-of-merit are calculated for these nanoridge waveguides. There is only one guided mode associated with the nanoridge, which is a quasi-TEM mode with longitudinal field components one order of magnitude smaller than transverse field components. The quasi-TEM nature of the mode reveals that free electron oscillations located at the top of the nanoridge is the main contributor to tightly confined nature of plasmon modes. When the height of a triangular nanoridge or the curvature of an elliptical nanoridge is large, the nanoridge plasmon mode approaches a wedge plasmon mode. The optimal triangular nanoridge waveguide is obtained when the top wedge angle is approximately 120 degrees, and the optimal elliptical nanoridge waveguide is obtained when the elliptical waveguide cross section approaches a semicircular cross section. |
