  We propose a topological plasmonic crystal structure composed of an array of
parallel nanowires with unequal spacing. In the paraxial approximation, the
Helmholtz equation that describes the propagation of light along the nanowires
maps onto the Schr\"{o}dinger equation of the Su-Schrieffer-Heeger (SSH) model.
Using full three-dimensional finite difference time domain solution of the
Maxwell equations we demonstrate the existence of topological defect modes,
with sub-wavelength localization, bound to kinks of the plasmonic crystal.
Furthermore, we show that by manipulating kinks we can construct spatial mode
filters, that couple bulk modes to topological defect modes, and topological
beam-splitters that couple two topological defect modes. Finally, we show that
the structures are robust to fabrication errors with inverse length-scale
smaller than the topological band gap.
