  We propose a plasmonic device consisting of a concentric ring grating acting
as an efficient tool for directional launching and detection of surface
plasmon-polaritons (SPPs). Numerical simulations and optical characterizations
are used to study the fabricated structured gold surface. We demonstrate that
this circularly symmetrical plasmonic device provides an efficient interface
between free space radiation and SPPs. This structure offers an excellent
platform for the study of hybrid plasmonics in general and of plasmon-emitter
couplings in particular, such as those occurring when exciting dye molecules
placed inside the ring. As illustrated in this work, an interesting property of
the device is that the position of excitation determines the direction of
propagation of the SPPs, providing a flexible mean of studying their
interactions with molecules or dipole-like emitters placed on the surface.
