  Tailoring the emission of plasmonic nanowire-based lasers represents one of
the major challenges in the field of nanoplasmonics, given the envisaged
integration of such devices into on-chip all-optical circuits. In this study,
we proposed a mode selection scheme based on distributed feedback, achieved via
the external coupling of single zinc oxide nanowires to an aluminum grating,
which enabled a quasi-single mode lasing action. The nano-manipulation of a
single nanowire allowed for a reliable comparison of the lasing emission
characteristics in both planar (i.e. nanowire on the metallic substrate) and
on-grating configurations. We found that, by varying the orientation of the
nanowire on the grating, only when the nano-cavity was perpendicular to the
ridge direction, an additional peak emerged in the emission spectrum on the
low-energy side of the gain envelope. As a consequence of the fulfillment of
the Bragg condition, such a peak was attributed to a hybrid mode dominating the
mode competition. Simulation results showed that the hybrid mode could be
efficiently waveguided along the nanowire cavity and supported by localized
plasmon polaritons building up at the raised features ("fences") on top of the
metal grating ridges. Moreover, the hybrid mode was found to experience an
extra reflectance of nearly 50% across the grating periods, in addition to that
provided by the nanowire end facets.
