Mode Conversion of Propagating Surface Plasmons in Nanophotonic Networks Induced by Structural Symmetry Breaking

Nanophotonic plasmon circuits may play important roles in next- generation information technology as semiconductor- based electronics is approaching the physical limit. The functions of such circuits rely on the rigorous control of plasmon propagation. One important aspect of such control is controlling the conversion of different plasmon modes for designed plasmon routing in complex nanophotonic networks. Here, for the first time, we experimentally prove that the conversion of plasmon modes occurs widely in metallic nanowire waveguides, the basic components of plasmonic circuits, by introducing local structural symmetry breaking. In further simulations for the structure of a nanowire with a particle in its proximity, it is shown that the mode conversions originate from the redistribution of electric field on the wave front which is caused by the scattering of localized modes in the nanogap and on the nanoparticle. This mode conversion effect can be applied to flexibly control the plasmon propagation behavior in plasmonic nanowire networks.