Directionally-controlled periodic collimated beams of surface plasmon polaritons on metal film in Ag nanowire/Al2O3/Ag film composite structure.

Plasmonics holds promise for the realization of miniaturized photonic devices and circuits in which light can be confined and controlled at the nanoscale using surface plasmon polaritons (SPPs), surface waves of collective oscillations of electrons at a metal/dielectric interface. However, realizing plasmonic applications fundamentally requires the ability to guide and transfer SPPs in different plasmonic structures. Here the generation and control of periodic collimated SPP-beams are reported in composite structures of silver nanowire on silver film with a dielectric spacer layer between them. It is revealed that the collimated beams on the silver film originate from the interference between film-SPPs generated by two SPP modes on the nanowire. The direction of the collimated beams can be readily tuned by changing the thickness of the dielectric spacer. These findings demonstrate the transfer of nanowire SPPs to film SPPs and offer a new approach to generate nondiffracting SPP-beams, which could facilitate the design and development of complex plasmonic systems for device applications and enable the tailoring of SPP radiation and SPP-matter interactions.