Excitation and analyzation of different surface plasmon modes on a suspended Ag nanowire.

Silver nanowires (AgNWs), as one of the most important plasmonic waveguides, can support several different plasmonic modes. These surface plasmon polariton (SPP) modes have different electric field distributions, effective mode areas, propagation lengths and losses and thus can be used for different applications, from efficiently collecting single photons to carrying quantum entanglement. Therefore, the excitation and analysis of these different SPP modes are of pivotal importance for the development of subwavelength optical devices. In this work, we investigate different SPP modes on a suspended AgNW adhered to a fiber taper. Theoretical simulations and experimental results show that the desired SPP modes can be selectively excited by adjusting either the polarization of the excitation light or the coupling length between the fiber taper and the AgNW. Moreover, fundamental and higher-order SPP modes can be distinguished by means of a far-field method. Our results not only enable convenient and controllable excitation of the desired SPP modes but also provide unique insight into the optical properties of plasmonic waveguides.