We demonstrate surface plasmon (SP) excitation in Ag nanowires directly coupled with a microfiber in the presence of a
MgF<sub>2</sub> substrate. With scanning near-field optical microscopy, evident light output from the Ag nanowire and the
evanescent field of the coupling structure are observed in the near-field optical image. The tip enhancement of a Ag
nanowire is also analyzed from the optical intensity graph. Results presented in this work suggest a simple SP excitation
approach for plasmonic and photonic circuits with high compactness.