Near-field optical microscopy of surface plasmon polaritons excited by silicon nanoantenna

An optical nanoantenna is a device that transforms far-field electromagnetic radiation into near-field and vice versa. Naturally, it can serve as a conduit between free space light and localized optical modes, including surface waves. With the recent rise of all-dielectric nanophotonics, nanoantennas made of high-index materials were found to offer unparalleled means for manipulation of light due to presence of equally strong electric and magnetic responses in the visible spectral range. Here, we demonstrate excitation of surface plasmon polaritons by single silicon nanosphere on gold layer measured by means of scanning near-field optical microscopy. The interference patterns observed in the measured near-field maps allow us to retrieve information on directivity and relative excitation efficiency of surface plasmon polariton in the longer wavelength part of the visible spectral range. Our results demonstrate that all-dielectric nanoantennas could prove to be a valuable tool for controlling directivity and efficiency of excitation of surface waves.