Transverse excitation of plasmonic slot nano-resonators embedded in gold-coated microfiber tips

Nanoscale aperture in thin noble-metal films, with dimensions comparable to the light wavelength, can form plasmonic nano-resonators (PNRs) and show astonishing optical properties leading to enhanced and selective light transmission and confinement. In contrast to conventional optical systems using lenses and mirrors, PNRs can provide hot spots in the near field with dimensions determined mainly by the structure size rather than by the diffraction limit. A number of different nano-structures have been considered and studied in detail for their ability to concentrate light [1]. In this paper, for the first time we study both theoretically and experimentally the transverse excitation of a strongly-coupled 3D plasmonic slot nano-resonator (PSNR) by embedding a rectangular slot nano-cavity in a plasmonic structure formed by a thin-metal-film coated microfiber tip: a schematic of the structure is shown in the inset of Fig. 1(a). Light is launched from the untapered side of the fiber and coupled to the nano-cavity. The various resonances can be identified simply monitoring the reflected light. In the experiment, a PSNR with 400 nm length, 200 nm width and 30 nm depth was inscribed on a 30 nm gold-coated microfiber tip by focused ion beam (FIB). Light with the polarization state which is perpendicular to the PSNR was launched into the tip and reflection spectra were recorded.