Beaming light through a bow-tie nanoaperture at the tip of a single-mode optical fiber

We demonstrate coupling and directivity enhancement of electromagnetic fields emerging from a single metallic nanoaperture at the tip of a single-mode optical fiber. We achieve this by using circular grooves flanking the nanoaperture perforated in a 100 nm thick gold film. The film with nanostructure is transferred to the fiber tip by aligned stripping with optical epoxy. When incident from both sides of the nanoaperture, enhancement factors of 2.2 and 2.4 in power coupling into the fiber and in beaming into free-space were obtained. Numerical simulations show that the optimum grating period is nearly identical to the surface plasmon polariton wavelength that can be supported at the gold-epoxy interface. This integrated platform couples light between the single mode fiber and the nanoapeture without the need for cumbersome optics, with applications for optical trapping and single-photon detection.