RESUMO
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.
RESUMO
We demonstrate an optical trapping technique that integrates the light guiding of an optical fiber with the field localization of a nanoaperture in a gold film. A key innovation of our technique is to use template-stripping for easy planar fabrication without the need for nanofabrication on the tip itself. As a proof of principle, we demonstrate the trapping of 20 nm and 30 nm polystyrene nanoparticles in solution, as observed by a jump in the transmitted laser intensity through the aperture. We use the finite difference time domain technique to simulate this intensity jump with the addition of a nanoparticle in the aperture, showing reasonable agreement with the experimental data. This simple nano-aperture optical fiber tip eliminates the need for a microscope setup while allowing for trapping nanoparticles, so it is anticipated to have applications in biology (e.g. viruses), biophysics (e.g. protein interactions), physics (e.g. quantum emitters), and chemistry (e.g. colloidal particles).