Excitation of Radially Polarized Conical Surface Plasmon Polariton

Norik Janunts Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany Bayarjargal Tugchin Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany Angela Klein Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany Michael Steinert Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany Dmitry Sivun Institute of Applied Physics, Johannes Kepler University Linz, Linz, Austria Miguel Sison Laboratoire d’Optique Biomedicale, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland Ernst-Bernhard Kley Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany Andreas Tünnermann Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany Thomas Pertsch Institute of Applied Physics, Friedrich-Schiller-Universität Jena, Jena, Germany

We demonstrated experimentally the excitation of the radially polarized surface plasmon polariton (SPP) in a tapered and fully gold coated M-profile fiber (Fig. 1) which works as a Kretschmann configuration in conical geometry. The excitation process is based on the resonant coupling of the radially polarized fiber mode (Fig. 2) to the radially polarized SPP on the conical gold layer covering the tapered fiber. Due to the coupling the energy transfers from the fiber mode to the SPP mode (Fig. 3).

The SPP gets localized at the nano-scale apex of the tip producing a strong longitudinal field oscillating along the tip axis, and as a result emits to the side (Fig. 4). To probe the near-field characteristics at the tip apex, we placed the tip perpendicularly on a plane gold surface and studied the planar SPP generated on the plane gold surface by the tip (Fig.5). The SPP was shown to be radially polarized and radially symmetric.

We also demonstrated the reverse process when the induced longitudinal field at the tip apex serves as a source of conical radially polarized SPP originating from the tip apex.

$Fig.1. Cross-section and refractive index of the M-profile fiber.$ Fig.2. Radially polarized mode in the tapered region of the M-profile fiber tip. Fig.4. Side emission of the apex of the tapered and fully gold coated M-profile fiber tip.

Fig.3. Schematic of the excitation of radially polarized conical SPP in fully gold coated tapered M-profile fiber tip. Fig.5. Schematic of excitation of radially polarized planar SPPon a planar gold plane by a longitudinal field at the tip apex.

norik.janunts@uni-jena.de