Shaping plasmonic beams using curved surface optical elements

  Ana Libster-Hershko  ,  Roy Shiloh  ,  Shlomi Litman  ,  Ady Arie  
Tel Aviv University

Due to the two-dimensional nature of surface plasmon polaritons, they are a natural environment for studying the phenomena on wave propagation on curved surfaces. Previous research on curved surfaces has mainly approached the problem by applying an external potential on quantum particles bounding them to the interface, or by allowing light to propagate along thin dielectric waveguides attached to such a surface. These efforts are not needed with plasmonic waves that propagate only at the metal-dielectric interface. By changing the geometry of a surface, we can implement optical elements which will affect propagation dynamics of the surface plasmons propagating on it, thereby enabling to realize plasmonic elements such as lenses, prisms and waveguides in a compact manner.

We developed a simulation tool and an experimental platform for studying the propagation of plasmonic waves on curved surfaces. Specifically, we demonstrate here deflection of a plasmonic beam on a half cone made of silver that operates as a prism. The half cone, having a height of   3.8µm, a width of 12µm and a length of 16µ, was prepared by 3D direct laser printing. It was then covered by a silver layer of 100 nm. A coupling grating with a period of 1.053 microns was milled by focused ion beam milling. The plasmonic beam was excited by a free space laser beam, operating at 1064nm, through the coupling grating. The propagation of the plasmonic beam was then measured using a near field optical microscope. We have observed deflection of up to 9.3 degrees. This deflection occurs owing to the effective potential induced by the curved surface and by the phase difference accumulated along different geodesic lines along this half cone. The experimental results are in good agreement with a numerical simulation.