Experimental nanofocusing of surface plasmon polaritons using a gravitational field

How to capture electromagnetic fields into subwavelength spatial scales has been a major challenge in nanophotonics, especially confining surface plasmon polaritons into regions as small as a few nanometers. Although various methods are proposed to achieve this goal, these methods require complex fabrication process. Here, we demonstrate experimentally the achievement of nanofocusing of surface plasmon polaritons with an intensity enhancement of three, using the simple structure with just pasting a sliver microwire on a sliver layer. And the designed structure has a well-defined gravitational field inspired by transformation optics. This simple design structure has applications to enhance light-matter interactions, such as nonlinear optical process and Raman scattering.