Highly efficient nanofocusing in a single step-like microslit

Highly efficient plasmonic nanofocusing is numerically predicted in a single step-like microslit, which is placed on a high-index dielectric layer. Because of the high throughput of the impinging light on the wide microslit, highly efficient nanofocusing is achieved in the proposed structure based on the multimode interferences in the microslits, the constructive interference between the transmitted light and the scattered surface plasmon polaritons, and the Fabry-Perot resonator effect in the high-index dielectric layer. Compared with previous nanofocusing structures containing plenty of substructures arranged laterally, the proposed structure has a much smaller lateral dimension because of the vertical arrangement of the microslits. This is of importance for realizing densely integrated plasmonic circuits.