Ultrafocusing of surface plasmon-polariton in a narrowing concave gap

In a concave gap between the flat and cylindrically convex metallic surfaces, surface plasmon-polariton may be localized in nanoscale, in conditions of adiabatic narrowing of the gap minimum width and convex curvature radius. Waveguide channels of that type may serve as an elementary basis for creation of high-speed optical circuits in nanoscale, due to their small losses