Invariant properties of helical-circular metallic waveguides

This is the authors' abstract. We don't add key points for this paper.

Experimental evidence shows that toroidal or helical-circular metallic waveguides, operating on the whispering-gallery principle, can be bent significantly without affecting either their ray-guiding or modal properties. These remarkable properties, reported here for the first time for any type of surface guide, result from the fact that the allowed deformations are geodesic and conserve the curvature of the rays. Scanning in one or two dimensions with a diffraction-limited beam has been achieved.