Towards topological protection based millimeter wave devices

The feasibility of topological metawaveguides supporting helical propagation in the microwave range has been recently proven. The advantages of unidirectional propagation supported by such waveguides however can only be exploited in real devices if topological modes are endowed with the capability to interact within themselves as well as with trivial modes. Here we show a modal launcher to interface a topological metawaveguide with conventional circular waveguides with negligible reflection, and we exploit the properties of coupled topological modes to show a proof of concept of a topological contradirectional coupler.