Efficient coupling between a Circular Waveguide and Topologically Protected Helical Modes in metallic Photonic Crystals

A circular waveguide transition is used to selectively excite Topologically Protected Helical Edge Modes along an interface between metallic Photonic Crystals. Reflection coefficient lower than −20dB is observed in a frequency range of ≈ 150MHz for a single port excitation and quasi-unitary transmission, mediated by the topological interface, is observed between two circular waveguide ports for the mid-band frequency.