One of the main practical consequences of the topological nature of edge states in systems with broken time reversal symmetry, is their remarkable robustness against small imperfections of the lattice or disorder. This property, however, may become a drawback when some manipulations with such states are needed, in particular for switching applications. For resolving this problem, the only suggestion was reported so far, is based on utilization of strong localized defect in photonic systems supporting more than one edge state.

We propose an alternative and highly efficient way of transition between two edge states, which is based on the Bragg reflection from periodic modulations of the interface. A remarkable property of such scattering is that it occurs within the subspace of edge states and is mediated by any small (ultimately, infinitesimal) modulation, and at the same time it remains symmetry-protect from other scattering channels, in particular, into the bulk and back-propagating modes.

While our model is based on the atomic system and uses well-known Rashba and Dresselhaus couplings, the phenomenon that we report is of completely general nature (like famous Bragg scattering) and thus it can be observed in any of the known topological systems in condensed matter physics, optics, plasmonics, polariton condensates, and many others, where more than one topological states can exist at the edge.