Non-Hermitian topological light steering

How to define a light path topologically Controlling the flow of light in a robust and flexible manner will be critical for the development of the next generation of photonic integrated devices. Exploiting the inherent protection afforded by topology, topological photonics provides a solution for the robust propagation of light. Devices so far, however, have been fixed in their functionality. Zhao et al. created light paths that can be arbitrarily switched on and off by optical illumination. Propagation can be topologically steered along desired pathways by manipulating regions of gain and loss within the photonic structure through optical excitation. This approach provides a route to controlling topologically protected light paths in an integrated optical platform. Science , this issue p. 1163