For decades, many branches of physics have been dominated by the lattice symmetries and chemical composition as the key concepts in the classification and design of various solid-state materials. However, it has recently been demonstrated that topology may be more important than symmetry in determining certain material properties. Topology is a subtle global property of the system governing how its parts connect. Materials insulating in a bulk but conducting at the surfaces through topological edge states were discovered in solid state physics in 2006, and they are currently known as topological insulators.
Discovery of topological insulators has initiated searches for topological effects in other fields of physics, including topological states of electromagnetic waves. This is driven by a grand vision of the waveguiding and routing of light on an optical chip that is robust against scattering on imperfections due to the one-way topological nature of edge states. Importantly, light can bypass an obstacle in a judiciously engineered array of resonators. Several suggested realisations of topological states of light are based on passive structures with fixed parameters, whose properties are specified during fabrication. This project will be based on our recent advances [1,2], and it will study novel photonic structures and metadevices for a control of light flows topologically protected against scattering losses, energy leaking, or imperfections.
 S. Kruk et al, Nature Nanotechnology 14, 126-130 (2019).