Topological photonics

Topological photonics is a rapidly emerging field of research in which\ngeometrical and topological ideas are exploited to design and control the\nbehavior of light. Drawing inspiration from the discovery of the quantum Hall\neffects and topological insulators in condensed matter, recent advances have\nshown how to engineer analogous effects also for photons, leading to remarkable\nphenomena such as the robust unidirectional propagation of light, which hold\ngreat promise for applications. Thanks to the flexibility and diversity of\nphotonics systems, this field is also opening up new opportunities to realize\nexotic topological models and to probe and exploit topological effects in new\nways. This article reviews experimental and theoretical developments in\ntopological photonics across a wide range of experimental platforms, including\nphotonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon\nphotonics, and circuit QED. A discussion of how changing the dimensionality and\nsymmetries of photonics systems has allowed for the realization of different\ntopological phases is offered, and progress in understanding the interplay of\ntopology with non-Hermitian effects, such as dissipation, is reviewed. As an\nexciting perspective, topological photonics can be combined with optical\nnonlinearities, leading toward new collective phenomena and novel strongly\ncorrelated states of light, such as an analog of the fractional quantum Hall\neffect.\n