Photonic insulators with a twist

摘要

Photonics researchers have long been inspired by a conceptual analogy between electromagnetic waves in patterned media and quantum-mechanical electron waves in solids. In the late 1980s, Yablonovitch and John conceived of the photonic crystal - a spatially periodic nano-structure - as an analogue of an electronic insulator. In a photonic crystal, the frequencies of propagating light can be restricted to distinct bands, which are separated by gaps of forbidden frequency, akin to the electronic bandgaps in insulators within which no electron states exist. Photonic bandgaps are now a staple of optical nanostructure design, with applications ranging from low-loss optical resonators to slow-light waveguides. On page 196 of this issue, Rechtsman etal. Report the design and realization of a photonic device that mimics a state of insulating matter known as a topological insulator, which has properties strikingly distinct from those of conventional insulators. This points the way towards the development of fault-tolerant photonic devices that exploit 'topologically protected' light waves.