Photonic Crystal: Topology Protects Light Propagation

Researchers have seen light propagate in a special material without reflections. The material, a photonic crystal, consists of two parts that each have a slightly different pattern of perforations. Light can propagate along the boundary between these two parts in a special way: It is “topologically protected,” and therefore does not bounce back at imperfections. Even when the boundary forms a sharp corner, the light follows it without a problem.

The researchers are the first to directly observe the propagation of topologically protected light on the technologically relevant scale of nanophotonic chips. By purposely using silicon chips and light of a similar wavelength as used in telecommunication, they expect to increase the application prospects.

They are now going to investigate if there are any practical or fundamental boundaries to topological protection and which functionalities on an optical chip we could improve with these principles. The first thing they are thinking of is to make the integrated photonic crystal light sources on a photonic chip more reliable. This is important in view of energy-efficient data processing or green ICT. Also, the topological protection of light can be useful to transfer small packages of quantum information efficiently.

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