Rainbow trapped for the first time

In 2007, Ortwin Hess of the University of Surrey in Guildford, UK, and colleagues proposed a technique to trap light inside a tapering waveguide, which is a structure that guides light waves down its length. The waveguide in question would use metamaterials – exotic materials that can bend light sharply.

The idea is that as the waveguide tapers, the components of the light are made to stop in turn at ever narrower points. That’s because any given component of the light cannot pass through an opening that’s smaller than its wavelength. This leads to a “trapped rainbow”.