Photonic crystal fibres: An endless variety

A photonic crystal fibre has an array of microscopic air holes running alon g its length. The periodicity of the array is broken by a deliberate "defec t" that acts as a wave-guide core. Light is confined to this core by the ho les. Although some designs of photonic crystal fibre guide light by total i nternal reflection and so can be considered analogues of conventional optic al fibres, their properties can be strikingly different. Other designs guid e light by photonic bandgap confinement and represent a totally new type of fibre.