Trapping light behind bars

Summary form only given. Perhaps the most successful photonic crystal structure to have been demonstrated so far is in the form of photonic crystal fibre (PCF)-a strand of glass with an array of microscopic air channels running along its length. In these fibres, light is trapped at structural defects points where the periodicity is interrupted. The large glass:air refractive index difference and the photonic crystal structure permit greatly enhanced control of guided mode dispersion, birefringence and modal shape. Perhaps the most revolutionary example of this is the hollow-core fibre in which light is guided-in a hollow tube-by a two-dimensional photonic bandgap. Photonic crystal fibres represent a next-generation, radically improved, version of a well-established and highly successful technology. As a result they are finding applications in diverse areas of science and technology, including frequency metrology, laser-guiding of atoms and particles, medical diagnostics, industrial manufacturing, telecommunications and ultra-high power amplifiers and lasers. Furthermore, the ability to make a functioning structure from one solid material, thus avoiding the need for compatible core and cladding glasses, makes it much more straightforward to fashion fibres from traditionally "difficult" materials such as polymers and non-silica glasses such as tellurites and chalcogenides. Periodic microstructuring can transform everyday optical materials from mundane commodities into almost magical new substances full of new effects and useful in a host of applications.