Progress towards a photonic band gap fibre

We are currently developing an entirely new type of optical fibre that guides light by Bragg reflection instead of total internal reflection. The fibre will be made from pure silica, using conventional fibre drawing techniques to give a longitudinally invariant structure kilometres in length. In cross-section the fibre will include a hexagonal array of air holes with a pitch of 1-2µm. For a given optical frequency, there are ranges of axial wavevector B for which transverse propagation in this structure is forbidden: the photonic band gaps. It therefore acts as a totally reflecting "cladding" for such B values. A deliberate defect in the two-dimensional periodic structure (perhaps one hole is filled in, or is larger than its neighbours) provides a site for the localisation of light and so acts as the "core". The propagation of light along the defect can be engineered by modifying the unit cell and scale of the structure, giving rise to a number of unique applications.