2D Photonic Band Gap Structures in Fibre Form

A structure with a refractive index that varies periodically in three dimensions can fail to transmit light of certain “forbidden” frequencies, despite being non-absorbing. This is because Bragg diffraction, constructive multiple-beam interference from a periodic array of scatterers, takes place for all directions; only an exponentially-decaying evanescent field is supported. These frequencies ω are the full photonic band-gaps (PBGs) of the structure. Light that attempts to enter the structure is expelled and returns to the medium from which it came. If that medium is free space, the structure behaves as a totally-reflecting mirror; if the medium is a buried excited atom wanting to emit a photon at a forbidden frequency, the spontaneous emission is suppressed[1].