The energy gap in a PBG material can ideally be closed by means of inducing defects. Such doping or even switching will allow light of the forbidden energies to pass through the material in controllable ways, thus these materials hold potential for applications ranging from optical communications to quantum computation.

"Photonic Band Gap (PBG) Materials are similar to semiconductors, where the electrons are replaced by photons (also known as light). By creating periodic structures out of materials with contrast in their dielectric constants, it becomes possible to guide the flow of light through the PBG material in a way similar to how electrons are directed through doped regions of semiconductors. The period of the structure is related to the wavelength of light for which a PBG will exist, for instance a few hundred nanometers for visible light." - Trends in NanoTechnology (TNT) 2001