It's the property of the material which allow only certain bandwidth of wavelength. Materials that exhibit this property is known as photonic crystal. In order to exhibit this property the material has to have a periodic arrangement of dielectric structures with periodicity of the order of wavelength.

Anders Bjarklev has written:

'Optical fiber amplifiers' -- subject(s): Fiber optics, Lasers, Optical amplifiers, Optical communications

'Photonic Crystal Fibers'

bandgap has an importance role for conduction.if bandgap is max,the conduction of electron is min. and vice-versa.hence we can say that the bandgap desides the conductivity of any material(may be metal or nonmetal)

we already hit the galactic photonic belt said god the father.

Checkov radiation