Question

In a photonic band gap material, what is a general structure requirement in order to potentially exhibit an optical band gap.

Answer 1

The structures having periodic arrangements of dielectric or magnetic materials which forms stop bands are generally known as photonic band gap structures or electromagnetic band gap structures.

The electromagnetic wave which travels through such structures goes through the periodic variation of dielectric permittivity or magnetic susceptibility which is similar to that of periodic potential energy of an electron in atomic crystal structure. so the photonic states in photonic crystals are classified into band and gaps.

Photonic crystals can be categorised as 1d,2d and 3d. According to dimensionality of the building blocks.

For 1d photonic crystal consists alternate layers of materials with high and low refractive indices and dielectric constant is modulated only in one direction.

In 2d the dielectric constant is periodic in two directions i.e. in a plane and extends to infinity in the third direction.

In 3d crystals the refractive index is modulated along all the three directions.