Question

Why group velocity becomes zero at band edges in a periodic structure?

Answer 1

We have studied the optical properties,band structures and group velocities,of one dimensional photonic crystal (1-D PC) containing negative index materials using translational matrix method (TMM). The 1-D PC containing negative index materials is a periodic arrangement of positive index material (PIM) and negative index material (NIM). The observed group velocity of such structure is larger than the speed of light in certain range of normalized frequency which shown abnormal behaviors. The group velocity of the PC containing negative index materials have found larger than the speed of light. The values of the group velocity become zero,negative and positive for normalized frequencies. The structure containing negative index materials can be used to trap the photons inside the PC i.e.,light localization occurs without introducing the defects.