An unusual angular gap of 1-D photonic crystal containing negative refractive index materials

It is studied the transmission properties of the photonic crystal alternatively composed of material layers with positive and negative index,where the negative index materials(NIM) is described by a lossy Drude model.Investigations reveal that such structure possesses zero-n Bragg gap and conventional Bragg gaps.In additional,there is a new type of band gap emerged in the spectral region where the refractive index of NlM is approximately zero.The position of this so-called angular gap has no relation to crystal parameters,and the band width is quite small.The forbidden band disappears at normal incidence,the width of the angular gap increases while increasing the incidence angle,and the width of TM is larger than that of TE.