Different kinds of band-pass filters based on one-dimensional photonic crystal heterostructures

Three kinds of band-pass filters (BPFs), termed a TE BPF, a TM BPF and a BPF at oblique incidence, are designed by crossing the band edges of two different one-dimensional (1D) photonic crystals (PCs). The TE BPF, fulfilling the function of high reflectivity for p-polarization and high transmittance in a narrow pass-band for s-polarization, is constructed by two subPCs, one of which is obtained by decreasing the lattice constant of the other one while the other parameters keep the same. The TM BPF also comprises two subPCs, but the materials of one subPC are quite different with those of the other one. Similarly, the BPF at oblique incidence, from which both polarization waves can transmit in a narrow pass-band at oblique incidence, is composed of two different subPCs. Note that, the distribution of the wave impedance of material in each BPF should be periodic to prevent unexpected defect modes. The new filters not only provide narrow pass-bands and wide non-transmission bands, but also have simple structures. This is a result of the fact that the wave impedance ratio between composites is enlarged by introducing magnetic materials. The new designs have potential applications in optical filters and optical integrated circuits.