Tunable interface state in one dimensional composite photonic structure

Based on the Transfer Matrix method (TMM), we evaluate the conditions and controllability of interface states in one-dimensional photonic structures composed of two binary layered photonic crystals, PCI and PCII, having the same photonic bandgaps but different unit cells. For PCs with inversion symmetry but different symmetry centers, the composite photonic structure exhibits interface states in the middle of the corresponding bandgaps where the sum of the reflection phases of the PCs is zero. The observed interface states persist even when the inversion symmetry is broken by shifting the unit cell of the individual PC as long as the sum of the reflection phases is still zero. Moreover, the location of interface states inside the bandgaps can be controlled by adjusting the thicknesses of the adjacent layers at the interface of two PCs. The composite photonic structure can be realized easily by standard electron beam evaporation technology, opening more possible applications in multi-channel narrowband filters and other optical modulation devices.