Abstract: We studied the characteristics of interface states of photonic crystals with inverted symmetric composite structures, where the
 media composing the crystals were functional media with refractive index that was a function of spatial position. The results show that when the refractive index of the medium is a constant, photonic crystals composed of two different composite structures (PC1+PC2 and PC1+PC2+PC1) exhibit different interface state characteristics. The composite structure composed of PC1+PC2 can only generate one interface state, while the composite structure composed of PC1+PC2+PC1 can generate at most two interface states. When the refractive index of the medium is a function of spatial position, the photonic crystal with the composite structure composed of PC1+PC2 can realize the regulation of a single interface state and multiple interface states. As the two endpoint values n_b(0) and n_b(b) of the refractive index of the functional medium increase, the single interface state undergoes an obvious red shift, and its peak intensity is significantly attenuated. The position and number of multiple interface states remain unchanged, while the peak intensity is significantly enhanced.

Key words: functional medium, photonic bandgap material, transmission matrix,  , matching matrix, interface state