Narrow frequency and sharp angular defect mode in one-dimensional photonic crystals from a photonic heterostructure.

By combining two one-dimensional defective photonic crystals (PCs), we obtained a photonic heterostructure with narrow frequency and a sharp angular defect mode. The key to obtaining such a structure is to design the two sub-PCs to make the frequencies of their defect modes the same at one incident angle and different at all other incident angles. Filters designed on the basis of this heterostructure possess not only a narrow-frequency passband but also a sharp angular pass breadth. Optimization of the practical design is also suggested.