Criterion of omnidirectional reflection in a one-dimensional photonic heterostructure

We systematically investigate the criterion of omnidirectional reflection in one-dimensional photonic heterostructures and show that the photonic heterostructures can extend not only the frequency range of omnidirectional reflection but also the range of materials; that is, the refractive-index contrast between the composites can be much lower than those required in single periodic structures. This idea is of immense practical importance and can be extended to other structures whose underlying physics are the same as those of a photonic heterostructure, such as a staggered structure and some types of quasi-period structure.