Localized modes in defect-free two-dimensional circular photonic crystals

The localization of electromagnetic waves in defect-free circular photonic crystals (CPCs) is investigated using a multiple-scattering method. It is shown that electromagnetic waves of certain freqencies are localized in some special regions inside a perfect CPC with a high order of rotational symmetry. Localized modes with a high Q factor, greater than 106, are obtained. In particular, some unique localized modes such as circular modes and localized modes for both polarized waves are found in the present system, which are completely different from those in defect-free photonic quasicrystals and periodic structures. Their physical properties are also analyzed.