Active control of Kagome lattice defect mode using point-ring defect engineering

Kagome lattice defect modes with a point-ring structure are explored theoretically in two-dimensional germanium cylinder photonic crystals using plane wave expansion and supercell methods. The number and degeneracy of the transverse magnetic field defect mode are governed by the defect setting. By varying the distance and direction of the point-ring defects, we can manipulate and control the frequency width and coupling between defect modes and the defect frequency in the bandgap. Additionally, the intensity distribution localized in the defect position is related to the parity of defect structure symmetry axes. This characteristic is highly beneficial to applications such as in resonators and narrow band filters.