Intensity tuning of the edge states in the imperfect topological waveguides based on the photonic crystals with the C3 point group symmetry

Abstract

In this paper, we explore the topological behavior of a two-dimensional honeycomb photonic crystal (PC) based on the presence of double Dirac-cone connected the orbitals p and d, due to the C6 point group symmetry of the hexagonal PCs. Removing the four-fold degeneracies between the bands at the Dirac point can be achieved by introducing three small dielectric rods near the bigger ones to realize the perturbed PCs with the C3 point group symmetry with different topological features. By proposing the unique structure involving two PCs with different topological effects, one may study the one-way light distribution along the local boundary in spite of the defects, cavities, and disorders. Moreover, we investigate the variation of the transmitted intensity values under different defect conditions and realize that the size, location and material type affect the transmitted light. In the other words, tunable intensity of the edge states can be achieved through adjusting the defects such that by increasing the radius of rods, the intensity of the edge states can be enhanced or by increasing their distance from the unit cell center, the intensity will be decreased. For example, by increasing the radius of one of the rods, the intensity of the edge states is increased up to the 130%. Additionally, by moving the position of the mentioned rod along the direction, x, the intensity of the edge states will be decreased to 82.08%. Finally, topological rhombic resonator enables unidirectional filtering of guided mode. The fact that different light manipulation scenarios can be realized provides a unique aspect for topological photonic insulators.