Figure 2
From: Two-dimensional photonic crystal with ring degeneracy and its topological protected edge states
Band diagram and eigenmodes of the TPC and its topological phase. (a) PBS of the TPC. As the z-inversion symmetry is broken, the once degenerate TE and TM modes mix with each other, opening a complete band gap at the frequency range of 0.73 < ωa0/2πc < 0.76. The inset illustrates the unit cell, where the air gap perturbation (g = 0.1a0) causes bi-anisotropy response. (b) Fields profile of the four concerned modes at M point, out-of-plane magnetic component (Hz) for first, second and fourth mode, out-of-plane electric component (Ez) for third mode. (c) Berry phase of the bands below the band gap. It evolves with kx ranges from 0 to π. Note that all the green dots reside in nearly zero phase, which corresponding to the lower band that is not explicated in (a).
