We investigate topological insulator properties of the kagome helical waveguide array, by utilizing theoretical and numerical means. The time-reversal symmetry of the kagome lattice is broken by helicity, and a photonic topological insulator is formed. The Berry curvature and Chern number of the band structure are calculated, to verify the topological phase transition, caused by the helicity. Unidirectional propagation and topological protection properties of the edge states at certain momentum values are demonstrated. Interestingly, the same kagome helical waveguide array, may support topological edge states with different momenta propagating along the same boundary but in opposite directions.
Zhong, H., Wang, R., Ye, F., Zhang, J., Zhang, L., Zhang, Y., … Zhang, Y. (2019). Topological insulator properties of photonic kagome helical waveguide arrays. Results in Physics, 12, 996–1001. https://doi.org/10.1016/j.rinp.2018.12.053