Fig. 1. Schematic of a photonic crystal unit cell and two types of couplings. (a) Schematic of honeycomb lattice photonic crystal unit cell composed of perfect electric conductor cylinders; (b) schematic of mathematical model based on electrostatic interaction analogy, where circular dashed line area represents intra-lattice coupling and rectangular dashed line area represents inter-lattice coupling

Fig. 2. Intra-lattice and inter-lattice coupling strength changing with cylinder radius (the dimensionless coupling strength is used and normalized to the lattice constant a). Cylinder radius ranging from 0.05a to 0.25a when (a) N=6 and (b) N=12; cylinder radius ranging from 0.2770a to 0.2790a when (c) N=6 and (d) N=12

Fig. 3. Band diagrams of photonic crystals with different cylinder radii. (a) r=0.2783a; (b) r=0.1328a

Fig. 4. Simulated magnetic field H_z distributions of pseudospin dipole modes and pseudospin quadrupole modes with r=0.2783a and r=0.1328a at Brillouin zone center

Fig. 5. Simulated magnetic field H_z distributions of topological edge states at 1.06c/a excited by a pseudospin down source propagating along the zigzag interface