Valley pseudospin is an important approach to construct optical topological insulators, and its properties determine the topological transmission characteristics. Using topological structures to control light transmission makes it ideal to control light waves in all concerned wavebands. However, the previously reported valley topology photonic crystal studies often break only one degeneracy point in photonic crystal bands, achieve topological phase transition through band inversion, and obtain valley topological edge states of single wavebands. This can only play a role in light propagation in a very narrow range but cannot modulate light propagation in more wave ranges. Thus, this paper researches the light transport characteristics of dual-band valley topological photonic crystals to modulate light propagation in a wider wavelength range as far as possible. The designed photonic crystal structure has two degeneracy points in the band and can make the two points open at the same time by rotating the scatterer to generate two band gaps. In this way, valley topological phase transitions can occur in two ranges, and the light propagation within the two wavelength ranges can be modulated. Finally, a supercell structure with topological edge states is constructed, and the transport characteristics and robustness of topological edge states with different interface types are investigated, which provides a basis for the design and application of dual-band valley topological edge states.

In this paper, photonic crystal supercells with a dual-band valley structure are constructed. The transport characteristics and robustness of zigzag and armchair interface topological edge states in two bands are studied. The band structures of zigzag AB (interface I1), BA (interface I2), armchair AB (interface I3), and BA (interface I4) are calculated by the finite element method, and the electric field modes of light propagation corresponding to different interface topological edge states are compared and analyzed. The transport characteristics of plane waves along interfaces I1, I2, I3, and I4 are calculated in the first and second topological edge states. Finally, the disturbance of defects, impurities, and sharp corner structures on the transport characteristics of zigzag and armchair interfaces is investigated.

For zigzag interfaces, the edge states of AB (interface I1) and BA (interface I2) are different, regardless of the first or second topological edge states. For armchair interfaces, the rule is quite different from the zigzag interface, and the edge states of AB (interface I3) and BA (interface I4) are completely identical. For zigzag interfaces, the light transport characteristics of symmetric interfaces are significantly different from those of antisymmetric interfaces. Symmetric interfaces allow plane wave transmission while antisymmetric interfaces greatly inhibit plane wave transmission. However, the light propagation does not show any difference for armchair interfaces. For the interfaces allowing plane wave transmission, both zigzag and armchair interfaces feature good robustness against impurities, defects, sharp corners, etc.

Band range expansion of topological edge states is vital for the practical application of optical topological insulators. This paper constructs a photonic crystal supercell with a dual-band valley structure and compares the band structure and light transport characteristics of the interfaces I1, I2, I3, and I4. Different transmission phenomena of zigzag and armchair interfaces are discovered, and the robust transmission ability of topological edge states is verified. The constructed topological edge state can simultaneously modulate the light transport characteristics in two ranges, which will provide ideas and guidance for expanding the application fields of optical topological insulators. The physical mechanism of different interfaces exhibiting various transport characteristics needs to be further explored.