Multiple topological transitions and topological edge states of triple-site honeycomb lattice photonic crystals

We propose a two-dimensional (2D) triple-site honeycomb lattice (TSHL) photonic crystal (PC) by rotating the three dielectric rods six times, forming unit cell, and then arraying the unit cells in the triangular lattice. The TSHL PC structure can achieve topological phase transitions in three ways, which are changing the position or size of the rods, and rotating the rods. By calculating the band structure under different parameters, the law of topological phase transition for TSHL PC is analyzed. The topological edge state can be adjusted by changing the rotation angle of the dielectric rods. Based on this, a frequency-selective beam splitter is designed. Compared with previous studies, this flexible topological system shows more abundant physical phenomena, enriches the implementation of topological photonics , and promotes the research of topological edge states and the development of topological insulators in practical applications. • We propose a two-dimensional triple-site honeycomb lattice photonic crystal, which has the high degrees of freedom. • The triple-site honeycomb lattice unit cell can achieve topological phase transitions in three ways, which are changing the position or size of the cylinders, and rotating the cylinders. • We design a frequency-selective beam splitter, by changing the rotation angle of the dielectric rods.