Photonic higher-order topological insulator with enlarged non-trivial bandgaps

Abstract

Abstract Recently, the emergence of higher-order topological insulators (HOTIs) has drawn extensive investigations. The unconventional bulk-hinge correspondence featuring in-gap corner or hinge states have been observed in diversified platforms like acoustics and photonics. However, three-dimensional (3D) photonic HOTIs are less attached due to the complicated properties of electromagnetic (EM) waves and narrow photonic bandgaps. In this article, we propose a photonic HOTI with a simple multilayer structure to support hinge states. By inserting a central metallic pillar in the unit cell, the 3D bandgap can be extended to 17.9%, allowing for pure and distinguishable surface and hinge modes. Free from adjusting the distance between adjacent dielectric rods to construct a topological interface, the lattice distortions can be achieved by controlling the geometrical length of sub-lattices, which providing a reconfigurable and flexible scheme to realize the robust hinge and surface wave transmission. Our findings usher the door for high-performance topological optical apparatus with efficient one-way light propagation and energy concentration.