Actively Reconfigurable Valley Topological Edge and Corner States in Photonic Crystals Based on Phase Change Material GeSbTe

The immunity of topological states against backscattering and structural defects provides them with a unique advantage in the exploration and design of high-precision low-loss optical devices. However, the operating bandwidth of the topological states in certain photonic structures is difficult to actively tune and flexibly reconfigure. In this study, we propose a valley topological photonic crystal（TPC） comprising two inverse honeycomb photonic crystals, consisting of hexagonal silicon and Ge2Sb2Te5（GST） rods. When GST transitions from the amorphous phase to the crystalline phase, the edge band of the TPC appears as a significant redshift and is inversed from a “ ∪” to an“ ∩” shape with topological phase transition, which enables active tuning of the operating bandwidth and propagation direction of topological edge states. Both the topological edge and corner states in a triangular structure constructed using TPCs can be simultaneously adjusted and reconfigured via GST phase transition, along with a change in the group number of corner states. Using the adjustability of topological edge states and electromagnetic coupling between two different topological bearded interfaces, we develop a multichannel optical router with a high tuning degree of freedom, where channels can be actively reconfigured and their on/off states can be freely switched. Our study provides a strategy for the active regulation of topological states and may be beneficial for the development of reconfigurable topological optical devices.