Switchable Negative Group Delay Based on Sandwich Topological Protection Structure in Terahertz Band

A switchable enhancement group delay in the terahertz band based on a novel sandwich topology protection structure with graphene is proposed in this paper. The notable phase transition of the reflected beam comes from the topological edge-protected mode excited at the sandwich photonic crystal surface, and the non-trivial topology of the photonic crystal allows the structure to be immune against defects and imperfections, which lays the foundation for the enhancement of group delay in the terahertz band. And the introduction of graphene creates favorable conditions for the reversible switching of positive and negative reflection group delay. Moreover, the reflected group delay can also be flexibly and dynamically controlled by the incident angle. The positive and negative reversible switching reflected group delay proposed in the terahertz band greatly reduces the optical transmission loss and significantly increases the transmission efficiency compared with the traditional metal sandwich structure, which provides a feasible idea for the realization of multi-dimensional manipulation of the wavelength and phase of electromagnetic waves in the terahertz band. The novel scheme is expected to provide potential applications in fields such as optical buffers or ultrafast modulators.