Achieving self-guiding unidirectional electromagnetic bulk states by breaking time-mirror symmetry

摘要

Unidirectional waves are the waves propagating only in one direction and prohibited in the opposite direction. These kinds of waves can be surface waves realized by the topological edge state or bulk waves in the media with time-reversal and spatial inversion symmetry broken. In this work, we introduced unidirectional waveguide modes in quasi-one-dimensional waveguides composed of T-shaped gyromagnetic rods. The waveguide supported self-guiding unidirectional waves but could be switched to bidirectional waveguides by changing the rods' arrangement. We showed that the unidirectional guided waves resulted from the symmetry broken of mirror reflection, spatial inversion, and time-reversal of the chain. The results were validated by transmission measurements. Our work paves the way for manipulating electromagnetic waves by the symmetry mechanism. It also provides a simple and flexible way to fabricate devices, such as vortex wave generators which were designed and implemented theoretically.