  Unidirectional waves are the waves propagating only in one direction and
prohibited in opposite direction. This kind of waves can be surface waves
realized by topological edge state or bulk waves in the media with time
reversal and space inversion symmetry broken. Here, we introduce unidirectional
waveguide modes in the periodic dielectric chain comprised of gyromagnetic
rods. In this modes, the waves in the waveguide propagates unidirectional, but
can be converted into bi-directional waves by changing the arrangement of rods.
We show unidirectional guided waves result from the time-mirror symmetry broken
of the chain. Experiments confirm the theoretical results of waveguide modes. A
new vortex wave generator based on the unidirectional guided wave is
demonstrated theoretically. Our work opens a new avenue for manipulating the
electromagnetic wave in a simple and flexible way, and provides a new
possibility for novel devices.
