One-Way Leaky-Cladding Meta-Waveguides Based on Accidental Dirac Cones

Nonreciprocal waveguides play an important role in microwave and optical systems. Here we present a new concept for a one-way meta-waveguide: a waveguide that supports a guided mode in one direction while waves traveling in the opposite direction leak out into the waveguide cladding. This is achieved by placing a metasurface atop of a ferrite slab, and judiciously phase matching two radiant and one subradiant meta-waveguide modes in order to enhance the magneto-optical response and to create an accidental Dirac cone in the reciprocal space. By applying an in-plane magnetic field, the reciprocal and nonreciprocal contributions to magneto-optical response can interfere constructively/destructively depending on the propagation direction, thereby shifting the apex of the Dirac cone and creating a one-way propagation bandgap. The idea of one-way leaky-cladding waveguide provides an alternative way of designing nonreciprocal devices that do not require a gap in the Dirac cone.