Fusing electromagnetic one-way edge states to achieve broadband unidirectional wave transmission

There exist two types of electromagnetic (EM) one-way edge states in magnetic photonic crystal (MPC). One is associated with photonic band gap (PBG) relevant to Bragg scattering, while the other is associated with PBG originating from magnetic surface plasmon resonance. Both support robust unidirectional wave transmission, but each with relatively limited operating bandwidth. By optimizing the lattice spacing and filling ratio of MPC as well as tuning the external static biasing magnetic field, we are able to fuse the two types of EM one-way edge states together and therefore achieve broadband one-way transmission. The operating bandwidth could be about 4 GHz in a microwave regime; this is much larger than that based on either type, providing a way towards the practical applications of unidirectional wave propagation.