Self-collimated one-way light in gyromagnetic photonic crystals

One-way light has attracted much attention recently. They have wide range of applications, such as optical isolators and optical diodes. At present, two approaches can be used to realize the one-way light. One is one-way surface waves, which come from chiral edge states of photonic crystals [1, 2]. The other is one-way body waves, which may originate from the parity-time symmetry of a system [3, 4]. Here, we theoretically demonstrate that by breaking parity and time-reversal symmetries at the same time electromagnetic waves can self-collimate and propagate unidirectional in photonic crystals fabricated by semi-cylindrical ferrite rods in magnetized states. Self-collimated one-way body wave presents at certain unit cell configurations of the photonic crystal, and the one-way wave beam shows robustness in some way to certain kind of disorders in the wave channel. We find the propagation direction of the self-collimated one-way wave beams can be tuned using a bias magnetic field. Therefore, we can bend the self-collimated one-way body wave, which can be considered as a curved waveguide. Further, by applying the bias magnetic field in a complex configuration, the self-collimated one-way wave beam can be bent into arbitrary trajectories within the photonic crystal, providing a new avenue for controlling wave beams.