Reconfigurable topological states in valley photonic crystals

Valley photonic crystals can enable nontrivial topology locked to the valley index. Since time-reversal symmetry is preserved, no external magnetic field has to be applied. Therefore, the valley topological insulators can be easily used to construct photonic devices. Here, a reconfigurable valley photonic crystal is proposed, where the inversion symmetry is broken by constructing the unit cell with two different materials. Also, since one of the materials is electro-optic material barium titanate, by simply changing the applied voltage, not only the band-gap frequency will shift, but the topological phase transition can also happen. This is highly beneficial to the design and optimization of integrated photonic devices because a balance between the flexibility of devices and the robustness of topological properties is realized successfully. Moreover, a two-port optical switch as an example of the possible applications is proposed.