Two-dimensional photonic/phononic topological states

Photonic/phononic topological phases with symmetry-protected surfaces or edge modes in the bulk gap, analogous to the topological states in electronic systems, have drawn great attention due to their basic physics and potential applications in new types of optical/acoustic devices. In this review we shall mainly focus on the photonic/phononic topologically nontrivial states (such as photonic/phononic quantum Hall effects, photonic/phononic topological insulators,and Floquet topological insulators) in two-dimensional systems, including photonic, plasmonic,and phononic crystals. Finally, we give a summary and outlook on the development and prospects of these kinds of symmetry-protected topological states of bosons.