Physical mechanism of polarization-dependent optical phenomena in 2D materials. (a) Anisotropic 2D materials and the schematic view of 3D energy band. (b) TMD materials and their inequivalent valleys in the Brillouin zone. (c) Heterostructures of 2D materials and nanophotonic structures. The schematic view of multibody coupling among excitons, plasmons, and photons.