  In this paper, we study valley degree of freedom in all dielectric silicon
photonic graphene. Photonic band gap opening physics under inversion symmetry
breaking is revisited by the viewpoint of nonzero valley Chern number. Bulk
valley modes with opposite orbital angular momentum are unveiled by inspecting
time-varying electric fields. Topological transition is well illustrated
through photonic Dirac Hamiltonian. Valley dependent edge states and the
associated valley-protected backscattering suppression around Z-shape bend
waveguide have been demonstrated.
