Pseudospin-induced chirality with staggered optical graphene

Pseudospin has an important role in understanding many interesting physical phenomena that are associated with two-dimensional materials such as graphene. Pseudospin has been proposed to be directly related to angular momentum, and orbital angular momentum was recently experimentally demonstrated to be an intrinsic property of pseudospin in a photonic honeycomb lattice. However, in photonics, the interaction between spin and pseudospin for light has not been investigated. In this letter, we propose that in an optical analog of staggered graphene (that is, a photonic honeycomb lattice waveguide with in-plane inversion symmetry breaking), the pseudospin mode can strongly couple to the spin of an optical beam that is incident in certain directions. The spin–pseudospin coupling that is caused by the spin–orbit conversion in the scattering process induces a strong optical chiral effect for the transmitted optical beam. Spin–pseudospin coupling of light opens the door to the design of pseudospin-mediated spin or valley-selective photonic devices.