Binary grating graphene structures. (a) The bilayer graphene structure. (b) The multilayer graphene structure. h is the grating layer thickness. Λ is the period of grating. L1 is the width of dielectric with ε1. L(L2) is the width of dielectric with ε2. The duty ratio is f2 = L/Λ, and f1 = 1 - f2. In this paper, we simply set ε1 = 1 and ε2 = 4.