▎ 摘　　要

A directional coupler (DC) based on a graphene-enhanced Na-loaded plasmonic rib waveguide (GNPRW) is proposed. The coupling property of the DC are studied by using the finite element method (FEM). Compared with the plasmonic waveguides based on the Au and Ag substrates, the GNPRW has better plasmonic characteristics. The figure of merit (FoM) of the GNPRW can reach the scale of 10(5) by optimizing the dimension parameters. The coupling property of the DC based on the GNPRW can be improved by adjusting Fermi energy (EF) of graphene. The 3 dB coupling can be realized by changing the length (L) of the coupling region between two parallel straight GNPRWs. In addition, the silicon nitride and silicon dioxide make the GNPRW easy to manufacture, and the DC based on the GNPRW has potential applications in high density integrated optical circuit.