Compact graphene directional couplers based on dielectric ridges for planar integration

A compact graphene directional coupler incorporating high-index dielectric ridges and a uniformly biased graphene sheet for planar integration are proposed. By tuning the applied electrical field, the proposed coupler supporting two-dimensional field confinement can be switched from the bar state to the cross state within a device length less than 1 micrometer. The easy-to-fabricate coupler enabling the horizontal switch of graphene surface plasmons might have a great potential for graphene-based planar integrated optics.