Second-harmonic generation in subwavelength graphene waveguides

We suggest a novel approach for generating the second-harmonic radiation in subwavelength graphene waveguides. We demonstrate that the quadratic phase matching between plasmonic guided modes of different symmetries can be achieved in a planar double-layer graphene structure when conductivity of one of the layers becomes spatially modulated. We predict theoretically that, owing to graphene nonlocal conductivity, the second-order nonlinear processes can be actualized for interacting plasmonic modes with an effective grating coupler to allow external pumping of the structure with the generated radiation at the double frequency.