(a) Illustration of the principle of SHG phase control in the Au-WS2 interface. (b) SEM image for linear plasmonic nanosieves with the gradient phase. (c) Polarization distributions (indicated by the arrows) of the fundamental beam passed through the Au nanohole array in the area indicated by the square in (b). The deeper color indicates stronger local fields in the Au nanoholes. (d) The calculated local-field distributions in Au nanoholes of the same area by the FDTD method.