Topology optimization of grating couplers for the efficient excitation of surface plasmons

We propose a methodology for a systematic design of grating couplers for efficient excitation of surface plasmons at metal-dielectric interfaces. The methodology is based on a two-dimensional topology optimization formulation based on the H-polarized scalar Helmholtz equation and finite-element method simulations. The efficiency of the method is demonstrated by optimized designs for input and output grating couplers for an Ag-SiO2 interface. The results indicate that slanted grove gratings may raise the coupling efficiency above 68% where the highest previously reported value was 50%.