Highly efficient grating coupler between optical fiber and silicon-on-insulator waveguide

In or der to increase the coupling efficiency between single mode optical fiber and SOI waveguide, in this paper we present the design of a diffractive grating structure and then get the optimal parameters which can reach 67% coupling efficiency though FDTD simulation. The grating is fabricated on the SOI waveguide by focused ion beam (FIB) lithography. Because side wall roughness caused by fabrication tolerances and extra losses finally we measured a 17.5% coupling efficiency of the grating coupler between optical fiber and silicon waveguide.