Two-dimensional focusing grating couplers for SOI waveguides

We have designed a compact focusing two dimensional grating coupler which consist of 70 nm shallow etch and 160 nm poly-silicon overlay for coupling between the optical fiber and 220 nm silicon-on-insulator (SOI) waveguides. The maximum coupling efficiency is increased with the added poly-silicon cylinders, reaching a mean coupling efficiency of 44.4% (-3.52 dB) at 1550 nm wavelength. The focusing grating structure exhibits excellent size reduction advantages when compared to the standard nonfocusing grating structure.