Wide bandwidth silicon nitride grating coupler

We demonstrate a one-dimensional grating coupler in silicon nitride with a 67-nm 1-dB bandwidth, the largest reported for a grating coupler butt-coupled to standard singlemode fiber. The peak coupling efficiency is -4.2 dB. It requires no partial etch, requires only 0.6-ìm fabrication resolution, and exhibits less than -22 dB back reflection.