Compact Grating Coupler for 700-nm Silicon Nitride Strip Waveguides

700-nm-thick silicon nitride-on-insulator (SNOI) is widely used for nonlinear applications due to its broadband nearly zero flattened dispersion. In this paper, we present a grating coupler for the TE mode of strip waveguides on 700-nm-thick SNOI. Focusing grating structure and inverse taper are combined to reduce the footprint to 70.2 μm × 19.7 μm. The peak coupling efficiency is -3.7 dB and the 1-dB bandwidth is 54 nm. The fabrication process is CMOS-compatible with only one additional etching step required.