Compact grating coupler for thick silicon nitride

Thick Silicon nitride-on-insolater (SNOI) is widely used for nonlinear applications due to its broadband nearly-zero flattened dispersion. In this paper, we present a grating coupler for strip waveguides on 700-nm-thick SNOI. Focusing grating structure and inverse taper are combined to minify the footprint to 70μm × 19μm. The peak couplin g efficiency is -3.7dB and the 1-dB bandwidth is 54nm.