Comprehensive grating enabled silicon nitride fiber-chip couplers in the SNIR wavelength band.

We present silicon nitride grating enabled fiber-chip coupling in the sub-near-infrared band. We present a comprehensive design and simulation and experimental demonstration of uniform and apodized grating couplers, with and without bottom reflectors. The mode engineering yields a best efficiency of -1.6 dB for apodized grating design, which is further improved to -0.66 dB with a bottom reflector. Experimentally, we demonstrate a coupling efficiency of -2.2 dB for the optimized design. Furthermore, we present a detailed simulation and measurement comparison of various grating parameters and the effect of fabrication tolerances on the grating performance.