Efficient single-etch surface grating couplers in silicon nitride platforms for telecom and datacom wavebands

We present designs and experiments of single-etched amorphous silicon (α-Si) surface grating couplers on a silicon nitride (SiN) waveguide, operating at the telecom ( C -band) and datacom ( O -band) wavebands. SiN-only grating couplers demonstrate experimental coupling loss of -3.9 dB at 1.55 μm wavelength with a 1-dB bandwidth of 37 nm. Utilizing the hybrid α-Si/SiN platform with subwavelength grating structure, we obtain improved coupling performances, with the optimized fiber-chip coupling loss of -2.0 dB and a 1-dB spectral bandwidth of 42 nm centered at 1.31 μm.