Experimental demonstration of silicon nitride waveguide gratings with excellent efficiency and divergence angle

Silicon nitride (Si₃N₄) photonic platform has recently attracted increasing attention for Si₃N₄ photonic integrated circuits (PIC). A diffraction grating with the only etched top-layer in tri-layer Si₃N₄ optical waveguides is proposed, which shows a simple fabrication process, high upward diffraction efficiency, and lower far-field divergence angle. The measured results of the diffraction grating at a wavelength of 905 nm show the average upward diffraction efficiency of 90.5% and average far-field divergence angle of 0.154°, which shows a good agreement with the design results with the upward diffraction efficiency of 91.6% and far-field divergence angle of 0.105°.