Diffraction gratings based on a multilayer silicon nitride waveguide with high upward efficiency and large effective length

Diffraction gratings with high upward diffraction efficiency and large effective length are required for chip-scale light detection and ranging. We propose a diffraction grating based on a multilayer silicon nitride waveguide, which theoretically achieves an upward diffraction efficiency of 92%, a near-field effective length of 376 mu m, and a far-field divergence angle of 0.105 degrees at a wavelength of 850 nm. The diffraction grating has a high tolerance to process variations based on Monte Carlo analysis. When the conditions are +/- 5% layer thickness variation, +/- 50 nm lithographic variation, and +/- 20 nm wavelength drift, more than 71% of the grating samples have a diffraction efficiency higher than 80%, and100% of the samples have an effective length larger than 200 mu m(corresponding to a far-field divergence <0.2 degrees). Furthermore, the near-field effective length of the grating with an upward diffraction efficiency above 90% can be adjusted from hundreds of microns to centimeters by changing the etching layer thickness and the grating duty cycle. This diffraction grating has a potential application in optical sensing and imaging from visible to near-IR wavelengths. (C) 2022 Optica Publishing Group

Automated summary

In this study, a diffraction grating based on a multilayer silicon nitride waveguide is proposed, which demonstrates high upward diffraction efficiency and large effective length. The analysis shows that the diffraction grating has a high tolerance to process variations and can adjust the near-field effective length. The research results suggest that this diffraction grating has potential applications in optical sensing and imaging.