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

TL;DR

This paper introduces a multilayer silicon nitride diffraction grating with high efficiency and large effective length, suitable for chip-scale light detection and ranging, demonstrating robustness to fabrication variations.

Contribution

It proposes a novel multilayer silicon nitride diffraction grating with high upward efficiency, large effective length, and strong tolerance to process variations, advancing chip-scale optical sensing.

Findings

Achieves 92% upward diffraction efficiency at 850 nm

Effective length up to 376 μm with high tolerance to variations

Potential for optical sensing from visible to near-infrared

Abstract

Diffraction gratings with high upward diffraction efficiency and large effective length are required for chip-scale light detection and ranging. In this paper, 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$^{\circ}$ 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 $\pm$5$\%$ layer thickness variation, $\pm$50 nm lithographic variation and $\pm$20 nm wavelength drift, more than 71$\%$ of the grating samples have a diffraction efficiency higher than 80$\%$, and 100$\%$ of the samples have an effective length larger than 200 $\mu m$ (corresponding to a far-field divergence <0.2$ ^{\circ}$). Furthermore, the near-field effective length of the grating with an upward diffraction efficiency above 90$\%$ can be adjusted from hundreds of microns to centimeters by changing the etching layer thickness and the grating duty cycle. This diffraction grating has potential application in optical sensing and imaging from visible to near-infrared wavelengths.