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

Area of Science:

• Photonics
• Nanotechnology
• Optical Engineering

Background:

• Chip-scale light detection and ranging (LiDAR) requires diffraction gratings with high upward diffraction efficiency and extended effective length.
• Existing diffraction grating designs face limitations in achieving both high efficiency and large effective length simultaneously for miniaturized systems.

Purpose of the Study:

• To propose and theoretically analyze a novel diffraction grating based on a multilayer silicon nitride waveguide.
• To evaluate the grating's performance metrics, including upward diffraction efficiency, effective length, and far-field divergence.
• To assess the grating's robustness against process variations and explore tunability for optical sensing applications.

Main Methods:

• Theoretical modeling of a multilayer silicon nitride waveguide diffraction grating.
• Simulation of optical performance at a wavelength of 850 nm.
• Monte Carlo analysis to evaluate tolerance to variations in layer thickness, lithography, and wavelength drift.

Main Results:

• Theoretical upward diffraction efficiency of 92% achieved.
• Near-field effective length of 376 µm and far-field divergence angle of 0.105° obtained.
• High tolerance to process variations: >71% of samples maintain >80% diffraction efficiency and 100% have effective length >200 µm under specified variations.
• Tunable effective length from hundreds of microns to centimeters possible by adjusting etching parameters.

Conclusions:

• The proposed silicon nitride waveguide diffraction grating offers superior performance for chip-scale LiDAR.
• Demonstrated high efficiency, large effective length, and significant tolerance to fabrication imperfections.
• Potential applications in visible to near-infrared optical sensing and imaging systems.