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Overcoming stress limitations in SiN nonlinear photonics via a bilayer waveguide
Karl J McNulty1, Shriddha Chaitanya1, Swarnava Sanyal2
1Department of Electrical Engineering, Columbia University, New York, NY 10027, USA.
Nanophotonics (Berlin, Germany)
|November 17, 2025
Summary
We developed a novel silicon nitride (SiN) bilayer waveguide for on-chip nonlinear photonics. This approach overcomes film cracking issues, enabling high-performance devices like Kerr frequency combs.
Area of Science:
- Photonics
- Materials Science
- Nanotechnology
Background:
- Silicon nitride (SiN) is a promising material for on-chip nonlinear photonics due to low loss and high nonlinear index.
- High-thickness SiN deposition via LPCVD causes film stress, leading to cracking and limiting scalability in silicon photonics.
Purpose of the Study:
- To overcome the limitations of high-stress LPCVD SiN for nonlinear photonics.
- To enable scalable fabrication of high-performance SiN-based photonic devices.
Main Methods:
- Proposed a bilayer waveguide structure combining LPCVD SiN and low-stress PECVD SiN.
- Investigated group velocity dispersion tuning at 1550 nm.
- Fabricated low-loss resonators and demonstrated Kerr frequency combs.
Main Results:
- Achieved group velocity dispersion tuning without film cracking.
- Fabricated resonators with intrinsic quality factors exceeding 1 million.
- Demonstrated a locked, normal dispersion Kerr frequency comb spanning 120 nm in the C-band with 350 µW on-chip pump power.
Conclusions:
- The proposed SiN bilayer waveguide scheme effectively mitigates film stress and cracking issues.
- This approach enables scalable fabrication of high-performance nonlinear photonic devices, including broadband Kerr frequency combs.
