Deterministic soliton microcombs in Cu-free photonic integrated circuits

Area of Science:

• Photonics
• Materials Science
• Integrated Optics

Background:

• Chip-scale optical frequency combs (microcombs) offer broad bandwidth and compact form factors, compatible with wafer-scale manufacturing.
• Silicon nitride (Si3N4) photonic integrated circuits are a leading platform for microcombs, enabling applications in communications, lidar, and frequency synthesis.
• Deterministic soliton microcomb generation is hindered by thermal instabilities, limiting real-world deployment.

Purpose of the Study:

• To overcome thermal effects hindering deterministic soliton generation in Si3N4 microcombs.
• To identify and mitigate the root cause of thermal instabilities in Si3N4 photonic integrated circuits.

Main Methods:

• Investigated thermal effects in Si3N4 waveguides, tracing them to copper impurities from CMOS-grade Si wafers.
• Developed copper removal techniques to reduce impurity concentration and mitigate thermal effects.
• Demonstrated deterministic dissipative Kerr soliton generation using arbitrary and slow laser scanning profiles.

Main Results:

• Successfully identified and reduced copper impurities in Si3N4 waveguides, significantly mitigating thermal instabilities.
• Achieved deterministic soliton microcomb generation with improved stability and performance.
• Validated the effectiveness of the developed copper removal techniques.

Conclusions:

• Copper impurities are a primary cause of thermal instabilities in Si3N4 microcombs.
• The developed copper removal techniques enable deterministic soliton generation, overcoming a key obstacle for microcomb deployment.
• These techniques are readily applicable to foundry fabrication processes for Si3N4 devices.