High-Q Si₃N₄ microresonators based on a subtractive processing for Kerr nonlinear optics

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Microresonator frequency combs (microcombs) are crucial for frequency synthesis and metrology.
• High optical quality factor (Q) is essential for microcomb performance.
• Silicon nitride (Si3N4) microresonators offer dispersion engineering and integration potential but achieving high Q (>10^7) via standard methods is challenging.

Purpose of the Study:

• To develop ultra-smooth Si3N4 microresonators with high optical Q factors using subtractive processing.
• To demonstrate precise cross-section geometry engineering for dispersion control.
• To generate high-performance microcombs, including 100 GHz soliton microcombs.

Main Methods:

• Fabrication of ultra-smooth Si3N4 microresonators using subtractive processing.
• Engineering of microresonator cross-section geometry for dispersion control in the telecommunications band.
• Demonstration of mode-locked dark-pulse Kerr combs and soliton microcombs.

Main Results:

• Achieved mean intrinsic Q factors around 11 million for Si3N4 microresonators.
• Demonstrated precise control over normal and anomalous dispersion.
• Successfully generated 100 GHz soliton microcombs, a first for subtractively fabricated Si3N4 microresonators.

Conclusions:

• Ultra-smooth Si3N4 microresonators with high Q factors are achievable using standard subtractive fabrication.
• These high-Q microresonators enable the generation of 100 GHz soliton microcombs.
• The results pave the way for co-integration of advanced microcombs with other photonic devices.