Continuously tunable super-efficient microcombs.

Area of Science:

• Photonics and optical engineering
• Quantum optics and nonlinear phenomena

Background:

• Microcombs are advancing towards system-level applications, with high-Q silicon nitride microresonators enabling near-unity optical conversion efficiency.
• Efficient soliton microcombs in coupled cavities (photonic molecules) require precise control of avoided mode crossings to counteract soliton-induced spectral shifts.
• Current methods, while efficient, face challenges in achieving continuous broadband pump tuning, limiting practical deployment.

Purpose of the Study:

• To demonstrate offset-tunable, super-efficient microcombs in photonic molecules with low-noise operation and a smooth spectral envelope.
• To achieve broadband tunability of microcombs through thermal tuning of coupled cavities.
• To analyze the impact of thermal tuning on microcomb phase noise, repetition rate stability, and heater response.

Main Methods:

• Utilizing coupled microresonators (photonic molecules) fabricated from high-Q silicon nitride.
• Implementing tandem thermal tuning of the main and auxiliary cavities to control avoided mode crossings.
• Analyzing phase noise, repetition rate stability, and thermal response characteristics.

Main Results:

• Demonstrated offset-tunable, super-efficient microcombs with low noise and a constant spectral envelope.
• Achieved broadband tunability by thermally tuning coupled cavities across multiple free spectral ranges.
• Characterized the influence of thermal tuning on microcomb properties and system stability.

Conclusions:

• Photonic molecules offer a highly flexible and efficient platform for generating super-efficient microcombs.
• The demonstrated broadband, post-fabrication tunability enables microcombs at arbitrary pump wavelengths.
• This approach is particularly suitable for applications in metrology and precision spectroscopy.