Broadband microwave-rate dark pulse microcombs in dissipation-engineered LiNbO₃ microresonators

Area of Science:

• Integrated photonics
• Nonlinear optics
• Materials science

Background:

• Kerr microcombs are broadband light sources crucial for optical and microwave signal applications.
• Thin-film lithium niobate (LiNbO3) offers nonlinear optical functionalities but faces challenges with Raman scattering, hindering microcomb formation.
• Dark pulse microcombs, requiring a delicate balance of nonlinearities, gain, and dispersion, have been elusive in LiNbO3 microresonators.

Purpose of the Study:

• To demonstrate dark pulse microcombs in high-Q LiNbO3 microresonators.
• To overcome the limitations imposed by the strong Raman response in LiNbO3.
• To enable high-power, microwave-rate microcombs on LiNbO3 chips for integrated photonic applications.

Main Methods:

• Dissipation engineering was employed to suppress unwanted Raman scattering.
• A high-Q LiNbO3 microresonator was utilized.
• A pulley coupler was designed to control phase-matching conditions and damp resonances near Raman-active wavelengths.

Main Results:

• Successfully generated dark pulse microcombs with a 25 GHz repetition frequency and a 200 nm spectral span.
• Demonstrated effective damping of resonances near Raman-active wavelengths through engineered dissipation.
• Investigated the coherence and tunability of the generated dark pulse microcombs.

Conclusions:

• The study presents a viable method for realizing dark pulse microcombs in LiNbO3 microresonators, addressing previous limitations.
• This work paves the way for high-power microcomb generation at microwave rates on LiNbO3 platforms.
• The findings open new avenues for monolithic integration of advanced photonic functionalities in communications and microwave photonics.