Dispersion engineering and frequency comb generation in thin silicon nitride concentric microresonators.

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Kerr nonlinearity-based frequency combs and solitons are typically generated from on-chip microresonators.
• Initiation of these combs requires anomalous dispersion, which imposes significant limitations on material choice, film thickness, spectral range, and fabrication.

Purpose of the Study:

• To overcome the limitations associated with anomalous dispersion in microresonator-based frequency comb generation.
• To engineer resonator dispersion to be anomalous over a moderately broad bandwidth using a novel resonator design.

Main Methods:

• Utilized a concentric racetrack-shaped resonator design.
• Engineered anomalous dispersion in a 300 nm thick silicon nitride film, a material previously associated with normal dispersion.
• Employed a mode-selective, tapered coupling scheme.

Main Results:

• Demonstrated anomalous dispersion in silicon nitride microresonators, overcoming previous material and fabrication constraints.
• Successfully generated coherent mode-locked frequency combs.
• Showcased the ability to engineer anomalous dispersion for resonators at almost any wavelength.

Conclusions:

• The concentric racetrack resonator design effectively lifts constraints on material choice and fabrication for frequency comb generation.
• This approach offers material and process compatibility with semiconductor manufacturing.
• Enables broader applicability of on-chip frequency combs by overcoming anomalous dispersion limitations.