Near-octave-spanning breathing soliton crystal in an AlN microresonator

The soliton crystal (SC) was recently discovered as an extraordinary Kerr soliton state with regularly distributed soliton pulses and enhanced comb line power spaced by multiples of the cavity free spectral ranges (FSRs), which will significantly extend the application potential of microcombs in optical clock, signal processing, and terahertz wave systems. However, the reported SC spectra are generally narrow. In this Letter, we demonstrate the generation of a breathing SC in an aluminum nitride (AlN) microresonator (FSR similar to 374 GHz), featuring a near-octave-spanning (1150-2200 nm) spectral range and a terahertz repetition rate of similar to 1.87 THz. The measured 60 fs short pulses and low intensity-noise characteristics confirm the high coherence of the breathing SC. Broadband microcombs with various repetition rates of similar to 0.75, similar to 1.12, and similar to 1.5 THz were also realized in different microresonators of the same size. The proposed scheme shows a reliable design strategy for broadband soliton generation with versatile dynamic control over the comb line spacing. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

Automated summary

The generation of breathing soliton crystal in an aluminum nitride microresonator has enabled a wider spectral range and higher terahertz repetition rate, confirming high coherence. Broadband microcombs with different repetition rates were successfully realized in various microresonators of the same size, providing a reliable design strategy for dynamic control over comb line spacing.