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

Abstract

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 micro- combs 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) microres- onator (FSR ∼374 GHz), featuring a near-octave-spanning (1150–2200 nm) spectral range and a terahertz repetition rate of ∼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 ∼0.75, ∼1.12, and ∼1.5 THz were also realized in different microresonators of the same size. The proposed scheme shows a reliable design strategy for broad- band soliton generation with versatile dynamic control over the comb line spacing.