Hyperparametric solitons in nondegenerate optical parametric oscillators

Abstract: Dissipative solitons and their associated low-noise, chip-scale frequency combs hold great potential for applications in optical communications, spectroscopy, precision time-keeping, and beyond. These applications drive interest in shifting soliton spectra to frequency bands far detuned from the telecom's C-band pump sources. Recent demonstrations have utilized second-harmonic generation and degenerate optical parametric oscillators (OPOs) to shift soliton combs away from the primary pump. However, these approaches lack the tunability offered by nondegenerate OPOs. This work presents a proof-of-principle demonstration of solitons in a silicon-nitride microresonator-based nondegenerate OPO system with engineered dispersion and optimized coupling rates. By pumping a relatively low-Q resonance in the C-band, we excite a signal soliton comb centred around a far-detuned, high-Q O-band resonance. This process also generates repetition-rate-locked combs at the pump and idler frequencies, with the latter occurring at a wavelength beyond 2$\mu$m. We demonstrate that the solitons supported by this platform are distinct from other families of dissipative solitons and call them - hyperparametric solitons. They emerge when the narrow-band signal mode, phase-matched under negative pump detuning, reaches sufficient power to drive bistability in the parametric signal. We investigate the properties of hyperparametric solitons, including their parametrically generated background and multisoliton states, both experimentally and through theoretical modelling.