Rhythmic soliton interactions for integrated dual-microcomb spectroscopy

TL;DR

This paper demonstrates the generation and control of counter-propagating solitons in integrated microresonators, enabling high-coherence dual-comb spectroscopy with potential for miniaturized spectrometers.

Contribution

It introduces a method to synthesize and analyze synchronized counter-propagating solitons in silicon nitride microresonators, advancing integrated dual-comb spectrometer technology.

Findings

Achieved passive mutual coherence of CP solitons through rhythmic interactions

Demonstrated dual-comb spectroscopy with 0.6 microsecond acquisition time

Resolved complex soliton motion trajectories and synchronization behaviors

Abstract

Rotation symmetry of microresonators supports the generation of phase-locked counter-propagating (CP) solitons that can potentially miniaturize dual-comb systems. Realization of these dual-comb compatible solitons in photonic integrated circuits remains a challenge. Here, we synthesized such CP solitons in an integrated silicon nitride microresonator and observed forced soliton oscillation due to rhythmic, time-varying soliton interactions. The interactions result in seconds mutual-coherence passively. Temporal motion in the soliton streams is discerned by measuring a quadratic-scaling frequency noise peaks and an inverse quadratic-scaling microcomb sidebands. By generating a CP soliton trimer to have two synchronized solitons in one of the orbiting directions, we resolve the incapability of measuring two unsynchronized CP soliton dimer pulses by optical cross-correlation, and show CP solitons undergo complex motion trajectory. We further prove that precise dual-comb spectroscopy with an acquisition time as short as 0.6 $\mu$s is feasible using these solitons, although the temporal motion limits the dynamic range. Besides revealing soliton interactions with different group velocities, our work propels the realization of photonic integrated dual-comb spectrometers with high passive coherence.