Dual-comb generated in single thin-film lithium niobate microrings

Abstract

Dual-comb technology has emerged as an essential tool for high-precision spectroscopy, real-time ranging, and high-sensitivity sensing. Integrating dual-comb sources into a single microresonator would substantially reduce pump power, footprint, system complexity, and cost, yet this remains a significant challenge. Here, we demonstrate, for the first time, integrated dual-comb generation in a single thin-film lithium niobate (TFLN) microring, under single continuous-wave laser pumping. Rather than regarding TFLN's strong Raman nonlinearity as detrimental, as conventionally viewed, we harness it constructively. By engineering the dispersion of TFLN microrings, we leverage the fundamental and first-order transverse-electric mode families with loaded Q factors exceeding 5X10^6, comparable repetition rates, and suitable dispersion profiles, and bridge them through stimulated Raman scattering (SRS) processes. Pumping a first-order mode at 1551.28 nm initially excites both Stokes and anti-Stokes SRS in the fundamental mode family at low thresholds, and subsequently produces two independent, spectrally separated combs at a pump power of 320 mW via direct Kerr and Raman-assisted Kerr effects, respectively. The two combs span broad bandwidths, exhibit repetition rates of ~102 GHz with a slight difference of ~624 MHz, and do not merge spectrally. The broadest spectrum spans 654 nm, and the Raman-Kerr comb has a 3-dB bandwidth exceeding 29 nm. Further characterization confirms that the comb lines exhibit low phase noise, with an intrinsic linewidth of 410 Hz. This work establishes a robust pathway for on-chip dual-comb generation in a single-laser pumped microring, significantly advancing dual-comb systems toward simplified architectures, enhanced robustness, and scalable integration, while accelerating their practical deployment.