  The broad and equidistant spectrum of frequency combs has had a profound
impact on spectroscopic studies. Particularly, experiments involving the
coupling of frequency combs to cavities have already enabled unprecedented
broadband and sensitive spectroscopy on a single-molecule level. The emergence
of integrated, compact and broadband Kerr-microcombs holds promise to bring
many metrological and spectroscopic studies outside of the lab. However,
performing cavity-enhanced direct frequency comb spectroscopy on-chip has
remained a challenge. Here, we couple a microcomb source with a microcavity to
extend the advantages of cavity-enhanced spectroscopy to photonically
integrated circuits. By harnessing the coherent nature of the Kerr-comb and
high-Q microcavity enhancement, we obtain a detailed dispersion landscape of
the guided-wave mode and comprehensive frequency-dependent cavity lineshapes.
Our microcomb-cavity coupling can facilitate photonically integrated
cavity-enhanced biochemical spectroscopy by evanescently coupling analytes to
the cavity's guided mode, a mode of operation we analyze and provide guidelines
for. Demonstrated detailed dispersion measurements, overperforming
state-of-the-art table-top tunable lasers in available bandwidth, show
potential for integrated nonlinear optics applications, as precise dispersion
management is crucial for such processes. Our chip-scale comb-cavity coupled
platform suggests an integrated, broadband, cost-effective and accurate tool
for the nonlinear optics studies as well as for ultra-compact bio- and
chemical- sensing platform.
