  We present a chip-scale scanning dual-comb spectroscopy (SDCS) approach for
broadband ultrahigh-resolution spectral acquisition. SDCS uses Si3N4 microring
resonators that generate two single soliton micro-combs spanning 37 THz (300
nm) on the same chip from a single 1550-nm laser, forming a
high-mutual-coherence dual-comb. We realize continuous tuning of the dual-comb
system over the entire optical span of 37.5 THz with high precision using
integrated microheater-based wavelength trackers. This continuous wavelength
tuning is enabled by simultaneous tuning of the laser frequency and the two
single soliton micro-combs over a full free spectral range of the microrings.
We measure the SDCS resolution to be 319+-4.6 kHz. Using this SDCS system, we
perform the molecular absorption spectroscopy of H13C14N over its 2.3 THz (18
nm)-wide overtone band, and show that the massively parallel heterodyning
offered by the dual-comb expands the effective spectroscopic tuning speed of
the laser by one order of magnitude. Our chip-scale SDCS opens the door to
broadband spectrometry and massively parallel sensing with ultrahigh spectral
resolution.
