Shot-noise limited dual-comb supercontinuum

Dual-comb supercontinuum (SC) sources are promising for metrology and spectroscopy applications as their broad bandwidth supports the detection of multiple spectral features simultaneously. However, the limited sensitivity inherent to their high relative intensity noise (RIN) and low power per comb line so far hindered their huge potential in those fields. In this work, we overcome both of these issues with the first shot-noise limited dual-comb SC with gigahertz pulse repetition rate and >1 W output power. It is based on a high-power single-cavity dual-comb Yb:CALGO oscillator centered at 1053 nm, combined with a single polarization-maintaining all-normal-dispersion (ANDi) fiber for spectral broadening. The resulting SC spans 820 nm-1280 nm and has a gigahertz pulse repetition rate enabling high power per comb line and sufficient resolution in the optical domain for most spectroscopy applications. The SC exhibits a shot-noise limited spectrally-resolved RIN power spectral density for all spectral bands, including the spectral wings of the SC and record-low integrated RIN down to 2.7 × 10⁵ for the spectral band at 1100 nm ± 8 nm for the integration range [1 kHz, 10 MHz]. This exceptional performance originates from the pump laser's low noise properties and its high output power which is sufficient to drive the SC process directly without amplification, in combination with the unprecedented noise-suppression in the ANDi fiber reaching up to >20 dB around the oscillator wavelength. To better understand the observed noise-suppression mechanisms, we perform a numerical simulation of the RIN which is in excellent agreement with our measurements. We further analyze a dual-comb interferometry measurement with this source at a repetition rate difference of ~3.95 kHz, which supports the resolution of the entire SC spectrum in parallel without spectral aliasing. The dual-comb spectroscopy figure of merit (FOM) is >1.1 × 10⁷ Hz½ for all spectral bands, making it suitable for high-sensitivity applications. Our measurements further show that recording the entire SC spectrum at once with around 30 parallel detectors would yield an exceptionally high FOM of around 5 × 10⁸ Hz½.