Streaming self-corrected dual-comb spectrometer

Abstract

We radically simplify coherently averaged dual-comb spectroscopy by introducing a real-time self-correction system: a radio frequency system-on-chip computes each incoming dual-comb interferogram's phase, frequency, and arrival time; calculates changes in the combs' carrier-envelope offset frequency and repetition rate difference; and immediately phase-corrects the incoming interferogram data stream. The algorithm combines fast measurement times with broadband optical detection. Using this system, we achieve comb-resolved spectroscopy with Fourier-limited linewidth, coherent averaging over arbitrarily long durations, and high signal-to-noise ratios. Iodine and acetylene spectroscopy yield good agreement with literature over an optical bandwidth of 10 THz in the visible and near-infrared. Common dual-comb spectroscopy self-correction requires a continuous interferogram train. We lift this requirement by introducing cross-channel correction: the algorithm measures phase fluctuations from a reference channel to predict and correct a signal channel. This enables correcting unstable or intermittent signals (typical, e.g., in field measurements), or low-amplitude signals with amplified phase fluctuations (relevant for nonlinearly upconverted combs). The approach makes instantaneous dual-comb spectroscopy available to everyday applications.