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 supports up to 0.3 GHz interferogram frequency bandwidth and thus combines fast measurement times (corresponding to high detunings) 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 (e.g., up to 2900 for 150 s averaging time). Iodine and acetylene spectroscopy yield excellent agreement with literature over an optical bandwidth of 10 THz in the visible and near-infrared. Common dual-comb spectroscopy self-correction requires a bright and continuous interferogram train. We lift this requirement by introducing cross-channel correction: the algorithm measures phase fluctuations from a reference channel and predicts and corrects their influence on 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.