Two-color phase-stable dual-comb ranging without precise environmental sensing.

High-precision long geometrical distance measurement performs a vital role in large-scale manufacturing and future light detection and ranging (LIDAR) for tight formation. Its high precision, fast measurement rate, and large ambiguity range have traditionally made dual-comb ranging (DCR) a powerful tool for absolute distance measurement. However, DCR experiences the same issues caused by the refractive index of air as other laser-based ranging systems. The conventional method used to compensate refractive index of air is through using empirical equations by monitoring environment parameters. This real-time compensation method relies on precise sensors and cannot be easily applied to long-distance measurement. Thus, a two-color compensation method is proposed that requires only two co-propagating lights at different wavelengths, without specific identification of the refractive index of air. In this paper, the two-color method is combined with a low-noise DCR realized by a digital correction method. Mode resolved and phase-stable comb spectra are available for ranging at both two wavelengths with ~200 THz difference. The experimental result demonstrates 46 nm precision and 2.7 m ambiguity range by two-color DCR (TC-DCR) with 0.1 s coherent averaging at 1 kHz repetition rate difference. This method achieves a precision of the order of ~10 and an accuracy of the order of ~10, which is comparable to the single-color DCR results by empirical equations with environmental sensing. The proposed two-color DCR demonstrates great potential for long-distance measurement in open air.