Wavelength-scanned all-fiber cavity ring-down gas sensing using an L-band active fiber loop

We report an all-fiber wavelength-scanned cavity ring-down technique using an L-band active fiber loop. A software-based wavelength scanning scheme is developed to automatically sweep the absorption line of the analyte, by which the empty cavity loss can be directly obtained as well as the absorption information. Hence, analyte information can be further quantified by analyzing the whole calibration-free absorption spectrum. We choose the absorption transition of R(14) of CO2, as an example, for demonstration. The recovered absorption spectrum matches the theoretically computed absorption profile well with an R2 value of 0.9964. Under an optimized integration time of 308 s, the sensing system shows a noise equivalent absorption coefficient of 2.15 × 10–6 cm–1, suggesting its potential applications to gas sensing with easy optical assembly, simple operation, and long-term stability.