Multipoint Gas Detection Based on Photothermal Effect and Wavelength-Division Multiplexing (WDM) Interferometer

In this article, we propose a novel multipoint gas detection scheme based on the photothermal (PT) effect and interferometer working at different wavelengths. Several fiber Bragg gratings (FBGs) with different central wavelengths were incorporated in the linear Sagnac-like interferometer, which served as the wavelength-dependent reflection mirrors, to extract the gas concentration information from different gas cells. This structure allows for a more straightforward and efficient installation and layout, as it eliminates the need for sophisticated servo control and lock-in amplifiers. The experiment used a novel frequency-domain signal processing method to collect weak gas signals, and the results showed that an 18-cm-long gas cell can detect gas concentrations as low as 47 ppb with current technology. This method can significantly reduce noise, and crosstalk can be lowered to less than 30 dB. A three-point acetylene detection system is validated through experiments. The proposed method has potential application in the multipoint, multigas monitor in the monitoring field.