Dichloromethane detection based on near-infrared absorptive sensing

Dichloromethane (DCM), a clear and lipophilic liquid that has been primarily used in industrial applications, has caused organic poisoning upon inhalation during its wide use as a chlorinated organic solvent and in other industrial processes. In this paper, a biophotonic near-infrared sensor using a tunable fiber ring laser based on an absorption spectroscopic method has been demonstrated in order to perform DCM detection. A continuous wave near-infrared source operating in the C-band wavelength range has been developed and optically characterized. The principle of the Sagnac loop mirror, which operates as a saturable absorber to effectively narrow down the laser linewidth, has been reviewed. By forming a fiber-based interferometer loop with an unpumped erbium-doped fiber inserted, we could reduce the external noise and stabilize the laser frequency to achieve a narrow linewidth. The result shows an accuracy of 16 pm or 0.06 cm ^-1, which is much more precise than the previous results of 1 nm or 4 cm ^-1 using a method based on a broadband infrared light source.