Optical remote sensing system for hydrocarbon gases using infrared fibers

An infrared optical fiber made of As2S3 glass has been applied for remote sensing of hydrocarbon gases. The fiber has enabled a transmission of the radiation at 3.39‐μm wavelength, where hydrocarbon molecules have strong absorption bands. Using a 3.39‐μm He‐Ne laser as a light source, an effective remote sensing system has been established. A detection limit of the gas concentration is ∼300 ppm for CH4 gas, which is ∼0.6% of the lower explosion limit. The system is also expected as a pressure monitor since it is highly sensitive to the gas pressure.