Multipoint Chemical Gas Sensing Using Frequency-Shifted Interferometry

We apply frequency-shifted interferometry to interrogate multiple gas sensors along a single fiber. This method uses a tunable continuous-wave laser and a slow detector, and allows spectral overlap of sensors. It can be used to quantify the concentrations of single or different gas species at multiple locations. A three-sensor system was used to demonstrate this capability, achieving a minimum detectable acetylene concentration of 230 ppm with a 3-cm gas cell, or equivalently, 6.9 ppmmiddot m. The design considerations in the implementation and the system parameters are also discussed.