Fully Distributed CO2 Sensor Based on Optical Frequency Domain Reflectometry With Polyimide-Coated Fiber

In this study, a fully distributed carbon dioxide (CO₂) sensor based on optical frequency domain reflectometry (OFDR) system is proposed and experimentally demonstrated. Commercially available polyimide (PI)-coated single mode fibers (fibercore, SM1500(9/125)P) are used as sensing fibers without the additional step of a complex and expensive coating process. Changes of CO₂ concentration can induce a volume expansion effect in the PI coating layer to transfer strain to the fiber core, and the distributed measurement of CO₂ concentration can be indirectly realized by demodulating the spectrum shift induced by the strain at each position of the sensing fiber through OFDR. In experiments, the individual sensitivity of PI-coated fiber to CO₂ was verified with methane (CH₄) and nitrogen (N₂) as references. Distributed CO₂ concentration measurement was successfully verified with 5 cm spatial resolution over 12 m sensing fiber. Moreover, the system was proven to have good stability and reliability. This simple, novel, robust, and inexpensive distributed CO₂ measurement technique has potential applications in downhole fire monitoring, air quality monitoring, and greenhouse gas monitoring.