Optical Frequency Domain Reflectometer for Spatial-Resolved Gas Sensing

Distributed fiber optic sensors are a rapidly developing research area. Whereas distributed temperature, strain and pressure sensors are common, distributed gas sensing based on optical fibers is still to be investigated. In this paper, a method using the optical frequency domain reflectometry (OFDR) technique and the Tm-doped self-sweeping fiber laser is proposed to provide spatial-resolved measurement of gas properties. The method depends upon using low-reflective mirrors along the optical path of the test line, which is filled with gas and positioned in the in the sensitive arm of the reflectometer. The analysis of the mirrors' reflection spectra provides data on the integral gas absorption. As a result of the experiment, the room's air absorption lines were restored, and they agreed well with existing studies. The maximum measurement distance was 12.5 m, and the spatial resolution was better than 1 cm. Both parameters were determined by laser configuration and could be improved. The described reflectometry method provides the ability to conduct multi-point gas analysis using passive optical fibers. We believe, that the use of hollow core fibers as distributed mirrors enables fully distributed high spatial resolution gas sensing.