A practical gas sensing system utilizing absorption spectrum scanningtechniques was developed. Using the narrow-band transmission of a fiber tunablefilter (TOF) and wavelength modulation technique, the so-called cross-sensingeffects of the traditional spectrum absorption based gas sensor were reducedeffectively and thus the target gas was detected sensitively and selectively. Inorder to reduce the effects of nonlinearity of TOF on the measurement results andimprove the system stability in operation, the reflection spectrum of a referenceFBG was monitored and employed to control the modulation region and center of TOFwavelength precisely. Moreover, a kind of weak signal detecting circuits wasdeveloped to detect the weak response signal of the system with high sensitivity.The properties of the proposed system were demonstrated experimentally bydetection of acetylene. Approximate linear relationships between the systemresponses and the input acetylene concentrations were demonstrated byexperiments. The minimum detectable acetylene of 5×10-6, with signal-noise ratioof 3, was also achieved by experiments.(FBGs); Tunable fiber filter助项目