Optical fiber methane sensor using refractometry

One potential application of fiber refractometers is gas detection. In this work, a multimode fiber (MMF) refractomer has been designed as a CH4 sensor by de-cladding 2 cm of the MMF and then functionalizing this region using a polymeric thin film of cryptophane-A supramolecules incorporated within a styrene acrylonitrile (SAN) host. CH4 concentration is subsequently measured by observing the variation of the transmitted optical power along the MMF compared to an unfunctionalized MMF used as reference. This variation is induced by the modification of the refractive index of the functionalized film due to CH4 concentration variation. The proposed sensor is potentially of lower cost than alternative sensors and can detect CH4 concentration with a resolution of 186 ppm at a relatively fast response of ~25s.