Multiplexed Fiber-optic Methane Sensing System Based On Optical Coherence Domain Reflectometry

Optical fiber sensing technology develops rapidly and has been effectively used in the field of mechanical,petroleum,mining and chemical industry recent years,because of its great advantages,such as anti-electromagnetic interference,electric insulation,high sensitivity and distributed sensing capability.As one branch of this technology,gas sensor based on optical fiber is a powerful tool for gas detection in these areas.This research mainly focuses on the optical spectrum absorption technology and optical coherence domain reflectometry,to build a sensing system for methane gas detection.The novelty is to apply optical reflectometry to gas detection,which is secure,remote-monitoring,fast-responding,highly-sensitive and multiplexed.Therefore,this system is especially suitable for applications in dangerous and risky fields such as petroleum and mining industry.This proposed scheme utilizes OCDR as the effective tool to measure the optical intensity changes due to the gas absorption,and locates the sensing points,realizing the remote and multiplexed monitoring for methane concentration.Three compact gas cells were spliced in series at the end of 5 km fiber,then methane of different concentrations were filled in the cells,and the optical intensity variations were detected.The experiments demonstrate that the minimal measurable gas concentration is about 0.1 vol.%,and the stability of detection satisfies the request of some applications.Finally,the validity of this proposed scheme is well verified.