Journal
OPTICS EXPRESS
Volume 25, Issue 25, Pages 31568-+Publisher
OPTICAL SOC AMER
DOI: 10.1364/OE.25.031568
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Funding
- Hong Kong SAR government GRF grant [PolyU 152064/14E]
- National Natural Science Foundation of China (NSFC) [61535004, 61290313]
- Hong Kong Polytechnic University [4BCBE, 1-ZVG4, 4-BCD1]
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We report the first distributed optical fibre trace-gas detection system based on photothermal interferometry (PTI) in a hollow-core photonic bandgap fibre (HC-PBF). Absorption of a modulated pump propagating in the gas-filled HC-PBF generates distributed phase modulation along the fibre, which is detected by a dual-pulse heterodyne phase-sensitive optical time-domain reflectometry (OTDR) system. Quasi-distributed sensing experiment with two 28-meter-long HC-PBF sensing sections connected by single-mode transmission fibres demonstrated a limit of detection (LOD) of similar to 10 ppb acetylene with a pump power level of 55 mW and an effective noise bandwidth (ENBW) of 0.01 Hz, corresponding to a normalized detection limit of 5.5 ppb.W/Hz-root 5.5ppb.W/Hz. Distributed sensing experiment over a 200-meter-long sensing cable made of serially connected HC-PBFs demonstrated a LOD of similar to 5 ppm with 62.5 mW peak pump power and 11.8 Hz ENBW, or a normalized detection limit of 312 ppb.W/hz-root 312ppb.W/Hz. The spatial resolution of the current distributed detection system is limited to similar to 30 m, but it is possible to reduce down to 1 meter or smaller by optimizing the phase detection system. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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