Optics Letters · 1987 · 155 citations · 1 references
EngineeringFlame DetectionGas SensorLaser ApplicationsOptical AbsorptionAbsorption SpectroscopyFiber OpticsOptical PropertiesMethane GasLaser-based SensorHe–ne LaserPhotonicsLaser SpectroscopyOptical FibersFiber Optic SensingGas Detection3392-μM LineFiber OpticOptical SensorsSensor FiberSpectroscopyGas LasersOptical Sensor
Evanescent waves comprising 5–40 % of the guided power propagate outside the fiber. The study investigates gas sensing by exploiting evanescent waves in optical fibers. A single, 1.8–7 µm diameter silica fiber serves as both transmission line and sensor, detecting methane through absorption of the 3.392‑µm He–Ne laser line. Using a 1.8‑µm diameter, 10‑mm long fiber, the sensor detects methane at concentrations below the 5 % explosive limit.
Gas sensing using evanescent waves of optical fibers is investigated. Methane gas is detected by means of its strong optical absorption of the 3.392-microm line of a He-Ne laser. A single fiber is used as both a sensor and an optical transmission line. The sensor has a small diameter, ranging from 1.8 to 7microm, made by heating and expanding a part of a step-index silica fiber. An evanescent wave of 5 to 40% of the total propagating power is generated outside the fiber. When a sensor fiber of 1.8-microm diameter and 10-mm length is used, the minimum detectable concentration of methane is less than the lowest explosive limit of 5%.
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