Fully Distributed Fiber-Optic Hydrogen Sensing Using Acoustically Induced Long-Period Grating

A potential technique for fully distributed fiber-optic hydrogen sensing is demonstrated based on a traveling long-period grating (LPG) in a single-mode fiber coated with a platinum (Pt) catalyst layer. The traveling LPG is generated by an acoustic pulse propagating along the fiber. The Pt-coated fiber section is heated by the thermal energy released from Pt-assisted combustion of H₂ and O₂. The resulted temperature change gives rise to a measurable resonant wavelength shift in the transmission optical spectrum of the traveling LPG when it passes through the pretreated fiber segment. Hydrogen concentration from 1% to 3.8% was detected in the experiment. This traveling LPG-based fiber sensing technique may also serve other fully distributed chemical sensing applications by changing the properties of the fiber itself or by the assistance of a functional coating on the surface of the fiber.