Mach-Zehnder Interferometric Hydrogen Sensor Based on a Single Mode Fiber Having Core Structure Modification at Two Sections

We propose and experimentally demonstrate a fiber-optic hydrogen sensing method, which is based on a Mach-Zehnder interferometer made with a single piece of conventional single mode fiber. By modifying the core structure of the fiber at two points along its length with electric arc discharges, the fiber interferometer could be simply fabricated. By coating the cladding surface of the fiber with 100 nm thick palladium, the hydrogen sensing could be achieved. When the sensor was exposed to hydrogen gas, the refractive index of palladium was changed so that the transmission spectrum of the interferometer was shifted toward the short wavelength direction (blue shift). After the hydrogen gas sensing, with flowing of nitrogen gas, the spectral shift was recovered back to its initial position.