Temperature- and Ambient Pressure-Independent Sensing of Hydrogen in Fluids Using Cascaded Interferometers Incorporated in Optical Fibers

Abstract

Practical gas sensors are indispensable for the healthy operation of cutting-edge hydrogen-based systems. An optical fiber-based hydrogen sensor incorporating a robust Fabry？Perot interferometric structure on a fiber tip with high sensitivity, selectivity, and reliability of operation and a micrometer-scale footprint is demonstrated. The hydrogen-sensitive volume expansion of palladium provides bi-metal operation with a silicon nitride mirror to tune the interferometer cavity and therefore the resonance modes by switching the mirror form factor from a flat to convex shape. It does not require any peripherals, including a power supply or data communication modules. In addition to fiber-inherent advantages, such as remote and multiplexed monitoring without electromagnetic field interference, the sensor guarantees temperature- and pressure-independent operation by adding a simple glass sub-cavity and microwindows in the mirror layer, respectively. Critically, the sensor highlights reliable operation in a liquid fluid (electrical transformer oil) to monitor hydrogen as its “damage marker” escaping from a mechanical shield or selective gas screen. The detection limit, sensitivity, and response time of the sensor under atmospheric conditions are 15 ppm, 29.6 nm/%, and 12.5 s, respectively. In addition, the unimpaired operation of the sensor in 60 °C transformer oil is verified experimentally.