Hydrogen and temperature measurement using a functionalized superstructure of Bragg gratings in a helical-core fiber

As decarbonization is urgent in global climate, hydrogen, of which the product is pure water after burning, becomes a potentially clean and sustainable energy source as a replacement for fossil fuels. However, the hydrogen storge is challenging due to the highly flammable and explosive properties, limiting its enormous applications in industries. Real-time and sensitive detection of hydrogen is thus imperative to avoid leakage accidents, while the sensors based on electric signals have the risk of spark or arc discharge which may induce explosion. Here, we propose and experimentally demonstrate an optical hydrogen sensor using a functionalized superstructure of Bragg gratings in a helical-core fiber with a thin palladium film. Due to the cross sensing of the two sets of gratings, simultaneous detection of hydrogen concentration and temperature can be realized. By modifying the device diameter using wet etching technique, the sensitivity of hydrogen concentration is enhanced by 2.7 times. The utilization of the superstructure of Bragg gratings sampled in the helical-core fiber provides a promising platform for reliable and safe sensing of hydrogen with the ability of simultaneous monitoring of temperature.