Hydrogen leak detection using an optical fibre sensor for aerospace applications

An optical fibre sensor has been developed for the detection of hydrogen leakages on the cryotechnic engine of the European rocket ARIANE V. The principle of this sensor is based on the variation of reflectivity of a palladium micromirror deposited at the output end face of a multimode optical fibre. An experimental set-up using a monitored high power laser diode provides an optical heating of the palladium layer, which allows to keep up the performances in the wide range of temperatures between −196°C and +23°C. Depending on both the concentration and the temperature, detection responses between 1% and 17% with response times shorter than 5 s have been demonstrated. Fast and accurate detection of hydrogen concentrations inferior to the explosive limit has been performed.