Optically-heated Pt/WO₃-coated tilted fiber Bragg grating for humidity-tolerant hydrogen sensing

Hydrogen leaks are hard to detect by smell or sight alone, and its wide flammability range in air makes fast detection critical for safety. Hydrogen sensors based on fiber Bragg gratings (FBGs) coated with platinum-loaded tungsten trioxide (Pt/WO₃) detect hydrogen through the heat released by a catalytic reaction on the coating. A known limitation of this approach is that humidity raises the detection threshold, because water molecules compete with hydrogen for the active sites on the coating. This work shows that optical heating can reduce this humidity-related loss of performance. A Pt/WO₃-coated tilted FBG (TFBG) was tested with hydrogen concentrations from 0 to 1 vol% at different humidity conditions, both without and with 1 W of optical heating. Without optical heating, the detection threshold increased from 0.2 vol% at 10% RH to 0.8 vol% at 70% RH, and the linearity of the sensor response also worsened at higher humidity. With optical heating, the detection threshold stayed at 0.2 vol% for all the humidity values tested, and the linear fit remained strong (R² > 0.98) in every case. These results show that optically-assisted catalytic heating can make Pt/WO₃-coated TFBG sensors more reliable across a range of humidity conditions.