FBG Hydrogen Sensor Based on Pd87–Ni13/Pd4–Ag1 Thin Film and Femtosecond Laser Ablation

A novel laser machined spiral microstructure fiber Bragg grating (FBG) hydrogen sensor and coated with composite sensing film is presented. The sensor probes are sputtered with Pd/Ni and Pd/Ag film, respectively. Experimental results exhibit that a pitch 60 μm FBG with double spiral microstructures, coated with 520 nm Pd/Ni and Pd/Ag film has hydrogen gas sensitivity in air of 13 pm/%H and 25 pm/%H, respectively. The laser-ablated spiral microstructured probes with composite films shown greater sensitivity compared with standard FBG probes with similar coating. The optimum testing temperature (50 °C) enhanced the sensitivity and repeatability of the probes.