Spiral Micro-Structured FBG Hydrogen Sensor based on Pd87-Ni13/Pd4-Ag1 Thin Film and Femtosecond Laser Ablation

Abstract

A novel laser machined spiral microstructure fiber Bragg grating (FBG) hydrogen sensor coated with composite sensing film is presented. The sensor probes are sputtered with Pd/Ni and Pd/Ag film respectively. The atomic ratio of the Pd/Ni and Pd/Ag composite films is controlled at 87:13 and 4:1 respectively. Experimental results demonstrate 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 showed greater sensitivity compared with standard FBG probes with similar coating. The optimum testing temperature (50 °C) enhanced the sensitivity and repeatability of the probes. Due to its high gas response and reversibility, the sensor probe is a potential candidate for hydrogen monitoring.