Enhanced sensitivity of fiber Bragg grating hydrogen sensor using flexible substrate

A novel method was proposed to enhance sensitivity of fiber Bragg grating (FBG) hydrogen sensor in this paper. As sensing element, Pd/Ni composite film was deposited on side-face of etched fiber Bragg grating and surface of polypropylene substrate. The atomic ratio of Pd and Ni in hydrogen sensitive film was controlled at 91:9. The sensitivity of FBG hydrogen sensor is significantly improved due to the much lower Young's modulus of polypropylene substrate. FBG hydrogen sensor has 146 pm wavelength shift towards 4% hydrogen, and the sensor shows linear response and good repeatability during hydrogen concentration test. FBG hydrogen sensor has good stability even after six months, which demonstrates its great potential in hydrogen leakage monitoring.