Hydrogen sensor based on side-polished fiber Bragg gratings coated with thin palladium film

A hydrogen sensor based on side-polished fiber Bragg grating (FBG) coated with Pd thin film by magnetron sputtering is proposed. Hydrogen concentration is correlated with the shift of FBG central wavelength, since refractive index change in hydrogen sensitive Pd coating deposited on side-polished FBG affects the effective refractive index of FBG, and therefore Bragg wavelength is shifted. Experimental results demonstrate that FBG wavelength shifts to lower wavelength as the hydrogen concentration increases. The proposed optical fiber hydrogen sensor shows 15pm wavelength shift in 0.01% volume percentage of hydrogen concentration, and totally 246pm offset exists in pure hydrogen environment.