FBG hydrogen sensor based on spiral microstructure ablated by femtosecond laser

This paper proposed and demonstrated fiber Bragg grating (FBG) hydrogen sensor by integrating optical fiber laser micro-machining and thin film technology. The spiral microstructure ablated sensor probe was sputtered with hydrogen sensitive material, palladium-silver (Pd-Ag) composite film, in which the atomic ratio of the two metals is controlled at Pd:Ag = 4:1. Experimental work was conducted at ambient temperature and relative humidity of 25 °C and 32% respectively. Double spiral microstructure at pitch 90 μm and sputtered with 520 nm Pd/Ag film recorded hydrogen sensitivity of 51.5 pm/%H responding to hydrogen gas in air. This translated to approximately 7.5 times higher than the unprocessed standard FBG. The sensor's hydrogen response is reversible, has improved response time and could have potential for hydrogen gas monitoring.