Fabry-Pérot Cavities with Suspended Palladium Membranes on Optical Fibers for Highly Sensitive Hydrogen Sensing

Hydrogen (H) sensors are critical to various applications such as the situation where H is used as the clean energy for industry or the indicator for human disease diagnosis. Palladium (Pd) is widely used as the hydrogen sensing material in different types of sensors. Optical fiber H sensors are particularly promising due to their compactness and spark-free operation. Here, we report a Fabry-Pérot (FP)-cavity-based H sensor that is formed with a freestanding Pd membrane and integrated on a conventional single-mode optical fiber end. The freestanding Pd membrane acts both as the active hydrogen sensing material and as one of the reflective mirrors of the cavity. When the Pd film absorbs H to form PdH, it will be stretched, resulting in a change of the cavity length and thus a shift of the interference spectrum. The H concentration can be derived from the amplitude of the wavelength shift. Experimental results showed that H sensors based on suspended Pd membranes can achieve a detection sensitivity of about 3.6 pm/ppm and a detection limit of about 3.3 ppm. This highly sensitive detection scheme is expected to find applications for sensing low-concentration H.