Ultrahigh sensitivity of hydrogen detection with a perforated Pd film on a miniature fiber tip

Hydrogen (H-2) is a renewable energy gas and an important industrial raw material playing important roles in many fields. However, H-2 is colorless, odorless and highly flammable within a wide concentration range. So H-2 detection is very important for leakage monitoring especially at low concentration. Here we propose an ultrahigh sensitivity H-2 sensor with a perforated palladium (Pd) film on the tip of an optical fiber. The suspended Pd nanohole film forms a Fabry-P e'rot (FP) interferometer with a silica capillary fused onto the fiber. Upon H2 adsorption, the Pd nanohole film bends inwards leading to spectral shift of the FP cavity. With the film perforated, its Young's modulus becomes effectively smaller giving rise to larger spectral shift and higher H-2 sensitivity. We experimentally studied the effect of the structural parameters of the holey film on the H-2 sensing performance and achieved a H-2 detection sensitivity of 7.1 pm/ppm and a detection limit of 1.7 ppm. The sensor also shows good repeatability and gas selectivity and is expected to find applications as optical H-2 sensors working at low concentrations.