Hydrogen sensing performance comparison of Pd layer and Pd/WO3 composite thin film coated on side-polished single- and multimode fibers

Optical fiber hydrogen sensor based on side-polished fiber deposited with Pd/WO3 composite film is proposed and developed. Pd/WO3 composite films are magnetron sputtered on side-polished single mode fiber (SMF) and multimode fiber (MMF) as hydrogen sensitive elements. Hydrogen sensing performance and mechanical properties are investigated and compared with sensors coated with pure Pd film. Experimental results show that transmitted power increase when hydrogen concentration increases for both SMF and MMF samples, and much greater change of transmitted power can be found for MMF sensor than SMF one. Response linearity of SMF sensor to hydrogen concentration is much better than MMF sensor. Pd/WO3 thin film demonstrates better mechanical reliability than pure Pd layer due to coexistence of materials and the different sensing mechanism.