Optical gas sensing performance of optical fibers coated with sputtered Pd/WO<sub>3</sub> films was investigated for low concentration H<sub>2</sub>
sensing. This optical fiber H<sub>2</sub> sensor was prepared by RF sputtering of WO<sub>3</sub> on the tip of the multimode fiber at 260°C and
subsequently depositing a Pd catalytic layer. Highly uniform nanotextured film, with individual crystallites having diameters in the
range of 35-50 nm was observed. The sensing mechanism was based on the reflectance change of Pd/WO<sub>3</sub> layers towards H<sub>2</sub> reliant on
the gasochromic effect. Under the conditions of different sensing layer thicknesses and different operating temperatures, full Vis-NIR
spectra investigations were carried out during the sensor testing. It was found that the optical fiber H2 sensor coated with Pd/WO<sub>3</sub> film
show a remarkable optical reflectance response towards H<sub>2</sub> concentrations as low as 0.06%. The optimum sensing layer thickness was
200 nm and the optimum operating temperature was found to be 100°C.