Miniature Hydrogen Sensor Based on Fiber Inner Cavity and Pt-doped WO3 Coating

We demonstrate a miniaturized fiber device based on fiber inner air-cavity with periodical microstructures and platinum (Pt)-doped WO₃ coating for hydrogen concentration sensing. The fiber inner air-cavity is formed by use of femtosecond laser micromachining together with fusion splicing technique and the line shape microstructures are inscribed by femtosecond laser beam scanning. The Pt-doped WO₃ coating on the fiber surface near the cavity leads to the device sensitivity to hydrogen concentration, and the maximum wavelength shift obtained is ~2.64 nm when the hydrogen concentration is increased from 0% to 4% in volume percentage. The system is highly sensitive and miniature and exhibits a low temperature cross-sensitivity.