Hydrogen sensor based on high-birefringence fiber loop mirror with sol-gel Pd/WO3 coating

A hydrogen sensor based on high-birefringence fiber loop mirror (HBFLM) with sol-gel Pd/WO3 coating was demonstrated. The sensing structure was formed by inserting a section of polarization maintaining fiber (PMF) with Pd/WO3 coating in fiber loop mirror. The Pd/WO3 coating was prepared by sol-gel method and coated on PMF by dip-coating method, which is simple fabrication, low cost, and has good binding force with fiber. When the hydrogen concentration around Pd/WO3 coating was changed, it would induce the strain change of polarization maintaining fiber, and then shift the interference spectrum of HBFLM. Therefore, the hydrogen concentration can be measured by monitoring the wavelength shift of the interference spectrum. Experimental results showed that the resonance wavelength had a blue shift with the increase of hydrogen concentration and the total shift of the resonance wavelength was ∼2.18 nm within the concentration range of 0-1%. The sensor had simple structure, low cost, high sensitivity, good repeatability, and well stability.