Reflective optical fiber sensor based on light polarization modulation for hydrogen sensing

A simple reflective hydrogen-sensing system based on polarization modulation is proposed and experimentally demonstrated. The sensing unit consists of a polarizer, a polarization control, and a sensing head composed of a short segment of polarization-maintaining fiber (PMF) with a Pt-loaded ${{\rm WO}_3}$WO3 coating. When the sensing head is exposed to a hydrogen environment, heat is generated due to the interaction between hydrogen and ${{\rm WO}_3}$WO3 with the help of catalyst Pt in air; then, the local temperature of the PMF increases, which results in the reflection spectrum shift because the light polarization state changes due to the variation of the birefringence coefficient of the PMF. Experimental results show that the system is capable of producing a rapid response to hydrogen with a high sensitivity of $\sim{18.04}\;{\rm nm/}\% $∼18.04nm/% (vol%) within the concentration range of 0–4% (vol%). Additionally, the sensing head has a probe structure with reflective measurement and immunity to humidity. Such features make the sensing system promising in the fields of hydrogen transportation or storage.