Fast repeatable measurement of hydrogen concentration based on a reflective fiber hybrid interferometer probe with vernier effect

A hydrogen (H-2) sensor based on hybrid Fabry-Perot interference (FPI) and Michelson interference (MI) with Vernier effect is demonstrated. The optical probe is manufactured by fusing a multimode fiber (MMF) and a double -side hole fiber (DSHF) between a single -mode fiber (SMF) and a hollow core fiber (HCF) filled with polydimethylsiloxane (PDMS) at the end to form a cascaded FP and MI, which can generate a vernier envelope. by fusing a multimode fiber (MMF) and a double -side hole fiber (DSHF) between a single -mode fiber (SMF) and a hollow core fiber (HCF) filled with PDMS at the end. To accomplish H-2 sensing, palladium-tungstic oxide (PdWO3) powder is attached to the exterior surface of PDMS, which will cause an exothermic redox reaction with H-2. The released heat will lead to the volume expansion of PDMS with remarkable thermal response characteristics, and finally cause the movement of the vernier -like spectral envelope with the variation of H-2 concentration. The sensitivity of the proposed sensor is 2.2 nm/% in the range of 0 %-1% through the H-2 measurement experiment. For H-2 with a concentration of 1 %, it has the response time of 28 s and shows good reversibility in the cyclic experiment. In addition, the sensitivity of temperature and relative humidity (RH) is 0.21 nm/C and 0.0014 nm/%RH, respectively. The proposed sensor adopts a reflective probe, which is compact in structure and small in volume, and shows fast response and excellent repeatability. It has great advantages in H-2 measurement in narrow spaces and long distances.