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

Abstract

A hydrogen (H2) 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 H2 sensing, palladium-tungstic oxide (Pd-WO3) powder is attached to the exterior surface of PDMS, which will cause an exothermic redox reaction with H2. 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 H2 concentration. The sensitivity of the proposed sensor is 2.2 nm/% in the range of 0 %–1% through the H2 measurement experiment. For H2 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 H2 measurement in narrow spaces and long distances.