We present a novel fiber optic hydrogen sensor with fast response fabricated from a graphene-Au-Pd sandwich nano film and an ultrashort fiber Bragg grating. The response time is only 4.3 s at a 3.5 vol% hydrogen concentration. When the measured hydrogen concentration was increased from 0 to 4.5 vol%, the optical resonance dip in the sensor at near 1550 nm shifted by 290 pm. In addition, the sensor has an insertion loss of only −2.22 dB, spectral contrast of 10.8 dB, and spectral finesse of 5.
A new type of gas pressure sensor based on a phase-shifted fiber Bragg grating (PS-FBG) modulated by a hollow cavity is proposed and demonstrated. The device was fabricated by fusing a hollow-core fiber (HCF) between two single-mode fibers (SMFs) exhibiting FBGs inscribed using line-by-line femtosecond (fs) laser etching. A pair of micro-channels were drilled orthogonally to the HCF using an fs laser, to allow the argon gas to get in and out freely. This sensor has high spectral accuracy, for example, the Q factor is about 7302, which can be improved by reducing the number of grating pitches. Further, a high pressure sensitivity of 1.22 nm/Mpa was obtained, which corresponds to an improved sensor with a grating pitch of 300 and a cavity length of 88.3 um. In addition, the device exhibited a low temperature sensitivity of 8.92 pm/oC.
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