Sensitivity enhanced temperature and strain sensor based on parallel hybrid interferometers and the Vernier effect

A fiber sensor with significantly enhanced temperature and strain sensitivities is proposed. This sensor, which comprises a fiber Sagnac interferometer (FSI) in parallel with an improved fiber modal interferometer (FMI), has been validated in experiments. The FSI consists of a section of polarization-maintaining fiber (PMF) and a 2×2 3 dB optical coupler (OC), serving as the sensing interferometer. The improved FMI with a higher extinction ratio (ER) consists of a core-offset structure, no core fiber (NCF), single-mode fiber (SMF), and few mode fiber (FMF), serving as the reference interferometer. Different Vernier effect envelopes have distinct responses to temperature and strain, thereby making the sensor a good choice for concurrent monitoring of temperature and strain variations. The experimental outcomes demonstrate an enhancement in both temperature and strain sensitivity, advancing from –1.33 nm/°C of a conventional single FSI to 22.26 nm/°C and from 2.83 to –50.99 pm/µɛ, respectively. The proposed sensor, with its advantages of exceptional sensitivity, uncomplicated design, and economical cost, provides what we believe is a novel and effective solution for the practical measurement of temperature and strain.