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Nowadays, optical fiber sensors are extensively being explored for the detection of magnetic fields. Against this backdrop, a highly sensitive magnetic field sensor based on the combination of magnetostrictive material and Vernier effect is proposed and experimentally demonstrated. The proposed sensor consists of two Fabry-Perot interferometers (FPIs), each comprising two sections of hollow-core fiber as FP cavities and a single-mode fiber (SMF) as a separator. One of the FPIs, which is bonded to the magnetostrictive material, undergoes further modulation by a high-frequency CO2 laser to enhance its sensitivity. Both simulated and experimental results demonstrate that the proposed sensor exhibits significant spectral response to the extension effect of the material under magnetic field variation. Within the range of 0–11.34 mT, the highest sensitivity achieved is 1.10 nm/mT, while demonstrating excellent temperature stability and repeatability. With its low-cost, simple structure, easy fabrication process and high sensitivity, this proposed sensor exhibits great potential for magnetic field measurement.

High-precision axial strain sensors are extensively needed in various fields of strain measurement. In this article, a novel optical fiber strain sensor with high sensitivity is designed and experimentally testified. By introducing arched core into the single-mode fiber (SMF) with multimode–single-mode–multimode (MSM) structure, higher order cladding modes are excited and higher strain sensitivity is achieved. It is worth noting that the two resonant peaks (Dip 1: 1254.6 nm and Dip 2: 1343.2 nm) drift in opposite directions as the strain increases. The experiments prove that in the range of 0– $240 ~\mu \varepsilon $ , the strain sensitivity of Dips 1 and 2 is 63 and −51 pm/ $\mu \varepsilon $ , respectively. Since the two resonant peaks drift in opposite directions, the strain sensitivity of the sensor can reach 114 pm/ $\mu \varepsilon $ after stacking their corresponding sensitivities. The sensor has the ability to monitor temperature simultaneously, and the temperature sensitivity is 14 and 44 pm/°C. The temperature and strain resolution of the sensor are 0.7 °C and $0.19~\mu \varepsilon $ , respectively. The high sensitivity and resolution of the sensor have application potential in the fields of high-precision measurement.

We demonstrated a periodical helix-style long period fiber grating (HS-LPFG) based torsion sensor with both high sensitivity and the ability to discriminate torsion direction. The proposed structure has asymmetric refractive index modulation in radial and azimuthal directions, which leads to the HS-LPFG being highly sensitive to torsional sensing. Experimental results show that torsion sensitivity is obtained up to 1.65 nm/(rad/m) in the measuring range of -17.952 rad/m to 17.952 rad/m, which is about fifty times higher than that of the conventional LPFG induced by CO2 laser. Moreover, the structure has low crosstalk of 0.037 rad/m/°C and a compact length of 5 mm.