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A novel magnetic field measurement method based on the magneto-volume effect is proposed. The magnetic field sensing structure fabricated by the proposed measurement method is made by the magnetic fluid (MF) partially filled into the hollow core fiber (HCF). The presence of air provides conditions for the change of MF volume with the magnetic field in the proposed sensing structure. Therefore, the magneto-volume effect is introduced into the magnetic field sensing mechanism. From 109.6 to 125.8 Gs, the peak wavelength shift is −65480 pm and the sensitivity is −4219.15 pm/Gs, which is 28.16 times higher than that of the fabricated contrast sensing structure. The sensitivity of the magnetic field sensing structure is greatly improved by introducing the magneto-volume effect compared with the contrast sensing structure. The response time and recovery time of the sensing structure are equally 0.2 s. Therefore, the sensing structure has high sensitivity, good linearity, and short response time, which has potential application prospects in magnetic field sensing. [ABSTRACT FROM AUTHOR]

In this article, a reflective-type optical fiber probe, which can measure salinity and temperature simultaneously, is proposed. The proposed probe integrates Mach–Zehnder interferometer and Fabry–Perot interferometer in the same channel skillfully and effectively, which makes it possible to integrate more information into the sensor. The reflected spectrum is improved greatly by adopting special sputtering technology. The spectrums of Mach–Zehnder and Fabry–Perot are separated by applying the frequency division multiplex technique. The simulation and experimental results prove that the proposed probe has a highly sensitive response to temperature and salinity. The experiment result verifies that the salinity sensitivity is up to 2.7 nm/‰ and the temperature sensitivity is better than 0.4 nm/°C. The reflective probe makes the sensor easy to use and paves the way for practical application. [ABSTRACT FROM AUTHOR]

For the purpose of monitoring seawater temperature, a novel Mach–Zehnder (MZ) temperature-sensing structure with a wedge-shaped open cavity is presented and experimentally studied in this article. The open-cavity structure realizes the direct contact between the sensing optical path and the external environment, and ensures the high sensitivity of the structure. At the same time, it achieves not only low loss by direct fusion splicing instead of dislocation fusion splicing, but also low cost by hydrofluoric (HF) etching instead of femtosecond processing. In addition, the temperature sensitivity of the sensor structure proposed in this article can reach 1.5 nm/°C without temperature-sensitive material filled, and 6 nm/°C with silicone oil filled. Moreover, the resolution of the sensing structure is 0.24 °C based on the criterion of $3\sigma $. [ABSTRACT FROM AUTHOR]

• The magnetic field sensor composed of an ultra-short FPI filled with oil-based magnetic fluid cascaded with a bending coated single-mode-fiber MZI is proposed. • The FPI with ultra-short cavity (about 20 μm) composed of two sections of single mode fiber and a hollow core fiber drilled through by femtosecond laser. • The sensitivities of magnetic field and temperature are up to 240 pm/Gs and −2310 pm/℃ respectively. A fiber magnetic field sensor with temperature compensation is put forward and experimentally verified by utilizing Fabry-Perot interferometer (FPI) and multimode interferometer (MI). The FPI with ultra-short cavity (about 20 μm), which is proposed to improve the spectrum contrast after being filled with oil-based magnetic fluids (MF) and achieve the sensing of magnetic field, is drilled through by femtosecond laser. The FPI is composed of two sections of single mode fiber and a hollow core fiber, which is named as single mode fiber-hollow core fiber-single mode fiber (SHS). The MI composed of the coated-fiber-loop, which is only sensitive to temperature, is proposed to compensate the temperature on the sensing of magnetic field. The fiber loop is fabricated by only bending a section of coated single mode fiber (SMF). According to the experiment results, the spectrum visibility of magnetic field sensing part can be improved by 3.1 times by shortening the Fabry-Perot (FP) cavity length. The interference wavelength increases nonlinearly from 0 to 69.1 Gs while linearly from 69.1 to 137.7 Gs. In addition, its temperature sensitivity is −0.20 nm/℃ from 23.0 to 42.9 ℃. Moreover, the sensitivity of MI is −2.31 nm/℃ from 23.0 to 42.9 ℃. It could be used to compensate the temperature influence effectively. The structure boasts characteristics of simple manufacture, low cost and highly-sensitive, which can be applied in the fields of magnetic field sensing. [ABSTRACT FROM AUTHOR]