Temperature-compensated optical fiber magnetic field sensor with cascaded femtosecond laser micromachining hollow core fiber and fiber loop

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.