A compact all-fiber magnetic field sensor based on the magnetic gel coated hollow core fiber (HCF) has been proposed and experimentally demonstrated. A double-layered Fabry-Perot resonator is formed by coating a magnetic gel layer on the surface of the HCF. Anti-resonant reflecting guidance of light can be achieved in the HCF, and leaky mode is induced at resonant wavelength of the double-layered Fabry-Perot resonator, which results in lossy dips in the transmission spectrum of the HCF. Due to the tunable magneto-elastic effect, the shape of the magnetic gel is deformed with the external magnetic field, which results in a change of the resonate condition for the double-layered Fabry-Perot resonator. The magnetic field can be measured by interrogating the wavelength of the lossy dip. The experimental results show that a magnetic field sensitivity of 245 pm/Oe is achieved.
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