Magnetic Field Sensor Exploiting Light Polarization Modulation of Microfiber With Magnetic Fluid

We demonstrate an optical fiber magnetic field sensor that can measure both magnetic field intensity and directions. It is designed by immersing a microfiber into magnetic fluid (MF) and based on the light polarization detection. When there is external magnetic field, the magnetic nanoparticles of MF generate a noncircular symmetric distribution around the microfiber, and MF exerts magneto-optical dichroism. Light will be polarized after passing through the microfiber. The time response of the fiber magnetic field sensor is studied. It is found that the intensity of the magnetic field can be measured directly only when it satisfies the detectable threshold condition. Furthermore, the magnetic field sensor possesses good orientation response to the magnetic field directions. The signal analysis system consists of a polarization beam splitter and two photodetectors. The sensor designed has the advantages of both simple structure and low cost, without needing any precise spectral analyzer.