U-bend fiber optical sensor for magnetic field sensing

In this paper, we propose a method for fabricating a U-bend optical fiber magnetic field sensor. The working principle of the sensor is based on the use of bending to induce a whispering gallery mode. In experimental testing, a U-shaped optic fiber probe was fabricated using a lamping process and then coated on its surface with ferroferric oxide (Fe3O4), which served as the magnetic field sensing layer. The intensity of an applied magnetic field was then controlled by the vertical distance between an NbFeB magnet and the sensor. The magnetic field was monitored using a Gauss meter. As the external magnetic field was applied to the sensor, it produced magnetic attraction with the Fe3O4. The magnetic field intensity was increased from 0 to 900 Gauss, which in turn caused the magnetic attraction to become larger. This in turn caused the optic fiber sensor to deform, inducing changes in the bending radius. Therefore, the wavelength shifted toward a short wavelength and the transmission loss was gradually increased. The results show that the sensitivity of the sensor in the magnetic field experiment was -0.00130nm/Gauss and the linearity (R-2) was 0.888, while the corresponding average loss sensitivity was 0.00028dB/Gauss and the corresponding linearity (R-2) was 0.942.