Magnetic Field Sensor Using Fiber Ring Cavity Laser Based on Magnetic Fluid

A magnetic field sensor using fiber ring cavity laser based on magnetic fluid (MF) is proposed and experimentally demonstrated. MF-coated single-mode—no-core—single-mode fiber structure is inserted in the fiber ring laser cavity, which acts as a bandpass filter and the magnetic field sensing component simultaneously. The excellent bandpass filtering with a high side-mode suppression ratio (14 dB) and small insert loss of around (−1.03 dB) is caused by the self-imaging effect. The experimental results show that the lasing wavelength shifts to blue side with the increase of external magnetic field. The magnetic field sensing sensitivity of 12.05 pm/Oe is achieved within the range of 15.9–222.32 Oe. This configuration exhibits obvious advantages in term of high visibility ( $\sim 40$ dB) and relative narrow 3-dB bandwidth ( $\sim 0.19$ nm) of the lasing output spectrum. Therefore, its $Q$ value is more than 10 times larger than those of other reported magnetic field sensing structures.