Magnetic Field Sensing Based on Multimode Fiber Specklegrams

We demonstrate a fiber magnetic field sensor based on multimode fiber specklegrams. The magnetic field is detected by measuring the change of speckle patterns with digital correlation technology. When the magnetic induction increases by 50 mT, the response of correlation coefficient is more than 0.35. The sensitivity of the sensor is 0.00705 mT
^{- 1}
for the magnetic field range of 50-100 mT, and the resolution is 0.284 mT. The temperature cross sensitivity is studied by establishing the sensing matrix. In addition, dynamic range expansion and magnetic field direction sensing are explored as the application extensions of this kind of sensor.