Magnetic field sensor based on helical long-period fiber grating with a three-core optical fiber.

A high sensitivity optical fiber magnetic field sensor is proposed and implemented by using a helical long-period fiber grating (HLPFG) based on a three-core fiber (TCF) bonded to a U-shaped aluminum (Al) wire. An electrical current flowing through the Al wire in a perpendicular magnetic field can generate Ampere force, which changes the distance between the two arms of the U-shaped Al wire. Thus, when the intensity and direction of the magnetic field change, the bending curvature of TCF-HLPFG bonded to the U-shaped Al wire varies with the change of Ampere force, which is represented as the shift of resonant wavelength in the spectrum. The as-fabricated sensor can respond to the magnetic field direction and the intensity with a range from -15 mT to 15 mT, and the measured sensitivity is 456.5 pm/mT with Al wire electrical current 1A. The proposed sensor has the advantages of low cost, nondestructive measurement method and ease manufacture, and is expected to be applied to weak magnetic field measurements.