Ultrasensitive fiber-optic magnetic field sensor

Abstract

We propose a fiber-optic magnetometer capable of both vector and scalar measurements based on a concept different from those using magnetostriction or Faraday rotation. 1 The magnetic field measurement is to be done using an all-fiber Mach-Zehnder interferometer. One arm of the Mach-Zehnder will have a metallic coating. Field detection and measurement can be done by sensing the force this conductor will experience in the field when current passes through it. The generated interference pattern is sensitive to change in the interferometer path lengths. One would exploit this fact in developing the FO magnetometer. In the vicinity of a magnetic field, displacement of the current carrying conductor will cause the fiber to bow. The resulting stretch will increase the light path length by δL. δL can be related to the force exerted by the field on the conductor C and hence, to the magnetic field. The direction in which the fiber bows will depend on the magnetic field and current flow directions. Thus, knowing the current flow direction and using a stopper, the magnetic field direction can be inferred. If I is the current passing through C of length I , the force exerted on it by the unknown magnetic field B is F = II × B = / IB ⊥ . The force displaces the conductor in a direction determined by the above relation.