Fiber optics apparatus and method for accurate current sensing

Abstract

The fiber optics sensor includes a polarization maintaining optic fiber forming an optical loop, and a sensing medium coupled to the optic fiber and disposed generally midway in the optical loop. First and second quarter waveplates, coupled to the optic fiber and oriented at approximately 45° with one another in close proximity to the sensing medium, convert two counter-propagating linearly polarized light waves traveling in the optical loop into two counter-propagating circularly polarized light waves prior to passing through the sensing medium. The first and second quarter waveplates further convert the counter-propagating circularly polarized light waves into two linearly polarized light waves after exiting the sensing medium. The counter-propagating circularly polarized light waves passing through the sensing medium experience a differential phase shift caused by a magnetic field or current flowing in a conductor proximate to the sensing medium. A detector is coupled to the optic fiber and detects the differential phase shift and produces an output in response thereto.