Design of spun high-birefringent fiber for fiber optic current sensor

The residual linear birefringent of sensing fiber, temperature and vibration sensitivity severely influence the accuracy of Sagnac fiber optic current sensor (S-FOCS). A sensing fiber can be used in FOCS with spun high birefringent fiber (S Hi-Bi fiber) was designed. This S Hi-Bi fiber includes three sections: two terminal sections with variable spin-rate along fiber were utilized to substitute the fiber quarter-wave plates, respectively converting the light polarization state from the linear one to the circle one, and vice versa; and the middle section with a uniform spin-rate was utilized as the current sensing fiber which maintains the circular polarization state and compress the residual linear birefringent during the light propagation. In addition, the sensing fiber was wound into a special geometric structure so that the Sagnac phase shift was inherently eliminated and the sensing result did not depend on the position of the current conductor. In theory, used the coupled-mode theory the evolution of the light polarization state was simulated when linear polarization states light incident into the sensing fiber. A novel Sagnac fiber optic current sensor with vibration insensitivity based on this spun high birefringent fibers was proposed.