Magneto-optic current sensing with birefringent fibers

Abstract
To measure currents on high‐voltage lines, the Faraday rotation is used in a single‐mode optical fiber encircling the conductor. Disturbing linear birefringence is suppressed by twisting the fiber. With ∼10 m of fiber, coiled with a 3‐cm radius, we obtain 0.25 mrad/A polarization rotation, permitting measurement of currents of 0.2–2000 A.