U.S. Pat. No. 4,956,607 which issued on Sep. 11, 1990 to M. Abe et al. shows an arrangement including a polarizer, a magneto-optic element, an analyzer and a light sensitive element for measuring the polarization rotation of the light for measuring the current in a power line by directing a beam of light through the polarizer and magneto-optic element in the direction of the magnetic field.