Abstract: A multi-mode optical fiber is used to detect electrical currents or magnetic fields from a remote source. The optical fiber, which serves as the sensor, is composited with metal capable of conducting electricity. Optical radiation is introduced into the fiber from a source which may be either coherent or incoherent. An electrical current is applied to the portion of the electrically conducting optical fiber and a magnetic field is applied to the current-carrying optical fiber. A known value of one permits a determination of the presence or absence of the other through electromotive forces on a metallic conductor in a magnetic field, which are used to induce differential phase shifts (coherent optical radiation input) or losses (incoherent optical radiation input) between the fiber modes. These phase shifts or losses are detected by a suitable detector. For a magnetic field of 1 kGauss, good linearity is obtained in the 5 to 2,000 mA current range. Magnetic fields of about 0.