MAGNETIC FIELD SENSOR

PURPOSE:To obtain a compact optical magnetic sensor excellent in handling property and having high accuracy, by forming a reciprocal light path by arranging a polarizer, a Faraday element, an optical rotation element and a reflective plate to the leading end of one optical fiber. CONSTITUTION:A Faraday element 3 is arranged to a polarized beam spliter 1, and an optical rotation element 2 and a dielectric reflective film 6 are formed to the outer surface thereof. The light of a LED light source 4 enters the splitter 1 through an optical fiber 7 and, when linearily polarized and passes the element 3, a polarization angle is rotated in proportion to the intensity of a magnetic field. When transmitted light reciprocally passes the optical rotation element 2, a polarization surface is rotated by 45 deg. and, when further passes the element 3 and the splitter 1 again, returned to the optical fiber 7. Therefore, light havin intensity returning to the optical fiber 7 enters a light receiving element 5 by a half mirror 9 and an electric signal amplified by an amplifier 10 is separated into a DC component and an AC component by an active filter 13. When operation of (AC component)/(DC component) is performed by a divider 14, output is obtained. A magnetic field can be measured on the bases of this output.