OPTICAL MAGNETIC FIELD SENSOR

PURPOSE:To obtain a sensor easy to operate with a better temperature characterisitic using one poptical fiber for input and output of light each by arranging a means so that an output from a magnetic field sensor is converted into electricity from light and then, the output voltage is separated into the DC and AC components to determined the ratio therebetween. CONSTITUTION:Light from a light source 1 enters a magnetic field sensor 5 passing through an optical fiber 2a. The magnetic field sensor 5 comprises polarization plates 3a and 3b and a Faraday element 4 interposed therebetween and the polarization surfaces of the polarization plates 3a and 3b are arranged at 45 deg. to each other. Light passing through the magnetic sensor 5 is converted into electricity with a light receiving element 6 and fed to a DC current transformation separation circuit 7. Then, when it is sent to a division circuit 8 for computation, the final output voltage is in noway related to the P0. In addition, as the DC and AC components of an input light to the light receiving element 6 both pass through the same optical path, the optical coupling loss in the magnetic field sensor 5 and the transmission loss in an optical fiber 2b are both the same completely. Besides, as the coefficient of the photoelectric conversion is the same, the values of the AC component v/DC component V is free from errors due to effects of the temperature change and the bending of an optical fiber 2.