FIBER-OPTIC CURRENT AND MAGNETIC FIELD SENSOR

PROBLEM TO BE SOLVED: To improve the measurement accuracy of a fiber-optic current and magnetic field sensor against temperature changes by deciding the length of the optical path of a magneto- optical element from a specific formula by using the Verdet constant of the element and the temperature coefficient of the constant. SOLUTION: The light emitted from a light source 11 and having a wavelength of 850nm is polarized into linearly polarized light by means of a polarizer 12 after being propagated through a first fiber 20a and the polarized light is made incident to a magneto-optical element 13a by which the plane of polarization is rotated by a Farady effect. The linearly polarized light coming out from the element 13a is made incident to a Bi12 GeO20 element 13b by which the plane of polarization is further rotated by a Farady effect and further made incident to an analyzer 14 which gives intensity modification to the light. The linearly polarized light coming out from the analyzer 14 is made incident to an optical receiver 15 after being propagated through a second optical fiber 20b and the receiver 15 detects the light as the electric signal corresponding to the intensity of the light. As a result, the intensity of a magnetic field is measured. The length L of the optical path of the element 13a is decided from formula I when the optical axes of the polarizer 12 and analyzer 14 are parallel to each other or from formula II when the optical axes intersect each other at right angles. The VO and α in the formulae respectively represent the Verdet constant of the element 13a at the center operating temperature and the temperature efficiency of the constant.