Magnetic field sensors based on a ring interferometry

In this paper, magnetic field sensors based on ring interferometry are studied to enable the measurement of direct (DC) magnetic field as well as alternating (AC) magnetic field. By experiments using (CdMn)Te crystals as a Faraday element, the relative error within /spl plusmn/1% was obtained for AC magnetic field of up to 15 kA/m. Then, by introducing a phase modulation technique to this interferometry, DC magnetic field measurement with high sensitivity of 0.5/spl times/10/sup -2/%/A/m is realized.