Small Optical Magnetic Field Sensor Probe Using Rare-Earth Iron Garnet Crystals

Abstract

We developed highly accurate optical magnetic field sensor probes. New probe-type sensors 5 mm in width were designed, using a confocal optical system with two drum-shaped ball lenses. BiRIG films were prepared by the LPE method. We found a new garnet composition, Bi_0.98Gd_0.92La_0.03Y_1.07Fe_4.72Ga_0.28O₁₂, that showed high temperature stability for sensitivities less than 2.0% from - 20°C to +80°C. The linearity error of the sensor output was obtained within 1.0% for alternating magnetic fields from 5.0 Oe to 450 Oe. We also developed optical current transformers (OCTs), using this sensor and a permalloy magnetic core with a 6 mm air gap. The sensitivity of the new OCTs is about four times higher than that of our previous ones. The OCTs showed high performance in practical use.