Faraday Rotation and Sensitivity of Bi-Substituted Iron Garnet Single Crystal for Optical Current/Magnetic Field Sensors

This paper is concerned with the preparation and magneto-optic characterization of the Bi-substituted rare earth ferrite garnet bulk single crystal of (BiYbY)³(FeGa)₅O₁₂. Here we focus our studies on improving the sensitivity constant and its temperature dependence of iron garnet for optical current/magnetic sensors through compositional modification. Due to the Bi³⁺ ions substitution, the specific Faraday rotation of Bi_0.75Yb_1.02Y_1.23Fe_4.72Ca_0.28O₁₂ crystal under saturation magnetic field was enhanced greatly to be about -161.7 ⁰/mm and -144.1 ⁰/mm at lambda=1310 nm and 1550 nm respectively. Magneto-optic figure of merit is 87.6 ⁰/dB at lambda=1550 nm and room temperature. The smaller Faraday rotation temperature coefficient (FTC) of 3.99times10^-5/K at lambda=1550 nm have been obtained owing to the compensation effect. The sensitivity have been enhanced by a factor of 24 with respect to pure YIG, given the same sensor length and demagnetization factor, by substituting Bi ions into Y sites and substituting diamagnetic Ca ions into Fe sites in YIG. These results suggest that the new garnet composition is a high-performance material suitable for current/magnetic-field sensors.