Stabilizing Temperature Dependencies of Verdet Constant of Bi-doped Garnet and Development of High Sensitive Optical Magnetic Field Sensor

Abstract

Bi-doped garnet is a rare metal iron garnet made up of a ferrimagnetic substance of which some part of rare metal element is replaced with Bismuth. It illustrates a strong Faraday effect and has been applied to optical isolators. In magnetic field sensing applications, however, a shortcoming is apparent: Faraday rotation of Bi-doped garnet reveals temperature dependencies when the garnet is not magnetically saturated. Authors have paid close attention to the magnetization of each rare earth element's different temperature characteristics, and have been investigating compositions of garnets by calculations and experiments to find a garnet showing flat temperature characteristics between -10 and 80 °C. The LPE(Liquid Phase Epitaxy) method was established to get a single crystal of the garnet {Bi_1.3(Y, La)_0.9Ho_0.8Fe_4.5Ga_0.5O₁₂}. A magnetic field sensor of fiber optic based on the Faraday effect of this single crystal can detect conductor currents of power cables with high accuracy. The developed sensor is small and lightweight compared to conventional current transformers, and has the quality that optical fiber transmission of detected current signals is free from electric and magnetic noises.