Stabilization of temperature dependence of verdet constant of bi‐doped garnet and development of high sensitive optical fiber magnetic field sensor

Abstract

SUMMARYBi-doped garnet is a rare metal iron garnet made up of a ferrimagnetic substance, of which some portion of the 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. Close attention has been paid to the magnetization of each rare earth element's different temperature characteristics; garnet compositions have been investigated by calculations and experiments in order to find a garnet that shows flat temperature characteristics between -10 and 80°C. The liquid phase epitaxy (LPE) method was established to obtain a single crystal of the garnet [Bi,,(Y, La),,Ho,,Fe,,Ga,,O,,].A magnetic field sensor of fiber optic based on the Faraday effect of this single crystal is highly accurate in detecting conductor currents of power cables. The developed sensor is small and lightweight compared to conventional current transformers; additionally, optical fiber transmission of detected current signals is free from both electric and magnetic noise.