Optical fiber current sensor based on Bi4Ge3O12 crystal with enhanced Faraday rotation by critical angle reflections

The feasibility of utilizing Bi4Gi3O12 (BGO) crystals as sensing element for optical fiber current sensors (OCSs) with enhanced sensitivity is demonstrated. Based on the theoretical analyses of the magneto-optical properties of BGO crystal, the Verdet constants of the crystal at different wavelengths are measured by employing the double frequency method. By combining the measured absorption coefficients with the relations between the Verdet constants and wavelengths, the magneto-optical figure of merit of BGO crystal is obtained. After that an OCS based on a BGO crystal with a magnetic field concentrator and enhanced Faraday rotation by critical angle reflections is designed and experimentally demonstrated. Finally, the influences of the phase shift caused by reflection, which is the main resource of the deviation between the measured and the real values, are theoretically analyzed and numerically simulated. It is demonstrated that an OCS based on BGO crystals with enhanced Faraday rotation could be developed into a practical OCS with a good linearity and a large dynamic range.