Closed-Loop Resonant Fiber Optic Current Sensor Based on Broadband Source and Linear Cavity

Long-term current monitoring with low noise is essential for smart energy. This paper introduces a resonant fiber optic current sensor utilizing a broadband source and linear cavity. The theoretical analysis and experimental validation are carried out, and the performance of the open- and closed-loop systems is compared. The linear cavity employs a single-mode fiber for sensing, and two Faraday rotator mirrors to compensate for the linear birefringence. The Faraday effect, induced by a current, results in a resonance frequency difference between two co-propagating out-cavity lightwaves with orthogonal circular polarization. This sensor exhibits a sensitivity of 1.669 Hz/A, indicating that a current of 1 A causes a resonance frequency difference of 1.669 Hz, and achieves a mean relative error of less than 0.3% in the open-loop operation. The mean relative error in the closed-loop system is optimized to less than 0.04%. Additionally, the long-term bias instability of the closed-loop system is 0.5513 mA over 12 hours, indicating a 4.7-fold improvement compared to the bias instability of 2.602 mA in the open-loop system. This work offers valuable insights into current sensing technologies.