Fiber-Optic Current Sensing Based on Reflective Polarization-Bias-Added Structure

Polarimetric fiber-optic current-sensing technology is typically employed for measuring high current, as the low Verdet constant of optical fiber makes Faraday rotation not noticeable in low-current measurements and subsequently leads to low current sensitivity. To enhance current sensitivity, a polarimetric method based on a reflective polarization-bias-added (RPBA) structure is presented in this article. First, it is proved by the Jones matrix that current sensitivity would be compromised due to the constant term in the traditional sensing output. Then, the single-axis measurement method is employed to eliminate the constant term using the single-axis working (SAW) circulator. In consideration of the accuracy of subsequent signal decoding, the bias is generated by the RPBA structure to process optical signals between the circulator and the mirror. Next, a decoding algorithm based on parameter optimization is presented to restore the measured current from the photodetector output. Finally, the experimental results show that the current sensitivity of the presented method can be larger than 0.005 V/A under the premise of small measurement error in the vibration-and-temperature test. Compared with the existing polarimetric methods whose current sensitivity tends to be 0.002 V/A, the presented method has better current sensitivity without incurring additional sensor-head turns or optical devices.