Influence of Imperfect Faraday Rotation Mirror on All-Fiber Optic Current Sensor

Abstract

The effects of the Faraday rotation mirror on the all-fiber optic current sensor (AFOCS) are studied in this paper. The reflectivity degradation of FRM with the long-term operation, the misalignment of the optical axis between FRM and the sensing fiber, and the influence of temperature fluctuation on FRM are modeled and simulated in this paper. The effect of temperature is the biggest obstacle to the application of the Faraday rotation mirror, while other factors can be easy to overcome by the data processing method. The experiments are designed and realized for verification. The temperature fluctuation range is related to the measured electric current to satisfy the required accuracy for IEC 60044-8 class 0.2S.

Online measurement of birefringence of sensing fibers in the AFOCT system

“…Here, V represents the Verdet constant (rad/A 14 ), and N represents the number of turns in the sensing fiber.…”

“…In the ideal case, it is also the x ‐component of the Jones vector at the output of the polarizer. The system transmittance is defined as the ratio between the input signal power P i and the output signal power P o , and ideally given by 14 $$$B=\frac{{P}_{{\rm{o}}}}{{P}_{{\rm{i}}}}=\frac{1}{2}[1-\,\cos (\varphi +4F)].$$$…”

“…Thus, the final phase difference between the two circularly polarized lights is four times the Faraday phase shift 13 . After passing again through the 1/4 waveplate, they are restored to two orthogonal linearly polarized lights, which then undergo interference at the polarizer to obtain the output light 14 . This output light is coupled onto the photodetector, and converted to an electrical signal for the signal processing unit 15 …”

“…In Equation (), F represents the phase shift experienced by the circularly polarized lights in the sensing fiber. According to the Faraday magneto‐optic effect, F is proportional to the magnitude of the injected current I CT in the DC transmission line, 14,17 $$$F=NV{I}_{\text{CT}}.$$$…”

“…13 After passing again through the 1/4 waveplate, they are restored to two orthogonal linearly polarized lights, which then undergo interference at the polarizer to obtain the output light. 14 This output light is coupled onto the photodetector, and converted to an electrical signal for the signal processing unit. 15 The transfer equation of the system can be obtained by sequentially multiplying the Jones matrices of each optical device along the transmission path of the polarized light.…”