Polarization-Independent Optical Fiber Current Transformer

This article presents a polarization-independent, phase-demodulation-based all-fiber current sensor. The proposed scheme maintains the accuracy of phase detection measurement while eliminating complex components such as polarizers and $\lambda /4$ waveplates. The system is constructed with single-mode fibers, significantly simplifying the overall design and effectively addressing the measurement errors caused by environmental changes that affect the $\lambda /4$ waveplates. Moreover, signal demodulation is achieved through a passive multiplexing network, which allows the simultaneous measurement of ac and dc currents. The experimental results demonstrate that the system’s output remains essentially unchanged under varying input polarizations, thereby validating its polarization-independent nature. Compared with traditional phase-based current detection schemes, the proposed system demonstrates enhanced immunity to environmental interference.