Polarimetric Fiber-Optic Current Sensor With Integrated-Optic Polarization Splitter

We report on a simple, metering class polarimetric fiber-optic current sensor (FOCS) for electric power transmission systems. The sensor uses a fiber coil operated in reflection mode and an integrated-optic polarization splitter (IOPS) for interrogation. At alternating currents, the sensor performs comparably to high-end interferometric FOCS that work with an integrated-optic phase modulator in a closed-loop detection circuit. Besides the passive interrogation scheme, a particular advantage of the sensor is the use of standard single-mode fiber leads to the sensor head instead of polarization maintaining fiber. The IOPS introduces a 90° phase bias between the interfering light waves and generates two anti-phase sensor signals. By various measures, we obtain repeatable splitter performance between -40 °C and 85 °C. Like for interferometric FOCS, we employ the fiber retarder that generates the left and right circular or elliptical polarization states in the coil to compensate for the temperature dependence of the Faraday effect. We show that there are substantial differences, however, between interferometric and polarimetric FOCS in this regard. Finally, we demonstrate sensor accuracy well within ±0.1% during more than 200 hours of temperature cycling between -45 °C and 85 °C, which is unprecedented for polarimetric sensors.