Miniature All-Fiber Electric Current/Magnetic Field Sensor Based on Birefringence Induced in Magnetooptic Liquid

This work presents a compact fiber-integrated sensor designed for high-resolution measurement of electric currents and magnetic fields using a magnetooptic (MO) liquid microcell. The primary goal is to develop a miniature, customizable sensor capable of operating in challenging environments where electrical isolation, spatial constraints, and resistance to ambient electromagnetic noise are critical. The sensing element is based on barium hexaferrite nanoplatelets suspended in $n$ -butanol, whose birefringent properties vary in response to external magnetic fields. Microchannels inscribed into standard optical fibers enable precise filling of the microcell with minimal liquid volume, facilitating scalable sensor fabrication. The device measures both direct and alternating currents by detecting the surrounding magnetic field generated by a current-carrying wire. A ferrite toroid core and tunable bias magnetic field improve sensitivity and define three distinct sensor configurations. Theoretical models for each configuration were experimentally validated, demonstrating resolution down to $40~\mu $ A in the highest sensitivity setup and an ac measurement bandwidth of 2100 Hz. Temperature stability tests from $25~^{\circ }$ C to $50~^{\circ }$ C revealed a drift of about –0.004% of the total unambiguous measuring range per °C. These results highlight the sensor’s potential for integration into systems requiring miniature, interference-immune, and adaptable current sensing solutions.