High performance tunable fiber-optic current sensor based on Faraday rotation in toroidal sensing coil

Abstract

A high performance fiber-optic current sensor (FOCS) based on Faraday rotation in a toroidal sensing coil is proposed and demonstrated. The sensor performance has been improved by forming a toroidal sensing head to experience large magnetomotive force for a very small signal of electric current. In order to improve the sensor performance even further, the effective optical path length is increased by making a fiber coil, and the operating wavelength has been shifted to shorter wavelength (1064 nm) compared to the conventional telecom wavelengths (1550 nm) to benefit from a higher value of Verdet constant in conventional single mode fibers. Several toroid-core structures have been simulated using finite element analysis (COMSOL Multiphysics) to obtain enhanced sensitivity. The FOCS design includes an optimized 3D printed core structure along with toroidal windings and fiber loop inside it. Faraday rotator mirror (FRM) compensates for the birefringence along the sensing arm of the setup, while laser amplitude modulation is implemented using an electro-optic modulator (EOM) to enhance the signal to noise ratio at a particular modulated frequency. The developed FOCS set-up with four layers of copper wire windings in toroidal sensing head configuration is capable of detecting low currents of the order of 50 mA within a tested dynamic range of operation 0-10A. Detection of even lower order current (as low as several mA) could be achieved by tuning the design of sensing head.