A fiber-optic current sensor (FOCS) is a device designed to measure direct current. The FOCS can measure uni- or bi-directional DC currents up to 600 kA. This article explores the measurement of electric current using optical fibers, primarily through the Faraday effect, also known as the magneto-optic effect. Unlike traditional current sensing technologies, FOCS offer a range of advantages, including high accuracy, immunity to electromagnetic interference, and the ability to. Fiber optic current sensors are revolutionizing the way electrical currents are measured, providing high sensitivity, immunity to electromagnetic interference (EMI), and the ability to function in harsh environments. Amongst the parameters which may be measured conven iently with optical fiber techniques are current, voltage, temperature and strain/ pressure.