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The authors have developed and tested a prototype magnetostriction-based, passive optical current sensing device for high-voltage applications. The sensor contains a ferromagnetic yoke, a modulator of magnetostrictive Terfenol-D that responds to the magnetic field, and a fiber Bragg grating that converts this response into a wavelength-modulated optical signal and transmits it via an optical fiber to ground-level electronics. To linearize the output, the modulator material was subjected to both mechanical and magnetic biases. The prototype CT was found to have a useable linear range of 100-1000 A with a measured phase shift of around 30° for a steady-state 60-Hz excitation. Both the gain and the phase response have been found to be dependent on mechanical prestress and magnetic bias. The authors also report on materials characterization and modeling that support the actual design process.