"A fiber-optic current sensor with frequency-codified output for high voltage systems",
P. Pérez-Millán, Ll. Martínez-León, A. Díez, J. L. Cruz, and M. V. Andrés
IEEE Photonics Technology Letters14, 1339-1341 (2002)

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The authors present a frequency-output fiber-optic current sensor for high-power systems. The sensor exploits the magnetostriction of the ferromagnetic core of a standard current transformer, which is interrogated by a length of single-mode fiber coiled onto it and a Mach–Zehnder interferometer. The deformation of the core due to the magnetic field generated by the current produces a frequency-modulated output signal. The current is obtained from the frequency features of the optical signal, and so the sensor avoids certain shortcomings of other fiber optic current sensors such as light power fluctuations, phase drift, and polarization sensitivity.