**3.3. A twin-grating fiber Fabry-Perot interferometer-based power-frequency electric field sensor**

We will demonstrate an all-fiber power-frequency electric field sensor, based on a twin-grating fiber Fabry-Perot interferometer. This sensor technology intentionally is applied in the power industry for measuring of the power-frequency electric field strength near the high-voltage equipment.

Compared with other types of optical electric field sensing technologies based on several physical effects, such as Pockels, Kerr, piezoelectric, or electrostrictive effect [27–30], our electric filed sensing technology is based on the electrical polarization properties [28, 31] of the dielectric coating material with a variety of attractive features, such as small size, low cost, electrodeless, single-lead, high sensitivity, flexibility in a variety of environments and capability of remote sensing.
