This paper reports proof-of-principle of an optical fiber Bragg grating (FBG) operating as an electric field sensor. The system is based on a semiconductor diode laser, emitting around 1577.5 nm that interrogates the fiber sensor around its maximum reflectivity point. The application of a strong electric field causes a small variation of the optical path length of the waveguide due to electrostriction and thus perturbs the grating peak reflectivity wavelength. Calibration and dynamic range tests are performed using a parallel-plate capacitor to create a variable electric field (1-100 kV/cm). A great potential is pointed out in view of possible field applications for voltage graduation in power generators.

We report the theoretical description and the experimental demonstration of an optical resonator formed by inserting a Fiber Bragg Grating (FBG) in a closed fiber loop. The spectral characteristics of such a resonator strongly depend on the reflectivity of the FBG. In the wavelength region where the FBG reflectivity R is negligible, the system behaves like a conventional ring resonator. On the other hand, when R is not vanishing, a split-mode structure can be observed, associated to the degeneracy removal of two counterpropagating resonant modes. The magnitude of the mode splitting can be used to sense small variations of the FBG physical parameters, such as length, temperature or group index. An example of strain sensing with this setup is reported, showing that the mode splitting is sensitive to a mechanical strain applied to the FBG, while it is almost insensitive to a strain applied to any other point of the resonator. This peculiar feature allows to perform cavity-enhanced, local strain measurements with a reduced sensitivity to environmental perturbations, which represents an important improvement in the framework of the fiber-optic sensors.