Highly sensitive fiber optic current sensor using circular thin copper rod to directly fabricate Fabry–Perot cavity

In order to meet the demand for current measurement in industrial production, this study presents a novel high-sensitivity fiber-optic current sensor and conducts experimental verification. The current sensing measurement is achieved using a Fabry–Perot interferometer (FPI) manufactured directly on a thin copper rod. Two single-mode fibers, observed and aligned by a charge coupled device imaging system, are glued onto the surface of the thin copper rod to form a FPI. When the copper rod is powered on, abundant heat is generated and then the copper rod expands, directly changing the length of the FPI cavity. This variation changes the optical path length of the FPI, enabling the indirect measurement of current. The experiment shows that the current square sensitivity of a single FPI can reach 568 ± 10 pm/A2. To further enhance the sensitivity, we used the FPI as a sensing interferometer to fabricate the Vernier effect sensor S1. The experiments found that the current square sensitivity of S1 is 4.7 ± 0.1 nm/A2, which is 8.5 times higher than the sensitivity of a single sensing FPI. Owing to the direct fabrication of the F–P cavity on a copper rod with excellent electrical and thermal conductivity, the sensor is particularly easy to fabricate, robust, and highly sensitive, offering an extremely simple solution for measuring current.