This paper presents the design, fabrication, and characterization of two compact fiber-optic current sensors (FOCS) based on fiber Bragg gratings (FBG) and the magnetostrictive alloy Terfenol-D. Finite-element-method (FEM) simulations assisted key optimizations in the geometry of similar FOCS proposed previously, allowing the implementation of magnetic flux density concentration techniques that resulted in sensors using very small amounts of Terfenol-D. Two prototypes of FOCS with the same geometry and size were manufactured for performance comparison purposes, one using a 2.21-g solid, bulk bar of Terfenol-D onto which a sensing FBG was bonded, and the other using magnetostrictive polymer composite (MPC) with oriented magnetic domains using only 0.42 g of Terfenol-D powder and epoxy resin with a sensing FBG embedded within the composite block. Both FOCS were characterized with currents of up to 800 Arms, and presented linearity errors smaller than 1% of full-scale range (FSR). The prototypes presented greater sensitivities taking into account that only less than 6% of Terfenol-D was employed in comparison to previous FBG-based FOCS. Transient-responses of the FOCS prototypes were also measured showing that the proposed sensors might be applied not only to current metering, but also to fault detection in high-voltage lines. Temperature compensation methods were also proposed and discussed for the developed FOCS.

In this letter, we performed finite element method (FEM) simulations, fabrication, and experimental characterization of two prototypes of fiber-optic current sensors (FOCS) based on fiber Bragg grating (FBG) and Terfenol-D for monitoring current in high-voltage transmission lines. The proposed prototypes were designed in geometrical configurations that allowed a massive reduction of more than 98% in the amount of Terfenol-D employed compared to FBG-based FOCS proposed previously. Using only 5.6 and 2.0 g of Terfenol-D in each prototype, we show that not only the cost of the sensor can be reduced but also greater sensitivity, linearity, and fast response-time to transient events were achieved.

In this paper, a compact fiber-optic current sensor (FOCS) based on in-fiber Fabry-Perot interferometer (FPI) and magnetostrictive transducer is presented. The in-fiber FPI sensor employed in the proposed FOCS was fabricated with a 273-μm section of capillary fiber spliced between two pieces of standard single-mode fiber (SMF). The in-fiber FPI sensor and a commercial fiber Bragg grating (FBG), which was used as a reference sensor for sensitivity comparison, were bonded to a small magnetostrictive actuator (Terfenol-D) and assembled in the proposed FOCS for electric current monitoring up to 800 A _rms using a commercial FBG interrogator. The in-fiber FPI sensor presented a sensitivity 84.4% higher than that of the FBG sensor. An alternative interrogation system based on an edge-filter technique with temperature compensation was also developed and employed for characterization of the proposed FOCS under the same range of electric current. Using the edge-filter interrogation system developed, the in-fiber FPI sensor presented a sensitivity 169.8% higher than that shown by the FBG. The results show that the proposed FOCS using an in-fiber FPI sensor presented high sensitivity to electric current sensing and, therefore, is a potential candidate for current monitoring in complement to conventional current transformers (CTs) as well as to conventional optical current transformers (OCTs).

In this work, we present a comparative study on the influence of the geometric shape of plastic optical fiber (POF) sensors in their response to refractive index (RI) of external media. Three different geometric shapes were simulated using the finite element-method (FEM), one being a simple U-shaped POF sensor (FU), and the other two based on the same U shape but with one and two additional small curves in the fiber, FO1 and FO2, respectively, allowing for an increased exposure of the evanescent field. The results of simulations showed that the shapes of sensors FO1 and FO2 would allow for higher sensitivities compared to that of the simple U-shaped sensor FU, and that FO2 would show an even higher sensitivity due to an increased evanescent field exposure enabled by the additional curves on its shape. A set of POF sensors were fabricated according to the designs simulated, and then tested in several sucrose solutions corresponding to RI from 1.3330 to 1.4242. The POF sensors manufactured showed sensitivities (optical power loss) of 36, 102, and 217%/RIU for FU, FO1, and FO2, respectively, from air to pure water (RI 1.000 to 1.333), and 330, 656, and 904%/RIU for FU, FO1, and FO2, respectively, from pure water to sucrose solution (RI 1.333 to 1.381). The correlation between the results from simulations and experiments shows that POF sensors based on RI sensing, such as chemical sensors, gas sensors, and biosensors, can be significantly improved with small modifications in their shape design.

This work presents a theoretical–experimental study of a refractive index (RI) sensor based on lossy mode resonances (LMRs) generated with a side-polished low-index polymer optical fiber. The theoretical part involves conducting simulations to determine the optimal coating thickness for achieving the first (1st) and second (2nd) LMR, as well as to determine their respective sensitivities. In the experimental part, a cyclic transparent fluoropolymer optical fiber is used, which is first polished and then coated with tin oxide (SnO2) thin film to obtain the LMR. The simulated and experimental results exhibit a high level of agreement. In the visible light spectrum region, the sensitivities for the first LMR are, respectively, 11 300 nm/RI unit (RIU) and 15 973 nm/RIU within the RI range of 1.333–1.345. Similarly, for the second LMR, the sensitivities are, respectively, 520 and 467 nm/RIU within the same RI range. Furthermore, experiments conducted in the near-infrared light spectrum region show a record sensitivity of 57 200 nm/RIU, while the second LMR exhibits a sensitivity of over 5 000 nm/RIU within the RI range of 1.340–1.345. These results underscore the potential of utilizing cyclic transparent optical polymer (CYTOP) fiber in various applications requiring the detection in liquid samples, such as biosensors or chemical sensors.