A compact and inexpensive optical fiber sensor for the measurement of dc and ac currents is demonstrated. The sensor consists of a fiber Bragg grating bonded on two joined pieces of metal alloys, one being Terfenol-D and the other MONEL 400. Because Terfenol-D has much stronger magnetostriction, a magnetic field applied along the two alloy bars stretches the two portions of the grating in different proportions and, thus, results in a split in the reflection spectrum of the grating, which can be measured with a simple technique using a single photodetector. On the other hand, because Terfenol-D and MONEL 400 have almost identical thermal expansion coefficients, a change in temperature does not cause the reflected spectrum of the grating to split and, therefore, does not affect the magnetic field measurement.
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