High-sensitivity optical fiber magnetic field and current sensor based upon two cascaded Mach-Zehnder interferometers

In this article, we have designed a highly sensitive S1 that can measure magnetic field (MF) and current. S1 consists of two Mach-Zehnder interferometers (MZIs) cascaded together, namely, MZI1 and MZI2. MZI1 and MZI2 have simple structures and are fabricated by directly tapering single-mode fiber. MZI1 and MZI2 with tapered structures are sensitive to axial strain and temperature. MZI1 is pasted into Terfenol-D microgroove with magnetostrictive properties, and the MF acting on Terfenol-D corresponds to acting the strain to MZI1, so MZI1 has high sensitivity to MF. MZI2 is pasted onto a copper rod, which generates abundant heat, which is absorbed by MZI2 and causes the resonance wavelength drift, making MZI2 very sensitive to current. The experiment reveals that the MF sensitivity of MZI1 is −97.47 pm/mT, and the sensitivity of the current square of MZI2 is −45.44 pm/A2. S1 is a Vernier effect sensor composed of MZI1 and MZI2 cascaded together, which can improve the sensitivities of MZI1 and MZI2. The experiment reveals that S1 has the MF sensitivity of −1011.98 pm/mT and the sensitivity of the current square of 439.36 pm/A2, which increases the sensitivities of MZI1 and MZI2 by 10.4 and 9.7 times, respectively. The manufacturing of sensor S1 only requires fiber tapering, fiber cleaving, and material bonding. Therefore, this sensor boasts advantages such as simple structure, easy manufacturing, low cost, durability, and high sensitivity, providing a novel scheme for simultaneously measuring MF and current.