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Optical fiber based electro-magnetic field sensors is a diverse and expanding field in fiber sensor technology with applications spanning from geomagnetism, biomagnetism, nuclear magnetism to safety and operational monitoring of power grid systems. Particularly, because of the dielectric silica material of the fiber that provides high electric insulation and immunity to the electromagnetic interference (EMI), a major reason contributing to the limitations in conventional sensors, the efforts have been focused on developing the fiber-optic sensors with increased sensitivity, bandwidth, and detection range specific to an application but all benefit from the advantages of the platform. Various fiber structures, interrogation schemes and sensing materials have been investigated. One major interest is on the fiber-optic sensor based on multi-mode interference (MMI) where a multimode mode fiber is fusion spliced between two single mode fibers also known as SMS (single-mode/multimode/single mode) fiber sensor. Ease of fabrication, compactness, higher sensitivity, and low cost are some of the driving factors in addition to the potential for direct integration of the platform with functional sensor materials to tailor for specific applications. For the purpose of magnetic field sensing, the magnetic fluid is the most widely used functional material as the sensing/cladding layer on the fiber-structure. Here we present efforts to enhance and optimize the sensitivity of such SMS structure with magnetic fluid as the sensing material exploiting the unique “self-imaging” property of the SMS sensor where the sensor produces a filterlike spectral response and is highly sensitive to the change in magneto-optical property of surrounding medium. The performance metrics of the sensor are analyzed against DC magnetic field range keeping an eye in detecting typical current induced magnetic field in power grid systems.
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