Ultrasensitive Magnetic Field Measurement Using Two-Mode Microfiber-Based Sensors

This study presents a novel fiber-optic magnetic field sensor that synergistically combines a microfiber structure with a developed fiber Bragg grating (FBG)-based interrogation system. The sensor harnesses a two-mode fiber (TMF) with a precisely engineered ring-index distribution to effectively suppress higher order modes, thereby establishing a uniform modal interferometer predominantly involving the $HE_{{11}}$ and $HE_{{12}}$ modes. Experimental investigations reveal that the sensor attains an exceptional sensitivity of up to 29.928 nm/mT, markedly outperforming earlier designs. Furthermore, the FBG interrogation system effectively mitigates temperature-induced cross sensitivity, offering a low cost, portable alternative for real-time magnetic field strength detection. This approach provides a significant advancement in measurement precision and compact instrumentation for magnetic field sensing, suitable for a wide range of field applications.