Ferrofluid-Infiltrated Microstructured Optical Fiber Long-Period Grating

Long-period gratings (LPGs) were successfully inscribed in microstructured optical fibers (MOFs) filled with ferrofluid using a scanning CO₂ laser. Its formation mechanism and magnetic field tunability are investigated. The dispersion curve indicates that cladding modes are more viable to be tuned than the core mode for the ferrofluid-filled MOF. The relationship between the phase-matching curve of MOF-based LPG and the magnetic field intensity is theoretically analyzed, and the magnetic-field responses of the LPG with 660-μm-pitch and a resonance peak of 967.56 nm are also discussed. The results show that the MOF-based LPG reaches a sensitivity of 1.946 nm/Oe for a magnetic range of 0-300 Oe, demonstrating its potential application as a high-sensitivity magnetic-field sensor. The proposed magnetic-field sensor could detect the weak magnetic field with high accuracy. It has several unique advantages, such as compactness, good wavelength selectivity, high integration, ease of coupling, high flexibility, and extensibility. Consequently, the proposed device with tunable magnetic-field sensitivity is promising for future-related applications.