Magnetic-fluid-infiltrated bilaterally polished photonic crystal fiber with butterfly core for LSPR based magnetic field sensing via water based Fe3O4 magnetic fluid

In this manuscript, a sensor is devised employing photonic crystal fiber with localized surface plasmon resonance (PCF-LSPR), emphasizing the manipulation of refractive index (RI) through magnetic fluid (MF). The sensor's air holes adopt a hexagonal arrangement, forming a butterfly core design, and the transmission channels for the effective confinement of optical field energy relies significantly on the regions surrounding the central air hole in both directions. MF serves as the sensing medium, and the top and bottom polished surfaces are coated with gold and titanium dioxide. The sensor undergoes analysis using the finite element method, scrutinizing its model characteristics, structural parameters, and sensing performance. The results indicate a wavelength sensitivity of up to 45,600 nm/RIU and a maximum figure of merit (FOM) of 434 ${\mathrm{RIU}}^{-1}$. Within the range of magnetic field 30–150 Oe, the highest magnetic field sensitivity records 3350 pm/Oe. Over the temperature range of 27.4–114 °C, the temperature sensitivity measures only 310 pm/°C. A maximum sensor resolution of $2.19\times {10}^{-6}$ RIU is achieved for x$-$pol. The linear relationship between the resonant wavelength and the magnetic field yields $R^2=0.9945$, for degree (2) for x$-$pol. The proposed sensor exhibits notable advantages, including a structure which is very stable, high sensitivity, ease of integration, and resilience to electromagnetic interference. Additionally, it excels in detecting weak magnetic fields. Its potential applications span from industrial production, military technology, to medical equipment.