Ultrasensitive Fiber SPR Magnetic Field Sensor Using Au/TiO₂ Schottky Junction

This article presents an ultrasensitive fiber surface plasmon resonance (SPR) magnetic field sensor using an Au/TiO
₂
Schottky junction coated on a plastic-clad multimode fiber (PMF) and immersed in the magnetic fluid (MF). The MF acts as the magnetic-sensitive material, and the Au/TiO
₂
film with a high dielectric constant (DC) excites SPR with high sensitivity. When the magnetic field strength applied to the MF changes, the MF’s refractive index (RI) alters accordingly, which changes the phase-matching condition of the surface plasmon polaritons, shifting the resonance dip in the fiber transmission spectrum. Therefore, the magnetic field strength can be measured by monitoring the resonance dip shift. The proposed sensor achieved a maximum magnetic sensitivity of −2.791 nm/Oe in the 5–35 Oe range, higher than most MF-based fiber magnetic field sensors. Additionally, the temperature response of the sensor was measured to be −0.4861 nm/°C, which has little effect on the magnetic sensing performance. The experimental results indicate that the proposed fiber SPR sensor can measure magnetic field strength variations with high sensitivity and accuracy, making it suitable for practical applications in various scenarios.