Compact and High-Sensitivity Bismuth-Doped Silica Optical Fiber Weak Magnetic Sensor

Doped silica fibers are ideal for weak magnetic sensing in harsh environments, but there is a lack of high-sensitivity doping materials. Here, we developed a novel optical fiber weak magnetic sensor based on bismuth-doped silica optical fibers (BDSFs). Theoretical analysis indicates that the energy level splitting of Bi-2p orbital spin electrons enhances the interaction between Bi and O, improving the magnetorefractive characteristics of the fiber. We employed atomic layer deposition (ALD) technology to fabricate BDSF with good uniformity and a simple structure, forming low-valence Bi0 active sites through high-temperature melting induction. Using digital holographic refractive index measurement techniques, the holographic imaging of the refractive index distribution of BDSF under different magnetic fields was performed, obtaining a magnetorefractive effect variation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.22\times 10^{-{5}}$ </tex-math></inline-formula> refractive index unit (RIU)/mT. Subsequently, a stable all-fiber solid-state interferometric sensing system based on BDSF was constructed, successfully measuring weak magnetic signals. The sensor exhibits good linear response and low background noise at 500 Hz, with a resolution of 55.26 nT/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {\text {Hz}}$ </tex-math></inline-formula>. The BDSF provides promising material choices and new insights for constructing stable and viable optical fiber magnetic field sensors.