High-sensitivity vector magnetic field sensor based on a V-shaped multimode-no-core-multimode fiber structure.

This work proposes and investigates a bent multimode-no-core-multimode optical fiber structure for vector magnetic field sensing applications. The bent no-core fiber (NCF) serves as the sensing area, and the gold film is deposited on its surface to excite the surface plasmon resonance effect. Due to the strong evanescent field of the unclad and bent NCF, the as-fabricated sensor exhibits a high sensitivity of 5630 nm/RIU in the refractive index range of 1.36-1.39. Magnetic fluid is employed as the magneto-sensitive material for magnetic field sensing, exhibiting a high magnetic field intensity sensitivity of 5.74 nm/mT and a high magnetic field direction sensitivity of 0.22 nm/°. The proposed sensor features a simple structure, low cost, point sensing, and excellent mechanical performance.

Enhanced sensitivity of temperature and magnetic field sensor based on FPIs with Vernier effect.

A kind of temperature and magnetic field sensor using Fabry-Perot interferometers (FPIs) and Vernier effect to enhance sensitivity is proposed. The sensor structure involves filling the FP air cavities with polydimethylsiloxane (PDMS) and magnetic fluid (MF) to create the PDMS and MF cavities for temperature and magnetic field detection, respectively. The two cavities are reflective structures, which are interconnected in series through a fiber-optic circulator. Experimental data demonstrates that the Vernier effect effectively enhances the sensor sensitivity. The average temperature sensitivity of the sensor is 26765 pm/°C within the range of 35∼39.5°C. The magnetic field intensity sensitivity is obtained to be -2245 pm/mT within the range of 3∼11 mT. The sensitivities of the temperature and magnetic field using the Vernier effect are about five times larger than those of the corresponding single FP cavity counterparts.

In-line temperature-compensated vector magnetic field sensor with side-polished fiber.

A novel, to the best of our knowledge, vector magnetic field sensor with temperature compensation is proposed and investigated. The proposed sensor is realized by side polishing a multi-mode optical fiber and adopting the surface plasmon resonance (SPR) effect. The side-polished surface is coated with a magnetic fluid (MF) and polydimethylsiloxane (PDMS) successively along the fiber axis. The as-fabricated sensor can be used not only for magnetic field strength and direction sensing, but also for temperature detection. The achieved magnetic field intensity sensitivities are 1720 pm/mT (90° direction) and -710 pm/mT (0° direction), and the temperature sensitivity is -2070 pm/°C. On top of its temperature compensation ability, the easy fabrication and very high sensitivity of the proposed sensor are attractive features for vector magnetic field sensing applications.