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 5630â 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 5.74â nm/mT and a high magnetic field direction sensitivity of 0.22â nm/°. The proposed sensor features a simple structure, low cost, point sensing, and excellent mechanical performance.
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.
All-fiber-optic magnetic field sensor integrated with magnetic fluid has been investigated for decades, accompanied by the commitment to vectorization, miniaturization, integration and solving the temperature cross-sensitivity caused by thermo-optic effect of magnetic fluid. A kind of dual-channel-in-one temperature-compensated all-fiber-optic vector magnetic field sensor was proposed and investigated theoretically in this work. Three optical surfaces, including two sensing surfaces (plated with gold film of 40â nm thickness and then coated with magnetic fluid and polydimethylsiloxane, respectively, referred as CH1 and CH2) and one reflective surface, were integrated on a single-mode fiber tip to facilitate the dual-channel-in-one design. The Kretschmann configurations were formed by the waveguide fiber, gold film and functional materials at the sensing surfaces (CH1 and CH2). Surface plasmon resonance was excited in different wavelength bands corresponding to CH1 and CH2. Attenuation wavelengths corresponding to CH1 and CH2 depend on the magneto-induced and temperature-induced refractive index change of functional materials, respectively, which makes the temperature-compensated magnetic field sensing possible. The non-centrosymmetric evanescent field generated by micro-fiber-tip-prism enables the vector magnetic field sensing. Especially, the length of the sensing area is only 115.5â µm, which achieves ultra-integration and miniaturization. The current work provides a novel scheme for designing all-fiber-optic vector magnetic field sensing based on magnetic fluid and demonstrates the realization of lab-on-a-fiber and then promotes the industrial application of all-fiber-optic vector magnetic field sensing devices.
Fiber-optic magnetic field sensors based on magnetic fluid (MF) is encountering with thermal effects and demand for vectorization for several years. A common solution is to use axially processed fiber cascaded with fiber Bragg grating (FBG). However, the length of such sensors is usually in centimeter-level, which restricts the sensing applications in narrow space and gradient field cases. In this work, we present an ultracompact reflection-type dual-channel sensor for vector magnetic field (Channel 1, referred as CH1) and temperature (Channel 2, referred as CH2) monitoring, which is composed of a pair of gold-plated wedge-shaped multimode fiber (MMF) tip and gold-plated multimode-no-core fiber (MNF) tip. The surface plasmon resonance (SPR) effect was adopted. The two sensor probes are coated with magnetic-field-sensitive MF and temperature-sensitive polydimethylsiloxane (PDMS), respectively. The issue of vector magnetic field and temperature cross-sensitivity is tactfully resolved. Importantly, the proposed sensing probes are ultracompact and the spatial resolution is extremely small (615 µm for CH1 based on wedge-shaped fiber tip and 2â mm for CH2 based on MNF), which is very helpful for narrow space and gradient magnetic field detection. The obtained magnetic field intensity sensitivities are 1.10â nm/mT (90° direction) and -0.26â nm/mT (0° direction), and temperature sensitivity is -3.12â nm/°C.
A novel, compact, and easy fabrication vector magnetic field sensor has been proposed and investigated. The proposed sensor consists of a U-bent single-mode fiber fixed in a magnetic-fluid-filled vessel. Neither mechanical modification nor additional fiber grating is needed during the sensor fabrication. The results show that the response of magnetic fluid to magnetic field can be used to measure the direction and intensity of magnetic field via whispering gallery modes supported by the U-bent fiber structure with suitable bending radius. The sensitivity of direction is 0.251â nm/°, and the maximum magnetic field intensity sensitivity is 0.517â nm/mT. Besides, the results of this work prove the feasibility for realizing vector magnetic sensors based on other bending structures (such as bending multimode interference, bending SPR structure) in the future.
A kind of reflective all-fiber magnetic field sensor based on a non-adiabatically tapered microfiber with magnetic fluid is proposed and experimentally demonstrated. The modal interference effect is caused by the abrupt tapers, which result in an approximately sinusoidal spectral response. The reflection spectra of the proposed sensor under different magnetic field strengths have been measured and theoretically analyzed. The maximum sensitivity of 174.4 pm/Oe is achieved at wavelength of around 1511 nm. Besides, an intensity tunability of -0.02 dB/Oe is also achieved. Comparing with the traditional sensors operating at transmission mode, the presented sensor in this work owns the advantages of smaller size and higher sensitivity and resolution due to the enhanced extinction ratio. The proposed structure is also promising for designing other tunable all-in-fiber photonic devices.
