Excessively tilted fiber grating-based vector magnetometer

Ultrasensitive magnetic field sensor based on cladding-etched long-period grating

We demonstrate a high-sensitivity fiber-optic magnetic field sensor, which consists of a cladding-etched long-period fiber grating (LPFG) near the dispersion turning point (DTP) integrated with a magnetic fluid (MF). By reducing the cladding diameter of the LPFG, the fundamental mode is coupled to the lowest order cladding mode (LP_0,2) near the DTP, which has a much higher surrounding refractive index sensitivity. Thanks to the excellent magneto-optical characteristics of the MF, the proposed sensor can achieve a magnetic field intensity sensitivity of 44.69 nm/mT in the range of 3-7.4 mT. The minimum magnetic field intensity that can be detected is 0.45 µT due to the 0.02-nm wavelength resolution of the optical spectrum analyzer. The proposed etched DTP-LPFG-based sensor with ultrahigh magnetic field sensitivity could have potential applications in magnetic fields and electrical systems.

Packaged optofluidic microbottle resonator for high-sensitivity bidirectional magnetic field sensing

We demonstrate a high-sensitivity bidirectional magnetic field sensor based on a packaged optofluidic microbottle resonator (OFMBR) filled with magnetic fluid (MF). The relationship between sensitivity and different wall thicknesses and radial modes of OFMBR is theoretically analyzed. Then the thin-wall OFMBR is fabricated by etching a capillary with the fusion discharge process. The OFMBR and tapered fiber is packaged with a portable and robust coupling configuration. By applying perpendicular or parallel magnetic field directions to the OFMBR, opposite refractive index responses of the MF can be obtained, with resonant wavelengths redshifted or blueshifted as the magnetic field intensity is increased. A magnetic field sensitivity of 98.23 pm/mT can be obtained by using the second-order radial mode when the magnetic field is perpendicular to the packaged OFMBR. When the magnetic field is parallel to the packaged OFMBR, the sensitivity is -304.80 pm/mT by using the third-order radial mode and the detection limit reaches 0.0656 mT. The proposed sensor has the advantages of easy fabrication, high sensitivity, and reliability, showing a great potential in bidirectional magnetic field application.

Magneto-refractive properties and measurement of an erbium-doped fiber

The magneto-refractive properties of an erbium-doped fiber (EDF) are investigated by theoretically analyzing the change in mode characteristics with a magnetic field and experimentally measuring it based on a fiber-optic Mach-Zehnder interferometer (MZI). The numerical results indicate that the mode effective refractive index (RI) increases as the magnetic field increases, and the mode field intensity distribution tends to be more concentrated in the core region with an increasing magnetic field. The variation in the mode effective RI of the fundamental mode with the magnetic field is greater than that of the higher-order modes. A magneto-refractive measurement system based on a fiber-optic MZI is set up to analyze the magneto-refractive effect of the EDF. The changes in the mode effective RI measured with a direct-current (DC) magnetic field and with a 100 Hz alternating-current (AC) magnetic field are 4.838×10^-6 and 4.245×10^-6 RIU/mT, respectively. The experimental results are in reasonable agreement with the theoretical analysis. Furthermore, the error between the experimental and numerical results is discussed. The magneto-refractive properties of the EDF exhibit potential in all-fiber magnetic field or current sensing area.

Simultaneous measurement of magnetic field and temperature based on two anti-resonant modes in hollow core Bragg fiber

A simple and compact magnetic field and temperature dual-parameter sensor is proposed, which is based on a sandwich structure consisting of a section of hollow core Bragg fiber (HCBF) filled with magnetic fluid (MF) and two sections of single-mode fiber (SMF). The corresponding relationship between the resonant dip with different periods in the transmission spectrum and specific anti-resonant (AR) mode in the HCBF is determined. The resonant dips based on different AR modes shift differently when the magnetic field intensity and temperature change. Then, the simultaneous measurement of the magnetic field intensity and temperature can be achieved by utilizing a cross matrix. The experimental results show that the maximum magnetic field sensitivity in the range of 0-12 mT is 86.43 pm/mT, and the maximum temperature sensitivity in the range of 20-60 ℃ is 17.8 pm/℃. The proposed sensor has the advantages of compact structure, easy fabrication and low cost, thus, it has great potential applications in the field of simultaneous sensing of magnetic field intensity and temperature in complex environments.

Vector magnetic field sensor based on U-bent single-mode fiber and magnetic fluid

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 0.251 nm/°, and the maximum magnetic field intensity sensitivity is 0.517 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.

Half-side gold-coated hetero-core fiber for highly sensitive measurement of a vector magnetic field

A highly sensitive surface plasmon resonance fiber sensor for a vector magnetic field is proposed. The sensor is composed of a half-side gold-coated multimode-single-mode-multimode hetero-core fiber structure encapsulated with ferrofluids. The half-side gold film on the fiber not only produces the surface plasmon resonance, but also breaks the centrosymmetry of the light field in the fiber. Moreover, the magnetic-field-dependent anisotropy of the surrounding ferrofluids makes the sensor sensitive to both the intensity and direction of the magnetic field. Owing to the unique half-side coating configuration and the resulting enhancement of the evanescent field, the sensor can achieve a sensitivity as high as 1008 pm/Oe to the magnetic field intensity. The proposed sensor, possessing advantages such as high sensitivity, ease of fabrication, and low cost, has potential in the detection of a weak vector magnetic field.

Temperature compensated three-dimension fiber optic vector magnetic field sensor based on an elliptical core micro fiber Bragg grating

In this paper, a temperature-compensated three-dimension vector fiber optic magnetic field sensor based on an elliptical core micro fiber Bragg grating (FBG) has been proposed and experimentally demonstrated. The elliptical core fiber was tapered to form a microfiber, in which a FBG was inscribed. Due to the magnetism-manipulation of the anisotropic aggregation of ferromagnetism nanoparticles around the fiber surface, the effective refractive index of the evanescent field for two orthogonal polarization modes was modulated, and the magnetic field orientation can be detected by interrogating the wavelength interval between two reflection peaks. However, two reflection peaks show the identical response to ambient temperature. Hence the proposed sensor can achieve the measurements of the magnetic field intensity and the orientation simultaneously without the temperature cross-sensitivity. The experimental results show that the magnetic field orientation sensitivity of 15 pm/deg and intensity sensitivity of 81 pm/mT can be achieved, and the maximum standard variation of the temperature cross-sensitivity is only 0.02 nm. The proposed elliptical core micro FBG appears to have potential applications in navigation, vehicle detection, and current sensing.

All-fiber-optic vector magnetic field sensor based on side-polished fiber and magnetic fluid

A kind of compact all-fiber-optic vector magnetic sensor is proposed and demonstrated. The sensor consists of a side-polished-fiber (SPF)-integrated with singlemode-no core-singlemode (SNS) fiber structure. A section of side-polished fiber breaks the axially symmetry of the composite structure. The as-fabricated sensor supports vector sensing and has a magnetic field strength sensitivity of up to -2370 pm/mT over 2-6 mT range. The physical mechanism is that the modal interference is strongly influenced by the refractive index (RI) near the side-polished surface. The advantages of the proposed sensor lie in low cost, simple structure and easy manufacture, which make it attractive in the field of magnetic field vector sensing.

Magnetic Nanoparticles Functionalized Few-Mode-Fiber-Based Plasmonic Vector Magnetometer

In this work, we demonstrate a highly-sensitive vector magnetometer based on a few-mode-fiber-based surface plasmon resonance (SPR) sensor functionalized by magnetic nanoparticles (MNPs) in liquid. To fabricate the sensor, a few-mode fiber is side-polished and coated with a gold film, forming an SPR sensor that is highly sensitive to the surrounding refractive index. The vector magnetometer operates based on the mechanism whereby the intensity and orientation of an external magnetic field alters the anisotropic aggregation of the MNPs and thus the refractive index around the fiber SPR device. This, in turn, shifts the resonance wavelength of the surface plasmon. Experimental results show the proposed sensor is very sensitive to magnetic-field intensity and orientation (0.692 nm/Oe and −11.917 nm/°, respectively). These remarkable sensitivities to both magnetic-field intensity and orientation mean that the proposed sensor can be used in applications to detect weak magnetic-field vectors.