Magnetic fluid-filled microhole in the collapsed region of a photonic crystal fiber for the measurement of a magnetic field

Design and analysis of graphene- and germanium-based plasmonic probe with photonic spin Hall effect in THz frequency region for magnetic field and refractive index sensing

In this work, we analyze the design of a graphene- and germanium-based plasmonic sensor with photonic spin Hall effect (PSHE) for detection of refractive index (RI) of a gas medium and magnetic field (B) applied to the graphene monolayer in THz frequency region. The PSHE phenomenon is studied in both conventional as well as modified weak measurements. The effect of gaseous medium thickness (d₄), transverse magnetic (TM) mode's order, and amplified angle parameter (Δ) is studied on the sensor's performance. Parameters such as sensitivity, resolution, and figure of merit have been considered for sensor's performance evaluation. The results indicate that in the conventional weak measurements, for a TM₁ mode (with d₄ = 20 µm, B = 0, and Δ = 0.1°), an RI resolution of 2.32 × 10^-12 RIU is achievable for gas medium in the range 1-1.1 RIU. In the modified weak measurements, for a TM₃ mode (with d₄ = 100 µm, B = 0, and Δ = 0.1°), the RI resolution close to 1.39 × 10^-10 RIU is achievable for gas sensing. The same sensor design was also studied for magnetic field sensing while keeping the value of gaseous medium RI (n₄) as 1. The results indicate that for a TM₁ mode (with d₄ = 20 µm and Δ = 0.1°), in the conventional weak measurements, a magnetic field resolution of 5.31 × 10^-4 µT (i.e., 0.53 nT) is achievable for a range 0-1 T of B. Further, it is found that in contrast with the conventional case, the resolutions in the modified weak measurements are improved for large values of the Δ. Some of the results emerge better or comparable with the resolutions of RI and magnetic field measurement (5 × 10^-9 RIU and 0.7 µT or 1.22 × 10^-11 RIU and 1.46 × 10^-2 µT) existing in the literature.

Designing magnetic field sensor based on tapered photonic crystal fibre assisted by a ferrofluid

A novel magnetic field sensor is proposed based on the combination of in-line tapered photonic crystal fibre (PCF) Mach–Zehnder interferometer and magnetic nanoparticles. The sensor is theoretically investigated and experimentally realized. The effect of the mechanical strain and the magnetic field on the sensitivity of the sensor is studied. It is found that the proposed sensor shows a wavelength-sensitivity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-\,0.072\,\text {nm/mT}$$\end{document}-0.072nm/mT and a strain-sensitivity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1\,\text {pm/}\upmu \,\epsilon \,$$\end{document}1pm/μϵ. To evaluate the effect of the magnetic nanoparticles on the output light intensity, the sensitivity response of the device has been measured under different magnetic field strengths for different length scales. The experimental results show refractive index changes of the magnetic nanoparticles-infiltrated PCF—acting as fibre cladding—under the applied magnetic field leads to variations of the interferometric output. The sensitivity of magnetic field measurement with the sensor with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$30\,\text {mm}$$\end{document}30mm and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$40\,\text {mm}$$\end{document}40mm PCF could reach up to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.021\,\text {dB/mT}$$\end{document}0.021dB/mT and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.017\,\text {dB/mT}$$\end{document}0.017dB/mT, respectively. The results show a very good linear response that is an essential requirement for the practical sensors. The proposed magnetic field sensor finds applications in various areas, such as optical sensing, military, power industry, and tunable photonic devices.

High-sensitivity magnetic field sensor based on a dual-core photonic crystal fiber

A high-sensitivity magnetic field sensor based on a dual-core photonic crystal fiber has been designed with an extremely short device length of 2000 μm in this paper. The two cores of the fiber are separated by one air hole filled with magnetic fluid. The sensitive properties are investigated by the full-vector finite element method. Simulation results illustrate that the highest sensitivity can reach -442.7  pm/Oe in the magnetic field strength range of 30-520 Oe. The photonic crystal fiber filled with magnetic fluid, serving as an excellent platform for magnetic field sensing, has great potential applications in complex environments, remote sensing, and real-time monitoring fields.

A diaphragm-free fiber Fabry-Perot gas pressure sensor

A diaphragm-free fiber gas pressure sensor based on the extrinsic Fabry-Perot interferometer (EFPI) is proposed and experimentally demonstrated. The sensor is fabricated by fusion splicing a sandwich structure of a single mode fiber, a hollow core fiber (HCF), and a coreless fiber. A femtosecond (fs) laser is employed to drill a micro-channel on the side wall of the HCF to allow gas entering/exiting the HCF. The refractive index of the gas has a linear relationship with the gas pressure. Thus, the gas pressure can be detected by investigating the optical path difference of the EFPI. The experimental results show that the proposed sensor exhibits a high gas pressure sensitivity of ∼1.80 µm/MPa from vacuum to 10 MPa at room temperature. Pressure responses under high temperatures are also investigated. The proposed sensor has properties of robust structure, miniature size, large measuring range, and high sensitivity.

Mach-Zehnder interferometric magnetic field sensor based on a photonic crystal fiber and magnetic fluid

A Mach-Zehnder interferometric magnetic field sensor based on a photonic crystal fiber (PCF) and magnetic fluid (MF) was designed and experimentally demonstrated. The sensing probe consists of a single-mode-(SM)-multimode-PCF-SM fiber structure through arc fusion splicing. It was then laser engrave notched with the femtosecond laser so that the PCF cladding was selectively infilled MF. A well-defined interference pattern was obtained on account of the tunable refractive index of the MF infilled PCF cladding. The transmission spectra of the proposed sensor under different magnetic field intensities have been measured and theoretically analyzed. The results show that the sensitivity of the proposed sensor can reach -0.13  dB/mT and 0.07334 nm/mT in the magnetic field intensity from 1 mT to 20 mT and 2 mT to 20 mT, respectively.

Magnetic Field Sensing Based on Bi-Tapered Optical Fibers Using Spectral Phase Analysis

A compact, magnetic field sensor system based on a short, bi-tapered optical fiber (BTOF) span lying on a magnetic tape was designed, fabricated, and characterized. We monitored the transmission spectrum from a broadband light source, which displayed a strong interference signal. After data collection, we applied a phase analysis of the interference optical spectrum. We here report the results on two fabricated, BTOFs with different interference spectrum characteristics; we analyzed the signal based on the interference between a high-order modal component and the core fiber mode. The sensor exhibited a linear response for magnetic field increments, and we achieved a phase sensitivity of around 0.28 rad/mT. The sensing setup presented remote sensing operation and low-cost transducer magnetic material.

Photonic crystal fiber modal interferometer based on thin-core-fiber mode exciter

A thin-core-fiber excited photonic crystal fiber modal interferometer has been proposed and experimentally demonstrated. By employing a thin-core fiber as the mode exciter, both of the core and cladding modes propagate in the photonic crystal fiber and interfere with each other. The experimental results show that the transmission dips corresponding to different-order modes have various strain responses with opposite shift directions. The strain sensitivity could be improved to 58.57  pm/με for the applied strain from 0 to 491 με by utilizing the wavelength interval between the dips with opposite shift directions. Moreover, due to the pure silica property of the employed photonic crystal fiber, the proposed fiber modal interferometer exhibits a low-temperature sensitivity of about 0.56  pm/°C within a temperature range from 26.4°C (room temperature) to 70°C. Additionally, the proposed fiber modal interferometer has several advantages, such as good stability, compact structure, and simple fabrication. Therefore, it is more applicable for strain measurement with reducing temperature cross-sensitivity.

All fiber magnetic field sensor with Ferrofluid-filled tapered microstructured optical fiber interferometer

An ultra-compact optical fiber magnetic field sensor based on a microstructured optical fiber (MOF) modal interference and ferrofluid (FF) has been proposed and experimentally demonstrated. The magnetic field sensor was fabricated by splicing a tapered germanium-doped index guided MOF with six big holes injected with FF to two conventional single-mode fibers. The transmission spectra of the proposed sensor under different magnetic field intensities have been measured and theoretically analyzed. Due to an efficient interaction between the magnetic nanoparticles in FF and the excited cladding mode, the magnetic field sensitivity reaches up to117.9pm/mT with a linear range from 0mT to 30mT. Moreover, the fabrication process of the proposed sensor is simple, easy and cost-effective. Therefore, it will be a promising candidate for military, aviation industry, and biomedical applications, especially, for the applications where the space is limited.

Recent progress in ferrofluids research: novel applications of magnetically controllable and tunable fluids

Ferrofluids are suspensions of magnetic nanoparticles that have the attractive feature of being controlled by applied magnetic fields. Ferrofluids have been studied for decades in an ever growing number of applications that take advantage of their response to applied magnetic fields. Here, we provide a summary of recent advances in established and emerging applications of ferrofluids, including applications in optics, sensors, actuators, seals, lubrication, and static/dynamic magnetically driven assembly of structures.