Abstract
In this paper, a polymer micro-Fabry–Pérot interferometer (FPI) fabricated via direct laser writing using two-photon polymerization techniques on a single mode fiber tip is proposed, designed, simulated, and experimentally demonstrated as a magnetic field probe. The sensor comprises a tapered waveguide with a length of 100 µm and a diameter of 1 µm along the axis connecting the two reflecting surfaces of the micro-FPI open cavity. The cavity is filled with a magnetic fluid (MF) changing the evanescent coupling and consequently leading to a change in the phase of the FPI. To improve the signal reflection, a thin layer of Au is coated on the device before fabricating the probe sensor, which is then sealed in a MF-filled glass tube. The experimental results show that the proposed probe sensor has a low temperature sensitivity and a sensitivity to magnetic field as high as 1.54 nm/mT, and the magnetic field measurement accuracy is ∼649.4 μT within a range from 1 mT to 8 mT. The microsensor, which is very stable and easy to fabricate, can be used as a probe to detect weak magnetic fields.
Highlights
Magnetic field sensing is vitally important in the areas of electric power systems and aerospace
We propose and fabricate a novel and highly sensitive magnetic field probe based on a Fabry–Pérot interferometer (FPI) connecting a microwaveguide, which is 3D printed on an optical fiber tip by the two-photon direct laser writing (DLW) technique
The schematic diagram of the magnetic field measurement is shown in Fig. 4(a) where a superluminescent light emitting diode (SLED) source ranging from 1350 nm to 1650 nm is used to guide the light to the device through an optical fiber circulator (OC), and the reflected light is recorded by using an optical spectrum analyzer (OSA, AQ6317B) with a minimum resolution of 10 pm
Summary
Magnetic field sensing is vitally important in the areas of electric power systems and aerospace. The basic principle of MF for magnetic field sensing is that the refractive index of the MF increases as the surrounding magnetic field increases Based on this principle, various optical fiberbased magnetic field sensors filled with MF have been proposed and designed.. To overcome the above limitations, other kinds of optical fiber sensors have been proposed based on the principle that the presence of MF changes the guiding mode or the evanescent field and leads to a change in optical path difference (OPD) in a sensing scheme including MZIs, Sagnac interferometers (SIs), Fresnel reflectivity, multimode interferometers, long-period fiber gratings (LPGs), microfiber waveguides, and couplers.. Zhao et al presented a Sagnac interferometer magnetic field sensor with a ferrofluid-filled high-birefringence photonic crystal fiber, and the sensitivity was about 73 pm/mT.14 These proposed schemes were interesting; the sensing structures were not optimized, leading to limited sensitivity. The proposed device is novel and highly sensitive to the magnetic field, which can be used as a microprobe for weak magnetic field detection
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