A high-sensitivity wide-range magnetic field sensor based on polymer optical waveguide and a manufacturing method thereof

Abstract

This invention discloses a wide-range, high-sensitivity magnetic field sensor based on a polymer optical waveguide. The sensor comprises a Fabry-Perot interference microcavity constructed from a single-mode fiber-polymer optical waveguide-single-mode fiber structure. Fe3O4 nanoparticles are doped into the cladding of the polymer optical waveguide to enhance the magnetic response. This invention utilizes a broadband light source as the probe light incident on the sensing structure, and a spectrometer receives the Fabry-Perot interference spectrum formed after reflection from the gold-plated end face. When an external magnetic field acts on the sensing unit, the Fe3O4 nanoparticles in the cladding are subjected to magnetic force, causing a change in the length of the polymer optical waveguide microcavity, which in turn leads to a resonant wavelength drift through interference. Accurate measurement of the magnetic field strength can be achieved by detecting the wavelength drift. This invention has advantages such as compact structure, simple fabrication, high sensitivity, wide measurement range, and resistance to electromagnetic interference, and is suitable for industrial monitoring, biomagnetic signal detection, and spatial magnetic field distribution mapping.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a high-sensitivity, wide-range magnetic field sensor based on a polymer optical waveguide and its fabrication method. Background Technology

[0002] Fiber optic sensing technology, with its advantages of high sensitivity, inherent resistance to electromagnetic interference, corrosion resistance, and good long-term stability, has shown broad application prospects in environmental monitoring, industrial safety, biomedicine, and aerospace. As a fundamental physical quantity possessing both magnitude and direction, high-precision detection of magnetic fields is of great demand in fields such as the power industry, aerospace, biomedicine, geophysics, and nuclear fusion. Traditional magnetic field sensors, such as Hall elements and fluxgate sensors, while technologically mature, face challenges in areas such as adaptability to strong electromagnetic interference environments, system miniaturization, distributed measurement, and long-term reliability. The emergence of fiber optic magnetic field sensors provides an effective technical path to solve these problems.

[0003] Currently, mainstream fiber optic magnetic field sensing mechanisms are mainly divided into three categories: Faraday effect type, magneto-optical effect type (such as magnetohydrodynamics), and magnetostrictive type. Among them, sensors based on the Faraday effect usually require special magneto-optical materials or complex interference optical paths, making their fabrication demanding. While sensors based on magnetohydrodynamics can modulate optical properties by controlling the alignment of nanoparticles through magnetic fields, they suffer from problems such as temperature cross-sensitivity and long-term physical instability, posing challenges to packaging and practical application. In contrast, magnetostrictive sensors convert external magnetic fields into mechanical strain, which is then sensed by sensitive elements such as fiber optic gratings or interferometers. Due to their relatively simple structure, ease of integration, low cost, and good stability, they have attracted widespread attention.

[0004] In recent years, researchers have made significant progress in improving sensor performance through material innovation, structural design, and the integration of optical effects. For example, some studies have achieved high-sensitivity magnetic field measurement using the vernier effect of cascaded Fabry-Perot interferometers; others have achieved vector magnetic field direction sensing by optimizing the morphology of magnetostrictive materials and combining fiber gratings with Terfenol-D rods of different curvatures; still others have achieved ultra-high sensitivity and simultaneous measurement of temperature and magnetic fields by embedding a high-sensitivity Mach-Zehnder interferometer into a Terfenol-D cylinder. Furthermore, studies have extended the dynamic sensing range to 0–700 mT using "human-shaped" fiber optic structures coated with nickel ferrite.

[0005] However, despite the significant progress made in sensitivity and dynamic range by the aforementioned research, existing technologies still have the following shortcomings: First, some high-sensitivity designs often sacrifice measurement range, making it difficult to balance wide range and sensitivity; second, magnetic field detection typically requires complex structural designs or multi-parameter demodulation, increasing fabrication difficulty and system complexity; and third, the integration methods of magnetostrictive materials with fiber optic structures still need simplification to improve the structural flexibility and environmental adaptability of devices. Therefore, how to achieve a magnetic field sensor with both high sensitivity and wide measurement range through simplified structural design remains a pressing technical problem to be solved in this field. Summary of the Invention

[0006] To address the technical challenges of existing fiber optic magnetic field sensors, such as difficulty in achieving both high sensitivity and wide measurement range, as well as their complex structure and high fabrication difficulty, this invention proposes a high-sensitivity, wide-range magnetic field sensor based on a polymer optical waveguide and its fabrication method.

[0007] This invention proposes a wide-range, high-sensitivity magnetic field sensor based on a polymer optical waveguide, comprising: a first single-mode optical fiber serving as the input and output channel for optical signals; a polymer optical waveguide, the first end face of which is coupled to the end face of the first single-mode optical fiber to form the sensing region of a Fabry-Perot interference microcavity, wherein the cladding of the polymer optical waveguide is doped with Fe3O4 nanoparticles; and a second single-mode optical fiber, the first end face of which is coupled to the second end face of the polymer optical waveguide, wherein the first end face of the second single-mode optical fiber is provided with a high-reflectivity film, serving as the reflecting end face of the Fabry-Perot interference microcavity.

[0008] Preferably, the polymer optical waveguide adopts a refractive index distribution structure of "high refractive index core layer / low refractive index cladding layer", wherein the core layer is composed of UV-curable adhesive and the cladding layer is composed of UV-curable adhesive doped with Fe3O4 nanoparticles.

[0009] Preferably, the cavity length of the polymer optical waveguide is 50 μm to 60 μm.

[0010] Preferably, the cavity length of the polymer optical waveguide is 55 μm.

[0011] Preferably, the mass ratio of the UV-curable adhesive forming the coating to the Fe3O4 nanoparticles is 3:1 to 10:1.

[0012] Preferably, the mass ratio of the UV-curable adhesive to Fe3O4 nanoparticles is 3:1 to achieve the highest magnetic field sensitivity.

[0013] Preferably, the mass ratio of the UV-curable adhesive to Fe3O4 nanoparticles is 7:1 to achieve high linearity and stability over a wide range.

[0014] Preferably, the high-reflectivity film is a gold film.

[0015] This invention proposes a wide-range, high-sensitivity vector magnetic field sensor based on a polymer optical waveguide. This sensor constructs a polymer optical waveguide microcavity between a first single-mode fiber and a second single-mode fiber, forming a Fabry-Perot interference structure. Fe3O4 nanoparticles doped in the cladding generate magnetic force under the influence of an external magnetic field, causing elastic deformation of the polymer optical waveguide and thus altering the effective cavity length of the Fabry-Perot microcavity. When probe light emitted from a broadband light source is incident on the sensing structure, it is reflected by the gold-plated end face, forming an interference spectrum. By monitoring the resonant wavelength shift of the interference spectrum using a spectrometer, precise measurement of the magnetic field strength can be achieved.

[0016] This invention achieves performance modulation of the sensor by systematically optimizing the cavity length parameters of the polymer optical waveguide and the mass ratio of UV-curable adhesive to Fe3O4 nanoparticles in the cladding. In the preferred embodiment, the sensor achieves high sensitivity when the cavity length is 55 μm and the mass ratio is 3:1; when the mass ratio is 7:1, the sensor exhibits excellent linearity and stability over a wide measurement range.

[0017] The sensor described in this invention has advantages such as compact structure, simple manufacturing, high sensitivity, wide measurement range, and strong anti-electromagnetic interference capability. It can be widely used in fields such as industrial monitoring, biomagnetic signal detection, spatial magnetic field distribution mapping, and power system current detection. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a high-sensitivity, wide-range magnetic field sensor based on a polymer optical waveguide.

[0019] Figure 2 This is a schematic diagram of a test system for a high-sensitivity, wide-range magnetic field sensor based on a polymer optical waveguide. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Figure 1 This is a schematic diagram of the structure of a high-sensitivity, wide-range magnetic field sensor based on a polymer optical waveguide proposed in this invention.

[0021] like Figure 1As shown, this invention proposes a wide-range, high-sensitivity magnetic field sensor based on a polymer optical waveguide, comprising: a first single-mode fiber, a polymer optical waveguide, and a second single-mode fiber. The first single-mode fiber serves as the input and output channel for optical signals, and its end face is coupled to the first end face of the polymer optical waveguide. The polymer optical waveguide constitutes the sensing region of a Fabry-Perot interferometer microcavity, and its second end face is coupled to the first end face of the second single-mode fiber. The first end face of the second single-mode fiber is provided with a high-reflectivity film, serving as the reflecting end face of the Fabry-Perot interferometer microcavity.

[0022] The polymer optical waveguide adopts a refractive index distribution structure of "high refractive index core layer / low refractive index cladding". The core layer is composed of a high refractive index UV-curable adhesive, and the cladding is composed of a UV-curable adhesive doped with Fe3O4 nanoparticles. By adjusting the amount of Fe3O4 doping, the refractive index of the cladding is made lower than that of the core layer, satisfying the total internal reflection condition and realizing low-loss guided wave transmission.

[0023] In a preferred embodiment, the polymer waveguide has a core diameter of 20 μm and a cladding diameter of 125 μm, matching the dimensions of a standard single-mode fiber to reduce coupling loss. The high-reflectivity film is preferably a gold film, deposited by plasma sputtering on the end face of the second single-mode fiber, with a thickness of approximately 100-200 nm, to ensure high reflectivity and good visibility of interference fringes.

[0024] The key structural parameters of the sensor include the cavity length L of the polymer waveguide (i.e., the length of the polymer waveguide between the end faces of the first and second single-mode fibers) and the mass ratio of UV-curable adhesive to Fe3O4 nanoparticles in the cladding. By optimizing these parameters, the sensor's magnetic field sensitivity, linearity, and measurement range can be controlled.

[0025] Preferably, the cavity length of the polymer optical waveguide is 50 μm to 60 μm. More preferably, the cavity length is 55 μm, at which point the sensor achieves both high sensitivity and good linearity over a wide range.

[0026] Preferably, the mass ratio of the UV-curable adhesive forming the coating to the Fe3O4 nanoparticles is 3:1 to 10:1. Experiments showed that as the proportion of UV adhesive increased, the sensitivity initially increased and then decreased. The sensor achieved the highest sensitivity at a mass ratio of 3:1; and exhibited optimal linearity and stability over a wide range of 0-80 mT at a mass ratio of 7:1. Therefore, a suitable ratio can be selected based on application requirements: 3:1 is used when pursuing ultimate sensitivity, and 7:1 is used when pursuing wide-range linear measurement.

[0027] Accordingly, this embodiment also proposes a method for fabricating the above-mentioned fiber optic magnetic field sensor, comprising the following steps:

[0028] S1. Prepare a single-mode optical fiber with a length of about 3cm, cut the end face flat with a precision fiber cleaver, place it in a plasma sputtering system, and deposit a dense gold film on one of the end faces to form a reflective end face.

[0029] S2. Fix the gold-plated single-mode fiber in the fiber clamp on the rotary displacement stage. Take another section of single-mode fiber as the lead fiber, immerse its tip in a small amount of uncured UV-curing adhesive, and fix it on the displacement stage in the same way.

[0030] S3. By adjusting the displacement stage, the fiber tip coated with UV adhesive is gradually brought closer to the gold-plated end face. The relative position of the two fiber end faces is monitored in real time using top-view and side-view CCD cameras, and the rotation stage is precisely adjusted until the two end faces are coaxially aligned.

[0031] S4. After alignment, control the displacement stage to gently bring the adhesive tip into contact with the gold-plated surface. Then, retract the annealed fiber at a controlled speed, utilizing the surface tension and adhesion of the liquid to form a uniform cylindrical liquid bridge between the two fiber end faces. By precisely controlling the retraction distance and speed, the diameter of the liquid bridge is matched with the fiber core diameter (approximately 20 μm) after final curing.

[0032] S5. After the liquid bridge shape stabilizes, immediately irradiate it with a UV lamp to completely cure it, forming a highly transparent polymer core layer.

[0033] S6. Preparation of coating material: Weigh Fe3O4 nanoparticles and uncured UV adhesive according to the predetermined mass ratio, place them in a mixer and stir continuously for 15 minutes to ensure that the nanoparticles are uniformly dispersed and there is no visible agglomeration, so as to obtain a homogeneous coating material.

[0034] S7. Using another single-mode optical fiber, dip a small amount of cladding material and carefully transfer the droplet onto the cured core surface with CCD assistance. By controlling the amount of adhesive and utilizing the leveling and surface tension of the liquid, the mixture is made to uniformly coat the core layer, forming a concentric cladding. After the coating shape stabilizes, it is exposed to ultraviolet light again from all directions to ensure full cross-linking and curing.

[0035] This completes the fabrication of the SMF-POW-SMF sensor probe.

[0036] In the specific operation of the fiber optic vibration sensing system of this embodiment, the response of the sensor to changes in magnetic field strength is explained in more detail as follows: Light emitted from the broadband light source enters the first single-mode fiber through a circulator and is transmitted to the polymer waveguide microcavity. Since the core layer has a higher refractive index than the cladding, the light is confined within the core layer. When the light reaches the gold-plated end face of the second single-mode fiber, it is reflected, and the reflected light returns along the original path, forming a Fabry-Perot interference with the reflected light from the first end face. The resonant wavelength of the interference spectrum satisfies: λ = 2nL / m, where n is the effective refractive index, L is the cavity length, and m is the interference order.

[0037] When an external magnetic field is applied to the sensor, the Fe3O4 nanoparticles doped in the cladding are subjected to magnetic force, causing minute elastic deformation of the polymer waveguide, resulting in a change in the cavity length L, and consequently, a shift in the resonant wavelength. The magnetic field strength B can be deduced by monitoring the wavelength shift Δλ. The sensor sensitivity S = Δλ / ΔB.

[0038] For vector detection, the equivalent Young's modulus differs on both sides of the sensor due to the asymmetric coverage of the graphene film. When the magnetic field direction changes, the magnetostriction on different sides varies, causing the cavity length to change with the angle, thus making the sensitivity angle-dependent. By calibrating the wavelength response at different angles, the direction of the magnetic field can be determined.

[0039] To further illustrate the beneficial effects of the present invention, specific experimental test results are given below.

[0040] System setup and testing, such as Figure 2 The system includes a broadband supercontinuum light source, a spectrometer, a circulator, an electromagnet, an electromagnet power supply, and a fabricated sensor. Testing was conducted under constant temperature conditions. The electromagnet provides an adjustable magnetic field from 0-80 mT, and the magnetic field strength is calibrated in real-time using a gaussmeter.

[0041] Test results show that when an external magnetic field is applied to the sensor, the Fe3O4 nanoparticles doped in the cladding exhibit a magnetostrictive effect, causing deformation of the polymer waveguide microcavity and resulting in an increase in the effective cavity length. This leads to a shift of the resonant wavelength of the Fabry-Perot interference spectrum towards longer wavelengths. As the magnetic field strength increases from 0 mT to 80 mT, the resonant wavelength exhibits a regular redshift. For the sensor with a UV / Fe3O4 mass ratio of 7:1, the wavelength shift exhibits excellent linearity across the entire measurement range. This is because at this ratio, the Fe3O4 nanoparticles are uniformly dispersed, providing sufficient magnetic response while avoiding agglomeration at high concentrations, ensuring stable transmission of magnetostriction. When the mass ratio is adjusted to 3:1, although the sensitivity is further improved, the linearity decreases slightly in the high magnetic field region. This is due to the reduced uniformity of nanoparticle dispersion caused by the high polymer content, introducing a slight nonlinear response. This invention achieves high-sensitivity, wide-range magnetic field sensing through a polymer optical waveguide structure and Fe3O4 doped cladding. It has the advantages of compact structure, simple fabrication, and stable performance, and is suitable for various scenarios such as industrial monitoring, biomagnetic signal detection, and spatial magnetic field distribution mapping.

[0042] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical methods and inventive concepts of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A wide-range, high-sensitivity magnetic field sensor based on a polymer optical waveguide, characterized in that, include: The first single-mode fiber (1) serves as the input and output channel for optical signals; The polymer optical waveguide (2) has its first end face coupled to the end face of the first single-mode fiber to form the sensing region of the Fabry-Perot interference microcavity. The cladding (3) of the polymer optical waveguide is doped with Fe3O4 nanoparticles. And a second single-mode fiber (5), the first end face of which is coupled to the second end face of the polymer waveguide. The second end face of the second single-mode fiber is provided with a high-reflection film (4) as the reflecting end face of the Fabry-Perot interference microcavity.

2. The wide-range, high-sensitivity vector magnetic field sensor based on polymer optical waveguide according to claim 1, characterized in that, The polymer optical waveguide adopts a refractive index distribution structure of "high refractive index core layer / low refractive index cladding layer". The core layer is composed of UV-curable adhesive, and the cladding layer is composed of UV-curable adhesive doped with Fe3O4 nanoparticles.

3. The wide-range, high-sensitivity vector magnetic field sensor based on a polymer optical waveguide according to claim 1 or 2, characterized in that, The cavity length of the polymer optical waveguide is 50 μm to 60 μm.

4. The wide-range, high-sensitivity vector magnetic field sensor based on polymer optical waveguide according to claim 3, characterized in that, The cavity length of the polymer optical waveguide is 55 μm.

5. The wide-range, high-sensitivity vector magnetic field sensor based on polymer optical waveguide according to claim 2, characterized in that, The mass ratio of the UV-curable adhesive forming the coating to the Fe3O4 nanoparticles is 3:1 to 10:

1.

6. The wide-range, high-sensitivity vector magnetic field sensor based on polymer optical waveguide according to claim 5, characterized in that, The mass ratio of the UV-curable adhesive to Fe3O4 nanoparticles is 3:1 to achieve the highest magnetic field sensitivity.

7. The wide-range, high-sensitivity vector magnetic field sensor based on polymer optical waveguide according to claim 5, characterized in that, The mass ratio of the UV-curable adhesive to Fe3O4 nanoparticles is 7:1 to achieve high linearity and stability over a wide range of 0-80 mT.

8. The wide-range, high-sensitivity vector magnetic field sensor based on polymer optical waveguide according to claim 1, characterized in that, The high-reflectivity film is a gold film.

9. A fiber optic magnetic field sensing device, characterized in that, Including the magnetic field sensor according to any one of claims 1-8.

10. The fiber optic magnetic field sensing device according to claim 9, characterized in that, It also includes a spectrometer (6), a broadband light source (7), and a circulator (8). The spectrometer (6) and the broadband light source (7) are connected through the circulator (8). The output port of the circulator (8) is connected to one end of a magnetic field sensor (10). The magnetic field sensor is placed between the two poles of an electromagnet (9). Changing the current of the electromagnet power supply (11) can change the magnetic field generated by the electromagnet (9). The magnetic field strength is obtained by demodulating the wavelength shift of the interference spectrum from the magnetic field sensor (10).

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