Mf-filled sagnac interferometer-based photonic crystal fiber and corresponding magnetic field sensor

Abstract

The application belongs to the technical field of sensors, and discloses a kind of MF filled photonic crystal fiber based on Sagnac interferometer, including perfect matching layer, background material;Background material is wrapped air hole, air hole is regularly distributed along the inner periphery of background material, air hole includes first air hole, second air hole, third air hole and fourth air hole that aperture increases gradually, and magnetic fluid is filled in air hole;The application also discloses a kind of magnetic field sensor, including the above-mentioned MF filled photonic crystal fiber based on Sagnac interferometer.The MF filled photonic crystal fiber based on Sagnac interferometer provided by the application has high linearity and high stability, and can improve the sensitivity and detection range of the magnetic field sensor.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology and relates to a photonic crystal fiber structure, specifically a MF-filled photonic crystal fiber based on a Sagnac interferometer and a corresponding magnetic field sensor. Background Technology

[0002] With the continuous development of science and technology, photonic crystal fibers (PCF) based on Sagnac interferometers have been widely used in optical sensing and detection, becoming a series of new research hotspots. Fiber optic sensors, with their advantages of electromagnetic interference resistance, high sensitivity, ease of cascading and multiplexing, and high degree of design freedom, are widely used in aerospace, electromagnetic measurement, electromagnetic braking, military, and medical fields.

[0003] The Faraday magneto-optical effect is a magneto-optical effect in which the polarization direction of linearly polarized light propagating in a medium rotates by an angle when an external magnetic field is applied. The magnitude of this rotation is proportional to the magnetic field strength. It is currently widely used in optical communication, such as in optical isolators and optical circulators. Magnetic field sensors utilizing the Faraday magneto-optical effect are divided into polarization-type and interferometric-type sensors. Polarization-type sensors directly measure the angle change of polarized light in the magnetic field to obtain the magnetic field strength; however, because this angle is very small, the sensitivity and accuracy of direct measurement are not high. Interferometric sensors convert the change in polarization angle into a change in phase, which can improve the detection sensitivity. For example, the two interferometric paths of a Sagnac interferometer are completely identical, and it is only sensitive to non-reciprocal magneto-optical effects, making it very suitable for magnetic field and current sensors. Therefore, it has attracted many researchers to explore the design of photonic crystal fibers based on Sagnac interferometers for magnetic field sensors.

[0004] After years of research and development, magnetic field sensors have achieved improvements in sensitivity, from low to high, from single-function to multi-function, and from complex and fragile structures to compact designs. For example, Mingjian Ma et al. proposed a Sagnac magnetofluid-filled magnetic field sensor, a dual-core PCF magnetic field sensor. Magnetofluid (MF) is filled in two central atmospheric pores, and its sensitivity is detected by observing the shift in the transmission spectrum peak under different applied magnetic fields. Its highest sensitivity is 709.9 pm / Oe. Qiang Liu et al. proposed a dual-core defect fiber magnetic field sensor. The sensitivity of the PCF sensor is detected by observing changes in the transmission spectrum peak position by altering the PCF length, temperature, and magnetic field strength. After testing, its maximum sensitivity reached 900 pm / Oe, but its detection range is only 50-80 Oe, which is very small.

[0005] Existing research has highlighted many advantages of photonic crystal fiber magnetic field sensors based on Sagnac interferometers, but they also have disadvantages such as poor sensitivity and small detection range, which limit the development of photonic crystal fiber magnetic field sensors based on Sagnac interferometers. Summary of the Invention

[0006] The purpose of this invention is to provide a MF-filled photonic crystal fiber based on a Sagnac interferometer, which can improve the sensitivity and detection range of a magnetic field sensor;

[0007] Another object of the present invention is to provide a magnetic field sensor that utilizes the aforementioned MF-filled photonic crystal fiber based on a Sagnac interferometer.

[0008] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0009] A MF-filled photonic crystal fiber magnetic field sensor based on a Sagnac interferometer includes a perfectly matched layer, a background material within the perfectly matched layer, and air holes encapsulated within the background material. In the cross-section of the MF-filled Sagnac interferometer-based photonic crystal fiber, the air holes are periodically distributed in a regular hexagonal pattern along the inner periphery of the background material, with the central air hole missing to form a core region. The air holes include a first air hole, a second air hole, a third air hole, and a fourth air hole with sequentially increasing diameters, and each air hole is filled with a magnetofluid.

[0010] In the hexagonal periodically distributed air holes, the two opposite sides of the innermost layer of air holes form the first air hole, and the remaining sides form the fourth air hole; the two opposite sides of the middle layer of air holes form the second air hole, and the remaining sides form the first air hole; the hexagonal structure formed by the outermost layer of air holes is the third air hole.

[0011] As a limitation, the periodically distributed hexagonal air holes are nested in three layers. The innermost layer of air holes forms a hexagonal structure with two air holes on each side, the middle layer of air holes forms a hexagonal structure with three air holes on each side, and the outermost layer of air holes forms a hexagonal structure with four air holes on each side.

[0012] The innermost air vents consist of two fourth air vents surrounded by ten first air vents.

[0013] As a further limitation, the diameter of the fourth air hole is 8.0 μm, the diameter of the third air hole is 5.8 μm, the diameter of the second air hole is 5.0 μm, and the diameter of the first air hole is 3.2 μm.

[0014] As a further limitation, the feature is that the center-to-center distance between adjacent air holes is 6 μm.

[0015] As a second limitation, the magnetic fluid is Fe3O4.

[0016] As a third limitation, the background material is fused silica.

[0017] The present invention also provides a magnetic field sensor, which includes a photonic crystal fiber based on a Sagnac interferometer filled with the MF described above, and also includes a broadband light source, a spectrometer, a 3dB coupler, a polarization controller, an electromagnet, a power supply, and a magnetic field measuring instrument.

[0018] The input of the 3dB coupler is connected to a broadband light source, and the output of the 3dB coupler is connected to a spectrometer. One end of the MF-filled photonic crystal fiber based on the Sagnac interferometer is connected to one of the remaining two ports of the 3dB coupler, and the other end is connected to the other port of the remaining two ports of the 3dB coupler through a polarization controller, forming a Sagnac ring structure. Electromagnets powered by a power supply are arranged on both sides of the MF-filled photonic crystal fiber based on the Sagnac interferometer, and a magnetic field measuring instrument is used to detect the magnetic field strength generated by the electromagnets.

[0019] The present invention, by adopting the above-described technical solution, achieves the following technical advancements compared to existing technologies:

[0020] (1) This invention has the advantages of wide detection range and high sensitivity, and at the same time, it has a simple structure and is easy to manufacture, which will play a very positive role in future production and life.

[0021] (2) In this invention, the diameter of the fourth air hole is 8.0 μm, the diameter of the third air hole is 5.8 μm, the diameter of the second air hole is 5.0 μm, the diameter of the first air hole is 3.2 μm, and the center distance between adjacent air holes is 6 μm. By controlling the waveguide characteristics and structure of the photonic crystal fiber, and because the Sagnac interferometer is extremely sensitive to changes in refractive index and has high linearity and high stability, the obtained magnetic field sensor has an average sensitivity of 685.71 pm / Oe and -809.52 pm / Oe in the magnetic field strength range of 90-240 Oe; and an average sensitivity of 659.05 pm / Oe and -758.10 pm / Oe in the magnetic field strength range of 420-570 Oe.

[0022] (3) The air holes of the present invention are filled with magnetic fluid. Since the magnetic fluid has both the fluidity of liquid and the magnetism of solid magnetic materials, the magnetic fluid exhibits many special magnetic, optical and electrical phenomena, such as Faraday effect, birefringence effect and linear dichroism. The magnetic field sensor of the present invention utilizes the interference principle of Faraday magneto-optical effect.

[0023] In summary, the MF-filled photonic crystal fiber magnetic field sensor based on the Sagnac interferometer provided by this invention has high linearity and high stability, which can improve the sensitivity and detection range of the magnetic field sensor. Attached Figure Description

[0024] Figure 1 The figure shown is a schematic cross-sectional view of the MF-filled photonic crystal fiber based on the Sagnac interferometer in Embodiment 1 of the present invention;

[0025] Figure 2 The diagram shown is a schematic representation of the magnetic field sensor in Embodiment 2 of the present invention.

[0026] Figure 3 The figure shows the relationship between the effective refractive index and the magnetic field strength of the magnetic fluid filling the air hole in Embodiment 2 of the present invention;

[0027] Figure 4 The figure shows the relationship between transmission and wavelength of the magnetic field sensor of Embodiment 2 of the present invention under different magnetic field strengths (90-240 Oe) when the filling magnetic fluid concentration is 25%.

[0028] Figure 5 The figure shows the relationship between the immersion wavelength and different magnetic field strengths (90-240 Oe) of the magnetic field sensor in Embodiment 2 of the present invention after linear fitting;

[0029] Figure 6 The figure shows the relationship between transmission and wavelength of the magnetic field sensor of Embodiment 2 of the present invention under different magnetic field strengths (420-570 Oe) when the filling magnetic fluid concentration is 16.7%.

[0030] Figure 7 The figure shows the relationship between the immersion wavelength and different magnetic field strengths (420-570 Oe) of the magnetic field sensor in Embodiment 2 of the present invention after linear fitting;

[0031] In the figure: 1. Perfectly matched layer; 2. Background material; 3. First air hole; 4. Second air hole; 5. Third air hole; 6. Fourth air hole; 7. Broadband light source; 8. Spectrometer; 9. 3dB coupler; 10. Polarization controller; 11. Electromagnet; 12. MF-filled photonic crystal fiber based on Sagnac interferometer; 13. Power supply; 14. Magnetic field measuring instrument. Detailed Implementation

[0032] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1: A MF-filled photonic crystal fiber based on a Sagnac interferometer

[0034] like Figure 1 As shown, this embodiment includes a perfect matching layer 1, a background material 2 is provided in the perfect matching layer 1, and air holes are wrapped in the background material 2. In the cross-section of the MF-filled photonic crystal fiber 12 based on the Sagnac interferometer, the air holes are periodically distributed in a regular hexagonal shape along the inner periphery of the background material 2. The missing central air hole constitutes the core region. The air holes include a first air hole 3, a second air hole 4, a third air hole 5 and a fourth air hole 6 with successively increasing diameters. All air holes are filled with magnetic fluid.

[0035] The hexagonal air holes are arranged in three nested layers. The innermost layer of air holes forms a hexagonal structure with two air holes on each side, and the two opposite sides of the innermost layer are first air holes 3, while the remaining sides are fourth air holes 6. The middle layer of air holes forms a hexagonal structure with three air holes on each side, and the two opposite sides of the middle layer are second air holes 4, while the remaining sides are first air holes 3. The outermost layer of air holes forms a hexagonal structure with four air holes on each side, and the outermost layer of air holes forms a hexagonal structure with third air holes 5. The two fourth air holes 6 in the innermost layer are surrounded by ten first air holes 3.

[0036] In this embodiment, the magnetic fluid filling the air holes is Fe3O4, the background material 2 is fused silica, the diameter of the two middle fourth air holes 6 is 8.0 μm, the diameter of the outermost third air hole 5 is 5.8 μm, the diameter of the second air hole 4 is 5.0 μm, the diameter of the first air hole 3 is 3.2 μm, and the center distance between adjacent air holes is 6 μm.

[0037] Example 2: A magnetic field sensor

[0038] like Figure 2 As shown, this embodiment includes a photonic crystal fiber 12 based on a Sagnac interferometer filled with MF as in Embodiment 1, and also includes a broadband light source 7, a spectrometer 8, a 3dB coupler 9, a polarization controller 10, an electromagnet 11, a power supply 13, and a magnetic field measuring instrument 14.

[0039] The input of the 3dB coupler 9 is connected to the broadband light source 7, and the output of the 3dB coupler 9 is connected to the spectrometer 8. One end of the MF-filled photonic crystal fiber 12 based on the Sagnac interferometer is connected to one of the remaining two ports of the 3dB coupler 9, and the other end is connected to the other port of the remaining two ports of the 3dB coupler 9 through the polarization controller 10, forming a Sagnac ring structure. Electromagnets 11 powered by the power supply 13 are arranged on both sides of the MF-filled photonic crystal fiber 12 based on the Sagnac interferometer, and the magnetic field measuring instrument 14 is used to detect the magnetic field strength generated by the electromagnets 11.

[0040] In this embodiment, the broadband light source 7 outputs laser light to the 3dB coupler 9. The 3dB coupler 9 splits the laser light output from the broadband light source 7 into two polarized beams that propagate in clockwise and counterclockwise directions. The two polarized beams converge after circulating in opposite directions within the same loop. The polarization controller 10 rotates the polarization direction of the two polarized beams. A magnetic field is generated by electromagnets 11 powered by power supply 13 on both sides of the MF-filled photonic crystal fiber 12 based on a Sagnac interferometer, causing a phase difference between the two polarized beams. This results in interference fringes at the output of the 3dB coupler 9 for the two beams propagating in clockwise and counterclockwise directions. The spectrometer 8 measures the interference spectrum output by the 3dB coupler 9. When the magnetic field strength changes, the interference fringes on the screen of the spectrometer 8 will move, thus realizing the detection of the sensing performance of the magnetic field sensor in this embodiment based on the displacement of the immersion wavelength obtained under different magnetic field strengths.

[0041] In this embodiment, at an ambient temperature of 20°C, the following results were obtained: Figure 3 The relationship between the effective refractive index and magnetic field strength of the magnetic fluid filling the air hole shown is derived from... Figure 3 It can be seen that at an ambient temperature of 20℃, the effective refractive index of the magnetofluid increases with the increase of the magnetic field strength. When the magnetofluid concentration is 25%, the magnetic field exhibits a linear variation in the range of 90-390 Oe, and the fitting equation is y=7.9584E-6x+1.34046, R 2 The value is 1; when the magnetofluid concentration is 16.7%, the magnetic field exhibits a linear variation in the range of 420-630 Oe, and the fitting equation is y=7.44632E-6x+1.33632, R 2 The value is 1.

[0042] In this embodiment, the fiber length L of the MF-filled photonic crystal fiber 12 based on the Sagnac interferometer is set to 8.3 cm, resulting in the following: Figure 4 The diagram shows the relationship between transmission and wavelength of the magnetic field sensor under different magnetic field strengths (90-240 Oe). Figure 4The study demonstrates the dependence of the transmission of the tunable wavelength on different magnetic field strengths within the magnetic field range of 90-240 Oe when the filling magnetic fluid concentration is 25%. As the magnetic field increases, the immersion wavelength A undergoes a red shift and the immersion wavelength B undergoes a blue shift. Furthermore, the greater the magnetic field, the greater the shift in the immersion wavelength, which means the greater the sensitivity. Figure 5 The figure shows the relationship between the immersion wavelength and different magnetic field strengths (90-240 Oe) after linear fitting of the magnetic field sensor. It indicates that the immersion wavelength A increases with increasing magnetic field strength H, while the immersion wavelength B decreases with increasing magnetic field strength H, with the change being more pronounced at higher magnetic fields. The fitting equations for immersion wavelengths A and B are y = 6.85714E-4x + 2.26486 and y = -8.09524E-4x + 2.90857, respectively. R0 2 The values ​​are 0.98891 and 0.99367, respectively. Since the magnetic field strength is in Oe and the immersion wavelength is in μm, the average sensitivities are 685.71 pm / Oe and -809.52 pm / Oe, respectively.

[0043] In this embodiment, the fiber length L of the MF-filled photonic crystal fiber 12 based on the Sagnac interferometer is set to 8.9 cm, resulting in the following: Figure 6 The diagram shows the relationship between transmission and wavelength of the magnetic field sensor under different magnetic field strengths (420-570 Oe). Figure 6 The study demonstrates the transmission dependence of different magnetic fields on the tunable wavelength in the magnetic field range of 420-570 Oe when the filling magnetic fluid concentration is 16.7%. As the magnetic field increases, the immersion wavelengths A and B shift in opposite directions, and the shift of the immersion wavelengths increases with the increase of the magnetic field. Figure 7 The figure shows the relationship between the immersion wavelength and different magnetic field strengths (420-570 Oe) after linear fitting of the magnetic field sensor. It indicates that the immersion wavelength A increases with increasing magnetic field strength H, while the immersion wavelength B decreases with increasing magnetic field strength H, and the change is more pronounced with increasing magnetic field strength H. The fitting equations for immersion wavelengths A and B are y = 6.59048E-4x + 2.07777 and y = -7.58095E-4x + 3.16659, respectively. R0 2 The values ​​were 0.99001 and 0.99100, respectively, with average sensitivities of 659.05 pm / Oe and -758.10 pm / Oe.

[0044] By numerically analyzing the relationship between the immersion wavelength and the magnetic field of the photonic crystal fiber magnetic field sensor in this embodiment, it can be seen that the MF-filled photonic crystal fiber 12 based on the Sagnac interferometer in this embodiment has excellent sensing performance and a very large detection range.

[0045] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A MF-filled photonic crystal fiber based on a Sagnac interferometer, characterized in that, It includes a perfectly matched layer containing a background material, which contains air holes. In the cross-section of the MF-filled photonic crystal fiber based on the Sagnac interferometer, the air holes are periodically distributed in a regular hexagonal pattern along the inner periphery of the background material, wherein the missing central air hole constitutes the core region. The air holes include a first air hole, a second air hole, a third air hole, and a fourth air hole with successively increasing diameters, and each air hole is filled with a magnetic fluid. In the hexagonal periodically distributed air holes, the two opposite sides of the innermost layer of air holes form the first air hole, and the remaining sides form the fourth air hole; the two opposite sides of the middle layer of air holes form the second air hole, and the remaining sides form the first air hole; the hexagonal structure formed by the outermost layer of air holes is the third air hole.

2. The MF-filled photonic crystal fiber based on a Sagnac interferometer according to claim 1, characterized in that, The regular hexagonal periodically distributed air holes are nested in three layers. The innermost layer of air holes forms a regular hexagonal structure with two air holes on each side, the middle layer of air holes forms a regular hexagonal structure with three air holes on each side, and the outermost layer of air holes forms a regular hexagonal structure with four air holes on each side. The innermost air vents consist of two fourth air vents surrounded by ten first air vents.

3. The MF-filled photonic crystal fiber based on a Sagnac interferometer according to claim 2, characterized in that, The diameter of the fourth air hole is 8.0 μm, the diameter of the third air hole is 5.8 μm, the diameter of the second air hole is 5.0 μm, and the diameter of the first air hole is 3.2 μm.

4. The MF-filled photonic crystal fiber based on a Sagnac interferometer according to claim 3, characterized in that, The center-to-center distance between adjacent air holes is 6 μm.

5. The MF-filled photonic crystal fiber based on a Sagnac interferometer according to any one of claims 1 to 4, characterized in that, The magnetic fluid is Fe3O4.

6. The MF-filled photonic crystal fiber based on a Sagnac interferometer according to any one of claims 1 to 4, characterized in that, The background material is fused silica.

7. A magnetic field sensor, characterized in that, The magnetic field sensor includes a Sagnac interferometer-based photonic crystal fiber filled with MF as described in any one of claims 1 to 6, and also includes a broadband light source, a spectrometer, a 3dB coupler, a polarization controller, an electromagnet, a power supply, and a magnetic field measuring instrument. The input of the 3dB coupler is connected to a broadband light source, and the output of the 3dB coupler is connected to a spectrometer. One end of the MF-filled photonic crystal fiber based on the Sagnac interferometer is connected to one of the remaining two ports of the 3dB coupler, and the other end is connected to the other port of the remaining two ports of the 3dB coupler through a polarization controller, forming a Sagnac ring structure. Electromagnets powered by a power supply are arranged on both sides of the MF-filled photonic crystal fiber based on the Sagnac interferometer, and a magnetic field measuring instrument is used to detect the magnetic field strength generated by the electromagnets.

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