Four-core optical fiber multi-parameter sensor based on spiral structure and preparation method thereof

Abstract

The invention relates to a four-core optical fiber multi-parameter sensor based on a spiral structure and a preparation method thereof, the sensor is manufactured by cascading a single-mode optical fiber, a four-core optical fiber and a single-mode optical fiber, and the middle position of the four-core optical fiber is arranged to be a spiral structure; the whole cascade of the sensor is subjected to discharge welding by using a welding machine, and different discharge parameters are set to perform welding of different optical fibers; the spiral structure is manufactured by using a polarization maintaining optical fiber fusion splicer, and spiral structures with different parameters are manufactured by adjusting a program of the fusion splicer; the spiral structure optical fiber sensor is mainly used for sensing parameters of different axial forces, when the axial force is applied to the sensor, the transmission spectrum of the sensor drifts along with the magnitude of the applied force, and the spiral structure optical fiber sensor of the lattice four-core optical fiber is compact in structure, simple in preparation method and capable of being applied to multiple sensing fields of stress, temperature, torsion and the like.

Description

Technical Field

[0001] This invention relates to the field of multi-core fiber optic sensing technology, and in particular to a four-core fiber optic multi-parameter sensor based on a helical structure and its fabrication method. Background Technology

[0002] Since the 1970s, fiber optic sensors have attracted considerable attention from researchers due to their unique advantages. These advantages include high sensitivity, wide dynamic range, fast response speed, micron-sized components, good biocompatibility, high mechanical strength, and low cost. In recent years, fiber optic sensors employing microcavity structures have been widely used in industrial production, biomedicine, aerospace, and other fields, enabling the measurement of physical parameters such as temperature, pressure, strain, and refractive index.

[0003] In deformation sensing for AI robots, parameters such as torsion and vector bending are crucial. However, since most optical fibers are circularly symmetrical, most fiber optic torsion sensors can only detect the magnitude of the torsion, not its direction. Pre-twisted optical fibers break the circular symmetry of the fiber. Therefore, this invention introduces a helical torsion chiral structure to increase the sensor's torsion sensitivity and torsion direction recognition.

[0004] Chiral helical multicore optical fibers exhibit enhanced coupling between fiber cores due to their helical structure, and their axial non-uniformity makes them superior to ordinary multicore optical fibers in sensing and OAM mode modulation. Ordinary multicore optical fibers can be used in torsion sensing, but they cannot identify the direction of torsion. In torsion measurements, the pitch length of chiral helical multicore optical fibers varies with the direction of torsion. Therefore, chiral helical multicore optical fibers can not only increase torsion sensitivity but also identify the direction of their own torsion. Therefore, research on helical multicore optical fiber sensors is of great significance. Summary of the Invention

[0005] To address the aforementioned problems, the present invention provides a four-core fiber optic multi-parameter sensor based on a helical structure and its fabrication method. This sensor features a novel structure, low cost, and is suitable for measuring various parameters. It combines the advantages of multi-core fiber with those of helical fiber, thereby improving the sensitivity of multi-core fiber sensing.

[0006] The technical solution adopted in this invention is as follows:

[0007] The present invention proposes a four-core fiber optic multi-parameter sensor based on a helical structure, comprising a single-mode fiber and a four-core fiber; the single-mode fiber is cascaded at both ends of the four-core fiber; and the middle region of the four-core fiber is configured with a helical structure.

[0008] Furthermore, the cladding diameter of the single-mode fiber is 120~130μm, and the core diameter is 8~10μm; the cladding diameter of the four-core fiber is 120~130μm, and the four cores are arranged in a lattice triangle structure.

[0009] Furthermore, the spacing between the middle core and the outer core of the four-core optical fiber is 25μm~35μm, the spacing between the outer cores is 35μm~55μm and they form an equilateral triangle around the middle core, and the diameter of each of the four cores is 8μm~12μm.

[0010] Furthermore, the spiral structure is either a centerless offset spiral structure or a center-offset spiral structure.

[0011] Furthermore, the length of the spiral structure is 5mm to 10mm, and the spiral angle is 360° to 7200°.

[0012] A method for fabricating a four-core fiber optic multi-parameter sensor based on a helical structure, the method comprising the following steps: S1: First, prepare the required single-mode fiber and four-core fiber, remove the fiber coating and clean the surface impurities, and then cut the fiber to the required length for later use. S2: Place the single-mode fiber and the lattice four-core fiber at both ends of the fusion splicer, fused together and cascaded to prepare a cascaded structure of single-mode fiber-four-core fiber-single-mode fiber. S3: Place the single-mode fiber-four-core fiber-single-mode fiber cascade structure in a polarization-maintaining fusion splicer to create the helical structure in the middle of the four-core fiber.

[0013] Furthermore, in step S2, the welding parameters are set as follows: discharge intensity of 100~150mA, discharge time of 150~250ms, advance distance of 15~25μm, and discharge times of one.

[0014] Furthermore, in step S3, when the spiral structure is a center-offset spiral structure, the fabrication process is as follows: (1) Place the single-mode fiber-four-core fiber-single-mode fiber cascade structure in the polarization-maintaining fusion splicer, with the discharge electrode located 5-10 mm to the right of the center of the four-core fiber; (2) Move the sweep motor to the left at a speed of 0.5-1.5 μm / ms for a time of 4000-8000 ms; (3) Set the discharge current to 11-14 mA. The sweep motor moves to the right at a speed of 0.01~0.1 μm / ms for a duration of 100,000~200,000 ms. The left motor moves to the left at a speed of 0.01~0.03 μm / ms, and the right motor moves to the left at a speed of 0.05~0.025 μm / ms. Simultaneously, the rotary motor begins to rotate at a speed of 0.03~0.08° / ms for a duration of 100,000~200,000 ms.

[0015] Furthermore, in step S3, when the spiral structure is a center-offset spiral structure, the fabrication process is as follows: (1) Place the single-mode fiber-four-core fiber-single-mode fiber cascade structure in the polarization-maintaining fusion splicer, with the discharge electrode located 5-15 mm to the right of the center of the four-core fiber; (2) Move the sweep motor to the left at a speed of 0.05-0.1 μm / ms for a time of 5000-10000 ms; (3) Set the discharge current to 11-14 mM A. The sweep motor moves to the right at a speed of 0.01~0.1μm / ms for a time of 100,000~200,000ms. The left motor moves to the left at a speed of 0.05~0.025μm / ms. The right motor moves to the left at a speed of 0.1~0.03μm / ms. Simultaneously, the rotary motor starts rotating at a speed of 0.03~0.08° / ms for a time of 100,000~200,000ms.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a spiral method to fabricate the spiral structure, which significantly improves the sensitivity of the fiber optic sensor to strain and torsion. The sensor structure adopts a cascaded structure, making the sensor structure relatively simple and easier to fabricate. By changing the discharge program parameters, different types of spiral four-core fiber structures can be fabricated, making the sensor's application range wider. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the sensor structure without center offset in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the sensor structure with center offset in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the end face structure of the four-core optical fiber used in this invention; Figure 4 yes Figure 1 A schematic diagram of a microscope showing a medium-helical structure; Figure 5 yes Figure 2 A schematic diagram of a microscope showing a medium-helical structure; Figure 6 This is a schematic diagram of the manufacturing process of the spiral structure in this invention; Figure 7 This is a schematic diagram of the initial transmission spectrum of the sensorless transmission spectrum in this invention. Figure 8 This is a schematic diagram of the temperature transmission spectrum in the present invention without a center offset sensor; Figure 9 This is a schematic diagram of the fitting results of wavelength drift and temperature change in the temperature experiment without a center offset sensor in this invention; Figure 10 This is a schematic diagram of the strain transmission spectrum in the present invention without a center offset sensor; Figure 11 This is a schematic diagram of the fitting results between wavelength drift and temperature change in a strain experiment without a center offset sensor in this invention; Figure 12 This is the transmission spectrum of the torsion experiment of the spiral four-core fiber optic sensor without center offset in this invention; Figure 13 This is the fitting result of wavelength drift and temperature change in the torsion experiment of the spiral four-core fiber optic sensor without center offset in this invention; Figure 14 This is a schematic diagram of the torsional transmission spectrum of the present invention with a center offset sensor; Figure 15 This is a schematic diagram of the fitting results of the strain experiment wavelength drift and torsional change with a center offset sensor in this invention; Figure 16 This is a schematic diagram of the strain experiment transmission spectrum with a center offset sensor in this invention; Figure 17 This is a schematic diagram of the fitting results of wavelength drift and strain change in a strain experiment with a center offset sensor in this invention; In the attached diagram, the following labels are used: 1-single-mode fiber; 2-four-core fiber; 3-helical structure. Detailed Implementation

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] It should be noted that in the description of this invention, the terms "upper", "lower", "top", "bottom", "one side", "the other side", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not mean that the device or element must have a specific orientation, or be constructed and operated in a specific orientation.

[0020] Example 1 See appendix Figure 1 The present embodiment proposes a four-core fiber optic multi-parameter sensor based on a spiral structure, comprising a single-mode fiber 1 and a four-core fiber 2; the single-mode fiber 1 is cascaded at both ends of the four-core fiber; in this embodiment, the middle region of the four-core fiber 2 is configured as a center-offset spiral structure 3; the length of the spiral structure portion is 5mm~10mm, and the spiral angle is 360°~7200°.

[0021] The single-mode fiber 1 has a cladding diameter of 120-130 μm and a core diameter of 8-10 μm; the four-core fiber 2 has a cladding diameter of 120-130 μm and the four cores are arranged in a lattice triangle structure.

[0022] The spacing between the middle core and the outer core of the four-core optical fiber 2 is 25μm~35μm, and the spacing between the outer cores is 35μm~55μm, forming an equilateral triangle around the middle core. The diameter of each of the four cores is 8μm~12μm.

[0023] Example 2 like Figure 2 As shown, the four-core fiber optic multi-parameter sensor based on a helical structure proposed in this embodiment differs from prior art document 1 in that the central region of the four-core fiber 2 is configured with a center-offset helical structure 4. Other structures are the same as in prior art document 1.

[0024] The following specific examples further illustrate the fabrication process of the aforementioned sensor: A method for fabricating a four-core fiber optic multi-parameter sensor based on a helical structure, utilizing the arc discharge method, specifically includes the following steps: S1: First, prepare the required single-mode fiber 1 and four-core fiber 2. The parameters of each fiber are as follows: the cladding diameter of the single-mode fiber 1 is 125μm, and the core diameter is 9μm; the cladding diameter of the four-core fiber 2 is 125μm, and its four cores are arranged in a lattice triangular structure, with a spacing of 56.4μm between the outer cores, forming an equilateral triangle around the central core. The diameter of all cores is 8.5μm. Next, use wire strippers to remove the fiber coating and wipe with alcohol to remove impurities. Finally, use a cleaver to cut the fiber to the required length for later use. The length of the four-core fiber 2 is 3~10cm; in this embodiment, it is 4cm.

[0025] S2: Place the single-mode fiber 1 and the prepared 4cm lattice four-core fiber 2 at both ends of the fusion splicer. After splicing, cascade the single-mode fiber 1 at both ends of the lattice four-core fiber 2 to prepare a cascaded structure of single-mode fiber 1-four-core fiber 2-single-mode fiber 1. The welding parameters are set as follows: discharge intensity is 100~150mA, 110mA in this embodiment; discharge time is 150~250ms, 200ms in this embodiment; advance distance is 15~25μm, 17μm in this embodiment; and the number of discharges is once.

[0026] S3: Place the cascaded structure of single-mode fiber 1 - four-core fiber 2 - single-mode fiber 1 in a polarization-maintaining fusion splicer to create a helical structure in the middle of the four-core fiber, such as... Figure 6 As shown.

[0027] When the spiral structure has no center offset spiral structure 3, the fabrication process is as follows: (1) Place the cascaded structure of single-mode fiber 1-four-core fiber 2-single-mode fiber 1 prepared in step S2 in the polarization-maintaining fusion splicer to make the spiral structure (3), the discharge electrode is located 5~10mm to the right of the center of the four-core fiber, which is 6mm in this embodiment; (2) The sweep motor moves to the left, the moving speed is 0.5~1.5μm / ms, which is 1μm / ms in this embodiment; the moving time is 4000~8000ms, which is 6000ms in this embodiment; (3) The discharge current intensity is set to 11~14mA, which is 12.6mA in this embodiment; the sweep motor moves to the right, the moving speed is 0.5~1.5μm / ms, which is 1μm / ms in this embodiment; the moving time is 4000~8000ms, which is 6000ms in this embodiment; (4) The discharge current intensity is set to 11~14mA, which is 12.6mA in this embodiment; the sweep motor moves to the right, the moving speed is 0.5~1.5μm / ms, which is 1μm / ms in this embodiment; the moving time is 4000~8000ms, which is 6000ms in this embodiment; the moving time is 0.5~1.5μm / ms, which is 1μm / ... The speed is 0.01~0.1 μm / ms, 0.05 μm / ms in this embodiment; the movement time is 100,000~200,000 ms, 150,000 ms in this embodiment; the left motor moves to the left at a speed of 0.01~0.03 μm / ms, 0.015 μm / ms in this embodiment; the right motor moves to the left at a speed of 0.025~0.05 μm / ms, 0.03 μm / ms in this embodiment; simultaneously, the rotary motor starts rotating at a speed of 0.03~0.08° / ms, 0.05° / ms in this embodiment, and the rotation time is 100,000~200,000 ms, 150,000 ms in this embodiment. Through the above steps, a four-core fiber optic spiral structure sensor without center offset can be fabricated.

[0028] Connect one end of the fabricated sensor to a light source and the other end to a spectrometer. The light source used is a broadband light source, and the spectrometer used is an AQ6375 optical spectrometer. The original spectrum of the sensor is shown below. Figure 7 As shown.

[0029] Temperature, stress, and torsion experiments were conducted on the fabricated four-core fiber optic helical structure sensor without center offset. A temperature, strain, and torsion experimental system was built. The sensor was connected to a light source and a spectrometer at both ends. The light source used was a broadband light source, and the spectrometer used was an AQ6375 optical spectrometer. The temperature, strain, and torsion sensing experiments of the sensor were carried out in a laboratory temperature environment of 23℃.

[0030] like Figure 8 As shown, the sensor drifts at different temperatures. During the temperature sensing experiment, the resonance peak exhibits a redshift. Figure 9 As shown, within the temperature range of 25℃ to 100℃, the temperature sensitivity at dip1 is 58.8 pm / ℃ with a linear fit of 0.992, and the temperature sensitivity at dip2 is 72.5 pm / ℃ with a linear fit of 0.994.

[0031] like Figure 10As shown, the sensor drifts under different strains. During the strain sensing experiment, the resonance peak exhibits a blue shift as the strain increases. Figure 11 As shown, within the strain range of 0~1300με, the strain sensitivity at dip1 is -0.66nm / mε with a linear fit of 0.997, and the strain sensitivity at dip2 is -0.617nm / mε with a linear fit of 0.997.

[0032] like Figure 12 As shown, the sensor drifts under different torsion rates. During the torsion sensing experiment, the resonance peak exhibits a redshift phenomenon as the torsion angle increases, as shown... Figure 13 As shown, within the torsion range of 0~20.94 rad / m, the torsional sensitivity at dip1 is 52 pm / (rad / m) with a linear fit of 0.992, and the torsion sensitivity at dip2 is 124 pm / (rad / m) with a linear fit of 0.997.

[0033] When the spiral structure is a center-offset spiral structure 4, the manufacturing process is as follows: (1) Place the cascaded structure of single-mode fiber 1-four-core fiber 2-single-mode fiber 1 in the polarization-maintaining fusion splicer, change the discharge program parameters, and position the discharge electrode 5~15mm to the right of the center of the four-core fiber, which is 10mm in this embodiment; (2) Move the sweep motor to the left at a speed of 0.05~0.1μm / ms, which is 0.06μm / ms in this embodiment; the moving time is 5000~10000ms, which is 8000ms in this embodiment; (3) Set the discharge current to 11~14mA, which is 13.1mA in this embodiment; move the sweep motor to the right at a speed of 0 The moving speed is 0.01~0.1μm / ms, 0.07μm / ms in this embodiment; the moving time is 100,000~200,000ms, 150,000ms in this embodiment; the left motor moves to the left at a speed of 0.025~0.05μm / ms, 0.03μm / ms in this embodiment; the right motor moves to the left at a speed of 0.01~0.03μm / ms, 0.015μm / ms in this embodiment; simultaneously, the rotary motor starts rotating at a speed of 0.03~0.08° / ms, 0.05° / ms in this embodiment; the rotation time is 100,000~200,000ms, 150,000ms in this embodiment. Through the above steps, a four-core fiber optic spiral structure sensor with center offset can be fabricated.

[0034] Torsion and strain experiments were conducted on the fabricated four-core fiber optic helical structure sensor with center offset: A torsion and strain experimental system was built, with a light source and a spectrometer connected to both ends of the sensor. The light source used was a broadband light source, and the spectrometer used was an AQ6375 optical spectrometer. Temperature, strain, and torsion sensing experiments of the sensor were carried out in a laboratory temperature environment of 23℃.

[0035] like Figure 14 As shown, the sensor drifts under different torsion rates. During the torsion sensing experiment, the resonance peak exhibits a blue shift as the torsion angle increases, as shown... Figure 15 As shown, the torsional sensitivity at dip1 is -64.7 pm / (rad / m) with a linear fit of 0.998; the torsion sensitivity at dip2 is -64 pm / (rad / m) with a linear fit of 0.985; the torsion sensitivity at dip3 is -118 pm / (rad / m) with a linear fit of 0.994; and the torsion sensitivity at dip4 is -103 pm / (rad / m) with a linear fit of 0.978.

[0036] like Figure 16 As shown, the sensor drifts under different strains. During the strain sensing experiment, the resonance peak exhibits a blue shift as the strain increases. Figure 17 As shown, within the strain range of 0~1300με, the strain sensitivity at dip1 is -2.83nm / mε with a linear fit of 0.998, the strain sensitivity at dip2 is -3.15nm / mε with a linear fit of 0.986, the strain sensitivity at dip3 is -4.95nm / mε with a linear fit of 0.985, and the strain sensitivity at dip4 is -3.76nm / mε with a linear fit of 0.995.

[0037] In the above examples, refer to Figures 7-17 It is evident that both types of helical four-core fiber optic sensors prepared by this invention can achieve multi-parameter sensing and detection. Furthermore, the sensing principles of these two sensor configurations are completely different. Due to the enhanced sensitivity of the helical structure to torsion, the sensor prepared by this invention can better detect torsional parameters. Therefore, this sensor possesses advantages such as novel and compact structure, high sensitivity, and simultaneous detection of multiple parameters, and can be widely applied in fields such as aviation safety, transportation pipelines, and structural safety.

[0038] Matters not covered in this invention are common knowledge.

[0039] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A four-core fiber optic multi-parameter sensor based on a helical structure, characterized in that: The sensor includes a single-mode fiber and a four-core fiber; the single-mode fiber is cascaded at both ends of the four-core fiber; the middle region of the four-core fiber is configured as a spiral structure.

2. The four-core fiber optic multi-parameter sensor based on a helical structure according to claim 1, characterized in that: The single-mode fiber has a cladding diameter of 120~130μm and a core diameter of 8~10μm; the four-core fiber has a cladding diameter of 120~130μm and the four cores are arranged in a lattice triangle structure.

3. A four-core fiber optic multi-parameter sensor based on a helical structure according to claim 2, characterized in that: The spacing between the middle core and the outer core of the four-core optical fiber is 25μm~35μm, and the spacing between the outer cores is 35μm~55μm, forming an equilateral triangle around the middle core. The diameter of each of the four cores is 8μm~12μm.

4. A four-core fiber optic multi-parameter sensor based on a helical structure according to claim 1, characterized in that: The spiral structure is either a spiral structure without center offset or a spiral structure with center offset.

5. A four-core fiber optic multi-parameter sensor based on a helical structure according to claim 4, characterized in that: The length of the spiral structure is 5mm to 10mm, and the spiral angle is 360° to 7200°.

6. The method for fabricating a four-core fiber optic multi-parameter sensor based on a helical structure according to claim 5, characterized in that: The method includes the following steps: S1: First, prepare the required single-mode fiber and four-core fiber, remove the fiber coating and clean the surface impurities, and then cut the fiber to the required length for later use. S2: Place the single-mode fiber and the lattice four-core fiber at both ends of the fusion splicer, fused together and cascaded to prepare a cascaded structure of single-mode fiber-four-core fiber-single-mode fiber. S3: Place the single-mode fiber-four-core fiber-single-mode fiber cascade structure in a polarization-maintaining fusion splicer to create the helical structure in the middle of the four-core fiber.

7. The method for fabricating a four-core fiber optic multi-parameter sensor based on a helical structure according to claim 6, characterized in that: In step S2, the welding parameters are set as follows: discharge intensity of 100~150mA, discharge time of 150~250ms, advance distance of 15~25μm, and discharge times of one.

8. The method for fabricating a four-core fiber optic multi-parameter sensor based on a helical structure according to claim 6, characterized in that: In step S3, when the spiral structure is a center-offset spiral structure, the fabrication process is as follows: (1) Place the single-mode fiber-four-core fiber-single-mode fiber cascade structure in the polarization-maintaining fusion splicer, with the discharge electrode located 5-10 mm to the right of the center of the four-core fiber; (2) Move the sweep motor to the left at a speed of 0.5-1.5 μm / ms for a time of 4000-8000 ms; (3) Set the discharge current to 11-14 mA. The EEP motor moves to the right at a speed of 0.01~0.1 μm / ms for a duration of 100,000~200,000 ms. The left motor moves to the left at a speed of 0.01~0.03 μm / ms, and the right motor moves to the left at a speed of 0.05~0.025 μm / ms. Simultaneously, the rotary motor begins to rotate at a speed of 0.03~0.08° / ms for a duration of 100,000~200,000 ms.

9. The method for fabricating a four-core fiber optic multi-parameter sensor based on a helical structure according to claim 6, characterized in that: In step S3, when the spiral structure is a spiral structure with a center offset, the fabrication process is as follows: (1) Place the single-mode fiber-four-core fiber-single-mode fiber cascade structure in the polarization-maintaining fusion splicer, with the discharge electrode located 5-15 mm to the right of the center of the four-core fiber; (2) Move the sweep motor to the left at a speed of 0.05-0.1 μm / ms for a time of 5000-10000 ms; (3) Set the discharge current to 11-14 mA. The sweep motor moves to the right at a speed of 0.01~0.1μm / ms for a duration of 100,000~200,000ms. The left motor moves to the left at a speed of 0.05~0.025μm / ms, and the right motor moves to the left at a speed of 0.1~0.03μm / ms. Simultaneously, the rotary motor begins to rotate at a speed of 0.03~0.08° / ms for a duration of 100,000~200,000ms.

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