Method for manufacturing core-offset tapered fiber fabry-perot interferometer strain sensor
By constructing a core-offset tapered fiber Fabry-Perot interferometer strain sensor with a conical cladding and an ellipsoidal bubble at the fiber splice, the problems of fragile sensor structure and insufficient sensitivity are solved, achieving high-sensitivity strain measurement and reducing manufacturing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHEAST GASOLINEEUM UNIV
- Filing Date
- 2023-05-15
- Publication Date
- 2026-06-02
AI Technical Summary
Existing fiber optic Fabry-Perot interferometer strain sensors are structurally fragile and lack sufficient sensitivity in high-resolution micro-strain detection, making it difficult to improve the sensitivity of stress measurement while maintaining structural strength.
A strain sensor fabrication method using a core-offset tapered fiber Fabry-Perot interferometer is employed. By forming a tapered cladding and an ellipsoidal bubble at the fiber splice, the beam propagation trajectory is altered, thereby enhancing the sensitivity of strain measurement.
Under the same structural strength, it significantly improves strain sensitivity by more than 30%, and the sensor has a compact structure, is simple to manufacture, and has low cost.
Smart Images
Figure CN116719126B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of optical fiber application technology, specifically relating to a method for fabricating a strain sensor for a Fabry-Perot interferometer using a core-offset tapered optical fiber. Background Technology
[0002] Fiber optic sensors, due to their small size, light weight, high sensitivity, and strong resistance to electromagnetic interference, have been widely used in structural health monitoring, medical monitoring, and biochemical sensing. In strain measurement, fiber Bragg gratings, Mach-Zernd interferometers, and Fabry-Perot interferometers (FPIs) have been extensively studied. Compared with other sensors, FPI-based fiber optic sensors offer advantages such as high sensitivity, linear response, compact structure, and ease of manufacturing. Among these, due to the low coefficients of thermal expansion of both optical fibers and air, FPIs based on air microbubbles within optical fibers have been widely developed for temperature-insensitive sensors used to measure refractive index (RI), tensile strain, and pressure.
[0003] In recent years, much work has focused on modifying the shape of microbubbles embedded within optical fibers to achieve high-resolution microstrain detection. The aim is to enable the sensor to undergo greater deformation under tensile stress, but this obviously makes the sensor more fragile. For example, forming extremely thin-walled FP cavities inside the optical fiber significantly reduces the sensor's structural strength and detection range. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention proposes a method for fabricating a strain sensor for a core-offset tapered fiber Fabry-Perot interferometer. The reflected beam inside the sensor returns to the fiber core after being reflected by the cladding. The purpose is to change the beam propagation trajectory by altering the cladding deformation under strain conditions, thereby significantly improving the sensitivity of stress measurement under the same structural strength.
[0005] The technical solution adopted in this invention is: a method for fabricating a strain sensor for a core-offset tapered fiber Fabry-Perot interferometer, the method comprising the following steps:
[0006] Step 1: Place two single-mode optical fibers with the coating removed into the optical fiber fusion splicer and heat-fuse the end faces of the single-mode optical fibers into a spherical shape, with the diameter of the spherical shape being larger than the diameter of the cladding of the single-mode optical fiber.
[0007] Step 2: Take out the single-mode fiber that has been thermally fused to a spherical surface, apply glycerin to the spherical surface, and then place the single-mode fiber back into the fiber fusion splicer. By operating the stepper motor of the fiber fusion splicer, the single-mode fiber is made to be misaligned in the operating plane.
[0008] Step 3: Operate the stepper motor of the fiber optic fusion splicer to make the spherical ends of the two single-mode fibers come into contact with each other. Then, discharge the contacting spherical surfaces to make the ends of the single-mode fibers to be fused together. After discharging the two spherical surfaces several times, tiny bubbles are generated at the ends of the spherical surfaces. The bubbles are located at the misaligned fusion splice of the core offset tapered fiber.
[0009] Step 4: Perform several discharges on the fusion splice point of the microbubbles generated in Step 3, and apply axial tension so that the cladding at the fusion splice of the single-mode fiber forms a conical structure. At this time, the microbubbles embedded in the conical cladding at the fiber fusion splice are ellipsoidal bubbles, and the fiber core at the fiber fusion splice is offset relative to the axis of the fiber.
[0010] Furthermore, after the two single-mode optical fibers are tapered after being spliced with misalignment, the fiber core at the splice point is significantly offset relative to the fiber axis, and there is a noticeable indentation in the cladding at the splice point.
[0011] Furthermore, the length of the conical structure region within the cladding at the fiber optic splice of the interferometer strain sensor is 490μm-510μm; the major axis of the ellipsoidal microbubble is 42.32μm-44.72μm, its minor axis is 39.17μm-41.18μm, and the offset of the fiber core at the fiber optic splice relative to the fiber axis is 2.8μm-3.2μm.
[0012] Furthermore, the major axis of the ellipsoidal microbubble is 42.32 μm, its minor axis is 39.18 μm, and the offset of the fiber core at the fiber splice relative to the fiber axis is 2.8 μm.
[0013] Furthermore, the length of the conical structure region within the cladding at the fiber fusion splice of the interferometer strain sensor is 500 μm; the major axis of the ellipsoidal microbubble is 43.52 μm, its minor axis is 40.18 μm, and the offset of the fiber core at the fiber fusion splice relative to the fiber axis is 3 μm.
[0014] Furthermore, the major axis of the ellipsoidal microbubble is 44.72 μm, its minor axis is 41.18 μm, and the offset of the fiber core at the fiber splice relative to the fiber axis is 3.2 μm.
[0015] Furthermore, a core-offset tapered fiber Fabry-Perot interferometer strain sensor was fabricated using a core-offset tapered fiber Fabry-Perot interferometer strain sensor fabrication method. The cladding at the splice of the two single-mode fibers of this sensor has a tapered structure, and an ellipsoidal bubble is formed inside the tapered cladding. Moreover, the fiber core at the fiber splice is offset from the fiber axis by a certain amount.
[0016] The beneficial effects of this invention are as follows: This invention provides a method for fabricating a strain sensor for a core-offset tapered fiber Fabry-Perot interferometer; the reflected beam inside the sensor returns to the fiber core after being reflected by the cladding, the purpose of which is to change the beam propagation trajectory by altering the cladding deformation under strain, thereby significantly improving the sensitivity of stress measurement under the same structural strength. Compared with the prior art, its main advantages are as follows:
[0017] (1) Simple to manufacture, requiring only conventional single-mode optical fiber and a commercial optical fiber fusion splicer, which can significantly reduce manufacturing costs;
[0018] (2) Compared with the existing fiber Fabry-Perot interferometer, when the sensor is deformed, the core offset structure will change the trajectory of the reflected beam and enter the fiber core after multiple reflections through the cladding. Under the same structural strength, the strain sensitivity of the strain sensor of the core offset tapered fiber Fabry-Perot interferometer is increased by more than 30%.
[0019] (3) The interferometer consists of only a core offset tapered optical fiber and an embedded microbubble, so the sensor is highly compact in structure and small in size. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of step one in the fabrication method of the interferometer strain sensor in Example 1;
[0021] Figure 2 This is a schematic diagram of step two in the interferometer strain sensor fabrication method of Example 1;
[0022] Figure 3 This is a schematic diagram of step three in the interferometer strain sensor fabrication method of Example 1;
[0023] Figure 4 This is a schematic diagram of step four in the interferometer strain sensor fabrication method of Example 1;
[0024] Figure 5 This is a diagram showing the propagation trajectory of the light beam inside the strain sensor of the interferometer in Example 2;
[0025] Figure 6 This is the interference curve spectrum of the interferometer strain sensor in Example 2;
[0026] Figure 7 This is the interference curve spectrum of the strain sensor in Example 2. Implementation
[0027] Reference Figures 1-4 A method for fabricating a strain sensor for a Fabry-Perot interferometer with a core-offset tapered fiber, the method comprising the following steps:
[0028] Step 1: Place two single-mode optical fibers with the coating removed into the optical fiber fusion splicer 1, and heat-fuse the end face of the single-mode optical fiber into a spherical surface 2, wherein the diameter of the spherical surface 2 is larger than the diameter of the cladding of the single-mode optical fiber.
[0029] Step 2: Take out the single-mode fiber that has been thermally fused into a spherical surface, apply glycerin 3 to the spherical surface 2, and then place the single-mode fiber back into the fiber fusion splicer 1. By operating the stepper motor of the fiber fusion splicer 1, the single-mode fiber is made to be in a misaligned position in the operating plane.
[0030] Step 3: Operate the stepper motor of the fiber optic fusion splicer 1 to make the spherical surfaces 2 at the ends of the two single-mode optical fibers come into contact with each other. Then, discharge the contacting spherical surfaces 2 to make the ends of the single-mode optical fibers to be fused together. After discharging the two spherical surfaces 2 several times, tiny bubbles 4 are generated at the ends of the spherical surfaces 2.
[0031] Step 4: Perform several discharges on the fusion splice point of the microbubbles 4 generated in Step 3, and apply axial tension to make the cladding at the fusion splice of the single-mode fiber form a conical structure. At this time, the microbubbles 4 embedded in the conical cladding at the fiber fusion splice are ellipsoidal bubbles, and the fiber core 5 at the fiber fusion splice is offset relative to the axis of the fiber. Example 2
[0032] Reference Figures 5-7 The interferometer strain sensor fabrication method described in the above embodiment yielded a core-offset tapered fiber Fabry-Perot interferometer strain sensor. The cladding at the splice of the two single-mode fibers of the sensor has a tapered structure, and an ellipsoidal bubble is formed inside the tapered cladding. The fiber core 5 at the fiber splice is offset from the fiber axis by a certain amount. The length of the tapered structure region inside the cladding at the fiber splice of the interferometer strain sensor is 500 μm. The major axis 6 of the ellipsoidal microbubble 4 is 43.52 μm, its minor axis 7 is 40.18 μm, and the offset of the fiber core 5 at the fiber splice relative to the fiber axis is 3 μm.
[0033] like Figure 5 As shown, the beam propagation trajectory diagram inside the core-offset tapered fiber Fabry-Perot interferometer is shown. The solid line is the incident beam 8, and the dashed line is the reflected beam 9. Both main reflected beams return to the fiber core after being reflected by the cladding-air interface, which is very different from ordinary Fabry-Perot interferometers.
[0034] like Figure 6The figure shows the spectrum of the interference curve as a function of strain in the range of 0-1500 με. In the experimental measurement, a 10 cm section of fiber, including the core-offset tapered fiber Fabry-Perot interferometer, was used. A strain length of 10 μm was defined as applying 100 με to the sensor. By measuring the wavelength change at the troughs of the interference curve, the strain sensitivity of this sensor reached as high as 17.24 pm / με.
[0035] like Figure 7 As shown, the relationship between wavelength variation and tensile stress in a tapered fiber Fabry-Perot interferometer with different core offsets is illustrated within the 0-15 MPa range. A numerical model of the sensor was established using the finite element method. Using COMSOL simulation software, the sensor sensitivity was found to be 0.854 nm / MPa when the core offset was 0 μm, and 1.112 nm / MPa when the core offset was 3 μm. Under the same structural strength, the strain sensitivity of the core-offset tapered fiber Fabry-Perot interferometer strain sensor is improved by more than 30%. Example 3
[0036] Based on the technical solution of Embodiment 1, the major axis 6 of the microbubble 4 of the interferometer strain sensor is 42.32 μm, the minor axis 7 is 39.18 μm, and the offset of the fiber core 5 at the fiber splice relative to the fiber axis is 2.8 μm. Example 4
[0037] Based on the technical solution of Embodiment 1, the major axis 6 of the microbubble 4 of the interferometer strain sensor is 44.72 μm, the minor axis 7 is 41.18 μm, and the offset of the fiber core 5 at the fiber splice relative to the fiber axis is 3.2 μm.
Claims
1. A method for fabricating a strain sensor for a Fabry-Perot interferometer using a core-offset tapered fiber, characterized in that: The production method includes the following steps: Step 1: Place two single-mode optical fibers with the coating removed into the optical fiber fusion splicer (1) and heat-fuse the end face of the single-mode optical fiber into a spherical surface (2), and the diameter of the spherical surface (2) is larger than the diameter of the cladding of the single-mode optical fiber. Step 2: Take out the single-mode fiber that has been thermally fused to a spherical surface, apply glycerin (3) to the spherical surface (2), and then place the single-mode fiber back into the fiber fusion splicer (1). By operating the stepper motor of the fiber fusion splicer (1), the single-mode fiber is placed in a misaligned position in the operating plane. Step 3: Operate the stepper motor of the fiber optic fusion splicer (1) to make the spherical surfaces (2) at the ends of the two single-mode fibers come into contact with each other. Then discharge the contacting spherical surfaces (2) to make the ends of the single-mode fibers to be fused together. After discharging the two spherical surfaces (2) several times, tiny bubbles (4) are generated at the ends of the spherical surfaces (2). Step 4: Discharge the fusion point of the microbubbles (4) generated in Step 3 several times and apply axial tension so that the cladding at the fusion point of the single-mode fiber fusion forms a conical structure. At this time, the microbubbles (4) embedded in the conical cladding at the fiber fusion point are ellipsoidal bubbles, and the fiber core (5) at the fiber fusion point is offset relative to the axis of the fiber. The strain sensor of the Fabry-Perot interferometer was prepared by the method of fabricating a core offset tapered fiber Fabry-Perot interferometer strain sensor. The cladding of the splice of the two single-mode fibers of the sensor is tapered, and an ellipsoidal bubble is formed in the tapered cladding. The fiber core (5) at the fiber splice is offset from the axis of the fiber.
2. The method for fabricating a strain sensor for a core-offset tapered fiber Fabry-Perot interferometer according to claim 1, characterized in that: The major axis (6) of the ellipsoidal microbubble (4) is 42.32μm-44.72μm, and its minor axis (7) is 39.18μm-41.18μm. The offset of the fiber core (5) at the fiber splice relative to the fiber axis is 2.8μm-3.2μm.